A Critical Review of Recent Fatigue Crack Growth Data in Relation to ASME Code Case N-809

2019 ◽  
Author(s):  
Jonathan Mann ◽  
Chris Currie ◽  
David Tice ◽  
Norman Platts
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Water Environment ◽  
Low Carbon ◽  
Growth Data ◽  
R Ratio ◽  
Asme Code ◽  
Best Fit

Abstract ASME Code Case N-809 provides Fatigue Crack Growth (FCG) expressions for austenitic stainless steels operating in a primary water environment within a Pressurised Water Reactor (PWR). The code case currently contains different expressions for nominally low-carbon (304L, 316L) and conventional (304, 316) grades. Since the original work that provided the technical basis for N-809 was completed, an increased amount of FCG data has become available through industry testing, particularly for low-carbon stainless steels. A large database is now available that contains significantly more data than the one used in the original development of the code case. The data cover a wider range of testing conditions (temperature, loading rate, and mean stress) and represent a more diverse population of material types, including multiple heats. In this paper, the N-809 laws are re-analysed in terms of these new data, with a focus on each of the environmental dependencies that are currently included in the law. In particular, alternative R-ratio expressions from the literature are shown to provide an improved description of the effect of R-ratio for nominally low-carbon materials. The statistical distribution of FCG rates and the treatment of partially retarded data are also investigated as part of the derivation of revised descriptions of best-fit and bounding FCG rates. The analysis highlights a small amount of potential non-conservatism in the current N-809 description of best-fit FCG rates at higher R-ratios. The current description of upper-bounding behaviour is shown to still be valid, however significant over-conservatism exists at lower R-ratios.

Further Development of Fatigue Crack Growth Expressions for Austenitic Stainless Steels in PWR Water and Additional Validation of the WTKR Method

2020 ◽  
Author(s):  
Jonathan Mann ◽  
Chris Currie ◽  
Jennifer Borg ◽  
Norman Platts
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Water Environment ◽  
Austenitic Stainless Steels ◽  
Loading Conditions ◽  
Low Carbon ◽  
High Carbon ◽  
Further Development

Abstract The primary water environment in a Pressurised Water Reactor (PWR) can have a significantly detrimental effect on the Fatigue Crack Growth (FCG) rates of Austenitic Stainless Steels. Expressions to describe FCG in these materials are provided in ASME Code Case N-809, which was based on results from tests performed under isothermal, simple waveform loading. A previous re-analysis of a much larger database of FCG results highlighted improvements to the N-809 model for nominally low carbon material grades. For non-isothermal and/or complex mechanical loading conditions, further improvements of the prediction of FCG rates were demonstrated by using the Weighted Temperature and K-Rate (WTKR) method. The combined use of improved FCG expressions and the WTKR method is expected to provide significant reductions in over-conservatism when used to assess plant-realistic loading transients. This paper describes the further development of revised expressions to describe the effect of PWR environments on FCG in austenitic stainless steels. The analysis is extended to a wider range of different types of stainless steel, including nominally high carbon 304 variants and 316-type materials. The analysis highlights that previously specified differences in FCG behaviour between nominally low and high carbon materials are minimal, and that 316-type materials exhibit improved performance in these environments. Further testing has also been performed using non-isothermal and complex waveform loading conditions, and these results are used as additional validation of the WTKR methodology.

Fatigue Crack Growth in SA508-CL2 Steel in a High Temperature, High Purity Water Environment

1974 ◽  
Vol 96 (4) ◽  
pp. 255-260 ◽  
Author(s):  
T. L. Gerber ◽  
J. D. Heald ◽  
E. Kiss
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Rates ◽  
High Purity ◽  
Room Temperature ◽  
Water Environment ◽  
Cyclic Frequency ◽  
Asme Code ◽  
Temperature Rate

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.

Development of Fatigue Crack Growth Thresholds for Austenitic Stainless Steels Exposed to Air Environment for ASME Code Section XI

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Kunio Hasegawa ◽  
Saburo Usami
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Stress Ratio ◽  
Austenitic Stainless Steels ◽  
Stress Intensity Factor Range ◽  
Asme Code ◽  
American Society ◽  
Growth Experiments

Fatigue crack growth thresholds ΔKth define stress intensity factor range below which cracks will not grow. The thresholds ΔKth are useful in industries to determine durability lifetime. Although massive fatigue crack growth experiments for stainless steels in air environment had been reported, the thresholds ΔKth are not codified at the American Society of Mechanical Engineers (ASME) Code Section XI, as well as other fitness-for-service (FFS) codes and standards. Based on the investigation of a few FFS codes and review of literature survey of experimental data, the thresholds ΔKth exposed to air environment have been developed for the ASME Code Section XI. A guidance of the thresholds ΔKth for austenitic stainless steels in air at room and high temperatures can be developed as a function of stress ratio R.

