The Health and Safety Executive (HSE) has issued a circular to HSE Offshore Safety Division (OSD) inspectors describing how to assess the acceptability of riser emergency shut down valve (ESDV) leakage rates. The circular is a "semi-permanent circular", which is usually issued by the HSE if there is a particular 'hot topic' which they feel requires attention, and any new guidance regarding riser ESDVs should be of particular interest to operators in the North Sea.

A definition of an ESDV is provided in the Pipeline Safety Regulations 1996 (PSR), being a valve which is capable of adequately blocking the flow of fluid within the pipeline at the point at which it is incorporated. Specific provisions relating to ESDVs are contained within Schedule 3 of PSR, and include provisions relating to inspection, testing, maintenance, use and the mechanics of ESDVs. Whist an ESDV must be capable of "adequately" blocking the flow of fluid, minor internal leakage through the ESDV may be accepted in certain circumstances, providing there is no threat to safety.

Duty Holders are not required to meet fixed criteria for maximum riser ESDV leakage rates, rather, as stated in the circular issued to inspectors this week, the rate of leakage should be based on an installation's ability to control the hazards presented by such a leak. OSD's fire and explosion specialist inspectors will assess methodologies used by duty holders, and where inspectors find that ESDV leakage has risen above that previously considered acceptable (1sm3/min gas or 6kg/min oil), the issue will be re-assessed by OSD.

The circular details certain mitigation measures that can be taken into account by inspectors when assessing riser ESDV leakage rates, including automatic closure of wellhead, down hole, and process isolation shut down valves, automatic closure of other import and export ESDVs, and the extent to which any bunding and drainage can be shown to be unobstructed and have the required capacity. The location of the ESDV will also be of relevance, for example if it is in a well-ventilated area or on grated decks or platforms. Certain issues are expected to be included in the consequence-based hazard analysis of ESDV leakage, including the consequence of leakage (consequence to personnel, impairment of safety-critical elements etc), separation distances between safety critical elements, whether there are multiple ESDVs, and alarm and action levels.

These mitigating factors and hazard analysis issues are detailed in full within the circular, please click here to view the circular. 

This article was written for Law-Now, CMS Cameron McKenna's free online information service. To register for Law-Now, please go to www.law-now.com/law-now/mondaq

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The original publication date for this article was 28/07/2010.