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Negyesi, M.*; 河 侑成; 長谷川 邦夫; Lacroix, V.*
Proceedings of the ASME 2025 Pressure Vessels & Piping Conference (PVP2025) (Internet), 6 Pages, 2025/07
When evaluating allowable flaw sizes for high toughness ductile pipes, failure stresses are necessary for the flawed pipes. The failure stresses are estimated by flow stresses for the pipe materials and the flow stress is usually given by the average of the yield strength and the ultimate tensile strength. The American Society of Mechanical Engineers (ASME) Code Section XI states to use the yield strengths and the ultimate tensile strengths defined by the ASME Code Section II Materials. The ASME Code Section XI also states that actual measured yield strengths and ultimate tensile strengths are possible to be used, alternatively. Values of yield strength and ultimate tensile strength given by the ASME Code Section II are conservative, corresponding to lower bound values. Then, it is easily inferred that the allowable stresses calculated by the code given flow stress are lower than the allowable stresses calculated by the actual measured flow stress. The objective of this paper is to compare the allowable stresses and allowable flaw lengths based on both the code and actual measured flow stresses for pipes with axial flaws subjected to internal pressure. It is further demonstrated that allowable flaw lengths based on the code flow stress are substantially shorter than those calculated based on the actual measured flow stress.
Lacroix, V.*; Dulieu, P.*; 長谷川 邦夫; 河 侑成; Negyesi, M.*
Proceedings of the ASME 2025 Pressure Vessels & Piping Conference (PVP2025) (Internet), 8 Pages, 2025/07
When a subsurface flaw is detected close to the free surface of a pressure retaining component, it must be assessed whether the subsurface flaw shall be transformed into a surface flaw in accordance the ASME Code Sec. XI. The threshold of this proximity rule depends on the ratio between the subsurface flaw to the free surface distance and the flaw depth. This limit value depends neither on the flaw aspect ratio, nor on the thickness and the curvature of the component, nor on the type of loading. After demonstrating in a previous paper that the interaction between the subsurface flaw and the free surface of the component highly depends on the flaw aspect ratio, the present paper highlights the influence of the thickness and the curvature of the component. Consequently, the current flaw-to-surface proximity rule should account for those parameters as well. Then, the paper proposes an interaction limit criterion and presents a new limit value for the flaw-to-surface proximity factor.
河 侑成; Negyesi, M.*; 長谷川 邦夫; Lacroix, V.*
Proceedings of the ASME 2025 Pressure Vessels & Piping Conference (PVP2025) (Internet), 7 Pages, 2025/07
原子力発電用配管に欠陥が認められた場合、欠陥寸法に対する許容応力を求め、規格上の問題がないことを確認する必要がある。配管の許容応力は、配管材の降伏応力と引張強度を平均した流動応力が用いられるが、実機配管の引張特性が明確でない場合にはASME codeに定められる当該材料の下限値を用いることにより、保守的な評価が行われる。本研究では、計装化押込み試験により求めた引張特性を用いて許容応力及び許容欠陥寸法を評価した。計装化押込み試験による引張特性はやや高いものの、その流動応力は従来の引張試験結果から求めた場合の約3%の誤差範囲であった。また、計装化押込み試験及び従来の引張試験による許容応力及び許容欠陥寸法は、ASME codeによる当該材料の下限値で求められた値より大きく許容された。本研究の結果により、配管を用いた直接的な引張試験が困難な実機において、計装化押込み試験による引張特性を取得することにより、実際の引張特性に近い値が得られることを明らかにした。
山口 義仁; 長谷川 邦夫; Negyesi, M.*
Proceedings of the ASME 2025 Pressure Vessels & Piping Conference (PVP2025) (Internet), 8 Pages, 2025/07
Reference fatigue crack growth rates da/dN for ferritic steels in boiling water reactor environment are provided in Appendix Y of the ASME Code Section XI. Therein, da/dN are expressed as a function of stress intensity factor range 
K and as a function of the stress ratio parameter R. Different expressions apply for low K and high K. Current expressions result in lower fatigue crack growth rates in the water environment compared to the air environment for certain values of K. Therefore, the ASME Code states that reference fatigue crack growth rates in water environments are given by the expressions which results in higher fatigue crack growth rates. Sample calculations on fatigue crack growth under water and air environments were compared. The applicability of the current standard was confirmed.
