Application of partial safety factors for pressure containing equipment

摘要

An overview of the methodology that is used to incorporate uncertainty in a Fitness-For-Service (FFS) assessment for crack-like flaws using the procedures in API 579 [1] is provided in the paper. The description of the deterministic FFS assessment method is first provided including a description of how in-service margins are defined. A discussion of the uncertainties of the independent variables in the assessment and how they can be accounted for given a deterministic method is provided. In this discussion, the use of partial Safety Factors (PSF) is highlighted as an attractive method for introducing uncertainty into a determinstic assessment becasue the format of the analysis is similar to that used by many design codes. A general description fo PSFs including an example problem are then described to illustrate the concepts of partial safety factors and the reliability engineering technology requried to derive them for a specific application. The reliability technology used to develop the PSFs in API 579 for the assessment of crack-like flaws is described including how the resulting factors are used in a FFS assessment. A discussion of the current PSFs in API 579 and future directions to improve the existing PSFs in API 579 is also provided.