Analytical formulas of PFD and PFH calculation for systems with nonconstant failure rates. (August 2017)

• Record Type: Journal Article
• Authors: Rogova, Elena; Lodewijks, Gabriel; Lundteigen, Mary Ann
• Other Names: Podofillini Luca guest-editor.; Sudret Bruno guest-editor.; Stojadinović Božidar guest-editor.; Zio Enrico guest-editor.; Kröger Wolfgang guest-editor.
• Is Part Of: Proceedings of the Institution of Mechanical Engineers. Volume 231:Number 4(2017:Aug.)
• Page Start: 373
• Page End: 382
• Publication Date: 2017-08
• Subjects: Reliability assessment -- nonconstant failure rates -- Weibull distribution -- average probability of failure on demand -- average frequency of dangerous failures -- analytical formulas; Reliability (Engineering) -- Mathematical models -- Periodiclals; Risk assessment -- Mathematical models -- Periodicals; Engineering design -- Mathematical models -- Periodicals; 620.00452
• DOI: 10.1177/1748006X17694999
• Languages: English
• ISSNs: 1748-006X

Abstract

Most analytical formulas developed for the PFD and PFH calculation assume a constant failure rate. This assumption does not necessarily hold for system components that are affected by wear. This article presents methods of analytical calculations of PFD and PFH for an M-out-of-N redundancy architecture with nonconstant failure rates and demonstrates its application in a simple case study. The method for PFD calculation is based on the ratio between cumulative distribution functions and includes forecasting of PFD values with a possibility of update of failure rate function. The approach for the PFH calculation is based on simplified formulas and the definition of PFH. In both methods, a Weibull distribution is used for characteristics of the system behavior. The PFD and PFH values are obtained for low, moderate and high degradation effects and compared with the results of exact calculations. Presented analytical formulas are a useful contribution to the reliability assessment of M-out-of-N systems.