長谷川 邦夫; 山口 義仁; Udyawar, A.*
Journal of Pressure Vessel Technology, 147(3), p.034501_1 - 034501_7, 2025/06
被引用回数：0 パーセンタイル：0.00(Engineering, Mechanical)Fatigue crack growth thresholds and reference fatigue crack growth rate da/dN curves for ferritic steels in air environment are provided in Appendix Y of the ASME Code Section XI. Therein, the thresholds and da/dN are expressed as a function of stress ratio R; however, the R is not explicit, when R is negative. The thresholds are given as constant values for negative R. In addition, the ASME provides two equations for da/dN under negative R; however, the boundary between the two equations is not technically known. Thus, the dependency of negative R on da/dN is not well understood. Herein, revised threshold values for negative R are provided based on experimental data, and a new boundary between the two equations for da/dN is defined using crack opening behavior and the R dependency of da/dN based on a literature survey.
for negative stress ratios R based on trend in experimental data for fatigue crack growth rates of austenitic stainless steels for ASME code Section XINegyesi, M.*; 山口 義仁; 長谷川 邦夫; Lacroix, V.*; Morley, A.*
Journal of Pressure Vessel Technology, 147(2), p.021201_1 - 021201_7, 2025/04
被引用回数：0 パーセンタイル：0.00(Engineering, Mechanical)Fatigue crack growth rates for stainless steels in air environment are provided by the ASME Code Section XI. When the stress ratio R is positive from 0 to 1, the scaling parameter SR increases with the increasing ratio R, and the crack growth rates increase with the increasing stress ratio R. When R is less than 0, the parameter SR=1. Hence, fatigue crack growth rates under negative R ratios are independent of stress ratios R according to the ASME Code Section XI. However, from the literature survey, experimental data reveal that the fatigue crack growth rates decreases with decreasing R ratios below zero. The objective of this paper is to assess fatigue crack growth rates under such negative stress ratios for stainless steels in air environment. An equation determined from trends in experimental data surveyed in this study is proposed for negative stress R ratios to calculate the parameter SR for the ASME Code Section XI.
Morley, A.*; Negyesi, M.*; 長谷川 邦夫
Proceedings of ASME 2024 Pressure Vessels & Piping Conference (PVP 2024) (Internet), 7 Pages, 2024/07
大気中におけるステンレス鋼の疲労亀裂進展速度はASME (米国機械学会)規格Section XIに規定されている。この亀裂進展速度は温度の上昇とともに増加し、この温度効果はパラメータSTで表されている。現在のこのパラメータSTの式は扱いにくく、温度の関数とした根拠に疑問があり、かつ、ASME規格の対象としている機器の適用温度から外れた実験データも用いて作成されている。そこで、文献調査による実験データをもとに、大気中におけるステンレス鋼の温度パラメータSTの代替式を提案する。
Negyesi, M.*; 河 侑成; 長谷川 邦夫; Lacroix, V.*
Proceedings of ASME 2024 Pressure Vessels & Piping Conference (PVP 2024) (Internet), 6 Pages, 2024/07
Allowable stresses for pipes are determined by combining failure stresses and safety factors. When predicting the plastic collapse failure stresses for high toughness ductile pipes, flow stresses of the pipe materials are indispensable. The flow stress is usually given by the average of the yield strength and the ultimate tensile strength. Inservice Inspection of the American Society of Mechanical Engineers (ASME) Code Section XI states to use the yield strengths and the ultimate tensile strengths defined by the ASME Code Section II Materials. The ASME Code Section XI also states that actual measured yield strengths and ultimate tensile strengths are possible to be used, alternatively. Values of yield strength and ultimate tensile strength given by the ASME Code Section II are conservative, corresponding to lower bound values. Then, it is easily inferred that the allowable stresses calculated by the code given flow stress are lower than the allowable stresses calculated by the actual measured flow stress. The objective of this paper is to compare the plastic collapse failure and allowable stresses based on both the code and actual flow stresses for pipes with circumferential flaws subjected to bending and tensile loading. In addition, it is demonstrated that allowable flaw sizes based on both flow stresses do not differ much at low allowable stress. However, when the allowable stress is large, the allowable flaw size based on the code flow stress is substantially lower compared to that based on the actual flow stress.
