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.

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.

Review and Consideration of Unsettled Problems on Evaluation of Fatigue Damage in LWR Water

2006 ◽  
Vol 129 (1) ◽  
pp. 186-194
Author(s):  
Makoto Higuchi ◽  
Katsumi Sakaguchi
Keyword(s):  
Fatigue Life ◽  
Mechanical Test ◽  
Low Alloy Steels ◽  
Test Results ◽  
Considerable Effort ◽  
Test Conditions ◽  
Fatigue Data ◽  
Alloy Steels ◽  
Fatigue Life Reduction ◽  
Year 2000

Reduction in the fatigue life of structural materials of nuclear components in Light Water Reactor (LWR) water was initially detected and examined by the authors in the 1980s, who subsequently directed considerable effort to the development of a method for evaluating this reduction quantitatively. Since the first proposal of equations to calculate environmental fatigue life reduction for carbon and low-alloy steels was published in 1985 by Higuchi and Sakamoto (J. Iron Steel Inst. Jpn. 71, pp. 101–107), many revisions were made based on a lot of additional fatigue data in various environmental and mechanical test conditions. The latest models for evaluation using Fen of the environmental fatigue life correction factor were proposed for carbon and low alloy steels in the year 2000 and for austenitic stainless steel, in 2002. Fen depends on some essential variables such as material, strain rate, temperature, dissolved oxygen and sulfur concentration in steel. The equation for determining Fen is given by each parameter for each material. These models, having been developed three to five years ago, should be properly revised based on new test results. This paper reviews and discusses five major topics pertinent to such revision.

Stress Corrosion Cracking Susceptibility of Low Alloy Steels Used for Reactor Pressure Vessel in High Temperature Oxygenated Water

1985 ◽  
Vol 107 (4) ◽  
pp. 430-435 ◽  
Author(s):  
J. Kuniya ◽  
I. Masaoka ◽  
R. Sasaki ◽  
H. Itoh ◽  
T. Okazaki
Keyword(s):  
Dissolved Oxygen ◽  
Strain Rate ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Pressure Vessel ◽  
Corrosion Cracking ◽  
Reactor Pressure Vessel ◽  
Low Alloy Steels ◽  
Alloy Steels ◽  
Reactor Pressure

Studies have been done on stress corrosion cracking (SCC) susceptibility of low alloy steels in water containing dissolved oxygen. The fundamental factors which affect the SCC susceptibility were clarified, and the integrity of the reactor pressure vessel (RPV), in which these steels are used, was assessed from the standpoint of SCC initiation. The effects of applied stress, strain rate, dissolved oxygen concentration, and test temperatures, on the SCC susceptibility was examined utilizing uniaxial constant load tensile tests (UCL), and slow strain rate tests (SSRT).

Experimental and Numerical Investigation on the Influence of Thermally Induced Stress Gradients on Fatigue Life of the Nickel-Base Alloy Mar-M247

2019 ◽  
Author(s):  
Marcus Thiele ◽  
Stefan Eckmann ◽  
Min Huang ◽  
Uwe Gampe ◽  
Kathrin A. Fischer ◽  
...  
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Base Alloy ◽  
Low Cycle Fatigue ◽  
Heat Fluxes ◽  
Cycle Fatigue ◽  
Thermally Induced ◽  
Stress Gradients ◽  
Induced Stress ◽  
Nickel Base

