Most companies and industry experts would agree that if an operating company has many years of documented successful experience with a particular instrument or component then this should justify use of the instrument or component even if it is not SIL certified. IEC 61511 Clause 11.5 Requirements for the selection of devices details the requirements for Prior Use addresses this issue with consideration of:

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• Evidence of manufacturers QMS

• Identification and Specification of the instrument / component

• Demonstration of the performance of the instrument / component

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Companies that maintain a maintenance management system such as MAXIMO may have a number of years instrument / component data such as failure rates, modes, leakage rates which can be used to develop a prior use case.