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Vermont Yankee July 2008 Evidentiary Hearing - Applicant Exhibit E2-32-VY, Wrc Bulletin 487 Pvrc'S Position on Environmental Effects on Fatigue Life in LWR Applications
ML082490476
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Site: Vermont Yankee Entergy icon.png
Issue date: 12/31/2003
From: Asada Y, Bush S, Chakrabarti G, Chopra O, Donavin P, Hechmer J, Higuchi M, Hoffman C, Iida K, Mehta H, O'Donnell W, Vandersluys W, Vecchio R, Yukawa S
Welding Research Council
To:
NRC/SECY/RAS
SECY RAS
References
06-849-03-LR, 50-271-LR, Entergy-Applicant-E2-32-VY, RAS M-295
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PVRC'S POSITION ON ENVIRONMENTAL EFFECTS ON FATIGUE LIFE IN LWR APPLICATIONS W. Alan Van Der Sluys STEERING COMMITTEE ON CYCLIC LIFE AND ENVIRONMENTAL EFFECTSOCKETED Sumio Yukawa, Chair USNRC Robert S. Vecchio, Vice Chair Aunust 12 2nOn Ill .nn!m\

Asada, Yasuhide OFFICE OF SECRETARY Bush, Spencer H. RULEMAKINGS AND Chakrabarti, Gauranga S. ADJUDICATIONS STAFF Chopra, Omesh K.

Donavin, Paul R.

Hechmer, John L.

Higuchi, Makoto Hoffmann, Christopher L.

lida, Kunihiro Mehta, Har S.

O'Donnell, William J.

VanDerSluys, W. Alan Vecchio, Robert S.

Yukawa, Sumio WRC Bulletin 487-DECEMBER 2003 Publication of this report is sponsored by The Pressure Vessel Research Council of the Welding Research Council, Inc.

and The Board on Nuclear Codes & Standards of The Council on Codes & Standards of the American Society of Mechanical Engineers U.S. NUCLEAR REGULATORY 1buivnii,5*lU1 Inthe Matter of £t *WJW AI*u " U" -

WELDING RESEARCH COUNCIL, INC.

Docket No. 5o - 711 Official Exhibit No. -Z-3'-' Y PO Box 1942 New York, NY 10156 OFFERED by'i ,ntervenor_....

www.forengineers.org NRC Staft Other IDENTIFIED On+I'? 12-'0% Witness/Panel ?LJC ,

Action Taken: MITTEI REJECTED WITHDRAWN Reporter/Clerk A1f c--I,

ISBN No. 1-58145-494-5 Library of Congress Catalog Card Number: 85-647116 Copyright © 2003 by Welding Research Council, Inc.

All Rights Reserved Printed in U.S.A.

ii

FOREWORD This report describes the activities of the PVRC Steering Committee on Cyclic Life and Environmental Effects (CLEE) and the PVRC Working Group S-N Data Analysis. This report presents the PVRC recommendations to the ASME Board on Nuclear Codes and Stan-dards (BNCS) concerning needed modifications to the ASME fatigue analysis procedure. The proposed modifications will account for the effect of the environment on the fatigue properties of the pressure boundary materials. These recommendations are in response to the following request from the BNCS:

"BNCS Looks to PVRC to Obtain, Characterize, and Report in Sufficient Detail to ASME Such Data as May be Useful to ASME in its Evaluationof the Fatigue Curves of Sections IIII and XI" The PVRC Committee has worked closely with, and received com-ments from, investigators in Japan, Europe, and America and has re-viewed essentially all public domain data. We are particularly apprecia-tive of databases and analyses provided by those in Japan working on MITI projects and in America at the Argonne National Laboratory.

We believe we have been successful in guiding the experimental work and forging a consensus with regard to the key issues that were formerly much less than clear. Considering all well characterized, available data, PVRC has drawn the following major conclusions:

1. ASME Section III should adopt a procedure such as proposed in Section 7 of this report to apply an environmental correction factor, Fen; to life fractions calculated using the existing ASME S-N design curves when anticipated operating conditions are sufficiently severe that it is necessary to account for environmental effects.
2. ASME Section XI should adopt a procedure such as proposed in a draft code case in Section 7 of this report and apply the environ-mental correction factor, Fenw to life fractions calculated using the existing ASME S-N design curves when it is necessary to account for environmental effects.
3. The Fen models are shown to work well in predicting the effect of the coolant environments on the low cycle fatigue properties of stainless steel. The low cycle fatigue information on stainless steel in air, collected by the PVRC to perform the evaluation, does not appear to support the ASME mean data line for stainless steel, and more data are needed to adequately understand behavior.

