# Tank Inspection, Repair, Alteration, and Reconstruction

API STANDARD 653 FOURTH EDITION, APRIL 2009 ADDENDUM 1, AUGUST 2010 ADDENDUM 2, JANUARY 2012 ADDENDUM 3, NOVEMBER 2013

# Tank Inspection, Repair, Alteration, and Reconstruction

Downstream Segment
API STANDARD 653 FOURTH EDITION, APRIL 2009 ADDENDUM 1, AUGUST 2010 ADDENDUM 2, JANUARY 2012 ADDENDUM 3, NOVEMBER 2013

### Special Notes API publications necessarily addr ess problems of a general nature. With res pect to particular circumstances, local, state, and federal laws and regulations should be reviewed. Neither API nor any of API' s employees, subcontract ors, consultants, committees, or other assignees make any warranty or representation, either expres s or implied, with respect to the accu racy, completeness, or usefulness of the information contained herein, or assume any liability or responsibility for any use, or the results of such use, of any information or process disclosed in this publication. Neither API nor any of API' s employees, subcontractors, consultants, or other assignees represent that use of th is publication would not infringe upon privately owned rights. Classified areas may vary depending on the location, condi tions, equipment, and substances involved in any given situation. Users of this standar d should consult with the appropria te authorities having jurisdiction. Users of this standard should not rely exclusively on t he information contained in this document. Sound business, scientific, engineering, and safety judgment should be used in employing the information contained herein. API publications may be used by anyone desiring to do so. Ev ery effort has been made by t he Institute to assure the accuracy and reliability of the data cont ained in them; however, the Institute ma kes no representation, warranty, or guarantee in connection with this publicati on and hereby expressly discl aims any liability or re sponsibility for loss or damage resulting from its use or for the violation of any authoritie s having jurisdiction with which this publication may conflict. API publications are published to fac ilitate the broad availability of proven, sound engineering and operating practices. These publications are not intended to obviate the need for applying sound engineering judgment regarding when and where these publicati ons should be utilized. The formulation and publication of API publications is not intended in any way to inhibit anyone from using any other practices. Any manufacturer marking equipment or materials in confor mance with the marking requirements of an API standard is solely responsible for complying with all the applic able requirements of that st andard. API does not represent, warrant, or guarantee that such products do in fact conform to the applicable API standard. 10

All rights reserved. No part of this work may be reproduced, tr anslated, stored in a retrieval system, or transmitted by any me ans, electronic, mechanical, photocopying, record ing, or otherwise, without prior written permission from the publisher. Contact the Publisher, API Publishing Services, 1220 L Street, N.W., Washington, D.C. 20005. Copyright © 2009, 2010, 2012, 2013 American Petroleum Institute 10

13

### Foreword [text deleted] Nothing contained in any API publication is to be construed as granting any right, by implic ation or otherwise, for the manufacture, sale, or use of any method, apparatus, or product covered by letters pa tent. Neither should anything contained in the publication be constr ued as insuring anyone agains t liability for infringement of letters patent. Shall: As used in a standard, “shall” denotes a minimum requirement in order to conform to the specification. Should: As used in a standard, “should” denotes a recommendation or that which is advised but not required in order to conform to the specification. Each edition, revision, or addenda to this API standard may be used beginning with the date of issuance shown on the cover page for that edition, revision, or addenda. Each edition, revision, or addenda to this API standard becomes effective six months after t he date of issuance for equipment that is certified as bei ng rerated, reconstructed, relocated, repaired, modified (altered), inspected, and te sted per this standard. During the six-month time between the date of issuance of t he edition, revision, or addenda and the effective date, the purc haser and manufacturer shall specify to which edition, revision, or addenda the equipment is to be rated, re constructed, relocated, repaired, modified (altered), inspected, and tested. Portions of this publication have been changed from t he previous edition. The lo cations of changes have been marked with a bar in the margin, as shown to the left of this paragraph. In some ca ses the changes are significant, while in other cases the changes reflect minor editorial ad justments such as renumbering of a section/subsection or figure/table (the references within the text that have been subsequently updated are not marked). The bar notations in the margins are provided as an aid to users, but API makes no warranty as to the accuracy of such bar notations. This document was produced under API standardization pr ocedures that ensure appropriate notification and participation in the developmental process and is designated as an API standard. Questions concerning the interpretation of the content of this publication or comments and questi ons concerning the procedures under which this publication was developed should be directed in writ ing to the Director of Standards, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005. Reques ts for permission to reproduce or translate all or any part of the material published herein s hould also be addressed to the director. Generally, API standards are reviewed and revised, reaffirmed, or withdrawn at least ev ery five years. A one-time extension of up to two years may be added to this review cy cle. Status of the publicati on can be ascertained from the API Standards Department, telephone (202) 682-8000. A ca talog of API publications and materials is published annually by API, 1220 L Street, N.W., Washington, D.C. 20005. Suggested revisions are invited and s hould be submitted to the Standards De partment, API, 1220 L Street, NW, Washington, D.C. 20005, standards@api.org. 10

10

iii

### Contents
Page 1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1- 1 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 1.2 Compliance with This Standard. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 1.3 Jurisdiction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 1.4 Safe Working Practices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1 2 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1 2.1 Referenced Publications
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1 2.2 Other References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2 3 Definitions
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1 4 Suitability for Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 4.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 4.2 Tank Roof Evaluation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1 4.3 Tank Shell Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2 4.4 Tank Bottom Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-11 4.5 Tank Foundation Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-15 5 Brittle Fracture Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 5.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 5.2 Basic Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 5.3 Assessment Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1 6 Inspection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1 6.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1 6.2 Inspection Frequency Considerations
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1 6.3 Inspections from the Outside of the Tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1 6.4 Internal Inspection
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2 6.5 Alternative to Internal Inspection to Determine Bottom Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6 6.6 Preparatory Work for Internal Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6 6.7 Inspection Checklists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6 6.8 Records. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6 6.9 Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7 6.10 Nondestructive Examination (NDE). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8 7 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 7.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 7.2 New Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 7.3 Original Materials for Reconstructed Tanks
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 7.4 Welding Consumables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1 8 Design Considerations for Reconstructed Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1 8.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1 8.2 New Weld Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1 8.3 Existing Weld Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1 8.4 Shell Design
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1 8.5 Shell Penetrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1 8.6 Windgirders and Shell Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2 8.7 Roofs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2 8.8 Seismic Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2 10

10

12
13

13

13

13

13

13

vPage

vi 9 Tank Repair and Alteration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1 9.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1 9.2 Removal and Replacement of Shell Plate Material
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1 9.3 Shell Repairs Using Lap-welded Patch Plates
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-6 9.4 Repair of Defects in Shell Plate Material. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8 9.5 Alteration of Tank Shells to Change Shell Height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8 9.6 Repair of Defective Welds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8 9.7 Repair of Shell Penetrations
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8 9.8 Addition or Replacement of Shell Penetrations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10 9.9 Alteration of Existing Shell Penetrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10 9.10 Repair of Tank Bottoms
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-13 9.11 Repair of Fixed Roofs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-19 9.12 Repair of Floating Roofs

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-20 9.13 Repair or Replacement of Floating Roof Perimeter Seals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9- 20 9.14 Hot Taps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-21 10 Dismantling and Reconstruction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1 10.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1 10.2 Cleaning and Gas Freeing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1 10.3 Dismantling Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1 10.4 Reconstruction
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-3 10.5 Dimensional Tolerances10-5 11 Welding
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1 11.1 Welding Qualifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-1 11.2 Identification and Records . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-1 11.3 Preheat or Controlled Deposition Welding Methods as Alternatives to Post-weld Heat Treatment (PWHT)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1 11.4 Welding Safety
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-3 12 Examination and Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1 12.1 NDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1 12.2 Radiographs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-3 12.3 Hydrostatic Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-5 12.4 Leak Tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-7 12.5 Measured Settlement During Hydrostatic Testing
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-8 13 Marking and Recordkeeping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-1 13.1 Nameplates. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-1 13.2 Recordkeeping. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-2 13.3 Certification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-2 Annex A Background on Past Editions of API Welded Storage Tank Standards. . . . . . . . . . . . . . . . . . . . . . . A-1 Annex B Evaluation of Tank Bottom Settlement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1 Annex C Checklists for Tank Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C-1 Annex D Authorized Inspector Certification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . D-1 Annex E (Intentionally Left Blank) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . E-1 Annex F NDE Requirements Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . F-1 12 13

12

13

12

13

12

13
10

13

13

13

10 13 12

10 13Page Annex G Qualification of Tank Bottom Examination Procedures and Personnel . . . . . . . . . . . . . . . . . . . . . G-1 Annex H Similar Service Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H-1 Annex I Inquiries and Suggestions for Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I-1 Annex S Austenitic Stainless Steel Storage Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . S-1 Annex SC Stainless and Carbon Steel Mixed Materials Storage Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SC-1 Annex X Duplex Stainless Steel Storage Tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . X-1 Figures 4.1 Inspection of Corrosion Areas. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3 4.2 Pit Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5 5.1 Brittle Fracture Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2 5.2 Exemption Curve for Tanks Constructed from Carbon Steel of Unknown Material Specification . . . . 5-3 9.1 Acceptable Details for Replacement of Shell Plate Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2 9.2 Details for Door Sheets in Riveted Seam Tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4 9.3 Details for Door Sheets in Lap Weld Seam Tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4 9.4 Details for Door Sheet in Butt-Weld Shell Seam Tank—No Vertical Seam Offset . . . . . . . . . . . . . . . . . . 9-5 9.5 Details for Door Sheet in Bull-Weld Shell Seam tank—Vertical Seam Offset. . . . . . . . . . . . . . . . . . . . . . 9-5 9.6 Lapped Patch Repair Plates at the External Shell-to-bottom Joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-7 9.7 Typical Details for Addition of Reinforcing Plate to Existing Shell Penetration . . . . . . . . . . . . . . . . . . . 9-9 9.8 Typical Details for Addition of “Tombstone” Shape Reinforcing Plate to Existing Shell Penetration . 9-9 9.9 Method for Raising Shell Nozzles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9-11 9.10 Details for Installing a New Bottom Through an Existing Tombstone Reinforcing Plate . . . . . . . . . . . 9-12 9.11 Details for Installing a New Bottom Through an Existing Tombstone Reinforcing Plate . . . . . . . . . . . 9-13 9.12 Details for Installing a New Bottom Through an Existing Tombstone Reinforcing Plate . . . . . . . . . . . 9-14 9.13 Typical Welded-on Patch Plates on Tank Bottom Plates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-16 9.14 Hot Tap for Tanks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-23 10.1 Tank Shell and Bottom Cut Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2 13.1 Nameplate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-3 13.2 Certification Forms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13-4 B.1 Measurements of Shell Settlement (External) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2 B.2 Measurements of Bottom Settlement (Internal) Tank Out-of-service . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-2 B.3 Graphical Representation of Tank Shell Se ttlement per B.2.2.4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-3 B.4 Graphical Representation of Shell Settlement per B.2.2.5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-6 B.5 Graphical Representation of Shell Settlement per B.2.2.5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-6 B.6 Edge Settlement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-7 B.7 Correction for Measured Edge Settlement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-8 B.8 Bottom Settlement Near Shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-9 B.9 Localized Bottom Depressions or Bulges Remote from Shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1 0 B.10 Localized Tank Bottom Settlement Limits for Single Pass Weld s. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B- 12 B.11 Maximum Allowable Edge Settlement for Areas with Bottom Lap Welds Approximately Parallel to the Shell. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-14 B.12 Maximum Allowable Edge Settlement for Areas with Bottom Lap Welds Approximately Perpendicular to the Shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-15 B.13 Edge Settlement with a Lap Weld at an Arbitrary Angle to the Shell . . . . . . . . . . . . . . . . . . . . . . . . . . . B- 15 H.1 Steps in Conducting Similar Service Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H-6 H.2 Example Corrosion Rate Curves for Bottom of Storage Tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H-7 H.3 Example Corrosion Rate Curves for Top Course of Storage Tank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H-8 12 10 13 13 13 13

12

12

10

13

10

viiPage Tables 4.1 Maximum Allowable Shell Stresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7 4.2 Joint Efficiencies for Welded Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-8 4.3 Joint Efficiencies for Riveted Joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10 4.4 Bottom Plate Minimum Thickness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-15 4.5 Annular Bottom Plate Thicknesses (in.)
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-15 6.1 Tank Safeguard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4 9.1 Hot Tap Connection Sizes and Shell Plate Thicknesses
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-21 10.1 Maximum Thicknesses on New Welds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-4 10.2 Radii Tolerances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-5 11.1 Welding Methods as Alternatives to Post-wel d Heat Treatment (PWHT) Qualification Thicknesses for Test Plates and Repair Grooves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11-2 A.1 Editions of API Standard 650 and its Precursor, API Standard 12C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1 G.1 Suggested Essential Variables for Qualification Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . G-6 H.1 Similar Service Product Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . H-5 10
12

10

viii1-1 

## Tank Inspection, Repair, Al teration, and Reconstruction

1 Scope 1.1 Introduction 1.1.1 This standard covers steel storage t anks built to API 650 and its predece ssor API 12C. It pr ovides minimum requirements for maintaining the integrity of such tank s after they have been placed in service and addresses inspection, repair, alteration, relocation, and reconstruction. 1.1.2 The scope is limited to the tank foundation, bottom, shell, structure, roof, attached appurtenances, and nozzles to the face of the first flange, first threaded joint, or first welding-end c onnection. Many of the design, welding, examination, and material requirements of API 650 can be applied in the maint enance inspection, rating, repair, and alteration of in-service tanks. In the case of apparen t conflicts between the requirem ents of this standard and API 650 or its predecessor API 12C, this standard shall gov ern for tanks that have been placed in service. 1.1.3 This standard employs the principles of API 650; however, storage tank owner/operators, based on consideration of specific c onstruction and operating details, may apply this st andard to any steel tank constructed in accordance with a t ank specification. 1.1.4 This standard is intended for use by organizations that maintain or have access to engineering and inspection personnel technically trained and experi enced in tank design, fabrication, repair, construction, and inspection. 1.1.5 This standard does not contain rules or guidelines to co ver all the varied conditions which may occur in an existing tank. When design and co nstruction details are not given, and are not available in the as-built standard, details that will provide a level of integrity equal to the level provided by the current edition of API 650 must be used. 1.1.6 This standard recognizes fitness-for-service assessment concepts for evaluating in-service degradation of pressure containing components. API 579-1/ASME FFS-1, Fitness-For-Service , provides detailed assessment procedures or acceptance criteria for s pecific types of degradation referenced in this standard. When this standard does not provide specific eval uation procedures or acceptance criteria for a specific type of degradation or when this standard explicitly allows the use of fi tness-for-service criteria, API 579-1/A SME FFS-1 may be used to evaluate the various types of degradation or test requirements addressed in this standard. 

### 1.2 Compliance with This Standard The owner/operator has ultimate responsibility for comply ing with the provisions of this standard. The application of this standard is restricted to organizations that employ or have access to an authorized inspection agency as defined in 3.3. Should a pa rty other than the owner/operator be assig ned certain tasks, such as relocating and reconstructing a tank, the limits of responsibility for each party shall be defined by the owner/operator prior to commencing work. 

### 1.3 Jurisdiction If any provision of this standard presents a direct or implied conflict with any statutory regulation, the regulation shall govern. However, if the requirements of this standard are more stringent than the requirem ents of the regulation, then the requirements of this standard shall govern. 

### 1.4 Safe Working Practices An assessment shall be made of the potential hazards to which personnel may be exposed when conducting internal tank inspections, making repairs, or dismantling tanks. Procedures shall be developed according to the 101-2 API S TANDARD 653 guidelines given in API 2015, API 2016, and API 2217A that will include safeguard for personnel health and safety, prevention of accidental fires and explosions, and the prevention of property damage. Conformance to permit procedures is an essential safe work practice for protection of personnel and property.Where welding and hot work are involved, API 2009 states “Except in areas specifically designated as safe for hot work, a hot work permit shall be obtained before starting any work that can involve a source of ignition.” Special procedures may need to be developed for certain acti vities described in this standard that are not fully covered by the referenced API publicati ons; e.g. safety precautions for pers onnel accessing floating roof tanks that are in service, or gas freei ng the bottom side of a tank. Appendix B of API 2009 provides brief information on inerting tanks. Use of inerting as a safety precaution should address personnel hazards introduc ed when using inert gas in the workplace and implementation should be done in consultation with specialist s that are familiar with such processes. Finally, procedures must comply with any feder al or state safety regulations pertaining to “confined spaces” or any other relevant provisions. 10

102-1 

### Section 2—References

2.1 Referenced Publications The following standards, codes, publicatio ns, and specifications are cited in this standard. The latest edition or revision shall be used unless otherwise noted. API Recommended Practice 579-1/ASME FFS-1, Fitness-For-Service API Recommended Practice 580, Risk Based Inspection API Standard 620, Design and Construction of Large, Welded, Low-pressure Storage Tanks API Standard 650, Welded Tanks for Oil Storage API Recommended Practice 651, Cathodic Protection of Aboveground Storage Tanks API Recommended Practice 652, Lining of Aboveground Petroleum Storage Tank Bottoms API Standard 2000, Venting Atmospheric and Low-pressure Storage Tanks: Nonrefrigerated and Refrigerated API Recommended Practice 2003, Protection Against Ignitions Arising Out of Static, Lightning, and Stray Currents API Recommended Practice 2009, Safe Welding, Cutting, and Hot Work Practices in the Petroleum and Petrochemical Industries API Standard 2015, Requirements for Safe Entry and Cleaning of Petroleum Storage Tanks API Recommended Practice 2016, Guidelines and Procedures for Enteri ng and Cleaning Petroleum Storage Tanks API Recommended Practice 2201, Safe Hot Tapping Practices in the Petroleum and Petrochemical Industries API Recommended Practice 2207, Preparing Tank Bottoms for Hot Work API Standard 2217A, Guidelines for Safe Work in Inert Confined Spaces in the Petroleum and Petrochemical Industries ASME Boiler and Pressure Vessel Code (BPVC) 1 , Section V: Nondestructive Examination ASME BPVC , Section VIII: Pressure Vessels; Division 2: Alternative Rules ASME BPVC , Section IX: Welding and Brazing Qualifications ASNT SNT-TC-1A 2 , Personnel Qualificat ion and Certification in Nondestructive Testing ASTM A6 3 , Standard Specification for General Requirements for Rolled Struct ural Steel Bars, Plates, Shapes, and Sheet Piling ASTM A20, Standard Specification for General Requirements for Steel Plates for Pressure Vessels

1 ASME International, 3 Park Avenue, New York, New York 10016-5990, www.asme.org. 2 American Society for Nondestructive Testing, 1711 Ar lingate Lane, Columbus, Ohio, 43228-0518, www.asnt.org. 3 ASTM International, 100 Barr Harbor Drive, West Conshohocken, Pennsylvani a 19428-2959, www.astm.org. 10

12

10

122-2 API S TANDARD 653 ASTM A36, Standard Specification for Carbon Structural Steel ASTM A370, Standard Test Methods and Definitions fo r Mechanical Testing of Steel Products ASTM A992, Standard Specification for Structural Steel Shapes AWS D1.1 4 , Structural Welding Code—Steel AWS D1.6, Structural Welding Code—Stainless Steel NACE Standard RP 0205-2005 5 , Recommended Practice for the Design, Fabric ation, and Inspection of Tanks for the Storage of Petroleum Refining Al kylation Unit Spent Sulfuric Acid at Ambient Temperatures 

### 2.2 Other References Although not cited in this standard, the following publicat ion may be of interest. API Standard 2610, Design, Construction, Operati on, Maintenance, and Inspection of Terminal and Tank Facilities ANSI/AWS Z49.1, Safety in Welding and Cutting and Allied Processes

4 American Welding Society, 550 N.W. LeJeune Road, Miami, Florida 33135, www.aws.org. 5 NACE International (formerly the National Association of Corrosion Engineers), 1440 South Creek Drive, Houston, Texas 77218-8340, www.nace.org. 12

103-1 

### Section 3—Definitions For the purposes of this standard, the following definitions apply. 3.1 alteration Any work on a tank that changes its phy sical dimensions or configuration. 3.2 as-built standard The standard (such as API standard or UL 5 standard) used for the construction of the tank component in question. If this standard is not known, the as-built standard is the standard that was in effect at the date of the installation of the component. If the date of the installation of the component is unknown, then the current applicable standard shall be considered to be the as-built standard. See Annex A for a list of API welded storage tank standards. The standard used for repairs or alterations made after original constr uction is the as-built standard only for those repairs or alterations, so there may be more than one as-built standard for a tank. 3.3 authorized inspection agency One of the following organizations that employ an aboveground storage tank inspector certified by API. a) The inspection organization of the jurisdicti on in which the aboveground storage tank is operated. b) The inspection organization of an insurance company which is licensed or registered to and does write aboveground storage tank insurance. c) An owner/operator of one or more aboveground storage tank(s) who maintains an inspection organization for activities relating only to his/her equipment and not for aboveground storage tanks intended for sale or resale. d) An independent organization or indivi dual under contract to and under the direction of an owner/operator and recognized or otherwise not prohibited by the jurisdic tion in which the aboveground storage tank is operated. The owner/operator’s inspection program shall provide the controls necessary for us e by authorized inspectors contracted to inspect aboveground storage tanks. 3.4 authorized inspector An employee of an authorized inspecti on agency who is qualified and certified to perform inspections under this inspection standard. Whenever the term inspector is used in API 653, it refers to an authorized API Standard 653 inspector. 3.5 breakover point The area on a tank bottom where settlement begins. 3.6 candidate tank The tank(s) for which corrosion rates are not known. 3.7 change in service A change from previous operating conditions involving different properties of the stored product such as specific gravity or corrosivity and/or different service conditions of temperature and/or pressure.

5 Underwriters Laboratories, 333 Pfingsten Road, Northbrook, Illinois, 60062-2096, www.ul.com. 133-2 API S TANDARD 653
3.8 control tank The tank(s) for which corrosion rates an d service history are known and documented. 3.9 corrosion rate The total metal loss divided by the period of time over which the metal loss occurred. 3.10 critical zone The portion of the tank bottom or annular plate within 3 in. of the inside edge of the shel l, measured radially inward. 3.11 current applicable standard The current edition of the st andard (such as API standard or UL standard) that applies if the tank were built today. 3.12 door sheet A plate (or plates) cut from an existing tank shell to create a temporary access opening. After planned work is completed, the door sheet(s) shall be reinstalled or replaced. 3.13 examiner A person who assists the inspector by performing s pecific nondestructive exam ination (NDE) on aboveground storage tanks and evaluates to the applic able acceptance criteria, but does not interpret the results of those examinations in accordance with AP I 653, unless specifically trained and aut horized to do so by the owner/user. 3.14 external inspection A formal visual inspection, conducted or supervised by an authorized inspector, to assess all aspects of the tank as possible without suspending operations or requiring tank s hutdown (see 6.3.2). 3.15 fitness-for-service assessment A methodology whereby flaws contained within a structur e are assessed in order to determine the adequacy of the flawed structure for continued se rvice without imminent failure. 3.16 hot tap Identifies a procedure for installing a nozzle in the shell of a tank that is in service. 3.17 hydrotest A test performed with water, in which stat ic fluid head is used to produce test loads. 3.18 inspector A shortened title for an authorized tank inspector qualif ied and certified in accordance with this standard. 3.19 internal inspection A formal, complete inspection, as supervised by an authorized in spector, of all accessible internal tank surfaces (see 6.4.1). 12

13

13

13T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 3-3
3.20 major alteration/or major repair An alteration or repair that includes any of the following: a) installing a shell penetration larger than NPS 12 beneath the design liquid level; b) installing a bottom penetration within 12 in. of the shell; c) removing and replacing or adding a shell plate beneath the design liquid level where t he longest dimension of the replacement plate exceeds 12 in.; d) removing or replacing annular plate ring material wher e the longest dimension of t he replacement plate exceeds 12 in.; e) complete or partial (more than one-half of the weld th ickness) removal and replacement of more than 12 in. of vertical weld joining shell plates or radial weld joining the annular plate ring; f) installing a new bottom; NOTE Installation of a portion of a new bottom as described in 12.3.3.3 is not defined as a major repair. g) removing and replacing part of the weld attaching the shel l to the bottom, or to the annular plate ring, in excess of the amounts listed in 12.3.2.5.1 a); h) jacking a tank shell. 3.21 owner/operator The legal entity having both c ontrol of and/or responsibility for the oper ation and maintenance of an existing storage tank. 3.22 product-side The side of the tank that is in c ontact with the stored liquid product. 3.23 recognized toughness A condition that exists when t he material of a component is deemed acceptable for use by the provis ions of any of the following sections of this standard: a) Section 5.3.2 (based on edition of standard of tank ’s original construction, or by coupon testing); b) Section 5.3.5 (based on thickness); c) Section 5.3.6 (based on lowest design metal temperature); d) Section 5.3.8 (based on exemption curves). 3.24 reconstruction Any work necessary to reassemb le a tank that has been dismantled and relocated to a new site. 3.25 reconstruction organization The organization having assigned responsib ility by the owner/operator to des ign and/or reconstruct a tank. 103-4 API S TANDARD 653
3.26 repair Work necessary to maintain or restore a tank to a c ondition suitable for safe operation. Repairs include both major repairs (see 3.20) and repairs that are not major repairs. Examples of repairs include: a) removal and replacement of material (suc h as roof, shell, or bottom material, in cluding weld metal) to maintain tank integrity; b) re-leveling and/or jacking of a tank shell, bottom, or roof; c) adding or replacing reinforcing plates (or por tions thereof) to existing shell penetrations; d) repair of flaws, such as tears or gouges , by grinding and/or gouging followed by welding. 3.27 repair organization An organization that meets any of the following: a) an owner/operator of aboveground storage tanks who repair s or alters his/her own equipment in accordance with this standard; b) a contractor whose qualifications are acceptable to the owner/operat or of aboveground storage tanks and who makes repairs or alterations in accordance with this standard; c) one who is authorized by, acceptable to, or otherwise not pr ohibited by the jurisdiction, and who makes repairs in accordance with this standard. 3.28 similar service assessment The process by which corrosion rates and inspection interval s are established for a candidate tank using corrosion rates and service history from a control tank for t he purpose of establishing the next inspection date. 3.29 soil-side The side of the tank bottom that is in contact with the ground. 3.30 storage tank engineer One or more persons or organizations acceptable to the owner/operator who are knowledgeable and experienced in the engineering disciplines associated with evaluati ng mechanical and material characteri stics that affect the integrity and reliability of aboveground storage tanks. The storage tank engineer, by consulting with appropriate specialists, should be regarded as a composite of all entities needed to properly assess the technical requirements. 3.31 unknown toughness A condition that exists when it cannot be demonstrated that the material of a component satisfies the definition of recognized toughness. 134-1 

### Section 4—Suitability for Service

4.1 General 4.1.1 When the results of a tank inspection show that a change has occurred from the origi nal physical condition of that tank, an evaluation shal l be made to determine its su itability for continued use. 4.1.2 This section provides an evaluation of the suitability of an existing tank for continued service, or for a change of service, or when making dec isions involving repairs, alterations, di smantling, relocating, or reconstructing an existing tank. 4.1.3 The following list of factors for cons ideration is not all-incl usive for all sit uations, nor is it intended to be a substitute for the engineer ing analysis and judgment required for each situation: a) internal corrosion due to the product stored or water bottoms; b) external corrosion due to environmental exposure; c) stress levels and allo wable stress levels; d) properties of the stored product such as spec ific gravity, temperature, and corrosivity; e) metal design temperatures at the service location of the tank; f) external roof live load, wind, and seismic loadings; g) tank foundation, soil, and settlement conditions; h) chemical analysis and mechanical properties of the materials of construction; i) distortions of the existing tank; j) operating conditions such as filling/emptying rates and frequency. 

### 4.2 Tank Roof Evaluation 4.2.1 General 4.2.1.1 The structural integrity of the roof and roof support system shall be verified. 4.2.1.2 Roof plates corroded to an average thicknes s of less than 0.09 in. in any 100 in. 2 area or roof plates with any holes through the roof plate shall be repaired or replaced. 4.2.2 Fixed Roofs 4.2.2.1 Roof support members (rafters, girders, columns, and bases) shall be inspect ed for soundness by a method acceptable to the responsible inspecto r. Distorted (such as out-of-plumb columns), corroded, and damaged members shall be evaluated and repaired or replaced if necessary. Particul ar attention must be given to the possibility of severe internal corrosion of pipe columns (corrosion may not be evidenced by external visual inspection). 4.2.2.2 When a frangible roof-to-shell joint is required, evaluate for items impa cting compliance with requirements under API 650, Section 5.10.2.6. Examples of some items to evaluate include tank bottom-to-shell joint corrosion or 124-2 API S TANDARD 653 tank roof-to-shell joint modification (suc h as reinforcement of the joint, attachm ent of handrail, or other frangible joint area change). 4.2.3 Floating Roofs 4.2.3.1 Areas of roof plates and pontoons exhi biting cracks or punctures shall be repaired or the affected sections replaced. Holes through roof plat es shall be repaired or replaced. 4.2.3.2 Areas that are pitted shall be evaluated to determine the likelihood of through-pitting occurring prior to the next scheduled internal inspection. If so, the affected areas shall be repaired or replaced. 4.2.3.3 Roof support systems, perimeter seal systems, appur tenances such as a roof rolling ladder, anti-rotation devices, water drain systems, and venting systems s hall be evaluated for needed repairs or replacements. 4.2.3.4 Guidance for the evaluation of existing floating roofs s hall be based on the criteria of API 650, Annex C, for external floating roofs, and Annex H for internal floating roofs. However, upgrading to meet this standard is not mandatory. 4.2.4 Change of Service 4.2.4.1 Internal Pressure All requirements of the current applicable standard (e.g. API 650, Annex F) shall be considered in the evaluation and subsequent alterations to the tank roof and roof-to-shell junction. 4.2.4.2 External Pressure As applicable, the roof support structure (if any), and the r oof-to-shell junction shall be ev aluated for the effects of a design partial vacuum. The criter ia outlined in API 650, Annex V shall be used. 4.2.4.3 Operation at Elevated Temperature All requirements of API 650, Annex M, shall be considered before changing the se rvice of a tank to operation at temperatures above 200 °F. 4.2.4.4 Operation at Lower Temper ature Than Original Design If the operating temperature is changed to a lower temper ature than the original desi gn, the requirements of the current applicable standard for the lower temperature shall be met. 4.2.4.5 Normal and Emergency Venting 4.2.4.5.1 Effects of change in operating conditions (includi ng product service and pumping rates) on normal and emergency venting shall be considered. 4.2.4.5.2 Vents shall be inspected for proper operation and screen s shall be verified to be clear of obstruction. 

### 4.3 Tank Shell Evaluation 4.3.1 General 4.3.1.1 Flaws, deterioration, or other conditions (e.g. change of service, relocation, corrosion greater than the original corrosion allowance) that might adversely affect the performance or structural integrity of the shell of an existing tank must be evaluated and a determination made regarding su itability for intended service. 13

13

13

13T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 4-3
4.3.1.2 The evaluation of the existing tank shell shall be conducted by a storage tank engineer and shall include an analysis of the shell for the intende d design conditions, based on existing shell plate thi ckness and material. The analysis shall take into consideratio n all anticipated loading conditions and comb inations, including pressure due to fluid static head, internal and external pressure, wind loads, seismic loads, r oof live loads, nozzle loads, settlement, and attachment loads. 4.3.1.3 Shell corrosion occurs in many forms and varying degr ees of severity and may result in a generally uniform loss of metal over a large surface area or in localized areas . Pitting may also occur. Each case must be treated as a unique situation and a thorough inspection conducted to dete rmine the nature and extent of corrosion prior to developing a repair procedure. Pitting does not normally represent a significant threat to the overall structural integrity of a shell unless present in a severe form with pits in close proximity to one another. Criteria for evaluating both general corrosion and pitting are defined below. 4.3.1.4 Methods for determining the minimum shell thickness suitable for c ontinued operation are given in 4.3.2, 4.3.3, and 4.3.4 (see Section 6 for frequency of inspection)

.

4.3.1.5 If the requirements of 4.3.3 (welded) or 4.3.4 (riv eted) cannot be satisfied, the corroded or damaged areas shall be repaired, or the allowable liquid level of the tank reduc ed, or the tank retired. The allowable liquid level for the continued use of a tank may be established by using the equat ions for a minimum acceptable thickness (see 4.3.3.1 and 4.3.4.1) and solving for height, H . The actual thickness, as determined by inspection, minus the corrosion allowance shall be used to establish the liquid level limit. The maximum design liquid level shall not be exceeded. Figure 4.1—Inspection of Corrosion Areas A

L

A t 2 t nom

t avg tank diameter D

a bcde An area of corrosion

Key

Procedure SECTION A

**-** A a – e are inspection planes selected by inspector. t 2 = least min. thickness in entire area, exclusive of pits.
1) Determine t 2 . 2) Calculate L = 3.7 Dt 2 , but not more than 40 in. 3) Locate L to get minimum t avg , which is t 1 . Profile along Plane c , the plane having the lowest average thickness, t 1 .4-4 API S TANDARD 653
4.3.2 Actual Thickness Determination 4.3.2.1 For determining the controlling thicknesses in each shell course when there are corroded areas of considerable size, measured thicknesses shall be aver aged in accordance with the following procedure (see Figure 4.1). a) For each area, the authorized inspector shall determine the minimum thickness, t 2 , at any point in the corroded area, excluding widely scatter ed pits (see 4.3.2.2). b) Calculate the critical length, L : , but not more than 40 in. where
L is the maximum vertical length, in inches, over which hoop stresses are assumed to “average out” around local discontinuities;
NOTE The actual vertical length of the corroded area may exceed L

. D is the tank diameter, in feet;

t 2 is the least thickness, in inches, in an area of corrosion, exclusive of pits. c) The authorized inspector shall visually or otherwise decide which vertical plane(s) in the area is likely to be the most affected by corrosion. Profile measurements sh all be taken along each vertical plane for a distance, L . In the plane(s), determine the lowe st average thickness, t 1 , averaged over a length of L , using at least five equally spaced measurements over length L

. d) See 4.3.3.1 for minimum permitted values for t 1 and t 2 . The additional loads in 4.3.3. 4 shall also be considered. e) The criteria for continued operation is as follows: i) the value t 1 shall be greater than or equal to t min (see 4.3.3 or 4.3.4), subject to verification of all other loadings listed in 4.3.3.5; ii) the value t 2 shall be greater than or equal to 60 % of t min ; and iii) any corrosion allowance requir ed for service until the time of the next inspection shall be added to t min and 60 % of t min . 4.3.2.2 Widely scattered pits may be ignored provided that: a) no pit depth results in the remaining shell thickness being less than one-half the mi nimum acceptable tank shell thickness exclusive of t he corrosion allowance; and b) the sum of their dimensions along any vertical line does not exceed 2 in. in an 8-in. length (see Figure 4.2). 4.3.3 Minimum Thickness Calculation for Welded Tank Shell
NOTE In general, the minimum acceptable thickness ( t min ) for an entire shell course is determined using 4.3.3.1 a) with H determined to the bottom of each shell course and the results us ed as a basis for judging the suitability for continued service for the tank. If locally thinned areas are identified or if specific areas are investigated (s uch as for a shell nozzle installation), the method of 4.3.3.1 b) may be used to complete the evaluation with H determined for that particular location. L 3.7 Dt 2 =T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 4-5

4.3.3.1 The minimum acceptable shell plate thickness for c ontinued service shall be determined by one or more of the methods noted herein. These met hods are limited to tanks with diameters equal to 200 ft or less. a) When determining the minimum acceptable thickness for an entire shell course, t min is calculated as follows:

b) When determining the minimum acceptable thickness for any other portions of a shell course (such as a locally thinned area or any other location of interest), t min is calculated as follows:

where

t min is the minimum acceptable thickness, in inches for each course as calculated from the above equation; however, t min shall not be less than 0.1 in. for any tank course;
D is the nominal diameter of tank, in feet (ft);
H is the height from the bottom of t he shell course under consideration to the maximum liquid level when evaluating an entire shell c ourse, in feet (ft); or is the height from t he bottom of the length L (see 4.3.2.1) from the lowest point of the bottom of L of the locally thinned area to the maximum liquid level, in feet (ft); or is the height from the lowest point within any location of interest to the maximum liquid level, in feet (ft);
G is the highest specific gr avity of the contents; Figure 4.2—Pit Measurement d 1

d 2

d 3 8 in.

d 1 + d 2 + d 3 ... ≤ 2 in.

t min 2.6 H 1

– ( ) DG

SE ------------------------------------ =

t min 2.6 HDG SE ---------------------- =4-6 API S TANDARD 653

S

is the maximum allowable stress in pound force per square inch (lbf/in. 2 ); use the smaller of 0.80 Y or 0.429 T for bottom and second course; use the smaller of 0.88 Y or 0.472 T for all other courses. Allowable shell stresses are shown Table 4.1 for materials listed in the current and previous editions of API 12C and API 650;
NOTE for reconstructed tanks, S shall be in accordance with the current applicable standard; Y is the specified minimum yield str ength of the plate; use 30,000 lbf/in. 2 if not known;
T is the smaller of the specified minimum tens ile strength of the plate or 80,000 lbf/in. 2 ; use 55,000 lbf/in. 2 if not known;
E is the original joint efficiency for the tank. Use Table 4.2 if original E is unknown. E = 1.0 when evaluating the retirement thickness in a corroded plate, when away from welds or joints by at least the greater of 1 in. or twice the plate thickness. 4.3.3.2 If the tank will be hydrostatically tested, the hydrostatic test height, H t , shall be limited by one or more of the following methods. The tank shall not be filled above the level determined by the lesser value of H t determined below. a) After determining the controlling th ickness of an enti re shell course, H t calculated as follows:

b) After determining the controlling thicknes s by 4.3.2.1 for a locally thinned area, or at any other location of interest within a shell course, H t is calculated as follows:

where
H

t is the h eight from the bottom of the shell course under consideration to the hydrostatic test height when evaluating an entire shell course in feet; or is the height from the bottom of the length, L , (see 4.3.2.1) for the most severely thinned area in each shell course to the hydrostatic test height in feet; or is the height from the lowest point within any other location of interest to the hydrostatic test height in feet;
S

t is the maximum allowable hydrostatic test st ress in pound force per square inch (lbf/in. 2 ); use the smaller of 0.88 Y or 0.472 T for bottom and second courses; use the smaller of 0.9 Y or 0.519 T for all other courses.
NOTE 1 Depending on the specific gravity of the content used to determine t min , H t may be less than H . Testing the tank to H may yield the corroded area. NOTE 2 If H t is less than H , owner/operator shall determ ine the consequence and acceptability of operating the tank to H , its maximum design liquid level. Repairs to shell sections above H t shall comply with the requirements of 12.3.2. NOTE 3 For reconstructed tanks, S t shall be per the current applicable standard. 4.3.3.3 Alternatively, the minimum acceptable shell plate thickness for tank s with diameters equal to or less than 200 ft may be calculated in accordance with the variable design point method in API 650, 5.6.4, substituting “ S × E ” for

“ S ”; E and S may be defined as in 4.3.3.1. 4.3.3.4 The variable design point method shall be used for tanks greater than 200 ft in diameter, with all variables defined as in 4.3.3.1. H

t S t Et min 2.6 D --------------- 1 + =

H

t S t Et min 2.6 D --------------- =T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 4-7 Table 4.1—Maximum Allowable Shell Stresses (Not for Use for Reconstructed Tanks, See Note 6)

NOTE 1 ASTM A7, ASTM A9, ASTM A10 and ASTM A442 are obsolete ASTM mate rial specifications previously listed in API 12C and API 650. NOTE 2 The yield stress and tensile strength values shown are per API 653 for welded ASTM material of unknown origin. NOTE 3 This provision is for riveted ta nks, constructed of any gra de of material, evaluated per 4.3.4.1 of this standard. NOTE 4 This provision is for riveted tank s, constructed of known grades of materi al, evaluated per 4.3.4.2 of this standard. F or all courses, the maximum allowable shell stress for both produc t and hydrostatic test conditions are list ed under column for allowable product s tress, S

. NOTE 5 This provision is for riveted tank s, constructed of unknown gra des of material, evaluated per 4.3.4.2 of this standard. NOTE 6 The allowable stresses for reconstructed tanks are tabulated in API 650, Table 5-2a or 5-2b or calculated per 8.4 of this stand ard. NOTE 7 The allowable stresses are calculated per 4.3.3.1 and 4. 3.3.2 of this standard, unless otherwise noted. The calculated allowable stresses are rounded to the nearest 100 lbf/in. 2

.

