Comparison of International Codes for a Fatigue Crack Growth Flaw Tolerance Sample Problem

2021 ◽  
Author(s):  
Gary L. Stevens

Abstract As part of the development of American Society of Mechanical Engineers Code Case N-809 [1], a series of sample calculations were performed to gain experience in using the Code Case methods and to determine the impact on a typical application. Specifically, the application of N-809 in a fatigue crack growth analysis was evaluated for a large diameter austenitic pipe in a pressurized water reactor coolant system main loop using the current analytical evaluation procedures in Appendix C of Section XI of the ASME Code [2]. The same example problem was previously used to evaluate the reference fatigue crack growth curves during the development of N-809, as well as to compare N-809 methods to similar methods adopted by the Japan Society of Mechanical Engineers. The previous example problem used to evaluate N-809 during its development was embellished and has been used to evaluate additional proposed ASME Code changes. For example, the Electric Power Research Institute investigated possible improvements to ASME Code, Section XI, Nonmandatory Appendix L [3], and the previous N-809 example problem formed the basis for flaw tolerance calculations to evaluate those proposed improvements [4]. In addition, the ASME Code Section XI, Working Group on Flaw Evaluation Reference Curves continues to evaluate additional research data and related improvements to N-809 and other fatigue crack growth rate methods. As a part of these Code investigations, EPRI performed calculations for the Appendix L flaw tolerance sample problem using three international codes and standards to evaluate fatigue crack growth (da/dN) curves for PWR environments: (1) ASME Code Case N-809, (2) JSME Code methods [5], and (3) the French RSE-M method [6]. The results of these comparative calculations are presented and discussed in this paper.

Author(s):  
N. Platts ◽  
P. Gill ◽  
S. Cruchley ◽  
E. Grieveson ◽  
M. Twite

The Pressurized Water Reactor (PWR) primary coolant environment is known both to significantly reduce the fatigue life of austenitic stainless steels and to lead to enhanced fatigue crack propagation rates. Relationships for the impact of the PWR coolant environment on fatigue life have been presented in NUREG/CR-6909 using an environmental fatigue correction factor (Fen), which is a function of temperature. Fatigue crack growth behavior has been codified in ASME Code Case N-809 in terms of parameters such as rise time, stress intensity factor, load ratio and temperature. However, plant performance suggests that the application of these predicted environmental effects using current assessment procedures for fatigue for plant transient loading may be unduly pessimistic. One potential reason for this over-conservatism is thought to be that, although the majority of plant design transients result from variations in thermal loading, most available data are derived from isothermal testing. For the calculation of fatigue initiation life, NUREG/CR-6909 gives guidance on the effective temperature to be used in assessments of thermal transients. Recent results from Thermo-Mechanical Fatigue (TMF) testing on stainless steels in PWR coolant show that this guidance is conservative for out-of-phase cycling of temperature and loading, and potentially non-conservative for in-phase thermal loading. In contrast, code case N-809 gives no guidance on the effective temperature for fatigue crack growth assessments, resulting in maximum temperatures frequently being adopted for assessments of thermal transients. There is therefore a need for a clearer understanding of the impact of variable temperatures during transients on the predicted levels of environmental fatigue. This paper describes test facilities developed to permit measurements of both thermo-mechanical fatigue life and fatigue crack growth rates in pressurized water reactor environments. Initial test results obtained using these facilities are presented. The fatigue life data have been generated for a range of applied strain amplitudes, 0.45% to 1%, using temperature cycling between 100°C and 300°C. These data, for both in- and out-of-phase temperature and loading, are compared to the predictions of the “weighted Fen” model which is detailed in a separate paper, PVP2017-66030. Similarly, crack growth rate data generated for cycles between 140°C and 280°C are presented and comparisons made against the predictions of the “weighted K rate” (WKR) method detailed in paper PVP2017-65645. In both cases, the test results suggest that the weighted models are able to provide good predictions of an effective temperature to be used in fatigue assessment methods, which offer a significant improvement in the treatment of variable temperatures compared to current assessment practice.


