A Strategy for testing Safety Instrument Functionality

摘要

Safety Instrumented System must be periodically maintained and tested to ensure their Probability of Failure on Demand is kept below the upper limit in relation to its associated Safety Integrity Level (SIL). On this paper is described the strategy implemented to facilitate effectiveness and ease proof testing of the elements performing a Safety Instrumented Function (SIF) at a chemical plant facility for SIL 3 and SIL 2 protection. Strategy scope includes utilization of intelligent instrumentation delivering information about their healthy function, automation of SIF test with reporting capability and installation of digital ESD valves with partial-stroke capability in order to perform more frequent test (but partial) in those units where SIF test only can be performed during plant shutdown. During the execution of the project several potential options were discussed, current and desire states were analyzed, some performance metrics defined, human-machine interface designed, a set of typical configuration were defined from both hardware and software point of view. A pilot project was conducted to validate the concept before to rollout across the whole plant. Architecture implemented, lesson learned and benefits are discussed which can be helpful for those interested into apply a similar concept to reduce maintenance cost without compromise plant safety.