Material Specification and Grade Minimum Specified Yield Stress,

Y

(lbf/in. 2 ) Minimum Specified Tensile Strength, T (lbf/in. 2 ) Lower Two Courses Upper Courses Lower Two Courses Upper Courses

A 283-C 30,000 55,000 23,600 26,000 26,000 27,000 A285-C 30,000 55,000 23,600 26,000 26,000 27,000

A36 36,000 58,000 24,900 27,400 27,400 30,100 A131-A, B, CS 34,000 58,000 24,900 27,400 27,400 30,100

A131-EH 36 51,000 71,000 30,500 33,500 33,500 36,800

A573-58 32,000 58,000 24,900 27,400 27,400 28,800 A573-65 35,000 65,000 27,900 30,700 30,700 31,500 A573-70 42,000 70,000 30,000 33,000 33,000 36,300 A516-55 30,000 55,000 23,600 26,000 26,000 27,000 A516-60 32,000 60,000 25,600 28,200 28,200 28,800 A516-65 35,000 65,000 27,900 30,700 30,700 31,500 A516-70 38,000 70,000 30,000 33,000 33,000 34,200 A662-B 40,000 65,000 27,900 30,700 30,700 33,700 A662-C 43,000 70,000 30,000 33,000 33,000 36,300 A537-Class 1 50,000 70,000 30,000 33,000 33,000 36,300 A537-Class 2 60,000 80,000 34,300 37,800 37,800 41,500

A633-C, D 50,000 70,000 30,000 33,000 33,000 36,300

A678-A 50,000 70,000 30,000 33,000 33,000 36,300 A678-B 60,000 80,000 34,300 37,800 37,800 41,500 A737-B 50,000 70,000 30,000 33,000 33,000 36,300

A841 50,000 70,000 30,000 33,000 33,000 36,300 A10 (Note 1) 30,000 55,000 23,600 26,000 26,000 27,000 A7 (Note 1) 33,000 60,000 25,700 28,300 28,300 29,700 A442-55 (Note 1) 30,000 55,000 23,600 26,000 26,000 27,000 A442-60 (Note 1) 32,000 60,000 25,600 28,200 28,200 28,800
G40.21, 38W 38,000 60,000 25,700 28,300 28,300 31,100 G40.21, 44W 44,000 65,000 27,900 30,700 30,700 33,700 G40.21, 50W 50,000 65,000 27,900 30,700 30,700 33,700 G40.21, 50WT 50,000 70,000 30,000 33,000 33,000 36,300

Unknown (Note 2) 30,000 55,000 23,600 26,000 26,000 27,000
Riveted Tanks: A7, A9 or A10 (Note 1, Note 3) NA NA 21,000 21,000 21,000 21,000 Known (Note 4) Y T Note 4 Note 4 Note 4 Note 4 Unknown (Note 5) NA NA 21,000 21,000 21,000 21,000 ASTM Specifications

CSA Specifications Stress, S (lbf/in. 2 ) (Note 7) Test Stress, S t (lbf/in. 2 ) (Note 7) Allowable Product Allowable Hydrostatic

124-8 API S TANDARD 653

4.3.3.5 The thickness determinations of 4.3.3.1, 4.3.3.2, and 4.3.3.3 consider liquid l oading only. All other loads shall also be evaluated according to the original standar d of construction; and engineeri ng judgment shall be used to evaluate different conditions or new in formation. As applicable, the following loadings shall be taken into account: a) wind-induced buckling; b) seismic loads; c) operation at temperatures over 200 °F; d) vacuum-induced external pressure; e) external loads caused by piping, tank-mounted equipm ent, hold down lugs, etc.; f) wind-induced overturning; g) loads due to settlement. Table 4.2—Joint Efficiencies for Welded Joints
Standard Edition and Year Type of Joint Joint Efficiency E Applicability or Limits

API 650 Seventh and Later (1980 to Present) Butt 1.00 Basic Standard Butt 0.85 Annex A Spot RT Butt 0.70 Annex A No RT First to Sixth (1961 to 1978) Butt 0.85 Basic Standard Butt 1.00 Annexes D and G

API 12C 14th and 15th (1957 to 1958) Butt 0.85

3rd to 13th (1940 to 1956) Lap a 0.75 3 /8 in. max. t Butt c 0.85
First and Second

(1936 to 1939) Lap a 0.70 7 / 16 in. max. t Lap b 0.50 + k /5 1 / 4 in. max. t Butt c 0.85

Unknown Lap a 0.70 7 / 16 in. max. t Lap b 0.50 + k /5 1 / 4 in. max. t Butt 0.70 Lap d 0.35

a Full double lap-welded. b Full fillet weld with at least 25 % in termittent full fillet opposite side; k = percent of intermittent weld expressed in decimal form. c Single butt-welded joints with a back-up bar were permitted from the years of 1936 to 1940 and 1948 to 1954. d Single lap-welded only. 13T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 4-9
4.3.3.6 As an alternative to the procedures described above, any thinning of the tank s hell below minimum required wall thickness due to corrosion or other wastage may be evaluated to determine the adequacy for continued service by employing the design by analysis methods defined in Se ction VIII, Divisi on 2, Appendix 4 of the ASME Code; or API 579-1/ASME FFS-1, Section 4, Section 5 or Section 6, as applicable. When using the ASME criteria, the stress value used in the original tank design shall be substituted for the S m value of Division 2, if the design stress is less than or equal to the lesser of 2 / 3 Y (specified minimum yield strength) or 1 / 3 T (specified minimum tensile strength). If the original design st ress is greater than 2 / 3 Y or 1 / 3 T , then the lesser of 2 / 3 Y or 1 / 3 T shall be substituted for S m . 4.3.4 Minimum Thickness Calculation for Riveted Tank Shell 4.3.4.1 The minimum acceptable thickness for riveted tank shells shall be calc ulated using the equation in 4.3.3.1 except that the following allowable stress criteria and joint efficiencies shall be used:
S is 21,000 lbf/in. 2 ; E is 1.0 for shell plate 6 in. or more away from rivets. See Table 4.3 for joint effici encies for locations within 6 in. of rivets. 4.3.4.2 The rivet joint efficiencies given in Table 4.3 are conser vative minimums for riveted tank construction details and are included to simplify riveted tank evaluations. Howe ver, in some cases it may be advantageous to calculate the actual rivet joint efficiencies usi ng computational methods applicable to lap and butt type riveted joints. When this alternative of calculated joint effi ciencies is used, the following maxi mum allowable stre sses shall apply: a) for the maximum tensile stress in net section of plate, us e the lesser of 0.80 Y or 0.429 T ; use 21,000 lbf/in. 2 if T or Y is unknown; b) for the maximum shear in net se ction of rivet, use 16,000 lbf/in. 2 ; c) for the maximum bearing stress on pl ates or rivets, use 32,000 lbf/in. 2 for rivets in single shear, and 35,000 lbf/in. 2 for rivets in double shear. 4.3.4.3 For tanks with riveted joints, consideration shall be gi ven to whether, and to what extent, corrosion affects such joints. If calculations show that excess thickness exists , this excess may be taken as corrosion allowance. 4.3.4.4 Non-liquid loads (see 4.3.3.5) shall also be c onsidered in the analysis of riveted tanks. 4.3.5 Distortions 4.3.5.1 Shell distortions include out-of-roundness, buckled areas, flat spots, and peaking and banding at welded joints. 4.3.5.2 Shell distortions can be caused by many conditions such as foundat ion settlement, over- or underpressuring, high wind, poor shell fabricat ion, or repair techniques, and so forth. 4.3.5.3 Shell distortions shall be evaluated on an individual basis to determine if specific conditions are considered acceptable for continuing tank service and/ or the extent of corrective action. 4.3.6 Flaws Flaws such as cracks or laminations shall be thoroughly examined and evaluated to determine their nature and extent and need for repair. If a repair is needed, a repair procedure shall be developed and implemented. The requirement for repairing scars such as arc stri kes, gouges, or tears from temporary attachment welds must be evaluated on a case-by-case basis. Cracks in the s hell-to-bottom weld shall be removed. 10 104-10 API S TANDARD 653

4.3.7 Wind Girders and Shell Stiffeners The evaluation of an existing t ank shell for suitability for service must al so consider the details and condition of any wind girders or shell stiffeners. Degradati on by corrosion of these structural elem ents or their attachment welds to the shell may render these elements inadequate for the design conditions. 4.3.8 Shell Welds The condition of the tank she ll welds shall be evaluated for suitability for service using criteria from this standard, the as-built standard, or fitness-for-service assessment. Any flaws or deterioration such as corrosion or pitting of the existing welds shall be evaluated. If necessary, appropr iate repair procedures shall be established or the tank safe fill height reas sessed. Some typical shell bu tt-welded flaws and recommended procedures for repairs are given in 9.6. 4.3.9 Shell Penetrations 4.3.9.1 The condition and details of existing shell penetrations (nozzl es, manways, cleanout openings, etc.) shall be reviewed when assessing the integrity of an existing tank shell. Details such as type and extent of reinforcement, weld spacing, and thickness of components (r einforcing plate, nozzle neck, bolting flange, and cover plate), are important considerations and shall be reviewed for structural adequacy and compliance wi th the as-built standard. Existing welds on the tank shell that are not to be modified or affected by repairs and are closer than required by API 650 (Seventh Edition or later) are acceptable for continued service if the welds are examined by the magnetic particle method and have no rejectable defects or indi cations. Grinding to eliminate weld defec ts is permissible if the resulting profile satisfies base thickness and weld size requirements. Weld repairs may not be used to accept weld spacings closer than permitted by API 650 (Sev enth Edition or later) except as permitted by 9.10. 2.7. Any other noncompliance, or deterioration due to corrosion, mu st be assessed and repair procedures established where appropriate or the tank re-rated, as necessary. 4.3.9.2 Nozzle wall thickness shall be evaluat ed for pressure and all other loads. 4.3.10 Operation at Elevated Temperatures Tanks of welded construction that opera te at elevated temperatures (exceeding 200 ° F, but less than 500 ° F) shall be evaluated for suitability of service. The requirements of this section are based in part on the requirements of API 650, Annex M. Table 4.3—Joint Efficiencies for Riveted Joints Type of

Joint Number of Rivet Rows Joint Efficiency E Lap 1 0.45 Lap 2 0.60 Lap 3 0.70 Lap 4 0.75 Butt a 2 b 0.75 Butt 3 b 0.85 Butt 4 b 0.90 Butt 5 b 0.91 Butt 6 b 0.92

a All butt joints listed have butt straps both inside and outside. b Number of row on each side of joint center line.

10

13T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 4-11
4.3.10.1 Continued Operation at Elevated Temperatures 4.3.10.1.1 Existing tanks that were origina lly designed and constructed to the requirements of API 650, Annex M1a or M-1b, shall be evaluated fo r continued service, as follows. a) The tank shell shall be evaluated in conformance wi th 4.3.3, except that the allowable stress ( S ) for all shell courses shall not exceed 0.80 Y . The value of Y shall be taken as the minimum spec ified yield strength of the shell material multiplied by the yield str ength reduction factor in of API 650, T able M-1. When the minimum specified yield strength of the shell materi al is not known, the evaluation shall be based upon an assumed value of 30,000 lbf/in. 2

. b) If the bottom plate material in the critical zone has been reduced in thickness beyond the provisions of the original tank bottom corrosion allowance, if any , the shell-to-bottom joint shall be ev aluated for elevated temperature, liquid head and thermal cycles. The simplified analysis techni que recommended in API 650, Section M.4, may be used to satisfy this requirement. 4.3.10.1.2 Existing elevated temperature service tanks that we re not originally desi gned and constructed to the requirements of API 650, Annex M, but have a successful service history of operation shall be evaluated for continued service as noted in 4.3.10.1.1. If the tank diameter ex ceeds 100 ft and the tank was not constructed with a buttwelded annular ring, an analysis of the critic al zone is required [see 4.3.10.1.1 b)]. In additi on, the maximum operating temperature shall not exceed the temperatures at whic h the tank has operated successfully in the past. 4.3.10.2 Conversion to Operation at Elevated Temperatures Existing tanks that were not origi nally designed and constructed to th e requirements of API 650, Annex M shall be evaluated for a change to service to elevated temperatures as follows. a) The tank shell shall be evaluated in conformance with API 650, Annex M. The allow able shell stresses of this standard (API 653) shall not be used. b) The need for a butt-welded annular ring shall be determined in conformance with API 650, Annex M and installed if required. c) The shell-to-bottom joint shall be evaluated for fatigue conditions. In addition, the adequacy of the bottom plate material in the critical zone shall be based upon the requirements of this standard. 

### 4.4 Tank Bottom Evaluation 4.4.1 General Tank bottom inspection strategies shall provide suitable data which, when used with the procedures in this standard, will determine the tank bottom integrity nec essary to prevent leakage of fluids that may cause environmental damage. Each aspect of corrosion phenomena, and other potential leak or failure mechanism must be examined. Periodic assessment of tank bottom integrity shall be performed in addition to the internal inspections specified in 6.4. The assessment period shall be less than or equal to the appropriate internal inspection interval given in 6.4.2. T he use of leak detection tests or monito ring systems (such as double bottoms or liners under tank bottoms with leak de tection pipes) will satisfy the requirement for peri odic assessment between internal inspections. Excessive foundation settlement of storage tanks can affect the integrity of tank shells and bottoms. Therefore, monitoring the settlement behavior of tank s is a recognized practice to assess the integrity of tank bottoms. See Annex B for techniques for eval uating tank bottom settlement. 13 12

13

134-12 API S TANDARD 653
4.4.2 Causes of Bottom Failure The following list gives some historical causes of tank bottom leakage or fa ilure that shall be considered in the decision to line, repair, or replace a tank bottom: a) internal pitting and pitting ra tes in the anticipated service; b) corrosion of weld joints (weld and heat affected zone); c) weld joint cracking history; d) stresses placed on the bottom plates by roof support loads and shell settlement; e) underside corrosion (normally in the form of pitting); f) inadequate drainage resulting in surface water flowing under the tank bottom; g) the lack of an annular plate ring when required; h) uneven settlement that results in high lo calized stresses in the bottom plates; i) roof support columns or other supports welded to the tank bottom where adequate allowance for movement was not made; j) rock or gravel foundation pads wi th inadequately filled-in surface voids; k) nonhomogeneous fill under the tank bottom (e.g. a lump of clay in a sand foundation pad); l) inadequately supported sumps. 4.4.3 Tank Bottom Release Prevention Systems (RPSs) API supports the use of a release prev ention system (RPS) to maintain the in tegrity of tank bottoms. The term RPS refers to the suite of API standards and recommended practice s that are designed to maintain tank integrity and thus protect the environment. With respect to tank bottoms, these include: internal in spection of the tank bottom; leak detection systems and leak test ing of the tank; installing cathodic protection for the underside of the tank bottom; lining the bottom of the tank interior; providing a releas e prevention barrier (RPB) under the tank bottom; or some combination of these measures, depending on the oper ating environment and service of the tank. 4.4.3.1 Internal Inspection Internal inspection of the tank bottom is intended to assess the current bottom in tegrity and identify problem conditions that may lead to future loss of integrity. Internal inspection techniques, such as bottom settlement monitoring, and considerations for determining appropriate inspection frequenc y, are found in 4.4.6, Section 6, Annex B, Annex C, and elsewhere. 4.4.3.2 Leak Detection Systems and Leak Testing Tank leak detection systems and leak test ing are intended to identify, quantify, and/or locate a tank bottom integrity failure that is not detectable visually or through inventory reconciliation. Leak detection may be integral to the tank design, either as constructed or as modified (e.g. RPB with interstitial m onitoring) or may operate separately (e.g. soil vapor monitoring and chemical marker); ma y be operated by the tank owner or as a third party test or service; and may detect leaks continuously or on a per iodic basis. Tank leak detection sys tems and testing methods are listed and discussed in API 575.T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 4-13
4.4.3.3 Cathodic Protection Cathodic protection systems are intended to mitigate corrosion of steel surfaces in contact with soil, such as the underside of tank bottoms. A selection basis for ca thodic protection systems is covered by API 651. 4.4.3.4 Internal Lining Protection Internal linings and coatings for the top side of the t ank bottom are intended to mitigate corrosion by providing a barrier between the tank bottom and corrosion sources. Applied linings and coatings for in ternal surfaces of tank bottoms are covered by API 652. 4.4.3.5 Release Prevention Barriers (RPBs) An RPB includes steel bottoms, synthetic ma terials, clay liners, concrete pads, and all other barriers or combinations of barriers placed in the bottom of or under a tank, which have the function of: 1) preventing the escape of released material, and 2) containing or channeling released material for leak detection. RPB design is covered in detail in Annex I of API 650. Replacement of tank bottoms is covered in 9.10.2. If a decision is made to replace an ex isting bottom, API supports the evaluati on of installing an RP B or continued use of an RPS. The evaluation shoul d consider the effectiveness of other RPS c ontrols, the product stored, the location of the tank, and environmental sensitivities. 4.4.4 Bottom Plate Thickness Measurements Various methods for determining tank bottom plate soilside corrosion are available. The methods vary to the extent by which they can reliably measure general corrosion and pitting. A combination of these methods may be required along with extrapolation techniques and analysis to establish the prob able conditions of the entire tank bottom. Magnetic flux leakage (MFL) tools are commonly used, along with ultrasonic (UT) thickness measurement tools, to examine tank bottoms. Ultrasonic thickness measurement techniques are often used to confirm and further quantify data obtained by MFL examination, but these techniques may not be required depending on the specific procedure and application. The quality of data obtained from both MFL and ultrasonic thickness techniques is dependent on personnel, equipment and procedures. Annex G may be used to provide guidance in qualifying personnel and procedures for obtaining thickness data. 4.4.5 Minimum Thickness for Tank Bottom Plate Quantifying the minimum remaining thic kness of tank bottoms based on the re sults of measurement can be done by the method outlined in 4.4.5.1. Other approaches such as the probabilistic method in 4.4.5.2 may be used. 4.4.5.1 An acceptable method for calculati ng the minimum acceptable bottom thickness for the entire bottom or portions thereof is as follows:
MRT = (Minimum of RT bc or RT ip ) – O r ( StP r + UP r ) where
MRT is the minimum remaining thic kness at the end of interval O r . This value must meet the requirements of Table 4.4 and 4.4.5.4 and 4.4.6;
O r is the in-service interval of operation (years to next internal inspection) not to exceed that allowed by 6.4.2; 134-14 API S TANDARD 653

RT bc is the minimum remaining thickness fr om bottom side corrosion after repairs;
RT ip is the minimum remaining thickness from internal corrosion after repairs;
StP r is the maximum rate of corrosion not repaired on the top side. StP r = 0 for coated areas of the bottom. The expected life of the coat ing must equal or exceed O r to use StP r = 0;
UP r is the maximum rate of corrosion on the bottom side. To calculate the corrosion rate, use the minimum remaining thickness after repairs. Assume a linear rate based on the age of the tanks. UP r = 0 for areas that have effective cathodic protection.
NOTE 1 For areas of a bottom that have been scanned by the magnetic flux leakage (or exclusion) process, and do not have effective cathodic protection, the thickness used for calculating UP r must be the lesser of the MFL threshold or the minimum thickness of corrosion areas that are not repaired. The MFL threshold is defined as the minimum remaining thickness to be detec ted in the areas examined. This value should be predetermined by the tank owner based on the desired inspection interval. Areas of bottom side corrosion that are repaired should be evaluated with the corrosion rate for the repaired area unless the cause of corrosion has been removed. The evaluati on is done by using the corrosion rate of the repaired area for UP r , and adding the patch plate (if used) thickness to the term “minimum of RT bc or RT ip .” NOTE 2 Corrosion of the bottom plate includes loss of metal from isolated or general corrosion. 4.4.5.2 For the probabilistic method, a statis tical analysis is made of thickness data from measurements (see 4.4.6) projecting remaining thickness, bas ed on sample scanning of the bottom. 4.4.5.3 If the minimum bottom thickne sses, at the end of the in-ser vice period of operation, are calculated to be less than the minimum bottom renewal thick nesses given in Table 4.4, or less than the minimum bottom renewal thicknesses providing acceptable risk as determined by an RBI assessment per 6.4.2.4, the botto m shall be lined, repaired, replaced, or the interval to the next internal inspection shortened. 4.4.5.4 Unless a stress analysis is performed, the minimum bottom plate thickness in the critical zone of the tank bottom defined in 9.10.1.2 shall be the sm aller of one-half the original botto m plate thickness (not including the original corrosion allowance) or 50 % of t min of the lower shell course per 4.3. 3.1 but not less than 0.1 in. Isolated pitting will not appreciably affe ct the strength of the plate. 4.4.5.5 The repair of internal pitting, when performed to ext end the in-service period of operation, shall be by pit welding, overlay welding, or lap patching, followed by inspec tion and testing. The extent of weld repairs is limited in the critical zone in ac cordance with 9.10.1.2. 4.4.5.6 The treatment of bottom pitting by the use of non-wel ded repairs (e.g. coatings, caulking) can not be used to increase RT ip for calculating MRT

. 4.4.5.7 The thickness of the projection of the bottom plate beyond the shell as measured at the toe of the outside bottom-to-shell fillet weld shall not be less than 0.1 in. The projection of the bottom plate beyond the outside toe of the shell-to-bottom weld shell shall be at least 3 / 8 in. 4.4.6 Minimum Thickness for Annular Plate Ring 4.4.6.1 Due to strength requirements, the minimum thickness of annular plate ring is usually greater than 0.10 in. Isolated pitting will not appreciably affect the streng th of the plate. Unless a stress analysis is performed, the annular plate thickness shall be in accordance with 4.4.6.2 or 4.4.6.3, as applicable. 4.4.6.2 For tanks in service with a product s pecific gravity less than 1.0, which require annular plates for other than seismic loading considerations, the thickness of the annular plates shall be not less than the thicknesses given in Table 4.5, plus any specified corrosion allowance. Interpolation is allowed within Table 4.5 based on shell stress determined per Note b of Table 4.5. 13

11T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 4-15
4.4.6.3 For tanks in service with a product specific gravity of 1.0 or greater, which require annular plates for other than seismic loading considerations, the thickness of the annular pl ates shall be in accordance with API 650, Table 5-1a or 5- 1b, plus any specified corrosion allowance. Interpolation is allowed within API 650, Table 5-1a or 5-1b based on shell stress determined per Note b of API 650, Table 5-1. 4.4.6.4 For tanks that utilize thickened annu lar plates for seismic considerati ons, a seismic evaluation shall be performed in accordance with the requirements of the as built standard, using the actual thickness of the existing annular plate. 4.4.6.5 For the thickness and projection of the annul ar plate beyond the s hell, see 4.4.5.7.



### 4.5 Tank Foundation Evaluation 4.5.1 General 4.5.1.1 The principal causes of foundation deterioration are settlement, erosion, cracking, and deterioration of concrete initiated by: calcini ng, attack by underground water, attack by fros t, and attack by alkalies and acids. To ensure suitability for service, all tank foundat ions shall be inspected periodically (see 6.3). Table 4.4—Bottom Plate Minimum Thickness Minimum Bottom Plate Thickness at

Next Inspection (in.) Tank Bottom/ Foundation Design

0.10 Tank bottom/foundation design with no means for detection and containment of a bottom leak.

0.05 Tank bottom/foundation design with means to provide detection and containment of a bottom leak.

0.05 Applied tank bottom reinforced lining, > 0.05 in. thick, in accordance with API 652.
Table 4.5—Annular Bottom Plate Thicknesses (in.) (Product Specific Gravity < 1.0) Plate Thickness a

of First Shell Course

(in.) Stress b in First Shell Course (lbf/in. 2 ) < 24,300 < 27,000 < 29,700 < 32,400

t ≤ 0.75 0.17 0.20 0.23 0.30 0.75 < t ≤ 1.00 0.17 0.22 0.31 0.38
1.00 < t ≤ 1.25 0.17 0.26 0.38 0.48 1.25 < t ≤ 1.50 0.22 0.34 0.47 0.59

t > 1.50 0.27 0.40 0.53 0.68 NOTE The thicknesses specified in the table are based on the foundation providing a uniform support under the full wi dth of the annular plate. Unless the foundation is properly compacted, particular ly at the inside of a concrete ringwall, settlement will produce additional stresses in the annular plate.
a Plate thickness refers to t he tank shell as constructed. b Stresses are calculated from [2.34 D ( H – 1)]/ t

. 12

104-16 API S TANDARD 653
4.5.1.2 Some mechanisms of concrete deter ioration are briefly described below. a) calcining (loss of water of hydrat ion) can occur when concrete has been ex posed to sufficiently high temperature for a period of time. During intermediate cooling periods, the concrete can absorb moisture, swell, lose its strength, and crack; b) deterioration of concrete exposed to underground water can be caused by chemical atta ck, by cyclic changes in temperature, and by freezing moisture; c) expansion of freezing moisture in porous concrete, or in concrete with minor settle ment cracks or temperature cracks, can result in spalling and/or t he development of serious structural cracks; d) sulfate-type alkalies, and to a lesser extent, chlorides, can act corrosively to destroy the bond of the concrete; e) temperature cracks (hairline cracks of uniform width) do not seriously affect the streng th of the concrete foundation structure; however, these cracks c an be potential access points for moisture or water seepage that could eventually result in corrosion of the reinforcing steel. 4.5.1.3 When a tank is to be used in elevated temperature [> 93 ° C (200 ° F)] service, the provisions of API 650, Section B.6 shall be considered in the evaluation of the suitability for serv ice of the tank foundation. 4.5.2 Foundation Repair or Replacement 4.5.2.1 If there is a need for foundation replacement or installation, the new foundation elevation profile must meet the tolerance in 10.5.6. Alternatively, if the new foundation is to be constructed up to the bottom, changing the levelness of the tank is not required if reviewed and approved by a storage tank engineer considering the plumbness of the shell, presence, or absence of shell distortion, and original construction levelness which warrant leaving the tank at the current state of levelness. 4.5.2.2 Concrete pads, ringwalls, and piers, s howing evidence of spalli ng, structural cracks, or general deterioration, shall be repaired to prevent water from entering the concrete structur e and corroding the reinforcing steel. 4.5.3 Anchor Bolts Distortion of anchor bolts and excessiv e cracking of the concrete structur es in which they are embedded may be indications of either serious foundation settlement or a tank overpressure uplift condition. 10

135-1 

### Section 5—Brittle Fr acture Considerations

5.1 General This section provides a procedure for the assessment of existing tanks for suitability for continued operation or change of service with respect to the ri sk of brittle fracture and does not supp lement or replace the requirements of Section 12 for the examination and testing for the hydrostatic test ing of repaired, modified, or reconstructed tanks. The procedure applies to both welded and riveted tanks; however, the procedure is based primarily on experience and data obtained from welded tanks. 

### 5.2 Basic Considerations 5.2.1 A decision tree (see Figure 5.1) is used to present the as sessment procedure for failure due to brittle fracture. The decision tree is based on the following principles. 5.2.2 In all reported incidents of tank failure due to brittle frac ture, failure occurred either shortly after erection during hydrostatic testing or on the fi rst filling in cold weather, after a change to lower temperature service, or after a repair/ alteration. This experience shows that once a tank has demonstrat ed the ability to withstand the combined effects of maximum liquid level (highest stresses) and lowest operating te mperature without failing, the risk of failure due to brittle fracture with continued service is minimal. 5.2.3 Any change in service must be ev aluated to determine if it in creases the risk of failure due to brittle fracture. In the event of a change to a more severe service (such as operating at a lower temperature or handling product at a higher specific gravity) it is necessary to consider the need for a hydros tatic test to demonstr ate fitness for a new more severe service. The following aspects should be considered: a) the likelihood of repairs/alterations si nce the original hydrostatic test not meeting requirements of this standard; b) deterioration of the tank sinc e original hydrostatic test. 

### 5.3 Assessment Procedure 5.3.1 The assessment procedure illustrated in Figure 5.1 sha ll be used. Each of the key steps, numbered 1 through 11 on the decision tree, correspond sequentia lly to the explanations provided below. 5.3.2 Step 1— The tanks meet the requirements of API 650 (Seventh Edition or la ter) or API 650, Appendix G (Fifth and Sixth Editions) to minimize the risk of failure due to brittle fracture. Alternatively, tanks may also be shown to meet the toughness requirements of API 650 (S eventh Edition or later) by impa ct testing coupon samples from a representative number of shell plates. 5.3.3 Step 2 —Many tanks that continue to op erate successfully in the same service were not built to the requirements of API 650 (see editions and appendices named in 5.3.2). These tanks are potentially susceptible to failure due to brittle fracture and require an assessment as illustrated by the decision tree. 5.3.4 Step 3 —For the purpose of this assessment, hydrostatic testing demonstrates fitne ss for continued service with minimal risk of failure due to brittle fracture, provided that all governing requirements for repairs, alterations, reconstruction, or change in service are in accordance with this standard (including a need for hydrostatic testing after major repairs, major alterations or reconstruction). The effectiveness of the hydrostatic test in demonstrating fitness for continued service is shown by industry experience. 125-2 API S TANDARD 653

Tank meets API 650 (7th Edition or later) or API 650, Appendix G (5th or 6th Edition). Tank continues to operate in same service ?

Alterations, repairs and reconstruction Meets API 653?

Tank does not meet API 650 (1980) or API 650, Appendix G (5th or 6th Edition). Prior hydro demonstrates fitness for continued service ?

Tank thickness 0.5 in. or below

? Change in service

1 2 11 3 4 5 6 7 8 9

3 10

Is service more severe? Operates at metal temperature above 60 oF ?

Membrane stress below 7 ksi ? Tank full at lowest one day temperature per API 650 Fig. 4-2?

Does tank meet the requirements of API 650 or equal? Tank continues to operate in same service ? Hydrotest to demonstrate fitness for continued service

Yes Yes Yes Yes

Yes

Yes Yes Yes Yes Yes Yes Use

Use Use

Use

Use

Use

Use Use No

No No (See note) No Continue to use Continue to use Continue to use No No No No No Rerate tank based on prior operating history 	
	
	
 	
		 metal temperature 		

NOTE This does not exempt tanks from other hydrotest requirements stipulated in this standard.Tanksteel exemptfrom impacttesting API 650Table 4-1a or 4-1bor API 653Fig. 5.2?Figure 5.1—Brittle Fracture Considerations 12

12T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 5-3
5.3.5 Step 4 —If a tank shell thickness is no greater than 0.5 in., t he risk of failure due to br ittle fracture is minimal, provided that an evaluation for suitabili ty of service in accordance with Secti on 4 has been performed. The original nominal thickness for the thickest tank shell plate shall be used for this assessment. 5.3.6 Step 5 —No known tank failures due to brittle fracture have occurred at shell metal temperatures of 60 °F or above. Similar assurance against brittle fracture can be gained by increasing the metal temperature by heating the tank contents. 5.3.7 Step 6 —Industry experience and laboratory tests have shown that a membrane stress in tank shell plates of at least 7 ksi is required to cause failure due to brittle fracture. 5.3.8 Step 7 —Tanks constructed from steels list ed in Figure 4-1 of API 650 can be used in accordance with their exemption curves, provided that an evalua tion for suitability of service in confo rmance with Section 4 of this standard has been performed. Additionally, tanks constructed in accordance with another nationally recognized code or standard containing toughness rules (such as API 620) ma y be used in accordance with the current toughness rules of that standard. Tanks fabricat ed from steels of unknown materi al specifications, thicker than 1 / 2 in. and operating at a shell metal temperature below 60 °F, can be used if the tank meets the requirements of Figure 5.2. The original nominal thickness for thickest tank shell plate shall be used for the assessment. For unheated tanks, the shell metal temperature shall be the design metal temper ature as defined in API 650, Section 3.4.

5.3.9 Step 8 —The risk of failure due to brittle fracture is mini mal once a tank has demonstrated that it can operate at a specified maximum liquid level at the lowest expect ed temperature without failing. For the purpose of this assessment, the lowest expected temper ature is defined as the lowest one-day mean temperature as shown in API 650, Figure 4-2. It is necessary to check tank log records and meteorological records to ensure that the tank had operated at the specified maximum liquid level when the 1- day mean temperature was as low as shown in API 650, Figure 4-2.

Figure 5.2—Exemption Curve for Tanks Constructed from Carbon Steel of Unknown Material Specification 12

60 70

50

40

30

20

10

0 0.5

0.0 1.0 1.5 2.0 Shell thickness (in.)Shell metal temperature, °F

NOTE For unheated tanks, the shell metal temperature shall equal the design metal temperature as defined in API 650, Section 3.4. The original nominal thickness for the thickest tank shell plate shall be used for the assessment. Safe for use Safe for use

Additional assessment required

125-4 API S TANDARD 653
5.3.10 Step 9 —An evaluation can be performed to establish a safe operating envelope for a tank based on the operating history. This evaluation s hall be based on the most severe combination of temperature and liquid level experienced by the tank during its li fe. The evaluation may show that t he tank needs to be re-rated or operated differently; several options exist: a) restrict the liquid level. b) restrict the minimum metal temperature. c) change the service to a stored produc t with a lower specific gravity. d) combinations of It ems a), b), and c), above. The owner/operator can also make a more rigorous analysis to determine the risk of failure due to brittle fracture by performing a fracture mechanics anal ysis based on established principles and practices. The procedures and acceptance criteria for conducting an alternativ e analysis are not included in this standard. 5.3.11 Step 10 —All repairs, alterations, and relocations s hall be made in compliance with this standard. 5.3.12 Step 11 —An assessment shall be made to determine if the chan ge in service places the tank at greater risk of failure due to brittle fracture. The service can be considered more severe and create a greater risk of brittle fracture if the service temperature is reduced (e.g. changing from heated oil service to ambient temperature product), or the product is changed to one with a greater specific gravity and thus increased stresses.6-1 

### Section 6—Inspection
6.1 General Periodic in-service inspection of tanks shall be performed as defined herein. The purpose of this inspection is to assure continued tank integrity. Inspections, other than those defined in 6.3 shall be directed by an authorized inspector. 

### 6.2 Inspection Frequency Considerations 6.2.1 Several factors must be considered to determine inspecti on intervals for storage tanks. These include, but are not limited to, the following: a) the nature of the product stored; b) the results of visual maintenance checks; c) corrosion allowances and corrosion rates; d) corrosion prevention systems; e) conditions at prev ious inspections; f) the methods and materials of construction and repair; g) the location of tanks, such as t hose in isolated or high risk areas; h) the potential risk of air or water pollution; i) leak detection systems; j) change in operating mode (e.g. frequency of fill cycli ng, frequent grounding of floating roof support legs); k) jurisdictional requirements; l) changes in service (includi ng changes in water bottoms); m)the existence of a double bottom or a release prevention barrier. 6.2.2 The interval between inspections of a tank (both internal and external) should be determined by its service history unless special reasons indicate that an earlier inspection must be made. A history of t he service of a given tank or a tank in similar service (preferably at the same site) should be available so that complete inspections can be scheduled with a frequency commensurate with the corro sion rate of the tank. On-stream, nondestructive examination methods shall be considered when establishing inspection frequencies. 6.2.3 Jurisdictional regulations, in some cases, contro l the frequency and interval of the inspections. These regulations may include vapor loss requirements, seal condition, leakage, proper diking, and repair procedures. Knowledge of such regulations is necessary to ens ure compliance with scheduling and inspection requirements. 

### 6.3 Inspections from the Outside of the Tank 6.3.1 Routine In-service Inspections 6.3.1.1 The external condition of the tank shall be monitored by close visual inspection from the ground on a routine basis. This inspection may be done by owner/operat or personnel, and can be done by other than authorized 136-2 API S TANDARD 653 inspectors as defined in 3.4. Personnel performing this inspection should be knowledgeable of the storage facility operations, the tank, and the charac teristics of the product stored. 6.3.1.2 The interval of such inspections shal l be consistent with condi tions at the particular site, but shall not exceed one month. 6.3.1.3 This routine in-service inspection s hall include a visual inspection of the tank’s exterior su rfaces. Evidence of leaks; shell distortions; signs of se ttlement; corrosion; and condi tion of the foundation, paint coatings, insulation systems, and appurtenances should be documented for follow-up action by an authorized inspector. 6.3.2 External Inspection 6.3.2.1 All tanks shall be given a visual external inspecti on by an authorized inspector. This inspection shall be called the external inspection and must be conducted at least ev ery five years or RCA /4 N

years (where RCA is the difference between the measured shell thickness and the minimum required thickness in mils, and N is the shell corrosion rate in mils per year) whichever is less . Tanks may be in operation during this inspection. 6.3.2.2 Insulated tanks need to have insulation removed only to the extent necessary to determine the condition of the exterior wall of the tank or the roof. 6.3.2.3 Tank grounding system components such as shunts or mechanical connections of cables shall be visually checked. Recommended practices dealing with the prevent ion of hydrocarbon ignition are covered by API 2003. 6.3.3 Ultrasonic Thickness Inspection 6.3.3.1 External, ultrasonic thickness meas urements of the shell can be a means of determining a rate of uniform general corrosion while the tank is in serv ice, and can provide an indication of the integrity of the shell. The extent of such measurements shall be dete rmined by the owner/operator. 6.3.3.2 When used, the ultrasonic thickness measurements sha ll be made at intervals not to exceed the following. a) When the corrosion rate is not known, the maximum interv al shall be five years. Corrosion rates may be estimated from tanks in similar service based on thickness meas urements taken at an interval not exceeding five years. b) When the corrosion rate is known, the maximum interval shall be the smaller of RCA /2 N years (where RCA is the difference between the measured shell thickness and the minimum required thickness in mils, and N is the shell corrosion rate in mils per year) or 15 years. 6.3.3.3 Internal inspection of the tank shel l, when the tank is out of servic e, can be substituted for a program of external ultrasonic thic kness measurement if the inter nal inspection interval is equal to or less than the interval required in 6.3.3.2 b). 6.3.4 Cathodic Protection Surveys 6.3.4.1 Where exterior tank bottom corrosion is controlled by a cathodic protection system , periodic surveys of the system shall be conducted in accordance with API 651. T he owner/operator shall review the survey results. 6.3.4.2 The owner/operator shall assure competency of personnel performing surveys. 

