I penned down some of my thoughts based on my experiences in SIL studies and verification.
1) The Norwegian Guideline - Application of IEC 61508 and IEC 61511 In the Norwegian Petroleum Industry Rev 02, Dated 29th October 2004, Page 46, clearly states the proof testing requirements. (i.e. whereby partial stroking is acceptable practice to ensure reliability). This section also clearly indicates what should adopted as a procedure if partial stroking is applied on the facility.
Cut the long story short, if an integral test is not possible due to safety or operational reasons, a non-integral (partial) test may be performed for each sub-system comprising the SIS loop. Some sub-systems may be tested under normal operation by providing inhibit of the input signal or override of an output action. Testing of other sub-systems such as e.g. valves often causes process shutdown and may therefore be performed during planned shutdown periods.
“It should be noted that although partial function testing reduces the need to fully test the SIS loop, a complete integral test should still be performed at certain intervals”.
In standard practice, “Planned Shutdown Period” will be used to test all SCEs and this needs to be mentioned in Performance Standard.
2) GS-371 (i.e. TOTAL Specification) does recognize ESDV partial stroking which is quite norm in O&G facility. Once again based on my experience - Often PERIODICAL SHUTDOWN is utilized for full FUNTIONAL TEST and during normal production we live with PARTIAL STROKING.
3) Last but not the least, for SIL verification purpose, in line with GS-371, IEC 61508/61511 “partial stroking” can be taken into consideration for PFD calculation.