# Linings of Aboveground Petroleum Storage Tank Bottoms

API RECOMMENDED PRACTICE 652 THIRD EDITION, OCTOBER 2005

# Lining of Aboveground Petroleum Storage Tank Bottoms

Downstream Segment

API RECOMMENDED PRACTICE 652 THIRD EDITION, OCTOBER 2005

### SPECIAL NOTES
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### FOREWORD
Nothing contained in any API publication is to be construed as granting any right, by impli

cation or otherwise, for the manufacture, sale, or use of any method, apparatus, or product covered by letters patent. Neith er should anything contained in the publication be construed as insuring anyone against liability for infringement of letters patent.

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dard. Questions concerning the interpretation of the content of this publication or comments and questions concerning the procedures unde r which this publication was developed should be directed in writing to the Director of St andards, American Petroleum Institute, 1220 L Street, N.W., Washington, D.C. 20005. Requests for permission to reproduce or translate all or any part of the material published herein should also be addressed to the director. Generally, API standards are revi ewed and revised, reaffirmed, or withdrawn at least every five years. A one-time extension of up to two ye ars may be added to this review cycle. Status of the publication can be ascertained from th e API Standards Department, telephone (202) 682-8000. A catalog of API publications and ma terials is published annually and updated quarterly by API, 1220 L Street, N.W., Washington, D.C. 20005. Suggested revisions are invited and should be submitted to the Standards and Publications Department, API, 1220 L Street, NW, Washington, DC 20005, standards@api.org.

iii

### CONTENTS

Page 1 SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
2 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 2.1 Codes, Standards, and Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 2.2 Other References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
3 DEFINITIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
4 CORROSION MECHANISMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 4.2 Chemical Corrosion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 4.3 Concentration Cell Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 4.4 Galvanic Cell Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 4.5 Corrosion Caused by Sulfate-Redu cing Bacteria . . . . . . . . . . . . . . . . . . . . . . . . . .4 4.6 Erosion-Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 4.7 Fretting-Related Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
5 DETERMINATION OF THE NEED FOR TANK BOTTOM LINING . . . . . . . . . . . .5 5.2 Linings for Corrosion Prevention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 5.3 Tank Corrosion History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 5.4 Tank Foundation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
6 TANK BOTTOM LINING SELECTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 6.2 Thin-Film Tank Bottom Linings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 6.3 Thick-Film, Reinforced Tank Bottom Linings . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 6.4 Thick-Film, Un-reinforced Linings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 6.5 Circumstances Affecting Lining Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
7 SURFACE PREPARATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 7.2 Pre-cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 7.3 Bottom Repair and Weld Preparatio n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 7.4 Environmental Conditions During Bl asting . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 7.5 Surface Profile or Anchor Pattern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 7.6 Air and Abrasive Cleanliness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 7.7 Removal of Dust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
8 LINING APPLICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 8.2 Guidelines for Lining Application. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 8.3 Temperature and Humidity Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 8.4 Lining Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 8.5 Lining Curing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 9 QUALITY CONTROL INSPECTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 9.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11 9.2 Qualification of Inspection Personne l . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 9.3 Recommended Inspection Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
10 EVALUATION AND REPAIR OF EXISTING LININGS . . . . . . . . . . . . . . . . . . . . .12 10.2 Evaluation Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 10.3 Evaluation Criteria for Linings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

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### CONTENTS

Page 10.4 Evaluating Serviceability of Existing Linings . . . . . . . . . . . . . . . . . . . . . . . . . . .12 10.5 Determining the Cause of Lining Degradation/Fail ure . . . . . . . . . . . . . . . . . . . .13 10.6 Lining Repair and Replacement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
11 MAXIMIZING LINING SERVICE LIFE BY PROPER MATERIAL SELECTION AND SPECIFICATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13 11.1 Lining Material Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 11.2 Written Specification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
12 SAFETY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 12.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 4 12.2 Tank Entry. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 12.3 Surface Preparation and Lining Ap plication . . . . . . . . . . . . . . . . . . . . . . . . . . . .14 12.4 Manufacturer’s Material Safety Data Sheets . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
Tables 1 Thin-film Tank Bottom Lining Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 2 Thick-film, Tank Bottom Lining Resi ns. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 

## Linings of Abov eground Storage Tank Bottoms

1 Scope

This recommended practice provides guidance on achiev

ing effective corrosion control in aboveground storage tanks by application of tank bottom linings. It contains information pertinent to the selection of lining materials, surface prepara

tion, lining application, cure, and inspection of tank bottom linings for existing and new storage tanks. In many cases, tank bottom linings have proven to be an effective method of preventing internal corrosion of steel tank bottoms. The intent of this recommended practice is to provide information and guidance specific to aboveground steel stor

age tanks in hydrocarbon service. Certain practices recom

mended herein may also be applicable to tanks in other services. This recommended practice is intended to serve only as a guide. Detailed tank bottom lining specifications are not included. This recommended practice do es not designate specific tank bottom linings for every situation because of the wide variety of service environments.

NACE No.10/SSPC-PA 6 and NACE No. 11/SSPC-PA 8 are industry consensus standards for installation of linings on tank floors and vessels. They are written in compulsory lan

guage and contain specific criter ia intended for use by per

sons who provide written specifications for tank and vessel linings. These documents should be given consideration when designing and installing a lining system for steel bot

tom tanks. 

### 2 References
2.1 CODES, STANDARDS, AND SPECIFICATIONS

Unless otherwise specified, the most recent edition or revi

sion of the following standards, codes, or specifications shall, to the extent specified herein, form a part of this recom

mended practice. API RP 575 Inspection of Atmospheric and Low-Pres

sure Storage Tanks Std 620 Design and Construction of Large, Welded, Low-Pressure Storage Tanks Std 650 Welded Steel Tanks for Oil Storage RP 651 Cathodic Protection of Aboveground Petroleum Storage Tanks Std 653 Tank Inspection, Repair, Alteration, and Reconstruction Std 2015 Requirements for Safe Entry and Cleaning of Petroleum Storage Tanks RP 2016 Guidelines and Procedures for Entering and Cleaning Petroleum Storage Tanks ASTM 1 D 2583 Standard Test Method for Indentation Hardness of Rigid Plastics by Means of a Barcol Impressor D 4414 Standard Practice for Measurement of Wet Film Thickness by Notch Gauges D 4417 Standard Test Methods for Field Measure

ment of Surface Profile of Blast Cleaned Steel D 4940 Standard Test Method for Conductimetric Analysis of Water Soluble Ionic Contami

nants of Blasting Abrasives D 5402 Standard Practice for Assessing the Sol

vent Resistance of Organic Coatings Using Solvent Rubs E 96 Standard Test Methods for Water Vapor Transmission of Materials G 9 Standard Test Method for Water Penetra

tion into Pipeline Coating

DSTAN 2 Defense Standard 80-97 Paint System, Medium Build for the Inte

rior of Bulk Fuel Tanks and Fittings
Military Standards 3 MIL-PRF 4556 Coating Kit, Epoxy for Inter or Steel Fuel Tanks 23236 Coating Systems for Ship Structures

NACE 4 37519 Corrosion Data Survey —Metals Section TM0174 Laboratory Methods for the Evaluation of Protective Coatings and Lining Materials on Metallic Substrates in Immersion Service RP0188 Discontinuity (Holiday) Testing of New Protective Coatings on Conductive Substrates

1 ASTM International, 100 Bar Harb or Drive, West Colshohocken, Pennsylvania, 19428-2959. www.astm.org. 2 UK Defence Standardization, Ro om 1138, Kentigern House, 65 Brown Street, Glasgow, G2 8EX. www.dstan.mod.uk. 3 Department of Defense Single Stock Point, 700 Robbins Avenue, Building 4/Section D, Philadelphi a, Pennsylvania, 19111-5098. www.dodssp.daps.dla.mil. 4 NACE International, 1440 South Creek Drive, P.O. Box 218340, Houston, Texas 77218-8340. www.nace.org.2 API R ECOMMENDED P RACTICE 652

