Revision of allowable planar flaw tables of ASME B&PV Code Section XI for ferritic steel materials

Dulieu, P.*; Lacroix, V.*; Hasegawa, Kunio

Proceedings of ASME 2023 Pressure Vessels and Piping Conference (PVP 2023) (Internet), 7 Pages, 2023/07

When defects were found during in-service inspection in nuclear components, the ASME Code Section XI provides allowable flaw sizes to assess the flaw severity. For ferritic steel materials, the sizes of allowable planar flaws given in Table IWB-3510-1 were determined by the stress intensity factors. The objective of this methodology is including some basic criteria to prevent plastic collapse and brittle failure. As far as the prevention from plastic collapse, a uniform limit load reduction is considered whatever the flaw aspect ratios. For the prevention of brittle failure, a reference surface flaw configuration is defined to derive a reference stress intensity factor. This methodology is applied to surface flaws with various aspect ratios. It is also coherently applied to subsurface flaws considering the proximity of the flaw to the surface as an additional parameter. Finally, a revision of the allowable planar flaw Table IWB-3510-1 of ASME Code Section XI is proposed.

Improvement of the ASME B&PV code resolution of nonplanar flaws in pressure retaining components

Lacroix, V.*; Dulieu, P.*; Hasegawa, Kunio; Mares, V.*

Proceedings of ASME 2022 Pressure Vessels and Piping Conference (PVP 2022) (Internet), 7 Pages, 2022/07

In the ASME Code Section XI, a simplified approach is proposed: a nonplanar flaw is resolved into two planar flaws by projection of the flaw area into planes normal to the maximum principal stress. However, simplified resolution of nonplanar flaws is not conservative for all types of loading and flaw inclinations. Consequently, an improvement of the resolutions of nonplanar flaws must be provided in the ASME Code Section XI. This paper carries out an exhaustive assessment of the conservatism of the ASME approach and then proposes an alternative approach to deal with nonplanar flaws allowing to overcome the non-suitability of current ASME Code.

Assessment of flaw interaction under combined tensile and bending stresses; Suitability of ASME code case N877-1

Dulieu, P.*; Lacroix, V.*; Hasegawa, Kunio

Proceedings of ASME 2020 Pressure Vessels and Piping Conference (PVP 2020) (Internet), 7 Pages, 2020/08

https://doi.org/10.1115/PVP2020-21452

When detected flaws are in close proximity, proximity rules given in the Fitness-foe Service codes require to combine the interacting flaws into a single flaw. ASME Code Case N877-1 provides alternative proximity rules for multiple radial oriented planar flaws. The calculations of flaw interaction have been performed under pure membrane stress. However, actual loading conditions induce non-uniform stresses in the component thickness direction. The objective of this paper is assess the suitability of ASME Code Case N877-1 with regards to the presence of a bending part in the applied stress distribution. For that purpose, various applied stress profiles and flaw configurations are covered. The effect on flaw interaction is assessed trough three-dimensional XFEM analyses.

A Comparison of proximity rules for surface planar flaws

Bouydo, A.*; Dulieu, P.*; Lacroix, V.*; Hasegawa, Kunio; Mare, V.*

Proceedings of 2019 ASME Pressure Vessels and Piping Conference (PVP 2019) (Internet), 10 Pages, 2019/07

Rules for flaw interaction for subsurface flaws in operating pressurized vessels; Technical basis of code case N-877

Lacroix, V.*; Dulieu, P.*; Blasset, S.*; Tiete, R.*; Li, Y.; Hasegawa, Kunio; Bamford, W.*; Udyawar, A.*

Proceedings of 2018 ASME Pressure Vessels and Piping Conference (PVP 2018), 10 Pages, 2018/07

Introduction of subsurface proximity criteria in the world and stress intensity factors for transformed surface flaws

Hasegawa, Kunio; Li, Y.; Katsumata, Genshichiro*; Dulieu, P.*; Lacroix, V.*

Proceedings of 2017 ASME Pressure Vessels and Piping Conference (PVP 2017) (CD-ROM), 6 Pages, 2017/07

Net-section stress at the ligament between component free surface and subsurface flaw increases when the ligament distance is short. It can be easily expected that stress intensity factors increase when the subsurface flaw locates near the free surface. To avoid catastrophic failures caused by ligament failure, fitness-for-service (FFS) codes provide flaw-to-surface proximity rules. The proximity rules are used to determine whether the flaws should be treated as subsurface flaws as-is, or transformed to surface flaws. The stress intensity factor for the transformed surface flaw increases furthermore. The increment of the stress intensity factor before and after transformation depends on the location of the subsurface flaw. Although the concept of the proximity rules are the same, the specific criteria for the rules on transforming subsurface flaws to surface flaws differ amongst FFS codes. Particularly, the criteria are different amongst the same organizations of ASME (American Society of Mechanical Engineers). The proximity criteria of the FFS codes in the world were introduced in this paper. In addition, the stress intensity factors based on the different criteria used in the ASME Codes are compared.