### 6.4 Internal Inspection 6.4.1 General 6.4.1.1 Internal inspection is primarily required to do as follows. a) Ensure that the bottom is not severely corroded and leaking.T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 6-3 b) Gather the data necessary for the minimum bottom and shell thickness assessments detailed in Section 6. As applicable, these data shall also take into account ex ternal ultrasonic thickness measurements made during inservice inspections (see 6.3.3). c) Identify and evaluate any tank bottom settlement. 6.4.1.2 All tanks shall have a formal internal inspection conducted at the intervals defined by 6.4.2. The authorized inspector shall supervise or conduct a visual examination and assure the quality and completeness of the nondestructive examination (NDE) results. If the internal inspection is required solely for the purpose of determining the condition and integrity of the tank bottom, the internal inspection may be accomplished with the tank in-service utilizing various ultrasonic robotic thickness measurement and other on-stream inspection methods capable of assessing the thickness of the tank bottom, in combination with methods capable of assessing tank bottom integrity as described in 4.4.1. Electromagnetic methods may be used to supplement the on-stream ultrasonic inspection. If an in-service inspection is selected, the data and information collected shall be sufficient to evaluate the thickness, corrosion rate, and integrity of the tank bottom and establish the internal inspection interval, based on tank bo ttom thickness, corrosion rate, and int egrity, utilizing the methods included in this standard. 6.4.2 Inspection Intervals Initial and subsequent inspection interval s shall be in compliance with the r equirements of 6.4. 2.1 and 6.4.2.2. For existing tanks, tank owner/operators shall review the internal inspection interval and be in compliance with this section within 5 years from date of first publicat ion of API Standard 653, Fourth Edition, Addendum 3. 6.4.2.1 Initial Internal Inspection Interval The initial internal inspection interval s for newly constructed tanks and/or re furbished tanks shall be established either per 6.4.2.1.1 or 6.4.2.1.2. 6.4.2.1.1 The interval from initial service date until the first in ternal inspection shall not exceed 10 years unless a tank has one or more of the leak prevention, detection, co rrosion mitigation, or containment safeguards listed in Table 6.1. The initial internal inspection date shall be based on in cremental credits for the additi onal safeguards in Table 6.1 which are cumulative. For example, the maximum interval for a 1⁄4 in. bottom t hat has a release prevention barrier and a fiberglass lining would be determined as follows: 10 years (initial) + 5 years (fiberglass lining) + 10 years (release prevention barrier) = 25 years. The initial inspection interval shall not exceed 20 years for tanks without a Release Prevention Barrier, or 30 years for tanks with a Release Prevention Barrier. Table 6.1—Tank Safeguard Tank Safeguard Add to Initial Interval i. Fiberglass-reinforced lining of the product-side of the tank bottom installed per API RP 652. 5 yrs i Installation of an internal thin-film c oating as installed per API RP 652. 2 yrs iii. Cathodic protection of the soil-side of the tank bottom installed, maintained, and inspected per API RP 651. 5 yrs iv. Release prevention barrier install ed per API Std 650, Annex I. 10 yrs v. Bottom corrosion allowance greater than 0.150 in. (Actual corrosion allowance - 150 mils) / 15 mpy 13

136-4 API S TANDARD 653
6.4.2.1.2 As an alternative to establishing the initial interval in accordance with Secti on 6.4.2.1 and Table 6.1, the initial internal inspection date and reassessment can be established using Risk Based Inspection (RBI) assessment per 6.4.2.2.2. These assessments may establish an initial inspection inte rval exceeding 10 years but shall not exceed 20 years for tanks without a Release Prevention Barrier, or 30 years for t anks with a Release Prevention Barrier except as follows. If an RBI assessment has been performed, the maximum init ial internal inspection inte rval does not apply to tanks storing the following. 1) Highly viscous substanc es which solidify at temper atures below 110 °F, (some ex amples of these substances are: asphalt, roofing flux, residuum, vacuum bottoms and reduced crude), or; 2) Any substance or mixture that is: a) not identified or regulated either as a hazardous chemical or material under the applicable laws of the jurisdiction; and b) that the owner/operator has determined will not adver sely impact surface or groundwater beyond the facility or affect human health or the environment. 6.4.2.2 Subsequent Internal Inspection Interval The interval between subsequent internal inspections shall be determined in accordance with either the corrosion rate procedures of 6.4.2.2.1 or t he risk based inspection procedures as outlined in 6.4.2.2.2. 6.4.2.2.1 The subsequent inspection interval (beyond the initial inspection) c an be determined using the measured tank bottom corrosion rate and the minimum remaining thicknes s in accordance with 4.4. 5. During any examination to determine corrosion rates the owner/operator should ens ure they understand the effectiveness of the inspection techniques employed for detecting and m easuring potential damage mechanisms. When changing service, an owner/operator may decide to use internal corrosion rates obtained from similar service assessment (performed per Annex H of API 653) wh en setting subsequent inte rnal inspection dates. When using the corrosion rate procedures of 6.4.2.2.1 the maximum subsequent in ternal inspection interval shall be 20 years for tanks without a Release Prevention Barrier, or 30 years for tanks with a Release Prevention Barrier. 6.4.2.2.2 An owner/operator can establish the subsequent inter nal inspection interval us ing risk based inspection (RBI) procedures in accordance with API RP 580 and the additional requirements of this section. The results of the RBI assessment shall be used to est ablish a tank inspection stra tegy that defines the most appropriate inspection methods, appropriate frequency for in ternal, external and in-service inspections, and prevention and mitigation steps to reduce the like lihood and consequence of tank leakage or failure. An RBI assessment shall consist of a systematic evaluation of both the likelihood of failure and the associated consequences of failure, in accordan ce with API RP 580. The RBI assessment shall be thoroughly documented, clearly defining all factors contributing to both likelihood and consequence of tank leakage or failure. The RBI assessment shall be performed by a team incl uding inspection and engineering expertise knowledgeable in the proper application of API RP 580 pr inciples, tank design, construction, and modes of deterioration. The RBI assessment shall be reviewed and approved by a team as above at intervals not to exceed 10 years or more often if warranted by process, equipm ent, or consequence changes. 13T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 6-5 The applied RBI methodology (not every individual asse ssment) shall have a documented validation review to demonstrate that it has all the key el ements defined in API 580 and this sect ion. The validation should be performed by an entity external to the RBI assessment team. If corrosion rates are based on prior inspections, they s hall be derived from either high or medium inspection effectiveness as defined by the owner-user procedures. Refer to API RP 581 for examples of high and medium inspection effectiveness. Corrosion rates from low inspecti on effectiveness such as spot UT shall not be used in the RBI process. A tank shall be removed from service when the risk exceeds the acceptable risk criteria established per the owneruser procedure. NOTE API does not recommend running tank bottoms to failure, or operating tanks indefinitely with known or suspected bottom leaks. 6.4.2.2.2.1 Likelihood factors that shal l be evaluated in tank RBI assessments, in addition to the likelihood factors in API RP 580 include, but are not limited to, the following: a) original thickness, weld type, and age of bottom plates; b) analysis methods used to determine t he product-side, soil-side and external corrosion rates for both shell and bottom and the accuracy of the methods used; c) inspection history, in cluding tank failure data; d) soil resistivity; e) type and design quality of tank pad/cushion including quality contro l at construction; f) water drainage from berm area; g) type/effectiveness of cathodic pr otection system and ma intenance history; h) operating temperatures; i) effects on internal corrosion rates due to product service; j) internal coating/lining/ liner type, age and condition; k) use of steam coils and water draw-off details; l) quality of tank maintenance, includi ng previous repairs and alterations; m) design codes and standards and the details utilized in the tank construction, repair, and alteration (including tank bottoms); n) materials of construction; o) effectiveness of an inspection in cludes examination methods and scope which are to be determined by the inspector; p) functional failures, such as floating roof seals, r oof drain systems, etc.; q) settlement data; r) quality assurance/control during tank construction, including pad cleanliness, slope of bottom, foundation installation, document/records to s how how the tank was built, etc. 136-6 API S TANDARD 653
6.4.2.2.2.2 Consequence factors that shall be eval uated in tank RBI assessments incl ude, but are not limited to, the following: a) tank bottom with a Release Prevention Barrier (RPB) det ails (single, double, RPB, internal reinforced linings, etc.); b) product type and volume; c) mode of failure, (i.e. slow leak to the environment, tank bottom rupture or tank shell brittle fracture); d) identification of environmental receptors such as wetlands, surface waters, ground waters, drinking water aquifers, and bedrock; e) distance to environmental receptors; f) effectiveness of leak detection systems and time to detection; g) mobility of the product in the envir onment, including, for releases to soil , product viscosity and soil permeability; h) sensitivity characterist ics of the environmental receptors to the product; i) cost to remediate potential contamination; j) cost to clean tank and repair; k) cost associated with loss of use; l) impact on public safety and health; m) dike containment capabilitie s (volume and leak tightness). 

### 6.5 Alternative to Internal Inspection to Determine Bottom Thickness In cases where construction, size, or other aspects allow external access to the tank bottom to determine bottom thickness, an external inspection in lieu of an internal inspection is allowed to meet the data requirements of Table 4.4. However, in these cases, consideration of other maintenance it ems may dictate internal inspection intervals. This alternative approach shall be documented and made part of the permanent record of the tank. 

### 6.6 Preparatory Work for Internal Inspection Specific work procedures shall be pr epared and followed when conducting inspections that will assure personnel safety and health and prevent property damage in the workplace (see 1.4). 

### 6.7 Inspection Checklists Annex C provides sample checklists of items for consideration when c onducting in-service and out-of-service inspections. 

### 6.8 Records 6.8.1 General Inspection records form the basis of a scheduled inspection/maintenance program. (It is recognized that records may not exist for older tanks, and judgments must be based on ex perience with tanks in similar services.) The owner/ operator shall maintain a complete record file consisting of three types of records, namely: construction records, inspection history, and repair/alteration history. 13T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 6-7
6.8.2 Construction Records Construction records may include nameplate information, drawings, specifications, c onstruction completion report, and any results of material tests and analyses. 6.8.3 Inspection History The inspection history includes all measurements taken, th e condition of all parts inspected, and a record of all examinations and tests. A complete description of any unusual conditions with recommendations for correction of details which caused the conditions sha ll also be included. This file will also contain corrosion rate and inspection interval calculations. 6.8.4 Repair/Alteration History The repair/alteration history includes al l data accumulated on a tank from the time of its construction with regard to repairs, alterations, replacements, and service changes (re corded with service conditions such as stored product temperature and pressure). These records should include the results of any experiences with coatings and linings. 

### 6.9 Reports 6.9.1 General For each external inspection performed per 6.3.2 and each internal inspection performed per 6.4, the authorized inspector shall prepare a written report. These inspection reports along with inspector recommendations and documentation of disposition shall be maintained by the ow ner/operator for the life of the tank. Local jurisdictions may have additional reporting and record keeping requirements for tank inspections. 6.9.2 Report Contents Reports shall include at a mini mum the following information: a) date(s) of inspection; b) type of inspection (external or internal); c) scope of inspection, including any areas that were not inspected, with reasons given (e.g. limited scope of inspection, limited physical access; d) description of the tank (number, size, capacity, year constr ucted, materials of constructi on, service history, roof and bottom design, etc.), if available; e) list of components inspected and conditions found (a gener al checklist such as f ound in Annex C may be used to identify the scope of the ins pection) and deficiencies found; f) inspection methods and tests used (visual, MFL, UT, etc.) and results of each inspection method or test; g) corrosion rates of the bottom and shell; h) settlement survey measurem ents and analysis (if performed); i) recommendations per 6.9.3.1;6-8 API S TANDARD 653 j) name, company, API 653 certificati on number and signature of the authorized inspector responsible for the inspection; k) drawings, photographs, NDE reports and other per tinent information shall be appended to the report. 6.9.3 Recommendations 6.9.3.1 Reports shall include recommendations for repairs and moni toring necessary to restore the integrity of the tank per this standard and/or maintain integrity until the next inspection, together with reasons for the recommendations. The recommended maximum inspection interval and basis for calculation that interval shall also be stated. Additionally, reports may include other less critical observations, s uggestions and recommendations. 6.9.3.2 It is the responsibility of the ow ner/operator to review the inspec tion findings and recommendations, establish a repair scope, if needed, and determine the appropriate timing for repairs, monitoring, and/or maintenance activities. Typical timing considerations and examples of repairs are: a) prior to returning the tank to service —repairs critical to the integrity of the tank (e.g. bottom or shell repairs); b) after the tank is returned to service —minor repairs and maintenance activity (e.g. drainage improvement, painting, gauge repairs, grouting, etc.); c) at the next scheduled in ternal inspection —predicted or anticipated repairs and maintenance (e.g. coating renewal, planned bottom repairs, etc.); d) monitor condition for continued deterioration —(e.g. roof and/or shell plate corrosion, settlement, etc.). The owner/operator shall ensure that the disposition of all recommended repairs and monitoring is documented in writing and that reasons are given if reco mmended actions are delayed or deemed unnecessary. 

### 6.10 Nondestructive Examination (NDE) Personnel performing NDE shall meet t he qualifications identified in 12.1.1.2 , but need not be certif ied in accordance with Annex D. The results of any NDE work, however, mu st be considered in the eval uation of the tank by an authorized inspector.

### Section 7—Materials

7.1 General This section provides general requirements for the selection of materials for the repair, alteration, and reconstruction of existing tanks. Specific requirements for repairs and alterations are covered in Section 9. 

### 7.2 New Materials All new materials used for repair, alterations, or rec onstruction shall conform to the current applicable standard. 

### 7.3 Original Materials for Reconstructed Tanks 7.3.1 Shell and Bottom Plates Welded to the Shell 7.3.1.1 All shell plate materials and bottom pl ates welded to the shell shall be i dentified. Materials identified by original contract drawings, API nameplates, or other suitable documentat ion do not require furt her identification. Material not identified shall be tested and identified by the requireme nts as outlined in 7.3.1.2. After identification, determination shall be made as to suitabi lity of the material for intended service. 7.3.1.2 Each individual plate for which adequate identificati on does not exist shall be subjected to chemical analysis and mechanical tests as required in ASTM A6 and ASTM A370 including Charpy V-notch. Impact values shall satisfy the requirements of API 650, Se ction 4.2.9, Section 4.2.10, Section 4.2.11 , and Table 4-4a or Table 4- 4b. When the direction of rolling is not definitely known, two tension specimens shall be taken at right angles to each other from a corner of each plate, and one of thos e test specimens must meet the specification requirements. 7.3.1.3 For known materials, all s hell plates and bottom plates welded to t he shell shall meet, as a minimum, the chemistry and mechanical properties of material specified for the applicati on with regard to thickness and design metal temperature given in API 650, Figure 4-1a or Figure 4-1b. 7.3.2 Structural Existing rolled structural shapes that are to be reused shall meet the requirement of ASTM A7 as a minimum. New structural material shall meet the requiremen ts of ASTM A36 or ASTM A992 as a minimum.
NOTE ASTM A7 was a steel specification that was disc ontinued in the Fourth Edition of API 650, 1970. 7.3.3 Flanges and Fasteners 7.3.3.1 Flange material shall meet the minimum requirements of t he material specifications in the as-built standard. 7.3.3.2 Fasteners shall meet the material specific ations of the current applicable standard. 7.3.4 Roof, Bottom, and Plate Windgirders If existing plates are to be used to reconstruct the tank, they shall be checked for exce ssive corrosion and pitting (see Section 4 and Section 6). 

### 7.4 Welding Consumables Welding consumables shall conform to the AWS cl assification that is app licable to the intended use. 13 12

12 128-1 

### Section 8—Design Considerations for Reconstructed Tanks

8.1 General Any specific design considerations other than normal pr oduct loading shall be specified by the owner/operator. See 4.4.3 for release prevention systems and release prevention barrier definition. 

### 8.2 New Weld Joints 8.2.1 Weld joint details shall meet the welding requirements of the current applicable standard. 8.2.2 All new shell joints shall be butt-welded joints with complete penetration and complete fusion. 

### 8.3 Existing Weld Joints Existing weld joints shall meet the requirements of the as-built standard. 

### 8.4 Shell Design 8.4.1 Thickness to be used for each shell course when checking tank design shall be based on measurements taken within 180 days prior to relocation. (See 4.3.2 fo r measuring procedure, number, and locations of measured thicknesses.) 8.4.2 The maximum design liquid level for product shall be determined by calculating the maximum design liquid level for each shell course based on the s pecific gravity of the product, the actual th ickness measured for each shell course, the allowable stress for the ma terial in each course, and the design me thod to be used. The allowable stress for the material shall be determined usi ng API 650, Table 5-2a or Table 5-2b. For material not listed in Table 5-2a or Table 5-2b, an allowable stress value of the lesser of 2 / 3 yield strength or 2 / 5 tensile strength shall be used. 8.4.3 The maximum liquid level for hydrostatic test shall be determined by using the act ual thickness measured for each shell course, the allowable stress for the materi al in each course, and the design method to be used. The allowable stress for the material shall be determined using API 650, Table 5-2a or Table 5-2b. For material not listed in Table 5-2a or Table 5-2b, an allowable stress value of the lesser of 3 / 4 yield strength or 3 / 7 tensile strength shall be used. 8.4.4 If a corrosion allowance is required for the reconstr ucted tank, the required corrosion allowance shall be deducted from the actual thickness before calculating the maximum liquid level. If the actual thickness is greater than that necessary to allow the liquid le vel required, the extra thickness can be considered as corrosion allowance. 8.4.5 The joint efficiency and allowable stress levels used for t he design liquid level calculat ions shall be consistent with the design method used and with the degree and type of examination made on welded joints. The joint efficiency and allowable stress levels for existing welded joints that are not to be removed and replaced shall be based on the original degree and type of examination. 

### 8.5 Shell Penetrations 8.5.1 Replacement and new penetrations shall be designed, detai led, welded, and examined to meet the requirements of the current applicable standard. 8.5.2 Existing penetrations shall be evaluated fo r compliance with t he as-built standard. 12

12

138-2 API S TANDARD 653


### 8.6 Windgirders and Shell Stability 8.6.1 Top and intermediate windgirders for open top tanks s hall meet the requirements of the current applicable standard. 8.6.2 Tanks to be reconstructed shall be checked for wind-i nduced buckling in accordance with the procedures of the current applicable standard, using t he wind requirements for the location where the tank will be reconstructed. 

### 8.7 Roofs 8.7.1 Roof designs shall meet the requi rements of the as-built standard. 8.7.2 If the new site requires a larger design load than the original site, the adequacy of the existing r oof shall be evaluated using the current applicable standard. 

### 8.8 Seismic Design Tanks that will be reconstructed shal l be checked for seismic stability based on the rules of the current applicable standard using the dimensions and thicknes ses of the reconstructed tank. Recons tructed tanks shall be built to meet the stability requirements of the current applicable standard. Thickened bottom plates under the bottom shell course or anchoring of the tank may be requir ed even if not used on the original tank.9-1 

### Section 9—Tank Repair and Alteration
9.1 General 9.1.1 The basis for repairs and alterations shall be an API 650 equivalence. 9.1.2 Hydrostatic testing requirements, ND E requirements, acceptance criteria for the welds, and repairs to shell plate and existing welds are specified in Section 12. 9.1.3 All repair work must be authorized by the authorized inspector or an engineer ex perienced in storage tank design, before commencement of the work by a repair orga nization. Authorization for alterations to storage tanks that comply with API 650 may not be given without pr ior consultation with, and approved by, an engineer experienced in storage tank design. The authorized inspector will designate in spection hold points required during the repair or alteration sequence and minimum docu mentation to be submitted upon job completion. The authorized inspector may give prior general authorization fo r limited or routine repairs as long as the authorized inspector is sure that the repairs will not require hydrostatic testing or do not require an engineering evaluation. 9.1.4 All proposed design, work execution, materials, we lding procedures, examination, and testing methods must be approved by the authorized inspector or by an engineer experienced in storage tank design. The authorized inspector or an engineer experienced in storage tank design shall approve all specified repair and alteration work at the designated hold points and after repairs and alterations have been completed in accordance with the requirements of this standard. 9.1.5 Annex F summarizes the requirements by method of examination and provides the acceptance standards, examiner qualifications, and procedure requirements. Annex F is not int ended to be used alone to determine the examination requirements for work covered by this docum ent. The specific requirement s as listed in Section 1 through Section 12 shall be followed in all cases. 

### 9.2 Removal and Replacement of Shell Plate Material 9.2.1 Minimum Thickness of Replacement Shell Plate The minimum thickness of the replacement shell plate material shall be calculat ed in accordance with the as-built standard. The thickness of the replacement shell plate shall not be less than the greatest nominal thickness of any plate in the same course adjoining t he replacement plate except where the adjoining plate is a thickened insert plate. Any changes from the original desi gn conditions, such as s pecific gravity, design pr essure, liquid level, and shell height, shall be considered. 9.2.2 Minimum Dimensions of Replacement Shell Plate 9.2.2.1 The minimum dimension for a replacem ent shell plate is 12 in. or 12 time s the thickness of the replacement plate, whichever is greater . The replacement plate may be circular , oblong, square with rounded corners, or rectangular with rounded corners except when an entire shell pl ate is replaced. See Figure 9.1 for typical details of acceptable replacem ent shell plates. 9.2.2.2 Where one or more entire shell plates or full height segments of shell plates are to be removed and replaced, the minimum spacing requirements specified in Figure 9.1 for vertical weld joints shall be maintained. It is acceptable to remove and replace entire shell plates or full height segments of shell plates by cutting and rewelding along the existing horizontal weld joints. Prior to welding the new vertical joints, the exis ting horizontal welds shall be cut for a minimum distance of 12 in. beyond the new vertical joints. The vertical joints shall be welded prior to welding the horizontal joints.9-2 API S TANDARD 653

9.2.3 Weld Joint Design 9.2.3.1 Shell replacement plates shall be welded with butt joints with complete penetration and complete fusion, except as permitted for lapped patch shell repairs. 9.2.3.2 Weld joint design for replacement shell plates shall be in accordance with API 650, Section 5.1.5.1 through Section 5.1.5.3. Joints in lap-welded shell tanks may be repaired according to the as-built standard. Lap-welded joint design for lapped patch shell repairs shall meet the requirement s of 9.3. Details of weldi ng shall be in accordance with 7.2 of API 650, and Section 9 of this standard. 9.2.3.3 For existing shell plates over 1 / 2 -in. thick, the outer edge of the butt weld attaching the replacement shell plate shall be at least the greater of 8 times the weld thickness or 10 in. from the outer edge of any existing buttwelded shell joints. For existing shell plates 1 / 2 -in. thick and less, the spacing may be reduced to 6 in. from the outer edge of vertical joints or 3 in. from the outer edge of horizontal joints. See Figure 9.1 for minimum dimensions. Figure 9.1—Acceptable Details for Replacement of Shell Plate Material R

A

V V

V

R VA

Note 2

R

R RBHHB Weld joint (annular or bottom plates) C * See Note 3 Existing welds Existing welds Greater of R

or H

Bottom plate

R B H V A 6 in. 6 in. 3 in. 6 in. 12 in. Dimension t ≤ 0.5 in. t > 0.5 in. Greater of 6 in. or 6 t Greater of 10 in. or 8 t Greater of 10 in. or 8 t Greater of 10 in. or 8 t Greater of 12 in. or 12 t Minimum Weld Spacing Between Edges (Toes) of Welds for Thickness of Replacement Shell Plate, t , (inches)

NOTE 1 All weld intersections shall be at approximately 90o. NOTE 2 Prior to welding new vertical joints, cut existing horizontal weld for a minimum of 12 in. beyond the new vertical joints. Weld the horizontal joint last. NOTE 3 Prior to welding new vertical joints, cut existing shell-to-bottom weld for a minimum of 12 in. beyond the new vertical joints. The cut shall extend past or stop short of existing bottom plate welds by at least 3 in. or 5 t . Weld the shell-to-bottom weld last. Greater of 3 in. or 5 t C * * * SeeT ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 9-3 For existing shell plates over 1 / 2 -in. thick, the outer edge of the butt weld attaching the replacement shell plate shall be at least the greater of 8 times the weld size or 10 in. from the edge (toe) of the fille t weld attaching the bottom shell course to the bottom except when the replacement shell plate extends to and intersects the bottom-to-shell joint at approximately 90 ° . For existing shell plates 1 / 2 -in. thick and less, this spacing may be reduced to 6 in. For shell plates of unknown toughness not meeting the exemption criteria of Figure 5.2, the edge of any vertical weld joint attaching a replacement plate shall be at 3 in. or 5 t . from the edge of a weld joint in the bottom annular ring or weld joints in bottom plates under the tank shell. Figure 9.1 has minimum dimensions. 9.2.3.4 To reduce the potential for distortion of an existing tank due to welding a replacement plate into an existing tank shell, fit-up, heat input, and welding sequence must be considered. 9.2.4 Door Sheet Installation This section describes the requirements for reinstallation or replacement of a door sheet. The requirements of Figure 9-1, Figure 9-2, Figure 9-3, Figure 9-4 and Figure 9-5 sha ll be used to locate door sheets relative to existing seams, unless an alternative design is des igned by a Storage Tank Engineer a nd the Owner/Operator approves the alternative in writing. 9.2.4.1 Door sheet installation shall meet the requirements of Section 9.2.1, Secti on 9.2.2, Section 9.2.3 and Section 12.2.1.6. 9.2.4.2 The removed shell plate section of a door sheet in a butt-welded tank may be re-i nstalled in its original location or the section may be replaced wi th new shell plate material. In either case the door sheet installation shall utilize joints with complete penetration and complete fusion. 9.2.4.3 For lap welded and riveted tanks, reinstallation of an orig inal plate section that crosses an existing horizontal seam is not permitted. Door sheets that cross vertical riveted or lap weld ed seams are not permitted in any case. 9.2.4.4 If a door sheet vertical cut-line crosses an existing s eam in a butt-welded tank without an offset and the removed section is reinstalled then addi tional weld examination shall be requi red at the intersection of the new vertical weld seam and existing horizontal weld seam. In addition to the examination requirements of 12.1.5.1 the back gouged surface of the root pass and the final pass (eac h side) of the new welds shall be examined by magnetic particle or liquid penetrant methods. The existing horizontal weld seam intersected by the new vertical weld shall also be examined by magnetic particle or liquid penetr ant methods for a 6 in. distance on both sides.
NOTE “Offset” is the horizontal distance bet ween the vertical welds above and below a ho rizontal seam, as shown in Figure 9.2, Figure 9.3, and Figure 9.5. 9.2.4.5 If a door sheet vertical cut-line crosses an existing seam in a butt-welded tank with an offset, the minimum offset must equal dimension ‘V’ as show n in Figure 9.5. Prior to welding the new vertical seams, cut existing horizontal seam weld for a minimum of 12 in. beyond the new vertical join ts. Weld the horizontal seam last. 9.2.4.6 If a door sheet cut line crosses a lap-welded or a riveted horizontal seam, the replacement assembly shall be constructed of two separate plates, with the lower secti on butt-welded to the adjacent she ll course by means of full penetration, full fusion vertical welds. The upper section shall be lapped ov er or under the lower section and the upper plate shall be butt welded to the existing s hell plate. After the butt welds are comple ted, the horizontal lap shall be fillet welded along both inside and outside edges. 9.2.4.7 New weld seams in riveted tanks shall be located a mini mum of 12 in. from existing rivet seams to minimize potential for rivet and rivet seam leaks or the rivets and exis ting lap rivet seams shall be seal welded or sealed by the application of caulk or coating that is co mpatible with the s pecified stored product.
NOTE The heat created by welding may cause nearby rivets and rivet seams to leak. 129-4 API S TANDARD 653

Figure 9-2—Details for Door Sheets in Riveted Seam Tank

Figure 9-3—Details for Door Sheets in Lap Weld Seam Tank Seal rivets and rivet seams Greater of R or H See Note 4 See Note 4

See Note 4

12 in. minimum (see Note 5) 3 in. or 5t minimum (see Note 5) See Note 4 R V

Plug weld rivet holes (see Note 6)

NOTES: 1. See table in Figure 9-1 for minimum weld spacing and dimensions H, R, and V. 2. When a door sheet crosses the horizontal joint between two courses, a replacement door sheet assembly shall be constructed of two separate plates. The upper door sheet thickness shall be the same as the higher shell course thickness. The lower door sheet thickness shall be the same as the lower shell course thickness. 3. Fillet Weld size shall be equal to thickness of thinner of two plates. 4. Rivets and existing lap rivet seams located within 12 in. of a weld may need to be sealed with calk/coating or seal-welded to prevent product seepage. 5. Prior to welding new vertical seam which intersect the bottom plate, cut existing shell-to-bottom weld for a minimum of 12 in. beyond the new vertical weld seam. The cut shall extend past or stop short of existing bottom plate welds by at least 3 in. or 5t. Weld the shell-to-bottom weld last. 6. Plug weld all rivet holes in the shell plate where rivets are removed. Filler weld to full plate thickness and grind flush. 7. Door sheets need not extend to shell-to-bottom weld provided that weld spacing and corner radii are in accordance with Figure 9-1.

12

Greater of R or H 6 in. minimum See Note 3

12 in. minimum (see Note 4) Greater of 3 in. or 5t (see Note 4) R V Existing weld V Existing weld

NOTES: 1. See table in Figure 9-1 for minimum weld spacing and dimensions H, R, and V. 2. When a door sheet crosses the horizontal joint between two courses, a replacement door sheet assembly shall be comprised of two separate plates. The upper door sheet thickness shall be the same as the higher shell course thickness. The lower door sheet thickness shall be the same as the lower shell course thickness. 3. Fillet Weld size shall be equal to thickness of thinner of two plates. 4. Prior to welding new vertical joints which intersect the bottom plate, cut existing shell-to-bottom weld for a minimum of 12 in. beyond the new vertical weld joint. The cut shall extend past or stop short of existing bottom plate welds by at least 3 in. or 5t. Weld the shell-to-bottom weld last. 5. Door sheets need not extend to shell-to-bottom weld provided that weld spacing and corner radii are in accordance with Figure 9-1.T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 9-5

Figure 9-4—Details for Door Sheet in Butt Weld Shell Seam Tank—No Vertical Seam Offset

Figure 9-5—Details for Door Sheet in Butt Welds Shell Seam Tank—Tank-Vertical Seam Offset Greater of R or H

12 in. minimum (see Note 3) Greater of 3 in. or 5t (see Note 3) H

V Door sheet seam

R

V Existing weld

NOTES: 1. See table in Figure 9-1 for minimum weld spacing and dimensions H, R, and V. 2. Detail shown for door sheet that utilizes removed section of tank shell. If new material is utilized, see Figure 9-1 for requirements. 3. Prior to welding new vertical weld seam which intersects the bottom plate, cut existing shell-to-bottom weld for a minimum of 12 in. beyond the new vertical weld seam. The cut shall extend past or stop short of existing bottom plate welds by at least 3 in. or 5t. Weld the shell-to-bottom weld last. 4. Door sheets need not extend to shell-to-bottom weld provided that weld spacing and corner radii are in accordance with Figure 9-1.

12

Greater of R or H Door sheet seams

12 in. minimum (see Note 3) Greater of 3 in. or 5t (see Note 3) R
V Existing weld V H

See Note 2 See Note 2 Existing weld

NOTES: 1. See table in Figure 9-1 for minimum weld spacing and dimensions H, R, and V. 2. Prior to welding new vertical joints, cut the existing horizontal weld for a minimum of 12 in. beyond the new vertical weld seam. Weld the horizontal seam last. 3. Prior to welding new vertical joints which intersect the bottom plate, cut the existing shell-to-bottom weld for a minimum of 12 in. beyond the new vertical weld joint. The cut shall extend past or stop short of existing bottom plate welds by at least 3 in. or 5t. Weld the shell-to-bottom weld last. 4. Door sheets need not extend to shell-to-bottom weld provided that weld spacing and corner radii are in accordance with Figure 9-1.9-6 API S TANDARD 653


### 9.3 Shell Repairs Using Lap-welded Patch Plates 9.3.1 Lapped patch shell repairs are an acceptable form of repair for butt-welded, lap-welded, and riveted tank shells, under the conditions outlined in 9.3.2, 9.3.3, and 9.3.4; only when specified by the owner. In addition, the repair details shall comply with the requirements of 9.3.1.1 through 9.3.1.10. These repairs are permanent repairs subject to an ongoing inspection and maintenance program. These requirements may be used to evaluate existing lapped patch shell repairs; however, the plate thickness limits need not apply. 9.3.1.1 All repair material shall comply wit h the requirements of the current applicable standard of construction and API 653. 9.3.1.2 Lapped patch shell repairs shall not be used on any sh ell course thickness (original construction) that exceeds 1 / 2 in., nor to replace doorsheets or shell plates. 9.3.1.3 Except as permitted in 9.3.3.2 and 9.3.4.3, the repair plate ma terial shall be the smaller of 1 / 2 in. or the thickness of the shell plate adjacent to the repairs, but not less than 3 / 16 in. 9.3.1.4 The shape of the repair plate may be circular, oblong, squar e, or rectangular. All corners, except at the shellto-bottom joint, shall be rounded to a minimum radius of 2 in. The nozzle reinforcing pl ate shapes of API 650, Figure 5-8, are also acceptable. 9.3.1.5 The repair plate may cross any butt-welded vertical or horizontal shell seams that have been ground flush, but must overlap a minimum of 6 in. beyond the shell seam. The weld spacing requirements of Figure 9.1 shall be used as a basis for locating repair plat es relative to butt-welded, fillet-we lded, and riveted seams and other repair plates. 9.3.1.6 Repair plates may extend to and intersect with the exter nal shell-to-bottom joint if the vertical si des intersect the tank bottom at a 90 ° angle and the shell-to-bottom weld is in c onformance with Figure 9.6. Repair plates positioned on the shell interior shall be located such that t he toe-to-toe weld clearances ar e a minimum of 6 in. to the shell-to-bottom weld. 9.3.1.7 The maximum vertical and horizontal di mension of the repair plate is 48 in. and 72 in., respectively. The minimum repair plate dimension is 4 in. The re pair plate shall be formed to the shell radius. 9.3.1.8 Shell openings and their reinforcements shall not be positioned within a lapped patch shell repair. 9.3.1.9 Prior to application of a lapped patch shell repair, the areas to be welded shall be ultrasonically examined for plate defects and remaining thickness. 9.3.1.10 Repair plates shall not be lapped onto lap-welded s hell seams, riveted shell seams, other lapped patch repair plates, distorted areas, or unrepaired cracks or defects. 9.3.2 Lapped patch repair plates may be used for the closure of holes caused by the removal of existing shell openings or the removal of severely corroded or eroded areas. In addition, the follo wing requirements shall be satisfied. 9.3.2.1 The welding shall be continuous on the outer perimeter of the repair plate and the inner perimeter of the hole in the shell plate. The minimum hole diameter is 2 in. Shell openings due to plate removal shall have a minimum corner radius of 2 in. 9.3.2.2 Nozzle necks and reinforcing plates shall be entirel y removed prior to installation of a repair plate. 9.3.2.3 The repair plate thickness selecti on shall be based on a design that conf orms to the as-built standard and API 653, using a joint efficiency not exceeding 0.70. The weld s of the repair plate shall be full fillet welds. The minimum repair plate dimensi on shall be 4 in. with a minimum overlap of 1 in. and a maximum overlap of 8 times the shell thickness (8 t ). 9.3.2.4 The repair plate thickness shall not exceed the nominal thickness of the shell plate adjacent to the repair. 12

13T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 9-7

9.3.3 Lapped patch repair plates may be used to reinforce areas of severely deteriorated shell plates that are not able to resist the service loads to wh ich the tank is to be subjected. Lapped pa tch repair plates may also be used for shell plates that are below the retire ment thickness, providing the follow ing additional requirements are satisfied. 9.3.3.1 The selection of the repair plate thickness shall be bas ed on a design that conforms to the as-built standard and API 653, using a joint efficiency not exceeding 0.35. The perimeter weld shall be a full fillet weld. 9.3.3.2 The repair plate thickness s hall not exceed the shell plat e thickness at the perimeter of the repair plate by more than one-third, but no more than 1 / 8 in. The repair plate thickness shall not exceed 1 / 2 in. 9.3.3.3 The remaining strength of the deterio rated areas under the repair plate shall not be considered as effective in carrying the calculated service or hydrotest loads. 9.3.4 Lapped patch repair plates may be used to repair small shel l leaks, or minimize the potential from leaks from severely isolated or widely scattered pitting if the following requirements are satisfied. 9.3.4.1 The existing shell thickness, excludi ng the holes and pitting, meets the minimum acceptable shell thickness as determined by 4.3.2 and 4.3.3. 9.3.4.2 The repair plate is designed to withstand the hydrostatic pressure load between the repair plate and the shell assuming a hole exists in the sh ell using a joint efficiency of 0.35. 9.3.4.3 The repair plate thickness s hall not exceed the shell plat e thickness at the perimeter of the repair plate by more than one-third, but no more than 1 / 8 in. The repair plate thickness shall be no thinner than 3 / 16 in. nor thicker than 1 / 2 in. A full fillet perimeter weld is required. Figure 9.6—Lapped Patch Repair Plates at the External Shell-to-bottom Joint T

Tank shell

Repair Plate

W 3 / 16

Trim repair plate to clear shell-to-bottom weld T

Detail A For T > existing shell-to-bottom weld size Detail B For T ≤ existing shell-to-bottom weld size
W

= lesser of repair plate thickness or bottom plate thickness
129-8 API S TANDARD 653
9.3.4.4 This repair method shall not be us ed if exposure of the fillet welds to the product will produce crevice corrosion or if a corrosion cell between the shel l plate and repair plate is likely to occur. 9.3.4.5 This repair method shall not be used to repair shell leaks if the pres ence of product betw een the shell plate and repair plate will prevent gas freeing from the tank to perform hot work. 9.3.4.6 The existing shell plate under the repair plate shall be evaluated at each future inspection to ensure it satisfies the requirements of 9.3.4.1. If the existing shell pl ate thickness does not satisfy 9.3.4.1 or the repair plate does not satisfy 9.3.3, the area is to be repaired in accordance with 9.2 or 9.3.2. 

### 9.4 Repair of Defects in Shell Plate Material The need for repairing indications such as cracks, gouges or tears (such as t hose often remaining after the removal of temporary attachments), widely scattered pits, and co rroded areas discovered during an inspection of the tank shell shall be determined on an individual case basis in accordance with Section 4. In areas where the shell plate thickness exceeds that required by design conditions, it is permissible to grind surf ace irregularities to a smooth contour so long as the remaining th ickness is adequate for the design cond itions. Where grinding to a smoothly contoured surface will result in unacce ptable shell plate metal thickness, the shell plate may be repaired by deposition of weld metal, followed by examination and testi ng in accordance with 12.1.8. If more extensive areas of shell plate require repair, use of butt welded shell repl acement plate or lap-welded pa tch plate shall be considered. 

### 9.5 Alteration of Tank Shells to Change Shell Height Tank shells may be altered by adding new plate material to increase the height of the tank shell. The modified shell height shall be in accordance with the requirements of the current applicable standard and shall take into consideration all anticipated load ings such as wind and seismic. 

### 9.6 Repair of Defective Welds Types of weld flaws and nonconformances that need repair are described in 9.6.1 through 9.6.4. 9.6.1 Cracks, lack of fusion, and reject able slag and porosity that need repair shall be removed completely by gouging and/or grinding and the resulting cavity properly prepared for welding. 9.6.2 Generally, it is not necessary to remove existing weld reinforcement in excess of that allowed by API 650 when discovered on an existing tank with a satisfactory service history. Howe ver, if operating conditions are such that the excessive weld reinforcement may be deleterious (such as for a floating roof with flexible seals), consideration shall be given to repairing the welds by grinding. 9.6.3 Existing weld undercut deemed unacceptable based on suitabi lity for service consider ations shall be repaired by additional weld metal, or grinding, as appropriate. 9.6.4 Welded joints that have experienced loss of metal due to corrosion may be repaired by welding. 9.6.5 Arc strikes discovered in or adjacent to welded joints shall be repaired by grinding and/or welding. Arc strikes repaired by welding shall be ground flush with the plate. 

### 9.7 Repair of Shell Penetrations 9.7.1 Repairs to existing shell penet rations shall be in compliance with API 650, Section 5.7. 9.7.2 Reinforcing plates may be added to existing unreinforced noz zles when deemed appropriate. The reinforcing plate shall meet all dimens ional and weld spacing requirements of API 650, Section 5.7. See Figure 9.7 and Figure 9.8 for acceptable details. 12T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 9-9

Figure 9.7—Typical Details for Addition of Reinfo rcing Plate to Existing Shell Penetration

Figure 9.8—Typical Details for Addition of “Tombstone” Shape Reinforcing Plate to Existing Shell Penetration A

A A T t

T or t (1.5 in. max) Tank shell 1 / 4 in. tell tale hole, drill and tap for 1 / 8 -in. pipe thread

Greater of 2 in. or 6 T

1 / 16 in.

SECTION A

- A

9 / 16 in. 3 / 4 in. 15 / 16 in. 1 1 / 8 in. 1 5 / 16 in. 1 9 / 16 in. 1 3 / 4 in. 1 / 4 in. 5 / 16 in. 3 / 8 in. 7 / 16 in. 1 / 2 in. 9 / 16 in. 5 / 8 in. t and T (maximum) A

NOTE All details, dimensions, and weld spacing shall be in accordance with the requirements of API 650.

12

A

A A B T t

T or t (1.5 in. max) Tank shell 1 / 4 -in. telltale hole, drill and tap for 1 / 8 -in. pipe thread

Greater of 2 in. or 6 T

SECTION A

- A

9 / 16 in. 3 / 4 in. 15 / 16 in. 1 1 / 8 in. 1 5 / 16 in. 1 9 / 16 in. 1 3 / 4 in. 1 / 4 in. 5 / 16 in. 3 / 8 in. 7 / 16 in. 1 / 2 in. 9 / 16 in. 5 / 8 in. t and T (maximum) A
1 / 4 in. 1 / 4 in. 5 / 16 in. 5 / 16 in. 3 / 8 in. 3 / 8 in. 3 / 8 in.

B

NOTE All details, dimensions, and weld spacing shall be in accordance with the requirements of API 650. 1 / 16 in.

129-10 API S TANDARD 653
9.7.3 As an alternative, the reinforcing plates may be added to the inside of the tank prov ided that sufficient nozzle projection exists. 

### 9.8 Addition or Replacement of Shell Penetrations 9.8.1 New shell penetrations (addition or repl acement) shall be in accordance with material, design, and stress relief requirements of API 650, Section 5.7 and in acco rdance with 9.8.2 through 9.8.6 of this standard. 9.8.2 The required penetration reinforcement area of API 650, Section 5.7.2, shall be det ermined using the required shell thickness calculated by t he equation in 4.3.3.1 b) of th is standard except the variable S shall be the allowable design stress from API 650, Table 5-2a or Table 5-2b for the existing shell plate; use 20,000 lbf/in. 2 if of unknown material. A joint efficiency of 1.0 may be used (see 9.8.5). The variable H shall be the height from the centerline of the penetration to the maximum liquid level, in ft. 9.8.3 Penetrations shall be prefabricated in thermally stress relieved insert assemblies when required by API 650, Section 5.7.4. API 650, Section 4.1.5, may be used when reinforcing material is from API 650 Group-IV through Group-VI and the existing shell is a Group-I through Group-IIIA material. 9.8.4 The following erection requirements shall be met: a) if an integral reinforcement design is used, the insert pl ate at its periphery shall have a 1:4 reduction taper to match the shell plate thickness when the insert plate exceeds the shell plate thickness by more than 1 / 8 in.; b) spacing of welds shall be in accordance with Figure 9.1; c) the new insert plate shall be joi ned to existing shell plate with full penetration and full fusion butt welds. 9.8.5 Examinations shall be per Section 12, except penetrations located on a shell joint shall receive additional shell radiography in accordance with API 650, Section 5.7.3. 9.8.6 Penetrations larger than 2 in. NPS shall be installed with t he use of an insert plate if the shell plate thickness is greater than 1 / 2 in. and the shell plate material does not meet th e current design metal temperature criteria. In addition, the following r equirement shall be met: a) the minimum diameter of the insert pl ate shall be at least twice the diameter of the penetration or the diameter plus 12 in., whichever is greater; b) when reinforcing plates are used, t he minimum diameter of the insert pl ate shall equal the diameter of the reinforcing plate plus 12 in. 