RP0178 Fabrication Details, Surface Finish Requirements, and Proper Design Consid

erations for Tanks and Vessels to be Lined for Immersion Service RP0287 Field Measurement of Surface Profile of Abrasive Blast Cleaned Steel Surfaces Using a Replica Tape NACE/SSPC

NACE No. 1/ White Metal Blast Cleaning SSPC-SP 5 NACE No. 2/ Near-White Metal Blast Cleaning SSPC-SP 10 NACE No. 5/ Joint Surface Preparation Standard: SSPC-SP 12 Surface Preparation and Cleaning of Metals by Waterjetting Prior to Recoating NACE No. 10/ Fiberglass-Reinforced Plastic (FRP) SSPC-PA 6 Linings Applied to Bottoms of Carbon Steel Aboveground Storage Tanks NACE No. 11/ Thin-Film Organic Linings Applied in New SSPC-PA 8 Carbon Steel Process Vessels NACE 6A192/ Dehumidification and Temperature SSPC-TR 3 Control During Surface Preparation, Application, and Curing for Coatings/ Linings of Steel Tanks, Vessels, and Other Enclosed Spaces OSHA 5

29 CFR 1910.94 Ventilation 1910.132 Personal Protective Equipment, General Requirements 1910.146 Permit-Required Confined Spaces 1926.62 Lead Publ. 2254 Training Requirements in OSHA Standards and Training Guidelines SSPC 6

PA 1 Shop, Field, and Maintenance Painting PA 2 Measurement of Dry Paint Thickness with Magnetic Gages PA 3 A Guide to Safety in Paint Application SP 1 Solvent Cleaning SP 11 Power Tool Cleaning to Bare Metal TU 4 Field Methods for Retr ieval and Analysis of Soluble Salts on Substrates VIS 1 Guide and Reference Photographs for Steel Surfaces Prepared by Dry Abrasive Blast Cleaning 2.2 OTHER REFERENCES Although not cited in the text, these publications may be of interest or contain related material. API RP 2009 Safe Welding, Cutting and Hot Work Prac

tices in the Petroleum & Petrochemical Industries Publ 2207 Preparing Tank Bottoms for Hot Work ACGIH 7 Threshold Limit Values (TLVs ® ) and Bio

logical Exposure Indices (BEIs ® ) NACE Handbook 1 Forms of Corrosion Recognition and Pre

vention, Vol. 1 & 2 OSHA

29 CFR 1910.134 Respiratory Protection 1910.147 The Control of Hazardous Energy (Lockout/Tagout) 1910.1000 Air Contaminants 1910.1200 Hazard Communication 1926.354 Welding, Cutting, and Heating in way of Preservative Coatings SSPC

AB 1 Mineral and Slag Abrasives AB 2 Specification for Cleanliness of Recycled Ferrous Metallic Abrasives AB 3 Newly Manufactured or Re-manufactured Steel Abrasives 

### 3 Definitions 3.1 aboveground storage tank: A stationary container, usually cylindrical in shape, consisting of a metallic roof, shell, bottom, and support structure where more than 90% of the tank volume is above surface grade. 3.2 adduct: A curing agent, generally an amine that has been combined with a portion of the resin, usually an epoxy. 3.3 amine: An organic compound having amino func

tional groups, which provide chemical reactivity and utility as a curative for epoxy and other resins. 3.4 anchor pattern: Surface profile or roughness. 3.5 anode: The electrode of an el ectrochemical cell at which oxidation (corrosion) occurs. Electrons flow away 5 The Occupational Safety and Hea lth Administration, 200 Constitu

tion Avenue NW, Washington D.C. 20210. www.osha.gov. 6 The Society for Protective Coatings, 40 24th Street, 6th Floor, Pitts

burg, Pennsylvania 15222-4656. www.sspc.org. 7 The American Conference of Govern mental Industrial Hygienists, 1330 Kemper Meadow Drive, Cincinna ti, Ohio 45240. www.acgih.org.L INING OF A BOVEGROUND P ETROLEUM S TORAGE T ANK B OTTOMS 3
from the anode in the external circuit. Corrosion usually occurs and metal ions enter the solution at the anode. 3.6 aromatics: Strong hydrocarbon solvents whose chemical structure has one or more unsaturated ring struc

tures. Benzene, toluene, and xylene are common examples of aromatic solvents. 3.7 Bisphenol–A polyester: A polyester whose chemi

cal structure incorporates Bisphenol-A into the resin mole

cule in place of some or all of the glycol. The solid resin is generally provided as a solution in styrene, which acts as a solvent and as a cross-lin king agent for the resin. 3.8 cathode: The electrode of an electrochemical cell at which a reduction is the principle reaction. Electrons flow toward the cathode in the metal component. 3.9 cathodic protection: A technique to reduce corro

sion of a metal surface by maki ng that surface the cathode of an electrochemical cell. 3.10 coal tar: A black hydrocarbon residue remaining after coal is distilled. 3.11 coal tar epoxy: A coating in which the binder is a combination of coal tar and epoxy resin. 3.12 coating: See definition for lining. 3.13 copolymer: A large molecule whose chemical struc

ture consists of at least two different monomers. 3.14 corrosion: The deterioration of a material, usually a metal, because of a reaction with its environment. 3.15 curing: The setting up or hardening, generally due to a polymerization reaction betw een two or more chemicals (resin and curative). 3.16 dew point: The temperature at which moisture con

denses from the atmosphere. 3.17 differential aeration cell: An electrochemical cell, the electromotive force of which is due to a difference in air (oxygen) concentration at one electrode as compared with that at another electrode of the same material. 3.18 electrochemical cell: A system consisting of an anode and a cathode immersed in an electrolyte so as to cre

ate an electrical circuit. The anode and the cathode may be different metals or dissimilar areas on the same metal surface. 3.19 electrolyte: A chemical substance containing ions that migrate in an electric field. 3.20 epoxy: Resin containing epoxide (oxirane) func

tional groups that allow for curing by polymerization with a variety of curatives. Epoxy resins are usually made from Bisphenol-A and/or Bisphenol-F and epichlorohydrin. 3.21 forced-curing: Acceleration of curing by increasing the temperature above ambient, accompanied by forced air circulation. 3.22 holiday: A discontinuity in a protective coating that exposes unprotected surf ace to the environment. 3.23 isophthalic polyester: A resin polymerized from isophthalic acid (or anhydride), ethylene or propylene glycol and maleic acid (or anhydride). The solid resin is generally provided as a solution in styrene, which acts as a solvent and as a cross-linking agent for the resin. 3.24 lining: A material applied to the internal surfaces of a tank to serve as a barrier to corrosion and/or product contami

nation. The term coating is also used for the purposes of this document. 3.25 mil: One one-thousandth of an inch (0.001 in.). One mil = 25.4 μm; it is common practice to use 1 mil = 25 μm. 3.26 mill scale: An oxide layer formed on steel during hot-forming operations, typically “gun-metal” blue in color. 3.27 phenolic: A resin of the phenol formaldehyde type. 3.28 polyamide: A resin whose chemical structure con

tains adjacent carbonyl and amin o functional gro ups that is often used as a curative for epoxy resins. Commercially avail

able polyamides are reaction pr oducts of dimerized and trim

erized fatty acids with ammonia or polyamines. 3.29 polyamidoamine: A resin whose chemical struc

ture contains adjacent carbony l and amino functional groups that is often used as a curative for epoxy resins. Commer

cially available polyamidoamines are reaction products of monofunctional fatty acids and amines. 3.30 resin: A natural or synthetic substance that may be used as a binder in coatings. 3.31 thick-film lining: A lining with a dry film thickness of 20 mils (0.51 μm) or more. 3.32 thick-film reinforced lining: See 6.3 for interpre

tation. 3.33 thin-film lining: A lining with a dry film thickness less than 20 mils (0.51 μm). 3.34 vinyl ester: A polyester that usually contains Bisphenol-A in the resin backbone and two vinyl groups for polymerization reactivity. The solid resin is generally pro

vided as a solution in styrene, which acts as a solvent and as a cross-linking agent for the resin. 3.35 vinyl group: A functional group on a resin molecule that consists of a carbon-to-car bon double bond at the end of the molecule.4 API R ECOMMENDED P RACTICE 652

3.36 volatile organic compound (VOC): Compounds that have a high vapor pressure [greater than 0.27 kPa (2 mm of mercury) at 25oC] and low water solubility, excluding methane. VOCs typically are industrial solvents, fuel oxygen

ates, or components of petroleum fuels. 