河 侑成; 山口 義仁; 長谷川 邦夫; Negyesi, M.*
Proceedings of ASME 2024 Pressure Vessels & Piping Conference (PVP 2024) (Internet), 6 Pages, 2024/07
If a flaw in a high-toughness ductile pipe of a power plant is detected during periodic in-service inspection, stress applied at the flaw location of the pipe is compared with an allowable stress. When the applied stress is less than the allowable stress, the plant can operate continuously for a certain evaluation period in accordance with ASME Code Section XI. The flow stress given by the average of yield strength and ultimate tensile strength is an important material parameter for allowable stress. Recently, many fitness-for-service codes and technical reports have adopted conversions from hardness measurement values to yield strength and ultimate tensile strength. In this paper, we introduced the flow stress obtained from converted tensile properties from Vickers hardness using the presented equations for austenitic stainless steel. The allowable stress estimated by the Vickers hardness was compared with the allowable stress determined by actual tensile properties. As a result, the flow stress converted from hardness was about 1.48 times larger than that obtained by actual flow stress. The allowable flaw sizes calculated by the flow stress converted from hardness gave an appropriate indication when the allowable or applied stress was very low. However, the flow stress converted from hardness gave unconservative allowable stress, when the applied stress was large.
Negyesi, M.*; 山口 義仁; 長谷川 邦夫; Lacroix, V.*; Morley, A.*
Proceedings of ASME 2024 Pressure Vessels & Piping Conference (PVP 2024) (Internet), 8 Pages, 2024/07
Fatigue crack growth rates da/dN for stainless steels in air environment are provided by the ASME Code Section XI. The fatigue crack growth rates are given by da/dN = C
(K)
, where C is the fatigue crack growth rate coefficient, n is the fatigue crack growth rate exponent and K is the stress intensity factor range. The coefficient C contains a temperature parameter S
, and a scaling parameter, S
, which is a function of the stress ratio R. When the stress ratio R is positive from 0 to 1, the parameter S increases with increasing the ratio R, and da/dN increases with increasing stress ratio R. When R is less than 0, the parameter is given by S = 1.0. Accordingly, fatigue crack growth rates under negative stress ratio are always constant, independent of stress ratios. This means that a cyclic stress state with a minimum that is compressive is considered to cause the same degree of crack growth as one with the same range but a zero minimum. However, from the results of literature survey, experimental data reveal that the fatigue crack growth rates decrease with decreasing R ratios below zero, i.e. negative stress ratios. The objective of this paper is to assess fatigue crack growth rates under such negative stress ratios for stainless steels in air environment. An equation determined from trends in experimental data is proposed for negative R ratios for calculating the parameter S for the ASME Code Section XI, Appendix Y, based on the literature surveyed in this study.