### 9.9 Alteration of Existing Shell Penetrations 9.9.1 Existing shell penetrations may be altered if the alter ed details comply with the requirements of API 650, Section 5.7 including the requirements for minimum reinforcing area and the requirements for spacing of welds around connections. 9.9.2 When installing a new tank bottom above the existing bot tom, it may be necessary to alter existing shell penetrations in the bottom course of a tank shell. If the new bottom is slotted through the tank shell several inches above the existing bottom, the spacing between existing welds around penetrations and the new bottom-to-shell weld may not comply with API 650 requirements. Options for alte ring the penetrations and/or reinfo rcing plates are given in 9.9.2.1 through 9.9.2.3. 9.9.2.1 The existing reinforcing plate may be trimmed to in crease the spacing between the welds provided that the altered detail complies with the require ments of API 650, Section 5.7. Care must be exercised during the trimming 12

12

12

12T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 9-11 operation to avoid damaging the shell material beneath the rein forcing plate. The existing weld attaching the portion of the reinforcing plate to be removed shal l be completely removed by gouging and grinding. 9.9.2.2 The existing reinforcing plate may be removed and a new reinforcing plate added except that reinforcing plate replacement is not permitted in exis ting stress relieved assemblies unless the requirements of 11.3 are met. If it is not known whether the assembly wa s thermally stressed relieved, then the alteration shall meet the requirements of API 650, Section 5.7.4. Care must be exercised when removing the existi ng reinforcing plate to avoid damaging the shell plate beneath the reinforcing plate. When the upper half of the existing reinforcing plate meets all requirements of API 650, it can be left in place with approval of the purchaser. In this case, only the lower half of the existing reinforcing plate need be remov ed and replaced with the new one. The existing upper half of the reinforcing plate and the new lower section shall be provided with new a telltale hole, if needed, or drilled hole, and a welded pipe coupling for the pneumatic test. The shell plate thickness under the telltale hole or dril led hole shall be checked after drilling and the thickness shall not be less than 1 / 2 t min , as calculated in 4.3.3.1, plus any required corrosion allowance. The welds to be replaced around the perimeter of the reinforcing plate and between the reinforcing plate and neck of the penetration shall be completely removed by gouging and grinding. The new reinforcing plate shall be in accordance with Figure 9.7. If r equired to maintain weld spacing, a tombstone shaped reinforcing plate may be used (see Figure 9.8). 9.9.2.3 The existing penetration may be moved by cutting t he section of the shell containing the fitting and reinforcing plate, and raising the entire assemb ly to the correct elevation (see Figure 9.9).

Figure 9.9—Method for Raising Shell Nozzles 10

Filler plate same thickness as shell

Old bottom R —see Figure 9-1 + +

Spacing per Section 5.7.3 of API 650, or as permitted per 9.10.2.4

New bottom R

—see Figure 9-1

Old bottom Reinforcing plate Top of proposed new bottom

AFTER RAISING BEFORE RAISING Cut lines in shell plate

129-12 API S TANDARD 653
9.9.3 Any components of the penetration (neck, flange, and reinforc ing plate) that are in serviceable condition after removal may be reused. 9.9.4 A new bottom may be installed through an existing tombst one reinforcing plate, provided all weld spacing and reinforcement requirements, as spec ified in API 650, are met. One of the following methods shall be used. a) Remove only that portion of the exis ting reinforcing plate necessary to weld and test the new bottom-to-shell weld. The lower edge of the reinforcing plate shall be cut r easonably straight and horizontal and beveled to facilitate welding. See Figure 9.10 for weld joint details. b) Bevel the shell from the inside to allow for a full penetration weld between the bottom and shell. This method shall only be used on tanks where the annular plate or bottom sketch plate thickness is equal to or greater than 10 mm ( 3 / 8 in.). This weld detail shall be used along the full width of the reinforcing plate and shall extend a minimum of 25 mm (1 in.) beyond the edges of the reinforcing plate. Once beyond the reinforcing plate, the full penetration weld shall tie in to the outside shell-to-bottom fillet weld to create a “water stop” and then transition to the typical shell-to -bottom weld detail. See Figure 9.11 for weld joint details. c) The bottom portion of the reinforcing plate may be removed using a horizontal cut between the bottom invert of the nozzle neck and the new bottom per requirements of Figure 9.12. The removed (or new) reinforcing plate shall be prepared for a full fusion splice weld with telltale hole added (see Figure 9.12). The removed (or new) reinforcing plate shall be re-installed after the shell-to-bottom weld has been completed, inspected, and tested. The splice weld shall be made prior to the reinforcing plate weld to bottom plate weld. The completed splice weld shall be magnetic particle examined.

Figure 9.10—Details for Installing a New Bottom Through an Existing Tombstone Reinforcing Plate 10

12 10

Centerline of nozzle

Tank shell

Fillet weld sizes per API 650, Section 5.1.5.7

Not less than the greater of T /2 or the fillet size determined from API 650, Section 5.1.5.7 New bottom or

annular plate

Existing tombstone reinforcing plate

See Note 1

T t Existing shell penetration (existing welds not shown)

NOTE 1 In using this detail, it must be confirmed that the distance from top of new bottom to center of nozzle meets API 650, Table 5-6a or Table 5-6b. NOTE 2 All welds shown shall be individually examined to API 650, Section 7.2.4. 12T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 9-13

d) The lower portion of the existing reinforcing plate may be removed and re-installed after the new shell-to-bottom weld is complete. The existing reinforcing plate shall be cut at the horizontal centerline of the nozzle. Telltale holes are required in both parts of the reinforcing plate (see Figure 9.8). e) The existing reinforcing plate may be removed, modifi ed and re-installed after the new shell-to-bottom weld is complete (see Figure 9.8). NOTE 1 Options d) and e) are not permitted on existing post-weld h eat treated nozzles unless the requirements of 11.3 are met. NOTE 2 To minimize damage to the shell plate such that re pairs can be made, care must be exercised when removing the existing reinforcing plate. 

### 9.10 Repair of Tank Bottoms 9.10.1 Repairing a Portion of Tank Bottoms 9.10.1.1 General Repair Requirements The use of welded-on patch plates for repairing a portion of uniformly supported tank botto ms is permitted within the limitations given in this section and 9.10.1.2. See Figure 9.13 for acceptable details for welded-on patch plates. a) The minimum dimension for a welded-on patch plate that overlaps a bottom seam or existing patch is 12 in. The welded-on patch plate may be circular, oblong, or polygonal with rounded corners. b) A welded-on patch plate smaller than 12 in. in diameter is permi tted if: it is equal to or exceeds 6 in. in diameter; it does not overlap a bottom seam; it is not placed fully or partially over an existing patch; and it extends beyond the corroded bottom area, if any, by at least 2 in. Figure 9.11—Details for Installing a New Bottom Through an Existing Tombstone Reinforcing Plate Centerline of nozzle

Tank shell

Full penetration weld Fillet weld sizes per API 650, Section 5.1.5.7

New bottom or 	

 3 / 8 in.) Existing tombstone reinforcing plate
See Note 1 Existing shell penetration 



NOTE 1 In using this detail, it must be confirmed that the distance from top of new bottom to center of nozzle meets API 650, Table 5-6a or Table 5-6b. NOTE 2 All welds shown shall be individually examined to API 650, Section 7.2.4.
12 10

12

109-14 API S TANDARD 653

Figure 9.12—Details for Installing a New Bottom Through an Existing Tombstone Reinforcing Plate NOTE 1 In using this detail, it must be confirmed that the distance from top of new bottom to center of nozzle meets API 650, Table 5-6a or Table 5-6b and that additionally there is sufficient space to provide the minimum H and J spacings. NOTE 2 All welds shown shall be individually examined to API 650, Section 7.2.4. Fillet weld sizes per API 650, Section 5.1.5.7 Telltale Existing tombstone reinforcing plate

Re-installed existing or new reinforcing plate Full penetration weld Tank shell Existing welds Centerline of nozzle

H (min.)

J (min.)

New bottom or annular plate See Note 1 Existing shell penetration

Material Thickness H (the larger of) J (the larger of) Case 1, 2, and 3 Case 1: Case 2: Case 3: t  2 in.

1 t  2 in.

1 t  2 in.

1 t  2 in.

1 3 in.  2 t

4 in. or 4 t 5 in. or 4 t 1 3 in. 3 in. or 4 tw 3 in. or 4 tw 5 in. or 4 tw

Case 1—Shell material meets API 650, Seventh Edition or later toughness requirements and opening was PWHT’d. Case 2—Shell material meets API 650, Seventh Edition or later toughness requirements. Case 3—Shell material does not meet API 650, Seventh Edition or later toughness requirements. where tw is the required weld size from API 650, Section 5.1.5.7. T t 10

12T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 9-15 c) Welded-on patch plates shall not be pl aced over areas of the tank bottom t hat have global dishi ng, local dishing [except as allowed by 9.10.1.1 d)], settlement, or distortion gr eater than the limits of Annex B. NOTE If the tank is still undergoing settlement, the addit ion of welded-on patch plate may not be advisable. d) A welded-on patch plate may be placed over a mechanical dent or local dishing if: its unsupported dimension does not exceed 12 in. in any direction; it is at least 1 / 4 in. thick; it is at least as thic k as the existing bottom; and does not overlap seams nor other patches, except for tanks designed in accordance with API 650, Annex M, which shall have welded-on patch plates at least 3 / 8 in. thick. e) These repairs are permanent repairs subject to an on-going inspection and maintenance program. f) Installation of a new sump shall conform to API Standar d 650 Section 5, paragraph 5.8.7 (Water Drawoff Sumps), Tables 5-16a and 5-16b and Figure 5-21. 9.10.1.2 Repairs within the Critical Zone The use of welded-on patch plates is permitted for repairing a portion of tank bottoms with in the critical zone (see 3.10 for definition) provided 9.10.1.1 requirements and the following additional requirements are met. a) Maximum plate thickness for welded-on patc h plates within the critical zone is 1 / 4 -in. and must meet the toughness requirements of API 650, Section 4.2.10. b) When a welded-on patch plate is within 6 in. of the s hell, the welded-on patch plate shall be tombstone shaped. The sides of the tombstone shaped welded- on patch plate shall intersect the s hell-to-bottom joint at approximately 90 °

. c) Perimeter welds on welded-on patch plates within the cr itical zone shall be two-pass, minimum, and examined per 12.1.1.3 and 12.1.7.2. d) Installation of a welded-on patch plate by butt-welding to an adjacent existing patch is not permitted in the critical zone. e) Welded-on patch plates over existing patc hes are not allowed in the critical zone. f) The bottom plate under the perimeter of a welded-on patc h plate shall meet the thickness requirements in 4.4. g) For tanks with shell plat e of unknown toughness as defined in Section 3, new fillet welds utilized to install a tombstone patch plate in the critical zone shall be spaced at least the greater of 3 in. or 5 t from existing vertical weld joints in the bottom shell course, where t is the thickness of the bottom s hell course, in inches. See Figure 9.13 for further guidance on weld spacing. NOTE The bottom plate thickness at the attachment weld must be at least 0.1-in. thick before welding the welded-on patch plate to the bottom plate. Refer to API 2207 for further information. 9.10.1.2.1 No welding or weld overlays are permitted within t he critical zone except for the welding of: widely scattered pits (see 4.3.2.2), pinholes, cracks in the bottom plates, the shell-to-bottom we ld, welded-on patch plates, or where the bottom plate welded to the shell is being replaced. 9.10.1.2.2 A welded-on patch plate shall not be used if the cove red bottom plate minimum remaining thickness at the toe of the internal shell-to-botto m weld will be less than the minimum thic kness required by 4. 4.5 and 4.4.6 at the next internal inspection. 9.10.1.2.3 Welded-on patch plates are not permitted in the critical zone on a tank bottom with an operating temperature exceeding 200 ° F for carbon steel or 100 ° F for stainless steel. 9.10.1.2.4 If more extensive repairs are required within the crit ical zone than those listed in 9.10.1.2, the bottom plate welded to the shell shall be cut out and a new plate shall be installed. We ld spacing requirements shall be in accordance with 9.10.2.4 , and API 650, Section 5.1.5.4 and Section 5. 1.5.5. The shell-to-bottom weld shall be removed and replaced for a minimum distance of 12 in. on each side of the new bottom plate. 13

13

13

12

12

109-16 API S TANDARD 653Typical “tombstone-shaped”welded-on plates2 in.minimumradiusAAL1L2tNote 3Note 3Verticalshell weldsThe greater of 3 in.or 5t(see Note 7)Note 22 in.(min.)6 in.(min.)2 in. (min.)2 in. (min.)12 in. (min.)12 in.(min.)2 in. (min.)see Note 4Bottom seamBottom seamThree-plate lap(see Note 5)12 in. (min.)6 in. (min.)45° (min.)Shell plate3 in.CriticalzoneWelded-on patch plate(1/4in. maximumthickness in thecritical zone)ShellBottom plate or annular plate ringSectionA-APlan ViewNOTE 1 Dimensions given are from toe of fillet welds or to centerline of butt-weld and also apply to new-to-existingwelds.NOTE 2 Minimum distance between two welded-on patch plates in the critical zone shall be one half of the lesser ofL1 orL2.NOTE 3 The maximum dimension along the shell for welded-on patch plates in the critical zone is 24 in.NOTE 4 When the edge of a welded-on patch plate is approximately parallel to a bottom seam, the edge shall beheld at least 2 in. from weld seam.NOTE 5 Patches over three-plate laps shall extend a minimum of 12 in. in all directions along all laps beyond thethree-plate lap.NOTE 6 These rules apply to butt-welded bottoms, where applicable.NOTE 7 Applies to shells of unknown toughness. 12 in. (min)Three-plate lap(see Note 5)2 in. (min)12 in. (min)Bottom corrodedarea, if anyFor welded-on patch plates less than12 in. dimension, see 9.10.1.1 b)2 in.(min.)Three-plate lapFigure 9.13—Typical Welded-on Patch Plates on Tank Bottom Plates

12T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 9-17
9.10.1.3 The use of welded-on patch plates that do not meet the requirements of 9.10.1.1 or 9.10.1.2 is permitted if the repair method has been reviewed and approved by an engineer experienced in storage tank design in accordance with API 650. The review shal l consider brittle fractu re, stress due to settlement, stress due to shellbottom discontinuity, metal temperature, fractu re mechanics, and the extent and quality of NDE. 9.10.1.4 Unacceptable indications such as cracks, gouges, tears, and corroded areas discovered in bottom plates, located outside the critical zone, may be repaired by deposition of weld metal followed by examination and testing in accordance with 12.1.7.3. Surface irregularities and contamination within the area to be repaired shall be removed before welding. 9.10.1.5 The repair of sumps located within the crit ical zone shall be in accordance with 9.10.1.2. 9.10.1.6 The repair of corroded plates in the critical zone is limi ted to pit welding or overlay welding as noted in this section. The weld repair of bottom plate corrosion is permitted if all of the follow ing conditions are satisfied. a) The sum of the pit dimensions along an arc parallel to the shell-to-bottom joint does not exceed 2 in. in an 8-in. length. b) There must be sufficient remaining bottom plate thic kness for completion of a sound weld and to avoid burnthrough. The minimum acceptable bottom plate thickness for we ld repairs is 0.10 in. A lesser thickness is permitted for weld repairs only if reviewed and approved by an engi neer experienced in storage tank design and repair. c) All weld repairs shall be ground flush with the surr ounding plate material and be examined in accordance with 12.3.2.4. 9.10.2 Replacement of Tank Bottom Plates 9.10.2.1 Requirements governing the installation of a replac ement bottom over an existing bottom are given in 9.10.2.1.1 through 9.10.2.1.5. 9.10.2.1.1 Suitable noncorrosive material cushion such as sand, gravel, or concrete shall be used between the old bottom and the new bottom. 9.10.2.1.2 The shell shall be slotted with a uniform cut made paralle l to the tank bottom. The cut edges in the slot shall be ground to remove all slag and burrs from cutting operations. The new bottom pl ate shall extend outside the shell as required by API 650, Section 5.4.2. All rules for weld spacing shall be followed. 9.10.2.1.3 Voids in the foundation below the old bottom shall be filled with sand, crushed limestone, grout, or concrete. 9.10.2.1.4 Except as permitted in 9.10.2.7, existing shell penetrations shall be ra ised or their reinforcing plates modified if the elevation of the new bottom results in inadequate nozzle reinforcement details (see Figure 9.8 and API 650, Section 5.7.2) or if the weld space require ments given in API 650, Section 5.7.3 are not met. 9.10.2.1.5 For floating roof tanks, the new bottom profile must keep the roof level when it is resting on its support legs. The levelness of the floating r oof can be adjusted by changi ng the length of the support legs. The support legs can either remain the same length to maintain the or iginal height above the bottom or be shortened by the same amount as the thickness of t he cushion and new bottom plate. 9.10.2.2 New bearing plates for fixed roof support columns shall be installed. For steel floati ng roof legs, steel pads or other means shall be used to distribute the loads on the bottom of the tank and provide a wear surface. If pads are used, they shall be continuously welded to the tank bottom. For al uminum floating roofs, the pads may be omitted if the owner/ operator approves and new austenitic stainless steel or acceptable non-metallic (e.g., Teflon) spacers are installed to isolate legs from the carbon steel bottom. For aluminum floating roofs, austenitic stainless steel or acceptable non12

109-18 API S TANDARD 653 metallic (e.g., Teflon) spacers may installed to isolate legs from the carbon steel bottom instead of welded pads if the spacers will not damage bottom coatings, there is no evidence of corrosion damage from such spacers on the previous bottom, and if the owner/operator approves. 9.10.2.3 When removing an existing tank bottom, the tank she ll shall be separated from tank bottom either by: a) cutting the shell parallel to the tank bottom a minimum of 1 / 2 in. above the bottom-to-shell weld (cut line B-B as shown in Figure 10.1), or b) removing the entire shell-to-bottom attachment weld , including any penetration and heat affected zone by suitable methods such as arc gouging and/or grinding. All arc-gouged areas of the tank shell-to-bottom weld sha ll be magnetic particle examined, and defective areas repaired and re-examined. 9.10.2.4 Installation of a new tank bottom, after removal of t he existing tank bottom, shall meet all requirements of API 650. Except as permitted in 9.10.2.7 , existing shell penetrations shall be ra ised or their penetration reinforcing plates modified if the elev ation of the new bottom results in inadequate nozzle reinforcement (see Figure 9.8 and API 650, Section 5.7.2) or if the weld spac ing requirements given in API 650, Section 5.7.3 are not met. For tanks with shell plate of unknown toughness as defined in Section 3, new weld joints in the bottom or annular ring shall be spaced at least the greater of 3 in. or 5 t from existing vertical weld joints in the bottom shell course, where t is the thickness of the bottom shell course, in inches. 9.10.2.5 Replacement of portions of an existi ng tank bottom (entire rectangular pl ates or large segments of plates) not within the critical zone (s ee 3.10 for definition) are permitted under the same rules that govern installation of bottoms in new tank construction per API 650, Sections 5.4 and 5.5. 9.10.2.6 The following shall be considered for tanks with cathodic protection and under-bottom leak detection. a) For tanks having cathodic protection (CP) installed under the existing bottom, consider ation shall be given to removal of the entire bottom and unused dead shell to prevent shielding of CP current to the new bottom. Removal of the old bottom is also important in preventing galvanic corrosion (refer to API 651). Where this is possible, removal of the entire old bottom, except the unus ed dead shell and not more than 18 in. of bottom annulus attached to the shell, shall be considered. b) Consideration shall be given to insta lling under-bottom leak detecti on at this time (such as a RPB) to contain and channel any bottom leak to a location where it can readi ly be observed from outside of the tank. See 4.4.3.5 and Annex I. 9.10.2.7 For tanks constructed from materials having 50,000 lbf/in. 2 yield strength or less, existing shell penetrations need not be raised if t he following conditions are met. a) For reinforced penetrations, including lo w-types, a minimum of 4 in. shall be maintained between the shell-tobottom weld toe and the nearest penetrati on attachment weld toe (reinforcing plate periphery weld, or nozzle neck weld to low type reinforcing plate and shell welds). b) For self-reinforced penetrations, the greater of 3 in. or 2 1 / 2 t shall be maintained between the shell-to-bottom weld toe and the nearest penetration attachment weld toe. c) The shell-to-bottom weld is to be welded with low hydrogen electrodes and with welding procedures that are designed to limit distor tion and residual stress. d) The toes of the welds shall be blend-ground to minimize stress concent rations as follows. 10

12

13T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 9-19 i) For circular reinforcing plates, blend- grind the periphery attachment weld from the “four o'clock” position to the “eight o'clock” positio n. Blend-grind the inside and outside of the shell-to-bottom weld a minimum of one pene

tration diameter length on either side of the penetration centerline. ii) For diamond-shaped reinforcing plates, blend-grind t he lower horizontal length of the diamond shaped attach

ment weld. Blend-grind the inside and outside of the shell-to-bottom weld a minimum of one penetration diameter length on either si de of the penetration centerline. iii) For low-type penetrations, blend-grind the nozzle attachm ent weld (shell and reinforcing plate) from the “four o'clock” position to the “eight o'clo ck” position. Blend-grind the inside and outside of the shell-to-bottom weld a minimum of one penetration diameter length on either side of the penetration centerline. e) The blend-ground lengths of welds listed in 9.10.2.1.7 d) shall be magnetic particle examined before and after hydrostatic test. 9.10.3 Additional Welded-on Plates 9.10.3.1 If other welded-on plates such as wear, isolation, striker, and beari ng plates, are to be added to tank bottoms, they shall be installed in accordance with 9.10.1, and examined in accordance with 12.1.7. For these additional welded-on plates, if the lap weld spacing requirements as set forth in Figure 9.13 are not met, magnetic particle (MT) or liquid penetrant (PT) examination is requi red for the exposed welds or portions of welds failing to meet minimum spacing criteria. See Section 12 for acceptance requirements. 9.10.3.2 Welded-on plates that fall within t he critical zone (see 3.10 for definiti on) shall be installed in accordance with 9.10.1.2 and comply with all of its requirements. 

### 9.11 Repair of Fixed Roofs 9.11.1 Repairs 9.11.1.1 Roof repairs involving tank venting shall be m ade such that normal and emergency venting meet the requirements of API 650, Section 5.8.5. 9.11.1.2 Roof repairs involving modification of the roof structure and the frangibl e joint (if applicable) shall be in compliance with the requirements of API 650, Section 5.10. 9.11.2 Supported Cone Roofs 9.11.2.1 The minimum thickness of new roof plates shall be 3 / 16 in. plus any corrosion allo wance as specified in the repair specifications. In the event r oof live loads in excess of 25 lbf/ft 2 are specified (such as insulation, operating vacuum, high snow loads), the plat e thickness shall be based on analysis using the allowable stresses in conformance with API 650, Se ction 5.10.3 (see 9.11.2.2). 9.11.2.2 The roof supports (rafters, girders, columns, and bases ) shall be repaired or altered such that under design conditions the resulting st resses do not exceed the stress levels given in API 650, Section 5.10.3. 9.11.3 Self-supporting Roofs 9.11.3.1 The nominal thickness of new roof plate shall be 3 / 16 in. or the required plate thickness given in API 650, Section 5.10.5 or Section 5.10.6, plus any specified co rrosion allowance, whichever is greater. 9.11.3.2 The details of the roof-to-shell junc tion shall meet the requirements of API 650, Section 5.10.5, Section 5.10.6, or Annex F of this standard, as applicable, for the intended service.9-20 API S TANDARD 653


### 9.12 Repair of Floating Roofs 9.12.1 External Floating Roofs Any method of repair is acceptable that will restore t he roof to a condition enabling it to perform as required. 9.12.2 Internal Floating Roofs Repairs to internal floating roofs shall be made in accordance with the original construction drawings, if available. If the original construction drawings are not available, the roof repairs shall be in compliance with the requirements of API 650, Annex H. 9.12.3 Repair of Leaks in Pontoons All leaks in pontoons or compartments of double deck floati ng roofs shall be repaired by rewelding the leaking joints and/or use of patch plates. 

### 9.13 Repair or Replacement of Floating Roof Perimeter Seals 9.13.1 Primary Seals Rim-mounted primary shoe seals and toroidal seal systems c an be removed, repaired, or replaced. To minimize evaporation losses and reduce potential hazard to the worker s, no more than one-fourth of the roof seal system should be out of an in-service tank at one time. Temporary spacers to keep the roof centered shall be used during the repairs. Primary seal systems mounted partly or fully belo w the bolting bar or top of the rim usually cannot be reached to allow removal in service. In this case, in-service repairs are limited to replacement of the primary seal fabric. 9.13.2 Secondary Seals Rim-mounted and shoe-mounted secondary seals may be readily installed, repaired, or replaced while the tank is in service. 9.13.3 Seal-to-shell Gap Repair and other corrective actions to maintain seal-to-shell gap requirement s, include the following. a) Adjusting the hanger system on primary shoe seal s, and adding foam filler in toroidal seals. b) Increasing the length of rim mounted secondary seals in the problem area. c) Replacing all or part of the primar y seal system along with possible instal lation of a rim extension for a secondary seal. This step shall be taken only after checking the annular space variation at several levels from low pump out to high liquid level. 9.13.4 Mechanical Damage Damaged parts shall be repaired or replaced. Prior to taki ng this action, the cause of the damage shall be identified and corrected. Buckled parts shall be replaced, not st raightened. Torn seal fabric shall be replaced. 9.13.5 Deterioration of Seal Material Material deterioration results from wear and corros ion on metallic elements, and chemical and weather deterioration of seal fabric. The se rvice life and inspection information shall be used to determine whether a change of material is warranted. 13T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 9-21
9.13.6 Installation of Primary and Secondary Seals 9.13.6.1 The replacement or addition of primary and sec ondary seals shall be in accordance with the recommendations of the seal manufactu rer. In addition, the final installa tion shall comply with all applicable jurisdictions. 9.13.6.2 If the roof rim thickness is less than 0.10-in. thic k, it shall be replaced. The new roof rim shall be 3 / 16 -in. thickness, minimum. 

### 9.14 Hot Taps 9.14.1 General 9.14.1.1 The requirements given herein cover the installation of r adial hot tap connections on existing in-service tanks. Hot taps are not permitted on shell material requiring thermal stress relief as specified in API 650, Section 5.7.4. a) For tank shell plates of recogniz ed toughness, as defined in Section 3, t he connection size and shell thickness limitations are shown in Table 9.1. b) For tank shell plates of unknown toughness, as defined in Sect ion 3, the following limitations apply. 1) Nozzles shall be limited to a maximum diameter of 4 in. NPS. 2) The shell plate temperature shall be at or above the minimum shell design metal temperature for the entire hot tapping operation. 3) All nozzles shall be reinforced. The reinforcement shal l be calculated per API 650, Se ction 5.7.2. The minimum thickness of the reinforcing plate s hall be equal to the shell plate thicknes s, and the minimum reinforcing plate diameter shall not be less than the diam eter of the shell cutout plus 2 in. 4) The maximum height of tank liquid abov e the hot tap location during the hot tapping operation shall be such that the hydrostatic tank shell stress is less than 7,000 lbf/in. 2 at the elevation of the hot tap.

9.14.1.2 The minimum height of tank liquid above the hot tap loca tion shall be at least 3 ft during the hot tapping operation. 9.14.1.3 Welding shall be done with low hydrogen electrodes. 9.14.1.4 Hot taps are not permitted on the roof of a tank or within the gas/vapor space of the tank. Table 9.1—Hot Tap Connection Sizes and Shell Plate Thicknesses Connection Size, NPS (in.) Minimum Shell Plate Thickness (in.)
≤ 6 3 / 16
≤ 8 1 / 4
≤ 14 3 / 8
≤ 18 1 / 29-22 API S TANDARD 653
9.14.1.5 Hot taps shall not be installed on laminated or severely pitted shell plate. 9.14.1.6 Hot taps are not permitted on tanks where the heat of welding may cause environmental cracking (such as caustic cracking or stre ss corrosion cracking). 9.14.2 Hot Tap Procedures A hot tap procedure specific to ca rrying out the work shall be devel oped and documented. The procedure shall include the practices given in API 2201. 9.14.3 Preparatory Work 9.14.3.1 Minimum spacing in any direction (toe-to-toe of welds) between the hot tap and adjacent nozzles shall be equivalent to the square root of RT where R is the tank shell radius, in inches, and T is the shell plate thickness, in inches. 9.14.3.2 Shell plate thickness measurements shall be taken at a minimum of four places along the circumference of the proposed nozzle location. 9.14.4 Material Limitations Only hot tap steels of recognized toughness, as defined in Section 3, unless the additional requirements of 9.14.1.1 b) are met. 9.14.5 Installation Procedure 9.14.5.1 Pipe nozzles shall be cut to the contour of the shell and beveled from the outside for a full penetration weld (see Figure 9.14). The nozzle neck-to-shell weld shall be examined in accordance with 12.1.2.3. 9.14.5.2 After the pipe is welded, the reinfo rcing plate shall be installed either in one piece or two pieces with horizontal weld. The reinforcing plate to nozzle shall be installed with a full penetration weld. Care shall be taken to limit the heat input to the welds. 9.14.5.3 After the reinforcing plate has been welded to the sh ell and NDE performed, the pad shall be pneumatically tested by the procedure described in API 650, Section 7.3. 4. After the valve has been installed on the flange, a pressure test at least 1.5 times the hydrostatic head s hall be performed on the nozzle prior to mounting the hot tap machine, which shall be bolted to the valve. The required pr essure for the pressure test shall be at least the value computed by the following equation:

where
H

2 is the height of tank shell in inches (in.);
G is the specific gravity of product stored, as specified by purchaser. The specif ic gravity shall not be less than 1.0;
γ

w is the density of water in pound force for cubic inch (lbf/in. 3 ). 9.14.5.4 A qualified operator s hall operate the hot tap machi ne and cut the hole in the tank following the hot tap machine manufacturer’s procedures. P psi

( ) 1.5 H 2 G γ w =T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 9-23

Figure 9.14—Hot Tap for Tanks (See Note 1) Flange, Class 150 W.N. or S.O. Reinforcing plate ( T = t ) rolled to outside radius of tank shell

Pipe nozzle, Schd extra strong

See Detail a t

T

T Grind out root and seal weld for nozzle size 10 in. NPS and larger

1 / 4 in. min HOT TAP ASSEMBLY

DETAIL a REINFORCING PLATE DETAIL (See Note 1 and Note 2) 12 in. min. D o

Vertical weld

Horizontal weld if reinforcing plate is in two pieces
Spacing per API 650, Section 5.7.3 Horizontal weldEqualEqual

NOTE 1 See 12.1 for NDE requirements. NOTE 2 Reinforcing plate dimensions are as given in API 650, Table 5-6a or Table 5-6b. Greater of 2 in. or 6 T 1 / 4 in. telltale hole, drill and tap for 1 / 8 -in. pipe thread

1210-1 

### Section 10—Dismantling and Reconstruction

10.1 General 10.1.1 This section provides procedures for dismantling and re constructing existing wel ded tanks that are to be relocated from their original site. 10.1.2 Hydrostatic testing requirements, NDE requirements, and acceptance criteria for the quality of welds for reconstructed tanks are specified in Section 12. 10.1.3 All reconstruction work must be authorized by the authorized inspector or an engineer experienced in storage tank design, prior to commencement of the work by a reconstruction organization (see 3.23). The authorized inspector will designate inspection hold points requir ed during the reconstruction process and minimum documentation to be submit ted upon job completion. 10.1.4 The authorized inspector or an engineer experienced in storage tank design shall approve all reconstruction work at the designated hold points and after reconstruction has been completed in accordance with the requirements of this standard. 

### 10.2 Cleaning and Gas Freeing The tank shall be cleaned and gas-freed pr ior to commencement of dismantling. 

### 10.3 Dismantling Methods 10.3.1 General Roof, shell, and bottom plates may be cut into any size pi eces that are readily transportable to the new site for reconstruction. 10.3.2 Bottoms 10.3.2.1 Bottom plates that will be reused shall be cut by desea ming of lapwelds; or by cutting alongside of the remaining welds at a minimum of 2 in. away from existi ng welds, except where cuts cross existing weld seams. 10.3.2.2 If the bottom is to be used, one of the following methods is acceptable: a) the bottom plates may be cu t from the shell along a line A-A and line B-B shown in Figure 10.1, scrapping the welds and the bottom plate directly attached to the shell; b) if the entire bottom is to be reused, the bottom may be cut from the shell on the line C-C leaving the shell with part of the bottom attached; c. if the tank has an existing butt-welded annular ring, this ri ng can be left attached to the shell or removed from the shell by cutting out along line B-B or otherwise removing the exis ting shell to annular ring welds. 10.3.3 Shells 10.3.3.1 Tank shell plates may be dismantled using one of the following methods or a combination thereof. a) Any shell ring may be dismantled by cu tting out existing weld seams and the heat affected zone (HAZ) of the weld. For the purpose of this method, the minimum HAZ to be removed will be 1 / 2 of the weld metal width or 1 / 4 in., whichever is less, on both sides of the weld seam.10-2 API S TANDARD 653 b) Any shell ring 1 / 2 -in. thick or thinner may be dismantled by cu tting through the weld without removing the HAZ. c) Shell rings may be dismantled by cutti ng vertical and/or horizontal cuts thr ough the shell a minimum of 6 in. away from existing welds, except w here cuts cross existing welds. 10.3.3.2 Shell stiffening rings, including wind gi rders and top angles, may be left attached to the shell plates or may be removed by cutting at the attachment welds. The area where temporary attachments are removed shall be ground flush with the shell plate. 10.3.3.3 The shell shall be cut from the bottom plate along line B
- B as shown in Figure 10.1. The existing shell-tobottom weld connection shall not be reused unle ss the entire bottom is to be reused intact. 10.3.4 Roofs 10.3.4.1 Roof plates shall be cut by deseami ng of lap welds, or by cutting al ongside of the remaining welds at a minimum of 2 in. away from existing welds, except where cuts cross existing welds.

10.3.4.2 Roof supporting structures shall be dismantled by re moving bolts (if bolted) or deseaming the structural attachment welds. 10.3.5 Piece Marking 10.3.5.1 Shell, bottom, and roof plates shall be marked prior to dismantling for ready identification and placement when the tank is reconstructed. Marki ng material shall be of a durable type. Dr awings showing piece mark locations are also a useful adjunct. Figure 10.1—Tank Shell and Bottom Cut Locations Shell

B B C

C Bottom plate 1 / 2 in. min. 1 / 2 in. min. A

A 12 in. min.T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 10-3
10.3.5.2 A minimum of two sets of matching center punch marks shall be located on the top and bottom edges of each shell plate to facilitate proper alignment during reconstruction. 

### 10.4 Reconstruction 10.4.1 General 10.4.1.1 The foundation for the reconstructed tank shall m eet the construction tole rances given in 10.5.6. 10.4.1.2 Temporary attachments shall be removed, and the at tachment area ground flush with the plate surface. 10.4.2 Welding 10.4.2.1 Provisions shall be made during the re construction of a tank to ensure t hat weld spacing requirements of Figure 9.1 are maintained. New vertical joints in adjacent shell courses, made in accor dance with 10.3.3.1, shall not be aligned but shall be offset from ea ch other a minimum distance of 5 t , where t is the plate thickness of the thicker course at the point of the offset. 10.4.2.2 Tanks and their structural attachments shall be wel ded in accordance with the processes specified in API 650, Section 5.8 and the requirement s of 10.4.2.3 through 10.4.2.11. 10.4.2.3 No welding of any kind shall be performed when the surfaces of the parts to be welded are wet from rain, snow, or ice; when rain or snow is falling on such surfac es; or during periods of high winds unless the welder and the work are properly shielded. No welding of any kind shall be performed when the temperature of the base metal is less than 0 °F. When the temperature of the base metal is between 0 ° F and 32 ° F or the thickness is in excess of 1 in., the base metal within 3 in. of the place where welding is to be started shall be heated to a temperature warm to the hand (approximately 140 ° F) before welding. (See 10.4.4.3 for preheat requirements for shell plates over 1 1 / 2 -in. thick.) 10.4.2.4 Each layer of weld metal of multilayer welding shall be cleaned of slag and other deposits before the next layer is applied. 10.4.2.5 The edges of all welds shall merge with the surf ace of the plate without a sharp angle. Maximum permissible weld undercut shall be in accordance with API 650, Section 7.2.1.4 and Section 8.5.1 b). 10.4.2.6 The reinforcement of the new welds on all butt join ts on each side of the pl ate shall not exceed the thicknesses shown in Table 10.1. 10.4.2.7 Tack welds used in the assembly of vertical joints of tank shells shall be removed and shall not remain in the finished joint when the joints are welded manually. W hen such joints are welded by the submerged-arc process, the tack welds shall be thoroughly cleaned of all welding slag but need not be removed prov ided that they are sound and are thoroughly fused into the subsequently applied weld be ads. Tack welds shall be made using a fillet-weld or butt-weld procedure qualified in accordance wi th Section IX of the ASME Code. Tack welds to be left in place shall be made by qualified welders. 10.4.2.8 If weldable primer coatings have been applied on surfaces to be welded, they shal l be included in welding procedure qualification tests for the brand, formulation, and ma ximum thickness of primer applied. All other coatings shall be completely removed from the weld area prior to welding. 10.4.2.9 Low-hydrogen electrodes shall be used for manual metal-ar c welds, including the at tachment of the first shell course to the bottom plates or annular plate ring, as follows: a) for all welds in shell courses over 1 / 2 -in. thick of API 650 Group I – III materials; b) for all welds in all shell courses of API 650 Group IV – VI materials. 1210-4 API S TANDARD 653
10.4.2.10 Low-hydrogen electrodes shall be used for weld ing temporary and new permanent attachments to shells of API 650 Group IV, IVA, V, or VI materials. The welding procedure selected shall not cause underbead cracking; also, the need for preheat of thick plates and the effect of low ambient temperature during welding shall be considered.

10.4.2.11 If existing welds are found to be uns atisfactory by the as -built standard, they shall be repaired in accordance with 9.6. 10.4.3 Bottoms 10.4.3.1 After the bottom plates are laid out and tacked, they s hall be joined by welding the joints in a sequence that results in the least distortion from shrinkage and provides, as nearly as possible, a plane surface. 10.4.3.2 The welding of the shell to the bottom (except for door sheets) shall be completed prior to the welding of bottom joints. 10.4.3.3 Plates shall be held in close contac t at all lap joints during welding. 10.4.4 Shells 10.4.4.1 Plates to be joined by butt welding shall be matched accurately and retained in position during welding. Misalignment in completed vertical joints over 5 / 8 -in. thick shall not exceed 10 % of the plate thickness, with a maximum of 1 / 8 in. Misalignment in joints 5 / 8 -in. thick or less shall not exceed 1 / 16 in. Vertical joints shall be completed before the lower horizontal weld is made. 10.4.4.2 In completed horizontal butt joints, the upper plate shal l not project beyond the face of the lower plate at any point by more than 20 % of the thickness of the upper plate, with a maximum projection of 1 / 8 in., except that a projection of 1 / 16 in. is acceptable for upper plates less than 5 / 16 -in. thick. 10.4.4.3 For horizontal and vertical joints in tank sh ell courses constructed of material over 1 1 / 2 -in. thick (based on the thickness of the thicker plate at the joint), multi-pass weld procedures are required, with no pass more than 3 /

4 -in. thick permitted. A minimum preheat of 200 ° F is required of these welds. 10.4.5 Roofs This standard does not include special stipul ations for reconstruction thereof, except that the structural framing (such as rafters and girders) must be reasonably true to line and surface. Other requirements shall be in accordance with the as-built standard. Table 10.1—Maximum Thicknesses on New Welds Plate Thickness (in.) Maximum Reinforcement Thickness (in.) Vertical Joints Horizontal Joints
≤ 1 / 2 3 / 32 1 / 8
> 1 / 2 through 1 1 / 8 3 / 16 > 1 3 / 16 1 / 4T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 10-5



### 10.5 Dimensional Tolerances 10.5.1 General 10.5.1.1 The tolerances given in this section have been establ ished to produce a reconstruc ted tank of acceptable appearance and structural integrity and to permit proper functioning of floating roofs and seals. 10.5.1.2 Measurements to verify these tolerances shall be tak en before the hydrostatic test of the reconstructed tank. 10.5.2 Plumbness 10.5.2.1 The maximum out-of-plumbness of the top of the shell relative to the bottom of the shell shall not exceed 1 / 100 of the total tank height, with a maximum of 5 in. The 1 / 100 criteria, with a maximum of 5 in., shall also apply to fixed roof columns. For tanks with internal floating roofs, apply the criteria of this section or API 650, Section 7.5.2 and Annex H, Section H.4.1.1, whichever is more stringent. 10.5.2.2 The out-of-plumbness in one shell course shall not exc eed the values specified for mill tolerances in ASTM A6 or ASTM A20, whichever is applicable. 10.5.3 Roundness Radii measured at 1 ft above the shell-to-bottom weld shall not exceed the tolerances shown in Table 10.2. Radius tolerances measured higher than one foot above the shell-to-bottom weld shall not exceed three times the tolerances given in Table 10.2. 10.5.4 Peaking With a horizontal sweep board 36-in . long, peaking shall not exceed 1 / 2 in. The sweep board shall be made to the true outside radius of the tank. 10.5.5 Banding With a vertical sweep board 36-in. long, banding shall not exceed 1 in. Table 10.2—Radii Tolerances Tank Diameter (ft) Radius Tolerances (in.) < 40 ± 1 / 2 40 to < 150 ± 3 / 4 150 to < 250 ±1
≥ 250 ±1 1 / 4

1310-6 API S TANDARD 653
10.5.6 Foundations 10.5.6.1 To achieve the tolerances specified in 10.5.1 through 10.5.5, it is ess ential that foundations true to a plane be provided for the tank reconstructi on. The foundation shall hav e adequate bearing capacity to maintain the trueness of the foundation. 10.5.6.2 Where foundations true to a horizontal plane are specified, tolerances shall be as follows: a) where concrete ringwalls are provided under the shel l, the top of the ringwall shall be level within ± 1 / 8 inches in any 30 ft of the circumference and within ± 1 / 4 inches in the total circumferenc e measured from the average elevation; b) where concrete ringwalls are not provided, t he foundation under the shell shall be level within ± 1 / 8 in. in any 10 ft of circumference and within ± 1 / 2 in. in the total circumference measured from the average elevation. 10.5.6.3 For foundations specified to be sloped from a horizontal plan, elevatio n differences about the circumference shall be calculated fr om the specified high point. Act ual elevation differences about the circumference shall be determined from the actual elevation of the specif ied high point. The actual elevation differences shall not deviate from the calculated differences by more than the following tolerances: a) where concrete ringwalls are provided ± 1 / 8 inches in any 30 ft of circumference and ± 1 / 4 inches in the total circumference; b) where concrete ringwalls are not provided, ± 1 / 8 inches in any 10 ft of circumference and ± 1 / 2 inches in the total circumference.11-1 

### Section 11—Welding

11.1 Welding Qualifications
11.1.1 Welding procedure specifications (WPSs) and weld ers and welding operators shall be qualified in accordance with Section IX of the ASME Code, the additional requirements of API 650, Section 9, and this standard. Welding procedures for ladder and platform assemblies, handrails, stairways, and other miscellaneous assemblies, but not their attachments to the tank, shall comply with ei ther AWS D1.1, AWS D1.6, or Section IX of the ASME Code, including the use of SWPSs. 11.1.2 Weldability of steel from existing tank s shall be verified. If the material specification for the steel from an existing tank is unknown or obsolete, test coupons for the welding proc edure qualification shall be taken from the actual plate to be used. 

