Development of scaling parameter S for negative stress ratios R based on trend in experimental data for fatigue crack growth rates of austenitic stainless steels for ASME code Section XI

Negyesi, M.*; Yamaguchi, Yoshihito; Hasegawa, Kunio; Lacroix, V.*; Morley, A.*

Journal of Pressure Vessel Technology, 147(2), p.021201_1 - 021201_7, 2025/04

https://doi.org/10.1115/1.4067484

Allowable circumferential flaw sizes based on code given and actual measured flow stresses for high toughness ductile pipes subjected to bending and tensile loads

Negyesi, M.*; Ha, Yoosung; Hasegawa, Kunio; Lacroix, V.*

Proceedings of ASME 2024 Pressure Vessels & Piping Conference (PVP 2024) (Internet), 6 Pages, 2024/07

Proposal of a new flaw-to-surface proximity rule for the re-characterization of a subsurface flaw into a surface flaw

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

Proceedings of ASME 2024 Pressure Vessels & Piping Conference (PVP 2024) (Internet), 5 Pages, 2024/07

When a subsurface flaw is detected close to the surface of a pressure retaining component, the subsurface flaw shall be transformed into a surface flaw in accordance with flaw to surface proximity rules. This re-characterization process from subsurface to surface flaw is adopted in ASME Code Section XI. The limit value for this proximity rule depends on ratio between the subsurface flaw to the free surface distance and the flaw depth. This limit value does not depend on the flaw aspect ratio. This paper proposes an interaction limit criterion and presents a new limit value for the flaw-to-surface proximity factor, depending on the flaw depth, the remaining ligament and the flaw aspect ratio.

Characteristics of allowable axial cracks for pressurized pipes governed by limit load criteria

Hasegawa, Kunio; Li, Y.; Udyawar, A.*; Lacroix, V.*

International Journal of Pressure Vessels and Piping, 204, p.104952_1 - 104952_7, 2023/08

https://doi.org/10.1016/j.ijpvp.2023.104952

When axial cracks were detected in pipes, failure stresses for high toughness pipes are estimated using the Limit Load Criteria. The allowable stresses for the cracked pipes are derived from the combination of the failure stresses and safety factors. The allowable sizes of crack depths and lengths are determined from the allowable stresses. From the comparison of the allowable and failure stresses for through-wall cracks, the allowable cracks are not uniform. They can be separated into three different characteristics, i) leak-before-break (LBB) and crack growth stability, ii) non-LBB and crack growth stability and iii) non-LBB and crack growth instability. Inspectors and users should pay special attention to allowable cracks with the third characteristic to prevent unexpected failure, particularly for thin-wall pipes. The allowable crack depths and lengths that require special attention can be expressed by appropriate equations.

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.

Safety assessment of allowable through-wall crack angles for pipes subjected to tensile loading

Hasegawa, Kunio; Strnadel, B.*; Lacroix, V.*; Udyawar, A.*

International Journal of Pressure Vessels and Piping, 199, p.104722_1 - 104722_5, 2022/10

https://doi.org/10.1016/j.ijpvp.2022.104722

Fully plastic collapse stresses for high toughness pipes with circumferential cracks subjected to tensile loading can be predicted by Limit Load Criteria. The Limit Load Criteria are provided by the ASME Code Section XI. Allowable membrane stresses for part-through cracks were determined by plastic collapse stresses in combination with safety factors. The allowable stresses decrease with increasing angles of the part-through cracks. When crack angles are large, the allowable stresses of the part-through cracks are larger than the collapse stresses of through-wall cracks. For such large cracks, allowable stresses greater than the collapse stresses cause instability, and are thus detrimental to pipe integrity, especially in thin-wall pipes. In order to avoid the anxiety, it is necessary to establish maximum allowable crack angles. This paper proposes maximum allowable crack angles for allowable stresses.

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

https://doi.org/10.1115/PVP2022-84957

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.

Empirical correction factor to estimate the plastic collapse bending moment of pipes with circumferential surface flaw

Lacroix, V.*; Hasegawa, Kunio; Li, Y.; Yamaguchi, Yoshihito

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

https://doi.org/10.1115/PVP2022-84958

Assessment of the resolution of nonplanar flaws in pressure retaining components in terms of stress intensity factors

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

Proceedings of ASME 2021 Pressure Vessels and Piping Conference (PVP 2021) (Internet), 5 Pages, 2021/07

When flaws are detected, assessments are done to demonstrate the fitness-for-service. The first step is the flaw characterization determining the flaw geometry for analyses. This key step is done by flaw characterization rules provided in FFS Codes. According to the flaw characterization rules of ASME Code Section XI, a nonplanar flaw shall be resolved into two planar flaws by projection of the flaw area into planes normal to the maximum principal stresses. This approach allows to simplify the flaw assessment but remains conservative. Therefore, the conservatisms by the simplified projection for nonplanar flaws are investigated in this paper. Current computations have been improved so that the modelling of nonplanar flaws are not significant difficulty. This paper compares the stress intensity factors (SIF) of projected nonplanar flaws and the mixed mode SIF of actual nonplanar flaws. The scope is to quantify how the flaw projection into planes normal to the maximum principal stresses is conservative.

Fatigue crack growth for ferritic steel under negative stress ratio

Yamaguchi, Yoshihito; Hasegawa, Kunio; Li, Y.

Journal of Pressure Vessel Technology, 142(4), p.041507_1 - 041507_6, 2020/08

https://doi.org/10.1115/1.4046768

The phenomenon of crack closure is important in the prediction of fatigue crack growth. Several experimental data indicate the closing of fatigue cracks both under negative and positive loads at constant amplitude loading cycles, depending on the magnitude of stress amplitude and stress ratio. Appendix A-4300 of the ASME Code Section XI provides two equations of fatigue crack growth rates expressed by the stress intensity factor range for ferritic steels under negative stress ratio. The boundary of two fatigue crack growth rates is classified with the magnitude of applied stress intensity factor range, in consideration of the crack closure. The boundary value provided by the ASME Code Section XI is validated in this study through an investigation of the influence of the magnitude of the applied stress intensity factor range on crack closure, with the application of fatigue crack growth tests using ferritic steel specimens in air environment at room and high temperatures. Crack closures are obtained as a parameter of stress ratio, and herein, were found to occur at a smaller applied stress intensity factor range, as opposed to the definition given by Appendix A-4300.