The above conclusions are based on two principles:

1. The environmental correction factors can be determined using equa-tions developed either by Argonne National Laboratory or by MITI's investigators in Japan. While these equations are somewhat differ-ent; in real situations, they are expected to give similar results, within the bounds of experimental error and operating uncertainties.

111..

2. The factor of 20 on life, originally used in the development of the fatigue design curves to account for uncertainties, is adequate to account for reductions in fatigue life due to the environment under well controlled operating conditions. Under those condi-tions, provision for further reductions in fatigue life due to the environment is not essential.

The PVRC has reviewed the ASME Section III Fatigue Analysis procedure to determine what modifications are needed to take into account the effects of the coolant environment on the S-N fatigue proper-ties. In performing this review, the PVRC evaluated the following areas:

1. The margins used in the development of the Section III procedure.
2. Laboratory data used in the development of the Section III procedure.
3. Laboratory fatigue data on smooth specimens in simulated reac-tor coolant environments.
4. Models to predict the S-N properties in Light Water Reactor (LWR) coolant environments of the pressure boundary materials.
5. Laboratory data on structural tests conducted in water environ-ments.

This report is divided into 10 sections that describe in detail the development of the PVRC recommendations and present examples of the Code changes needed to implement the recommendations. The S-N fatigue data for carbon steel, low alloy steel, and stainless steels, collected by the PVRC are compared with the available S-N models. Both the models developed by Argonne National Laboratory and MITI are shown to ade-quately predict the S-N results in simulated LWR coolant environments.

i The available data from laboratory specimens tested in simulated LWR coolant environments were used to evaluate expected reduction in life in plants. It was determined that the margins applied to laboratory data to develop the ASME Fatigue Design Curves need not be adjusted when certain operating thresholds are not exceeded. These thresholds identified by PVRC pertain to oxygen level, temperature, stain rate, etc. The PVRC developed thresholds, or more rigorous analysis without thresholds, can be used to determine the effect of the environment on specific components.

A limited amount of laboratory data exist on the effect of coolant flow rates on carbon and low alloy steels. These data show a reduction in the environmental effect with increasing flow rates. These flow rate effects need to be incorporated into the Fen models and the thresholds for carbon and low alloy steels. At this time no information exists as to the effect of flow rate on stainless steel.

Available data from the literature on the results of laboratory tests of structural components in water environments were evaluated using the proposed procedure. This evaluation supported the concept of a moderate reduction in fatigue life without applying the environmental correction factor, Fen) to the ASME Fatigue Design Curves.

In section 9, of this report a copy of the MITI Guidelines For Evaluating Fatigue Initiation Life Reduction in LWR Environments is reproduced. These guidelines recommend the use of the Fen factor to account for the effect of the environment but do not utilize the concept of thresholds to deal with moderate environmental effects.

iv

CONTENTS FOREW ORD ............................................................. iii

1. Introduction ........................................................... 1 1.1 BNCS Response and Request to PVRC .............................. 1 1.2 Proposed Environmental Factor Approach to Account for Environmental Effects in LWR Applications ........................ 2 1.3 Summaries of Programs External to PVRC .......................... 2 1.4 Summary of PVRC Activities ....................................... 3
2. Summary of Technical Basis of Section III Fatigue Evaluation Procedure .............................................................. 3 2.1 ASME Air Curve .................................................... 4 2.2 M argins ............................................................. 4
3. Early Tests and Results in Simulated Reactor Coolant Environments ... 6
4. Thresholds ............................................................. 7 4.1 Carbon and Low Alloy Steel .............. .................. 8 4.1.1 Verification of the Thresholds .............. .................... 9 4.1.1.1 Comparison with Fen Models ................................ 9 4.1.1.1.1 Strain Rate ............................................... 9 4.1.1.1.2 Oxygen Content ......................................... 9 4.1.1.1.3 Temperature ....... ...................................... 9 4.1.1.1.4 Strain Amplitude ................... , .................... 9 4.1.2 Other Factors .................................................. 12 4.1.2.1 Sulfur Effect ............................................... 12 4.1.2.2 Flow Rate Effects ........................................... 12 4.1.3 Comparison of the Threshold Values with Fatigue Crack Growth Inform ation .................................................... 14 4.2. Austenitic Stainless Steels ........................................ 14 4.2.1 Fen M odels ..................................................... 14 4.2.2 Strain Rate ..................................................... 15 4.2.3 Temperature ................................................... 15 4.2.4 Dissolved Oxygen .............................................. 15 4.2.5 Strain Amplitude ............................................. 16 4.2.6 Discussion of Austenitic Thresholds ........................... 17
5. M argins ............................................................... 17 5.1 Initial Consideration of ASME Code Margins ...................... 17 5.2 PVRC Review of the Margins ...................................... 17 5.3 Sub-Factor for Size Effects ......................................... 18 5.4 Sub-Factor for Surface Finish ..................................... 18 5.5 Sub-Factor for Data Scatter ........................................ 20 5.6 Atmosphere Factor ................................................ 20 5.7 Load History Effects ........................... 20 5.8 Application of Fen..................................................... 21 5.9 Conservatism of Fen............................................. 21 5.10 Evaluation of the Z Factor ........................................ 22
6. Review of S-N Models....................................... 22 6.1 ASME Code S-N Models. ............................... . ...... 22 6.2 Argonne National Laboratory Air Fatigue Data Models .......... 24 6.3 Japanese Air Fatigue Data Models ................................ 24 6.4 Comparison of Model Predictions for Air Fatigue Data .......... 24 6.5 Reactor Water Environmental Effects ....... ................ 27 6.6 Environmental Model Comparisons .......................... 29 V