### 11.2 Identification and Records 11.2.1 Each welder and welding operator shall be assigned an ident ifying number, letter, or sy mbol. Records of this identification, along with the date and results of the welder’s qualification tests shall be accessible to the inspector. 11.2.2 The welder or welding operator’s identification mark shall be hand- or machine-stamped adjacent to and at intervals not exceeding 3 ft along the co mpleted welds. In lieu of stamping, a re cord may be kept that identifies the welder or welding operator employed for each welded joint; these records shall be accessible to the inspector. Roof plate welds and flange-to-nozzle-neck weld s do not require welder identification. 

### 11.3 Preheat or Controlled Deposition Welding Methods as Alternatives to Post-weld Heat Treatment (PWHT) Preheat and controlled deposition welding, as described in 11.3 .1 and 11.3.2, may be used in lieu of PWHT for repairs to existing nozzles where PWHT is required by API 653 or was performed in the original construction but is inadvisable or mechanically unnecessary for the repair. Prior to using any alternative method, a metallurgical review conducted by a storage tank engi neer shall be performed to assess whether the proposed alternative is suitable for the application. The review shall consi der the reason for the original PWHT of the equipment, susceptibility of the service to promote stress corrosion cracki ng, stresses in or near the weld, etc. If materials are of unknown toughness and fall under the Figure 5.2 exemption cu rve, follow the requirements of 11.3.2. The storage tank engineer must c oncur in writing with the PWHT exem ption. Also, the tank owner/operator must authorize the exemption in writing. Selection of the welding met hod used shall be based on technical considerat ion of the adequacy of the weld in the aswelded condition at operati ng and hydrotest conditions. 11.3.1 Preheating Method (Impact Testing Not Required) If impact testing is not required, the following additional preheat requirements apply. a) This method is limited to use on P-1 ma terials that were not required to be im pact tested as part of the original construction or under current requirements of API 650, Section 9.2. b) The welding shall be limited to the shielded-metal-arc welding (SMAW), gas-metal-arc welding (GMAW), flux-cored arc welding (FCAW) and gas-tungsten-arc welding (GTAW) processes. c) The welders and welding procedures shall be qualified in ac cordance with the applicable rules of the original code of construction, except t hat the PWHT of the test coupon used to qu alify the procedure shall be omitted. 12

10

1211-2 API S TANDARD 653 d) The weld area shall be preheated and maintained at a minimum temperature of 150 ° C (300 ° F) during welding. The 150 ° C (300 ° F) temperature shall be checked to assure that 100 mm (4 in.) of the material or four times the material thickness (whichever is greater) on each side of the groove is maintained at the minimum temperature during welding. The maximum inter-pass temperature shall not exceed 315 ° C (600 ° F). When the weld does not penetrate through the full thickness of the material, t he minimum preheat and maximum inter-pass temperatures need only be maintained at a distance of 100 mm (4 in.) or f our times the depth of the repair weld (whichever is greater) on each side of the joint. 11.3.2 Controlled-deposition Welding Method (Impact Testing Required) If impact testing is required, th e following welding requirements apply. a) This method may be used when welding is to be performed on materials that were required to be impact tested per 4.2.9 and 4.2.10 of API 650 as part of the origi nal construction or under current requirements of API 650, Section 9.2, and is limited to P-1, P-3 and P-4 steels. b) The welding shall be limited to the shielded-metal-arc welding (SMAW), gas-metal-arc welding (GMAW), flux-cored arc welding (FCAW) and gas-tungsten-arc welding (GTAW) processes. c) A weld procedure specification shall be developed and qualified for each application. The welding procedure shall define the preheat temperature, the inter-pass te mperature and the post heating temperature requirement in Item e), 8) below. The qualification thickness for the test plates and repair grooves shall be in accordance with Table 11.1.

The test material for the welding procedure qualification shall be of the same materi al specification (including specification type, grade, class and conditi on of heat treatment) as the original ma terial specification for the repair. If the original material specification is obsolete, the test material used shoul d conform as much as possible to the material used for construction, but in no case shall the material be lower in strength or have a carbon content of more than 0.35 %. d) When impact tests are required by the construction code applic able to the work planned, the PQR shall include sufficient tests to determine if the toughness of the weld metal and the heat-af fected zone of the base metal in the as-welded condition are adequate at the minimum design metal temperature. If special hardness limits are necessary for corrosion resistance (e.g. those set fo rth in NACE RP 0472, NACE MR 0103 and NACE MR 0175), the PQR shall include hardness test results. e) The WPS shall include the fo llowing additional requirements. 1) The supplementary essential variables of ASME Code, Section IX, Paragraph QW-250, shall be required. 2) The maximum weld heat input for each layer shall not exceed that used in the pr ocedure qualification test. Table 11.1—Welding Methods as Alternatives to Post-weld Heat Treatment (PWHT) Qualification Thicknesses for Test Plates and Repair Grooves Depth t of Test Groove Welded a Repair Groove Depth Qualified Thickness T of Test Coupon Welded Thickness of Base Metal Qualified

t < t < 50 mm (2 in.) < T

t < t ≥ 50 mm (2 in.) 50 mm (2 in.) to unlimited

a The depth of the groove used for procedure qualification must be deep enough to allow removal of the required test specimen. 10

13 12T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 11-3 3) The minimum preheat temperature for welding shall not be less than that used in the procedure qualification test. 4) The maximum inter-pass temperature for welding sh all not be greater than that used in the procedure qualification test. 5) The preheat temperature shall be checked to assure that 100 mm (4 in.) of the material or four times the material thickness (whichever is greater) on each side of the weld join t will be maintained at the minimum temperature during welding. When the weld does not penet rate through the full thickness of the material, the minimum preheat temperature need only be maintained at a distance of 100 mm (4 in.) or four times the depth of the repair weld, whichever is greater, from the edge of each weld. 6) For the welding processes in 11.3.2 b), use only electrodes and filler metals that are cl assified by the filler metal specification with an optional supplement al diffusible-hydrogen designator of H8 or lower. When shielding gases are used with this process, the gas shall exhibit a dew point that is no higher than –50 ° C (–60 ° F). Surfaces on which welding is to performed shall be maintained in a dry condition during the welding and free of rust, mill scale and hydrogen-producing contaminants such as oil, grease and other organic materials. 7) The welding technique shall be a controlled-deposition, temper-bead or half-bead technique. The specific technique shall be used in the procedure qualification test. 8) For welds made by SMAW, after completion of welding and without allowing the weldment to cool below the minimum preheat temperature, the te mperature of the weldment shall be raised to a temperature of 260 ° C ± 30 ° C (500 ° F ± 50 ° F) for a minimum period of two to four hours to assist out-gassing diffusion of any weldmetal hydrogen picked up during welding. This hy drogen bake-out treatment may be omitted provided the electrode used is classified by the filler metal specification with an option al supplemental di ffusible-hydrogen designator of H4 (such as E7018-H4). 9) After the finished repair weld has cooled to ambient temperature, the final temper bead reinforcement layer shall be removed substantially flush wi th the surface of the base material. 

### 11.4 Welding Safety Welding shall conform to the permit and safety precautions of Section 1. 4 of API 2009. Permits shall consider tank conditions in the hot-work areas which mi ght release flammable vapors (such as perforation resulting from corrosion). 1012-1 

### Section 12—Examinat ion and Testing
12.1 NDE 12.1.1 General 12.1.1.1 NDE shall be performed in accordance with API 650, Section 8, and any supplemental requirements given herein. 12.1.1.2 Personnel performing NDE shall be qualified in accordance with API 650, Section 8, and any supplemental requirements given herein. 12.1.1.3 Acceptance criteria shall be in accordance with API 650, Section 8, and any supplemental requirements given herein. 12.1.1.4 Each newly deposited weld or any cavity resulting fr om gouging or grinding operations shall be visually examined over its full length. Additiona l NDE of these welds may be required as described in the following relevant sections. 12.1.1.5 Annex G may be used to provide additional guidanc e in qualifying personnel and procedures when magnetic flux leakage (MFL) tools are used to examine tank bottoms. Owner/operators should determine specific requirements to meet their tank bottom integrity needs. 12.1.2 Shell Penetrations 12.1.2.1 Ultrasonic examination of shell pl ate for laminations shall be made in the immediate area affected when: a) adding a reinforcing plate to an existing unreinforced penetration, b) adding a hot tap connection. 12.1.2.2 Cavities resulting from gouging or gr inding operations to remove attach ment welds of existing reinforcing plates shall be examined by magnetic particle or liquid penetrant methods. 12.1.2.3 Completed welds attaching nozzle neck to shell, and reinforcing plate to shell and to nozzle neck, shall be examined by the magnetic particle or liquid penetrant methods. Consider addi tional examination (e.g. fluorescent magnetic particle examinati on and/or ultrasonic examination) for hot t ap connections to shell plates of unknown toughness as defined in Section 3. 12.1.2.4 Completed welds of stress-relieved assemblies shal l be examined by the magne tic particle or liquid penetrant methods after stress relief , but before hydrostatic testing. 12.1.3 Repaired Weld Flaws 12.1.3.1 Cavities resulting from gouging or gr inding operations to remove weld defects shall be examined by the magnetic particle or liquid penetrant methods. 12.1.3.2 Completed repairs of butt-welds shall be examined ov er their full length by radiographic or ultrasonic methods. 12.1.3.3 Completed repairs of fillet welds shall be examined over their full length by the appropriate NDE method listed herein. 12

12

12

1312-2 API S TANDARD 653
12.1.4 Temporary and Permanent Attachments to Shell Plates 12.1.4.1 The welds of permanent attachments (not including shell-to-bottom welds) and, areas where temporary attachments are removed and the remaining weld proj ections have been removed, shall be examined visually. 12.1.4.2 Completed welds of new permanent attachments (not including shell-to-bottom welds) and areas where temporary attachments have been removed (API 650 tank shel l materials of Groups IV, IVA, V, or VI), shall be examined by either the magnetic particle method (or, at the option of the pur chaser, by the liquid penetrant method). 12.1.5 Shell Plate to Shell Plate Welds 12.1.5.1 New welds attaching existing shell plate to existing or new shell pl ate shall be examined by radiographic methods (see 12.2). In addition, for plate thicknesses great er than 1 in., the back-gouged surface of the root pass and final pass (each side) shall be examined for its complete length by magnetic particle or liquid penetrant methods. 12.1.5.2 New welds joining new shell plate material to new sh ell plate material (parti al or full shell course replacement or addition) need only be examined radiogr aphically in accordance with API 650, Section 8.1. 12.1.6 Shell-to-bottom Weld 12.1.6.1 New welding on the shell-to-bottom joint shall be exam ined for its entire length by using a right-angle vacuum box and a solution film, or by applying light diesel oil. Additionally, the first weld pass shall be examined by applying light diesel oil to the side opposite the first weld pass made. The oil shall be allo wed to stand at least 4 hours (preferably overnight) and then the weld examined for wicking action. The oil shall be removed before the weld is completed. 12.1.6.2 As an alternative to 12.1.6.1, the in itial weld passes, inside and outside of the shell, s hall have all slag and non-metals removed from the surface of the welds and exam ined visually. Additionally, af ter completion of the inside and outside fillet or partial penetration weld s, the welds shall be tested by pressurizing the volume between the inside and outside welds with air pressure to 15 psig and applying a solution film to both welds. To assure that the air pressure reaches all parts of the welds, a sealed blockage in the annular pass age between the inside and outside welds must be provided by welding at one or more points. Additionally, a small pipe c oupling communicating with the volume between the welds must be welded on each side of and adjacent to the blockages. The air supply must be connected at one end and a pressure gauge connected to a c oupling on the other end of the segment under test. 12.1.6.3 The existing weld at the shell-to-bo ttom joint shall be examined by visual, as well as by magnetic particle or liquid penetrant methods, for the full length under a welded- on patch plate. An additional 6 in. of the shell-to-bottom joint on each side of the welded-on patch plate shall be ex amined similarly before placement of the repair plate to assure weld integrity and to confirm the absence of weld cracks. 12.1.7 Bottoms 12.1.7.1 Upon completion of welding on a tank bottom, the plat es and the entire length of new welds for tank bottom plates shall be examined visually for any potential defects and leaks. Particular attention shall apply to areas such as sumps, dents, gouges, three-plate laps, bottom plate breakdowns, arc strikes, temporary attachment removal areas, and welding lead arc burns. Visual examination acceptance and re pair criteria are specified in API 650, Section 8.5. In addition, all new welds, includi ng the weld attaching a patch plate to the bot tom, the areas of bottom plate restored by welding, and the restoration of welds found with def ects during an internal inspection shall be examined by one of the methods specified in API 650, Section 7.3.3. Leaking areas shall be repaired by grinding and rewelding as required, and the repaired area shall be retested. 12.1.7.2 In addition to the requirements in 12. 1.7.1, the root and final pass of a welded-on patch plate weld in the critical zone (see 3.10 for definition) s hall be visually examined and examined by either magnetic particle or liquid penetrant method over its full length. 12

13

13T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 12-3
12.1.7.3 In addition to the requirements in 12.1.7.1, areas of bottom plate repaired by we lding shall be examined by the magnetic particle method or the liquid penetrant method. In addition, the repaired area shall also be tested using a vacuum box and solution or a tracer gas and detector. 12.1.8 Shell Plate 12.1.8.1 Shell Plate Repairs by Weld Metal Deposit Areas of shell plate to be repaired by welding shall be ex amined visually. In addition, shell plate areas repaired by welding shall be examined by t he magnetic particle method (o r the liquid penetrant method). 12.1.8.2 Shell Plate Repairs by Lap-welded Patches The attachment welds of new lap-welded shell patches s hall be visually examined, and shall be examined by either the magnetic particle or liquid penetrant methods. 12.1.9 Fixed Roofs Newly welded roof joints and repairs shall be examined in accordance with API 650, Section 7.3.2.2 and Section 7.3.7. 12.1.10 Floating Roofs 12.1.10.1 Repair Work to Steel Floating Roofs After repair work is complete: a) perform a visual examination from the top and bottom side of the floating roof; b) perform an air leak, vacuum box, penetrating oil, tracer gas, or other applicable non destructive test of the repaired welds (see Annex F). As an alternative to Item b), conduct a flotation test of the repaired roof. Examination and acceptance criteria fo r NDT shall be in accordance with 12.1. 

### 12.2 Radiographs 12.2.1 Number and Location of Radiographs The number and location of radiographs shall be in accordance with API 650, Section 8.1.2 and the following additional requirements: 12.2.1.1 For vertical joints: a) new replacement shell plates to new shell plates, no additional radiographs required, other than those required by API 650, Section 8.1.2.2 and Fi gure 8-1 for new construction; b) new replacement shell plates to existing shell plates, one additional r adiograph shall be taken in each joint; c) repaired joints in existing shell plates shal l have one additional radiograph taken in each joint. 12.2.1.2 For horizontal joints: a) new replacement shell plates to new shell plates, no additional radiographs required, other than those required by API 650, Section 8.1.2.3 and Figur e 8-11 for new construction; 12

12

1212-4 API S TANDARD 653 b) new replacement shell plates to ex isting shell plates, one additional radiograph for each 50 ft of repaired horizontal weld; c) repaired joints in existing shell plates shall have one additi onal radiograph taken for each 50 ft of repaired horizontal weld. 12.2.1.3 For intersections of vertic al and horizontal joints: a) new replacement shell plates to new shell plates, no additional radiographs required, other than those required by API 650, Section 8.1.2 and Figur e 8-1 for new construction; b) new replacement shell plates to existing shell plates, each intersection shall be radiographed; c) all repaired intersections in exis ting shell plates shall be radiographed. 12.2.1.4 For reconstructed tanks, each butt-welded annular pl ate joint shall be radiographed in accordance with API 650, Section 8.1.2.9. 12.2.1.5 For reconstructed tanks, radiographi c examination is required for 25 % of all junctions of new welds over existing seams. The owner/operator shall, with the consent of the contract or, determine the extent of further examination and repair that may be required. Any further examination or repair of existing welds w ill be handled by contractual agreement between the owner/ operator and tank reconstruction contractor. 12.2.1.6 New and replaced shell plate and door sheet welds shall be radiographed. All junctions between repair and existing welds shall be radiographed. If defects are found, 100 % radiography shall be performed on the repaired weld. 12.2.1.6.1 For circular replacement plates, a minimum of one radiograph shall be taken regardless of thickness. When the circular replacement plate is located in a shell pl ate with thickness exceeding 1 in., the weld shall be fully radiographed. 12.2.1.6.2 For square and rectangular replacement plates, at least one radiograph shall be taken in a vertical joint, and at least one in a horizontal joint, and one in each cor ner. When the square or rectangular replacement plate is located in a shell plate with thickness exceeding 1 in., the vertical joints shall be fully radiographed. 12.2.1.7 The minimum diagnostic length of each radiograph shall be 6 in. 12.2.1.8 For penetrations installed using insert plates as described in 9.8.6, the completed butt welds between the insert plate and the shell plate shall be fully radiographed. 12.2.2 Acceptance Criteria for Existing Shell Plate to Shell Plate Welds If the radiograph of an intersection bet ween a new and old weld detects unacceptable welds by the current applicable standard, the existing welds shall be: a) evaluated according to the as-built standard, or b) evaluated using fitness-fo r-service assessment, or c) repaired in accordance with 9.6. 12.2.3 Marking and Identification of Radiographs 12.2.3.1 Each film shall show an identificat ion of the welder(s) making the weld . A weld map showing location of welds, weld number, radiograph number, welder identificati on, and grading of each weld is an acceptable alternative to this requirement. 12

12

13

10T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 12-5
12.2.3.2 Radiographs and radiograph records of all repaired welds shall be marked with the letter “R.” 

### 12.3 Hydrostatic Testing 12.3.1 When Hydrostatic Testing is Required A full hydrostatic test, held for 24 hours, shall be performed on the following. a) A reconstructed tank. b) Any tank that has undergone major repairs or major alterations (see Section 3) unless exempted by 12.3.2 for the applicable combination of materials, design, and construction features. c) A tank where an engineering evaluation indicates the need for the hydrostatic test due to an increase in the severity of service. Exampl es of increased service severity are an incr ease in operating pressure (such as storing a product with a higher specific gravity), lowering the se rvice temperature (see Figure 5.2), and using tanks that have been damaged. 12.3.2 When Hydrostatic Testing is Not Required 12.3.2.1 General A full hydrostatic test of the tank is not required for majo r repairs and major alterations if 12.3.2.2 is satisfied plus either of the following: a) appropriate parts of 12.3.2.3 thr ough 12.3.2.6, or alternatively; b) fitness-for-service ev aluation per 12.3.2.7. 12.3.2.2 Review/Approval/Author ization Requirements Items a) and b) below must be satisfied. a) The repair has been reviewed and approved by an engineer experienced in storage tank design in accordance with API 650. The engineer must concur in writin g with taking the hydrostatic testing exemption. b) The tank owner/operator has authorized the exemption in writing. 12.3.2.3 Shell Repair 12.3.2.3.1 For welds to existing metal, develop welding pr ocedure qualifications bas ed on existing material chemistry, including strength requirements. Welding procedures shall be qualified with existing or similar materials, and shall include impact testing. Impact testing requirements shall follow appr opriate portions of API 650, Section 9.2.2 and shall be specified in the repair procedure. 12.3.2.3.2 New materials used for the repair shall meet the current edition of API 650, Section 4 requirements. 12.3.2.3.3 Existing tank materials in the repair area shal l meet at least one of the following requirements. a) API 650 requirements (Seventh Edition or later). b) Fall within the “safe for use” area on Figure 5.2. 13

1212-6 API S TANDARD 653 c) Stress in the repair area shall not exceed 7000 lbf/in. 2 . This limiting stress shal l be calculated as follows:

where
S is the shell stress in pound force per square inch (lbf/in. 2 );
H is the tank fill height above the bottom of repair or alteration in feet (ft);

t is the shell thickness at area of interest in inches (in.);
D is the tank mean diameter in feet (ft);
G is the specific gravity of product. 12.3.2.3.4 New vertical and horizontal shell butt-weld s shall have complete penetration and fusion. 12.3.2.3.5 The root pass and final pass examination shall be in accordance with 12.1.5. In addition, the finished weld shall be fully radiographed. 12.3.2.3.6 Shell welds for the reinforcing plate-to-nozzle nec k and nozzle neck-to-shell joints shall have complete penetration and fusion. The root pass of the nozzle attachment weld shall be back-gouged and examined by magnetic particle or liquid penetrant methods. The complet ed weld shall be examined by magnetic particle or liquid penetrant methods and by the ultrasoni c method. Examination and acceptance criteria for NDE shall be in accordance with 12.1. 12.3.2.3.7 See 12.3.2.5 for shell-to- bottom weld restrictions. 12.3.2.3.8 Door sheets shall comply with the requirements of th is standard for shell plate installation, except they shall not extend to or intersect the bottom-to-shell joint. 12.3.2.4 Bottom Repair within the Critical Zone 12.3.2.4.1 Repairs to the annular ring or bottom plates, within the critical zone (see 3.10) shall comply with the following. a) Meet the requirements of 12.3.2.3.1 through 12.3.2.3.3. b) Be examined visually prior to welding, and examined after t he root pass and the final pass by the magnetic particle or liquid penetrant methods. Annular plate butt-welds shall also be examined by ultrasonic methods after the final pass. Examination and acceptance criteria for NDE shall be in accordance with 12.1. 12.3.2.5 Shell-to-bottom Weld Repair 12.3.2.5.1 Repair of the weld attaching the shell to the annular ring or the shell to the bo ttom plate shall meet one of the following requirements. a) A portion of the weld (of any length) may be removed and replaced as long as the replaced weld meets the size requirements of API 650, Section 5.1.5.7, and t he portion replaced does not represent more than 50 % of the required weld cross-sectional area. b) The weld on one side of the shell may be completely removed and replaced for a length not exceeding 12 in. Shell-to-bottom weld repa irs replacing more than 50 % of the required weld cross-sectional area shall not be closer than 12 in. to each other, including repairs on the opposite side of the shell. S 2.6 HDG t ------------------------- =T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 12-7
12.3.2.5.2 Repairs shall be examined prior to welding, after the r oot pass, and after the final pass by visual, as well as magnetic particle or liquid penetrant methods. Examination and acceptance cr iteria for NDE shall be in accordance with 12.1. 12.3.2.6 Minor Shell Jacking 12.3.2.6.1 Tank shell and critical zone materials shal l meet one of the requirements of 12.3.2.3.3. 12.3.2.6.2 The engineer shall consider all pertinent variables when exempting a minor shell jacking repair from hydrostatic testing, including but not lim ited to: the magnitude of jacking requir ed; material; toughness; quality control; inspection before and after repair; material temperature; fu ture foundation stability; and ja cking techniques (including controls and measurement). Careful consideration shall be given to potential stresses and damage that may result from jacking. 12.3.2.7 Fitness-for-service Evaluation The owner/operator may utilize a fitness-for-service or other appropriate evaluation methodology based on established principles and practices to exempt a repair from hydrostatic testing. The procedures and acceptance criteria for conducting an alternative analysis are not included in this standard. This evaluation shall be performed by an engineer experienced in storage tank des ign and the evaluati on methodologies used. 12.3.3 Other Cases Not Requiring Hydrostatic Testing 12.3.3.1 General For clarity, the situations of 12.3.3.2 and 12.3.3.3 do not in themselves r equire a hydrostatic test because they are not major repairs or major alterations. 12.3.3.2 Repair or Alteration Made to a Floating Roof No hydrotest is required. 12.3.3.3 Bottom Repair or Replacement Outside the Critical Zone Portions of new bottoms (any or all re ctangular plates or large segments of pl ates) in tanks may be replaced without a hydrotest when the subgrade under the new plates is found to be in a condition acceptable to the authorized inspector or is restored to such condition and eit her of the following conditions is met. 1) For tanks with annular rings, the annular ring and the area of support under the annular ring (concrete foundation or grade material) remains intact. 2) For tanks without annular rings, the bottom repair or re placement does not result in welding on the remaining bottom within the critic al zone and the shell and bottom support in the critical zone remains intact. See 3.10 for a definition of t he critical zone. 

### 12.4 Leak Tests New or altered reinforcing plates of shell penetrations shall be gi ven an air leak test in accordance with API 650, Section 7.3.4. 1212-8 API S TANDARD 653


### 12.5 Settlement Survey During Hydrostatic Testing 12.5.1 When Settlement Survey is Required A settlement survey shall be conducted for all existing tanks that undergo a hydrostatic test, except for tanks that have a documented service history of acceptable settlement values, and no settlement is anticipated to occur during the hydrotest. 12.5.2 Initial Settlement Survey When a settlement survey is required in accordance with 12.5. 1, the tank settlement shall initially be surveyed with the tank empty, using an even number of elevation measurement points, N , uniformly distributed around the circumference. An initial settlement survey, prio r to the first hydrostatic test, provides baseline readings for future settlement evaluation. In the absence of this initial survey, the tank shall be assumed to be initially level. The minimum number of elevation points shal l be as indicated by the following equation:
N

= D/ 10 where
D is the tank diameter, in feet (ft). And
N is the minimum required number of settlement measur ement points, but no less than eight. All values of N shall be rounded to the next higher even whole num ber. The maximum spaci ng between settlement measurement points shall be 32 ft. 12.5.3 Settlement Survey During Hydrostatic Testing When a settlement survey is required in accordance with 12.5.1, tank settle ment shall be measured during filling and when the test water reaches 100 % of the test level. 1313-1 

### Section 13—Marking and Recordkeeping

13.1 Nameplates 13.1.1 Reconstructed Tanks 13.1.1.1 Tanks reconstructed in accordance with this standar d shall be identified by a corrosion-resistant metal nameplate similar to that shown in Figur e 13.1. Letters and numerals not less than 5 / 32 in. high shall be embossed, engraved, or stamped in the plate to indicate information as follows: a) reconstructed to API 653; b) edition and revision number; c) year reconstruction was completed; d) if known, the as-built standard and the year of original construction; e) nominal diameter; f) nominal shell height; g) design specif ic gravity; h) maximum permissible operating liquid level; i) the name of the reconstructi on contractor and the assigned seri al number or contract number; j) the owner/operator’s tank number; k) shell material for each shell course; l) maximum operating temperature; m)allowable stress used in calc ulations of each shell course. 13.1.1.2 The new nameplate shall be attached to the tank shel l adjacent to the existing nameplate, if any. An existing nameplate shall be left attached to the tank. Name plates shall be attached as s pecified in API 650, Section 10.1 and Figure 10-1. 10
13.1.2 Tanks Without Nameplates 13.1.2.1 At the owner’s request a nameplate may be attached to a tank meeting the requirements in 13.1.2.2 through 13.1.2.4. 13.1.2.2 If information required to complete the nameplate as required by the as-built standard is available and traceable to the tank, a new Replacement Nameplate, si milar to that shown in Figure 10-1 in API 650, may be attached under the direction of the Au thorized inspector. The new nameplate shall contain all of the information required by the as-built standard and be marked ‘Replacement Nameplate.’ 13.1.2.3 If information required to complete the nameplate as r equired by the as-built st andard is not available, an ‘Assessment Nameplate’ may be attached under the direction of the Authorized inspector, provided a suitability for service assessment is performed per API 653, Sections 4 and 5. The new nameplate shall contain the following information: a) API Standard 653, Assessment Nameplate ; 10

10 12

13

1013-2 API S TANDARD 653 b) Owner's tank number; c) the company performing the assessment; d) the date the assessment was performed; e) the date of the edition and the addendum number of API 653 used to perform the assessment; f) the nominal diameter and nominal height, in meters (ft and in.); g) the maximum capacity in m 3 (42-gallon barrels); h) the liquid level in meters (ft. and in.) used to perform the assessment; i) the specific gravity of the liqui d used to perform the assessment; j) the design metal temperature in °C (°F) used to perform the assessment; k) the pressure and vacuum used to perform the assessment; l) the maximum design temperature in °C (°F) used to perform the assessment; m) the material specification, if known, for each shell course; n) the allowable stress va lues in MPa (psi) used to perform the assessment; o) the joint efficiency used to perform t he assessment (see 4.3.3. or 4.3.4). 13.1.2.4 The nameplate shall be made of a corrosion resistant metal embossed, engraved, or stamped with letters and numerals not less than 4 mm ( 5 / 32 in.) high. Nameplates shall be attac hed as specified in API Std. 650. In addition, the nameplate shall be clearly marked as an API 653, Assessment Nameplate . Refer to Figure 13-2. 

### 13.2 Recordkeeping When a tank is evaluated, repaired, al tered, or reconstructed in accordance with this standard, the following information, as applicable, shall be made a part of the owner/operator’s records for the tank (see 6.8). 13.2.1 Calculations for: a) component evaluation for integrity, including brit tle fracture considerations (see Section 5); b) re-rating (including liquid level); c) repair and alteration considerations. 13.2.2 Construction and repair drawings. 13.2.3 Additional support data including, but not limited to, information pertaining to: a) examinations (including thicknesses); b) material test reports/certifications; c) tests; 10

13T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION 13-3 d) radiographs (radiographs shall be retained for at least one year); e) brittle fracture considerations; f) original tank construction data (date, as-built standard, etc.); g) location and identification (owner /operator’s number, serial number); h) description of the tank (diameter, height, service); i) design conditions (liquid level, specific gravity, allowable st ress, unusual design loadings, etc.); j) shell material and thickness by course; k) tank perimeter elevations; l) construction completion record; m)basis for hydrosta tic test exemption. 

### 13.3 Certification Tanks reconstructed in accordance with this standard s hall require documentation of such reconstruction, and certification that the design, reconstr uction, inspection, and testing was perfo rmed in compliance with this standard. The certification shal l contain information as shown in Figure 13.2 for design and/or reconstruction as applicable.

Figure 13.1—Nameplate RECONSTRUCTED TO API 653 EDITION

Original Standard Tank No. Tank Diam. Height Specific Gravity Design Pressure Orig. Const. Date Year Reconstructed Liquid Level Max. Capacity Max. Operating Temp. Date Completed Serial No.
Shell Course Allowable Stress Material Reconstructed by:13-4 API S TANDARD 653

Figure 13.2—Certification Forms CERTIFICATION FOR TANK RECONSTRUCTED TO API 653

We hereby certify that the tank reconstructed at ___________________________________________ and described as follows: Location

Serial No. Owner's No. Height Capacity Floating or Fixed Roof

Reconstruction Organization

Authorized Representative

Date

Reconstruction Organization

Authorized Representative

Date was reconstructed, inspected, and tested in accordance with all applicable requirements of API Standard 653, ________________ Edition, ________________ Revision, Dated ________________ (including all material supplied by the reconstruction organization).

CERTIFICATION FOR TANK DESIGNED TO API 653

We hereby certify that the design evaluation of the tank reconstructed at ____________________________________________
___ and described as follows: Location

Serial No. Owner's No. Height Capacity Floating or Fixed Roof was performed by the undersigned organization in accordance with all design requirements of API Standard 653, ________________ Edition, ________________ Revision, Dated ________________.A-1 

## Annex A Background on Past Editions of API Welded Storage Tank Standards API published a specification fo r welded steel storage tanks in 1936 entitled API Standard 12C, All-Welded Oil Storage Tanks . Fifteen editions and seven supplements to AP I 12C were published between 1936 and 1958. API 12C was replaced by API Standard 650, Welded Tanks for Oil Storage ; 11 editions and 19 supplements, revisions or addenda to API 650 have been issued. The current edition of API 650 is the 11th Editio n, Addendum 1, published in November 2008. The table below provides a li st of editions, supplements, and revisions to API 12C and API 650. Table A.1—Editions of API Standard 650 and its Precursor, API Standard 12C API Standard 12C, All-Welded Oil Storage Tanks API Standard 650, Welded Tanks for Oil Storage Edition Date Edition Date First July 1936 First December 1961 Second October 1937 Supplement 1963 Supplement 1 April 1938 Second April 1964 Supplement 2 September 1938 Third July 1966 Supplement 3 April 1939 Supplement 1 December 1967 Third April 1940 Fourth June 1970 Fourth March 1941 Supplement 1 April 1971 Fifth May 1942 Fifth July 1973 Sixth August 1944 Supplement 1 October 1973 Seventh August 1946 Supplement 2 April 1974 Supplement 1 September 1947 Supplement 3 March 1975 Eighth September 1948 Sixth April 1977 Supplement 1 December 1949 Revision 1 May 1978 Ninth October 1950 Revision 2 December 1978 Tenth September 1951 Revision 3 October 1979 Eleventh September 1952 Seventh November 1980 Supplement 1 September 1953 Revision 1 February 1984 Twelfth October 1954 Eighth November 1988 Thirteenth September 1955 Ninth July 1993 Supplement 1 October 1956 Addendum 1 December 1994 Fourteenth October 1957 Addendum 2 December 1995A-2 API S TANDARD 653

Fifteenth 1958 Addendum 3 December 1996 Addendum 4 December 1997 Tenth November 1998 Addendum 1 March 2000 Addendum 2 November 2001 Addendum 3 August 2003 Addendum 4 December 2005 Eleventh June 2007 Addendum 1 November 2008 NOTE Ordering information for past editions of API 12C and API 650 is available by calling IHS Inc. at 1-800-854-7179 (www.global.i hs.com). Table A.1—Editions of API Standard 650 and its Precursor, API Standard 12C (Continued) API Standard 12C, All-Welded Oil Storage Tanks API Standard 650, Welded Tanks for Oil Storage Edition Date Edition DateB-1 

## Annex B Evaluation of Tank Bottom Settlement

B.1 Introduction B.1.1 In determining the effects of soil settlement on storage tanks, it is common practice to monitor settlement of the tank bottom. In most cases, such a monitoring prog ram is initiated during the construction and continued during hydrostatic testing and operations. During operations, settlement measurements should be taken at a planned frequency, based on an assessment of soil settlement predictions. For exis ting tanks that do not have initial settlement data, a program of settlement monitori ng should be based on prior service history. B.1.2 If at any time settlement is deemed excessive, the t ank should be emptied and re-leveled. Re-leveling of a sizable tank is expensive and rather di fficult to achieve. Thus, a decision to re-level a tank is a crucial one, and relies very much on the proper interpretation and evaluation of the monitored settlement data. B.1.3 Approaches used to correct tank shell and bottom se ttlement include techniques such as localized repairs of the bottom plates, partial re-leveling of the tank periphery, and major re-lev eling of the entire tank bottom. Major re-leveling of the tank, involving total lifting of the tank shell and bottom at one time, can introduce highly localized stresses in the structure and impair its integrity. Theref ore, when choosing techniques for correcting settlement problems, an alternative to total lifting of the tank shell and bottom should be considered as a first choice. If it is decided to lift the entire tank shell and bottom at one time, it should be done by personnel with demonstrated experience in this technique. 

### B.2 Types of Settlement B.2.1 Settlement Measurements Measurements of tank settlement should be performed by personnel experienced in the types of measurement procedures being performed, using equipment capable of sufficient accuracy to distinguish settlement differences. The principle types of tank se ttlement consist of se ttlements that relate to the t ank shell and bottom plate. These settlements can be recorded by taking el evation measurements around the tank circumference and across the tank diameter. Figure B.1 and Figure B.2 show minimum reco mmended locations on a tank shell and bottom plate for settlement measurements. Data obtained from such meas urements should be used to ev aluate the tank structure. Additional settlement readings may be required to better define local bottom depressions or edge settlements, to refine shell settlement measurements in areas suspected to have local out-of-plane settlements, or to otherwise improve bottom or shell settlement evaluation. Settlem ent measurement locations should be re-used in any future settlement surveys and evaluations. In cases of distortion or corrosion of the tank bottom extending beyond the shell, s hell settlement measurements taken near lap welds in the tank bottom can result in significant errors in measured elevation. Repaired or replaced bottom plates, or new slotted-in botto ms may not have been installed parallel to the bottom shell course. In some cases, more consistent and accurate results may be obtained by surveying the elevation of the weld between the first and second courses. Measure bottom and edge settlement carefully, taking into ac count that measurements taken when the bottom is not in contact with the soil or foundation under the tank ca n overestimate or underestimate edge or bottom settlement significantly. If the measured settlement is near the maximum allowable settlement , consider repeating the measurement with the bottom forced down to the soil, e.g. standing on it, or ta ke an additional set of measurements in the same area, where the bottom is in firm contact with the soil.B-2 API S TANDARD 653

Figure B.1—Measurements of Shell Settlement (External)

Figure B.2—Measurements of Bottom Settlem ent (Internal) Tank Out-of-service 0 11

10

9 3 1

7 8

6 5 4 2 Tank shell Maximum spacing of 32 ft around circumference. There must be at least 4 equally spaced diametrical measurement lines.

NOTE 1 There must be at least eight settlement points. The maximum spacing of the settlement points is 32 ft around the circumference. NOTE 2 Points shall be equally spaced around the tank shell. See 12.5.1.2 for method of determining the number of measurement points.

Maximum spacing of 32 ft around circumference. There must be at least 4 equally spaced diametrical measurement lines. Tank shell

Maximum spacing of 10 ft across diameter. 0 5 1

2 4

3 3

4 2

1 5 0 NOTE See 12.5.1.2 for method of determining the number of measurement points.T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION B-3


### B.2.2 Shell Settlement Evaluation Settlement of a tank is the result of either one, or a combination of t he following three settlement components. B.2.2.1 Uniform settlement. This component often can be predicted in advance, with sufficient accuracy from soil tests. It may vary in magnitude, depending on the soil char acteristics. Uniform settlement of a tank does not induce stresses in the tank structure. However, piping, tank nozzles, and attachments must be given adequate consideration to prevent problems caused by such settlement. B.2.2.2 Rigid body tilting of a tank (planar tilt). This component rotates the tank in a tilted plane. The ti lt will cause an increase in the liquid level and, therefore, an increase in t he hoop stress in the tank shell. Also, excessive tilting can cause binding of peripheral seals in a float ing roof and inhibit roof travel. This type of settlement could affect tank nozzles that have piping attached to them. Figure B.3 shows that the settled location of the tank shell, after rigid body tilt, can be represented by either a cosi ne or sine wave with respect to its original position in a horizontal plane.

