Flaw Evaluation Procedure for Cast Austenitic Stainless Steel Materials Using Thermal Aging Models

2017 ◽  
Author(s):  
M. F. Uddin ◽  
G. M. Wilkowski ◽  
S. Pothana ◽  
F. W. Brust
Keyword(s):  
Fracture Toughness ◽  
Thermal Aging ◽  
Austenitic Stainless Steels ◽  
Full Scale ◽  
Evaluation Procedure ◽  
Chemical Compositions ◽  
Large Variability ◽  
Acceptance Criterion ◽  
Operating Temperatures ◽  
Aging Models

Thermal embrittlement of cast austenitic stainless steels (CASS) can occur at reactor operating temperatures potentially leading to a reduction in their fracture toughness. Some aged CASS materials have the potential to have exceedingly low toughness and also show high toughness variability due to the nature of their microstructure. The experimentally measured JIc values for CASS materials showed a large scatter when plotted against ferrite number (FN) or chrome equivalent number (Creq). Because of their low aged toughness with such a large variability, flaw evaluations of CASS material needs to be done carefully, especially since most US PWR nuclear plants have been given plant-life extensions for 60-year operation, and consideration of further extension to 80 years is underway. However, the ASME Section XI Appendix C flaw acceptance criterion currently does not have a recommended procedure for flaw evaluation for CASS materials with FN ≥ 20, and the Working Group recognizes that the changes might also be needed for CASS with FN less than 20. In this paper, a flaw evaluation procedure for fully aged CASS materials is presented using JIc values at LWR operating temperatures predicted from several existing thermal-aging toughness degradation models. All available thermal aging models for CASS materials were evaluated which predict fully aged (lower saturated toughness condition) fracture toughness of CASS based on their chemical compositions. A set of 20 experimental test data was analyzed by using all models to find the most accurate thermal aging models. Using the most accurate models, correlations between predicted JIc values and French Creq-Fr and ASTM A800 FN were developed from a database of 274 pipe/elbows in US PWR plants whose chemical compositions were known. Finally, the correlation was used to determine the elastic-plastic fracture correction factor (Z factor) for CASS pipe and fittings as a function of pipe diameter and their chemical compositions from material certification sheet using the Dimensionless-Plastic-Zone-Parameter (DPZP) analysis. The DPZP analysis is a relatively simple curve-fitting procedure through full-scale circumferential surface-cracked pipe tests developed in pipe fracture projects funded by the USNRC, and was checked against a full-scale aged CF8m pipe fracture test. After determining the chemical composition specific Z factor for CASS materials, the flaw evaluation can be performed according to the ASME Section XI Appendix C procedures.

Comparison of Different Thermal Aging Models to Assess Fully Aged Toughness in Cast Austenitic Stainless Steels

2015 ◽  
Author(s):  
M. F. Uddin ◽  
G. M. Wilkowski ◽  
R. E. Kurth ◽  
F. W. Brust ◽  
D.-J. Shim ◽  
...  
Keyword(s):  
Stainless Steels ◽  
Thermal Aging ◽  
Austenitic Stainless Steels ◽  
Evaluation Procedure ◽  
Chemical Compositions ◽  
Nuclear Plants ◽  
Thermal Embrittlement ◽  
Aging Models ◽  
Reactor Operating ◽  
Relationship Of

Thermal embrittlement of cast austenitic stainless steels (CASS) occurs at reactor operating temperatures during the reactor design lifetime of 40 years leading to a reduction in their toughness and an increase in strength. Additionally most US nuclear plants have been given plant life extensions for 60-year operation, and consideration of further extension to 80 years is underway. As the fracture toughness reduces due to thermal embrittlement, some aged CASS materials have the potential to have exceedingly low toughness. CASS can also show high toughness variability due to the variability of its microstructure. Recently an ASME Section XI Code Case N-838 has been proposed to evaluate the flaw tolerance based on probabilistic fracture mechanics (PFM). An assessment of mechanical-property degradation is an input to perform the flaw evaluation procedure in CASS components. There are at least four different models for predicting the change in J-R curves in CASS due to thermal aging. One model is proprietary and the other three are the Argonne/NUREG-CR/4513R1, the French/EDF and a Japanese model. In this work, two of the thermal aging models were reviewed, reproduced and validated against their example cases for each individual model. Both models were then utilized to assess the fully aged conditions for cases that covers a large spectrum of CASS J R curves with high COV (coefficient of variance). Finally, J-R curves distributions using both Argonne and French models were established by examining the actual chemical compositions of CASS materials found in some US PWR plants. The J-R curves distributions include 21 pipes/fittings in primary pipe loop as well as data from an EPRI report. The calculated toughness variability in a single LBB plant is compared using the Argonne and French models. Additionally the relationship of the “C” and “m” parameters used in the power-law J-R curve equations (J = C×Δam) was explored to determine the proper way to statistically vary the J-R curve in probabilistic analyses.