7.0 Code Implementation ................................................ 33 7A Appendix: Recommendation for Code Implementation ............ 34 7J.A1 Potential Section III Implementation .......................... 34 7.A.2 Potential Section XI Implementation.......................... 35 7.A.3 Potential Implementation asSection XI Code Case ............ 35 7.A.4 Nonmandatory Appendix XX ....... ! ........................... 35 8.0 PVRC Data Base and Analysis ....................................... 38 8.1 Carbon Steel ................................ ...................... 38 8.2 Low-Alloy Steel .................................................... 42 8.3 Austenitic Stainless Steel .......................................... 45 8.4 Structural Test Results ............................................ 50 8.4.1 PVRC Pressure Vessel Tests ...... ...................... 51 8.4.2 Tests on Butt-Welded Piping ................................... 51 8.4.3 KWU Tube Tests................................................ 54 9.0 M ITI Procedure ..................................................... 57 10.0 Conclusions and Recommendations ................................ 58 Acknowledgment This report represents the culmination of ten years of activities within the PVRC. The author would like to acknowledge the help and contributions of a number of persons:

Throughout most of the ten years the work was preformed under the guidance of Sumio Yukawa. Without his guidance and contributions this report could not have been written.

Throughout this effort there has been continuous support from the following committees in Japan:

" Thermal and Nuclear Power Engineering Society (TENPES), EFD Project

" Japan Power Engineering and Inspection Corporation (JAPEIC), EFT project

" Japan Nuclear Energy Safety Organization (JNES)

These Japanese committees contributed much of the fatigue data collected by the PVRC as well as participated in the activities of the PVRC subcommittees. M Higuchi, Ishikawajima-Harima Heavy Industries Co. Ltd, attended many -of the committee meetings, contributing in the discussions and keeping the PVRC informed as to activities in Japan.

In addition representatives from Hitachi, Mitsubishi Heavy Industries, Toshiba Corp, Tokyo Electric Power, Kansai Electric frequently attended meetings and contributed valuable test results.

Another major contributor to the committee activities was 0. Chopra from Argonne National Laboratory.

He attended most of the PVRC meetings, supplied significant data to the PVRC, and contributed in the discussions of the subcommittees.

EPRI contributed several figures from EPRI Report MRP-49.

vi

PVRC's Position on Environmental Effects on Fatigue Life in LWR Applications W. Alan Van Der SluysI 1.0 Introduction entitled "SPECIAL CONSIDERATIONS," and "Cor-The rules and requirements provided in Section rosion" stated:

III of the ASME BOILER and PRESSURE VESSEL "It should be noted that the tests on which the fatigue CODE has been widely used in the US and in other design curves (Figs 1-9.0) are based did not include tests countries for the design, fabrication, and pressure in the presence of corrosive environments which might integrity evaluation of the components for light wa- accelerate fatigue failure."

ter-cooled reactor (LWR) type of commercial nuclear Within a few years, results for fatigue tests con-power systems. Among its many features,Section III ducted in water environments which simulated LWR includes procedures for analyzing fatigue damage coolant water became available in technical. Ex-and the possibility of crack formation by fatigue as a amples include:

result of pressure and temperature cycling during operation. D. Hale, S.A. Wilson, J.W. Kass, and E. Kiss "Low Beginning in the 1950's, design, fabrication, and Cycle Fatigue of Commercial Piping Steels in a construction activities related to nuclear power expe- BWR Primary Water Environment," Journal of rienced a major increase and the ASME Code in- Engineering Materials and Technology, Vol. 103, creased its scope and activities to keep pace with the pp. 16-25 (1981) increase. Emphasis .on the "Design by Analysis" in- M. Higuchi and K. Iida, "Fatigue Strength Correc-cluded additional effort on fatigue analysis with the tion Factors for Carbon and Low-Alloy Steels in formation of a Task Group for the determination of Oxygen-Containing High-Temperature Water,"

allowable fatigue stresses chaired by B.F Langer. Nuclear Engineering and Design, Vol. 129, pp.