### 4 Corrosion Mechanisms 4.1 GENERAL Corrosion rates of carbon steel in various hydrocarbons have been determined and are given in many reference texts such as “NACE Corrosion Da ta Survey-Metals Section.” These rates apply only if ther e are no accelerating mecha

nisms. For example, corrosion would not be expected in ambient temperature crude oil or product service with no water present; however, corrosion may occur when a layer of water settles to the bottom of a crude oil, intermediate prod

uct, or finished product storage tank. This water, which may enter the tank with the product, through the seals, or during “breathing” of the tank, often contains corrosive compounds. For example, crude oil may cont ain salt water and sediment that settles out on the bottoms of storage tanks. Chlorides and other soluble salts contained in the water may provide a strong electrolyte that can promote corrosion. The common mechanisms of internal tank bottom corrosion include: a. Chemical corrosion. b. Concentration cell corrosion. c. Galvanic cell corrosion. d. Corrosion caused by sulfate-reducing bacteria. e. Erosion-corrosion. f. Fretting-related corrosion.

These mechanisms are discussed in detail in the following sections.
4.2 CHEMICAL CORROSION Chemical corrosion may occu r in environmental and prod

uct cleanup tanks as well as in chemical storage facilities. For example, a wastewater treatment tank operates by adding heat and/or concentrated sulfuric acid to the water to break the emulsion of oil and water. The acid, unless added properly, immediately becomes diluted and hence much more corro

sive, especially in the area of the acid inlet piping. Chemical attack is also prevalent in corro sive services such as caustic, sulfuric acid, ballast water, and water neutralization services.
4.3 CONCENTRATION CELL CORROSION Concentration cell corrosion may occur when a surface deposit, mill scale, or crevice creates a localized area of lower oxygen concentration. The area under a surface deposit may be penetrated by a thin layer of electrolyte, which soon becomes depleted of oxygen. The difference in oxygen con

centration between the inacce ssible area and the bulk electro

lyte creates a galvanic cell, with the contact area of the surface deposit being anodic to the surrounding tank plate. Concentration cell corrosion will cause pitting and may result in significant localized metal loss. Pitting of a bare steel tank bottom may occur at a rate as high as 80 mils (2.0 mm) per year.
4.4 GALVANIC CELL CORROSION Hot-rolled carbon steel, typicall y used for the construction of petroleum storage tanks, is covered with a thin layer of oxide called mill scale, which is cathodic to the base steel. In the presence of a corrodent (such as dissolved oxygen) and an electrolyte, a galvanic corrosion couple forms at breaks in the mill scale. Accelerated pitting corrosion of the steel at breaks in the mill scale can result. Mill scale may be removed from both sides of the tank bottom plate by abrasive blast cleaning or by pickling, but removal of mill scale from the underside of the steel bottom is not commonly done.

In some cases, welding can produce large differences in the microstructure of a steel bottom plate resulting in a built-in galvanic couple. In the presence of a corrodent and an elec

trolyte, preferential corrosion can occur at the heat-affected zones (HAZ) of the base metal near the welds. This type of corrosion can cause significant localized metal loss.
4.5 CORROSION CAUSED BY SULFATEREDUCING BACTERIA Sulfate-reducing bacteria (S RB) are widespread in the petroleum industry. The role of SRB in corrosion is univer

sally recognized but the mechan isms are not well understood. Generally, the effect of SRB on the corrosion of bare steel tank bottoms is negligible. In some cases, however, severe corrosion has been attributed to SRB. The SRB colonies form deposits on the steel that may provide an effective barrier to the diffusion of dissolved oxygen. Thus, the mere physical presence of bacterial deposits ca n promote aggressive pitting corrosion by the concentration cell mechanism described in 4.3. The metabolism of SRB is important with regard to the corrosion of storage tank bott oms. SRB are strict anaerobes that do not proliferate in the presence of oxygen; however, the dense bacterial colonies creat e a local anaerobic condition even if some oxygen is availabl e. By creating the local anaer

obic condition, the bacteria can stay alive in the presence of oxygen even though the colonies do not expand. SRB colo

nies derive energy principally from the reduction of sulfates to sulfide, and this metabolic end product is corrosive to steel. Moreover, the iron sulfide corrosion product is cathodic to the base steel and may promote accel erated pitting corrosion by a galvanic mechanism as described in 4.4, if dissolved oxygen is available as a corrodent.L INING OF A BOVEGROUND P ETROLEUM S TORAGE T ANK B OTTOMS 5

4.6 EROSION-CORROSION Erosion-corrosion may occur in wastewater treating or mixing tanks where soil or small abrasive aggregate is present. To a lesser extent, eros ion-corrosion can also occur at tank mixers in crude oil storage tanks. A water treatment tank blends chemicals into contamin ated water to break any emul

sions of oil and water. Agitation may increase corrosion by delivering more corrodent, such as dissolved oxygen, from the bulk of the stored product to the surface of the tank steel. Turbulence also moves any fine aggregate that is present, cre

ating an abrasive environment in which adherent, semi-pro

tective corrosion products can be dislodged, exposing the underlying steel to the corrosive environment. Severe erosion conditions may scour the base metal directly. Erosion-corro

sion causes highly localized metal loss in a well-defined pat

tern.
4.7 FRETTING-RELATED CORROSION

Fretting-related corrosion may occur in hydrocarbon ser

vice on the bottoms of external floating roof tanks. When the tank is emptied, the floating roof is typically supported on roof-support legs constructed of open-ended pipe. Most bot

tom designs require “striker plates” under each roof support leg. When the floating roof is landed, the pipe legs rest on the striker plates supporting the weight of the roof. Repeated, fre

quent contact between the strike r plate and the open end of the pipe leg removes any protective layer of rust scale that may have formed on the striker plate surface. When the roof is floated again, any water on the tank bottom causes corro

sion at the location on the st riker plate where the coating and/ or any protective rust scale has been damaged. Experience has shown that frequent roof landings over a long period of time causes corrosion severe and localized enough to corrode a hole through the striker plat e and the floor plate like a cookie cutter. 

### 5 Determination of the Need for Tank Bottom Lining 5.1 GENERAL

The bottom plates of aboveground storage tanks are sus

ceptible to internal and external corrosion. Storage tank bot

toms are generally fabricated fr om carbon steel plate sections that are typically 0.25 in. (6 mm) thick. Annular floor plates of storage tanks frequently have thicker plate sections ranging from 0.25 to 1.0 in. (6 to 25 mm). The bottom plate sections and the attachment fillet lap we lds are intended to function as a membrane and prevent leaks. Uniform soil support beneath the bottom plate minimizes stress in the bottom plate. The need for an internal tank bottom lining in an above

ground storage tank is generally based on several consider

ations: a. Corrosion prevention. b. Tank design. c. Tank history. d. Environmental considerations. e. Reduce time and effort for future tank cleaning. f. Federal, state, and local regulations. g. Product quality.
5.2 LININGS FOR CORROSION PREVENTION

The proper selection, applicat ion, and maintenance of tank bottom linings can prevent internal corrosion of the steel tank bottom. Unless means of corrosion prevention are used on the soil side, perforation of the tank bottom may still occur.

