Track 2 Session 2
10:20 to 11:30 a.m. Wednesday April 11, 2007

 Estimating Reliability Parameters and Demand Availability for Well Emergency Shut-Down Systems on Offshore Platforms

The valves activated by the Emergency Shut-Down (ESD) system on an offshore platform act to shut off the flow of oil or gas from the wells in the event of a breach of the topsides process equipment, downstream of the flow wing valve. Reliability-wise, each well forms a 3-component parallel system with the platform reliability being given by up to 40 wells comprising a series system. The ESD system is a Safety Instrumented System (SIS) to which the general requirements of IEC 61508 may be applied. This presentation analyses the ESD test data from a large platform consisting of 35 wells showing the issues around the estimation of the component failure rates, specifically the valves. Failure rates from well test histories are calculated using parametric, non-parametric and Bayesian methods and the results are compared with failure rates published in industry databases. The test interval and the next test date, given the valve failure rates and the ESD availability at the platform level to meet Safety Integrity Level (SIL) 3, are predicted using spreadsheet functions. A spreadsheet simulation of the combined well ESD testing is used to validate the ESD availability calculations for the platform.