Margins for ASME Code Fatigue Design Curve: Effects of Surface Finish and Material Variability

2003 ◽  
Author(s):  
O. K. Chopra ◽  
W. J. Shack
Keyword(s):  
Pressure Vessel ◽  
Nuclear Power ◽  
Environmental Parameters ◽  
Light Water Reactor ◽  
Code Design ◽  
Low Alloy Steels ◽  
Design Curve ◽  
Fatigue Design ◽  
Asme Code ◽  
Alloy Steels

The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components. This Code specifies fatigue design curves for structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. Existing fatigue strain-vs.-life (ε-N) data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. This report provides an overview of the existing fatigue ε-N data for carbon and low-alloy steels and wrought and cast austenitic SSs to define the effects of key material, loading, and environmental parameters on the fatigue lives of the steels. Experimental data are presented on the effects of surface roughness on the fatigue life of these steels in air and LWR environments. Statistical models are presented for estimating the fatigue ε-N curves as a function of the material, loading, and environmental parameters. Two methods for incorporating environmental effects into the ASME Code fatigue evaluations are discussed. Data available in the literature have been reviewed to evaluate the conservatism in the existing ASME Code fatigue evaluations. A critical review of the margins for the ASME Code fatigue design curve is presented.

Development of a Fatigue Design Curve for Austenitic Stainless Steels in LWR Environments: A Review

2002 ◽  
Author(s):  
Omesh K. Chopra
Keyword(s):  
Stainless Steels ◽  
Pressure Vessel ◽  
Type Strain ◽  
Nuclear Power ◽  
Austenitic Stainless Steels ◽  
Environmental Parameters ◽  
Light Water Reactor ◽  
Code Design ◽  
Fatigue Design ◽  
Asme Code

The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components and specifies fatigue design curves for structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. Existing fatigue strain–vs.–life (ε–N) data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. This paper reviews the existing fatigue ε–N data for austenitic stainless steels in LWR coolant environments. The effects of key material, loading, and environmental parameters, such as steel type, strain amplitude, strain rate, temperature, dissolved oxygen level in water, and flow rate, on the fatigue lives of these steels are summarized. Statistical models are presented for estimating the fatigue ε–N curves for austenitic stainless steels as a function of the material, loading, and environmental parameters. Two methods for incorporating environmental effects into the ASME Code fatigue evaluations are presented. Data available in the literature have been reviewed to evaluate the conservatism in the existing ASME Code fatigue design curves.

A Consideration of Margin on Fatigue Design Curves for Carbon and Low-Alloy Steels

2011 ◽  
Author(s):  
Makoto Higuchi ◽  
Masahiro Takanashi ◽  
Ichiro Tamura ◽  
Toshiaki Takada
Keyword(s):  
Stainless Steels ◽  
Fatigue Curve ◽  
Light Water Reactor ◽  
Ferritic Steels ◽  
Low Alloy Steels ◽  
Light Water ◽  
Fatigue Design ◽  
The Us ◽  
Asme Code ◽  
Alloy Steels

In 2007, the US NRC issued Regulatory Guide 1.207[1] and NUREG/CR-6909[2] for evaluating fatigue incorporating the life reduction due to the effects of light-water reactor environment for new reactors. NUREG/CR-6909 provides new design fatigue curves (DFC) for carbon, low-alloy and stainless steels which are different from those in the ASME Boiler and Pressure Vessel Code Section III[3] (2007 Edition). The design fatigue curves for carbon and low-alloy steels in NUREG/CR-6909 are higher than that for ferritic steels of which specified minimum tensile strength is 552 MPa (80 ksi) or less in the ASME Code Section III. The design fatigue curve for stainless steel in the ASME Code Section III was changed to the same curve as NUREG/CR-6909 in the 2009 Addenda. However, those for carbon and low-alloy steels are still different from the NUREG curves.

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.

