Proof testing procedure

Problem A pressure transmitter is needed for a safety instrumented function. What proof test procedures should be performed and what coverage factors should be used for those procedures ... 

Solution Many manufacturers recommend proof test procedures for low demand safety instrumented system applications. The information is found in the safety manual. That document may be part of another manual or may be a separate document. Referring to the safety manual section of a pressure transmitter (Ref. 4), proof test options with associated coverage factors are given (Figure 7-2). The test titled Five Year Proof Test has a manual proof test coverage of 65%. The test titled Ten Year Proof Test has a manual proof test coverage of 99%. 

Remember that in continuous demand mode credit can be given for automatic diagnostics or for proof test procedures only for redundant systems. In addition, many of the calculation assumptions made for low demand mode do not apply. The "probability of dangerous failure per hour" must be calculated based on all dangerous failures. 

Written proof-test procedures shall be developed for every SIF to reveal dangerous failures undetected by diagnostics. These written test procedures shall describe every step that is to be performed and shall include... 

Does review of product history support the current inspection, preventive maintenance, condition-based mairttenance, proof-test procedures, and intervals List improvement opportunities and attach details to this form Yes No... 

Bypass, start up override, and manual shutdown operational Well-documented proof test procedure Correct operation of SIS in utility failure, EMI, etc. 

To check and document proof test procedure and set proof test interval. Suitable measure towards this is necessary. 

Manufacturers also specify useful lifetime of components contributing to Adu (viz. in lA transmitter of Invensys). Also suggested preventive maintenance details such as periodic proof testing procedure are included as a part of the manual. 

Proof test interval for SIF This is an important issue. Proof tests are meant to test the function as far as possible (could be dangerous in a shutdown condition). Major issues related to this shall include but not be limited to the following [12] Description of the proof test procedure Precaution and safety to be under taken for proof test Required proof tests in life cycle... 

Human aspect Consequence because of wrong proof test procedure Documentation of proof test activity Process safety response time consists of three components ... 

Proof testing principles Proof testing types and procedures Format of proof testing procedures Proof test records Planning and scheduling Competence MOC... 

The partial proof test details need to be recorded in the proof test procedure. This also is applicable for direct testing and/or other methods. 

Human error The proof test procedures should be designed in such a manner that it would minimize human error. For this, a checklist including tick boxes and cross-checking for critical steps could be helpful. Many structure the tests in a way so that errors that could be introduced are revealed by subsequent test steps [17]. 

Procedure documents and timings In an actual case the proof test procedure may not follow a single procedure document, but may be made up of different documents, for example, reference to other procedures. Also it may include procedures for testing different parts of SIS at different times. However, in all such cases, measures should be taken to ensure no failure modes or components are missed. It may include partial test procedures and full test procedures. 

K. Ando, M. C. Chu, M. Matsushita and S. Sato, Effect of Crack-healing and Proof-testing procedures on fatigue strength and reliability of SisN/SiC Components, / Eur. Ceram. Soc., 23, 977-84 (2003)... 

Another advantage of factory testing is it provides an opportunity to verify the functional test procedures. These are going to be repeated at the site in the so-called PSAT stage. These same tests form the basis of regular proof testing procedures so the FAT is an ideal opportunity to get these procedures right with the equipment and with the end-user support technicians. 

The reliability of these protective systems was quantified as the probability that the protective system is in a failed state when a demand is placed upon it. This was a dimensionless number between 0 and 1 also known as the fractional dead time. The reliability of the protective systems was calculated using component failure data, Teesside Power Station proof testing procedures, and generic human error rates for plant operators. 

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