Partial stroke tests as a procedure for the extension of the proof test interval

Abstract: This paper describes a procedure to reduce the probability of failure on demand (PFD) for systems and to extend the proof test interval by using partial stroke test (PST). The goal of partial stroke tests is to discover a part of the dangerous undetected failures at an earlier time. The difference between a partial stroke test and a proof test (PT) is that a component is only partially tested by a PST. However, after carrying out a PST, the system has a residual of dangerous undetected failures. This residual can be eliminated by a proof test. The probability of failure can be improved with the diagnostic coverage factor for partial stroke tests. It is important to know the difference between probability of failure PFD and the average probability of failure PFDavg. The values of both PFDs with partial stroke test are lower than the probability of failure without partial stroke test. The factor B shows the improvement between a system with and without partial stroke tests at the time of the proof test. The larger the factor B is the larger is the system’s improvement