Sample Environmental Fatigue Calculations Associated With the Review of Draft Regulatory Guide DG-1144

2007 ◽  
Author(s):  
Gary L. Stevens ◽  
J. Michael Davis ◽  
Les Spain
Keyword(s):  
Stainless Steel ◽  
Lessons Learned ◽  
Light Water Reactor ◽  
Low Alloy Steels ◽  
Light Water ◽  
New Model ◽  
Asme Code ◽  
Alloy Steels ◽  
Reactor Materials ◽  
License Renewal

Draft Regulatory Guide DG-1144 “Guidelines for Evaluating Fatigue Analyses Incorporating the Life Reduction of Metal Components Due to the Effects of the Light-Water Reactor Environment for New Reactors”, July 2006 [1], and Associated Basis Draft Document NUREG/CR-6909 (ANL-06/08), “Effect of LWR Coolant Environments on the Fatigue Life of Reactor Materials”, July 2006 [6] provided methods for addressing environmentally assisted fatigue (EAF) in all new nuclear plant designs. In these documents, a new model was proposed that more accurately accounts for actual plant conditions. The new model includes an EAF correction factor, Fen, which is different from Fen methods previously and currently being considered for adoption into the ASME Code. The Fen methods proposed in DG-1144 are also different than the Fen methods utilized by license renewal applicants, as required by the Generic Aging Lessons Learned (GALL) report [2], as documented in NUREG/CR-5704 [4] (for stainless steel) and NUREG/CR-6583 [3] (for carbon and low alloy steels).

Overview of Fatigue Crack Initiation in Carbon and Low-Alloy Steels in Light Water Reactor Environments

1999 ◽  
Vol 121 (1) ◽  
pp. 49-60 ◽  
Author(s):  
O. K. Chopra ◽  
W. J. Shack
Keyword(s):  
Crack Initiation ◽  
Fatigue Crack Initiation ◽  
Light Water Reactor ◽  
Code Design ◽  
Low Alloy Steels ◽  
Light Water ◽  
Water Reactor ◽  
Short Cracks ◽  
Alloy Steels ◽  
Current Code

Recent test data illustrate potentially significant effects of light water reactor (LWR) coolant environments on the fatigue resistance of carbon and low-alloy steels. The crack initiation and crack growth characteristics of carbon and low-alloy steels in LWR environments are presented. Decreases in fatigue lives of these steels in high-dissolved-oxygen water are caused primarily by the effect of environment on growth of short cracks <100 μm in depth. The material and loading parameters that influence fatigue life in LWR environments are defined. Statistical models have been developed to estimate the fatigue lives of these steels in LWR environments, and design fatigue curves have been developed for carbon and low-alloy steel components in LWR environments. The significance of environmental effect on the current Code design curve is evaluated.

Review of Margins Needed to Develop Fatigue Design Curves From Laboratory Test Data

2003 ◽  
Author(s):  
W. A. Van Der Sluys
Keyword(s):  
Fatigue Testing ◽  
Low Cycle Fatigue ◽  
Light Water Reactor ◽  
Fatigue Properties ◽  
Low Alloy Steels ◽  
Test Results ◽  
Cycle Fatigue ◽  
Fatigue Design ◽  
Current Design ◽  
Alloy Steels

The PVRC has just completed a review of the effect of LWR (Light Water Reactor) coolant environment on the low cycle fatigue properties of carbon and low alloy steels. The PVRC has made recommendations to the ASME on changes to the boiler and pressure vessel codes to account for the environmental effects. In developing the recommendations, the margins used to produce the design curves from fatigue test results of laboratory specimens, were studied. This paper describes the margins used by the ASME in the development of the current design curves and discusses what margins should be applied when the laboratory fatigue testing includes tests in simulated LWR coolant environments.

