This is Part 1 of two papers discussing the significance of two key factors of crack like flaw assessment in the Fitness for Service assessment. In FFS assessments of crack like flaw as well as local thin area, Folias factor Mt and surface correction factor Ms, are praying a key role since those factors enables us to predict a maximum allowable pressure of a cylinder from a flat plate model that contain same size of defected area. This is conversion process of flat pate model to cylinder model is important to characterize the flaw in an appropriate model. Folias factor, Mt, is well known to express the relationship between the reference stress of a through wall crack flat plate and a through wall crack cylinder. The application of Mt is clearly defined in ASME/API 579 FFS-1 part 9C. While this, the significance of the surface correction factor for surface flaw, Ms, has not been commonly understood enough in general. At a glance, it looks like a similar factor with Mt, and attempts simply applying to primary membrane stress term like Mt. Eventually, it would lead to a wrong discussion of a flaw characterization. Often, there raise a question on ASME/API 579 FFS-1 Part 9C reference stress solutions, especially for ASME/API 579 FFS-1 eq.9C.76, from the misunderstanding perspective of Ms. Addressing this issue is important to maintain the integrity of the Fitness-For-Service technology.

In this paper, authors reviewed and organized step by step procedure of each reference stress solutions for flat plates and cylinders. Through this discussion, authors clarified the significance of Mt and Ms that defined in ASME/API 579 FFS-1 Part 9C.


Significance of Ms and Validation of Reference Stress Solutions for Crack Like Flaws Part1

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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