The minimum thickness of the steel tank bottom should be determined according to API Std 653. An internal tank bot

tom lining may be deemed neces sary if inspection shows that the minimum thickness of the bottom steel plate is less than 0.100 in. (2.5 mm), or if corrosion is expected to proceed so that the steel thickness may reach this minimum thickness prior to the next scheduled inspection. When using API Std 653 to determine appropriate internal inspection intervals for aboveground storag e tanks, the antici

pated life of the lining as well as the corrosion rate anticipated in the event of premature lining failure should be considered.
5.3 TANK CORROSION HISTORY

The corrosion history of a particular tank should be consid

ered when determining the need for an internal lining. The corrosion history of tanks in si milar service should also be considered. The items to be c onsidered are dictated by indi

vidual circumstances, but some of the more important consid

erations are as follows: a. Where is the corrosion occurring (product side, soil side, or both)? b. What is the internal a nd soil-side corrosion rate? c. Have there been significant changes in the corrosion rate? d. What type of corrosion is occurring? e. Has corrosion caused perforation of the steel tank bottom? f. What was the prior service of the tank and how corrosive was that product?
5.4 TANK FOUNDATION

The foundation must be adequa te to prevent excessive set

tlement of the tank. If uniform foundation support is not pro

vided, flexing of the tank bottom can result as the tank is filled or emptied. Flexing occurs on all steel floors; however, excessive flexing of the steel bottom may cause an internal bottom lining to crack.6 API R ECOMMENDED P RACTICE 652
The tank pad material beneath the steel bottom has a sig

nificant effect on the potent ial for underside corrosion. If there is pad contamination (e.g. rock, lumps of clay, welding electrodes, paper, plastic, wood, etc.) in contact with the underside of the steel, differential aeration or other corrosion cells can form where the contamin ates are in contact with the tank bottom and severe corrosion may result (see API RP 651). The use of wood under a tank floor is not recommended given that it promotes bacteria l activity and will cause accel

erated corrosion. 

### 6 Tank Bottom Lining Selection 6.1 GENERAL

Tank bottom linings can generally be divided into two classes: thin-films [with a dry film thickness less than 20 mils (0.51 μm)] and thick-films [with a dry film thickness of 20 mils (0.51 μm) or more]. Linings may be applied to the bot

toms of storage tanks when they are first constructed or they may be installed after some peri od of service. Generally, thinfilm linings may be applied to new tanks and to bottoms of storage tanks that have experienced minimal corrosion. The advantages and disadvantages of thin and thick-film tank bot

tom lining systems are discussed in this section. Most tank bottom lining materials are initially selected based on chemical resistance or compatibility with the stored product. However, resistance to moisture permeation should also be a major consideration for long-term service since most storage tanks will typically have a layer of water on the floor. All lining materials absorb moisture over time and this absorption can ultimately result in its failure. The moisture vapor transmission of various lining materials can be compar

atively tested using ASTM E 96, ASTM G 9, or other equiva

lent test methods. Because tank bottoms flex during operation, a bend test on coat ing candidates should be per

formed to ASTM D 522, or another appropriate standard.

Recent advancements in technology have produced coat

ings with zero VOCs. These 100% solid coatings provide reduced safety concerns durin g the application; can be applied in a single coat and of fer a reduction in the tank turn

around schedule. With exceptions, typically these coatings are classified as thick-film linings.
6.2 THIN-FILM TANK BOTTOM LININGS

Thin-film tank bottom lining systems are frequently based on epoxy or epoxy-copolymer resins. Table 1 lists several generic types of thin-film linings and their suitability for vari

ous stored hydrocarbon and petrochemical products. All lin

ings that are employed to protect tank bottoms also must be resistant to water, since water mu st be present at the tank bot

tom for electrochemical corrosi on to occur. NACE No. 11/ SSPC-PA 8 should be given cons ideration when designing and installing a thin-film lining system for steel bottom tanks. Table 1—Thin-film Tank Bo ttom Lining Systems
Lining System a (resin/curative) Typical Services Maximum Temperature Range °F (°C) b Coal tar epoxy/amine Foul water services and crude oil 120–170 (49–77) Epoxy phenolic/amine Light products, distil

lates, aromatics, high purity water, sour prod

ucts, crude, and gasoline 180–220 (82–104)

Epoxy/amine Water, light products, distillates, aromatics, crude, and gasoline 160–220 (71–104)

Epoxy/polyamide Water, distillates, crude, and gasoline 160–180 (71–82) Epoxy/polyamidoam

ine Water, distillates, crude, and gasoline 160–180 (71–82)

Note: a. Generally applied over a white or near-white abrasive blast cleaning in two or three coats. No primer is required. Information related to the performance limitatio ns of specific coatings with regard to chemical immersion and elevated temperatures should be obtained from the lining manufacturer. b. For tanks containing a water layer on the bottom, the maximum temperature will be at the lowe r end of the specified range.
6.2.1 Advantages of Thin-film Linings

Thin-film lining systems are often used for application to the topside of the bottoms of new storage tanks. New steel plates provide a smooth surface that easily can be made ready for lining application. Corrosion of bare steel tank bottoms is rarely uniform. Generally, corrosion due to immersion expo

sure creates a surface that is ro ugh and pitted, and it is often difficult to completely coat and protect a corroded steel bot

tom with a thin-film lining system. The principal advantages of thin-film linings are as follows: a. Initial cost is typically less than thick-film reinforced linings. b. Most are easier to apply than thick-film reinforced linings. c. Experience has shown that when properly selected, applied, and not damaged, the life of thin-film linings can be greater than 20 years. d. Most thin-film epoxy linings exhibit good flexibility. e. Generally more accura te MFL floor scans. f. It is often easier to remove a thin-film lining at the end of its useful life.
6.2.2 Limitations of Thin-film Linings a. API Std 653, requires a minimum of 0.050 in. (1.3 mm) remaining bottom plate thickness at the next internal inspec

tion, when thick, reinforced linings are used. However, for thin-film linings, API Std 653 requires the bottom plate thick

-L INING OF A BOVEGROUND P ETROLEUM S TORAGE T ANK B OTTOMS 7
ness be a minimum of 0.100 in. (2.5 mm) at the end of the next service interval. b. Thin-film linings are more susceptible to mechanical dam

age than thick-film linings. c. Rough weld surfaces and weld spatter can protrude through the finished lining thickness and result in holidays, therefore, weld surfaces should be relatively smooth and weld spatter removed before a lining is applied. Alternately, caulk

ing compatible with the lining product may be used to cover rough welds. Optimally, require ments for weld surface qual

ity are part of the welding specification and not part of the lining contractor’s responsibility. d. Some thin-film linings require the application of multiple coats. e. Thin-film linings are most often solvent-borne coatings that require the evaporation of solvent from the film to achieve proper cure. If the solvent vapors are not effectively removed from the tank or vessel, because they are heavier than air, they will hover at the floor level and impede the progress of the cure. f. Presence of moisture in the air during the cure can cause amine blush, which must be removed before the application of subsequent coats.
6.3 THICK-FILM, REINFORCED TANK BOTTOM LININGS Thick-film, reinforced linings may be used as tank bottom linings for both new and old storage tanks. Table 2 lists generic types of resins typically used in such linings. These resins are commonly reinforced with chopped glass fibers, chopped glass mat, woven glass mat, or organic fibers.

The properties of composite li nings are a function of the properties of the constituent ph ases (polymer matrix and rein

forcing filler), their relative am ounts, and the geometry of the dispersed, reinforcement phase (e .g., particle size, shape, dis

tribution, orientation). Some particulate fillers strengthen and reinforce the matrix a little, whereas others do not. Reinforcement capability is very much size and shape dependent and elongated fibers provide the best reinforce

ment for plastics. The over all strength of a composite depends on the tensile strength of the fibers and on the degree to which a load can be transmitted from the matrix to thefibers. With small particle fillers having an acicular or needlelike shape (e.g., talc), a plat y shape (e.g., mica), or flake shape (e.g., glass), the tensile strength is of little consequence. Small reinforcing particles restrain movement of the matrix only over a miniscule area at the particle. Tensile strength of fiber reinforcement is important and only fibers can distribute the stress over their elongated area. Only fiber-reinforced lin

ings are well proven to have hole-bridging capability.