The Effect of LWR Coolant Environments on the Fatigue Life of Reactor Materials

2006 ◽  
Author(s):  
Omesh K. Chopra ◽  
William J. Shack
Keyword(s):  
Stainless Steels ◽  
Type Strain ◽  
Water Flow Rate ◽  
Austenitic Stainless Steels ◽  
Environmental Parameters ◽  
Light Water Reactor ◽  
Low Alloy Steels ◽  
Alloy Steels ◽  
Reactor Materials ◽  
American Society

The existing fatigue strain–vs.–life (ε–N) data illustrate potentially significant effects of light water reactor (LWR) coolant environments on the fatigue resistance of pressure vessel and piping steels. This paper reviews the existing fatigue ε–N data for carbon and low–alloy steels and austenitic stainless steels in LWR coolant environments. The effects of key material, loading, and environmental parameters, such as steel type, strain amplitude, strain rate, temperature, dissolved oxygen level in water, flow rate, surface finish, and heat-to-heat variation, on the fatigue lives of these steels are summarized. An updated version of the ANL statistical models is presented for estimating the fatigue ε–N curves for these steels as a function of the material, loading, and environmental parameters. The Fen (environmental fatigue correction factor) approach for incorporating the effects of LWR coolant environments into the fatigue evaluations of the American Society of Mechanical Engineers Code is presented.

Validity of Hardness Criteria to Demonstrate Acceptable Temper Bead HAZ Impact Properties for Nuclear Power Applications

2013 ◽  
Author(s):  
Steven L. McCracken ◽  
Richard E. Smith ◽  
Darren Barborak
Keyword(s):  
Fracture Toughness ◽  
Pressure Vessel ◽  
Nuclear Power ◽  
Welding Process ◽  
Impact Testing ◽  
Low Alloy Steels ◽  
Maximum Hardness ◽  
Impact Properties ◽  
Pressure Vessel Steels ◽  
Alloy Steels

Temper bead welding is used routinely for weld repair on low alloy pressure vessel steels in the nuclear power industry. Temper bead procedure qualification is contingent on demonstration that the welding process does not degrade the mechanical properties, including fracture toughness, in the base metal weld heat affected zone (HAZ). Historically for temper bead qualification acceptance, adequate HAZ properties have been verified by tensile, impact, and bend testing, while hardness criteria has not been specified. In fact, temper bead welding has been successfully applied for welding on low alloy steels without any hardness criteria for many years. In 2004, ASME Section IX added hardness testing for temper bead procedure qualification when impact testing is not required. The Eurocode, ISO standards, and numerous other European specifications include maximum hardness criteria for general welding procedure qualification and have invoked these same criteria for temper bead procedures. Test results indicate that imposing maximum hardness criteria can actually lead to acceptance of less than optimum fracture toughness in the temper bead weld HAZ due to rapidly changing microstructures in low alloy steels. Impact properties for such microstructures can vary widely even though similar levels of hardness are exhibited. This paper investigates the legitimacy of using maximum hardness criteria to demonstrate acceptable HAZ fracture toughness in low alloy pressure vessel steels.

Proposed New Fatigue Design Curves for Carbon and Low Alloy Steels in High Temperature Water

2005 ◽  
Author(s):  
William J. O’Donnell ◽  
William John O’Donnell ◽  
Thomas P. O’Donnell
Keyword(s):  
High Temperature ◽  
Environmental Effects ◽  
Low Alloy Steels ◽  
Fatigue Design ◽  
High Temperature Water ◽  
Safety Margins ◽  
Asme Code ◽  
Alloy Steels ◽  
Order Of Magnitude ◽  
Temperature Water

High temperature (&gt; 300 °F, 149 °C) water has been found to greatly accelerate fatigue crack growth rates in carbon and low alloy steels. Current ASME Code fatigue design curves are based entirely on data obtained in air. While a factor of two on life was applied to the air data to account for environmental effects, the actual effects have been found to be an order of magnitude greater in the low cycle regime. A great deal of work has been carried out on these environmental effects by talented investigators worldwide. The ASME Code Subgroup on Fatigue Strength has been working for 20 years on the development of new fatigue design methods and curves to account for high temperature water environmental effects. This paper presents an overview of the data and analyses used to formulate proposed new environmental fatigue design curves which maintain the same safety margins as existing Code fatigue design curves for air environments.

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