A Novel Approach to Estimating Proof Test Coverage for Emergency Shutdown Valves using a Fuzzy Inference System

Published proof test coverage (PTC) estimates for emergency shutdown valves (ESDVs) show only moderate agreement and are predominantly opinion-based. A Failure Modes, Effects, and Diagnostics Analysis (FMEDA) was undertaken using component failure rate data to predict PTC for a full stroke test and a partial stroke test. Given the subjective and uncertain aspects of the FMEDA approach, specifically the selection of component failure rates and the determination of the probability of detecting failure modes, a Fuzzy Inference System (FIS) was proposed to manage the data, addressing the inherent uncertainties. Fuzzy inference systems have been used previously for various FMEA type assessments, but this is the first time an FIS has been employed for use with FMEDA. ESDV PTC values were generated from both the standard FMEDA and the fuzzy-FMEDA approaches using data provided by FMEDA experts. This work demonstrates that fuzzy inference systems can address the subjectivity inherent in FMEDA data, enabling reliable estimates of ESDV proof test coverage for both full and partial stroke tests. This facilitates optimized maintenance planning while ensuring safety is not compromised.