Testing of Safety Systems: Bad Effects and Their Modelling with Comparative Studies

Abstract

Safety systems are used in the process industry for many years. The application of these system is based on IEC 61508 standard. In this standard, proof testing is recommended in order to achieve the required SIL. It is common to assume that all the proof tests are complete and all the failure modes are covered. However, it is not always true. The main objetive of this thesis is to assess the impact of degradation due to proof test and also evaluate the impact of incomplete testing. In order to do that the ATSV and MTSV failure rate models are proposed based on DNV-GL papers. Another approach using multi state models are used. The Multiphase Markov model is used to reflect the effect degradation due to proof testing and test incompleteness. The BOP and the HIPPS valves were used as example to PFD assessment since there are historical data that theses system can face degradation if a complete test is performed. ii