Living with 61508 [relay based trip systems replacement at refinery]

This paper describes the experience gained over the 3 years at the Phillips Imperial Petroleum Refinery, Teesside. PIP is a joint venture between Imperial Chemical Industries and Phillips Petroleum Ltd. The crude oil refinery is operated by ICI. It is a CIMAH registered site, COMAH application is in progress in line with changes in legislation. During 1997, the plant availability was not as good as it could have been, due to spurious safe tripping of the installed relay based trip systems. The opportunity was identified to replace this system with a new black box trip system, to improve plant availability. This developed from analysis of trip data, which is reported as part of existing procedures. This analysis demonstrated the root cause of several trips had been fail safe action of the trip system. The review of options for replacement identified the value of a digital data link between a programmable replacement and the existing plant distributed control system. The paper describes the replacement of the relay trip system by linking existing ICI group procedures to the draft 1508 standard. The system has been operated and maintained to the adopted 61508 standard by applying the same mapping process from ICI group procedures. The result is a functionally safe programmable trip system, within the bounds of 61508