Lacroix, V.*; Dulieu, P.*; 長谷川 邦夫
Proceedings of ASME 2024 Pressure Vessels & Piping Conference (PVP 2024) (Internet), 5 Pages, 2024/07
内部欠陥が耐圧機器の表面近傍に検出された場合、この内部欠陥は接近性ルールに従って表面欠陥に置き換えなければならない。この内部欠陥から表面欠陥へのモデル化はASME(米国機械学会)規格のSection XIに採用されている。この接近性ルールの限界値は内部欠陥と自由表面の距離と欠陥深さによって決まる。この限界値は欠陥のアスペクト比に依存していない。本報告は、干渉効果の限界クライテリアを提案し、欠陥深さに依存し、かつ残余長さや欠陥のアスペクト比に依存する欠陥の接近性因子のための新しい限界値について述べる。
長谷川 邦夫; Li, Y.; Udyawar, A.*; Lacroix, V.*
International Journal of Pressure Vessels and Piping, 204, p.104952_1 - 104952_7, 2023/08
被引用回数：3 パーセンタイル：40.53(Engineering, Multidisciplinary)高靭性の耐圧配管に軸方向の亀裂が検出された場合、極限荷重基準によって破壊応力が推定される。亀裂配管の許容応力は破壊応力と安全率の組み合わせで導かれる。すなわち、亀裂深さと長さが許容応力から決定される。この許容応力と貫通亀裂の破壊応力の比較から、許容亀裂は一様でない。この許容亀裂は3つの特性に分かれる。1つは、破断前漏洩(LBB)と亀裂の安定成長、2つめはLBBは成り立たないが亀裂の安定成長。3つめはLBBが成り立たず亀裂の不安定成長である。検査技術者やユーザーは、LBBが成り立たず亀裂の不安定成長の特性を有する3つめの許容亀裂に対し特別な注意を払う必要がある。この特別な注意を要求される許容亀裂深さと長さの境界を表す近似式を記述する。
Lacroix, V.*; Dulieu, P.*; 長谷川 邦夫
Proceedings of the ASME 2023 Pressure Vessels and Piping Conference (PVP 2023) (Internet), 5 Pages, 2023/07
原子力機器に欠陥が検出された場合、ASME Code Section XIは許容欠陥寸法を用意している。フェライト鋼の許容寸法は表IWB-3510-1で与えられている。この寸法は、機器の肉厚、欠陥のアスペクト比と内部欠陥の機器表面への接近性の3つのパラメータに依存している。しかし、これらをグラフで表すといくつかの不具合があることが分かる。そこで、ロバストな手法でASME Codeの許容される表面欠陥の見直しの必要性に光を当てるものである。この論文は現行の不具合を詳細に述べ、改善案を提案するものである。
Dulieu, P.*; Lacroix, V.*; 長谷川 邦夫
Proceedings of the ASME 2023 Pressure Vessels and Piping Conference (PVP 2023) (Internet), 7 Pages, 2023/07
供用期間中の検査で原子力機器に欠陥が検出されたとき、ASME Code Section XIでは欠陥を評価するために許容欠陥寸法が用意されている。フェライト鋼では表IWB-3510-1に許容欠陥寸法があり、この許容欠陥寸法は応力拡大係数をもとに定められた。この論文の手法は塑性崩壊と脆性破壊の防止が含めるため、塑性崩壊については欠陥のアスペクト比に関かわらず一様な極限荷重の低下を考えている。脆性破壊の防止では表面欠陥の参照応力拡大係数を基にしている。この方法で種々なアスペクト比の許容寸法を規定している。さらに、この手法は機器の表面近傍にある内部欠陥と表面欠陥の整合性をとるために追加のパラメータを加えている。最後に、ASME規格の表IWB-3510-1の許容欠陥寸法の改定を提案する。
長谷川 邦夫; Strnadel, B.*; Li, Y.; Lacroix, V.*
Journal of Pressure Vessel Technology, 144(6), p.061202_1 - 061202_6, 2022/12
被引用回数：2 パーセンタイル：14.46(Engineering, Mechanical)配管の肉厚が薄いとき、未貫通亀裂は貫通亀裂になりやすく、冷却材の漏洩の可能性が高まる。ASME Code Section XIでは、薄肉配管に対して貫通亀裂の最終許容角度が定められている。この最終許容角度は、もし未貫通亀裂が貫通亀裂になったとき、塑性崩壊しないように設けられている。この安定性を保つために貫通亀裂の塑性崩壊応力が許容応力と組み合わされている。しかしながら、薄肉配管の貫通亀裂の最終許容角度が求められない。この論文は貫通亀裂の塑性崩壊応力と未貫通亀裂の許容応力を比較する。これらの応力の比較により、貫通亀裂の最終許容応力式を導いた。この角度を、厳密解として表すとともに、オプションとして種々な運転状態における近似解で表すことができた。
長谷川 邦夫; Strnadel, B.*; Lacroix, V.*; Udyawar, A.*
International Journal of Pressure Vessels and Piping, 199, p.104722_1 - 104722_5, 2022/10
被引用回数：2 パーセンタイル：23.90(Engineering, Multidisciplinary)周方向亀裂を有する高靭性配管が引張り荷重を受けるときの塑性崩壊応力は極限荷重クライテリアで予測される。この極限荷重クライテリアはASME Code Section XIで与えられており、未貫通亀裂の許容膜応力は、塑性崩壊応力と安全率の組み合わせで決定される。ここで、許容応力は亀裂角度が大になると減小する。亀裂角度が大になると、未貫通亀裂である許容応力は貫通亀裂より大になる。このような許容応力は不安定になり、特に薄肉配管にとっては健全性を損なう恐れがある。このような懸念を払拭するために最大亀裂角度を設定する必要がある。本報告は、貫通亀裂の塑性崩壊応力を基にして、許容応力に最大許容亀裂角度の設定を提案するものである。
長谷川 邦夫; Li, Y.; Strnadel, B.*; Udyawar, A.*
Journal of Pressure Vessel Technology, 144(5), p.051305_1 - 051305_6, 2022/10
被引用回数：1 パーセンタイル：6.80(Engineering, Mechanical)周方向未貫通亀裂を有し曲げ応力を受ける配管の塑性崩壊応力はASME Code Section XIに用意された極限荷重評価法で推定される。極限荷重評価法を使って許容亀裂深さが決定され、ASME Code Section XIでは各運転状態における許容欠陥深さが表で用意されている。一方、未貫通亀裂が貫通するときの応力は局所近似極限荷重評価法で推定される。これらの評価法を用いて未貫通亀裂を有する配管の許容欠陥深さを検討した。これらの2つの評価法から各運転状態における許容欠陥深さを比較したところ、局所近似極限荷重評価法から得られる許容欠陥深さは、ほとんどの場合極限荷重評価法からえられる許容欠陥深さより小さいことが明らかになった。ASME Code Section XIで与えられる許容欠陥深さは亀裂の貫通に対して非安全であることが分かった。