Figure B.3—Graphical Representation of Tank Shell Settlement per B.2.2.4U10U11U12U13

Max. settlement at (Pt. 11) Min. settlement

(Pt. 22)

Plane of rigid tilt represented by optimum cosine curve Actual edge settlement Uniform or minimum settlementDatum line for adjusted settlementDatum line for net settlement

N (23) data points, equally ( L ) spaced apart. Tank circumference envelope ( π D ) 13 5 7

2 46 9 8 11 10 13 12 15 14 17 16 19 18 21 20 23 22 1

Out-of-plane deflection for Point “i” is

S i = U i − ( 1 / 2 U i − 1 + 1 / 2 U i + 1 ), for example S 11 = U 11 − ( 1 / 2 U 10 + 1 / 2 U 12 ) U i = out-of-plane settlement of Point, “i”

(+) when above cos. curve; (−) when below cos. curve, for example:

U

11 = (+) U

13 = (−) NOTE See 12.5.1.2 for definition of “ N .”B-4 API S TANDARD 653
B.2.2.3 Due to the fact that a tank is a rather flexible stru cture, the tank may settle in a non-planar configuration, inducing additional stresses in the tank shell. The out-of-plane settlement s of the shell can lead to out-of-roundness at the top of the shell, and depending on t he extent of the induced out-of-roundnes s, may impede the proper functioning of the floating roof in such a way that re-leveling is required. The out-of-roundness caused by settlement may also affect internal roof support st ructures such as columns, rafters, and gir ders. Also, such settlements may cause flat spots to develop in the tank shell. This type of settlement could affect tank nozzles that have piping attached to them. B.2.2.4 While uniform settlement and rigid body tilt of a t ank may cause problems as described in B.2.2.1 and B.2.2.2, the out-of-plane settlement is the important co mponent to determine and evaluate in order to ensure the structural integrity of the shell and bottom. Based on this principle, a common approach is to determine the magnitudes of the uniform settlement and ri gid body tilt (if a rigid tilt plane exis ts or can be identified) for each data point on the tank periphery. If a plane of rigid tilt can be distinguished, it becom es important as a datum from which to measure the magnitudes of the out-of- plane settlements. When the out-of-plane se ttlement pattern of a tank has an easily distinguishable plane of rigid tilt, the methodology in this paragraph can be used to evaluate the acceptability of the tank’s out-of-plane settleme nt. If a rigid tilt plane can not be readily determined, the methodology in B.2.2.5 can be used to evaluate the acceptability of the tank’s out-of-plane settlement. A graphical representation illustrating tank shell settlement with a rigid tilt plane well–defined by a cosine curve fit is shown in Figure B.3. The construction of this settlement plot has been devel oped in accordance with the following. a) The actual settlement (in most cases an irregular curv e) is plotted using points around the tank circumference as the abscissa. b) The vertical distance between the abs cissa and the lowest point on this curve (Point 22) is the minimum settlement, and it is called the uniform settlement component . A line through this point, parallel to the abscissa, provides a new base or datum line for settle ment measurements called adjusted settlements. c) The plane of rigid tilt settlement, if well-defined, is represented by the optim um cosine curve. Several methods exist for determining the optimum cosine curve. The least accu rate method is by free hand drawing techniques, a kind of trial and error procedure to fit the best cosine curve thr ough the data. A better method is to use the mathematical and graphical capabilities of a computer. d) The vertical distances between the ir regular curve and the cosine curve r epresent the magnitudes of the out-ofplane settlements ( U i at Data Point i). e) A commonly used and accepted method is to use a computer to solve for constants a , b , and c , to find the optimum cosine curve of the form: Elev pred = a + b × cos ( θ + c ) Where Elev pred is the elevation predicted by t he cosine curve at angle theta. A ty pical starting point for a computer best-fit cosine curve is a least-square fit where a , b , and c are chosen to minimize the sum of the square of the differences between measured and predict ed elevations. The optimum cosine cu rve is only considered valid (i.e. accurately fits the measured data) if the value R 2 is greater than or equal to 0.9.

where
S

yy is the sum of the squares of the differences between average measured el evation and the measured elevations;
SSE is the sum of the s quare of the differences between t he measured and predicted elevations. R 2 S yy SSE

– ( ) S

yy -------------------------- - =T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION B-5 Linear least square fitting and the R 2 method of curve fitting are basic statis tical tools. The use of a more rigorous statistical method to determine the optim um cosine curve, such as non-linear or iterative procedures, may be used by those experienced in their use. Obtaining a statistically valid cosine curve may require taking more measurements than the minimums shown in Figure B.1. In many cases, the out-of- plane settlement may be concentrated in one or more areas. In such cases, the least-squares fit approach may under predict the local out-o f-plane settlement and is not conservative. In these cases, R 2 will typically be less t han 0.9, and more rigorous curve-fitt ing procedures should be considered. Alternatively, the settlement may not indicate a well-def ined rigid tilt plane and the procedure in B.2.2.5 should be considered. f) The vertical distances between the i rregular curve and the optimum curve represent the magnitudes of the out-ofplane settlements ( U i at Data Point i). S i is the out-of-plane deflection at Point i (see Figure B.3). NOTE When determining the optimum cosi ne curve described in B.2.2.4 e), taking additional measurements around the shell will result in a more accurate cosine curve fit. However, usin g all of the measurement points in the equation shown in B.3.2.1 will result in very small allowable out-of-plane settlements, S max since the arc length L between measurement points is small. It is acceptable to all measurement points to develop the optimum cosine curve, but only use a subset of these points spaced no furth er than 32 ft (8 minimum) when calculating S i and S max . The points used must include the poi nts furthest from the optimum cosine curve. For example, if 8 points are requi red, but 16 measurements are taken, and t he arc length between measurement points is only 15 ft, calculate the optimum cosine curve usi ng all 16 points, but use only 8 points to calculate S i . The equations in Figure B.3 would be revised to read: S

i = U i – ( 1 / 2 U i – 2 + 1 / 2 U i + 2 )
S 11 = U 11 – ( 1 / 2 U 9 + 1 / 2 U 13 ) B.2.2.5 If a well-defined rigid tilt plane can not be determined or the maximu m out-of-plane settlement determined in accordance with B.3.2.1 is exceeded, t he procedures given in this section may be used in lieu of more rigorous analysis or repair. B.2.2.5.1 For settlement profiles without a well-defined rigid tilt plane, the settlement arc length, S arc , and out-ofplane settlement at the point under consideration, S i , must be determined from a plot of the measurement data. Figure B.4 is a graphical illustration of the various measurement terms and procedures for determining estimates of the settlement arc length and the corresponding out-of-plane settlement, including the refinement of measurements, when needed. a) The actual settlement is plot ted using points around the tank circumference as the abscissa. b) An initial settlement arc length and maximum settlem ent is determined from the points on the plotted data that indicate a change in direction of settlement slope (see Figure B.4). c) Additional settlement measurement points may be needed halfway between the points indicating a change in direction of the settlement slope to further refine the settlement arc length and location and magnitude of maximum settlement. d) Step c) may need to be repeated. The best estimate of the settlement arc length and maximum settlement shall be considered in the procedure given in B.3.2.2. B.2.2.5.2 If a valid cosine fit of the rigid tilt plane can be determined, but the maxi mum out-of-plane settlement determined in accordance with B.3.2.1 is exceeded, the pr ocedure in B.3.2.2 may be used to evaluate the settlement. In this case, see Figure B.5 for a graphical illustration of the determination of the settlement arc length and the corresponding out-of-plane settlement.B-6 API S TANDARD 653

Figure B.4—Graphical Representation of Shell Settlement per B.2.2.5 (Tilt Plane Not Described by an Optimal Cosine Curve)

Figure B.5—Graphical Representation of Shell Settlement per B.2.2.5 (Tilt Plane Described by an Optimal Cosine Curve) S i, 1 S

arc i , 1

P O IN T 16 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 S unif has been eliminated from all measurements

S j, 1 S

arc

j, 1

S k, 1 S arc k,1

S

i, 2 S arc i, 2

initial 16 measurements additional measurements to better define settlement arc and maximum settlement S

i,N = maximum out

- of

- plane settlement measured from indicated plane , N th estimate S

arc i,N = settlement arc corresponding to S i, N

S

i S j S

arc i

S arc j

S

i = maximim out

- of

- plane settlement measured from tilt plane for i th arc S

arc i = settlement arc corresponding to S i S

unif has been eliminated from all measurements P O IN T 1 2 ... 16T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION B-7
B.2.2.5.3 If an examination of the measured settlement plot indi cates a fold pattern about a diameter of the tank, the maximum out-of-plane settlement should be determined us ing a settlement arc lengt h of 50 % of the tank’s circumference. 

### B.2.3 Edge Settlement B.2.3.1 Edge settlement occurs when the t ank shell settles sharply around the periphery, resulting in deformation of the bottom plate near the shell-to-bottom corner j unction. Figure B.6 illust rates this settlement.

B.2.3.2 The equation given in B.3.4 can be used to evaluat e edge settlement. Alternat ively, a rigorous stress analysis can be carried out for the def ormed profile. The determination of the deformed profile should take into consideration the following. [text moved to B.2.1] a) Locating the breakover point where the settled area begi ns requires some judgment. Placing a straight edge on the unsettled bottom as shown in Figure B.6, and observing where the bottom separates from the straight edge will help define the breakover point. b) If the tank bottom is cone up or cone down, the settlement B , should be measured from a projection of the unsettled bottom, not from level. See Figure B.7. B.2.3.3 The measured edge settlement B is defined as shown in Figure B.6. B ew is defined as the allowable edge settlement in an area where there is a bottom lap weld in the settled area that is essentially parallel (±20 ° ) to the shell. B e is defined as the allowable settlement in an area with no bottom welds, or only butt-welds in the bottom, or lap welds in the bottom that are essentially perpendicular (±20 ° ) to the shell. B.2.3.4 Section B.3.4 provides methods for ev aluation of measured edge settlement B against allowable edge settlement B ew and B e . Since B ew is more conservative than B e , the simplest approach is to initially evaluate measured Figure B.6—Edge Settlement Breakover point Tank shell

Tank shell Original bottom position

Original bottom position R

R Tank bottom

Tank bottom B

B R = Radius width of settled area B = Settlement Use straight edge to determine the breakover point

Breakover pointB-8 API S TANDARD 653

settlement B against B ew for all settled areas. If all areas meet this criterion, the settlem ent is acceptable and no further evaluation is necessary. If necessary, differ ent settled areas can be evaluated separately against B ew and B e . For areas containing lap welds at an arbitrary angle to the s hell, interpolation to find an allowable settlement between B ew and B e based on the angle of the weld to the shell is allowed. 

### B.2.4 Bottom Settlement Near the Tank Shell
B.2.4.1 Figure B.8 illustrates bottom sett lement near the tank shell. B.2.4.2 The equation given in B.3.3 can be used to evaluate settlement near the tank shell. Alternatively, a rigorous stress analysis can be carried out for the deformed profile. 

### B.2.5 Localized Bottom Settlement Remote from the Tank Shell B.2.5.1 Localized bottom settlement remote from tank shel l are depressions (or bulges) that occur in a random manner, remote from the shell (see Figure B.9). Figure B.7—Correction for Measured Edge Settlement Cone down bottom Cone up bottom

Shell

Original bottom position

Settled bottom position Shell

Original bottom
Breakover

Settled bottom

B — Measured from original bottom position

B — Incorrect! Measured from level line from breakover point to shellT ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION B-9

B.2.5.2 Acceptability of these lo calized settlements is dependent on localized st resses in the bottom plate, design and quality of the lap welds (single-pass or multi-pass), and voids below the bottom plate. The equation given in B.3.3 can be used to evaluate localized settlement remote from the tank shell. T hese limits are applicable to tank bottoms that have single-pass lap-welded joints. 

### B.3 Determination of Acceptable Settlement B.3.1 General For existing tanks with history of successful service, it may be possible to accept greater settlement and distortion of the foundation from a true plane than new tank construction standards allow. Each tank must be evaluated based on service conditions, materials of construction, soil characteristics, tank foundation design, and tank service history. The methods discussed in following sections are not mandatory and approximate the maximum permissible settlement. However, experience has shown that if settlements exceed the following requirements, further assessment or repair is required. 

### B.3.2 Permissible Out-of-plane Settlement From the measurements procedures described in B.2. 2.4 and B.2.2.5, determine the maximum out-of-plane settlement.The magnitude (absolute value) of the maximum settlement shall be compared to the permissible values given in B.3.2.1 or B.3.2.2, as applic able. The permissible out-of-plane settlem ent given in B.3.2.1 and B.3.2.2 do not Figure B.8—Bottom Settlement Near Shell R R B B Tank shell

A A

SECTION A
- A
R = Radius of inscribed circle in bulged or depressed area B = Settlement or depression depth or height of bulge R

R R

R
R ≤ 2 RB-10 API S TANDARD 653

take into consideration abrupt changes in shell elevation (ridges) or discontinuities near the bo ttom of the tank in the settled region, such as low nozzles. They also do not consi der fold patterns in cone roof tanks when the fold line is adjacent to or through a line of one or more roof columns, or to patterns of settlement that include combined shell and edge settlements. The permissible settlement criteria in B.3.2.2 are applicable to API 650 carbon steel and stainless steel tanks and diameter ranges given in B.3.2.2. Out-of-pl ane settlement that does not m eet these limitations should be further examined by a more rigor ous engineering assessment to determine the need for repairs, see B.3.2.4 B.3.2.1 When using the procedure with an optimal cosine cu rve approach defined in B.2. 2.4 to determine out-ofplane settlement, the permiss ible out-of-plane settlement is giv en by the following equation (see Note): Figure B.9—Localized Bottom Depressions or Bulges Remote from Shell Localized depressions or bulges in tank bottom plate R R

B B Tank shell

A A

R R R

R = Radius of inscribed circle in bulged or depressed area B = Settlement depth or height of bulge
SECTION A
- A

S

max, ft L 2 Y × 11 × ( ) 2 E H × ( ) [ ] ------------------------------ - =T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION B-11
where
S

max, ft is permissible out-of-plane settlement, in feet (ft); L is arc length between measurement points, in feet (ft); Y is yield strength of the shell material, in pound force per square inch (lbf/in. 2 ); E is Young’s Modulus, in pound force per square inch (lbf/in. 2 ); H is tank height, in feet (ft). NOTE This equation is based on “Criteria for Settlement of Tank s,” W. Allen Marr, M. ASCE, Jose A. Ramos, and T. William Lambe, F. ASCE, Journal of Geotechnica l Engineering Division , Proceedings of the American Soci ety of Civil Engineers, Vol. 108, August, 1982. B.3.2.2 When using the procedure in B.2.2.5 to determine out-of-plane settlement, t he permissible out-of-plane settlement is given by the following equation (see Note):

where
S

max, in is permissible out-of-plane settlement, in inches (in.); S

arc is effective settlement arc, see B.2.2.5.1, in feet (ft); D is tank diameter, in feet (ft); Y is yield strength of the shell material , in pound force per square inch (lbf/in. 2 ); E is Young’s Modulus, in pound force per square inch (lbf/in. 2 ); H is tank height, in feet (ft). NOTE This equation is based on “Final Report on the Study of Out-of-Plane Tank Settlement,” J. Andreani, N. Carr, Report to API SCAST, May, 2007. B.3.2.3 Serviceability may also be a concern for tanks with significant out-of-plane settlement. Out-of-roundness can impede floating roof operation and also affect internal roof support stru ctures. The out-of-roundness that a tank experiences with out-of-plane settlement is fairly sensitive to the actual patt ern of settlement. The owner may wish to specify additional inspection or a more rigorous assessment of the tank’s out-of-roundness. Tank Diameter ft K , Open Top Tanks K , Fixed Roof Tanks D 50 28.7 10.5 50 < D 80 7.8 5.8 80 < D 120 6.5 3.9 120 < D 180 4.0 2.3 180 < D 240 3.6 Not applicable 240 < D 300 2.4 Not applicable 300 < D Not applicable Not applicable S

max, in min K S arc × D H ---     Y E ---     , 4.0 × × =

5 ≤ 5

≤ 5 ≤ 5 ≤ 5 ≤ 5 ≤B-12 API S TANDARD 653
B.3.2.4 If measured out-of-plane settlement exceeds the applic able limits described in B.3.2.1 or B.3.2.2, a more rigorous evaluation may be performed to determine the need for repairs. This evaluation should be done by an engineer experienced in tank settlement analysis. 

### B.3.3 Internal Bottom Settlements or Bulges Measure the bulge or depression. The pe rmissible bulge or depression is given by the following equation (see Note).
B

B = 0.37 R where
B

B is maximum height of bulge or dept h of local depression, in inches;
R is radius of inscribed circle in bulged area or local depression, in feet. Figure B.10 is a graphical repr esentation of this equation. NOTE This equation is based on “Criteria for Settlement of Tank s,” W. Allen Marr, M. ASCE, Jose A. Ramos, and T. William Lambe, F. ASCE, Journal of Geotechnica l Engineering Division , Proceedings of the American Soci ety of Civil Engineers, Vol. 108, August 1982.



### B.3.4 Edge Settlement B.3.4.1 Maximum allowable settlement B ew is shown in Figure B.11 for settled areas that include bottom lap welds essentially parallel to the shell (±20 ° ). In settled areas where the measured settlement B exceeds 75 % of allowed settlement B ew , all shell-to-bottom weld s and bottom welds should be examined visually and with magnetic particle Figure B.10—Localized Tank Bottom Settlement Limits for Single Pass Welds

15
14
13
12
11
10
9
8 7
6
5
4 3
2
1
0 0 5 10 15 20 25 30 35 40 45 Repairs or a rigorous assessment should be conducted if the depth of the observed bulge or depression is above this line

B

R R R R R B RR RR

Partial ringtype depression or bulge (at edge only) where R < 2 R

Depression or bulge (anywhere)B= Depth of depression or bulge at center (in.)

R = Radius of inscribed circle in depression or bulge (ft)

13T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION B-13 or liquid penetrant methods. All indications should be repair ed, or evaluated for risk of brittle fracture, and/or fatigue failure prior to returnin g the tank to service. B.3.4.2 For settled areas where measured settlement B exceeds 75 % of B ew , any welds within 12 in. of either side of the breakover area (see Figure B.6) should be exam ined visually. Any suspect areas should be examined with either magnetic particle examination or liquid penetrant examination. All i ndications should be repaired or evaluated for risk of fatigue prior to returning the tank to service. B.3.4.3 Maximum allowable settlement B e is shown in Figure B.12 for areas of edge settlement with no welds, butt welds, or lap welds in the bottom that ar e essentially perpendicular to the shell (±20 ° ). In settled areas where the measured settlement exceeds 75 % of t he allowed settlement, all shell-to-bottom welds and bottom welds should be examined visually and with magnetic particle or liquid penetrant methods. All indica tions should be repaired or evaluated for risk of brittle fr acture and/or fatigue prior to returning the tank to service. B.3.4.4 Maximum allowable settlement for areas of edge settlement with a lap weld at an arbitrary angle to the shell may be interpolated from B e and B ew from Figure B.11 and Figure B.12, and the following equation:
B α = B e – ( B e – B ew ) × sin α Where α is the angle of the weld to a tank centerline and B α is the allowable settlement for an area with a weld at that angle (see Figure B.13). B.3.4.5 In general, settlement occurs slowly, and for most exis ting tanks, the majority of settlement is presumed to have occurred in the first few years of service. Significant additional settlement will not be expected after the initial inspections. Therefore, typical practice is to compare the measured edge settlement with the maximum allowable edge settlement B ew and B e , and not include allowance for additional se ttlement during subsequent operation. Note that erosion of the pad adjacent to the tank may cause loca l settlement. In this case the settlement will continue unless the pad is repaired and future erosion prevented. For cases where significant additional settlement is expected, an engineer experienced in tank settlement evaluation should evaluate the settlement ex pected at the next inspection with the limits in B.3.4. This is analogous to a corrosion allowance for components expected to corrode. B.3.4.6 The edge settlement limits described in B.2. 3.1 through B.2.3.4 were developed for typical 1 / 4 -in. thick tank bottoms with minimal corrosion. a) Edge settlement limits can be a pplied with reasonable accuracy to 5 / 16 - and 3 / 8 -in. thick tank bottoms. b) Edge settlement limits can be applied with reasonable accu racy to bottoms with general corrosion, as long as the areas near all welds are thicker than 3 / 16 in. c) Edge settlement limits can be applied wi th reasonable accuracy to bottoms with local corrosion, if all locally thin areas in the settled area (closer than “ R ” to the shell) thinner than 3 / 16 in. are smaller than 12 in. in diameter and the thin area does not include a weld. d) Settlement is presumed to be slow, and a small amount of additional settlement is expected to occur prior to the next inspection. B.3.4.7 Edge settlement increases secondary stress at the bottom-to-shell weld. If weld repairs are made to the bottom-to-shell weld in an ar ea where settlement exceeds 1 / 2 of B e , these additional stresses should be evaluated by an engineer experienced in tank settlement evaluat ion before waiving a hydrostatic test per 12.3. 

### B.4 Repairs B.4.1 If it is determined that settlements have occurred which are beyond the permissible limits established in the previous sections, then consideration should be given to making repairs or a rigorous stress analysis should be 13

12

13

12B-14 API S TANDARD 653

performed to evaluate the deformed pr ofile. Various repair techniques hav e been discussed above. The judgment on repairs should be tempered with knowledge of tank serv ice history, previous repairs, previous inspections, tank foundation conditions, soil characteristics, the material of construction, and estimates of future settlement. See 9.10 for suggested repair details. B.4.2 For tanks with edge settlement exceeding the limits an d assumptions given in B.2.3.1 through B.2.3.7, the tank should be repaired. Any plate exceeding acceptable strains (typically 2 % to 3 %) should be replaced. Re-leveling the tank will not remove the plastic strain, so leveling the tank without replacing the strain may not be a sufficient repair. Welds in the area of the high strains should be removed and replaced, or be subjected to a fitness-for-service evaluation by an engineer experienced in tank settlement evaluation. The condition leading to the unacceptable settlement should be corrected. Depending on the severity and location of the settlement, required repairs may include regrading the soil under the tank bottom, and/or repairing the foundation. Jacking and re-leveling the shell may be required to prevent ad ditional settlement damage. Jacking and leveling are usually done in conjunction with, not instead of, replacing damaged plate and welds. In lieu of repairs, a detailed analysis of the settled area may be performed by an engineer experienced in tank design and settlement evaluation. The analysis should consider primary and secondary stress and the risk of brittle fracture. Figure B.11—Maximum Allowable Edge Settlement for Areas with Bottom Lap Welds Approximately Parallel to the Shell 10.00

9.00

8.00

7.00

6.00

5.00

4.00

3.00

2.00

1.00

0.00 0 123456 Tanks with larger edge settlements are to be repaired, or have detailedanalysis of bottom, and bottom-toshell junction

Welds in tanks with settlement greater than or equal 75 % of B ew , and larger than 2 in., are to be examined with magnetic particle or liquid penetrant methods Diameter, ft

Tanks with settlement less than 75 % of B ew may be returned to service 160 & Larger
120
100 80 60 50 40 30
20

R = Radius of settled area, ftBew= Maximum allowable settlement, (in.)

13T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION B-15

Figure B.12—Maximum Allowable Edge Settlement for Areas with Bottom Lap Welds Approximately Perpendicular to the Shell

Figure B.13—Edge Settlement with a Lap Weld at an Arbitrary Angle to the Shell 10.00

9.00

8.00

7.00

6.00

5.00

4.00

3.00

2.00

1.00

0.00 0 123456 Tanks with larger edge settlements are to be repaired, or have detailedanalysis of bottom, and bottom-toshell junction

Welds in tanks with settlement greater than or equal 75 % of B ew , and larger than 2 in., are to be examined with magnetic particle or liquid penetrant methods Diameter, ft

Tanks with settlement less than 75 % of B ew may be returned to service 160 & Larger 120 100

80
60 50 40 30 20

R = Radius of settled area, ftBe= Maximum allowable settlement, (in.) 13

Angle alpha Settled area

Tank centerline

Bottom plate layoutC-1 

## Annex C Checklists for Tank Inspection Annex C contains sample checklists illust rating tank components and auxiliary items that should be considered for internal and external inspection of tanks. This informat ion is provided as guidance to the owner/operator for developing an inspection assessment schedule for any specific tank inst allation. The checklist format facilitates the recording of inspection findings. NOTE 1 Users of checklists should not rely exclusively on the information contained in this document. Sound business, scientific, engineering, and safety judgment should be used in employing the information contained herein. NOTE 2 Where applicable, authorities hav ing jurisdiction should be consulted.T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION C-3

Tank In-service Inspection Checklist

Item Completed √ Comments
C.1.1 Foundation Measure foundation levelness and bottom el evations (see Annex B for extent of measurements). C.1.1.1 Concrete Ring a) Inspect for broken concrete, spalling, and cracks, particularly under backup bars used in welding butt-welded annular rings under the shell. b) Inspect drain openings in ring, back of wa terdraw basins and top surface of ring for indications of bottom leakage. c) Inspect for cavities under foundatio n and vegetation against bottom of tank. d) Check that runoff rainwater from the shell drains away from tank. e) Check for settlement around perimeter of tank. C.1.1.2 Asphalt a) Check for settling of tank into asphalt bas e which would direct runoff rain water under the tank instead of away from it. b) Look for areas where leaching of oil has le ft rock filler exposed, which indicates hydrocarbon leakage. C.1.1.3 Oiled Dirt or Sand Check for settlement into the base which woul d direct runoff rain water under the tank rather than away from it. C.1.1.4 Rock Presence of crushed rock under the steel bo ttom usually results in severe underside corrosion. Make a note to do additional botto m plate examination (ultrasonic, hammer testing, or turning of coupons) when the tank is out of service. C.1.1.5 Site Drainage a) Check site for drainage away from t he tank and associated piping and manifolds. b) Check operating condition of the dike drains. C.1.1.6 Housekeeping Inspect the area for buildup of trash, v egetation, and other inflammables buildup. C.1.1.7 Cathodic Protection Review cathodic protec tion potential readings. C.1.2 Shells C.1.2.1 External Visual Inspection a) Visually inspect for paint failures, pitting, and corrosion. b) Clean off the bottom angle area and inspect for corrosion and thinning on plate and weld. c) Inspect the bottom-to-foundation seal, if any. C.1.2.2 Internal (Floating Roof Tank) Visually inspect for grooving, corr osion, pitting, and coating failures. C.1.2.3 Riveted Shell Inspection a) Inspect external surface for rivet and seam leaks. b) Locate leaks by sketch or photo (locatio n will be lost when shell is abrasive cleaned for painting). c) Inspect rivets for corrosion loss and wear. d) Inspect vertical seams to see if they hav e been full fillet lap-welded to increase joint efficiency.C-4 API S TANDARD 653

Tank In-service Inspection Checklist (Continued)
Item Completed √ Comments e) If no record exists of vertical rivet ed seams, dimension and sketch (or photograph) the rivet pattern: number of rows, rivet size, pitch length, and note whether the joint is butt-riveted or lap-riveted. C.1.2.4 Wind Girder (Floating Roof Tanks) a) Inspect wind girder and handrail for corros ion damage (paint failure, pitting, corrosion product buildup), especially where it occurs at tack-welded junction, and for broken welds. b) Check support welds to shell for pitting, especially on shell plates. c) Note whether supports have rein forcing pads welded to shell. C.1.3 Shell Appurtenances C.1.3.1 Manways and Nozzles a) Inspect for cracks or si gns of leakage on weld joint at nozzles, manways, and reinforcing plates. b) Inspect for shell plate dimpling around nozz les, caused by excessive pipe deflection. c) Inspect for flange leaks and leaks around bolting. d) Inspect sealing of insulation around manways and nozzles. e) Check for inadequate manway flange and cover thickness on mixer manways. C.1.3.2 Tank Piping Manifolds a) Inspect manifold piping, flanges, and valves for leaks. b) Inspect fire fighting system components. c) Check for anchored piping which would be ha zardous to the tank shell or bottom connections during earth movement. d) Check for adequate thermal pressure relief of piping to the tank. e) Check operation of regulators for tanks with purge gas systems. f) Check sample connections for leaks and for proper valve operation. g) Check for damage and test the accuracy of temperature indicators. h) Check welds on shell-mounted davit cl ips above valves 6 in. and larger. C.1.3.3 Autogauge System a) Inspect autogauge tape guide and lower sheave housing (floating swings) for leaks. b) Inspect autogauge head for damage. c) Bump the checker on autogauge head for proper movement of tape. d) Identify size and construction material of autogauge tape guide (floating roof tanks). e) Ask operator if tape tends to hang up during tank roof movement (floating roof tanks). f) Compare actual product level to the read ing on the autogauge (maximum variation is 2 in.). g) On floating roof tanks, when the roof is in the lowest position, check that no more than two ft of tape are exposed at the end of the tape guide. h) Inspect condition of board and legi bility of board-type autogauges. i) Test freedom of movement of marker and float. C.1.3.4 Shell-mounted Sample Station a) Inspect sample lines for function of valves and plugging of lines, including drain or return-to-tank line. b) Check circulation pump fo r leaks and operating problems.T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION C-5

Tank In-service Inspection Checklist (Continued)
Item Completed √ Comments c) Test bracing and supports for sample lines and equipment. C.1.3.5 Heater (Shell Manway Mounted) Inspect condensate drain for pres ence of oil indicating leakage. C.1.3.6 Mixer a) Inspect for proper mounting flange and support. b) Inspect for leakage. c) Inspect condition of power lines and connections to mixer. C.1.3.7 Swing Lines: Winch Operation a) Nonfloating. Raise, then lower the swi ng line with the winch, and check for cable tightness to confirm that swing line lowered properly. b) Floating. With tank half full or more, lo wer the swing line, then let out cable and check if swing has pulled cable tight, indicating that the winch is operating properly. c) Indicator. Check that the indicator moves in the proper direction: Floating swing line indicators show a lower level as cable is wound up on the winch. Non-floating swing line indicators show the opposite. C.1.3.8 Swing Lines: External Guide System Check for leaks at threaded and flanged joints. C.1.3.9 Swing Lines: Identify Ballast Varying Need Check for significant differenc e in stock specific gravity. C.1.3.10 Swing Lines: Cable Material and Condition a) For nonstainless steel cable, check for corrosion over entire length. b) All cable: check for wear or fraying. C.1.3.11 Swing Lines: Product Sample Comparison Check for water or gravity differences t hat would indicate a leaking swing joint. C.1.3.12 Swing Lines: Target Target should indicate direction of swing opening (up or down) and height above bottom where suction will be lost with swing on bottom support. C.1.4 Roofs C.1.4.1 Deck Plate Internal Corrosion For safety, before accessing the roof, check with ultrasonic instrument or lightly use a ball peen hammer to test the deck plate near the edge of the roof for thinning. (Corrosion normally attacks the deck plate at the edge of a fixed roof and at the rafters in the center of the roof first.) C.1.4.2 Deck Plate External Corrosion Visually inspect for paint failure, holes, pitting, and corrosion product on the roof deck. C.1.4.3 Roof Deck Drainage Look for indication of standing water. (Significant sagging of fixed roof deck indicates potential rafter failure. Large standing water areas on a floating roof indicate inadequate drainage design or, if to one side, a nonlevel roof with possible leaking pontoons.) C.1.4.4 Level of Floating Roof At several locations, measure distance from roof rim to a horizontal weld seam above the roof. A variance in the readings indicates a nonl evel roof with possible shell out-of-round, out-of-plumb, leaking pontoons, or hang-up. On small diameter tanks, an unlevel condition can indicate unequal loading at that level.C-6 API S TANDARD 653

Tank In-service Inspection Checklist (Continued)
Item Completed √ Comments C.1.4.5 Gas Test Internal Floating Roof Test for explosive gas on top of the intern al floating roof. Readi ngs could indicate a leaking roof, leaking seal system, or inadequat e ventilation of the area above the internal floating roof. C.1.4.6 Roof Insulation a) Visually inspect for cracks or leaks in t he insulation weather coat where runoff rain water could penetrate the insulation. b) Inspect for wet insulation under the weather coat. c) Remove small test sections of insulation and check roof plate for corrosion and holes near the edge of the insulated area. C.1.4.7 Floating Roof Seal Systems a) Inspect the condition of the seal, measur e and record maximum rim spaces and sealto-shell gaps around the full roof circum ference at the level of inspection. NOTE Inspection of the seal and measurem ent of the rim spaces and seal-to-shell gaps at more than one level may be necessary to more fully determine if any problems exist at other levels of tank operation). b) Measure and record annular space at 30-ft spacing (minimum of four quadrants) around roof and record. Measurements s hould be taken in directly opposite pairs. 1) _______ _______ Opposite pair 1. 2) _______ _______ Opposite pair 2. c) Check if seal fabric on prim ary shoe seals is pul ling shoes away from shell (fabric not wide enough). d) Inspect fabric for deteriora tion, holes, tears, and cracks. e) Inspect visible metallic parts for corrosion and wear. f) Inspect for openings in seals t hat would permit vapor emissions. g) Inspect for protruding bolt or rivet heads against the shell. h) Pull both primary and secondary seal syst ems back all around the shell to check their operation. i) Inspect secondary seals for si gns of buckling or indications that their angle with the shell is too shallow. j) Inspect wedge-type wiper seals for flex ibility, resilience, cracks, and tears. C.1.5 Roof Appurtenances C.1.5.1 Sample Hatch a) Inspect condition and functioning of sample hatch cover. b) On tanks governed by Air Quality Monitoring District rules, check for the condition of seal inside hatch cover. c) Check for corrosion and plugging on thief and gauge hatch cover. d) Where sample hatch is used to reel gauge stock level, check for marker and tab stating hold-off distance. e) Check for reinforcing pad where samp le hatch pipe penetrates the roof deck. f) On floating roof sample hatch and recoil s ystems, inspect operation of recoil reel and condition of rope. g) Test operation of system. h) On ultra clean stocks such as JP4, c heck for presence and condi tion of protective coating or liner inside sample hatch (prev enting rust from pipe getting into sample). 12T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION C-7

Tank In-service Inspection Checklist (Continued)
Item Completed √ Comments C.1.5.2 Gauge Well a) Inspect visible portion of the gauge well for thinning, size of slots, and cover condition. b) Check for a hold-off distance marker a nd tab with hold-off distance (legible). c) On floating roofs, inspect condition of roof guide for gauge well, particularly the condition of the rollers for grooving. d) If accessible, check the distance from the gauge well pipe to the tank shell at different levels. e) If tank has a gauge well wa sher, check valve for leakage and for presence of a bull plug or blind flange. C.1.5.3 Fixed Roof Scaffold Support Inspect scaffold support for corrosion, wear, and structural soundness. C.1.5.4 Autogauge: Inspection Hatch and Guides (Fixed Roof) a) Check the hatch for corrosion and missing bolts. b) Look for corrosion on the tape guide’s and float guide’s wire anchors. C.1.5.5 Autogauge: Float Well Cover a) Inspect for corrosion. b) Check tape cable for wear or fray ing caused by rubbing on the cover. C.1.5.6 Sample Hatch (Internal Floating Roof) a) Check overall conditions. b) When equipped with a fabric seal, check for automatic sealing after sampling. c) When equipped with a recoil reel opening device, check for proper operations. C.1.5.7 Roof-mounted Vents (Internal Floating Roof) Check condition of screens , locking and pivot pins. C.1.5.8 Gauging Platform Drip Ring On fixed roof tanks with drip rings under the gauging platform or sampling area, inspect for plugged drain return to the tank. C.1.5.9 Emergency Roof Drains Inspect vapor plugs for emergency drain: that seal fabric discs are slightly smaller than the pipe ID and that fabric seal is above the liquid level. C.1.5.10 Removable Roof Leg Racks Check for leg racks on roof. C.1.5.11 Vacuum Breakers Report size, number, and type of vacuum breaker s. Inspect vacuum breakers. If high legs are set, check for setting of mec hanical breaker in high leg position. C.1.5.12 Rim Vents a) Check condition of the screen on the rim vent cover. b) Check for plating off or removal of rim vents where jurisdictional rules do not permit removal. C.1.5.13 Pontoon Inspection Hatches a) Open pontoon inspection hatch covers and vi sually check inside for pontoon leakage. b) Test for explosive gas (an indicator of vapor space leaks).C-8 API S TANDARD 653

Tank In-service Inspection Checklist (Continued)
Item Completed √ Comments c) If pontoon hatches are equipped with locked down coves, check for vent tubes. Check that vent tubes are not plugged up. Inspect lock-down devices for condition and operation. C.1.6 Accessways See Tank Out-of-service Ins pection Checklist, Item C.2.12. NOTEST ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION C-9
Tank Out-of-service Inspection Checklist (Continued)
Item Completed √ Comments
C.2.1 Overview a) Check that tank has been cleaned, is gas free, and safe for entry. b) Check that the tank is completely isolated from product lines, all electrical power, and steam lines. c) Check that roof is adequately supported, including fixed roof structure and floating roof legs. d) Check for presence of falling object hazards, such as corroded-through roof rafters, asphalt stalactites, and trapped hydrocar bons in unopened or plugged equipment or appurtenances, ledges, etc. e) Inspect for slipping hazards on the bottom and roof decks. f) Inspect structural welds on accessways and clips. g) Check surfaces needing inspection for a heavy-scale buildup and check weld seams and oily surfaces where welding is to be done. Note areas needing more cleaning, including blasting. h) Review cathodic protection potential readings. C.2.2 Tank Exterior a) Inspect appurtenances opened during cleaning such as lower floating swing sheave assemblies, nozzle interiors (after removal of valves). b) Hammer test or ultrasonically test the roof. c) Enter and inspect the floating roof pontoon compartments. C.2.3 Bottom Interior Surface a) Using a flashlight held close to and parall el to the bottom plates, and using the bottom plate layout as a guide, visually inspect and hammer test the entire bottom. b) Measure the depth of pitting and describe the pitting appearance (sharp edged, lake type, dense, scattered, etc.) c) Mark areas requiring patchi ng or further inspection. d) Mark locations for turn ing coupons for inspection. e) Inspect all welds for corrosion and leaks, particularly the shell-to-bottom weld. f) Inspect sketch plates for corrosion. g) Check condition of internal sump, if applic able. Standing liquid should be removed from the sump to allow for complete inspection and vacuum testing of weld seams as appropriate. Sump bottom and sidewall plate and seams need to be evaluated for both product-side and soil-side corrosion. h) Locate and mark voids under the bottom. i) Record bottom data on a layout sketch using the existing bottom plates as a grid. List the number and sizes of patches required. j) Vacuum test the bottom lap welds. k) Hammer test or ultrasonically examine any slightly discolored spots or damp areas. l) Check for reinforcing pads under all bottom attached clips, brackets, and supports. m) Inspect floating roof leg pads for pitting or cutting, and excessiv e dimpling (indicating excessive loading). n) Check the column bases of fixed roof supports for adequate pads and restraining clips. o) In earthquake Zones 3 and 4, check that roof supports are not welded down to the tank bottom, but are only restrained from horizontal movement. p) Check area beneath swing line cable for indications of cable cutting or dragging. q) Mark old oil and air test connec tion for removal and patching. r) Identify and report low areas on the bottom that do not drain adequately. s) Inspect coating for holes, disbondi ng, deterioration, and discoloration.C-10 API S TANDARD 653

Tank Out-of-service Inspection Checklist (Continued)
Item Completed √ Comments
C.2.4 Shell Seams and Plate a) On cone up bottoms, closely inspect and gauge the depth of metal loss on the lower 2 in. to 4 in. of the shell (area of standing water). b) Measure the depth of pitting on each course. c) Inspect and estimate the amount of metal loss on the heads of rivets and bolts. d) Inspect shell-to-bottom riveted lap joints. e) Inspect for vertical grooving damage from seal assembly protrusions. f) Inspect existing protective coatings for damage, deterioration, and disbonding. g) Check for areas of rubbing (indicating too mu ch pressure by the seal assembly shoes or inadequate annular space). h) Visually inspect the shell plates and seams for indications of leakage. i) If the shell has riveted or bolted seams, reco rd the leak locations by film or chart in case the locations are lost during surface preparation for painting. j) Measure annular space at 40-ft intervals. k) Survey the shell to check for roundness and plumb. C.2.5 Shell-mounted Overflows a) Inspect overflow for corrosion and adequate screening. b) Check location of overflow that it is not above any tank valves or equipment. C.2.6 Roof Interior Surface C.2.6.1 General a) Visually inspect the underside surface of t he roof plates for holes, scale buildup, and pitting. b) Hammer test or ultrasonically examine to check for thin areas , particularly in the vapor space of floating roofs and at edge of roof on cone roof tank. c) Check all clips, brackets, braces, etc., welded to the roof deck plate for welded reinforcing pads and see that they have not broken free. d) If no pad is present, penetrant test for cracking of the weld or deck plate. e) Inspect for protective coating for breaks, disbondment, and deterioration. f) Spark test the interior surface coating if recoating is not planned. C.2.6.2 Fixed Roof Support Structure a) Inspect the support columns for thinning in the upper 2 ft. b) On API columns (two channels welded t ogether) check for corrosion scale breaking the tack welds, unless the joint between the channels is completely seal welded. c) Check that the reinforcing pad on the botto m is seal-welded to the tank bottom with horizontal movement restraining clips welded to the pad. d) Determine if pipe column supports are conc rete filled or open pipe. If open pipe, check for a drain opening in the bottom of the pipe. e) Inspect and gauge rafters for thinning, particularly near the center of the roof. Report metal loss. f) Check for loose or twisted rafters. g) Inspect girders for thinning and check that they are attached securely to the top of the columns.T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION C-11

Tank Out-of-service Inspection Checklist (Continued)
Item Completed √ Comments h) Report if the columns have cross bracing in the area between the low pump out of the top of the shell (for future internal floating roof installation). i) Inspect and report presence of any roof-mounted swing line bumpers. j) Photograph the roof structure if no rafter layout drawing exists. C.2.7 Fixed Roof Appurtenances C.2.7.1 Inspection and Light Hatches a) Inspect the hatches for corrosion, paint and coating failures, hol es, and cover sealing. b) On loose covers, check for a safety chain in good condition. c) On light hatches over 30 in. across, check for safety rods. d) Inspect the condition of the gaskets on bold or latched down hatch covers. C.2.7.2 Staging Support Connection Inspect the condition of the st aging support for corrosion. C.2.7.3 Breathers and Vents a) Inspect and service the breather. b) Inspect screens on vents and breathers. C.2.7.4 Emergency P/V Hatches a) Inspect and service pressure/vacuum hat ches. (Setting should be high enough to prevent chattering of breather during normal operation. See breather manufacturer’s guide.) b) Inspect liquid seal hatches for corros ion and proper liquid level in the seal. C.2.7.5 Sample Hatch a) Inspect sample hatch for corrosion. b) Check that the cover operates properly.c) If the tank has no gauge well, check for a hold-off distance marker and check measurement. C.2.8 Floating Roof C.2.8.1 Roof Deck a) Hammer test the area between roof rim and shell. (If access for hammer testing is inadequate, measure the distance from the bottom edge of the roof to the corroded area and then hammer test from inside the pontoon.) b) In sour water service, clean and test all deck plate weld seams for cracking unless the lower laps have been seal-welded. c) Check that either the roof drain is open or the drain plug in the roof is open in case of unexpected rain. d) On flat bottomed and cone bottom roof decks, check for a vapor dam around the periphery of the roof. The dam should be c ontinuous without break to prevent escape of vapors to the seal area from under the center of the roof. C.2.8.2 Floating Roof Pontoons a) Visually inspect eac h pontoon for liquid leakage. b) Run a light wire through the gooseneck vent s on locked down inspection hatch covers to make sure they are open. c) Inspect lockdown latches on each cover.C-12 API S TANDARD 653

