Seismic Evaluation of Topsides Systems on Existing Platforms
Authors: Johnson Gayle S. , Smith Charles E. 
Published: October 2008

This paper summarizes the results of a joint industry project (EQE, 1995) with development funding from the United States Minerals Management Service (MMS) to develop and implement on a trial basis a methodology to evaluate offshore platform topsides equipment and appurtenances for seismic loads. Voluntary peer review was provided by several operators with platforms in seismic regions. The methodology has been tested on a trial basis on several platforms located in different regions of the world.

A screening evaluation criteria has been developed, focusing largely on lessons learned from earthquake experience of onshore processing facilities. Guidance is given that can be used in a methodical visual review of the platform, coupled with limited analytical checks to governing codes. A method of limiting and prioritizing the scope of the review by focusing on critical elements is defined, using process safety management techniques.

Introduction

The primary focus of this paper is to present the overall evaluation methodology, screening evaluation criteria, and methods of documentation for evaluation of topsides equipment and systems for seismic loads. This paper presents background information with regards to requirements for seismic evaluation of topsides, and the details of the methodology. It also presents results of trial assessments of several platforms utilizing the methodologies presented in this paper.

The development project has defined a detailed methodology for platform topsides seismic evaluation that is intended to be cost-effective, yet consistent with the intent of API RP 2A. The trial assessments have demonstrated the methodology on a trial basis and provided a means for critical review of the methodology.

Background

A great deal of effort has been expended in recent years to address the requalification of offshore platforms. Although the primary focus has been on the platform structures, i.e., jackets, the risks associated with topsides equipment and topsides have also come under increased scrutiny.

In December 1992, the Operations Working Group at the International Workshop on Seismic Design and Reassessment of Offshore Structures, held in Pasadena, CA, developed a detailed brief which included recommendations for focused efforts to improve the practice of seismic reassessment. The first recommendation was for the development of assessment procedures for existing equipment, including a practical "checklist" reflecting post-earthquake experiences from onshore refineries and processing plants.

API has incorporated topsides seismic provisions into the 19th and 20th Editions of RP 2A. The guidelines and commentary give guidance as to primary areas of emphasis for evaluations as well as guidance for how to evaluate existing equipment, including a recommendation that field inspections of equipment and piping be performed by experienced personnel.

Section 17 of RP 2A recommends that the 20th edition topsides provisions be used to evaluate equipment on existing platform.

Other forums have addressed the issue, such as the MMS and California State Lands Commission Workshop on Public Policy Issues on Seismic Requalification of Offshore Platforms, held in Camarilla, CA, in November, 1993, and the Workshop on Assessment and Requalification of Offshore Production Structures held in New Orleans in December 1993.

All of these forums have included input from industry representatives, regulatory authorities, and engineering specialists.