山口 義仁; 長谷川 邦夫; Li, Y.; Lacroix, V.*
Proceedings of ASME 2022 Pressure Vessels and Piping Conference (PVP 2022) (Internet), 4 Pages, 2022/07
Four-point bending tests without internal pressure were performed for Type 304 stainless steel pipes with circumferential flaws at room temperature. The specimens are 1-inch diameter (33.7 mm) Schedule 160 pipes (6.3 mm wall thickness). The flaws were part-through flaws located at the pipe external side. The flaw angles are from 120
to 240, and the flaw depths are two cases of 50% and 75% of the wall thickness. Plastic collapse stresses obtained from experiments were compared with those calculated using Limit Load Criteria from Appendix C of the American Society of Mechanical Engineers Code Section XI. Limit Load Criteria were developed using flow stress at flawed section of the pipe. The plastic collapse stress test results were larger than those of the calculation results. For flaws with flaw depths less than 50% of the wall thickness, the experimental stresses were significantly large. The Limit Load Criteria given by Section XI provide conservative collapse stresses and could be improved.
Lacroix, V.*; 長谷川 邦夫; Li, Y.; 山口 義仁
Proceedings of ASME 2022 Pressure Vessels and Piping Conference (PVP 2022) (Internet), 7 Pages, 2022/07
The structural integrity assessment of pipes with circumferential surface flaw under the plastic collapse regime consists of net section collapse analysis. In recent years various researchers showed that this analysis, which has been developed based on classic beam theory, suffers from certain inaccuracies. As such, assessment purely based on net-section collapse and beam theory can reveal both conservative and unconservative results. To address those inaccuracies, in this paper authors introduced a correction factor which aims to mitigate the difference between the ASME B&PV Code Section XI equations and the experimental results. This correction factor is calculated using an empirical formula developed on the basis of a large experimental database of pipe collapse bending tests containing variety of diameter, thickness, flaw depth and flaw length values. Within this work, authors took a systematic approach to identify the most influencing factors on such a correction factor and showed that by applying this correction factor to the current solution of ASME B&PV Code Section XI, this solution becomes more accurate. This corrected approach also is in line with ASME B&PV Code Section XI Appendix C practice for axial flaw in pipes, where a semi-empirical correction factor has been considered as well.
Lacroix, V.*; Dulieu, P.*; 長谷川 邦夫; Mares, V.*
Proceedings of ASME 2022 Pressure Vessels and Piping Conference (PVP 2022) (Internet), 7 Pages, 2022/07
現行のASME Code Section XIでは、非平面状欠陥に対して簡易的な手法が提案されている。すなわち、非平面状欠陥面を最大主応力方向に投影し2つの平面状欠陥に分解する。しかしながら、この非平面状欠陥の簡易的な投影は荷重に対して、あるいは非平面状欠陥の傾きに対して常に保守的であると言えない場合がある。本論文は、ASME Codeのアプローチに保守性のある包括的な評価を実施し、現行のASME Code Section XIの不適正を克服した非平面状欠陥の代替アプローチを提案する。
