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

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

Times Cited Count：0 Percentile：0.00(Engineering, Multidisciplinary)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.

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

Proceedings of ASME 2023 Pressure Vessels and Piping Conference (PVP 2023) (Internet), 5 Pages, 2023/07

In case of flaw detection during In-Service inspection of nuclear components, ASME Code Section XI provides Acceptance Standards. For ferritic steel materials, the size of allowable planar flaws is given in Table IWB-3510-1. The allowable flaw size only depends on three parameters: the component thickness, the flaw aspect ratio and the proximity of the flaw to the surface. However, a graphical analysis of the impact of those parameters highlights some inconsistencies. Consequently, the need to revise the allowable planar flaws of ASME Code Section XI Acceptance Standards using a robust technical basis is brought to light. This paper details the inconsistencies related to the present allowable planar flaws table and proposes improvement points to revise the allowable planar flaw Table IWB-3510-1.

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.

Hasegawa, Kunio; Strnadel, B.*; Li, Y.; Lacroix, V.*

Journal of Pressure Vessel Technology, 144(6), p.061202_1 - 061202_6, 2022/12

Times Cited Count：1 Percentile：17.53(Engineering, Mechanical)When pipe walls are thin, part-through flaws are easily develop into through-wall flaws, and the likelihood of coolant leakage is high. The ASEM Code Section XI provides final allowable flaw angles of through-wall flaw for thin-wall pipes. The final allowable angles are applied to pipes in order to maintain structural integrity if the part-through flaws become through-wall flaws. To ensure that this stability is compromised, plastic collapse stresses for through-wall flaws are combined with allowable stresses. However, the final allowable angles of through-wall flaws are not identified for thin-walled pipes. This paper compares plastic collapse stresses of through-wall flaws and allowable stresses of part-through flaws for pipes. The comparison of these stresses is used to derive the final allowable angles of through-wall flaws. The angles can be expressed either in the form of exact solutions or as conventional options that are appropriate for various service level conditions.

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

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

Times Cited Count：1 Percentile：25.25(Engineering, Multidisciplinary)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.

Hasegawa, Kunio; Li, Y.; Strnadel, B.*; Udyawar, A.*

Journal of Pressure Vessel Technology, 144(5), p.051305_1 - 051305_6, 2022/10

Times Cited Count：1 Percentile：17.53(Engineering, Mechanical)Fully plastic collapse stresses for circumferentially part-through cracked pipes subjected to bending stresses are estimated by Limit Load Criteria provided by the ASME Code Section XI. Allowable crack depths were determined by using the Limit Load Criteria and that are tabulated in the ASME Code Section XI for different plant service level conditions. On the other hand, crack penetration bending stresses for part-through cracked pipes were estimated by using the Local Approach of Limit Load Criteria. By using these Criteria, the study presented in this paper obtained allowable crack depths at penetration for circumferentially part-through cracked pipes. Comparing the allowable crack depths obtained by both methods for each service level, it is evident that the allowable crack depths at penetration calculated by the Local Approach of Limit Load Criteria are almost always smaller than those at fully plastic collapse stresses calculated by the Limit Load Criteria. It was found that the allowable crack depths provided by the ASME Code Section XI are less conservative for crack penetrations.

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

Proceedings of ASME 2022 Pressure Vessels and Piping Conference (PVP 2022) (Internet), 4 Pages, 2022/07

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

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

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.

Hasegawa, Kunio*; Dvok, D.*; Mare, V.*; Strnadel, B.*; Li, Y.

Journal of Pressure Vessel Technology, 144(1), p.011303_1 - 011303_6, 2022/02

Times Cited Count：5 Percentile：64.61(Engineering, Mechanical)Fully plastic failure stress for circumferentially surface-cracked pipe subjected to tensile loading can be estimated by means of limit load criterion (LLC) based on the net-section stress approach. LLC of the first type (labelled LLC-1) was derived from the balance of uniaxial forces. LLC of the second type, derived from the balance of bending moments and axial forces (labelled LLC-2), is adopted in Section XI of the ASME (American Society of Mechanical Engineering) Code. From the literature survey of experimental data, failure stresses obtained by both types of LLCs were compared with the experimental data. It can be stated that failure stresses calculated by LLC-1 are better than those calculated by LLC-2 for shallow cracks. On the contrary, for deep cracks, LLC-2 predictions of failure stresses are fairly close to the experimental data. It can be stated that the allowable cracks given in Section XI of the ASME Code are conservative.

