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.

Revised and New Proposal of Environmental Fatigue Life Correction Factor (Fen) for Carbon and Low-Alloy Steels and Nickel Base Alloys in LWR Water Environments

2006 ◽  
Author(s):  
Makoto Higuchi ◽  
Katsumi Sakaguchi ◽  
Akihiko Hirano ◽  
Yuichiro Nomura
Keyword(s):  
Fatigue Life ◽  
Dissolved Oxygen ◽  
Strain Rate ◽  
Test Data ◽  
Base Alloy ◽  
Low Cycle Fatigue ◽  
Low Alloy Steels ◽  
Alloy Steels ◽  
Nickel Base ◽  
Fatigue Life Reduction

Low cycle fatigue life of carbon and low alloy steels reduces remarkably as functions of strain rate, temperature, dissolved oxygen and sulfur in steel in high temperature water simulating LWR coolant. A model for predicting such fatigue life reduction was first proposed in the early 1980s and since then has been revised several times. The existing model established in 2000 is used for the MITI Guideline [6] and the TENPES Guideline [7] which stipulate procedures for evaluating environmental fatigue damage at LWR plants in Japan. This paper presents the most recent environmental fatigue evaluation model derived based on additional fatigue data provided by the EFT Project over the past five years. This model differs not significantly with previous version but does provide more accurate equations for the susceptibility of fatigue life to sulfur in steel, strain rate, temperature and dissolved oxygen. Test data on environmental fatigue of nickel base alloys are available only to a limited extent and there is yet no model for predicting fatigue life reduction in such an environment. The EFT Project has made available considerable environmental fatigue test data and developed a new model for calculating Fen of nickel base alloys. The contribution of environment to fatigue of nickel base alloy is much less compared to that in austenitic stainless steel.

Evaluation of Fatigue Damage in LWR Water With and Without Threshold and Moderation Factor

2003 ◽  
Author(s):  
Makoto Higuchi ◽  
Kazuya Tsutsumi ◽  
Katsumi Sakaguchi
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Stainless Steels ◽  
Power Plants ◽  
Light Water Reactor ◽  
Low Alloy Steels ◽  
Light Water ◽  
Water Reactor ◽  
Fatigue Data ◽  
Fatigue Life Reduction

During the past twenty years, the fatigue initiation life of LWR structural materials, carbon, low alloy and stainless steels has been shown to decrease remarkably in the simulated LWR (light water reactor) coolant environments. Several models for evaluating the effects of environment on fatigue life reduction have been developed based on published environmental fatigue data. Initially, based on Japanese fatigue data, Higuchi and Iida proposed a model for evaluating such effects quantitatively for carbon and low alloy steels in 1991. Thereafter, Chopra et al. proposed other models for carbon, low alloy and stainless steels by adding American fatigue data in 1993. Mehta developed a new model which features the threshold concept and moderation factor in Chopra’s model in 1995. All these models have undergone various revisions. In Japan, the MITI (Ministry of International Trade and Industry) guideline on environmental fatigue life reduction for carbon, low alloy and stainless steels was issued in September 2000, for evaluating of aged light water reactor power plants. The MITI guideline provide equations for calculations applicable only to stainless steel in PWR water and consequently Higuchi et al. proposed in 2002 a revised model for stainless steel which incorporates new equations for evaluation of environmental fatigue reduction in BWR water. The paper compares the latest versions of these models and discusses the conservativeness of the models by comparison of the models with available test data.

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.

A Review of the Effects of Coolant Environments on the Fatigue Life of LWR Structural Materials

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
O. K. Chopra ◽  
W. J. Shack
Keyword(s):  
Fatigue Life ◽  
Pressure Vessel ◽  
Nuclear Power ◽  
Power Plants ◽  
Fatigue Crack Initiation ◽  
Austenitic Stainless Steels ◽  
Structural Materials ◽  
Low Alloy Steels ◽  
Asme Code ◽  
Alloy Steels