The Task Group collected and analyzed the available 293-306(1991) fatigue test data and developed curves of allowable O.K. Chopra, and W.J. Shack, "Environmental Ef-fatigue stresses as a function of number of imposed fects on Fatigue Crack Initiation in Piping and cycles. Pressure Vessel Steels," NUREG 6717, ANL-0027 The methodology utilized by the Langer Task 7 May 2001, U.S. Nuclear Regulatory Commission Group to formulate Fatigue Design Curves (desig-These results all indicated that LWR coolant water nated as Figs 1-9.0 in the Code) is described in could have a significant detrimental effect on the Section 2 of this report. The work of the Langer Task fatigue life of metals utilized for the pressure bound-Group was limited by the fact that the technology of ary of LWR Nuclear systems.

fatigue testing in elevated temperature water at pressures and chemistries typical of LWR operating 1.1 BNCS Response and Request to PVRC conditions was not well developed, which limited the These results produced serious concerns within available amount of fatigue test data for LWR cool- the ASME Board on Nuclear Codes and Standards ant water environments. This limitation was recog- (BNCS) regarding the structural integrity of Nuclear nized by the ASME in the 1974 and 1992 editions of power plants and BNCS made the following request the Code, wherein, Articles NB3120 and NB3121 to PVRC to assist in resolving the concerns:

"BNCS Looks to PVRC to Obtain, Characterize, and 1

Consultant, Alliance, OH Report in Sufficient Detail to ASME Such Data as May WRC Bulletin 487 1

be Useful to ASME in its Evaluation of the Fatigue LWR environmental effects on the calculated Curves of Sections III and XI" fatigue usage factor of representative ASME 1.2 Proposed Environmental Factor Approach to Class 1 components. As expected, the lower cy-Account for Environmental Effects in LWR clic life of the adjusted curve increases the calcu-Applications lated usage factor. However, it was observed In 1994-95, GE with EPRI support developed the that in a number of instances, conservative and environmental factor procedure for ASME Code-type bounding values were utilized in the original Analysis of Environmental Effects in Fatigue Usage usage factor calculations. Using more realistic Evaluation. In Oct 1999, PVRC forwarded this proce- values in the usage analysis could compensate dure to the BNCS with a recommendation that the for a significant portion of the environmental procedures be considered for Code application and effect on usage factor.

implementation. The Procedure has been utilized for " The NRC program, titled Fatigue Action Plan, fatigue life evaluation in several License Submittals included studies of a number of issues associ-to the NRC. This report presents available data, ated with the assessment of fatigue perfor-models to predict the environmental factors and mance of structural components in a LWR envi-suggested Code Cases for Code implementation. ronment. For example, it included a much Starting in 1992, the Pressure Vessel Research broader and detailed study of situations noted Council (PVRC) has had a continuing activity con- in the DOE study mentioned above; these re-cerned with the effect of the Light Water Reactor sults are described by Ware et al. [1-6, 1-7]..

(LWR) coolant environment on the fatigue perfor- Based in part on the results of the study, the mance of the pressure boundary materials used in NRC concluded that no major actions were LWR applications. The activity has involved three needed by the NRC regarding environmental main aspects of fatigue performance and applica- effects for currently operating LWR plants [1-8].

tions. These are: (a) cyclic life under repeated stress

  • In the 1996 Addenda to the ASME Code, Section and strain, the so-called S-N properties, (b) fatigue XI added a new nonmandatory Appendix L titled crack growth under repeated loading, and (c) evalua- Operating Plant Fatigue Assessment. In es-tion of the design procedures and methodology used sence, the Appendix permits a re-evaluation of to assure performance and life of the structural com- the original usage factor analysis to determine ponents under anticipated cyclic duty. The primary acceptability for continued service. Addition-focus of this paper concerns the effect of the LWR ally, the Appendix also contains flaw tolerance environment on the first aspect of fatigue perfor- based procedures and acceptance criteria to de-mance, namely the S-N properties. The PVRC effort termine acceptability for continued service. An in this area has consisted of compiling and evaluat- EPRI supported activity to develop procedures ing the available test data and assessing the various that could be used in conjunction with generally correlations of cyclic life and various mechanical and available data and information in existing ASME environmental parameters. The interim status and Code stress and fatigue analyses to account for findings of this effort have been reported by Van Der LWR water environmental effects was com-Sluys and Yukawa [1-1, 1-2 and 1-3]. It may be noted pleted in 1995 by Mehta and Gosselin [1-9, 1-10].