Author(s):  
Jennifer Borg ◽  
Norman Platts ◽  
Peter Gill ◽  
Jonathan Mann ◽  
Chris Currie

Abstract Laboratory data have indicated that light water reactor environments can significantly reduce the fatigue life and crack growth performance of austenitic stainless steels. These environmental effects have been codified into design procedures and documents such as NUREG/CR-6909 Rev 1 (fatigue life) and ASME code case N-809 (crack growth). However, there is considered to be significant conservatism in these methods when applied to plant relevant loadings. The Weighted K-Rate, WKR, method was initially developed by J. Emslie et.al (PVP2016-63497) to address the influence of waveform shape as one of the potential sources of the over-conservatism in code case N-809. This method was found to significantly reduce the over-conservatism associated with ASME code case N-809. However, this method was based solely on isothermal data, and was shown to also retain significant over-conservatism, especially for out-of-phase non-isothermal waveforms typical of many thermally induced loading transients. The WKR method was further evolved into the Weighted Temperature and K-rate (WTKR) method, by Currie et.al (PVP2019-93855), further updated by Mann et.al (PVP2020-21585), which partitions the damage across the loading cycle, under non-isothermal conditions, and has been shown to significantly reduce the perceived over-conservatism associated with ASME code case N-809 when applied to many plant-relevant loading waveforms. This paper describes work that was done to investigate the impact of non-isothermal temperature / loading waveforms, and forms the bulk of non-isothermal data from which the WTKR method was derived. The data presented in this paper indicate that for out-of-phase transient loading (typical of most thermally induced plant loadings), and simple isothermal loading at low temperatures and longer rise times, the WTKR method provides a more accurate prediction of fatigue crack growth rates than the application of ASME code case N-809.


Author(s):  
Warren H. Bamford ◽  
Russell C. Cipolla ◽  
Anees Udyawar ◽  
Nathan L. Glunt

Reference fatigue crack growth (da/dN) curves for pressurized water reactor (PWR) environments have been proposed for ASME Section XI flaw evaluation applications in Code Case N-809. The reference curves are dependent on temperature, loading rate, mean stress, and cyclic stress range which are all contained in the da/dN model. This paper presents the application of N-809 in a fatigue crack growth analysis for a large diameter austenitic pipe in a PWR Reactor Coolant System main loop using the current analytical evaluation procedures in Appendix C of ASME Section XI. The example problem was used to evaluate the reference fatigue crack growth curves during the development of the code case and the results have been compared with other industry codes.


1974 ◽  
Vol 96 (4) ◽  
pp. 255-260 ◽  
Author(s):  
T. L. Gerber ◽  
J. D. Heald ◽  
E. Kiss

Fatigue crack growth tests were conducted with 1 in. (25.4 mm) plate specimens of SA508-CL2 steel in room temperature air, 550 deg F (288 deg C) air and in a 550 deg F (288 deg C), high purity, water environment. Zero-tension load controlled tests were run at cyclic frequencies as low as 0.037 CPM. Results show that growth rates in the simulated Boiling Water Reactor (BWR) water environment are 4 to 8 times faster than growth rates observed in 550 deg F (288 deg C) air and these rates are 8 to 15 times faster than the room temperature rate. In the BWR water environment, lowering the cyclic frequency from 0.37 CPM to 0.037 CPM caused only a slight increase in the fatigue crack growth rate. All growth rates measured in these tests were below the upper bound design curve presented in Section XI of the ASME Code.


Author(s):  
Yuichiro Nomura ◽  
Kazuya Tsutsumi ◽  
Hiroshi Kanasaki ◽  
Naoki Chigusa ◽  
Kazuhiro Jotaki ◽  
...  

Although reference fatigue crack growth curves for austenitic stainless steels in air environments and boiling water reactor (BWR) environments were prescribed in JSME S NA1-2002, similar curves for pressurized water reactors (PWR) were not prescribed. In order to propose the reference curve in PWR environment, fatigue tests of austenitic stainless steels in simulated PWR primary water environment were carried out. According to the procedure to determine the reference fatigue crack growth curve of BWR, which of PWR is proposed. The reference fatigue crack growth curve in PWR environment have been determines as a function of stress intensity factor range, Temperature, load rising time and stress ratio.


