Sensitivity Analysis of Fitness-for-Service Assessment Based on Reliability for Cylindrical Pressure Vessels With Local Metal Loss

Abstract

Concern about fitness-for-service (FFS) assessments using stochastic analyses for aged pressure equipment with local metal loss has been growing. When a decision must be made regarding whether to run or repair equipment with local metal loss, a structural integrity assessment based on reliability helps. In analyses of failure probability, it is important to identify which variables strongly affect the structural integrity. The stochastic properties of influential parameters must be clarified, but few data have been published regarding the quantitative analysis of the sensitivity of the parameters in FFS assessments of components with local metal loss. Here, we investigated the effects of parameters on the plastic collapse of a damaged cylindrical pressure vessel with local metal loss, in an evaluation of parameter sensitivity. We also analyzed sensitivity indices for the component with several shapes of local metal loss. We found that the corrosion rate has a major influence on the probability of failure. We propose a practical stochastic analysis procedure for components with local metal loss. In this procedure, the parameter that has consistently low sensitivity to the limit state is used as a constant value.