scholarly journals Fracture Resistance of Cast Austenitic Stainless Steels

2016 ◽  
Author(s):  
Y. Chen ◽  
W-Y. Chen ◽  
A. S. Rao ◽  
Z. Li ◽  
Y. Yang ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Growth Rate ◽  
Corrosion Resistance ◽  
Neutron Irradiation ◽  
Stainless Steels ◽  
Thermal Aging ◽  
Austenitic Stainless Steels ◽  
Light Water Reactor ◽  
Delta Ferrite ◽  
Light Water

Cast austenitic stainless steels (CASS) possess excellent corrosion resistance and mechanical properties and are used alongside with wrought stainless steels (SS) in light water reactors for primary pressure boundaries and reactor core internal components. In contrast to the fully austenitic microstructure of wrought SS, CASS alloys consist of a dual-phase microstructure of delta ferrite and austenite. The delta ferrite is critical for the service performance since it improves the strength, weldability, corrosion resistance, and soundness of CASS alloys. On the other hand, the delta ferrite is also vulnerable to embrittlement when exposed to reactor service temperatures and fast neutron irradiations. In this study, the combined effect of thermal aging and neutron irradiation on the degradation of CASS alloys was investigated. Neutron-irradiated CASS specimens with and without prior thermal aging were tested in simulated light water reactor environments for crack growth rate and fracture toughness. Miniature compact-tension specimens of CF-3 and CF-8 alloys were tested to evaluate the extent of embrittlement resulting from thermal aging and neutron irradiation. The materials used are static casts containing more than 23% delta ferrite. Some specimens were thermally aged at 400 °C for 10,000 hours prior to the neutron irradiation to simulate thermal aging embrittlement. Both the unaged and aged specimens were irradiated at ∼320°C to a low displacement damage dose of 0.08 dpa. Crack growth rate and fracture toughness J-integral resistance curve tests were carried out on the irradiated and unirradiated control samples in simulated light water reactor environments with low corrosion potentials. While no elevated crack propagation rates were detected in the test environments, significant reductions in fracture toughness were observed after either thermal aging or neutron irradiation. The loss of fracture toughness due to neutron irradiation seemed more evident in the samples without prior thermal aging. Transmission electron microscope (TEM) examination was carried out on the thermally aged and neutron irradiated specimens. The result showed that both neutron irradiation and thermal aging can induce significant changes in the delta ferrite. A high density of G-phase precipitates was observed with TEM in the thermally aged specimens, consistent with previous results. Similar precipitate microstructures were also observed in the neutron-irradiated specimens with or without prior thermal aging. A more extensive precipitate microstructure can be seen in the samples subjected to both thermal aging and neutron irradiation. The similar precipitate microstructures resulting from thermal aging and neutron irradiation are consistent with the fracture toughness results, suggesting a common microstructural origin of the observed embrittlement after thermal aging and neutron irradiation.

Flaw Evaluation Procedure for Cast Austenitic Stainless Steel Materials Using a Newly Developed Statistical Thermal Aging Model

2019 ◽  
Author(s):  
M. Uddin ◽  
C. Sallaberry ◽  
G. Wilkowski
Keyword(s):  
Statistical Model ◽  
Failure Modes ◽  
Austenitic Stainless Steels ◽  
Limit Load ◽  
Evaluation Procedure ◽  
Compositional Variation ◽  
Chemical Compositions ◽  
Test Results ◽  
Thermal Embrittlement ◽  
Reactor Operating

