A Review of Fatigue Crack Growth Thresholds for Metals in Fitness-for-Service Codes: On the Uncertainty of Using the Thresholds at Negative Stress Ratios

2021 ◽  
Author(s):  
Kunio Hasegawa ◽  
Bohumir Strnadel ◽  
Vratislav Mares ◽  
David Dvorak ◽  
Saburo Usami
Keyword(s):  
Stainless Steel ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Ferritic Steel ◽  
Literature Survey ◽  
Ferritic Steels ◽  
Section Viii ◽  
Stress Ratios

Abstract Fatigue crack growth thresholds deltaKth for metals are provided in many fitness-for-service codes. However, fatigue thresholds at negative stress ratios are not uniform. There are two forms of thresholds at negative stress ratios: constant thresholds irrespective of stress ratios, or increasing thresholds with decreasing stress ratios. The definitions of the thresholds at negative stress ratios also take two forms: either deltaKth = Kmax - Kmin, or deltaKth = Kmax. ASME Section VIII, Section XI (ferritic steel) and IIW give constant thresholds expressed by deltaKth = Kmax. API 579 and ASME Section XI (stainless steel) give increases in thresholds with decreasing stress ratios and the thresholds are expressed by deltaKth = Kmax - Kmin. BS 7910 gives constant thresholds expressed by deltaKth = Kmax - Kmin. The fatigue thresholds differ significantly among different FFS codes. Appropriate thresholds for ferritic steels, stainless steels and aluminum alloys are demonstrated in the literature survey.

Analysis of Environmental Fatigue Crack Growth Behavior of Type 347 Stainless Steels Under Simulated PWR Water Conditions

2017 ◽  
Author(s):  
Seokmin Hong ◽  
Ki-Deuk Min ◽  
Soon-Hyeok Jeon ◽  
Bong-Sang Lee
Keyword(s):  
Stainless Steel ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Growth Behavior ◽  
Crack Growth Behavior ◽  
Fatigue Crack Growth Behavior ◽  
Water Conditions ◽  
Asme Code

In this study, the fatigue crack growth behavior of Type 347 stainless steel (SS) used in pressurizer surge line in Korea Standard Nuclear Power Plant was analyzed. Environmental fatigue crack growth rates (FCGRs) were evaluated using pre-cracked compact tension (CT) specimens under the various simulated PWR water conditions; different levels of dissolved oxygen (DO) and loading frequencies. FCGRs of 347SSs were accelerated under PWR water conditions. When DO levels increased and frequency decreased, FCGR of 347SS increased. Under the more corrosive environment at crack tip, FCGRs were accelerated more. FCGRs of 347SSs under PWR water condition were compared with reference FCGR curves of stainless steel in ASME code section XI, ASME Code Case N-809, and JSME based on FCGR data of 304SS and 316SS. In this study, FCGRs of 347SS were slightly faster than reference curves in JSME under PWR environment but slower than that in JSME under BWR environment. Compared to reference FCGR curve in ASME Code Case N-809, FCGRs of 347 stainless steels are similar or slightly higher.

Definition of Fatigue Crack Growth Thresholds for Ferritic Steels in Fitness-for-Service Codes

2018 ◽  
Author(s):  
Kunio Hasegawa ◽  
Bohumir Strnadel
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
Stress Ratio ◽  
Fatigue Tests ◽  
Ferritic Steels ◽  
Stress Ratios ◽  
Definition Of ◽  
Crack Growth Rates

Fatigue crack growth rates are expressed as a function of the stress intensity factor ranges. The fatigue crack growth thresholds are important characteristics of fatigue crack growth assessment for the integrity of structural components. Almost all materials used in these fatigue tests are ferritic steels. As a result, the reference fatigue crack growth rates and the fatigue crack growth thresholds for ferritic steels were established as rules and they were provided by many fitness-for-service (FFS) codes. However, the thresholds are not well defined in the range of negative stress ratio. There are two types of thresholds under the negative stress ratio. That is, constant thresholds and increment of thresholds with decreasing stress ratios. The objective of this paper is to introduce the thresholds provided by FFS codes and to analyze the thresholds using crack closure. In addition, based on the experimental data, definition of the threshold is discussed to apply to FFS codes. Finally, threshold for ferritic steels under the entirely condition of stress ratio is proposed to the ASME Code Section XI.