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.

Technical Basis for Revision of Code Case N-809 on Reference Fatigue Crack Growth Curves for Austenitic Stainless Steels in Pressurized Water Reactor Environments

2021 ◽  
Author(s):  
Russell C. Cipolla ◽  
Warren H. Bamford ◽  
Kiminobu Hojo ◽  
Yuichiro Nomura
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Growth Curves ◽  
Austenitic Stainless Steels ◽  
Pressurized Water Reactor ◽  
Pressurized Water ◽  
R Ratio ◽  
Technical Basis

Abstract Reference fatigue crack growth curves for austenitic stainless steels exposed to pressurized water reactor environments have been available in the ASME Code, Section XI in their present form with the publication of Code Case N-809 in Supplement 2 to the 2015 Code Edition. The reference curves are dependent on temperature, loading rate (loading rise time), mean stress (R-ratio), and cyclic stress intensity factor range (ΔK), which are all contained in the model. Since the first implementation of this Code Case, additional data have become available, and the purpose of this paper is to provide the technical basis for revision of the Code Case. Changes have been made in three areas: R-ratio behavior, threshold for crack growth (ΔKth), and crack growth rate dependence on ΔK. In addition, the temperature model was revisited to study the temperature effects for T < 150°C, where the current model predicts an increase in da/dN based on limited test data at about 100°C (200°F). At this point, the current temperature model is considered conservative and no change is proposed in this revision to N-809. The R-ratio model has been revised for both high and low carbon stainless steels, a significant improvement over the original procedures. Perhaps the most important revision is in the area of the threshold for the initiation of fatigue crack growth; such data are difficult to obtain, and the previous model was very conservative. Finally, the crack growth exponent was revised slightly to make it consistent with the regression analysis of the original data.

An Approach to Account for Negative R-Ratio Effects in Fatigue Crack Growth Calculations for Pressure Vessels Based on Crack Closure Concepts

1994 ◽  
Vol 116 (1) ◽  
pp. 30-35 ◽  
Author(s):  
J. M. Bloom
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Pressure Vessels ◽  
Nuclear Industry ◽  
Closure Models ◽  
R Ratio ◽  
Compressive Loads ◽  
Asme Code

Current fatigue crack growth procedures in the commercial nuclear industry do not clearly specify how compressive loads are to be handled and, therefore, regulatory agencies usually recommend a conservative approach requiring full consideration of the loads. This paper demonstrates that a more realistic approach to account for compressive loads can be formulated using crack closure concepts. Several empirical plasticity-induced crack closure models were evaluated. An approach in the Section XI ASME Code for tensile loading only has been extended and evaluated for negative R-ratios. However, the paper shows this approach to be overly conservative. The approaches using crack closure models are shown to be more accurate. An analytically based crack closure model, while more complicated, is shown to give a theoretical basis to the empirically derived crack closure models. The paper concludes with a recommendation for modifying the current ASME Code practices consistent with the crack closure models and fatigue crack growth data from negative R-ratio tests.

Effect of Stress Ratio on Fatigue Crack Growth Threshold for Austenitic Stainless Steels in Air Environment

2017 ◽  
Vol 741 ◽  
pp. 88-93 ◽  
Author(s):  
Kunio Hasegawa ◽  
Saburo Usami
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Test Data ◽  
Stainless Steels ◽  
Stress Ratio ◽  
Austenitic Stainless Steels ◽  
R Ratio ◽  
Growth Assessment ◽  
Growth Threshold

The fatigue crack growth threshold ΔKth is an important characteristic of crack growth assessment for the integrity of structural components. However, the accurate threshold ΔKth values for austenitic stainless steels in air environment are lacking in many fitness-for-service (FFS) codes, although fatigue crack growth tests have been performed and many test data had been published. This paper focuses on fatigue crack growth threshold ΔKth values for austentic stainless steel in air environment. The paper introduces the current ΔKth values provided by four major FFS codes and summarizes the available test data based on the literature survey. The paper then discusses the applicability of the existing ΔKth for stainless steels and proposes a new relation as a function of the stress ratio (the R ratio) for use by FFS codes.