Abstract Today’s and future parameters of stationary gas turbines and aircraft engines require intensive and highly efficient cooling of hot gas path components. High temperature and thermally induced stress gradients with impact on fatigue life are the consequence. Thermally induced stress gradients differ from geometrically induced stress gradients with respect to stress mechanics by the independence from external loads and material mechanics by the influence of temperature on material properties and strength. Regarding the contribution and evaluation on damage, the latter characteristic feature in turbomachinery is currently not fully understood. Therefore, a test facility has been designed, set up, and reported in GT2018-76519 for the investigation of the influence of stationary temperature, and thus thermally induced stress gradients, on the damage evolution of cooled high-temperature components. To achieve high temperature and thermally induced stress gradients, large heat fluxes are required. A unique radiation heating has been developed allowing very high heat fluxes of q̇ ≥ 1.5 MW/m2 for testing of hollow cylindrical specimens. The conventional cast nickel-base alloy Mar-M247 has been chosen to study the influence of thermally induced stress gradients on fatigue life. The low-cycle fatigue testing of the hollow cylindrical specimens has been conducted both with and without superimposed stationary temperature gradients. In addition, Complex Low-Cycle Fatigue (CLCF) tests with symmetric and nonsymmetric loading conditions have been performed to provide the necessary database for the adaptation of a viscoplastic deformation model. To calculate the local stress-strain field and service life of the test specimens, linear elastic and viscoplastic finite element studies have been performed and were assessed by means of a fracture mechanics-based lifetime model. The test results show the considerable influence of the temperature gradient on the low-cycle fatigue life for the investigated material. Both the radial temperature variation over the specimen wall with a hot outer surface and a cooled inner surface as well as the thermally induced stresses are stated to be the main drivers for the change in low-cycle fatigue life. The test results enhance the understanding of fatigue-damage mechanisms under local unsteady conditions and can be used as a basis for improved service life predictions.

Reactor Water Environmental Fatigue

2003 ◽  
Author(s):  
William J. O’Donnell
Keyword(s):  
Fatigue Life ◽  
Fatigue Damage ◽  
Corrosion Fatigue ◽  
Low Alloy Steels ◽  
Nuclear Plants ◽  
Alloy Steels ◽  
Stress Concentration Factors ◽  
Rapid Transients ◽  
License Renewal ◽  
Fatigue Life Reduction

Existing nuclear plants were designed based on fatigue data obtained entirely in air environments. We now seek to extend the life of these plants, recognizing that many conservatisms were included in the fatigue stress calculations, stress concentration factors and lumped transients. Since we know how these plants were operated, we can quantify the cyclic rates and coolant chemistry. This makes it feasible to use environmental fatigue life evaluation technology which takes credit for the reduced corrosion fatigue damage which occurs during more rapid transients and for reduced dissolved oxygen levels which produce lesser corrosion fatigue damage in carbon and low alloy steels. Accordingly, the use of Fen environmental fatigue life reduction factors which depend on the cyclic rates, coolant chemistry and temperature are quite useful for evaluating the safe fatigue life of aging plants and for license renewal.

Experimental and Numerical Investigation on the Influence of Thermally Induced Stress Gradients on Fatigue Life of the Nickel-Base Alloy Mar-M247

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Marcus Thiele ◽  
Stefan Eckmann ◽  
Min Huang ◽  
Uwe Gampe ◽  
Kathrin A. Fischer ◽  
...  
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Base Alloy ◽  
Low Cycle Fatigue ◽  
Heat Fluxes ◽  
Cycle Fatigue ◽  
Thermally Induced ◽  
Stress Gradients ◽  
Induced Stress ◽  
Nickel Base

Abstract Today's and future parameters of stationary gas turbines and aircraft engines require intensive and highly efficient cooling of hot gas path components. High temperature and thermally induced stress gradients with impact on fatigue life are the consequence. Thermally induced stress gradients differ from geometrically induced stress gradients with respect to stress mechanics by the independence from external loads and material mechanics by the influence of temperature on material properties and strength. Regarding the contribution and evaluation on damage, the latter characteristic feature in turbomachinery is currently not fully understood. Therefore, a test facility has been designed, setup, and reported in GTP-18-1482 for the investigation of the influence of stationary temperature, and thus thermally induced stress gradients, on the damage evolution of cooled high-temperature components. To achieve high temperature and thermally induced stress gradients, large heat fluxes are required. A unique radiation heating has been developed allowing very high heat fluxes of q˙ ≥ 1.5 MW/m2 for testing of hollow cylindrical specimens. The conventional cast nickel-base alloy Mar-M247 has been chosen to study the influence of thermally induced stress gradients on fatigue life. The low-cycle fatigue testing of the hollow cylindrical specimens has been conducted both with and without superimposed stationary temperature gradients. In addition, complex low-cycle fatigue (CLCF) tests with symmetric and nonsymmetric loading conditions have been performed to provide the necessary database for the adaptation of a viscoplastic deformation model. To calculate the local stress–strain field and service life of the test specimens, linear elastic and viscoplastic finite element studies have been performed and were assessed by means of a fracture mechanics-based lifetime model. The test results show the considerable influence of the temperature gradient on the low-cycle fatigue life for the investigated material. Both the radial temperature variation over the specimen wall with a hot outer surface and a cooled inner surface as well as the thermally induced stresses are stated to be the main drivers for the change in low-cycle fatigue life. The test results enhance the understanding of fatigue-damage mechanisms under local unsteady conditions and can be used as a basis for improved service life predictions.