Technical Basis of Fatigue Crack Growth Threshold for Stainless Steel in Air Environment for ASME Code Section XI

2017 ◽  
Author(s):  
Kunio Hasegawa ◽  
Saburo Usami
Keyword(s):  
Stainless Steel ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Austenitic Stainless Steels ◽  
Threshold Values ◽  
Asme Code ◽  
American Society ◽  
Growth Threshold

The fatigue crack growth threshold is an important characteristic of crack growth assessment for the integrity of structural components. However, threshold values for austenitic stainless steels in air environment are not well provided in many fitness-for-service (FFS) codes, although extensive amount of fatigue crack growth tests data has been published. This paper focuses on fatigue crack growth threshold values for austenitic stainless steel in air environment at room and high temperatures. The paper introduces the current fatigue crack growth rates provided by the ASME (American Society of Mechanical Engineers) Code Section XI and summarizes the available test data of fatigue crack growth thresholds based on the literature survey. The paper then discusses the applicability of the existing fatigue crack growth thresholds for stainless steels and proposes a new relation as a function of the stress ratio for use by the ASME Code Section XI.

scholarly journals Fatigue Crack Growth Thresholds at Negative Stress Ratio for Ferritic Steels in ASME Code Section XI

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Kunio Hasegawa ◽  
Bohumir Strnadel ◽  
Saburo Usami ◽  
Valery Lacroix
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stress Ratio ◽  
Maximum Stress ◽  
Ferritic Steels ◽  
Intensity Factors ◽  
Asme Code ◽  
Maximum Stress Intensity ◽  
Stress Ratios

Thresholds of fatigue crack growth rates are important characteristics for fatigue crack growth assessment for the integrity of structural components. ASME Code Section XI provides fatigue crack growth thresholds for ferritic steels in air and water environments. The threshold is given as a constant value under a negative stress ratio. However, the thresholds are not clearly defined in the range of negative stress ratios. The definition seems to be maximum stress intensity factors. Besides, the thresholds expressed by the maximum stress intensity factors decrease with decreasing stress ratios. This means that the thresholds under negative stress ratios become unconservative assessments. The objective of this paper is to discuss the definition of fatigue crack growth threshold and to propose the threshold equation for the ASME Code Section XI, based on experimental data obtained from a literature survey.

Fatigue Crack Growth for Ferritic Steel Under Negative Stress Ratio

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Yoshihito Yamaguchi ◽  
Kunio Hasegawa ◽  
Yinsheng Li
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Intensity Factor ◽  
Crack Growth ◽  
Applied Stress ◽  
Ferritic Steel ◽  
Asme Code ◽  
Stress Ratios

Abstract The phenomenon of crack closure is important in the prediction of fatigue crack growth behavior. Many experimental data indicate crack closures during fatigue crack growths both under tensile–tensile loads and tensile–compressive loads at constant amplitude loading cycles, depending on the magnitude of applied load amplitudes and stress ratios. Appendix A-4300 of the ASME Code Section XI provides two equations of fatigue crack growth rates for ferritic steels expressed by stress intensity factor ranges at negative stress ratios. The boundary of the two equations is classified with the magnitude of applied stress intensity factor ranges, in consideration of the crack closures. However, the boundary value provided by the ASME Code Section XI is not technically well known. The objective of this paper is to investigate the influence of the magnitudes of the applied stress intensity factor ranges on the crack closures. Fatigue crack growth tests using ferritic steel specimens were performed in air environment at room and high temperatures. From the crack closures obtained by the tests, it was found a new boundary which is smaller than the definition given by the Appendix A-4300.

Fatigue Crack Growth Rate Studies on Stainless Steel Welds

2018 ◽  
Author(s):  
Manuel Thomas ◽  
Raghu V. Prakash ◽  
Ganesh Sundararaman ◽  
Vasudevan Muthukumaran
Keyword(s):  
Stainless Steel ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Heat Input ◽  
Tig Welding ◽  
Weld Penetration ◽  
Structural Members ◽  
Single Pass

