The 2012 edition of ASME B31.3 Process Piping Code [1] included an update to the fatigue assessment rules which limited the allowable stress value used in the fatigue assessment to 138 MPa (20 ksi). This change was made due to the knowledge that higher strength materials, especially those materials with yield strength to tensile strength ratios above 0.8, do not tend to exhibit significantly longer fatigue life as compared to lower strength materials. This change means that for existing high-strength piping in plants that were designed using pre-2012 B31.3 [2] and are in fatigue service, the end-user must now recalculate the piping remaining life based on new requirements. Depending on the size of the plant under consideration and the level of high-strength piping used, such a recalculation may be an extensive scope of work.

This paper uses a comparison between the rules in ASME B31.3 and the fatigue life prediction methods outlined in API RP 579-1 / ASME FFS-1 [3] in order to establish a categorization methodology which is used to identify which pre-2012 high strength piping systems will require re-assessment, more frequent monitoring and/or may have a shorter than anticipated life than the original design basis. The methodology allows for easy categorization of the piping systems to allow efforts to be focused on the most appropriate piping systems. The need for this work came from concerns regarding the extensive use of Duplex Stainless Steel piping on a large offshore platform that was designed prior to ASME B31.3 2012.

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