that Hechmer [1-4] has presented a summary of the The approach and procedures have been re-PVRC effort related to the design and evaluation viewed and evaluated by the PVRC and deter-aspects of fatigue performance.

mined to be a reasonable and workable ap-1.3 Summaries of Programs External to PVRC proach for Code implementation. The detailed During the 1993-1995 period, the US Department evaluation combined with some trial uses of the of Energy (DOE) and the US Nuclear Regulatory procedures has revealed areas where revisions Commission (NRC) initiated and supported several and modifications are needed, and PVRC effort programs that evaluated and assessed the ASME is being applied to this need. This development Code design criterion for fatigue life performance of made full use of the results of the statistical operating LWR nuclear power plants. In addition, modeling and analysis effort performed by the the ASME Code adopted an enabling rule for reanaly- Argonne National Laboratory [1-11] and by Japa-sis of usage factor calculations, and the Electric nese investigators [1-12].

Power Research Institute (EPRI) supported develop- 0 In 2000 MITI Guidelines for Evaluating Fatigue ment of an approach and procedures that could be Initiation Life Reduction in LWR Environments implemented into the ASME Code to perform envi- were issued by the Nuclear Power Safety Admin-ronmental effects analysis. The findings and/or ensu- istration, Public Utilities Department, Agency ing actions from these activities included the follow- of Natural Resources, and Energy Ministry of ing: International Trade and Industry. These guide-lines are presented in Section 9 of this report.

0 A DOE supported study [1-5], examined the These guidelines use Fen as a fatigue life correc-effect of applying an early version of a fatigue tion factor in the same way as recommended by design curve that included an adjustment for the PVRC. The equations for the calculation of 2 WRC Bulletin 487

Fe' give very similar results as Fen calculations Conservatisms In Fatigue Evaluation of ASME Class 1 Pressure Vessels and Piping," PVP-Vol. 286, ASME, 1994, pp. 19-29.

developed by Argonne National Laboratory and 1-6. Ware, A.G., Morton, D.K., and Nitzel, M.E., "Application of Environ-mentally-Corrected Fatigue Curves To Nuclear Power Plant Components,"

used in the PVRC approach. Both sets of equa- PVP-Vol. 323, ASME, 1996, pp. 141-150.

tions are presented in this report. The MITI 1-7. Ware, A.G., Morton, D.K., and Nitzel, M.E., "Application of NUREG/

CR-5999 Interim Fatigue Curves to Selected Nuclear Power Plant Compo-approach differs from the PVRC approach in nents," NUREG/CR-6260, U.S. Nuclear Regulatory Commission, March 1995.

that it does not accept a moderate environmen- 1-8. SECY-95-245, "Completion of the Fatigue Action Plan," James M.

Taylor, Executive Director for Operations, U.S. Nuclear Regulatory Commis-tal effect which is discussed in sections 4 and 5 sion, Washington, DC, September 25, 1995.

of this report. 1-9. Mehta, H.S. and Gosselin, S.R., "An Environmental Factor Ap-proach to Account for Reactor Water Effects In Light Water Reactor 0 In 2001 EPRI published MRP-49 Materials Reli- Pressure Vessels and Piping Fatigue Evaluations," PVP-Vol. 323, ASME, 1996, pp. 171-185.

ability Program (MRP) Evaluation of Fatigue 1-10. Mehta, H.S. and Gosselin, S.R., "An Environmental Factor Ap-Date Including Reactor Water Environmental roach to Account for Reactor Water Effects in Light Water Reactor essure Vessels and Piping Fatigue Evaluations," EPRI Report No. 105759, Dec. 1995.

Effects. This report recommends the use of the 1-11. Meisler, J. and Chopra, 0., "Statistical Analysis of Fatigue Strain-PVRC procedure in plant life extension evalua- Life Data for Carbon and Low-Alloy Steels," PVP-Vol. 296, Risk and Safety Assessments: Where is the Balance? Book No. H00959-1995.

tions. Many of the figures and some of the text in 1-12. Nakao, G., Higuchi, M., lida, K., and Asada, Y., "Effects of Tempera-this PVRC report are the same as in this EPRI ture and Dissolved Oxygen Contents on Fatigue Lives of Carbon and Low Alloy Steels in LWR Water Environments," Effects of the Environment on report. the Initiationof Crack Growth, ASTM STP 1298, ASTM, 1997, pp. 232-245.

