SIL 3-certified valve assemblies

19 October 2021

Emerson has introduced the first valve assemblies that meet the design process requirements of Safety Integrity Level (SIL) 3 per the International Electrotechnical Commission’s IEC 61508 standard. These Fisher Digital Isolation final element solutions are suited to use as shutdown valves in critical safety instrumented system (SIS) applications.

Without this solution, users must specify all the individual valve components, procure each one, and assemble them into a working whole. Even if these steps are done correctly, this type of custom assembly will still not provide all the benefits of the Digital Isolation assembly.

Because the assembly is built as a complete solution, it boasts an improved probability of failure on demand (PFD) rate. In some cases, the failure rate of the assembly will be up to 50% less than the combination of the same valve components purchased individually and assembled by an end user.

This improved PFD results from the assembly being certified as a whole system by exida, to meet its rigorous Remote Actuated Valve Assembly requirements. By using this certified assembly, SIS designers can realise a substantial reduction in dangerous undetected failure rates.

In one example, an Emerson customer was hoping to achieve a six-year test interval for a SIL 2 safety interlock. When they performed a component SIL calculation on a standard shutdown valve, they could only achieve a SIL 1 level reliability at a six-year test interval. However, the Digital Isolation assembly exceeded SIL 2 requirements using the same components. This allowed the plant to safely extend their run time to six years, generating millions of dollars in additional revenue.

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