Crediting Check Valves As IPLs: a Testing Protocol to Better Understand Check Valve Reliability

Conventional process safety wisdom assumes that check valves are not reliable safeguards. Experience indicates that check valves are prone to failure and that they may fail undetected. Therefore, the conservative assumption is that check valves may be listed in process hazard analyses as safeguards, but they are rarely considered to meet the standards required of an independent protection layer (IPL). Independent protection layers must be effective, independent, and auditable. Although independence is readily achievable by check valves, confirming and routinely auditing effectiveness is rarely pursued. Remarkably little data is available from operating companies regarding failure and leakage rates for various check valve types in various service applications or at various stages of service life. From an equipment reliability standpoint alone, the lack of concern and information regarding the functionality and performance of check valves is surprising. This paper describes testing protocol that was put in place in 2014 for the purpose of testing check valves in order to apply layer of protection analysis (LOPA) credit to these valves for reverse flow scenarios. In order to understand check valve performance expectations, leakage allowances for new check valves are reviewed. Industry guidance and standards regarding consideration of check valves as safeguards or IPLs are also discussed. The analysis of new valve standards and the assessment of process safety requirements are the basis for establishing the pass/fail thresholds for the tests. The goal of sharing this information is that the discussion will stimulate others to consider the opportunity and the need to set-up similar testing and to begin gathering and sharing a larger body of data on check valve performance in various applications. Accumulation of check valve performance data and sharing of that data should lead to better understanding of check valve performance by type, size, age, and service, as well as better design and selection as learnings are incorporated into design and application. In certain instances where requirements are met and credit is due, check valves may potentially be credited in PHA and LOPA.