Abstract: As the earliest in-service LNG terminal in China, GDLNG terminal had adding/modifying some equipments and safety instrumented function (SIF) after five years' heavy duty operation. To ensure the integrity and reliability of the safety instrumented system(SIS) in terminal, and the availability under heavy duty operation, terminal had performed Hazard and operability study(HAZOP). Based on the hazardous scenarios identified in HAZOP, Safety integrity level(SIL) classification, SIL verification and SIL re-validation had been performed to LNG terminal. The SIL classification is using layer of protection analysis(LOPA) method, which is less conservative than risk graph method used in design phase. According to SIL verification result, some SIFs in the terminal can not match SIL classification requirement. Sensitivity analysis had been performed to those SIFs. Impacts of optimizing SIS system configuration (without component hardware change,i.e., proof test interval, proof test coverage etc.) to the probability of failure on demand(PFD) had been studied. According to the sensitivity study result, SIL level can be somehow modified without component hardware change. Under certain circumstance, it can help us to a more cost-effective approach to fulfill company SIL requirement or risk acceptance criteria. Key technical points/difficulties and its possible solutions with SIL verification study are summarized, as well as the prospective development of SIL study.

Key words: natural gas; process control; safety instrumented system; SIL validation; PSMSuites; Markov model; sensitivity study