Tank Out-of-service Inspection Checklist (Continued)
Item Completed √ Comments d) Check and report if each pontoon is: 1) vapor tight (bulkhead seal welded on one side on bottom, sides, and top), 2) liquid tight (seal-welded on bottom and sides only), or 3) unacceptable (minimum accept able condition is liquid tight). C.2.8.3 Floating Roof Cutouts a) Inspect underside of cutouts for mechanical damage. b) Inspect welds for cracks. c) Inspect plate for thinni ng, pitting, and erosion. d) Measure mixer cutouts and record plate th ickness for future mixer installation or replacement. Plate thickness ______ . C.2.8.4 Floating Roof Supports a) Inspect fixed low and removable hi gh floating roof legs for thinning. b) Inspect for notching at bottom of legs for drainage. c) Inspect for leg buckling or felling at bottom. d) Inspect pin hole in roof guide for tears. e) Check plumb of all legs. f) Inspect for adequate reinforcing gussets on all legs through a single portion of the roof. g) Inspect the area around the roof legs for cra cking if there is no internal reinforcing pad or if the topside pad is not welded to the deck plate on the underside. h) Inspect the sealing system on the two-posi tion legs and the vapor plugs in the fixed low leg for deterioration of the gaskets.i) On shell-mounted roof supports, check for adequate clearance based on the maximum floating roof movement as determined by the position of the roof relative to the gauge well and/or counter-rotational device. C.2.9 Floating Roof Seal Assemblies C.2.9.1 Primary Shoe Assembly a) Remove four sections of foam log (foam-f illed seals) for inspection on 90° locations. b) Inspect hanger attachment to roof rim for thinning, bending, broken welds, and wear of pin holes. c) Inspect clips welded to roof rim for thinning. d) Shoes—inspect for thinning and holes in shoes. e) Inspect for bit-metal bolts, clips, and attachments. f) Seal fabric—inspect for deterioration, stiffening, holes, and tears in fabric. g) Measure length of fabric from top of shoe to roof rim, and check against maximum anticipated annular space as roof operates. h) Inspect any modification of shoes over s hell nozzles, mixers, etc., for clearance. i) Inspect shoes for damage caused by striking shell nozzles, mixers, etc. C.2.9.2 Primary Toroidal Assembly a) Inspect seal fabric for wear, deterioration, holes, and tears.T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION C-13

Tank Out-of-service Inspection Checklist (Continued)
Item Completed √ Comments b) Inspect hold-down system for buckling or bending. c) Inspect foam for liquid absorption and deterioration. C.2.9.3 Rim-mounted Secondaries a) Inspect the rim-mounted bolting bar for corrosion and broken welds. b) Measure and chart seal-to-shell gaps. c) Visually inspect seam fr om below, looking for holes as evidenced by light. d) Inspect fabric for deterioration and stiffness. e) Inspect for mechanical damage, corrosion, and wear on tip in contact with shell. f) Inspect for contact with obs tructions above top of shell. C.2.10 Floating Roof Appurtenances C.2.10.1 Roof Manways a) Inspect walls of manways for pitting and thinning. b) On tanks with interface autogauges, check seal around gauge tape cable and guide wires through manway cover. c) Inspect cover gasket and bolts. C.2.10.2 Rim Vent a) Check rim vent for pitting and holes. b) Check vent for condition of screen. c) On floating roof tanks where the environm ental rules require closing off the vent, check the vent pipe for corrosion at the pi pe-to-rim joint and check that the blinding is adequate. C.2.10.3 Vacuum Breaker, Breather Type a) Service and check operation of breather valve. b) Check that nozzle pipe projects no more than 1 / 2 in. below roof deck. C.2.10.4 Vacuum Breaker, Mechanical Type Inspect the stem for thinning. Measure how fa r the vacuum breaker cover is raised off the pipe when the roof is resting on high or low legs. a) On high legs: _________ . b) On low legs: _________ . C.2.10.5 Roof Drains: Open Systems, Including Emergency Drains a) Check liquid level inside open roof drains for adequate freeboard. Report if there is insufficient distance between liquid level and top of drain. b) If tank comes under Air Quality Monitoring District rules, inspect the roof drain vapor plug. c) If emergency drain is not at the center of the roof, check that there are at least three emergency drains. C.2.10.6 Closed Drain Systems: Drain Basins a) Inspect for thinning and pitting. b) Inspect protective coating (topside). c) Inspect basin cover or screen for corrosion. d) Test operation of check valve.C-14 API S TANDARD 653

Tank Out-of-service Inspection Checklist (Continued)
Item Completed √ Comments e) Check for presence of check valve wher e bottom of basin is below product level. f) Inspect drain basin(s) to roof deck welds for cracking. g) Check drain basin(s) outlet pipe for ade quate reinforcement to roof deck (including reinforcing pad). C.2.10.7 Closed Drain Systems: Fixed Drain Line on Tank Bottom a) Hammer test fixed drain line on tank bottom for thinning and scale/debris plugging. b) Inspect supports and reinforcing pads for weld failures and corrosion. c) Check that pipe is guided, not rigidly locked to support, to avoid tearing of tank bottom plate. C.2.10.8 Closed Drain Systems: Flexible Pipe Drain a) Inspect for damage to exterior of pipe. b) Check for obstructions that pipe could catch on. c) Inspect shields to protect pipe from snagging. d) Inspect results of hydrostatic te st on flexible roof drain system. C.2.10.9 Closed Drain Systems: Articulated Joint Drain a) Hammer test rigid pipe in flexible joint systems for thinning and scale/debris plugging. b) Inspect system for signs of bending or strain. c) Inspect results of system hydrostatic test. d) Inspect landing leg and pad. C.2.10.10 Autogauge System and Alarms a) Check freedom of movement of tape through autogauge tape guide. b) Inspect sheaves for freedom of movement. c) Test operation checker. d) Inspect tape and tape cable for twisting and fraying. e) Test the tape’s freedom of movement through guide sheaves and tape guide pipe. f) On open-top tanks, check that gate tapes with cables have no more than one foot of tape exposed with float at lowest point. g) Check float for leakage. h) Test float guide wire anchors for spring action by pulling on wire and releasing. i) Inspect floatwells in floating roofs for th inning and pitting of walls just above the liquid level. j) Check that the autogauge tape is firmly attached to the float. k) Inspect the tape cable and float guide wire fabric seals through the float well cover. l) Inspect the bottom guide wire attachment clip: inspect for a temporary weighted bar instead of a permanent welded down clip. m) Inspect board-type autogauge indicators for legibility and freedom of movement of indicator. n) Measure and record these distances to dete rmine if seal damage will occur if tank is run over from: 1) Shell top angle to underside of tape guide system. 2) Liquid level on floating top to top of secondary seal.T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION C-15

Tank Out-of-service Inspection Checklist (Continued)
Item Completed √ Comments o) Identify floating roofs where the tape is connected directly to the roof. p) Overfill alarm: Inspect t ank overfill prevention alarm switches for proper operation. C.2.11 Common Tank Appurtenances C.2.11.1 Gauge Well a) Inspect gate well pipe for thinning at about two-thirds distance above the bottom: look for thinning at the edge of the slots.b) Check for corrosion on the pipe joint. Check that sample cords, weights, thermometers, etc., have been removed from the pipe. c) Check for cone at bottom end of pipe about one foot above the bottom. d) Check condition of well washer pipe and that its flared end is directed at the near side of the hold off pad. e) Check that supports for gauge well are welded to pad or to shell and not directly to bottom plate. f) Check operation of gauge well cover. g) Check presence of a hold-off distance mark er in well pipe and record hold-off distance. Hold-off distance _________ . h) Identify and report size and pipe schedule, and whether pipe is solid or slotted. Report slot size. i) Check that the hold-off distance plate is seal-welded to the bottom and that any gauge well supports are welded to the plate and not directly to the bottom. j) Inspect vapor control float and cable. k) Check for presence and condition of gauge well washer. l) Check for bull plug or plate blind on gauge well washer valve. m) Inspect gauge well guide in float ing roof for pitting and thinning. n) Inspect the guide rollers and sliding plates for freedom of movement. o) Inspect condition of gauge well pipe seal system. p) On black oil and diesel services: if gauge we ll is also used for sampling, check for presence of a thief- and gauge-type hatch to avoid spillage. q) Visually inspect inside of pipe for pipe weld protrusions which could catch or damage vapor control float. C.2.11.2 Sampling Systems: Roof Sample Hatches a) Inspect roof-mounted sample hatches for reinforcing pads and cracking. b) Inspect cover for operation. c) For tanks complying with Ai r Quality Monitoring District rules, inspect sample hatch covers for adequate sealing. d) Check horizontal alignment of internal floating roof sample hatches under fixed roof hatches. e) Inspect the sealing system on the internal floating roof sample hatch cover. f) Inspect floating roof sample hatch cover recoil reel and rope. C.2.11.3 Shell Nozzles a) Inspect shell nozzles for thinning and pitting. b) Inspect hot tap nozzles for trimming of holes.C-16 API S TANDARD 653

Tank Out-of-service Inspection Checklist (Continued)
Item Completed √ Comments c) Identify type of shell nozzles. d) Identify and describe internal piping, including elbow-up and elbow-down types. C.2.11.4 For Nozzles Extended Into the Tank a) Inspect pipe support pads welded to tank bottom. b) Inspect to see that pipe is free to move along support without strain or tearing action on bottom plate. c) Inspect nozzle valves for packing leaks and damaged flange faces. d) Inspect heater stream nozzle fl anges and valves for wire cutting. e) Report which nozzles have thermal pressure relief bosses and valves. f) In internal elbow-down fill line nozzles, inspect the wear plate on the tank bottom. g) On elbow-up fill lines in floating roof tanks, check that openi ng is directed against underside of roof, not against vapor spac e. Inspect impact are for erosion. C.2.11.5 Diffusers and Air Rolling Systems a) Inspect diffuser pipe for erosion and thinning. b) Check holes in diffuser fo r excessive wear and enlargement. c) Inspect diffuser supports for damage and corrosion. d) Check that diffuser supports restrain , not anchor, longitudinal line movement. e) Inspect air spiders on bottom of lube oi l tanks for plugging and damaged or broken threaded joints. C.2.11.6 Swing Lines a) Inspect flexible joint for cracks and leaks. b) Scribe the flexible joint across the two moving faces and raise end of swing line to check the joint’s freedom of movement, indicated by separation of scribe marks. c) Check that flexible joints over 6 in. are supported. d) Inspect the swing pipe for deep pitting and weld corrosion. e) Loosen the vent plugs in the pontoons and listen for a vacuum. Lack of a vacuum indicates a leaking pontoon. f) Check the results of air test on pontoons during repairs. g) Inspect the pontoons for pitting. h) Inspect the pull-down cable connections to the swing. i) Inspect the condition of the bottom-mounted support, fixed roof limiting bumper, or shell-mounted limiting bumper for wood condi tion, weld and bolt corrosion, and seal welding to bottom or shell. j) Inspect safety hold-down chai n for corrosion and weak links. k) Check that there is a welded reinforcing pad where the chain connects to the bottom. l) If the floating swing in a floating or intern al floating roof tank does not have a limiting device preventing the swing from exceedi ng 60 degrees, measure and calculate the maximum angle possible with the roof on overflow. Max. angle on overflow _____________ . (If the calculated angle exceeds 65 degrees , recommended installation of a limiting bracket.) m) Inspect pull-down cable for fraying.T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION C-17

Tank Out-of-service Inspection Checklist (Continued)
Item Completed √ Comments n) Inspect for three cable clamps where cabl e attaches to end of swing line (singlereeved) or to roof assembly (double-r eeved). Inspect sheaves for freedom of movement. o.) Inspect winch operation and check the heigh t indicator for legibility and accuracy. p) Inspect bottom-mounted sheave assembly at end of pontoon for freedom of rotation of sheave. q) Inspect shell-mounted lower sheave assembly for freedom of rotation of sheave, corrosion thinning, and pitting of sheave housing. r) Inspect upper sheave assembly fo r freedom of movement of sheave. s) Inspect the cable counterbalance assemb ly for corrosion and freedom of operation. C.2.11.7 Manway Heater Racks a) Inspect the manway heater racks for br oken welds and bending of the sliding rails. b) Measure and record the length of the heater and length of the track. C.2.11.8 Mixer Wear Plates and Deflector Stands a) Inspect bottom and shell plates and deflector stands. b) Inspect for erosion and corrosion on the wear plates. Inspect for rigidity, structural soundness, corrosion, and erosion of deck plat es and reinforcing pads that are sealwelded to the bottom under the deflector stand legs. c) Measure for propeller clearance between the bottom of deflector stand and roof when the roof is on low legs. C.2.12 Access Structures C.2.12.1 Handrails a) Identify and report type (steel pipe, galvani zed pipe, square tube, angle) and size of handrails. b) Inspect for pitting and holes, paint failure. c) Inspect attachment welds. d) Identify cold joints and sharp edges . Inspect the handrails and midrails. e) Inspect safety drop bar (or safety chai n) for corrosion, functioning, and length. f) Inspect the handrail between the rolling ladder and the gaging platform for a hazardous opening when the floating roof is at its lowest level. C.2.12.2 Platform Frame a) Inspect frame for corrosion and paint failure. b) Inspect the attachment of frame to supports and supports to tank for corrosion and weld failure. c) Check reinforcing pads where suppor ts are attached to shell or roof. d) Inspect the surface that deck plate or grating rests on, for thinning and holes. e) Check that flat-surface-to-flat -surface junctures are seal-welded. C.2.12.3 Deck Plate and Grating a) Inspect deck plate for corros ion-caused thinning or holes (not drain holes) and paint failure. b) Inspect plate-to-frame weld for rust scale buildup. c) Inspect grating for corrosion-caused thinning of bars and failure of welds.C-18 API S TANDARD 653

Tank Out-of-service Inspection Checklist (Continued)
Item Completed √ Comments d) Check grating tie down clips. Where grat ing has been retrofitted to replace plate, measure the rise of the step below and above the grating surface and compare with other risers on the stairway. C.2.12.4 Stairway Stringers a) Inspect spiral stairway stringers for corros ion, paint failure, and weld failure. Inspect attachment of stairway treads to stringer. b) Inspect stairway supports to shell welds and reinforcing pads. c) Inspect steel support attachment to concrete base for corrosion. C.2.12.5 Rolling Ladder a) Inspect rolling ladder stringers for corrosion. b) Identify and inspect ladder fixed rungs (square bar, round bar, angles) for weld attachment to stringers and corrosion, particularly where angle rungs are welded to stringers. c) Check for wear and corrosion where rollin g ladder attaches to gaging platform. d) Inspect pivot bar for wear and secureness. e) Inspect operation of self -leveling stairway treads. f) Inspect for corrosion and wear on moving parts. g) Inspect rolling ladder wheels for freedom of movement, flat spots, and wear on axle. h) Inspect alignment of rolling ladder with roof rack. i) Inspect top surface of rolling ladder track fo r wear by wheels to assure at least 18 in. of unworn track (track long enough). j) Inspect rolling ladder track welds for corrosion. k) Inspect track supports on roof for rein forcing pads seal-welded to deck plate. l) Check by dimensioning, t he maximum angle of the rolling ladder when the roof is on low legs. Max. angle ____________ . m) If rolling ladder track extends to within 5 ft of the edge of the roof on the far side, check for a handrail on the top of the shell on that side. NOTESD-1 

## Annex D Authorized Inspector Certification D.1 Examination A written examination to certify an authorized inspector within the scope of API 653 shall be administered by a third party designated by API. The examination shall be based on the current API 653 body of knowledge as published by API. 

### D.2 Certification D.2.1 An API 653 authorized inspector certif icate will be issued when an applicant has successfully passed the API 653 certification examination, and satisf ies the criteria for education and exper ience. Education and experience, when combined, shall be equal to at least one of the following. a) A bachelor of science degree in engineering or technol ogy plus one year of exper ience in supervision or performance of inspection activi ties as described in API 653. b) A two-year degree or certificate in engineering or tec hnology, plus two years of experience in the design, construction, repair, inspection, or operation of aboveground storage tanks, of which one year must be in supervision or performance of inspection activities as described in API 653. c) A high school diploma or equivalent, plus three years of experience in the desi gn, construction, repair, inspection, or operation of aboveground storage tanks, of which one year must be in supervision or performance of inspection activities as des cribed in API 653. d) A minimum of five years of experienc e in the design, construction, repair, inspection, or operation of aboveground storage tanks, of which one year must be in supervision or performance of ins pection activities as described in API 653. D.2.2 An API certificate for an authoriz ed inspector is valid for three years from its date of issuance. D.2.3 An API 653 authorized inspector certificate is valid in a ll jurisdictions and any other location that accepts or other wise does not prohi bit the use of API 653. 

### D.3 Certification Agency API shall be the certifying agency. 

### D.4 Retroactivity The certification requirements of API 653 shall not be retroa ctive or interpreted as applying before 12 months after the date of publication of this edition or addendum of API 653. The recertification requirements of D.5 shall not be retroactive or interpreted as applying before three years af ter the date of publication of this edition or addendum of API 653. 

### D.5 Recertification D.5.1 Recertification is required three years from the date of issuance of the AP I 653 authorized inspector certificate. Recertification by writt en examination will be required for authoriz ed inspectors who have not been actively engaged as authorized inspectors within the most recent thr ee-year certification period. Recertification exams will be in accordance with all of the provisions contained in API 653.D-2 API S TANDARD 653
D.5.2 Actively engaged as an authorized in spector shall be defined as one of the following provisions: a) a minimum of 20 % of the time spent performing inspection activities, or s upervision of inspecti on activities, or engineering support of inspection activiti es as described in API 653 over the mo st recent three-year certification period; b) performance of inspection activities or supervision of inspection activiti es or engineering support of inspection activities on 75 aboveground storage tanks as described in API 653 over the most recent three-year certification period
NOTE Inspection activities common to other API inspection doc uments (NDE, record keeping, review of welding documents, etc.) may be considered here. D.5.3 Once every other recertification period (every six years) , inspectors actively engaged as an authorized inspector shall demonstrate knowledge of revisions to API 653 that were instituted during the previous six years. This requirement shall be effective six years from the inspector’s initial certification date. Inspectors who have not been actively engaged as an authorized inspector within the most recent three-year period shall recertify as required in D.5.1.E-1 

## Annex E (Intentionally Left Blank)F-1 

## Annex F NDE Requirements Summary F.1 Introduction This annex is a summary of all NDE requirements for repairs and reconstruction of tanks. It is provided only as a guide to assure that the proper examinations are pe rformed and that the acceptance standards, examiner qualifications, and procedure requirements are followed. 

### F.2 Visual Examination F.2.1 Visual examinations are required for: a) cavities from removal of repads (see API 653, 12.1.2.2); b) completed welds of stress-relieved assemblies after stress relief but before hydr ostatic testing (see API 653, 12.1.2.4); c) all fillet welds and completed repairs of fillet we lds (see API 650, Section 7.3.2.2 and API 653, 12.1.3.3); d) completed welds of new permanent attachments and ar eas of removed temporary attachments (see API 653, 12.1.4.2); e) new shell plate-to-shell plate welds (see API 653, 12.1.5); f) tack welds left in place (see API 650, Section 7.2.1.8); g) bottom plate and all welds, including the weld attaching a patch plate to the bottom, for new bottom plates (see API 653, 12.1.7.1); h) root and final weld pass of pa tch plate to bottom in the crit ical zone (see API 653, 12.1.7.2); i) areas of a bottom plate repaired by welding (see API 653, 12.1.7.3); j) areas of a shell plate to be repa ired by welding (see API 653, 12.1.8); k) cavities from removal of weld defects (see API 653, 12.1.3.1); l) annular plate butt-welds root pass and final pass [see API 653, 12.3.2.4.1 b)]; m)repaired areas of the shell-to-bottom weld (see API 653, 12.3.2.5.2). F.2.2 The examination acceptance st andard is API 650, Section 8.5. F.2.3 The examiner’s employer shall determine and certify that each visual examiner meets the requirements of API Standard 650, Section 8.5.1. 

### F.3 Magnetic Particle and Liqui d Penetrant Examination F.3.1 Magnetic particle or liquid penetr ant examinations are required for: a) cavities from removing existing reinfo rcing pad welds (see API 653, 12.1.2.2); 12F-2 API S TANDARD 653 b) new welds of nozzle neck-to-shell, nozzle neck-to -repad, and repad-to-shell (see API 653, 12.1.2.3); c) completed welds of stress-relieved assemblies after st ress relief, before hydrostatic testing (see API 653, 12.1.2.4); d) cavities from removal of weld defects (see API 653, 12.1.3.1); e) completed welds of new permanent attachments and areas of removed temporary attachments on API 650 material Groups IV, IVA, V, or VI (see API 653, 12.1.4.2); f) the back-gouged surface of the root pass and the final surfac e of new shell plate welds where the shell is thicker than 1 in. (see API 653, 12.1.5); g) existing shell-to-bottom welds that will be under a patc h plate, plus 6 in. on each side (see API 653, 12.1.6.3); h) root and final weld pass of pa tch plate to bottom in the crit ical zone (see API 653, 12.1.7.2); i) bottom plate restored by weld ing (see API 653, 12.1.7.3); j) areas of a shell plate repaired by welding (see API 653, 12.1.8); k) MT or PT repairs to the annular plate or bottom plates wi thin the critical zone after root and final pass [see API 653, 12.3.2.4.1 b)]. l) MT or PT repairs to the shell-to-bottom welds before and after root pass, and after final pass (see API 653, 12.3.2.5.2); m)the back-gouged surface of the root pass of full penetra tion nozzle neck-to-shell and repad welds as required by API 653, 12.3.2.3.6, spec ific hydrostatic test exemption requirement; n) the back-gouged surface of the root pass and final surface of new vertical and hor izontal shell joints as required by API 653, 12.3.2.3.5, spec ific hydrostatic test exemption requirement. F.3.2 Magnetic particle examination alone is required for weld removal areas of the bottom-to-shell welds when removing a bottom [see API 653, 9.10.2.2 b)]. F.3.3 The magnetic particle examination acceptance standard is ASME Section V, Ar ticle 7. The acceptance standards for the removal and repair of defects shall be in accordance with ASME Section VI II, Annex 6, Paragraphs 6-3, 6-4, and 6-5. F.3.4 The liquid penetrant examination a cceptance standards is ASME Sectio n V, Article 6. The acceptance standards for the removal and repair of defects shall be in accordance with ASME Section VIII, Appendix 8, Paragraphs 8-3, 8-4, and 8-5. F.3.5 The requirements for examiner qualifications shall foll ow API 650, Section 8.2.3, requiring an examiner with adequate vision and competent in the examination, interpretation, and evaluation of results. F.3.6 Procedure requirements shall follow ASME Section V. 

### F.4 Ultrasonic Examination F.4.1 Ultrasonic examinations are required for: a) shell areas over which lap patch plates are to be welded (see API 653, 9.3.1.9); 13T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION F-3 b) shell areas over which new reinforcing or hot t ap nozzles are to be welded (see API 653, 12.1.2.1); c) completed repairs of butt-welds unl ess radiographed (see API 653, 12.1.3.2); d) the full penetration nozzle neck-to-shell and repad welds as required by API 653, 12.3.2. 3.6, specific hydrostatic test exemption requirement; e) repairs to annular plate butt-welds afte r final pass [see API 653, 12.3.2.4.1 b)]. F.4.2 The ultrasonic examination accept ance standard shall be agreed upon by t he owner/operator and contractor (see API 650, Section 8.3.2.5). F.4.3 The requirements for examiner qualificat ions shall follow ASNT Level II or III, according to ASNT SNT-TC-1A. Level I personnel may be used if they are gi ven written acceptance/rejection criteria prepared by Level II or Level III personnel, and are under the di rect supervision of Level II or Level III personnel. F.4.4 Procedure requirements shall follow ASME Section V. 

### F.5 Vacuum Box Testing F.5.1 Vacuum box testing is required for: a) new shell-to-bottom welds, unless diesel tested (see API 653, 12.1.6); b) new bottom welds, unless tracer gas tested (see API 653, 12.1.7); c) new roof plate welds for tanks designed to be gas tight (see API 650, Section 7.3.7); d) potential bottom plate leak paths, (see API 653, 12.1.7.1); e) patch plates welded on to the bottom, (see API 653, 12.1.7.1 and 12.1.7.2); f) bottom plate restored by weld ing (see API 653, 12.1.7.3). F.5.2 The requirements for examiner qualifications shall foll ow API 650, Section 8.6.4, requiring an examiner with adequate vision and competence in the examination met hod, interpretation, and evaluation of results. F.5.3 Procedure requirements shall follow API 650, Section 8.6 (3 lbf/in. 2 gauge minimum). 

### F.6 Tracer Gas Testing F.6.1 Tracer gas testing is required for new bottom we lds, unless vacuum box te sted (see API 653, 12.1.7). F.6.2 There are no requirements for examiner qualifications. F.6.3 Test must be performed to a procedure that has been reviewed and approved by the tank owner/operator.F-4 API S TANDARD 653 

### F.7 Diesel Oil Test F.7.1 Diesel oil testing is required for: a) the first pass of new shell-to-bottom welds and the final new shell-to-bottom weld, unless the final weld is vacuum box tested (see API 653, 12.1.6); b) floating roof deck seams and other joints required to be li quid tight or vapor tight (s ee API 650, Section H.6.2 and Section C.4.2). F.7.2 There are no requirements for examiner qualifications. F.7.3 There are no procedure requirements. 

### F.8 Air Leak Testing F.8.1 Air leak testing is required for: a) repad-to-shell, repad-to-nozzle, and nozzle-to-shell weld s of new or altered shell nozzles (see API 653, 12.4); b) initial pass of the shell-to-bottom welds and inside and outside of the shell, if the weld is not tested by vacuum box or diesel oil (see API 653, 12.1.6.2). F.8.2 There are no requirements for examiner qualifications. F.8.3 Procedure requirements shall follow API 650, Section 7.3.5. 

### F.9 Radiographic Examination F.9.1 Radiographic examinations are required for: a) insert plates for installing penetration butt-weld s shall be fully radiographed (see API 653, 12.2.1.8); b) repairs to butt welds, unless ultras onically examined (see API 653, 12.1.3.2); c) vertical and horizontal joints and juncti ons of new shell plates welded to new shell plates and new plates welded to existing plates (see API 653, 12.2) This section covers shell r eplacement plates and door sheets; d) tank shell butt welds on reconstr ucted tanks (see API 653, 12.2.1.5); e) new annular plate joints (see API 650, Section 8.1.2.9); f) new and replaced shell insert plate and door sheet welds (see API 653, 12.2.1.6); g) vertical and horizontal shell joints as required by AP I 653, 12.3.2.3.5, specific hydrostatic test exemption requirement. F.9.2 The examination acceptance standard is ASME Section VIII, Paragraph UW-51(b). F.9.3 The requirements for examiner qualificat ions shall follow ASNT Level II or III, according to ASNT SNT-TC-1A. Level I personnel may be used if they are gi ven written acceptance/rejection criteria prepared by Level II or Level III personnel. These procedures must contain the applicable requi rements of ASME Section V, Article 2. All Level I personnel must be under the di rect supervision of Level II or Level III personnel. F.9.4 Procedure requirements shall follow ASME Section V, Article 2. 12G-1 

## Annex G Qualification of Tank Bottom Examination Pr ocedures and Personnel G.1 Introduction G.1.1 This annex provides guidance for qualifying both tank bottom examination procedures and individuals that perform tank bottom examinations. Owner/operators may elect to either apply this annex as written or modify it to meet their own applications and needs. Tank bottom examinations are an important factor in providing the owner/operator increased assurance of tank integrity. As a result, it is important that qualified examination procedures and personnel are used in these examinations. Specific agreements and requirements for qualification of tank bottom examination procedures and tank bottom examiners should be established between the owner/operator and the authorized inspection agency. G.1.2 There have been many NDE tools devel oped for examining tank bottoms. Most of these tools are complex and require the operator to have a high level of knowledge an d skill. The effectiveness of these examinations may vary greatly depending on the equipment used, the exami nation procedure, and the skill of the examiner. Often the owner/operator will not have the ability to easily determine if the tank bottom examination has been effective in assessing the actual condition of t he tank bottom. The requirements in this annex will provide the owner/operator additional assurance that the tank bottom examination wi ll find significant metal loss. 

### G.2 Definitions G.2.1 authorized inspection agency Organizations that employ an aboveground storage tank inspector certified by API (see 3.3). G.2.2 bottom scan The use of equipment over large portions of the tank bot tom to detect corrosion in a tank bottom. One common type of bottom-scanning equipment is the magnetic flux leakage (MFL) scanner. G.2.3 essential variables Variables in the procedure that cannot be changed wit hout the procedure and scanning operators being re-qualified. G.2.4 examiners Scanning operators and NDE technicians who prove-up bottom indications. G.2.5 non-essential variables Variables in the procedure that can be changed without hav ing to re-qualify the procedure and/or scanning operators. G.2.6 qualification test The demonstration test that is used to prove that a proc edure or examiner can successfully find and prove-up tank bottom metal loss. 13G-2 API S TANDARD 653
G.2.7 scanning operator operator The individual that operat es bottom-scanning equipment. G.2.8 sizing prove-up The activity that is used to accurately determine the remaining botto m thickness in areas where indications are found by the bottom scanning equipment. This is often accomplished using the UT method. G.2.9 tank bottom examination The examination of a tank bottom using special equipment to determine the remaini ng thickness of the tank bottom. It includes both the detection and pr ove-up of the indicati ons. It does not include the visual examination that is included in the internal inspection. G.2.10 tank bottom examination procedure TBP A qualified written procedure that addresses the essent ial and non-essential variables for the tank bottom examination. The procedure can in clude multiple methods and tools, i.e. bottom scanner, hand scanner, and UT prove-up. G.2.11 tank bottom examiner qualification record TBEQ A record of the qualification test for a specific scanning operator. This record must contain the data for all essential variables and the results of the qualification test. G.2.12 tank bottom procedure qualification record TBPQ A record of the qualification test for a tank bottom examinat ion procedure. This record must contain the data for all essential variables and the resu lts of the qualification test. G.2.13 variables or procedure variables The specific data in a procedure that provides directi on and limitations to the scanni ng operator. Examples include: plate thickness, overlap of adjacent botto m scans, scanning speed, equipment settings, etc. 

### G.3 Tank Bottom Examination Procedures G.3.1 Each authorized inspection agency performing tank bottom examinations is responsible to have and use TBPs. These procedures provi de direction for examiners performing tank bottom examinations. A procedure also allows the owner/operator or authorized inspector to ve rify whether the examiners are correctly performing the examinations. G.3.2 The authorized inspection agency that performs the tank bottom examinations should develop the TBPs. G.3.3 Each TBP shall address essential and non-essential variables. Section G.5.4 provides guidance for determining appropriate TBP essential and non-essential variables. Each procedure should specify limits on appropriate variables, e.g. plate thickness range.T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION G-3 

### G.4 Tank Bottom Examiners G.4.1 Examiners need only to be qualified for the work they do in the field. For example, scanning operators who only use the bottom scanning equipment and do not prove-up the flaw with a follow-up method need only to be qualified for the scanning operation. G.4.2 The purpose of qualifying the tank bottom examiner is to det ermine if the examiner is capable of satisfactorily using a qualified procedure to determine the condition of the tank bottom. G.4.3 Each authorized inspection agency is responsible to train, test and qualif y the scanning operators and examiners they employ using foll ow-up techniques. Qualif ications gained through one authorized inspection agency are not necessarily valid for any other aut horized inspection agency [see G.4.4 and G.4.9 f)]. G.4.4 The authorized inspection agency is responsible for training each scanning operator they employ. Each scanning operator should receive a minimum of 40 ho urs of training. This training should include: a) instruction on the NDE principles/m ethods used by the bottom scanner, limita tions and application of the specific scanning equipment and procedure, scanning equipment calibration and operation, key scanning equipment operating variables, etc.; b) hands-on operation of the bottom scanner under the direct supervision of a qualified scanning examiner. When hiring experienced examiners, the authorized inspection agency shoul d verify and document previous examiner training and provide any add itional training if necessary. Exper ienced examiners should be provided training regarding specific procedural requirements and test equipment to be utilized by the new employer. G.4.5 The authorized inspection agency is responsible for te sting each scanning operator by written examination. The test questions should be appropriate for the scanni ng method to be used. The authorized inspection agency should establish the passing scor e for the written examination. G.4.6 The authorized inspection agency is re sponsible for qualifying all exami ners they employ. All examiners (scanning operators and examiners performing prove-up on t he indications) shall be qualified by performing an examination on test plates as s pecified in G.5. Only third-party companies, having no conflict of interest in tank bottom examination applications, or owner/operator companies may facilitate qua lification tests. The examiner shall be considered qualified if the acceptance cr iteria specified in G.5.3 has been met. Examiners performing prove-up of indi cations using ultrasonic testing methods should be qualified in accordance with API 650, Section 8.3.2 and supplemental requirements given in this annex. G.4.7 During the qualification test, a TBEQ must be completed for each examiner. The TBEQ is a record of the variables used during the qualification test. On the TBEQ, the qualifying company must record: a) the essential variables from the qualification test; b) the qualification test results; c) number of hours the individual has been trained; d) test score from the written training examination. The TBEQ shall be certified (signed) as accurate by a representative of the authorized inspection agency and a representative of the company facilitating the test. G.4.8 The TBEQ may be written in any format that contains all the required information. 12G-4 API S TANDARD 653
G.4.9 The bottom-scanning examiners (operators and/or UT ex aminers) should be re- qualified when any of the following apply: a) when the examiner is not qualified to the TBP t hat is to be used at the owner/operator facility; b) when the authorized inspection agenc y changes the TBP and that change requires the procedure to be requalified; c) when the operator has not performed a tank bottom scan in six months; d) when the operator has not used the spec ific procedure (TBP) for 12 months; e) when the authorized inspection agency has reason to question the ability of the examiner; f) when an examiner changes to a new employing authorized inspection agency that uses procedures with essential variables that are different from t he previous employer’s procedures. 

### G.5 Qualification Testing G.5.1 Qualification Test Plates G.5.1.1 The qualification test will be performed on a sample tank bottom with designed flaws. The sample tank bottom should be a minimum of 70 ft 2 to provide space for the designed flaws. T he plate material used to fabricate sample plates may be either new steel or used steel. It should be noted that the results obtained during qualification tests might not be indicative of the results of examinations performed on ot her plates of differing quality or permeability. When used steel is utilized for qualification purposes, the qualificati on test acceptance standards recommended in G.5.2 may not be appropriate. The owner/operator should establish its own acceptance standards in such cases. G.5.1.2 The minimum number and types of underside test pits located on the test plates are described below:

where
T is nominal bottom thickness;

t is the remaining bottom thickness at test plate flaws.
NOTE Test pits should generally be hemispherical having a depth-to- diameter ratio of from 20 % to 50 %. Test pits should not be flat bottom holes since examiners may interpret these as a lamination. Also, machined conical holes should not be used since they are difficult to size with UT methods. The owner/operator may consider placi ng additional flaws near the pl ate edge, i.e. less than 6 in. from the edge, to determine if such flaws can be detected by authorized inspection agency procedures. An y flaws placed closer than 6 in. to the plate edge should be in addition to thos e shown above and should not be included in determining qualification unless specifica lly required by an owner/operator and such defects are stated as being detectable in authorized inspection agency procedures. Remaining Bottom Thickness ( t ) (in.) Minimum Number of Pits

t < 0.050 2 0.050 < t < 1 / 2 T 5
1 / 2 T < t < 2 / 3 T 4T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION G-5
G.5.1.3 The minimum number and types of product side test pi ts located on the test plates are described below.

G.5.1.4 There should also be at least one area representing gener al soilside corrosion. This area should be at least 10 in. 2 (64.52 cm 2 ) and have a remaining bottom thickness of about 1 / 2 T (nominal plate thickness). 

### G.5.2 Qualification Test Acceptance Standards G.5.2.1 The following acceptance criteria must be met w hen qualifying either an examination procedure or an examiner. If all the acceptance criteria are met, the pr ocedure or examiner shall be considered qualified. Owner/ operators may substitute alternative acc eptance criteria, either more or less conservative, based on their specific needs and requirements. G.5.2.2 When qualifying either a proc edure or a scanning operator, the operator must be able to detect the following flaws.

G.5.2.3 When qualifying either a procedure or an examiner, who proves up the indications , the examiner must be able to determine the flaw depth as follows:

The owner/operator should determine if additional flaw dimensions must be addressed in the qualification process. Remaining Bottom Thickness ( t ) (in.) Minimum Number of Pits
0.050 < t < 1 / 2 T 2
1 / 2 T < t < 2 / 3 T 2

Remaining Bottom Thickness ( t ) (in.) Flaws That Must be Found

t < 0.050 90 % to 100 %
0.050 in. < t < 1 / 2 T 70 % to 90 %

1 / 2 T < t < 2 / 3 T 40 % to 60 % Area of general corrosion 100 %

Type of Tank Bottom Prove-up (Flaw Depth)
Not coated ±0.020 in. Thin coating < 0.030 in. ±0.030 in.
Thick coating > 0.030 in. Per agreement with owner/operatorG-6 API S TANDARD 653
G.5.2.4 While false calls, also referred to as over-calls, t end to be more of an examination efficiency issue than a tank bottom integrity issue, the ow ner/operator should determine if they should be addressed in the qualification process. 

### G.5.3 Qualification Test Variables G.5.3.1 Essential variables are those items th at may have a significant effect on t he quality of the exam ination if they are changed from those used during the qualification test.

G.5.3.2 Table G.1 lists suggested items that may be considered as essential variables for the qualificati on test when qualifying either a tank bottom examination procedure or a ta nk bottom examiner. Essential variables may be different for different types of tank bottom scanners. Authorized inspection agencies are responsible for determining what additional variables should be c onsidered essential variables for each tank bottom scanner. G.5.3.3 Essential variables and the values must be recorded on the TBP and on the TBEQ. G.5.3.4 Non-essential variables are those item s that will have a lesser affect on the quality of the examination. Nonessential variables may be different for different types of tank bottom scanners. G.5.3.5 Non-essential variables must be listed on the TBP but need not be addr essed on the TBPQ or the TBEQ. The following is a list of examples of items that might be considered as non-essential variables. Equipment Table G.1—Suggested Essential Variables for Qualification Tests Essential Variable Used During Test Qualified Scanner Equipment As tested Same as tested Prove-up Equipment As tested Same as tested Prove-up Procedure As tested Same as tested Plate Thickness ( T ) T T +0.005 in. – T –0.130 in. Coating Thickness ( t c ) No coating used 0.000 in.
0.001 in. < t c < 0.030 in. 0.001 in. to 0.030 in.
0.031 in. < t c < 0.080 in. 0.031 in. to 0.080 in.

t c > 0.080 0.081 in. to t c Distance from Shell ( d s ) d s Lesser of 8 in. or d s Critical Equipment Settings As tested Per manufacturer Threshold Settings ( T h ) T h < 10 % T h Calibration or Functional Check As tested Same as tested 13T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION G-7 manufacturers and authorized inspection agencies are res ponsible to determine what addition factors should be considered non-essential variabl es for each tank bottom scanner: a) scanner speed; b) scanning pattern; c) height limitations; d) overlap between scans; e) plate cleanliness; f) non-critical equipment settings.
NOTE Some of the listed non-essential va riables may actually be essential vari ables for specific types of scanners.H-1 

## Annex H Similar Service Assessment This annex is provided as guidance for per forming a similar service assessment. Th is annex is not al l inclusive and is not mandatory. It is not intended to prev ent the use of other similar service as sessment methods. This annex contains sample datasheets illustrating items that should be c onsidered when conducting a similar service assessment. The datasheet format facilitates the recording of assessment findings.
NOTE 1 The following examples are merely exam ples for illustration purposes only. Each company should develop its own approach. They are not to be considered ex clusive or exhaustive in nature. API make s no warranties, express or implied for reliance on or any omissions from the in formation contained in this document. NOTE 2 Where applicable, authorities hav ing jurisdiction should be consulted.H-2 API S TANDARD 653 

### H.1 Scope This annex provides guidance for conducting a similar service assessment to establish inspection intervals for tanks for which corrosion rates have not been directly measured as referenced in 6.3.2 and 6.4.2. This annex is intended for use by an authorized inspector, storage tank engineer and other person(s) having knowledge and experience in performing similar service assessments. 

### H.2 Similar Service Assessment Several criteria must be evaluated to determine whether the candidate tank is in similar service with the control tank. Similar service assessment requires a sufficient amount of data collection and analysis and needs to be performed in a comprehensive and thorough fashion in accordance with an established risk management program. Similar service assessment is conducted using design, construction, oper ation, maintenance and inspection data. Data should be obtained by using direct and indirect examination procedur es such as MT and UT, evaluating product corrosivity, measuring CP levels, determining soil properties, and othe r factors. Refer to the “Similar Service Assessment— Datasheet,” which provides a place to record the required data. Data should be collected for each of the tank characteristics listed on the datasheet for both the control tank and candidate tanks and an assessment made to determine if the services are similar. Typically, there will not be an exact match of all data, or some of the required data will not even be known. When there is not an exact ma tch between one or more criteria, additional evaluation is necessary to determine whether the tanks can be considered to be in similar service. Figure H.1 illustrates the steps in conducting a similar service assessment. The “Similar Serv ice Assessment—Datasheet” is to facilitate the comparison of data for the two tanks. If the criteria for the control tank and candidate tank match, the candidate tank may be considered in similar service as the control tank for that particular criterion. 