Desclaux, C.*; Lacroix, V.*; Hasegawa, Kunio

Proceedings of ASME 2021 Pressure Vessels and Piping Conference (PVP 2021) (Internet), 10 Pages, 2021/07

The plastic collapse bending stress for a pipe is defined in ASME Code Section XI, using simplified equilibrium equations. One of the authors demonstrated that the simplified equilibrium equations are not conservative for externally cracked pipes and he proposed taking into account the cracked ligament mean radius. This paper demonstrates that the accuracy of the collapse bending stress equation can be refined considering the neutral axis position of the cracked pipe section. This leads to exact collapse bending moment equations. As the results, it is shown that the ASME equations for externally cracked pipes might be less conservative collapse bending stress than with the exact equations.

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.

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

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

Times Cited Count：0 Percentile：0.00(Engineering, Mechanical)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.

Hasegawa, Kunio; Li, Y.; Lacroix, V.*; Mare, V.*

Proceedings of ASME 2020 Pressure Vessels and Piping Conference (PVP 2020) (Internet), 6 Pages, 2020/08

Authors have developed more precise equations using the Limit Load Criteria, which is called Modified Limit Load Criteria, hereafter. As the results of the Modified Limit Load Criteria, failure stresses for external flawed pipes are always smaller than the failure stresses obtained by the Limit Load Criteria provided by the ASME Code Section XI. It seems that the allowable flaw sizes of the Acceptance Standards provided by the ASME Code Section XI are less conservative for external flaws. The objective of this paper is to demonstrate difference of failure stresses by the Limit Load Criteria and Modified Limit Load Criteria for external flawed pipes. In addition, the allowable flaws of the Acceptance Standards are examined by large and small diameter pipes with external flaws using the Modified Limit Load Criteria.

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

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

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.

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

Proceedings of ASME 2020 Pressure Vessels and Piping Conference (PVP 2020) (Internet), 8 Pages, 2020/08

When flaws are detected in pressure retaining components, a flaw characterization has to be carried out in order to determine unequivocally the flaw geometry. This flaw characterization is done according to rules provided in the FFS codes. The first step of the flaw characterization addresses the interaction of the flaw and the free surface. The second step of the flaw characterization addresses the interaction of the flaw with the adjacent flaws. In the ASME Code Sec. XI, there is a lack on how to treat the interaction of a combined flaw and the free surface of the component. The ASME Code Sec. XI flaw characterization is not clear. Some typical examples of unrealistic flaw assessment rules are depicted in this paper. The paper is used as technical basis for improvement of the ASME Code in order to clarify the treatment of combined flaw in the flaw characterization (IWA-3300, IWB/IWC-3510-1)

Hasegawa, Kunio; Li, Y.; Lacroix, V.*; Mare, V.*

Journal of Pressure Vessel Technology, 142(3), p.031506_1 - 031506_7, 2020/06

Times Cited Count：1 Percentile：7.57(Engineering, Mechanical)Bending stress at plastic collapse for a circumferentially cracked pipe is predicted by limit load criterion provided by the Appendix C of the ASME Code Section XI. The equation of the Appendix C is applicable for pipes with both external and internal surface cracks. On the other hand, the authors have developed a more precise equation. From the comparison of Appendix C equation and the new equation, the plastic collapse stress estimated by the Appendix C equation gives less conservative bending capacity prediction for external cracked pipes with thick wall thickness and large crack angle. This paper discusses the limitation scope to use the limit load criterion of the Appendix C equation.

Hasegawa, Kunio; Li, Y.; Lacroix, V.*; Mare, V.*

Proceedings of 2019 ASME Pressure Vessels and Piping Conference (PVP 2019) (Internet), 8 Pages, 2019/07

Bending stress at plastic collapse for a circumstantially cracked pipe is predicted by limit load equation provided by the Appendix C of the ASME Code Section XI. The equation of the Appendix C is applicable for pipes with both external and internal surface cracks. On the other hand, authors had developed an equation taking into account the pipe mean radii at non-cracked area and at cracked ligament area. From the comparison of Appendix C equation and the new equation, the plastic collapse stress estimated by the Appendix C equation gives 20 to 30% less conservative for external cracked pipes with small , where is the pipe mean radius and t is the pipe wall thickness. This paper discusses the limitation of the use of for the Appendix C equation.

Hasegawa, Kunio; Usami, Saburo*; Lacroix, V.*

Proceedings of 2019 ASME Pressure Vessels and Piping Conference (PVP 2019) (Internet), 6 Pages, 2019/07

Fatigue crack growth thresholds are provided by several fitness-for-service (FFS) codes. When evaluating cracked components subjected to cyclic loading, maximum stress intensity factor and/or minimum stress intensity factor are required. However, the definitions of the thresholds under negative stress ratio are not clearly written. In addition, the thresholds are given by constant values under negative . This paper shows that the maximum stress intensity factor converted by the thresholds obtained by experimental data are not constant values under negative . The thresholds for the FFS codes are less conservative. The definition of the thresholds under negative ratio are discussed.

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