Thermal Aging Effect on Environmental Fatigue Life of CF8M Cast Stainless Steel at Strain Rate 0.04%/s Under PWR Operating Condition

2010 ◽  
Author(s):  
Ill-Seok Jeong ◽  
Wan-Jae Kim ◽  
Hyun-Ik Jeon
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Strain Rate ◽  
Thermal Aging ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Operating Conditions ◽  
Pressurized Water ◽  
Operating Condition ◽  
Term Operation

In order to see the effect of thermal aging on environmental fatigue life of CF8M cast austenitic stainless steel (CASS), low-cycle environmental fatigue tests of thermally aged CF8M CASS at the condition of fatigue strain rate 0.04%/s were conducted at the operating condition, 15MPa, 315°C of pressurized water reactor (PWR) environment. Test results of low cycle fatigue life tests for thermally aged specimens simulating 60 operating years were compared with ones of un-aged CF8M CASS in room temperature air and PWR operating conditions to see the effect of the thermal aging on environmental fatigue life. This kind of experiment would be useful to verify the fatigue integrity of long-lived components and to predict plant safety of long term operation beyond design life because current approach of evaluating environmental fatigue is so conservative to apply it to the long-lived components in pressure boundary of nuclear power plants.

Influence of the Strain Rate on the Low Cycle Fatigue Life of an Austenitic Stainless Steel with a Ground Surface Finish in Different Environments

2014 ◽  
Vol 891-892 ◽  
pp. 1320-1326 ◽  
Author(s):  
Thibault Poulain ◽  
José Mendez ◽  
Gilbert Hénaff ◽  
Laurent de Baglion
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Austenitic Stainless Steel ◽  
Strain Rate ◽  
Surface Finish ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Total Strain Amplitude ◽  
Cycle Fatigue ◽  
Pressurized Water

This paper focuses on the influence of strain rate in Low Cycle Fatigue (LCF) of a 304L austenitic stainless steel at 300 °C in different environments (secondary vacuum, air and Pressurized Water Reactor (PWR) water environment). Moreover test samples are ground to obtain a surface finish rougher than all that could be found in nuclear power plants. Different strain rates (4x10-3, 1x10-4and 1x10-5s-1) are studied, with a triangular waveform at a total strain amplitude of ±0.6%. The influence of strain rate on cyclic stress-strain behavior and fatigue life is firstly analyzed in secondary vacuum, considered as a non-active environment. Then, interactions between stain rate and environmental effects in Air and in PWR environment are presented. In all environments, a decrease in strain rate leads to a negative strain rate dependence of the stress response and a reduction in fatigue life. Finally, SEM observations of fatigue striations in PWR environment indicate a crack propagation rate enhancement when the strain rate is decreased.

Environmental Fatigue Test of CF8M With a Small Autoclave Simulating PWR Conditions

2008 ◽  
Author(s):  
Il-Seok Jeong ◽  
Gag-Hyeon Ha ◽  
Tae-Ryoung Kim
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Test Procedure ◽  
Cyclic Strain ◽  
Fatigue Tests ◽  
Operating Conditions ◽  
Measuring Instruments ◽  
Pressurized Water Reactor ◽  
Pressurized Water

To develop a fatigue design curve of cast stainless steel CF8M used in primary piping material of nuclear power plants, low-cycle fatigue tests have been conducted by Korea Electric Power Research Institute (KEPRI). A small autoclave simulated the environment of a pressurized water reactor (PWR), 15 MPa and 315 °C. Fatigue life was measured in terms of the number of cycles with the variation of strain amplitudes at 0.04%/s strain rate. A small autoclave of 1 liter and cylindrical solid fatigue specimens were used for the strain-controlled low cycle environmental fatigue tests to make the experiments convenient. However, it was difficult to install displacement measuring instruments at the target length of the specimens inside the autoclave. To mitigate the difficulty displacement data measured at the shoulders of the specimen were calibrated based on the data relation of the target and shoulder length of the specimen during hot air test conditions. KEPRI developed a test procedure to perform low cycle environmental fatigue tests in the small autoclave. The procedure corrects the cyclic strain hardening effect by performing additional tests in high temperature air condition. KEPRI verified that the corrected test result agreed well with that of finite element method analysis. The process of correcting environmental fatigue data would be useful for producing reliable fatigue curves using a small autoclave simulating the operating conditions of a PWR.

scholarly journals Parameters influencing the low-cycle fatigue life of materials in pressure water reactor nuclear power plants / Parametry ovlivòující únavové chování materiálù pro tlakovodní jaderné reaktory v režimu nízkocyklové únavy