### H.2.1 Additional Assessment When additional assessment is required because an individual basic criterion does not match, the table references the section describing additional factors that must be assessed. If the additional factors in the specified reference section are assessed to be sufficiently si milar, the tanks are considered in simila r service for that factor. If all additional provisions are satisfied, the tanks are considered in si milar service. Additional as sessment(s) must be documented and maintained in the record file as per 6.8. H.2.1.1 Year Tank Erected : If the criteria for the control tank and candidate tank do not match, the following additional provisions must be satisfied to consider both tanks in similar service: a) the difference in ages of the tanks must be c onsidered in the corrosion rate calculations, and b) any substantive differences in the design and/or construction standards to wh ich the tanks were constructed must be considered in the si milar service evaluation. H.2.1.2 Bottom Material : If the criteria for the control tank and candi date tank do not match, the following additional provisions must be satisfied to c onsider both tanks in similar service: a) the bottom material of the candidate tank must have sim ilar corrosion-resistance properti es as the bottom material of the control tank, b) the candidate tank, or both th e candidate and the control tanks, utilize an effective lining to prevent corrosion of the product-side of the bottom, and c) the potential for corrosion of the soil-side of the botto m is assessed to be similar fo r both tank bottom materials.T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION H-3
H.2.1.3 Shell Material : If the criteria for the control tank and candidate tank do not match, the following additional provisions must be satisfied to consider both tanks in similar service: a) the shell material of the candidate tank must have similar corrosion-resistanc e properties as the shell material of the control tank, b) the candidate tank, or both the candidate and the control t anks, utilize a suitable lining to prevent corrosion of the product-side of the shell, and c) the candidate tank, or both the candidate and the control tanks, utilize a suitable paint or coating to prevent corrosion of the exter nal side of the shell. H.2.1.4 Corrosion Allowance, Bottom/Shell : If the criteria for the control t ank and candidate tank do not match, the difference in corrosion allowance should be accounted for in the remaining life and inspection interval calculations to consider both tanks in similar service. H.2.1.5 Bottom Lining Type/Thickness/Age : If the criteria for the control tank and candidate tank do not match, the differences in the bottom lining systems must be assessed. The provisions of API 652 should be used to assess the relative corrosion protection provid ed by the different lining systems. H.2.1.6 Cathodic Protection : If the criteria for the control tank and candidate tank do not match, the following additional provisions shall apply. The prov isions of API 651 should be used to assess the relative corrosion protection provided by the cathod ic protection systems: a) if the candidate tank is protected with a properly designed and functional cathodi c protection system, and the control tank is not, the candidate t ank may be considered to be in simila r service with respect to cathodic protection; b) if the control tank is protected with a properly designed and functional cathodi c protection system, and the candidate tank is not, the candidate tank may not be considered to be in similar service with respect to cathodic protection; c) if the control tank and the candidate tank are protec ted with properly designed and functional cathodic protection systems, the tanks may be considered to be in si milar service with respect to cathodic protection. H.2.1.7 Double Bottom : If the candidate tank and/or the control tank has multiple bottoms, the similar service assessment of soil-side corro sion should be based on the materi al that is in contact with the underside of the primary (upper) bottom plate H.2.1.8 Soil/Material in Contact with Bottom Plate : Any differences in the following factors between the control and the candidate tank must be assessed in determining whether the cand idate tank is in similar service as the control tank: a) soil or material type; b) pH; c) alkalinity; d) moisture; e) salinity; f) resistivity;H-4 API S TANDARD 653 g) oil type (if oiled sand foundation); h) soil/material cleanliness; i) soil gradation; j) chlorides; k) sulfates. H.2.1.9 Ambient Conditions : Any differences in the following factor s between the control tank and the candidate tank must be assessed in determining whether the candidate tank is in si milar service as the control tank: a) low one day mean temperature; b) exposure to salt air or other corrosive elements. H.2.1.10 Current Service Conditions : Any differences in the following fa ctors between the control tank and the candidate tank must be assessed in dete rmining whether the candidate tank is in similar serv ice as the control tank: a) product classification (see Table H.1); b) specific gravity of liquid; c) Reid vapor pressure at 60 ° F; d) normal operating temperature; e) inert gas blanket, if used; f) water bottom, if used; g) sulfur content; h) length of time in service; i) product corrosivity. H.2.1.11 Previous Service Conditions : If the control tank and/or candidate tank have previously been used for different services than the current service, the same factors described in H.2.1.10 should be evaluated for the previous service conditions. H.2.1.12 Product Classification : Table H.1 classifies a wide variety of liquids commonly stored in aboveground storage tanks. This table serves as guidance in a ssessing current or previ ous service conditions. H.2.1.13 Additional Considerations : In addition to the factors discussed above, the following data, if available for the control tank and the candidate tank, should be assessed in determining whether the candidate tank is in similar service as the control tank: a) MFL data for the tank bottom; b) ultrasonic thickness (UT) measurement data; c) fiber optic monitoring system data;T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION H-5 d) cathodic protection monitoring tube data; e) tank bottom integrity testing data; f) maintenance procedures, including fr equency and methods of tank cleaning. 

### H.3 Example of Remaining Life Determination H.3.1 Tank Bottom Figure H.2 illustrates one method of dete rmining the time interval in which a tank bottom will reach its minimum bottom plate thickness, beyond which t he tank should be repaired or removed from service. In this example, the original metal thickness was 1 / 4 in. when the tank was constructed in 1970. The minimum bottom plate thickness at the next inspection interval was 0.05 in. (See also Table 4.4. ) At the time of this evaluation (June 10, 1990), the tank was in sour crude service. Previous service included 20 years in sour crude se rvice. Based on thicknesses measured and the calculated corrosion rate, the remaining life, or ti me to reach the minimum bottom plate thickness of 0.050 in. is projected to be approximately 20 years, or June 10, 2010. See 4.4.5 for the minimum thickness calculation for a tank bottom. 

### H.3.2 Tank Shell Figure H.3 illustrates one method of dete rmining the time interval in which a ta nk shell course will reach its limit of metal loss, beyond which the tank should be repaired or re moved from service. In this example, the original metal thickness was 1 / 2 in. when the tank was constructed in 1990. The limit of metal loss of the top shell course was calculated to be 1 / 4 in. At the time of this evaluation (November 15 , 2002), the tank was in sweet gasoline service. Previous services included nearly seven years in sweet cr ude and nearly three years in sour crude service. Based on thicknesses measured at periodic inspections and corrosion rates calculated from them, the remaining life, or time to reach the metal loss limit of 1 / 4 in. is projected to be approximately four years, or August 1, 2006. See 4.3.3 for the minimum thickness calculation for an entire shell course.

Table H.1—Similar Service Product Classification Class Description Example

A Low sulfur light oil (< 1 % sulfur) No. 2 fuel oil, diesel, kerosene, jet fuel, gasoline B High sulfur light oil (> 1 % sulfur) Unfinished heating oil, distillate C Sweet sulfur heavy oil (< 1 % sulfur) Heavy gas oil and sweet residual D Sour sulfur heavy oil (> 1 % sulfur) Sour residual E Slop and process water See description F Finished lube oil Automotive, diesel and aviation oil G Sludge Acidic, non-acidic

H Crude oils Light volatile oil (Class 1) Non-sticky oil (Class 2) Heavy sticky oil (Class 3) Non-fluid (heavy crude, high paraffin) (Class 4) I Additive Gasoline performance additives J Solvent Ketones, alcohol, toluene, xyle ne, glycols, glycol ethers K Chemicals Phosphoric, sulfuric, hydrochl oric, formic, and nitric acids NOTE This table is not all inclusive. Additionally, there may be significant variability in the chemical composition of products within a listed classification.H-6 API S TANDARD 653

Figure H.1—Steps in Conducting Similar Service Assessment Collect Tank Data for the Control Tank and the Candidate Tank

Collect Similar Service Assessment Using the Datasheet

Determine if Similar Service Can be Applied to the Candidate Tank

Determine the Corrosion

Rates to Apply to the

Candidate Tank

Establish the Next Internal Inspection Date for the Candidate Tank

Document the Revised Internal Inspection Date for the Candidate Tank

As Additional Inspection Data Becomes Available, Validate the Corrosion Rate Established for Candidate Tank Determine if the Additional Inspection Data Changes the Inspection Schedule for the Candidate TankT ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION H-7

Figure H.2—Example Corrosion Rate Curves for Bottom of Storage Tank 2010 3/16 7/32 0 1/32 1/16 3/32 1970

2000 1/8 5/32 METAL THICKNESS, IN INCHES
1/4

1980

1990Min. Bottom Plate Thickness at Next Inspection (See Table 4.4) Tank New January 21, 1970YEAR First Internal Inspection June 10, 1990 S

o u r C

r u d

e

S o u r C

r u d

e

Extended Corrosion Curve

Limit of metal loss June 10, 2010 Tank Bottom Repaired to 1/4-in. 1/16H-8 API S TANDARD 653

Figure H.3—Example Corrosion Rate Curves for Top Course of Storage Tank 2010 3/8 7/16 0 1/16 1/8 3/16 1990

2005 1/4 5/16 METAL THICKNESS, IN INCHES
1/2

1995

2000Limit of thickness for top course

Limit of metal loss August 1, 2006 Fourth Inspection November 15, 2002 Third Inspection July 20, 1999 - Service Changed Second Inspection December 2, 1996 - Service Changed First Inspection June 10, 1992

Extended Corrosion Curve Tank New Januar y 21, 1990YEAR S o u r C

r u d e S w ee t C

r ud

e

G a so li n eT ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION H-9

: N O I T A C O L : D I K N A T L O R T N O C S L B B : Y T I C A P A C : ) T F ( T H G I E H : ) T F ( R E T E M A I D

: N O I T A C O L : D I K N A T E T A D I D N A C S L B B : Y T I C A P A C : ) T F ( T H G I E H : ) T F ( R E T E M A I D SECTION 1—TANK BOTTOM (PRODUCT-SIDE) ASSESSMENT H.1.1 TANK CHARACTERISTICS a) YEAR TANK ERECTED b) BOTTOM MATERIAL c) CORROSION ALLOWANCE d) BOTTOM LINING TYPE e) BOTTOM LINING THICKNESS f) BOTTOM LINING AGE H.1.2 CURRENT SERVICE CONDITIONS a) CURRENT PRODUCT NAME b) PRODUCT CLASS. (TABLE H.1) c) SPECIFIC GRAVITY OF PRODUCT d) NORMAL OPERATING TEMP. e) WATER BOTTOM? f) SULFUR CONTENT g) TIME IN THIS SERVICE h) PRODUCT CORROSIVITY H.1.3 PREVIOUS SERVICE CONDITIONS a) PREVIOUS PRODUCT NAME b) PRODUCT CLASS. (TABLE H.1) c) SPECIFIC GRAVITY OF PRODUCT d) NORMAL OPERATING TEMP. e) WATER BOTTOM? f) SULFUR CONTENT g) TIME IN THIS SERVICE h) PRODUCT CORROSIVITY H.1.4 CONCLUSIONS a) Does this assessment include additional assessment documentation (see H.2.1), YES or NO b) Based on the criteria reviewed in this similar service evaluation, similar service is OR is NOT recommended for this tank (check appropriate box) c) The corrosion rate to be applied to the product side of the tank bottom is: ___________mpy.
COMMENTS:

NOTE THE DATASHEET SHALL BE MAINTAINED IN THE RECORD FILE AS PER 6.8.

: E T A D : Y B D E S S E S S A

: E T A D : Y B D E V O R P P A

NOTE 1 The control tank is the tank for which service conditions and corrosion rates are well known. NOTE 2 The candidate tank is the tank to be compared to the control tank to determine if similar service concepts apply. NOTE 3 “Y” or “Yes” indicates that the candidate tank criterion essentially matches the control tank . NOTE 4 If the candidate tank criterion does not match the control tank criterion, see H.2.1. (tank owner/operator) H.2.1.5 MATCH 3 Yes No Control Tank 1 MATCH 3 No Control Tank 1 Candidate Tank 2 Yes

Candidate Tank 2

Control Tank 1 MATCH 3 Yes No Candidate Tank 2 H.2.1.10 IF NO,

H.2.1.10 H.2.1.10

H.2.1.10 H.2.1.10 H.2.1.10 H.2.1.10 H.2.1.10

H.2.1.10 SEE SEC. 4

IF NO, SIMILAR SERVICE ASSESSMENT—DATASHEET

SEE SEC. 4 SEE SEC. 4

IF NO,

H.2.1.5 H.2.1.1 H.2.1.2 H.2.1.4
H.2.1.5

H.2.1.10 H.2.1.10 H.2.1.10 H.2.1.10 H.2.1.10 H.2.1.10 H.2.1.10H-10 API S TANDARD 653

: N O I T A C O L : D I K N A T L O R T N O C S L B B : Y T I C A P A C : ) T F ( T H G I E H : ) T F ( R E T E M A I D

: N O I T A C O L : D I K N A T E T A D I D N A C S L B B : Y T I C A P A C : ) T F ( T H G I E H : ) T F ( R E T E M A I D SECTION 2—TANK BOTTOM (SOIL-SIDE) ASSESSMENT
H.2.1 TANK CHARACTERISTICS a) YEAR TANK ERECTED b) BOTTOM MATERIAL c) CORROSION ALLOWANCE d) DOUBLE BOTTOM H.2.2 SOIL/MATERIAL IN CONTACT WITH OR AROUND BOTTOM PLAT E 5 a) SOIL TYPE b) SOIL pH c) SOIL ALKALINITY d) SOIL MOISTURE e) SOIL SALINITY f) SOIL CONDUCTIVITY g) OIL TYPE (IF OIL SAND FOUNDATION) h) SOIL CLEANLINESS H.2.3 CURRENT OPERATING CONDITIONS a) NORMAL OPERATING TEMP. b) CATHODIC PROTECTION 5 c) PONDING/WATER H.2.4 PREVIOUS OPERATING CONDITIONS a) NORMAL OPERATING TEMP. b) CATHODIC PROTECTION 5 c) PONDING/WATER H.2.5 CONCLUSIONS a) Does this assessment include additional assessment documentation (see H.2.1), YES or NO b) Based on the criteria reviewed in this similar service evaluation, similar service is OR is NOT recommended for this tank (check appropriate box) c) The corrosion rate to be applied to the soil side of the tank bottom is: ___________mpy.
COMMENTS:

NOTE THE DATASHEET SHALL BE MAINTAINED IN THE RECORD FILE AS PER 6.8.

: E T A D : Y B D E S S E S S A

: E T A D : Y B D E V O R P P A

NOTE 1 The control tank is the tank for which service conditions and corrosion rates are well known. NOTE 2 The candidate tank is the tank to be compared to the control tank to determine if similar service concepts apply. NOTE 3 “Y” or “Yes” indicates that the candidate tank criterion essentially matches the control tank . NOTE 4 If the candidate tank criterion does not match the control tank criterion, see H.2.1. NOTE 5 See API 651, Section 5.3. (tank owner/operator) H.2.1.8

H.2.1.8 IF NO, MATCH 3

H.2.1.6 Yes No SEE SEC. 4 H.2.1.10 Yes No

Control Tank 1 Candidate Tank 2 Control Tank 1 SIMILAR SERVICE ASSESSMENT—DATASHEET

IF NO, MATCH 3 No

IF NO, SEE SEC. 4

H.2.1.10 SEE SEC. 4

H.2.1.8 H.2.1.8 H.2.1.8

H.2.1.8 H.2.1.8

H.2.1.6 H.2.1.1 H.2.1.2 H.2.1.4 H.2.1.7

H.2.1.8 H.2.1.8

H.2.1.8 SEE SEC. 4

IF NO,

MATCH 3 Yes No Candidate Tank 2 Control Tank 1 Candidate Tank 2 Yes

Control Tank 1 Candidate Tank 2 MATCH 3T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION H-11

: N O I T A C O L : D I K N A T L O R T N O C S L B B : Y T I C A P A C : ) T F ( T H G I E H : ) T F ( R E T E M A I D

: N O I T A C O L : D I K N A T E T A D I D N A C S L B B : Y T I C A P A C : ) T F ( T H G I E H : ) T F ( R E T E M A I D SECTION 3—TANK SHELL (PRODUCT-SIDE) ASSESSMENT H.3.1 TANK CHARACTERISTICS a) YEAR TANK ERECTED b) SHELL MATERIAL c) CORROSION ALLOWANCE d) SHELL LINING TYPE e) SHELL LINING THICKNESS f) SHELL LINING AGE H.3.2 AMBIENT CONDITIONS a) LOW ONE DAY MEAN TEMP. b) EXPOSURE TO SALT AIR H.3.3 CURRENT SERVICE CONDITIONS: a) CURRENT PRODUCT NAME b) PRODUCT CLASS. (TABLE H.1) c) SPECIFIC GRAVITY OF PRODUCT d) REID VAPOR PRESSURE @ 60 o F e) NORMAL OPERATING TEMP. f) INERT GAS BLANKET? g) WATER BOTTOM? h) SULFUR CONTENT i) TIME IN THIS SERVICE j) PRODUCT CORROSIVITY H.3.4 PREVIOUS SERVICE CONDITIONS a) PREVIOUS PRODUCT NAME b) PRODUCT CLASS. (TABLE H.1) c) SPECIFIC GRAVITY OF PRODUCT d) REID VAPOR PRESSURE @ 60 o F e) NORMAL OPERATING TEMP. f) INERT GAS BLANKET? g) WATER BOTTOM? h) SULFUR CONTENT i) TIME IN THIS SERVICE j) PRODUCT CORROSIVITY H.3.5 CONCLUSIONS a) Does this assessment include additional assessment documentation (see H.2.1), YES or NO b) Based on the criteria reviewed in this similar service evaluation, similar service is OR is NOT recommended for this tank (check appropriate box) c) The corrosion rate to be applied to the product side of the tank shell is: ___________mpy.
COMMENTS: H.2.1.5 H.2.1.5

H.2.1.9 SEE SEC. 4

H.2.1.10 SEE SEC. 4

H.2.1.10

MATCH 3 IF NO, Control Tank 1 H.2.1.5 H.2.1.1 H.2.1.3 H.2.1.4 SIMILAR SERVICE ASSESSMENT—DATASHEET

H.2.1.10 H.2.1.10 H.2.1.9 IF NO,

H.2.1.10 H.2.1.10

Candidate Tank 2 Yes No SEE SEC. 4 H.2.1.10 H.2.1.10

H.2.1.10 H.2.1.10 MATCH 3 IF NO, Control Tank 1 Candidate Tank 2 Yes No SEE SEC. 4

MATCH 3 IF NO, Control Tank 1 Candidate Tank 2 Yes No

MATCH 3 Yes No Control Tank 1 Candidate Tank 2

H.2.1.10 H.2.1.10 H.2.1.10 H.2.1.10 H.2.1.10 H.2.1.10 H.2.1.10

H.2.1.10 H.2.1.10 H.2.1.10H-12 API S TANDARD 653

NOTE THE DATASHEET SHALL BE MAINTAINED IN THE RECORD FILE AS PER 6.8.

: E T A D : Y B D E T T I M B U S

: E T A D : Y B D E V O R P P A

NOTE 1 The control tank is the tank for which service conditions and corrosion rates are well known. NOTE 2 The candidate tank is the tank to be compared to the control tank to determine if similar service concepts apply. NOTE 3 “Y” or “Yes” indicates that the candidate tank criterion essentially matches the control tank . NOTE 4 If the candidate tank criterion does not match the control tank criterion, see H.2.1. SIMILAR SERVICE ASSESSMENT—DATASHEE TT ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION H-13

: N O I T A C O L : D I K N A T L O R T N O C S L B B : Y T I C A P A C : ) T F ( T H G I E H : ) T F ( R E T E M A I D

: N O I T A C O L : D I K N A T E T A D I D N A C S L B B : Y T I C A P A C : ) T F ( T H G I E H : ) T F ( R E T E M A I D SECTION 4—TANK SHELL (EXTERNAL SIDE) ASSESSMENT H.4.1 TANK CHARACTERISTICS a) YEAR TANK ERECTED b) SHELL MATERIAL c) CORROSION ALLOWANCE d) INSULATION TYPE e) INSULATION THICKNESS f) INSULATION AGE g) COATING TYPE h) COATING THICKNESS i) COATING AGE H.4.2 AMBIENT CONDITIONS a) LOW ONE DAY MEAN TEMP. b) EXPOSURE TO SALT AIR H.4.3 CURRENT OPERATING CONDITIONS a) PONDING/WATER b) NORMAL OPERATING TEMP. H.4.4 PREVIOUS OPERATING CONDITIONS a) PONDING/WATER b) NORMAL OPERATING TEMP. H.4.5 CONCLUSIONS a) Does this assessment include additional assessment documentation (see H.2.1), YES or NO b) Based on the criteria reviewed in this similar service evaluation, similar service is OR is NOT recommended for this tank (check appropriate box) c) The corrosion rate to be applied to the ambient side of the tank shell is: ___________mpy.
COMMENTS:

NOTE THE DATASHEET SHALL BE MAINTAINED IN THE RECORD FILE AS PER 6.8.

: E T A D : Y B D E S S E S S A

: E T A D : Y B D E V O R P P A

NOTE 1 The control tank is the tank for which service conditions and corrosion rates are well known. NOTE 2 The candidate tank is the tank to be compared to the control tank to determine if similar service concepts apply. NOTE 3 “Y” or “Yes” indicates that the candidate tank criterion essentially matches the control tank . NOTE 4 If the candidate tank criterion does not match the control tank criterion, see H.2.1. (tank owner/operator) H.2.1.10 H.2.1.10 Candidate Tank 2

MATCH 3 IF NO, Control Tank 1 Candidate Tank 2 Yes No SEE SEC. 4 Yes No

MATCH 3 Yes No Yes No Control Tank 1 Candidate Tank 2

Candidate Tank 2 SIMILAR SERVICE ASSESSMENT—DATASHEE T

H.2.1.9 MATCH 3 MATCH 3 IF NO, SEE SEC. 4

H.2.1.1 H.2.1.3 H.2.1.4

H.2.1.4 H.2.1.4 H.2.1.4

IF NO, H.2.1.4 H.2.1.4
H.2.1.4

H.2.1.10 IF NO,
H.2.1.10 SEE SEC. 4

H.2.1.9 SEE SEC. 4

Control Tank 1 Control Tank 1H-14 API S TANDARD 653

: N O I T A C O L : D I K N A T L O R T N O C S L B B : Y T I C A P A C : ) T F ( T H G I E H : ) T F ( R E T E M A I D

: N O I T A C O L : D I K N A T E T A D I D N A C S L B B : Y T I C A P A C : ) T F ( T H G I E H : ) T F ( R E T E M A I D
SECTION 5—CONCLUSION SUMMARY a) From Section 1, the corrosion rate to be applied to the product-side of the tank bottom is: ___________mpy. b) From Section 2, the corrosion rate to be applied to the soil-side of the tank bottom is: ___________mpy. c) From Section 3, the corrosion rate to be applied to the product-side of the tank shell is: ___________mpy. d ) F rom S ec ti on 4 , th e corros i on ra t e t o b e app li e d t o th e ex t erna l s id e o f th e t an k s h e ll i s: ___________mpy. e) Based on the corrosion rates applied, the next internal inspection for this tank will be completed in Year _________.
COMMENTS:

NOTE THE DATASHEET SHALL BE MAINTAINED IN THE RECORD FILE AS PER 6.8.

: E T A D : Y B D E S S E S S A

: E T A D : Y B D E V O R P P A (tank owner/operator) SIMILAR SERVICE ASSESSMENT—DATASHEE TI-1 

## Annex I (normative) Inquiries and Suggest ions for Change I.1 Introduction This annex describes the process established by API for subm itting inquiries to API and for submitting suggestions for changes to this standard. Inquiries and suggestions for change are welcom e and encouraged, however, submittals not complying with this annex and additional API policies will be returned unanswered. These submittals provide useful reader feedback to the responsible API Committee re garding technical accuracy, current technology use, clarity, consistency, and complet eness of the standard. API will atte mpt to answer all valid inquiries. 

### I.2 Inquiry References I.2.1 API maintains several websites that provide in formation that should be c onsidered when considering submitting an inquiry. I.2.2 Your inquiry may have been previously formally addressed by the Subcommittee and the resulting interpretation posted on the API web site at:

— For all Standards: http://mycommittees.api.org/s tandards/techinterp/default.aspx

— Refining only: http://mycommittees.api.org/standar ds/techinterp/re fequip/default.aspx For both links, click on the standard in question to download the file. I.2.3 In addition, an addendum or errata, which may have addresse d your issue, can be found on the API web site at:

— For all Standards: http://www.api.org/Standards/addenda/

— Refining only: http://www.api.org/Standards/addenda/add-ref.cfm 

### I.3 Definitions of Terms I.3.1 inquiry A question that asks what is the meaning of a specific paragraph, figure, or table in the standard; i.e., what do the words say. It is not a question that asks about the intention of the standard. I.3.2 interpretation The subcommittee’s answer to the inquiry. Typically, the answer is simply a “Yes” or “No” response, with a brief clarification if needed. This term is also us ed to refer to the combined question and answer. I.3.3 suggestion for change As opposed to an inquiry, a suggestion for change is a proposal to API for modify ing the standard to make additions or to resolve apparent conflicts or omissions. API encour ages both; however the submittal and handling procedures are different. 13I-2 API S TANDARD 653 

### I.4 API Policy Regarding Inquiries I.4.1 API has established the following limits on it s activity in the handling of inquiries.

— API does not approve, certify, rate, or endorse any it em, construction, proprieta ry device, or activity.

— API does not act as a consultant on specific engineering problems.

— API does not provide information on the general under standing, rationale or application of the Standard. I.4.2 All inquiries that result in interp retations will therefor e be made available to the general public on the API website. 

### I.5 Submission of Inquiries I.5.1 All background and policies for submitting inquirie s are stated in the following API web pages: 1) Click on: http://www.api.org/publications-standards -and-statistics/faqs -and-inquiries.aspx 2) Then click on: “Technical Questions and Requests for Interpretation” 3) Then click on: “Click here for detailed information on Technical Questions and Requests for Interpretation” 4) Then click on: “RFI website here” to access t he required electronic form for submitting an inquiry. I.5.2 All inquiries must comply with the following: a) be limited to a single subject or closely related subjects; b) be stated as briefly and precisely as possible, incl uding the applicable paragraph, figure, or table numbers; c) providing a background explanation is optional, but is encouraged to assist the subcommittee in understanding the query; d) be in the form of a “yes” or “no” question; e) be technically and editorially correct and written in understandable English; f) be related to the current edition/addendum of the document in question (Note: API will not issue interpretations of superseded or withdrawn documents); g) The general format of the inquiry shou ld be as follows: “Does Paragraph XXX of API-6XX require that ....?”. The inquirer shall also state the potential ans wer to the inquiry. In addition, if the inquirer believes a revision to the Standard is also needed, he or she shall provide recommended wording. 

### I.6 Typical Inquiry Process I.6.1 The typical process of an inquiry is: a) The Inquirer must prepare the inquiry , including any necessary background informa tion, in full compliance with this Annex and submit via the API web page link. b) API Standards Coordinator checks the i nquiry to verify compliance with the requirements of submitting an inquiry. 13T ANK I NSPECTION , R EPAIR , A LTERATION , AND R ECONSTRUCTION I-3 c) If the inquiry cannot be answered for any reason, the Coordinator will issue th e form letter to the inquirer advising the reason(s) for not answering the inquiry. d) If the inquiry is valid, it will be fo rwarded to the Subcommittee for study, and the inquirer will be advised using the form letter. e) The Subcommittee will eval uate the inquiry and either develop a respons e or determine that the inquiry cannot be answered, and advise the Coordinator ac cordingly. The Subcommittee will consider the need for modifying the standard to resolve technical issues, add new requirements, make editorial corrections, improve clarity, remove conflicts, etcetera. f) The interpretation will be published on the API website when approved by the Subcommittee. I.6.2 The time required to process a valid inquiry as described in I.6.1 may take as long as a year. 

### I.7 Responses to Inquiries I.7.1 If the inquiry is properly phrased, the interpretation can be a one-word response. Wi th many inquiries, there may be a need to provide clarifying statements, such as limits on the applicability. I.7.2 The industry benefits as a whole w hen inquiries are utilized as a means to understand the technical requirements of the standard. I.7.3 It is not possible to develop interpreta tions quickly to resolve immediate needs. I.7.4 A form letter or email will be used to reply to inquirers indicating the action taken by API, and, if applicable, the reason(s) for not being able to accept the inquiry. 

### I.8 Suggestions for Changes I.8.1 A Suggestion for Change is a communication (email preferr ed) from a reader to API proposing that a specific change be made to the standard. I.8.2 Any format is acceptable, as long as the content is clear. I.8.3 Submit suggestions to: pubweb@api.org

. I.8.4 The content of a suggestion should include the Standard number, edition, and addendum, and the relevant paragraph, table or figure numbers, et c. Provide as much explanation as necessary to be sure the reader understands the technical issues. Prov ide specific language that you thin k is needed to implement the change. I.8.5 API will forward all sugges tions that are suitably written to t he Subcommittee for consideration. The Subcommittee will evaluate each suggestion and determine if a change is needed. The change may be included in a future edition or addendum. 13S-1 

## Annex S Austenitic Stainless Steel Storage Tanks S.1 Scope S.1.1 This annex covers the inspection, repa ir, alteration, and reconstruction of stainless steel tanks that were constructed in accordance with API 650, Annex S. S.1.2 This annex states only the requirement s that differ from the basic rules in this standard. For requirements not stated, the basic ru les must be followed. 

### S.2 References No changes to Section 2. 

### S.3 Definitions No changes to Section 3. 

### S.4 Suitability for Service S.4.1 In 4.2.4.1, the requirements of API 650, Section S.3.5 shal l also be satisfied. S.4.2 In 4.2.4.3, Annex M requirements s hall be met for stainless steel tanks with design temperatures over 40 ° C (100 ° F) as modified by API 650, Sect ions S.3.6.2 thru S.3.6.7. S.4.3 In 4.3.3.1, the maxi mum allowable stress S shall be modified as follow s, for the design condition ( S d ) and the hydrostatic test condition ( S t ) the maximum allowable stre ss for all shell courses shall be the lesser of 0.95 Y or 0.4 T

. S.4.4 Table 4.2 shall be in accordance with API 650, T able S-4. When the radiogr aphy schedule applied to the existing weld is unknown, the join t efficiency of 0.7 shall be used. S.4.5 Section 4.3.3.5 c), shall be changed to read “Operation at temperatures over 40 ° C (100 ° F).” S.4.6 In 4.3.3.6, the factor 2 / 3 Y

shall be replaced with 3 / 4 Y

. S.4.7 In 4.3.4, these rules do not cover stainless steel tanks. 

### S.5 Brittle Fracture S.5.1 The tank is suitable for continued use in ambient temperature service. 

### S.6 Inspection No changes to Section 6. 

### S.7 Materials S.7.1 In 7.3.1.2, add reference to ASTM A480. S.7.2 Structural may be shapes fabricated fr om plate. Plate and structural materi al shall meet API 650, Section S.2. 13

12

10

10S-2 API S TANDARD 653 

### S.8 Design Considerations fo r Reconstructed Tanks S.8.1 In 8.4.3, the allowable stre ss shall be revised to meet the allowabl e stresses of API 650, Section S.3.2.2.1. 

### S.9 Tank Repair and Alteration S.9.1 In applying 9.1.1 to fabrication and construction requirements, API 650, Se ctions S.4.1 thr ough S.4.9 shall be met as applicable. S.9.2 Hot taps for stainless steels (reference Section 9.14) are not addressed by this annex. 

### S.10 Dismantling and Reconstruction S.10.1 In 10.4.2, welding shall also meet the requirements of API 650, Section S.4.11. S.10.2 Thermal cutting of stainless steel shall be by the iron powder burning, carbon arc, pl asma-arc, water jet, or laser cutting methods. S.10.3 The storage requirements of API 650, Section S.4.2 shall be met. S.10.4 If specified by the owner/operator, the require ments of API 650, Section S.4.5 shall be met. 

### S.11 Welding S.11.1 Welding shall also meet the requirements of API 650, Sections S.4.11 and S.4.12. 

### S.12 Examination and Testing S.12.1 Any reference to magnetic particle method s hall be replaced with the liquid penetrant method. S.12.2 In 12.3, the quality of test water shall meet API 650, Section S.4.10.2. 

### S.13 Annexes S.13.1 Annex F (NDE Requirements Summary)—any referenc es to magnetic particle examination shall be disregarded. 12

12

12

10

12

12SC-1 

## Annex SC Stainless and Carbon St eel Mixed Storage Tanks SC.1 Scope SC.1.1 This annex covers the inspection, repa ir, alteration and reconstruction of mi xed material tanks constructed in accordance with API 650, Annex SC. SC.1.2 This annex states only the requirements that differ from the basic rules in this standard, Annex S of this standard, Annex X of this standard and API 650, Annex SC. For requirements not stated, the basic rules shall be followed. SC.1.3 In this annex the term “stainless steel” includes aust enitic or duplex stainless steel unless noted otherwise. 

### SC.2 References No changes to Section 2. 

### SC.3 Definitions No changes to Section 3. 

### SC.4 Suitability for Service SC.4.1 Add to 4.2.4.1: The requirements of API 650, Sections S.3.5 and API 650, and X.3.6, shall also be satisfied for the stainless steel components of the tank. SC.4.2 Add to 4.2.4.3: This annex applies only to tanks in non-refrigerated services with a maximum design temperature not exceeding 93 ° C (200 ° F). Mixed material tanks operating at temperatures greater than 93 °C (200 °F) are not addressed in this annex ex cept for tanks covered in SC.4.3 below. For the purposes of this annex, the design temperature shall be t he maximum design temperature as specified by the owner/operator.
NOTE Exothermic reactions occurring inside unhe ated storage tanks can produce temper atures exceeding 40 °C (100 °F). SC.4.3 Tanks containing mixed materials which do not meet t he temperature limitations specified in SC.4.2, but have a successful service history of oper ation, shall be evaluated fo r thermal differential exp ansion at mixed material interface in order to remain in continued service. This analysis shall be performed in ac cordance with API 650 Annex SC, Section SC.3 and by an engineer experienced in storage tank design and evaluation methodologies. If no accounting for differential expansion ef fects in prior design work is document ed, then such effects shall be evaluated at the time of existing tank assessment. SC.4.4 Add to 4.3.3.1: The ma ximum allowable stress S shall be modified as follows, for the design condition ( Sd ) and the hydrotest condition ( St ) the maximum allowable stress for austenitic stainless steel shell courses shall be the smaller of 0.95 Y or 0.4 T

. SC.4.5 Table 4-2—Joint efficiencies for welded joints shall be in accordance with API 650, Table S-4, or API 650, Table X-3. When the radiography schedule applied to the existing we ld is unknown, then the joint efficiency of 0.7 shall be used. SC.4.6 Revise 4.3.3.5.c to read ‘Operation at temperatures over 40 °C (100 °F).’ SC.4.7 Revise 4.3.3.6 by replacing the 2 / 3 Y factor with 3 / 4 Y for austenitic stainless steel components. 10

13

10

13

10SC-2 API S TANDARD 653
SC.4.8 The rules in 4.3.4 for riveted tanks do not cover mixed material tanks. 

### SC.5 Brittle Fracture Considerations Evaluation of brittle fracture shall be done according to Sect ion 5 of this standard for carbon steel, Section S.5 of this standard for austenitic stainless steel , and Section X.5 of this standard for duplex stainless steel components. 

### SC.6 Inspection No Changes to Section 6. 

### SC.7 Materials Materials requirements for mixed mate rials situations are unchanged from the base document except as modified by API 653 Appendices S and X (S.7 and X.7) for stainless steels. 

### SC.8 Design Considerations for Reconstructed Tanks The allowable stress in 8.4.2 and 8.4.3 for stainless steel components shall be re vised to meet the allowable stresses of API 650 Annex S or API 650 Annex X. 

### SC.9 Tank Repair and Alteration SC.9.1 Revise 9.2 to read: Shell insert plates shall be made in accordan ce with API 650, Annex SC 3.2.2. SC.9.2 Revise 9.3 to read: Lap patches shall be made carbon st eel to carbon steel and stainless steel to stainless steel SC.9.3 Revise 9.8 to read: Shell penetrations and reinforcing shall be made in accordance with API 650, Annex SC 3.4. SC.9.4 Revise 9.10 to read: Repair of tank bottoms sha ll be made in accordance wi th API 650, Annex SC 3.1. SC.9.5 Revise 9.14 to read: Hot taps in stainl ess steel are not addressed by this annex. 

### SC.10 Other For Dismantling and Reconstruction, Weldi ng, Examination and Testing, and Annex es see the following sections of the basic document: S.10 through S.13 for austenitic stainless steel, and X.10 through X.13 for duplex stainless steel components. 10

10 13X-1 

## Annex X Duplex Stainless Steel Storage Tanks X.1 Scope X.1.1 This annex covers the inspection, re pair, alteration and reconstruction of duplex stainless steel tanks that were constructed in accordance with API 650, Annex X. X.1.2 This annex states only the requirements that differ from the basic rules in this Standard. For requirements not stated, the basic rules shall be followed. 

### X.2 References No changes to Section 2. 

### X.3 Definitions No changes to Section 3. 

### X.4 Suitability for Service X.4.1 In 4.2.4.1, the requirements of API 650, Section X.3.6 shal l also be satisfied. X.4.2 In 4.2.4.3, the requirements of AP I 650, Annex M requirements shall be sa tisfied for duplex stainless steel tanks with design temperatures over 40 °C (100 °F ) as modified by API 650, X.3.7.2 thru X.3.7.5. X.4.3 In 4.3.3.1, the maximum allowable stress S shal l be calculated the same way as for carbon steel. X.4.3.1 Y = specified minimum yield strength of the plate at design temperature; use material S32304 properties if duplex material/specific ation is not known. X.4.3.2 T = specified minimum tensile strength of the plate at design temperature; use material S32304 properties if duplex material/specific ation is not known. X.4.4 Table 4-2 shall be in accordance with API 650, T able X-3. When the radiogr aphy schedule applied to the existing weld is unknown; the join t efficiency of 0.7 shall be used. X.4.5 4.3.3.5c, shall be changed to read “Operation at temperatures over 40 °C (100 °F).” X.4.6 The rules of 4.3.4 for riveted tanks do not cover duplex stainless steel tanks. 

### X.5 Brittle Fracture Considerations X.5.1 In 5.3.2 the applicable API 650 edition and addendum for duplex stainless steel t anks is 11th edition, Addendum 1 or later. X.5.2 5.3.5 does not apply to duplex stainless steel tanks. X.5.3 The rules of 5.3.8 shall be replaced with the followi ng: Tanks constructed of dupl ex stainless steels whose toughness testing or testing exemption conformed to API 650, X.2.3.2 may be considered to be adequately tough for continued operation. 10

13

10

12
13

10X-2 API S TANDARD 653 

### X.6 Inspection No Changes to Section 6. 

### X.7 Materials X.7.1 In 7.3.1.2, add reference to ASTM A480 and A240. X.7.2 Structural sections may be shapes fabr icated from plate. Plate and structural material shall meet API 650, X.2. 

### X.8 Design Considerations fo r Reconstructed Tanks In 8.4.2 and 8.4.3 the allowable stress shall be revised to meet the allowable stre sses of API 650, Annex X. 

### X.9 Tank Repair and Alteration X.9.1 In applying 9.1.1 to fabrication and construction requirements, API Standard 650, Sections X.4.1 through X.4.9 shall be met as applicable except as permitted in X.10.2 of this annex. X.9.2 Hot taps for duplex stainless steels (reference section 9.14) are not addressed by this annex. 

### X.10 Dismantling and Reconstruction X.10.1 In 10.4.2, welding shall also meet the requirements of API 650, Section X.4.11. X.10.2 Carbon arc cutting shall not be used except when agreed to , in writing, by Purchas er as an exception to X.9.1, for certain dismantling operations. X.10.3 The storage requirements of API 650, Section X.4.2 shall be met. X.10.4 When specified by the Purchaser the requirem ents of API 650, Section X.4.5 shall be met. 

### X.11 Welding Welding shall also meet the requirement s of API 650, Sections X.4.11 and X.4.12. 

### X.12 Examination and Testing X.12.1 Any reference to magnetic particle method s hall be replaced with the liquid penetrant method. X.12.2 In 12.3, the quality of test water shall meet API 650, Section X.4.10. 

### X.13 Annexes Annex F, NDE Requirements Summary; any reference to ma gnetic particle method shall be replaced with the liquid penetrant method. 10

13

12#FFKVKQPCNEQRKGUCTGCXCKNCDNGVJTQWIJ+*52JQPG1TFGTU6QNNHTGGKPVJG75CPF%CPCFC.QECNCPF+PVGTPCVKQPCN(CZ1TFGTU1PNKPG1TFGTUINQDCNKJUEQO+PHQTOCVKQPCDQWV#2+2WDNKECVKQPU2TQITCOUCPF5GTXKEGUKUCXCKNCDNGQPVJGYGDCVYYYCRKQTI.5VTGGV099CUJKPIVQP&% 75# 

Product No. C65304