As with thin-film linings, a white (NACE No. 1/SSPC-SP 5) or near-white (NACE No. 2/SSPC-SP 10) abrasive blast cleaning should be provided for good adhesion. The NACE No. 10/SSPC-PA6 specification should begiven consideration when designing and installing a thickfilm lining system fo r steel bottom tanks.
Table 2-Thick-film, Tank Bottom Lining Resins

Glass-reinforced Lining Resins a Typical Services Maximum Temperature Range °F (°C) b Isophthalic Polyester Water, crude oil, distil

lates, and gasoline 140 – 160 (60 – 71) Bisphenol-A Polyester Water, crude oil, distil

lates, and gasoline 160 – 180 (71 – 82) Vinyl Ester Water, crude oil, aromatics, solvents, alcohols, gasohol, oil, and chemicals 180 – 220 (82 – 104)

Epoxy Water, crude oil, aromatic distillates, and gasoline 180 (82)

Note: a. Generally applied over a white or near-white abrasive blast cleaning in several coats. No prime r is required. Information related to the performance limitations of sp ecific coatings with regard to chemical immersion and elevated te mperatures should be obtained from the lining manufacturer. b. For tanks containing a water layer on the bottom, the maximum temperature will be at the lowe r end of the specified range. Installation of a chopped glass reinforced lining via a chop

per gun requires applicators with specific expertise. The device held and controlled by the applicator must deposit not only the correct ratio of components in the resin mixture, but also the correct amount of fibe rs vs. resin. Too much resin results in a lack of reinforcement strength. Too little resin results in poor barrier properties. A reinforced lining must possess optimum barrier and stress-carrying properties. A typical installation sequence for a hand laid mat type reinforced linings is: a. Spray application of a resin (or flood) coat, typically 20 – 30 mils (508 – 762 (m)). b. Lay sections of pre-cut mat into the wet resin, overlapping edges of mat approx. 2 in. (5 cm). c. Roll the resin into the mat using ribbed rollers to fully sat

urate it and remove entrapped air. d. Spray apply another coat of resin, approx. 25 – 30 mils (635 – 762 (m)) to achieve 45 – 55 mils (1143 – 1397 (m)) total thickness. e. Sand to remove protruding fibers. f. Spray apply a final coat of resin (gel coat).

Many types of polyester require wax addition to topcoats to ensure timely and complete surface cure. Information related to the performance limitations of specific coatings with regard to chemical immersion and elevated temperatures should be obtained from the lining manufacturer.8 API R ECOMMENDED P RACTICE 652
Special consideration must be given to the coving at the transition from the tank bottom to the shell, so as to prevent cracking of the lining when the ta nk is put into service. As the tank is loaded, the hoop stress on the shell may cause the lin

ing to crack at the transition from the bottom to the shell if the lining is not properly supported. The manufacturer’s instruc

tions for the lining system should be followed in this regard.
6.3.1 Advantages of Thick-film, Reinforced Linings Thick-film, reinforced linings are often used on aged floors that have incurred corrosion and are roug h and pitted. Because they are less susceptible to mechanical damage than other linings, they would be the lining of choice for tanks in which routine personnel entry and/or mechanical work is anticipated during the life of the lining. Experience has shown that thick, glass-reinforced linings can provide suffi

cient strength to bridge over small perforations in the steel bottom that may develop due to soil-side corrosion. However, this benefit cannot be claimed as part of a maintenance plan because API Std 653 requires re -inspection and repair before a perforation occurs. An API Std 653 internal inspection must be performed before the steel bo ttom thickness is reduced to 0.050 in. (1.3 mm).

The principal advantages of thick-film, reinforced linings are as follows: a. Easier to achieve coverage when applied over rough, pit

ted steel and other surface irregularities. b. Ability to bridge future perforations in the floor steel. c. Resistant to m echanical damage. d. Choice of hand lay-up or chopper gun application. e. Few or no discontinuities to repair following the “holiday” test. f. Long term service–greater th an 20 years resulting in low life-cycle costs. g. Generally provides greater resistance to moisture permeation.
6.3.2 Limitations of Thick-film, Reinforced Linings a. They can require more time and effort to apply b. Are normally more expensiv e to install than thin-film, tank bottom linings c. MFL Floor Scan Inspection of the steel bottom plate through a thick-film, reinforced lining can be more difficult than a thin-film lining. d. Thick-film linings are more prone to cracking if tank bot

tom plate flexure occurs due to non-uniform soil support, and if the strain at the corner weld caused by hoop stress on the shell (e.g., filling and emptying the tank) exceeds the elastic limits of the lining. 6.4 THICK-FILM, UN-REINFORCED LININGS Thick-film, un-reinforced linings may be used as tank bot

tom linings for both new and old storage tanks. However, it is important to note that only fiber-reinforced linings are well proven to have hole-bridging capability.
6.4.1 Advantages of Thick-film Un-reinforced Linings a. Some thick-film linings can be built up to 100 mils (2540 μm) in a single coat. b. Better coverage over rough surfaces. c. No overlap or intercoat contamination and blushing issues with a single co at application. d. High solids may have better edge retention with reduced material shrinkage. e. Typically, fast curing and can be put back in service after 24 hours at normal ambient temperatures. f. Few or no discontinuities to repair following the “holiday” test. g. Reduced labor costs compared to multi-coat thin-film or labor-intensive reinforced thick-film linings. h. Promotes a reduced tank turn around schedule. i. Long term service–greater than 20 years resulting in low life–cycle costs. j. Generally provides greater resistance to moisture permeation.
6.4.2 Limitations of Thick-film, Un-reinforced Linings a. Typically requires the use of plural component spray equipment. b. Difficult to install on complex geometry due to plural component application. c. Contractor experience level should be a consideration. d. MFL Floor Scan Inspection of underlying steel condition may be limited on linings of very high thickness. e. Depending on resin type and thickness, cracking due to plate flexure may be a concern.
6.5 CIRCUMSTANCES AFFECTING LINING SELECTION In addition to corrosion history and the potential for corro

sion, circumstances that must be taken into account during the selection of a tank bottom lining are described in 6.5.1 through 6.5.6.
6.5.1 Temperature

Temperature (e.g. temperatur e changes generated by steam coils) must be taken into account during the selection of an internal lining system. Stor age tanks may operate above ambient temperature in order to maintain low viscosity of theL INING OF A BOVEGROUND P ETROLEUM S TORAGE T ANK B OTTOMS 9
stored product. As temperatures increase, this consideration becomes more critical and the need for careful lining selec

tion is required. Information related to performance limita

tions with elevated service temperatures may be obtained from the lining manufacturer. If this information cannot be obtained from the lining manu facturer, the owner may evalu

ate linings in accordance wi th NACE TM0174 before the selection of the lining system. Tables 1 and 2 list temperature limitations for some common generic lining systems.
6.5.2 Product Quality

With many refined products, such as gasoline, jet fuel, lubricating oils, solvents and other petrochemical products, tank bottoms may be lined not only to prevent internal corro

sion but also to maintain product quality. If lining selection is principally based on product purity, thin-film lining systems may be suitable. However, in some circumstances a combina

tion of product quality and corrosion resistance must be con

sidered. Coatings that are cer tified to MIL-PRF-23236 for fuel service must meet a range of test requirements that are designed to ensure that a lining does not negatively impact key properties of jet fuel and aviation gasoline. Coatings that are certified to MIL-PRF-4556 have tightly controlled chemi

cal composition, which minimizes the threat of fuel contami

nation by the coating. MIL-PRF-4556 does not contain a test requirement to ensure fuel qu ality, therefore, when MILPRF-4556 is specified, a separa te fuel degradation test such as UK Defence Standard 80

– 97, Annex G may also be speci

fied.

