Fatigue assessment, including the development of a crack of engineering significance, is an integral and important part of design as well as life assessment/extension for long term operation of pressurized components. Additionally, in some cases, environmental effects on fatigue need to be taken into account. These areas are also part of several engineering Codes, such as the ASME B&PV Code, in which the related design margins and decision making are influenced by inherent material/physical variability, uncertainty in inputs, and modeling uncertainty. The code procedures are based on the use of a deterministically calculated measure — the cumulative usage factor (CUF) for a specified service envelope of load transients — to assess the component fatigue performance.

This paper presents the results of an assessment on the relative significance of key S–N adjustment factors (material variability, surface roughness, size, and load history) on the estimation of the CUF. The assessment is based on the recently proposed uncertainty quantification (UQ) and sensitivity analysis (SA) [PVP2017-65850], including the environmentally assisted fatigue. It takes into account the expected uncertainty in the key adjustment factors with sample limiting cases. The significance of these results is discussed in relation to their implications for design/analysis based on the CUF approach and the related fatigue margins.

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