Flowserve MX Electronic Actuator SIL Safety IOM - Manual (Page 8)

Limitorque MX Electronic Actuator FCD LMENIM2350-01 – 9/13
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FLOWSERVE PROPRIETARY INFORMATION
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2.4 Proof Test Period (Tpt)
Full stroke test at least once per year ==> 8760 hr
Based upon the extent of the proof test, failures undetected during normal operation or during PST may be uncovered
during full proof test.
2.5 Failures in Time (FIT)
Number of failures in time.
2.6 Mean Time to Restoration (MTTR)
Average failure detection time plus average repair time.
2.7 SFF
Safe failure fraction.
2.8 PFD
avg
The average probability of failure on demand for a safety function (approximate).
2.9 RRF
Risk reduction factor.
2.10 SIL vs PFD
avg
vs RFF
Table 1 is based upon “low-demand Mode,” i.e., the safety function is required to be operated no more frequently than
twice the proof test period (see 2.4 ).
Table 2.1 - SIL vs PFD
avg
SIL PFDavg RFF
4 10 -5 … < 10 -4 10,000 to 100,000
3 10 -4 … < 10 -3 1,000 to 10,000
2 10 -3 … < 10 -2 100 to 1000
1 10 -2 … < 10 -1 10 to 100