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code specifies design curves for the fatigue life of structural materials in nuclear power plants. However, the effects of light water reactor (LWR) coolant environments were not explicitly considered in the development of the design curves. The existing fatigue-strain-versus-life (ε-N) data indicate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. Under certain environmental and loading conditions, fatigue lives in water relative to those in air can be a factor of 15 lower for austenitic stainless steels and a factor of ≈30 lower for carbon and low-alloy steels. This paper reviews the current technical basis for the understanding of the fatigue of piping and pressure vessel steels in LWR environments. The existing fatigue ε-N data have been evaluated to identify the various material, environmental, and loading parameters that influence fatigue crack initiation and to establish the effects of key parameters on the fatigue life of these steels. Statistical models are presented for estimating fatigue life as a function of material, loading, and environmental conditions. An environmental fatigue correction factor for incorporating the effects of LWR environments into ASME Code fatigue evaluations is described. This paper also presents a critical review of the ASME Code fatigue design margins of 2 on stress (or strain) and 20 on life and assesses the possible conservatism in the current choice of design margins.

scholarly journals Characterization of Austenitic Stainless Steels with Regard to Environmentally Assisted Fatigue in Simulated Light Water Reactor Conditions

Metals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 307
Author(s):  
Matthias Bruchhausen ◽  
Gintautas Dundulis ◽  
Alec McLennan ◽  
Sergio Arrieta ◽  
Tim Austin ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Fatigue Life ◽  
Elevated Temperature ◽  
Strain Rate ◽  
Power Plants ◽  
Research Effort ◽  
Hold Time ◽  
Strain Range ◽  
Austenitic Steels ◽  
Mean Strain

A substantial amount of research effort has been applied to the field of environmentally assisted fatigue (EAF) due to the requirement to account for the EAF behaviour of metals for existing and new build nuclear power plants. We present the results of the European project INcreasing Safety in NPPs by Covering Gaps in Environmental Fatigue Assessment (INCEFA-PLUS), during which the sensitivities of strain range, environment, surface roughness, mean strain and hold times, as well as their interactions on the fatigue life of austenitic steels has been characterized. The project included a test campaign, during which more than 250 fatigue tests were performed. The tests did not reveal a significant effect of mean strain or hold time on fatigue life. An empirical model describing the fatigue life as a function of strain rate, environment and surface roughness is developed. There is evidence for statistically significant interaction effects between surface roughness and the environment, as well as between surface roughness and strain range. However, their impact on fatigue life is so small that they are not practically relevant and can in most cases be neglected. Reducing the environmental impact on fatigue life by modifying the temperature or strain rate leads to an increase of the fatigue life in agreement with predictions based on NUREG/CR-6909. A limited sub-programme on the sensitivity of hold times at elevated temperature at zero force conditions and at elevated temperature did not show the beneficial effect on fatigue life found in another study.

The Effect of Strain Rate on Low Cycle Fatigue Life with Hold Time for USC Candidate Rotor Material

2010 ◽  
pp. 217-229
Author(s):  
Kuk-cheol Kim ◽  
Byeong-ook Kong ◽  
Min-soo Kim ◽  
Sung-tae Kang
Keyword(s):  
Fatigue Life ◽  
Strain Rate ◽  
Low Cycle Fatigue ◽  
Hold Time ◽  
Cycle Fatigue

scholarly journals Fatigue life time modelling of Cu and Au fine wires

2018 ◽  
Vol 165 ◽  
pp. 06002
Author(s):  
Golta Khatibi ◽  
Ali Mazloum-Nejadari ◽  
Martin Lederer ◽  
Mitra Delshadmanesh ◽  
Bernhard Czerny
Keyword(s):  
Fatigue Life ◽  
Strain Rate ◽  
High Cycle Fatigue ◽  
Fatigue Testing ◽  
Low Cycle Fatigue ◽  
Load Ratio ◽  
Life Time ◽  
Material Model ◽  
Cycle Fatigue ◽  
Rate Dependency

In this study, the influence of microstructure on the cyclic behaviour and lifetime of Cu and Au wires with diameters of 25μm in the low and high cycle fatigue regimes was investigated. Low cycle fatigue (LCF) tests were conducted with a load ratio of 0.1 and a strain rate of ~2e-4. An ultrasonic resonance fatigue testing system working at 20 kHz was used to obtain lifetime curves under symmetrical loading conditions up to very high cycle regime (VHCF). In order to obtain a total fatigue life model covering the low to high cycle regime of the thin wires by considering the effects of mean stress, a four parameter lifetime model is proposed. The effect of testing frequency on high cycle fatigue data of Cu is discussed based on analysis of strain rate dependency of the tensile properties with the help of the material model proposed by Johnson and Cook.

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