2015 ◽  
Vol 59 (3) ◽  
pp. 91-98
Author(s):  
V. Šefl
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Carbon Steel ◽  
Austenitic Stainless Steel ◽  
Literature Review ◽  
Nuclear Power ◽  
Power Plants ◽  
Nuclear Power Plants ◽  
Low Cycle Fatigue ◽  
Cycle Fatigue

Abstract In this literature review we identify and quantify the parameters influencing the low-cycle fatigue life of materials commonly used in nuclear power plants. The parameters are divided into several groups and individually described. The main groups are material properties, mode of cycling and environment parameters. The groups are further divided by the material type - some parameters influence only certain kind of material, e.g. sulfur content may decreases fatigue life of carbon steel, but is not relevant for austenitic stainless steel; austenitic stainless steel is more sensitive to concentration of dissolved oxygen in the environment compared to the carbon steel. The combination of parameters i.e. conjoint action of several detrimental parameters is discussed. It is also noted that for certain parameters to decrease fatigue life, it is necessary for other parameter to reach certain threshold value. Two different approaches have been suggested in literature to describe this complex problem - the Fen factor and development of new design fatigue curves. The threshold values and examples of commonly used relationships for calculation of fatigue lives are included. This work is valuable because it provides the reader with long-term literature review with focus on real effect of environmental parameters on fatigue life of nuclear power plant materials.

Direct Strain-Controlled Variable Strain Rate Low Cycle Fatigue Testing in Simulated PWR Water

2016 ◽  
Author(s):  
Tommi Seppänen ◽  
Jouni Alhainen ◽  
Esko Arilahti ◽  
Jussi Solin
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Strain Rate ◽  
Fatigue Testing ◽  
Low Cycle Fatigue ◽  
Reference Value ◽  
Hot Water ◽  
Feedback Signal ◽  
Cycle Fatigue ◽  
Experimental Values

A tailored-for-purpose environmental fatigue testing facility was previously developed to perform direct strain-controlled tests on stainless steel in simulated PWR water. Strain in specimen mid-section is generated by the use of pneumatic bellows, and eddy current measurement is used as a feedback signal. The procedure conforms with the ASTM E 606 practice for low cycle fatigue, giving results which are directly compatible with the major NPP design codes. Past studies were compiled in the NUREG/CR-6909 report and environmental reduction factors Fen were proposed to account for fatigue life reduction in hot water as compared to a reference value in air. This database exclusively contained non-stabilized stainless steels, mainly tested under stroke control. The applicability of the stainless steel Fen factor for stabilized alloys was already challenged in past papers (PVP2013-97500, PVP2014-28465). The results presented in this paper follow the same overall trend of lower experimental values (4.12–11.46) compared to those expected according to the NUREG report (9.49–10.37). In this paper results of a dual strain rate test programme on niobium stabilized AISI 347 type stainless steel are presented and discussed in the context of the NUREG/CR-6909 Fen methodology. Special attention is paid to the effect of strain signal on fatigue life, which according to current prediction methods does not affect the value of Fen.

Fatigue Crack Initiation of 304L Stainless Steel in Simulated PWR Primary Environment: Relative Effect of Strain Rate

2012 ◽  
Author(s):  
Nicolas Huin ◽  
Kazuya Tsutsumi ◽  
Laurent Legras ◽  
Thierry Couvant ◽  
Dominique Loisnard ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Initiation ◽  
Strain Rate ◽  
Early Stage ◽  
Laboratory Data ◽  
Fatigue Crack Initiation ◽  
304L Stainless Steel ◽  
Pressurized Water

The French Regulatory Commission insisted on a survey justifying the assumed mechanical behavior of components exposed to Pressurized Water Reactor (PWR) water under cyclic loading without taking into account its effect. In the US and Japan, the fatigue life correlation factors, so called Fen, are formulated and standardized on the basis of laboratory data to take into account the effect on fatigue life evaluation. However, the current fatigue codification, suffers from a lack of understanding of environmental effects on the fatigue lives of stainless steels in simulated hydrogenated PWR environments. Samples tested in a recent study were analyzed to highlight the strain rate effect (within a range 0.4%/s to 0.004%/s) at the early stage of fatigue life in PWR primary environment for a 304L stainless steel. The deleterious effect of PWR primary environment on fatigue crack initiation was observed with a quantitative microscopic approach. Multi scale observations of oxide morphology and microstructure were carried out from common optical microscopy using recent technologies such as 3D oxide reconstruction, and DualBeam observations.