Author(s):  
Masayuki Kamaya ◽  
Takao Nakamura

Incorporation of the flaw tolerance concept in plant design and maintenance is discussed in order to consider the reduction in fatigue life due to the high-temperature water environment of class 1 components of NPPs. The flaw tolerance concept has been included in Section XI of the ASME BPVC. The structural factor (safety factor) for the flaw evaluation is considered in the stress, whereas it was considered in the design fatigue curve in Section III of the ASME BPVC. In order to apply the flaw tolerance concept to plant design and maintenance, it is necessary to assume the crack initiation and growth behavior. In this study, first, crack initiation and growth behavior during fatigue tests was reviewed and a relationship between the crack growth and fatigue life was quantified. Then, the safety factor was considered in the crack growth curve. It was shown that the crack size could be correlated to the usage factor and the flaw tolerance concept was reasonably considered in the plant maintenance by using the proposed virtual fatigue crack growth curve.


Author(s):  
Kunio Hasegawa ◽  
Yinsheng Li ◽  
Katsumasa Miyazaki ◽  
Koichi Saito

If a subsurface flaw is located near a component surface, the subsurface flaw is transformed to a surface flaw in accordance with a flaw-to-surface proximity rule. The re-characterization process from subsurface to surface flaw is adopted in all fitness-for-service (FFS) codes. However, the criteria of the re-characterizations are different among the FFS codes. Cyclic tensile experiment was conducted on a carbon steel flat plate with a subsurface flaw at ambient temperature. The objective of this paper is to compare the experiment and calculation of fatigue crack growth behavior for a subsurface flaw and the transformed surface flaw, and to describe the validity of the flaw-to-surface proximity rule defined by ASME Code Section XI, JSME S NA1 Code and other codes.


2014 ◽  
Vol 891-892 ◽  
pp. 1009-1014
Author(s):  
R. Craig McClung ◽  
Michael P. Enright ◽  
Jonathan P. Moody ◽  
Yi Der Lee ◽  
John McFarland

Recently a new methodology was developed for automated fatigue crack growth (FCG) life analysis of components based on finite element stress models, weight function stress intensity factor solutions, and algorithms to define idealized fracture geometry models. This paper describes how the new methodology is being used to integrate FCG analysis into highly automated design assessments of component life and reliability. In one application, the FCG model automation is supporting automated calculation of fracture risk due to inherent material anomalies that can occur anywhere in the volume of the component. Automated schemes were developed to divide the component into a computationally optimum number of sub-volumes with similar life and risk values to determine total component reliability accurately and efficiently. In another application, the FCG model automation is supporting integration of FCG life calculations with manufacturing process simulation to perform integrated computational materials engineering. Calculation of full-field, location-specific residual stresses or microstructure is being linked directly with automated life analysis to determine the impact of manufacturing parameters on component reliability.


Author(s):  
Jens P. Tronskar ◽  
Gudfinnur Sigurdsson ◽  
Olav Fyrileiv ◽  
Olav Forli ◽  
Joseph H. Kiefer ◽  
...  

Probabilistic methods have been used to develop the basis for free-span inspection of a gas pipeline system in the South China Sea. The objective of the probabilistic analysis was to study the probability of fatigue failure associated with postulated planar flaws in the HAZ of repair welds performed on some of the girth welds. The impact of flaws on the fatigue life under different free-span conditions were studied. Conventional free-span analysis involves computation of allowable free-span lengths based on onset of in-line vibrations and does not normally consider fatigue crack growth. To consider the effect of the weld flaws on the failure probability a combined probabilistic fatigue and fracture model is required. For the particular pipelines analysed automatic ultrasonic testing (AUT) was used replacing the conventional radiography of the girth welds. Conservatism in the free-span assessment can then be significantly reduced by taking into account detailed flaw sizing information from the AUT. The inspection records provide distribution of flaw height, length and position. Combined with information on current distribution, material strength and fracture toughness distribution, a detailed probabilistic fatigue crack growth and unstable fracture assessment can be conducted as per the Det Norske Veritas (DNV) 2000 Rules for Submarine Pipeline Systems [1] using the response models of the DNV Guideline 14 for free-span analyses [2]. The objective of this analysis is to estimate the critical free-span lengths and the time for fatigue cracks to penetrate the pipe wall.


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