The owner may also have to evaluate the product immer

sion liquid to ensure that product contamination by the pro

spective internal lining will no t occur. Certain products, such as fiber-grade ethylene glycol, have quality requirements that can be affected by solvent residues leaching from a newly applied lining into the stored ethylene glycol product. These contaminants (even at very low levels) can interfere with the quality control tests for the high purity fiber-grade ethylene glycol (used in the manufacture of polyurethane fiber). In sit

uations such as this, linings should be evaluated to determine their suitability for the intended service. Linings intended for product quality and corrosion protection must be resistant to the intended tank service and th e probable presence of a con

taminated water layer on the floor.
6.5.3 Presence of Tank Internals

Existing tanks may have design and fabrication features that make the application of a lining impractical or can seri

ously jeopardize the integrity of a lining. For example, inter

nal steam coils, which are used to heat a product to maintain a desirable viscosity, limit accessib ility to the tank bottom dur

ing surface preparation and application of the lining. As a result, a good quality installation may be difficult to achieve. In service, steam coils create local areas where the tempera

ture can be much greater than that of the bulk product. The resulting thermal effects on a tank bottom lining may cause localized coating damage such as blistering or cracking.
6.5.4 Flexibility for Service Change

Changes in tank service may af fect the performance of an existing tank bottom lining. Tank linings do not offer univer

sal resistance. A properly applied tank bottom lining may provide more than 20 years of se rvice life in storing a particu

lar product. A lining that has provided many years of satisfac

tory protection in one pro duct may have inadequate resistance to a new service envi ronment. The need for opera

tional flexibility at some facilities requires that some tanks be available for swing service. Such factors should be consid

ered during the selection an d design of a lining system.
6.5.5 Construction Details that Can Impact the Lining It is difficult to achieve lining continuity when irregular surfaces caused by discontinuous connections such as rivets, butt straps, and skip welding exist because they are difficult to cover and protect with a lining. In old tanks, the problem of poor coverage may be comp licated by chemical contami

nants, which may be difficult to remove. It is common to use caulk to seal lap joints between riveted plates and around riv

ets to provide a continuous surf ace for the lining application. Welded tanks generally require less preparation than riveted tanks.Support steel under cone-roof column supports or floatingroof support column landing plates may be necessary to pro

tect the floor and the lining from impact and wear. The type and extent of previous repairs to the tank (such as internal lap patches or nozzle additions with no back weld) should be taken into consideration.
6.5.6 Upset Conditions

The degradation of a lining is a complex process and, unlike the steel that is to be protected, degradation is not readily quantified by a corrosion rate. A relatively short-term exposure to an unusually aggressive environment can cause irreversible damage to a lining, compromising the protection afforded to the steel. For this reason, a lining must resist potential upset conditions in addition to the usual service environment. 

### 7 Surface Preparation 7.1 GENERAL

As recommended in the scope of this document, NACE No. 10/SSPC-PA 6 and NACE No. 11/SSPC-PA 8 should be considered when determining sp ecific criteria for surface preparation and lining application. Following is a general out

-10 API R ECOMMENDED P RACTICE 652
line of surface preparation c onsiderations covered in these referenced documents. Surface preparation is a criti cal part of the lining applica

tion. Continuous immersion is a severe exposure. Inadequate surface preparation is a major cau se of lining failure. Surface preparation is performed to pr ovide the appropriate combina

tion of surface cleanliness and su rface profile, or the anchor pattern (see 7.5) required to establish good chemical and mechanical adhesion of the li ning resin to the steel. Gener

ally, abrasive blast cleaning to a white metal finish (NACE No. 1/SSPC-SP5) is desired. Ab rasive blast cleaning to a near-white metal finish (NAC E No. 2/SSPC-SP10) is often specified as the minimum degr ee of surface cleanliness. For small areas, SSPC SP 11 is often desirable to avoid damage to the surrounding lining that may be in very good condition. Use of power tools to meet SSPC SP 11 requirements must include the use of abrasive disk s or flapper wheels that pro

vide the specified anchor profile and must be followed by sol

vent wipe per SSPC SP 1 to re move oil conta minants from the power tool. To facilitate inspection and to ensure good adhesion of the lining, surface preparation by abra sive blasting should extend several inches beyond the area to be lined. This practice of framing the area where lining is to be applied helps to ensure that unprepared steel is not inadvertently coated.
7.2 PRE-CLEANING

Prior to abrasive blasting, all hydrocarbon residues such as oil, tar, and grease, must be removed from the area to be lined. Solvent cleaning (see SSPC-SP 1) and high-pressure water or steam cleaning, using the proper chemicals, are effective methods of accompli shing complete hydrocarbon removal. Cleaning is typically fo llowed by a fresh water rinse to ensure complete remova l of cleaning chemicals. It is important to note that typically abrasive blasting is not effective in the removal of sol uble salts. The presence of solu

ble salts on the steel can advers ely affect the performance of a lining resulting in blistering by osmosis. Consideration should be given to a field evaluation for the presence of solu

ble salts whenever there is th e possibility of such contamina

tion. SSPC TU 4 describes common methods for this evaluation. The use of high pressure and ultra-high pressure water jetting NACE No. 5/SSPC -SP 12 has proven to be effective in the reduction of so luble salt contamination. Typi

cally, this specification is used for substrates th at already pos

sess a surface profile and do not require abrasive blasting. For substrates that require a surfa ce profile, there are commercial products available that can be added to a water wash to reduce the presence of soluble sa lts prior to abrasive blasting. 7.3 BOTTOM REPAIR AND WELD PREPARATION The preferred technique for the repair of perforations of the steel tank bottom is welding of steel patches. API Std 653 should be consulted for information on tank bottom repair.

Welds should be inspected before and after blast cleaning. All sharp edges and protrusions should be ground to provide a smooth surface that can be completely and uniformly cov

ered with the lining material . Sharp edges and protrusions may be caused by such things as weld spatter, sharp weld crests, undercutting of the we ld, arc burns, erection clips, plate joints, burrs, and gouges. Chipping, followed by grind

ing, can be used to remove sharp edges. NACE RP0178 can be used to specify the surface fini sh of welds. Typically, weld finish “C” or “D” is specified.
7.4 ENVIRONMENTAL CONDITIONS DURING BLASTING Abrasive blasting should not be performed if the tempera

ture of the steel surface is le ss than 5°F (3°C) above the dew point or if the relative humidity is greater than 80% (see 8.3). The surface to be lined should be of the specified level of cleanliness at the time the lining is applied. If the surface is degraded or contaminated subsequent to surface preparation and before lining application, the specified level of cleanli

ness should be restored before lining application.
7.5 SURFACE PROFILE OR ANCHOR PATTERN

The abrasive used for blasting should be selected to pro

duce the necessary profile depth, or anchor pattern, for the lining to be applied. The li ning manufacturer’s recommenda

tion for surface profile depth must be achieved in order to optimize the mechanical adhesion of the lining to the steel tank bottom. The anchor pattern required for linings is typi

cally 1.5 – 4.0 mils (38 – 102 (m) and generally increases with the thickness of the lini ng. To achieve adhesion neces

sary for long-term performance , it is important that the anchor pattern is sharp and angular.
7.6 AIR AND ABRASIVE CLEANLINESS

The abrasive and compressed ai r supply used for abrasive cleaning of tank bottoms should be free of contaminants such as water soluble salts, dirt, cl ay, oil, and grease (per SSPC AB1, AB2, AB3, and ASTM D 4940, as appropriate). If present in the blasting abrasive , small amounts of these con

taminants may be delivered to the steel surface during the cleaning operation. This contamin ation will reduce the useful life of the lining.L INING OF A BOVEGROUND P ETROLEUM S TORAGE T ANK B OTTOMS 11

7.7 REMOVAL OF DUST Spent abrasive (dust) must be removed from surfaces. Standard practice has been to blow-down surface s with clean, compressed air, but this can be a messy operation, especially in small tanks. Vacuum cleaning methods have proved to be more efficient. 