Final Proposal of Environmental Fatigue Life Correction Factor (Fen) for Structural Materials in LWR Water Environment

2007 ◽  
Author(s):  
Makoto Higuchi ◽  
Katsumi Sakaguchi ◽  
Yuichiro Nomura ◽  
Akihiko Hirano
Keyword(s):  
Fatigue Life ◽  
Strain Rate ◽  
Stainless Steels ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Structural Materials ◽  
Reduction Factor ◽  
Low Alloy Steels ◽  
The Past ◽  
Nickel Base

Low cycle fatigue life of structural materials diminishes remarkably as functions of various parameters in high temperature water simulating LWR coolant. Such reduction was estimated by the fatigue life reduction factor (Fen) and the equations to calculate Fen were developed and have undergone revision over the past ten years. The authors have endeavored to establish the method assessing fatigue damage at LWR power plants for the past 13 years in the Japanese EFT (Environmental Fatigue Tests) project under the financial support from the JNES (Japan Nuclear Safety Organization). The project terminated at the end of March in 2007. Final proposals of Fen equations were established for carbon, low-alloy, and austenitic stainless steels and nickel base alloys based on all the data obtained in the project. As the results, a small change in saturated strain rate for carbon and low-alloy steels in highly dissolved oxygen water and newly revised equations including slight change in saturated strain rate for stainless steels in BWR water as well as those for nickel base alloys were proposed. The difference between revised and previous model is essentially not large.

scholarly journals Influence of Strain Rate and Waveshape on Environmentally-Assisted Cracking during Low-Cycle Fatigue of a 304L Austenitic Stainless Steel in a PWR Water Environment

Metals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 197 ◽  
Author(s):  
Thibault Poulain ◽  
Laurent de Baglion ◽  
Jose Mendez ◽  
Gilbert Hénaff
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Strain Rate ◽  
Crack Growth ◽  
Growth Rates ◽  
Low Cycle Fatigue ◽  
Water Environment ◽  
Cycle Fatigue ◽  
Pressurized Water ◽  
Environmentally Assisted Cracking

In this paper, the low cycle fatigue resistance of a 304L austenitic stainless steel in a simulated pressurized water reactor (PWR) primary water environment has been investigated by paying a special attention to the interplay between environmentally-assisted cracking mechanisms, strain rate, and loading waveshape. More precisely, one of the prime interests of this research work is related to the consideration of complex waveshape signals that are more representative of solicitations encountered by real components. A detailed analysis of stress-strain relation, surface damage, and crack growth provides a preliminary ranking of the severity of complex, variable strain rate signals with respect to triangular, constant strain-rate signals associated with environmental effects in air or in PWR water. Furthermore, as the fatigue lives in PWR water environment are mainly controlled by crack propagation, the crack growth rates derived from striation spacing measurement and estimated from interrupted tests have been carefully examined and analyzed using the strain intensity factor range ΔKε. It is confirmed that the most severe signal with regards to fatigue life also induces the highest crack growth enhancement. Additionally two characteristic parameters, namely a threshold strain εth* and a time T*, corresponding to the duration of the effective exposure of the open cracks to PWR environment have been introduced. It is shown that the T* parameter properly accounts for the differences in environmentally-assisted growth rates as a function of waveshape.

Fatigue Life of the Strain Hardened Austenitic Stainless Steel in Simulated PWR Primary Water

2012 ◽  
Author(s):  
Kazuya Tsutsumi ◽  
Nicolas Huin ◽  
Thierry Couvant ◽  
Gilbert Henaff ◽  
Jose Mendez ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Strain Hardening ◽  
Fatigue Testing ◽  
Low Cycle Fatigue ◽  
Axial Strain ◽  
Correlation Factor ◽  
304L Stainless Steel ◽  
Pressurized Water ◽  
Primary Water

Over the last 20 years or so, many studies have revealed the deleterious effect of the environment on fatigue life of austenitic stainless steels in pressurized water reactor (PWR) primary water. The fatigue life correlation factor, so-called Fen, has been standardized to consider the effect on fatigue life evaluation. The formulations are function of strain rate and temperature due to their noticeable negative effect compared with other factors [1,2]. However, mechanism causing fatigue life reduction remains to be cleared. As one of possible approaches to examine underlying mechanism of environmental effect, the authors focused on the effect of plastic strain, because it could lead microstructural evolution on the material. In addition, in the case of stress corrosion cracking (SCC), it is well known that the strain-hardening prior to exposure to the primary water can lead to remarkable increase of the susceptibility to cracking [3,4]. However, its effect on fatigue life has not explicitly been investigated yet. The main effort in this study addressed the effect of the prior strain-hardening on low cycle fatigue life of 304L stainless steel (SS) exposed to the PWR primary water. A plate of 304LSS was strain hardened by cold rolling or tension prior to fatigue testing. The tests were performed under axial strain-controlled at 300 °C in primary water including B/Li and dissolved hydrogen, and in air. The effect on environmental fatigue life was investigated through a comparison of the Fen in experiments and in regulations, and also the effect on the fatigue limit defined at 106 cycles was discussed.

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