Forum: Reliability & Maintainability Questions and Answers

Topic: Reliability & Maintainability Questions and Answers

Topic Posted by: Reliability & Maintainability Forum (src_forum@alionscience.com )
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998
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Original Message:

Posted by: Geoffrey Hampden-Smith (geoff.hampden-smith@shell.com )
Organization:Shell UK
Date posted: Fri Jun 24 5:40:18 US/Eastern 2005
Subject: Component failure rate and availability of unrevealed failure data
Message:
We carry out valve testing at irregular periods ranging from 12 to 364 days. (This arises as we take advantage of opportunities duringprocess shut downs). A series of successful tests (valve passes)takes place, and then the valve is found to have failed (once the failure is revealed it is repaired immediately in about 1 hour). Can the average availability calculated as: 1) [SUM TEST PERIODS (days) VALVE PASSED + 1/2*(SUM OF TEST PERIODS (days) IN WHICH VALVE FAILURES ARE REVEALED]/ [SUM TEST PERIODS VALVES PASSED (days) + TEST PERIODS (days) IN WHICH VALVES FAILED] (The Denominator equals the TOTAL TIME) 2) Is the valve failure rate calculated as: [NUMBER OF VALVE FAILURES]/[TOTAL of TEST PERIODS (days) VALVES PASSED + 1/2*(SUM OF TEST PERIODS (days) IN WHICH VALVE FAILURES ARE REVEALED)]

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