1.4 Summary of PVRC Activities 2.0 Summary of Technical Basis of Section III This report recommends an approach which en- Fatigue Evaluation Procedure tails the use of a life reduction factor, Fen for the cases when the characteristics of the transient being The fatigue evaluation procedure in Section III of evaluated exceed a set of threshold conditions for the the ASME Boiler and Pressure Vessel Code was existence of an environmental effect on the fatigue developed in the early 1960's. It was based on the life of the material. It has been shown that this Bureau of Ships Design Bases developed in the late approach will account for the environmental effects 1950's. The S-N fatigue curves and a description of observed in laboratory studies. This approach is ap- the technical basis for the curves for the BuShips plicable because there is no observed effect of the Design Basis Ref 2-1. The following is taken from environment on the fatigue limit of the material; this reference and is the description of the procedure thus, a factor of fatigue life alone will account for all used to develop the S-N curves.

observed effects. The laboratory studies have not "This curve was constructed in the following man-shown an effect of the environment on the fatigue ner.

limit and the experience in Germany with oxygen water treatment in fossil boilers, that will be dis- (a) Available strain fatigue data for this general cussed later in this paper, has not observed such an class of material were plotted in the form of effect. total strain (elastic plus plastic) range versus The following sections of this report will present cycles-to-failure. Machined specimens without the technical bases for the life reduction factor ap- notches that were tested at temperatures less proach. These sections will show the development of than 600'F were considered. The mean curve the threshold values for carbon, low alloy and stain- for each material was drawn.

less steel in the environment and present the models (b) A lower limit of the mean curves was drawn used to calculate the life reduction factors Fen. and then converted to a stress amplitude ver-This report will also describe the application of sus cycles-to-failure curve by multiplying the this procedure to the results from a number of labora- strain range by E/2, where E was taken as tory tests programs in which structures were tested 26 X 106 psi.

under fatigue loading conditions in water environ- (c) The design fatigue curve was then constructed ments until failure. In these cases the recommended by applying a factor of safety of either 2.0 on procedure is shown to work very well to predict the stress amplitude of a factor of 20 on cycles, life of the structures. whichever was more conservative at each point.

The factor of 20 on life is the product of the following sub-factors:

References a. Scatter of data (minimum to mean) 2.0 1-1. Van Der Sluys, W.A., "Evaluation of the Available Data on the Effect of the Environment on the Low Cycle Fatigue Properties in Light Water b. Size Effect 2.5 Reactor Environments," presented at Sixth Int. Sympos. on Environmental Degradation in Nuclear Power Systems-Water Reactors, TMS/NACE, c. Surface finish, atmosphere, etc. 4.0 Aug. 1-5, 1993, San Diego. (d) The design fatigue curve stress amplitude for 1-2. Van Der Sluys, W.A. and Yukawa, S., "Studies of PVRC Evaluation of LWR Coolant Environmental Effects on the S-N Fatigue Properties of less than 100 cycles was taken as the value at Pressure Boundary Materials," in: PVP-Vol. 306, pp. 47-58, presented at ASME PVP 1995, Honolulu, HI, July 23-27, 1995. 100 cycles."

1-3. Van Der Sluys, W.A. and Yukawa, S., "S-N Fatigue Properties of Pressure Boundary Materials in LWR Coolant Environments," in: PVP.Vol.

374, pp. 269-276, presented at ASME PVP 1998, San Diego, July 26-30, This procedure is essentially the same as used in the 1998. development of the ASME curves as described in Ref.

1-4. Hechmer, J., "Evaluation Methods For Fatigue-A PVRC Project,"

in: PVP-VoI. 374, pp. 191-196, presented at ASME PVP 1998, San Diego, 2-2. The data and equations used in this develop-July 26-30, 1998.

1-5. Smith, J.K.,

Deardorff,

A.F., and Nakos, J.T., "An Assessment of the ment are described in the next section.

