I have customers that are asking for SIL (safety integrity level) certification on industrial valves.

I don't have experience on this filed
I read some technical notes and the reference ISO / EN (EN 61508, EN 62061, prEN ISO 13849-1) standards and not it's clear to me what is SIL.

By I still have some unsorted pratical questions:

1) how to calculate pratically the SIL parameters (in detail the PFD) for a industrial valve? It's necessary to make serial test or what?

2) the SIL certifcation must be issued by an indipended body or by the valve manufacturer?

3) they are already on the market some brands that offer SIL certification? I yes who?

Mi questions are realted mainly to
- gate valves NPS 2" and over
- buttefly valves as above
- check valves as above
- ball valves as above

Prior to discussing certifications, understanding of the required Safety Integrity Level (SIL) is necessary. SIL levels are not reached by purchasing certificates.

In IEC61511-3 it is explained how to determine the required SIL, which then in turn also explains the SIL.
The IEC61508-7 B6.6.5 refers to the IEC61025 for the Fault Tree Analysis which I feel show very well what happens when you calculate the PFD of the system you are installing. Then the system PFD should be compared with the required PFD (according to required SIL).

1) A PFD should be calculated for the complete system and the applicable element (e.g. valve) only.
In order to calculate it the failure rate applicable for your specific situation is required. So the failure rate applicable for: your stroking time, your environment (like desert or arctic), your fluids (like contains sand or not), your process (like size / rating etc.).
A failure rate from serial test should not be used, field experience should be used.

You also need the testinterval. How often you want to perform a full stroke test?

2) The product certificate shall be issued by an independent authority. Dependent of the required SIL a verification of the complete system shall be performed by an independent authority as well. You shall also read and verify the report yourself for all SIL levels.

3) They exist on the market.

Typically shutdown valves are line class valves specified in compliance with ASME B 16.34 and API SPEC 6D (ISO 14313).  API 6D addresses bonnet and stem leakage in addition to seat leakage.  Soft seated valves are initially bubble tight.

"Leakage for soft-seated valves and lubricated plug valves shall not exceed ISO 5208 Rate A (no visible leakage).
For metal-seated valves the leakage rate shall not exceed ISO 5208 Rate D, except that the leakage rate during the
seat test in 10.4.5.5.2 shall not be more than two times ISO 5208 Rate

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