### 8 Lining Application 8.1 GENERAL

For thick-film laminates, the coating manufacturer may recommend that a prime coat be applied at a film thickness less than that of th e anchor pattern achie ved by the abrasive blast cleaning. If a primer coat is applied, it is important to follow such instructions to prevent disbonding or delamina

tion of the subsequently applie d lining. Experience has shown that it is difficult to consistently apply primer coats at the low thickness required. When not mandatory, it may be better to omit the primer. Subsequent coats must be applied within the recoat interval recommended by the lining manufacturer and/or as deter

mined by the owner’s inspector. Generally, the recommenda

tions and procedures prescrib ed in SSPC-PA 1 should be followed. After sufficient curing of the completed lining, hol

iday testing (as described in 9.3. 4) should be carried out. Any defects should be repaired in accordance with the coating material manufacturer’s recommendations and the written specification.
8.2 GUIDELINES FOR LINING APPLICATION SSPC-PA 1 provides general gui delines for good lining application practice. Proper on -site storage conditions, mix

ing, applying, and curing of the lining are essential proce

dures, and the lining manufacturer’s recommendations should be followed. Any differences between the owner’s specifica

tion and the lining manufacturer’s recommendations should be resolved before beginning the job.
8.3 TEMPERATURE AND HUMIDITY CONTROL

The temperature of the steel surface should conform to the lining manufacturer’s recommended application and curing ranges. As a general rule, the surface temperature must be at least 5 ° F (3 ° C) above the dew point temperature in the tank and the relative humidity should be below 80% at the steel surface. If the surface temper atures and/or humidity level expected to deviate from the recommended range, temporary climate control equipment should be employed to ensure the proper conditions are maintained. It should be noted that durations of surface preparation, lining application, and cure may be continuous over a 24-h our period. If so, the required environmental conditions must be maintained around the clock. NACE 6A192/SSPC-TR 3 provides guidance on the use of dehumidification and heating equipment for environmental controls during tank lining work.

Temporary climate-control equipment is also used to advantage by protecting worker s from heat stress during hot summer months. Improved productivity, due to better work

ing conditions, is a secondary benefit.
8.4 LINING THICKNESS

Insufficient film thickness will not provide adequate cover

age or protection. Excessive film thickness beyond the manu

facturer’s recommended rang e can compromise lining adhesion and film integrity. Excess primer thickness is a com

mon cause of failure of thick-film lining systems. The lining thickness shall be in accordance with the lining specification. Thickness should be determined in accordance with the meth

ods outlined in 9.3.2. Changing or alternating colors between coats can aid in assuring un iform coverage and thickness.
8.5 LINING CURING

Improper application and inad equate curing time are major causes of premature lining failur e. The adhesion and integrity of the film are adversely affected if a lining has not been applied and cured properly. Prior to removing forced ventila

tion or closing the tank, the lining should be completely cured to obtain optimum service life. Refer to the coating manufac

turer to determine the proper cu re time and temperature. The proper curing conditions should be ensured for the full dura

tion of the cure time, or forced-curing of the lining may be accomplished by circulating warmed, dehumidified air (see 8.3 and NACE No. 10/SSPC-PA 6). Solvent-borne linings require forced ventilation of the air space adjacent the lining. As th e heavier-than-air solvents evolve from the wet lining, they will rest atop the lining, impairing the completion of this process. Dissipation of sol

vent vapors must occur so enough solvent can evolve from the film to achieve a level of cure necessary for hydrocarbon or chemical resistance. 

### 9 Quality Control Inspection
9.1 GENERAL

Inspection is strongly recommended to ensure that the lin

ing specification has been met. The lining should be inspected during all phases of the work and upon completion of the work. Records should be made to briefly describe the products and procedures that were used during installation of the lining. Records will be important the next time the tank is opened to associate the lining product and installation process with the lining performance. Records will also be valuable if repairs are needed and a repair product and repair procedure must be developed.12 API R ECOMMENDED P RACTICE 652

9.2 QUALIFICATION OF INSPECTION PERSONNEL All lining inspectors should be either NACE or SSPC certi

fied, or persons who have demonstrated a thorough knowl

edge of coating and lining practices.
9.3 RECOMMENDED INSPECTION PARAMETERS 9.3.1 Surface Cleanliness and Profile

Verification that the specified surface cleanliness and pro

file have been achieved before application of any lining is of utmost importance. It is important that the coating be com

pleted before any flash rusting is observed. SSPC-VIS 1 pro

vides reference photographs that may be used to visually assess surface cleanliness. NACE RP0287 provides a method of measuring surface profile. Other types of profile compara

tors are available from the SS PC and coating instrument ven

dors.
9.3.2 Film Thickness

As the lining is being applied, wet film thickness measure

ments should be made in acco rdance with ASTM D 4414. After the lining has cured sufficiently to allow handling, dry film thickness measurements should be made in accordance with SSPC PA 2.
9.3.3 Hardness

If specified to aid in determination of degree of cure, hard

ness of the lining should be measured in accordance with ASTM D 2583. It should be noted that this test could be destructive to organic resin linings that are not sufficiently thick, hard, and/or cured.
9.3.4 Lining Discontinuities

Holiday testing of thick-film linings shall be carried out with a high-voltage detector in accordance with NACE RP0188. Holiday testing of thin-film linings should be per

formed with a low-voltage (67.5 volts) wet sponge detector. 

### 10 Evaluation and Repair of Existing Linings 10.1 GENERAL

A properly selected and applied tank bottom lining should be expected to provide a minimum service life of 20 years. Some lining systems, most nota bly thick-film laminates, have provided 25 – 30 years of service life. Lining “failure” is not well defined and fitness for service is not well established for polymeric coatings. Linings degrade with time. However, blistering is a common mode of lining deterioration. How

ever, blistered linings may remain fully functional, providing corrosion protection to the steel for many years. Lining deg

radation does not necessarily translate to putting the steel at significant corrosion risk.

When available, tank bottom linings should be thoroughly inspected to assess their condition and determine the need for any repairs. Timely maintenance can keep repairs to a mini

mum and greatly extend lining service life. Care should be taken not to damage the lining (especially thin-films) during cleaning and inspection. API St d 653 provides guidance for visual in-service and detaile d out-of-service inspection and repair methods for tank compon ents. These inspections may reveal conditions that necessita te lining repair, which are not covered in API Std 653. All repairs to the tank should be completed before any repair of the lining.
10.2 EVALUATION METHODS

Lining evaluation methods include: a. Visual inspection. b. Adhesion measurement. c. Audible testing (to find areas of delamination on thick film reinforced linings via tapping with a solid metal object). d. Physical examination of lining sample, including possible laboratory testing (to determin e permeation by the tank’s pre

vious product, film thickness, brittleness, and/or adequacy of cure). e. Holiday testing (This is not typically recommended for linings that have been in prev ious service, si nce the presence of moisture in the film can cause damage when exposed to voltage. In some instances, this has been successfully achieved after tank has remain ed open and the lining exposed to normal ventilation for seve ral months. Consultation with the coating manufacturer prior to attempting this type of inspection is necessary).
10.3 EVALUATION CRITERIA FOR LININGS

Evaluation of existing tank linings should be based on the following criteria: a. How long has the existing lining been in-service? b. How well has the existing lining performed to date? c. The desired service life of the lining (i.e. how long must the lining do its job before it will be inspected and receive required maintenance?) d. The intended exposure conditio ns (i.e. intended service of the tank, operating temperature, whether water will be present, whether other contamin ants or chemicals will be present and their concentrations. e. The specifications and character istics of the existing lining.
10.4 EVALUATING SERVICEABILITY OF EXISTING LININGS The evaluation methods listed in 10.2 should be used to determine if an existing lining is suitable for service. Blister

-L INING OF A BOVEGROUND P ETROLEUM S TORAGE T ANK B OTTOMS 13
ing, cracking, crazing, discolor ation, and areas of missing lin

ing are modes of degradation that can be detected by visual inspection. However, these types of degradation may not be readily visible unless the floor is thoroughly lighted, cleaned, and accessible. Other modes of degradation, that may not be readily visible, are permeation of the lining by hydrocarbon, delamination, and loss of thickness due to abrasion and/or chemical attack. These modes of degradation may require the use of the other examination techniques in 10.2 to be detected. Following the examinations, the evaluator should apply the criteria in 10.3 to determine if the lining is suitable for service.
10.5 DETERMINING THE CAUSE OF LINING DEGRADATION/FAILURE If lining degradation is detect ed, the cause and extent of coating degradation must be es tablished, as well as whether or not the existing lining is suitable for a repair. When evalu

ating the condition of an existing lining, one should consider whether deterioration is premature or whether the lining has achieved its anticipated performance life.