Re-Evaluation of Fatigue Crack Growth Curve for Austenitic Stainless Steels in BWR Environment

2012 ◽  
Author(s):  
Masao Itatani ◽  
Takuya Ogawa ◽  
Chihiro Narazaki ◽  
Toshiyuki Saito
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Curve ◽  
Stainless Steels ◽  
Austenitic Stainless Steels ◽  
Reference Curve ◽  
Growth Data ◽  
Crack Growth Curve ◽  
Confidential Limit

The Rules on Fitness-for-Service for Nuclear Power Plants of the Japan Society of Mechanical Engineers (JSME Code) has the reference fatigue crack growth curve for austenitic stainless steels in BWR environment. This reference curve was determined as the upper bound of crack growth data excluding the outlier data. However, the other reference curves for fatigue crack growth rate such as austenitic stainless steels and ferritic steels in air environment and ferritic steels in water environment in the ASME Boiler and Pressure Vessel Code, Section XI and the JSME Code, austenitic stainless steels in PWR environment in the JSME Code and Ni-base alloys in PWR environment in the JSME Code Case are determined based on the 95% upper confidential limit by statistic data treatment. In the present study, the fatigue crack growth data of austenitic stainless steels in BWR environment were re-evaluated statistically. It was found that the current reference curve almost coincides with 95% upper confidential limit of fatigue crack growth data in the Paris region. Consequently, the current reference fatigue crack growth curve for austenitic stainless steels in BWR environment in the JSME Code can be regarded to stand on the same technical bases with other reference fatigue crack growth curves. Furthermore, the authors proposed to extend applicable upper bound of load rising time tr from 1000 s to 32000 s.

Fatigue Crack Growth Rates for Ferritic Steels Under Negative R Ratio

2016 ◽  
Author(s):  
Kunio Hasegawa ◽  
Vratislav Mares ◽  
Yoshihito Yamaguchi ◽  
Yinsheng Li
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Closure ◽  
Growth Rates ◽  
Ferritic Steels ◽  
R Ratio ◽  
Asme Code ◽  
Reference Curves ◽  
Crack Growth Rates

Reference curves of fatigue crack growth rates for ferritic steels in air environment are provided by the ASME Code Section XI Appendix A. The fatigue crack growth rates under negative R ratio are given as da/dN vs. Kmax, It is generally well known that the growth rates decreases with decreasing R ratios. However, the da/dN as a function of Kmax are the same curves under R = 0, −1 and −2. In addition, the da/dN increases with decreasing R ratio for R < −2. This paper converts from da/dN vs. Kmax to da/dN vs. ΔKI, using crack closure U. It can be obtained that the growth rates da/dN as a function of ΔKI decrease with decreasing R ratio for −2 ≤ R < 0. It can be seen that the growth rate da/dN vs. ΔKI is better equation than da/dN vs. Kmax from the view point of stress ratio R. Furthermore, extending crack closure U to R = −5, it can be explained that the da/dN decreases with decreasing R ratio in the range of −5 ≤ R < 0. This tendency is consistent with the experimental data.

A Fatigue Crack Growth Model for Type 304 Austenitic Stainless Steels in an Elevated Temperature Air Environment

2021 ◽  
Author(s):  
Kathleen C. Barron
Keyword(s):  
Fatigue Crack ◽  
Elevated Temperature ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Stainless Steels ◽  
Austenitic Stainless Steels ◽  
Reference Curve ◽  
Paris Law ◽  
R Ratio ◽  
Type 304

Abstract The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section XI utilizes reference fatigue crack growth rate (FCGR) curves for flaw evaluations. The current ASME reference curve for austenitic stainless steels in air environments is a Paris-Law relation with a single ΔK exponent that covers the entire ΔK range. Since generation of the model that became the ASME reference curve, extensive additional FCGR testing of Type 304, Type 304L, and Type 304/304L dual-certified stainless steel and the corresponding weld metal has been performed in an elevated temperature air environment. This testing revealed fatigue crack growth (FCG) behaviors that were not adequately captured by the ASME reference curve. In particular, the ASME reference curve failed to capture a flattening of the FCGR curve in the intermediate ΔK range before the FCGRs sharply dropped off as the threshold behavior is approached. Additionally, the FCGR data showed a slight frequency-dependence. Based on this new data, a new FCGR model was generated for Type 304 austenitic stainless steels in air environments between 250°C and 338°C. A tri-linear Paris-Law style correlation was chosen for the updated FCGR model to accommodate both the flattening of the FCGR curve at intermediate ΔK levels and the sharp downturn in the near-threshold ΔK regime. Each of the three branches of the FCGR curve exhibit a different R-ratio dependence, with the near-threshold regime being the most sensitive to changes in the R-ratio.

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