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Lacroix, V.*; Dulieu, P.*; Blasset, S.*; Tiete, R.*; Li, Y.; 長谷川 邦夫; Bamford, W.*; Udyawar, A.*
Proceedings of 2018 ASME Pressure Vessels and Piping Conference (PVP 2018), 10 Pages, 2018/07
When multiple flaws are detected in pressure retaining components during inspection, the first step of evaluation consists of determining whether the flaws shall be combined into a single flaw or evaluated separately. This combination process is carried out in compliance with proximity rules given in the Fitness-for-Service (FFS) Codes. However, the specific criteria for the rules on combining multiple flaws into a single flaw are different among the FFS Codes. In this context, revised and improved criteria have been developed, to more accurately characterize the interaction between multiple subsurface flaws in operating pressure vessels. This improved approach removes some of the conservatism in the existing ASME Code approach, which was developed in the 1970s based on two flaws interacting with each other. This paper explains in detail the methodology used to derive improved flaw proximity rules through three-dimensional FEM and XFEM analyses. After the presentation of the calculations results and the improved criteria, the paper also highlights the multiple conservatisms of the methodology using several sensitivity analyses.
Dulieu, P.*; Lacroix, V.*; 長谷川 邦夫; Li, Y.; Strnadel, B.*
Proceedings of 2018 ASME Pressure Vessels and Piping Conference (PVP 2018), 10 Pages, 2018/07
When multiple surface flaws are detected in pressure components, their potential interaction is to be assessed to determine whether they must be combined or evaluated independently of each other. This assessment is performed through the flaw characterization rules of Fitness-For-Service (FFS) Codes. However, the specific combination criteria of surface flaws are different among the FFS Codes. Most of the time, they consist of simple criteria based on distance between flaws and flaw depth. This paper aims at proposing alternative characterization rules reflecting the actual level of interaction between surface planar flaws. This interaction depends on several parameters such as the relative position of flaws, the flaw sizes and their aspect ratio. Thanks to numerous threedimensional XFEM simulations, best suited combination criteria for surface planar flaws are derived by considering the combined influence of these parameters.