If degradation or failure of a lining is premature, it is important to understand and address the cause of such degra

dation prior to determining whether the lining should be allowed to be repaired or re furbished vs. be completely replaced. A review of the tank’s operating history and a visual examination of the lining should be conducted to determine whether the problems were a result of environmental attack, local mechanical damage, and/or if inadequate surface prepa

ration or improper lining installation were contributing fac

tors.
10.6 LINING REPAIR AND REPLACEMENT

The term “repair” of a lining is typically used when either portions of the lining will be re placed or when al l or a portion of the lining will be topcoated. The term “replacement” is used when all of the existing lining is removed and a new lin

ing is applied.
10.6.1 Localized vs. General Degradation

The amount of the floor area that has failed or deteriorated and the size of the tank are significant factors in determining whether only portions of, or the entire lining, should be replaced. If only a few, small areas require lining replace

ment, and the tank is fairly large, it is usually more cost effec

tive to use power tools to achieve the required level of cleanliness and anchor profile depth rather than to introduce abrasive into the tank. For thin-film linings in good condition, open blasting in a tank is not advised as the removal of the abrasive material often damages the existing lining. 10.6.2 Spot Repairs Spot repairs are made when there are only localized fail

ures, such as blisters, pinholes, delamination, or mechanical damage. Usually, the existing linin g is removed, the surface is prepared, and lining materials are applied at the failed areas only.
10.6.3 Topcoating an Existing Lining

Thick-film reinforced linings can be topcoated to extend the life of an existing coating that has good adhesion and integrity. The topcoat is applied to ensure the fibers are not exposed to the product. Accepted practice involves removal of contaminants, then brush-blasting and application of one or more topcoats. To ensure good adhesion of the repair, the lining manufacturer should be consulted to assess the com

patibility of the topcoat material with the existing lining.
10.6.4 Repair or Topcoating Specifications

Consideration should be given to the lining manufacturer’s recommendations when developing the repair specifications. All differences between this recommended practice and any other should be resolved before starting any lining repairs.
10.6.5 Lining Removal Methods

Considerations that affect the method of lining removal are: a. Size of repair. b. Type of lining. c. Whether steel is contaminat ed with oil or chemicals.

If the mode of degradation of a thick-film, reinforced lin

ing included delamination, it should be noted that manual removal of the un-adhered laminate is more cost effective.
10.6.6 Sequence of Contamination Removal vs. Lining Removal by Blasting Regardless of whether a lining will be completely removed and replaced or will receive spot repairs or topcoating, it is important to detect and to identify visible and/or non-visible contaminants. If such conta minants include hydrocarbons, grit blasting without first removing the oily hydrocarbon may adversely affect the new lining ’s adhesion. If oily hydrocar

bon has come into contact with the steel, it is critical that the contaminant be removed before abrasive blasting. 

### 11 Maximizing Lining Service Life by Proper Material Selection and Specification API Std 653 specifies the maximum interval between inter

nal tank inspections to be 20 years without the application ofalternate internal inspection intervals determined by riskbased inspection. Corrosion on the topside of the tank bottom14 API R ECOMMENDED P RACTICE 652
is a factor in determining a proper interval between tank inspections. Corrosion protection afforded by an internal lin

ing mitigates the corrosion rate on the topside of the tank bot

tom and allows the se rvice interval betw een tank inspections to be maximized. However, linings do not last forever. Typically, they become less effective over time. The deterioration rate can be fast or slow. Experience has shown that some linings have failed in less than a year and some linings have been found to provide adequate corrosion protection after more than 20 years of service.
11.1 LINING MATERIAL SELECTION

Unless the specifier has experience with a given lining material’s performance in a given service, he/she should require third-party test data and references supporting the considered material’s suitability for the intended service and operating conditions.
11.2 WRITTEN SPECIFICATION

The specification should be ve ry job-specific and include a detailed scope, a specific description of the components to be lined, and a list of all responsibilities and tasks of the contrac

tor. As a minimum, the specifi cation should address the rele

vant aspects cove red by NACE No.10/SSPC-PA 6 and NACE No. 11/SSPC-PA 8 as follows: a. Steel plate preparation and weld surface quality. b. Applicator qualifications and submissions. c. Surface preparation, including criteria describing the abra

sive, steel cleanliness, anchor profile, removal of dust and contaminants, and waste handling, and removal. d. Environmental controls. e. Control of solvent vapors. f. Need for wet film thickness measurements. g. Applicable heat curing requirements. h. Dry film thickness range required and criteria as to method of measurement. i. Holiday testing requirements. j. Method for determination of cure. k. Final inspection requirements. l. Labeling or stenc iling requirements for lining identification. m. Inspection requirements. 

### 12 Safety 12.1 GENERAL

Prior to the application of internal tank linings, proper training of employees regarding safe work procedures and the provision of the necessary supervision and/or inspection throughout the progress of the job is required. Guidance on federal training requirements is given in OSHA 2254. A doc

umented hazard evaluation as outlined in OSHA 29 CFR 1910.132 is required to determine what personal protective equipment (PPE) may be needed.

This section will not attempt to detail all of the safety pre

cautions and procedures required to safely enter a tank, pre

pare the necessary surfaces for lining, and apply the specified lining material. Some of this information is presented in regu

latory and industry documents. General safety concerns are emphasized in 12.2 through 12.4.
12.2 TANK ENTRY

All necessary precautions to protect personnel shall be taken before entry and while working in a storage tank. Working in a confined space such as a pe troleum storage tank presents special respiratory, e xplosion, and fire hazards that must be addressed. Tank entry and/or hot work permits should be issued and enforced as local work rules and appli

cable regulations require. Guidelines for issuing permits and preparing a tank or confined sp ace for entry are detailed in API Std 2015 and RP 2016, including evaluation of the atmo

spheric hazards and lockout-ta gout of process lines and equipment. Federal (OSHA 29 CFR 1910.146) and state reg

ulations pertaining to confined space entry also should be reviewed to ensure conformance.
12.3 SURFACE PREPARATION AND LINING APPLICATION Health hazards are a prime co ncern during surface prepara

tion and lining application. Proper respiratory equipment and personal protective clothing should be employed where nec

essary. Information regarding safety precautions and proce

dures during surface preparatio n and lining application are found in OSHA 29 CFR 1910.94, and SSPC PA 3.

If lining materials containing or previously exposed to lead are to be removed, special prec autions are required to protect both the personnel and the en vironment. The specific require

ments for worker protection from lead can be found in OSHA 29 CFR 1926.62. Relevant federa l and state regulations should also be reviewed to ensure conformance.
12.4 MANUFACTURER’S MATERIAL SAFETY DATA SHEETS The chemical make-up of high performance, internal tank lining materials can present heal th hazards to workers if not handled properly. Material safety data sheets (MSDS) con

cisely inform employees about the materials being used so that they can protect themselves and respond properly to emergencies.L INING OF A BOVEGROUND P ETROLEUM S TORAGE T ANK B OTTOMS 15
The purpose of an MSDS is to tell the worker: a. A material’s physical properties, which make it hazardous to handle. b. The type of personal protective equipment needed. c. The first aid treatment necessa ry if exposed to a hazard. d. The planning needed for safely handling normal opera

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