The low carbon, nitrogen enhanced SS 304 L(N) stainless steels are one of the most potential candidates for the structural members in chemical industries and powerplants operating at hostile environments of temperature and corrosion. In service, the structural members fabricated using welding process, when subjected to a combination of mechanical load and elevated temperature can fail by fatigue. The Welding of Austenitic stainless steels using Tungsten Inert gas (TIG) is often limited by the depth of weld penetration, which can be achieved during a single pass. This necessitates for the use of multiple passes resulting in weld distortion and generation of residual stress. The Use of an electronegative flux (Activating flux) during the TIG welding (A-TIG) is known to enhance the weld penetration, thereby reducing the number of passes. The present study evaluates the fatigue crack growth in stainless steel weldment (304L(N) welds) joined using conventional Multipass TIG welding and Activated flux TIG welding at 673K. Compact Tension (C(T)) specimens having a width of 50.8 mm and a thickness of 4 mm were extracted from the location of heat-affected zone (HAZ) and weld metal (WM) for A-TIG and MP-TIG configurations. From the micro-structural evaluation of A-TIG welds, it is noted that high heat input in a single pass has favored the formation of coarse equiaxed grains along the weld center. The use of multiple passes at reduced heat input has resulted in the formation of finer grains, with the orientation of grains changing along each weld pass interface. This finer randomly oriented grains has resulted in increasing crack path resistance through the MP-TIG welds compared to A-TIG welds. Thus from a view point of fatigue crack growth, due to the presence of fine grains, conventional Multi-pass weld is superior compared to A-TIG, but in cases where there is a creep or creep-fatigue combination, the A-TIG weld may prove to be useful.

scholarly journals Advantageous Description of Short Fatigue Crack Growth Rates in Austenitic Stainless Steels with Distinct Properties

Metals ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 475
Author(s):  
Lukáš Trávníček ◽  
Ivo Kuběna ◽  
Veronika Mazánová ◽  
Tomáš Vojtek ◽  
Jaroslav Polák ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Growth Rates ◽  
Large Scale ◽  
J Integral ◽  
Scale Yielding ◽  
Residual Fatigue ◽  
Crack Growth Rates

In this work two approaches to the description of short fatigue crack growth rate under large-scale yielding condition were comprehensively tested: (i) plastic component of the J-integral and (ii) Polák model of crack propagation. The ability to predict residual fatigue life of bodies with short initial cracks was studied for stainless steels Sanicro 25 and 304L. Despite their coarse microstructure and very different cyclic stress–strain response, the employed continuum mechanics models were found to give satisfactory results. Finite element modeling was used to determine the J-integrals and to simulate the evolution of crack front shapes, which corresponded to the real cracks observed on the fracture surfaces of the specimens. Residual fatigue lives estimated by these models were in good agreement with the number of cycles to failure of individual test specimens strained at various total strain amplitudes. Moreover, the crack growth rates of both investigated materials fell onto the same curve that was previously obtained for other steels with different properties. Such a “master curve” was achieved using the plastic part of J-integral and it has the potential of being an advantageous tool to model the fatigue crack propagation under large-scale yielding regime without a need of any additional experimental data.

Effect of Hydrogenated Water on Fatigue Crack Growth for Austenitic Stainless Steel in Simulated BWR Water Environment

2004 ◽  
Author(s):  
Li H. Wang
Keyword(s):  
Stainless Steel ◽  
Fatigue Crack ◽  
Cyclic Loading ◽  
Austenitic Stainless Steel ◽  
Fatigue Crack Growth ◽  
Water Chemistry ◽  
Crack Growth ◽  
Growth Stage ◽  
Transgranular Fracture ◽  
Cyclic Loading Condition

Fatigue crack growth rates (FCGR) of sensitized austenitic stainless steel (SS) were measured in simulated BWR water at 288 °C using compact tension specimens under different cyclic loading modes, including saw-tooth, trapezoidal and constant loading pattern. This study tested sensitized SS in normal water chemistry (NWC) and hydrogen water chemistry (HWC) respectively, and attempted to clarify the effect of low electrochemical corrosion potential on the FCGR of sensitized stainless steel. Significant environment effects on FCGR of sensitized stainless steel were observed in both water chemistries when compared with air fatigue curve. The pronounced suppression effect of HWC on crack growth in statically sustained load was not observed in cyclic loading condition. ASME curve doesn’t seem to be conservative and could not bound all the FCGR data tested in this study. In contrast, all of the measured FCGR data were bound by the JSME disposition curve. PLEDGE model proposed by General Electric reasonably predicted the FCGR of sensitized SS in NWC, but underestimated the FCGR in HWC. ANL’s superposition model successfully estimated the FCGR measured in both water chemistries. The fractography exhibited transgranular fracture mode during the crack initiation and growth stage. No differences in the appearance of fracture surface were observed in HWC and NWC. Only in very high DO environments, the sensitized 304 SS exhibited the mixed mode of intergranular and transgranular during growth stage.

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