Abstract Thermal embrittlement of some cast austenitic stainless steels (CASS) occurs at reactor operating temperatures can lead to a reduction in the fracture toughness and increase in strength. Some aged CASS materials have the potential to have exceedingly low toughness and also show high variability due to the nature of their microstructure or compositional variation within the casting. Because of their low aged toughness with the variability, flaw evaluations of CASS material need to be done with an understanding of the materials aged condition, especially since most US PWR nuclear plants have been given plant life extensions for 60-year operation, and consideration of further extension to 80 years is underway. In this paper, a flaw evaluation procedure for CASS materials is presented using a new statistical model developed to predict the toughness of fully aged CASS using the material’s chemical composition. The new statistical model was developed based on the experimental toughness using standard 1T CT specimens (generally in the L-C orientation) at 288C to 320C and chemical compositions of the CF8m CASS materials. While the detail development of the model is beyond the scope of this paper, a brief validation of predicted toughness using chemical compositions is presented in this paper. Using the predicted toughness, a flaw evaluation procedure was developed using the Dimensionless-Plastic-Zone-Parameter (DPZP) analysis to determine when limit-load is applicable and also approximate the elastic-plastic correction factor (Z-factor) that needs to be applied to the limit-load solution to predict the failure stress for CASS pipe and fittings with a circumferential surface crack. Variability within a single casting was also determined from available test results which was included in the procedure to determine Z-factor. The procedure was then validated against several CF8m pipe test results which include various pipe diameters, crack sizes, ferrite contents, failure modes (i.e., limit load or EPFM), etc. The as-developed flaw evaluation procedure was also used to determine the Z-factors for four different pipe diameters for a database of 274 pipe/elbows in US PWR plants (whose chemical compositions were known) — essentially solving 1096 sample problems to understand what range of Z-factors might exists in US PWR plants (for CF8m CASS materials) considering all variations in pipe dimensions, ferrite contents, materials’ toughness, etc. Finally, the applicability of the CF8m-based statistical model for use with CF3 and CF8 CASS materials was also investigated by comparing the predictions with available test results.

Flaw Evaluation Procedure for Cast Austenitic Stainless-Steel Materials Using A Newly Developed Statistical Thermal Aging Model

2021 ◽  
Author(s):  
Mohammed F Uddin ◽  
Cédric Sallaberry ◽  
Gery Wilkowski
Keyword(s):  
Statistical Model ◽  
Failure Modes ◽  
Austenitic Stainless Steels ◽  
Limit Load ◽  
Evaluation Procedure ◽  
Chemical Compositions ◽  
Test Results ◽  
Pressurized Water Reactor ◽  
Pressurized Water ◽  
Reactor Operating

Abstract Thermal embrittlement of some cast austenitic stainless steels (CASS) occurs at reactor operating temperatures leading to very low fracture toughness. Because of their low aged toughness with high variability, flaw evaluations of CASS material need to be established with an understanding of the materials aged condition, especially since most US Pressurized Water Reactor (PWR) nuclear plants have been given plant life extensions for 60-year operation. A flaw evaluation procedure for CASS materials is presented here using a new statistical model developed to predict the toughness of fully aged CASS using the materials' chemical compositions. In this procedure, the Dimensionless-Plastic-Zone-Parameter (DPZP) analysis is used to determine when limit-load is applicable and also approximate the elastic-plastic correction factor (Z-factor) to predict the failure stress for CASS pipe/fittings with a circumferential surface crack. The procedure was validated against several CF8m pipe test results which include various pipe diameters, crack sizes, ferrite contents, failure modes. The as-developed flaw evaluation procedure was also used to determine the Z-factors for four different pipe diameters for a database of 274 pipe/elbows in US PWR plants -solving 1096 sample problems to understand what range of Z-factors in US PWR plants (for CF8m CASS materials). Finally, the applicability of the CF8m-based statistical model for use with CF3 and CF8 CASS materials was also verified with available test results. This work has been accepted as Code Case N-906 in ASME Boiler and Pressure Vessel (BPV) Code.

Fracture Toughness and Deformation Behavior of Cast Austenitic Stainless Steels After Thermal Aging

2017 ◽  
Author(s):  
Yiren Chen ◽  
Wei-Ying Chen ◽  
Chi Xu ◽  
Xuan Zhang ◽  
Zhangbo Li ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Stainless Steels ◽  
Thermal Aging ◽  
Cooling System ◽  
Austenitic Stainless Steels ◽  
Ferrite Content ◽  
Delta Ferrite ◽  
Light Water ◽  
Water Reactors ◽  
The Impact

Cast austenitic stainless steels (CASSs) are used in the cooling system of light water reactors (LWRs) for components with complex shapes, such as pump casings, valve bodies, coolant piping, etc. The CF grades of CASS alloys are the cast equivalents of 300-series stainless steels (SSs) and show excellent mechanical properties and corrosion resistance. In contrast to the fully austenitic microstructure of wrought SSs, CASS alloys consist of a dual-phase microstructure of delta ferrite and austenite and are vulnerable to thermal aging embrittlement. The service performance of CASS alloys is of concern after long-term exposure to high-temperature coolant. In this work, we studied the effects of thermal aging and ferrite content on the fracture resistance of CASS alloys. Crack growth rate and fracture toughness J–R curve tests were performed on aged and unaged CASS alloys in simulated light water reactor environments. The impact of thermal aging on the cracking susceptibility was investigated and the effect of ferrite content was evaluated. Significant embrittlement was observed in the CASS alloys after aging at 400°C. To understand the embrittlement mechanism, microstructural characterizations were performed with transmission electron microscope. The thermal aging produced G-phase precipitates and phase separation in the ferrite, but did not affect the microstructure of austenite. Consequently, the ferrite was hardened considerably after thermal aging while the hardness of austenite phase remained unchanged. The difference in hardness created a high incompatible strain at the interface between ferrite and austenite, leading to fracture at phase boundaries.

