ABSTRACT

Lord Cullen's report on the Piper Alpha disaster docs not recommend a mandatory requirement for all hydrocarbon pipelines to have subsea isolation valves(SSIVs) However, the requirement of SSlVs will be determined through a Formal Safety Audit This paper briefly reviews the impact of the Cullen report on the pipeline system design and the requirement of SSIVs including preliminary proposals to dispose off the mapped hydrocarbon Inventory An overview of the SSIV system design identifies the cost effective approach without affecting the SSIV reliability After identifying testing, inspection and maintenance requirements, the paper discusses their impact on the design Finally, a conceptual design of a maintenance frame is presented which should help In reducing diving time during SSIV maintenance.

INTRODUCTION

Unfortunate events In the North Sea over the past few years lead the U K Government to review safety policies and practices of North Sea operators and regulatory bodies As a result of this review, Statutory Instrument No 1029 was introduced which makes it mandatory for all offshore installations which Import or export hydrocarbons to incorporate Emergency Shutdown Valves Into the risers at locations above the splash zone These valves arc required to have a positive safe control system to close the valves which detects and responds to an emergency There are, however no mandatory requirements for pipeline operators to incorporate subsea emergency/isolation valves

The report by Lord Cullen following the Public Inquiry Into the Piper Alpha disaster makes comprehensive recommendations for improving overall safety of North Sea installations The whole safety process should start at the conceptual design stage by way of a Formal Safety Audit (FSA) and finally lead to a Safety Case which also includes safety management systems The inquiry looked Into the hydrocarbon pipeline operations and makes certain recommendations The Cullen report endorses Statutory Instrument no 1029 and docs not recommend a blanket requirement for subsea isolation valves(SS1Vs) The need of such valves would depend upon the Safety Case developed for each offshore installation

Although neither the Department of Energy nor the Cullen report spell out mandatory installation of SSIVs, it is expected that most pipelines transporting gas and many transporting oil will be fitted with some form of barrier system Many new and operational pipelines have already been fitted or planned to be fitted with isolation valves

The purpose of this paper is to briefly review the Impact of the Cullen report on the pipelines system design and to identify situations where SSIVs can lead to an improvement In the safety of the pipeline systems and hence that of the installation and the personnel working on oil Some modifications to riser design have been identified in this paper which would lead to rapid evacuation of the product, particularly the gas, trapped between the SSIV and the riser topsides ESDV during an emergency shutdown The paper presents a brief overview of the SSIV design and associated control and protection systems An Important aspect of the design should be its implicitly without sacrificing the integrity and operability

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