A Bayesian Framework for Estimation of Strain Life Lower Bounds and its Application to IN617

2019 ◽  
Author(s):  
Arinan Dourado ◽  
Firat Irmak ◽  
Felipe A. C. Viana ◽  
Ali P. Gordon
Keyword(s):  
Fatigue Life ◽  
Test Data ◽  
Base Alloy ◽  
Low Cycle Fatigue ◽  
Strain Range ◽  
Confidence Bands ◽  
Parameter Uncertainties ◽  
Plastic Strain Range ◽  
Median Response ◽  
Constant Variance

Abstract The practice of applying strain-life relationships to model materials subjected to low cycle fatigue conditions has been widely-accepted for the past seventy years. The Coffin-Manson rule employs a double, two-parameter power law equation to correlate cycles to failure to strain range (or vice versa). Plastic strain range dominates low life, while elastic strain dominates high life. In some settings with well-established materials, copious amounts of test data are available. The median response and the Coffin-Manson parameters are determined through regression. Scatter in both strain amplitude and fatigue life values are a consequence of material and specimen variation, test technician attributes or more. Recent initiatives have endeavored to transition deterministic approaches over to probabilistic analogies. Confidence bands, lower ones in particular, are useful for understanding reliability curves and implementing reliability-based design and optimization. In settings with accelerated product development schedules, intentionally sparse sets of test data are used to play “what if” scenarios in the context of life prediction. We propose a non-stationary variance to model deviations from the Coffin-Manson rule and use Bayesian statistical methods to estimate model parameter uncertainties. The proposed approach is applied to the calibration of strain-life parameters of the candidate material Inconel 617, a Ni-base alloy used is combustion equipment. When compared with constant variance (such as in traditional regression), the results show an improved characterization of the confidence bounds for fatigue life. This is important as it indicates that the methodology can be used to manage the number of coupon test to achieve an acceptable convergence.

Revised Proposal of Fatigue Life Correction Factor Fen for Carbon and Low Alloy Steels in LWR Water Environments

2004 ◽  
Vol 126 (4) ◽  
pp. 438-444 ◽  
Author(s):  
Makoto Higuchi
Keyword(s):  
Fatigue Life ◽  
Correction Factor ◽  
Light Water Reactor ◽  
Low Alloy Steels ◽  
Light Water ◽  
High Temperature Water ◽  
Fatigue Data ◽  
Alloy Steels ◽  
Fatigue Life Reduction ◽  
Temperature Water

The fatigue life of carbon and low alloy steels decreases with reduction in strain rate in high temperature water such as in the case of a light water reactor coolant. The fatigue life reduction also depends on temperature and dissolved oxygen. The fatigue life correction factor Fen has been proposed as a method to assess the fatigue life reduction in such environments. Three different models for calculating Fen for carbon and low alloy steels have been proposed by Higuchi et al., Chopra et al., and Mehta. These models were compared using considerable environmental fatigue data that were tested and published in Japan and USA and piled up in the database “JNUFAD” by the author. These models give somewhat different results in the specific conditions and a revised model for calculating Fen is thus proposed by remedying the particular drawbacks of each. In this model, the same formula is used for carbon and low alloy steels and S*,T*,O*, and ε˙* are adopted in the formula after reevaluating every parameter. The revised proposal shows better correlation with the test data than the previous models.

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