EnvironmentalFatigue in LWR Applications 3

2.1 ASME Air Curve Where In Reference [2-2] the ASME Sub-Task Group on S = value from curve Fatigue recommended to the ASME Boiler and Pres-S' = adjusted S value sure Vessel Committee, Special Committee to Re-view Code Stress Basis that the formula given below Su = ultimate tensile strength be use in low cycle fatigue. Langer describes the Sy = yield strength application of this equation to 18-8 stainless steels in The results from this correction for the mean stress ref [2-3]. are shown in the figures as dotted lines. It was felt E 100 that austenitic stainless steels due to their high Sn 100-RA Se endurance limit and low yield strength cannot sus-tain a mean stress at a cyclic strain level that would Where produce failure.

The best-fit lines, developed by Langer, appear to S = elastic modulus x stain amplitude (psi) fit the data well. In these cases all of the results are E = elastic modulus (psi)

N = cycles-to-failure from strain controlled experiments and the results RA = reduction of area in tensile test (percent) are all in what is considered the low cycle region.

S. = endurance limit or fatigue strength at 107 2.2 Margins cycles (psi)

The last step in the development of the ASME S-N The above formula was used to determine the low Fatigue Curve is the introduction of the margins of cycle fatigue curves for carbon steel, low alloy steel, 20 on life and 2 on stress. These are the same and austenitic stainless steel. A best-fit curve ob- margins as described earlier in this section. In Refer-tained from the method of least squares, applied to ence 2-4 W. Cooper describes this process as follows:

the logarithms of the measured S and N values, "The final step in the process was to shift the curves using the above equation as a model. The room in recognitionof the fact that laboratorydata were to temperature modulus, E, was known in each case, be applied to actual vessels. Reference [2-2] states and the computer code gave the best-fit value for RA that the 'design stress values were obtained from the and S.. These values are shown on the curves tepro- best-fit curves by applying a factor of two on stress of duced from this report as Figures 2-1, 2-2, and 2-3. a factor of twenty on cycles, whichever was more These curves were then corrected for the maxi- conservative at eachpoint.' Unfortunately, these have mum effect of mean stress using the formula below. been understood to be factors of safety, and nothing This was derived from the Goodman diagram consid- could be furtherfrom the truth.As stated in Reference ering the change in the mean stress that is produced [2-2] 'it is not to be expected that a vessel will actually by yielding. operatesafely for twenty times its specified life.'

The factor of twenty applied to cycles was devel-S'=S S. ] for S< S oped to account for real effects. Reference [2-1] states 1.E+07 I CARBON STEEL EN-2,A-201

0. 1.E+06 0

ccJ o I~RA = 68.5%

ISE=21,645psi I*- LagrModel II 1.E+05 IMean Stress CorrectionI

" 0 1.E+04 1.E+01 1.E+03 1.E+05 1.E+07 N

Fig. 2-1-ASME Mean Air Fatigue Curve for Carbon Steel 4 WRC Bulletin 487

Low-Alloy Steel IEn-25,A-225 and A-302 I 1.E+07 MSE=38'500psi rRA=61.4% i 1.E+06 CLJ II [Langer o. -ti U,1* 1.E+05 i I ean Stress Correctiorl 1.E+04 1.E+01 1.E+03 1.E+05 1.E+07 N

Fig. 2-2-ASME Mean Air Fatigue Curve for Low-Alloy Steel 18-8 Stainless Steel Curve 1.E+07

[R)

S,4S 1.E+06

.L 0 Lani CI II.E+05 II.E+04 4-1.E+0-1 1.E+02 1.E+03 1.E+i04 1.E+05 1.1E+06 Cycles To Failure Fig. 2-3-ASME Mean Air Fatigue Curve for Stainless Steel Comparison of Margins

'The factor of 20 on life is the product of the following "Etc," simply indicates that we thought this factor subfactors: was less than four, but rounded it to give the factor of 20.

a. Scatter of data (minimum to mean) 2.0 A factor on the number of cycles has little effect at a
b. Size Effect 2.5 high number of cycles, so a factor on stress was
c. Surface finish, atmosphere, etc. 4.0 required at the higher number of cycles. It was found Two terms in the last line require definition. 'Atmo- that at 10,000 cycles, approximately the border be-sphere' was intended to reflect the effects of the tween low- and high-cycle fatigue, a factor of two on industrial atmosphere in comparison with an air- stress gave approximately the same result as a factor conditioned lab, not the effects of a specific coolant. of twenty on cycles."

Environmental Fatiguein LWR Applications 5

  • The subject of the appropriate margins to be applied 4. Based on an admittedly few datapoints, the low to the mean of the fatigue data obtained in the cycle fatigue performanceof Inconel far exceeds laboratory on smooth cylindrical specimens tested in the ASME Section III Fatigue Design Curve.

simulated reactor coolant environments is one of the However, significant amounts of intergranular most important issues to be resolved by the PVRC in crackingwere observed in normally welded ma-order to develop an analysis procedure which takes terial.

into account the effect of the coolant environment on 5. Carbon steel material, whether welded or non-the fatigue life of the material. welded, displayed a reduction in fatigue perfor-mance in the BWR environment. This reduction 2.3 References appears to be related to the surface pitting.