EPRI P87

Alloy Digest ◽  
2011 ◽  
Vol 60 (1) ◽  
Keyword(s):  
Fracture Toughness ◽  
Tensile Properties ◽  
Stainless Steels ◽  
Austenitic Stainless Steels

Abstract EPRI P87 is a MMA electrode designed for dissimilation joints between austenitic stainless steels (i.e. 304H) and a creep resisting CrMo alloy (i.e. P91). This datasheet provides information on composition and tensile properties as well as fracture toughness. It also includes information on joining. Filing Code: Ni-685. Producer or source: Metrode Products Ltd.

CARPENTER STAINLESS 304+B

Alloy Digest ◽  
1961 ◽  
Vol 10 (9) ◽  
Keyword(s):  
Fracture Toughness ◽  
Cross Section ◽  
Stainless Steels ◽  
Austenitic Stainless Steels ◽  
Heat Treating ◽  
Neutron Absorption ◽  
Absorption Cross ◽  
Type 304 ◽  
Conventional Type ◽  
Neutron Absorption Cross Section

Abstract Carpenter Stainless 304+B is similar to conventional Type 304 with the addition of boron to give it a much higher thermal neutron absorption cross-section than other austenitic stainless steels. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as fracture toughness. It also includes information on corrosion resistance as well as forming, heat treating, machining, joining, and surface treatment. Filing Code: SS-121. Producer or source: Carpenter.

SENECA

Alloy Digest ◽  
1954 ◽  
Vol 3 (10) ◽  
Keyword(s):  
Fracture Toughness ◽  
Heat Treating ◽  
Type Iv ◽  
Hot Work Steel ◽  
Operating Temperatures ◽  
Red Hardness

Abstract SENECA is a tungsten-chromium type of hot work steel having good red hardness and resistance to abrasion. It will withstand high operating temperatures up to 1000 deg. F for long periods. It is a SAE type IV F-2 alloy. This datasheet provides information on composition and hardness as well as fracture toughness. It also includes information on forming, heat treating, and machining. Filing Code: TS-25. Producer or source: Atlas Steels Company.

NITRODUR 8524

Alloy Digest ◽  
2017 ◽  
Vol 66 (12) ◽  
Keyword(s):  
Fracture Toughness ◽  
Fatigue Strength ◽  
Tensile Properties ◽  
High Temperatures ◽  
High Surface ◽  
Surface Hardness ◽  
Operating Temperatures

Abstract NITRODUR 8524 (8CrMo16, 1.8524) is one of the Nitrodur family of nitriding steels that are used where high surface hardness and good fatigue strength are required and the material is also subjected to high temperatures. Nitrided surfaces maintain their hardness and strength at operating temperatures of up to approximately 500–550 deg C (932–1022 deg F). This datasheet provides information on composition, hardness, and tensile properties as well as fracture toughness. It also includes information on surface qualities as well as casting and forming. Filing Code: SA-807. Producer or source: Schmolz + Bickenbach Group.

ALLOY 0Cr25Ni6Mo3CuN

Alloy Digest ◽  
1998 ◽  
Vol 47 (2) ◽  
Keyword(s):  
Fracture Toughness ◽  
Stainless Steel ◽  
Corrosion Resistance ◽  
High Temperature ◽  
Physical Properties ◽  
Stainless Steels ◽  
Austenitic Stainless Steels ◽  
Temperature Performance ◽  
Steel Research ◽  
Oil Refinement

Abstract ALLOY 0Cr25Ni6Mo3CuN is one of four grades of duplex stainless steel that were developed and have found wide applications in China since 1980. In oil refinement and the petrochemical processing industries, they have substituted for austenitic stainless steels in many types of equipment, valves, and pump parts. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as fracture toughness. It also includes information on low and high temperature performance, and corrosion resistance as well as forming and joining. Filing Code: SS-706. Producer or source: Central Iron & Steel Research Institute.

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