2-1. "Tentative Structural Design Basis for Reactor Pressure Vessels and Directly Associated Components (Pressurized, Water Cooled Sys- However, all data fall above the ASME Section tems)," dated 1 December 1958, with Addendum dated 27 February 1959. III design curve and this material is fully ad-2-2. "Criteria of the ASME Boiler and Pressure Vessel Code for Design by Analysis in Sections III and VIII, Division 2," ASME International, New equate for field performance."

York, NY, 1969.

2-3. Langer, B.F., "Design of Pressure Vessels for Low-Cycle" ASME Journal of Basic Engineering, pp. 389-402, 1962. These conclusions appear to be inconsistent with 2-4. Cooper, W.B., 'The Initial Scope and Intent of the Section III Fatigue Design Procedure," Presented at PVRC Workshop on Cyclic Life the later results presented in this report. The and Environmental Effects in Nuclear Applications, Jan. 1992.

results from this program are, however, consistent 3.0 Early Tests and Results in Simulated with the results from latter programs. The loading Reactor Coolant Environments strain rates of from 0.03 to 0.06 in/in/sec., used in the Dresden experiments, are not low enough for It has been known for some time that under some, the fatigue lives to be less than the ASME design test conditions the low cycle fatigue properties of curves.

carbon and low alloy steels in simulated reactor The second series of experiments were conducted coolant environments could be reduced. The General on both cylindrical specimens under axial loading Electric Company conducted two series of experi-and butt welded pipe samples of carbon steel with ments that showed such effects [3-1, 3-21. The first of internal pressure and axial loading [3-2]. These ex-these was conducted at the Dresden Reactor and periments were conducted in simulated BWR cool-involved cantilever bending specimens exposed to the reactor coolant. ant with various dissolved oxygen contents. A sub-In these experiments, a special facility was set up stantial environment effect was observed in these at the Dresden-1 Nuclear Power Station, Morris, experiments and a Ke environmental correction fac-Illinois. Primary water from the Dresden-1 test loop tor was suggested.

BWR system was piped to this special test loop and Experiments were conducted on SA333-Gr6 car-circulated at 10 gpm through three test vessels. A bon steel pipe material in room temperature air, total of 35,535 loading cycles were applied to the 550F air and simulated BWR coolant with various fatigue specimens. Four materials were evaluated, dissolved oxygen contents. In this study, a number of Types 304 and 304L stainless steel, Inconel 600 and different specimen geometries was tested including A-516 carbon steel. A summary of the results is as butt-welded pipe specimens. The program resulted follows: in a number of recommendations as to changes "The results of this work confirm the adequacy of *needed in the ASME. Code fatigue analysis proce-the currentASME Section III fatigue design curves to dure and a Ke environmental correction factor. The accountfor the effect of a B WRprimary water environ- results from the butt-welded pipe specimen tests ment on the low cycle fatigue behavior of the four from this program will be discussed in more detail in materialstested. Specifically: Section 9 of this report.

In 1991 Higuchi and Tida [3-3] proposed a fatigue

1. Fatigueperformance of non-sensitized stainless life correction factor, Fen' for correcting the low cycle steel, even with slight chemical or machined notches, is consistent with the ASME Code Mean fatigue properties of carbon and low alloy steels for Data Curve and far exceeds the Design Curve. the effect of the LWR coolant environment. These Performance of 304L stainless steel is compa- results stimulated the current concern for the effect rable. of the environment on the low cycle fatigue proper-
2. There is a slight reduction in fatigue life associ- ties of the pressure boundary materials. A number of ated with zero-tension loading in the, Type-304 versions of the correction factor has evolved since stainless steel in the BWR water environment this original proposal but the basic concept has not and this can be accounted for by use of a mean changed. This concept is that the effect of the environ-stress correction. ment on the low cycle fatigue properties of carbon
3. Reduction in cyclic life can be expected for heavily and low alloy steel can be corrected for the effect of sensitized welded stainless steel. This is due to the environment by applying a correction to the the presence of stress corrosion cracking When fatigue life as determined from the ASME design such welds are subjeit to cycling with long times curve. A correction is not needed on the strain ampli-and stresses exceeding the yield level. tude.

6 WRC Bulletin 487

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