Austenitic alloy weldments in nuclear reactor systems are susceptible to stress corrosion cracking (SCC) failures. SCC has been observed for decades and continues to be a primary maintenance concern for both pressurized water and boiling water reactors. SCC can occur if the sum of residual stress and applied stress exceeds a critical threshold tensile stress. Residual stresses developed by prior machining and welding can accelerate or retard SCC depending on their sign and magnitude. The residual stress, cold work and yield strength distributions on the inside diameter of an Alloy 600 tube J-welded into a pressure vessel were determined by a combination of X-ray diffraction (XRD) and mechanical techniques. A new method was used to relate the XRD line broadening to the percent cold work or true plastic strain in the Alloy 600 tube. The accumulated cold work in the layers deformed by prior machining, in combination with the true stress-strain relationship for Alloy 600, was used to determine the increase in yield strength as a result of deformation due to machining and weld shrinkage. The yield strength of the deformed layer was found to be well in excess of the bulk yield for the alloy, and is therefore capable of supporting residual stresses correspondingly higher. Tension as high as +700 MPa, exceeding the SCC threshold stress, was observed in both the hoop and axial directions on the inside diameter of the Alloy 600 tubing adjacent to the weld heat affected zone (HAZ). The cold worked high tensile zones correlated with the locations of field SCC failures. The tensile residual stresses are shown to result from a combination of the high cold working from initial machining followed by weld shrinkage. The development of surface tension during weld shrinkage has been modeled using finite element methods, and the benefits of minimizing or removing the cold worked layer prior to welding are demonstrated. Further laboratory studies showing the influence of prior cold working on the formation of residual stresses following bulk plastic deformation are presented.

1.
Hall, J. F., and Scott, D. B., 1989, “Destructive Examination of Pressurizer Heater Sleeves from Calvert Cliffs Unit 2,” Report CE-NPSD-577.
2.
Gorman, J. A., 1986, “Status and Suggested Course of Action for Nondenting-Related Primary-Side IGSCD of Westinghouse-Type Steam Generators,” EPRI, Report MP-4594-LD.
3.
Hall, J. F., Molkenthin, J. P., and Preve´y, P. S., 1993, “XRD Residual Stress Measurements on Alloy 600 Pressurizer Heater Sleeve Mockups,” Proc., Sixth International Symposium on Environmental Degradation of Materials in Nuclear Power Systems-Water Reactors, San Diego, CA: TMS, ANS, NACE, pp. 855–861.
4.
Hall, J. F., Molkenthin, J. P., Preve´y, P. S., and Pathania, R. S., 1994, “Measurement of Residual Stresses in Alloy 600 Pressurizer Penetrations,” Conf. Contribution of Materials Investigation to the Resolution of Problems Encountered in Pressurized Water Reactors, Paris: Societe Francaise d’Energie Nucleare, September 12–16.
5.
US Patent 5,826,453, Oct. 1998.
6.
Prevey, P. S., 2000, “The Effect of Cold Work on the Thermal Stability of Residual Compression in Surface Enhanced IN718,” St. Louis, Missouri, 20th ASM Materials Solutions Conf. & Exp. October 10–12.
7.
Prevey, P. S., Telesman, J., Gabb T., and Kantzos, P., 2000, “FOD Resistance and Fatigue Crack Arrest in Low Plasticity Burnished IN718,” Chandler, AZ, 5th Nat. Turbine Engine High Cycle Fatigue Conf., March 7–9.
8.
Prevey, P. S., and Cammet, J., 2000, “Low Cost Corrosion Damage Mitigation and Improved Fatigue Performance of Low Plasticity Burnished 7075-T6,” Solomons, MD, 4th Int. Aircraft Corrosion Workshop, Oct.
9.
(200) “Diffraction Notes, Effect of Low Plasticity Burnishing (LPB) on the HCF Life of IN718,” (No. 26 Spring).
10.
Hilley, M. E., ed., 1971, Residual Stress Measurement by X-Ray Diffraction, SAE J784a, Warrendale, PA: Society of Auto. Eng.
11.
Noyan, I. C., and Cohen, J. B., 1987, Residual Stress Measurement by Diffraction and Interpretation, Springer-Verlag, New York, NY.
12.
Cullity, B. D., 1978, Elements of X-Ray Diffraction, 2nd Edition, Addison-Wesley, Reading, MA, pp. 447–476.
13.
Preve´y, P. S., 1986, “X-Ray Diffraction Residual Stress Techniques,” Metals Handbook, 10, Metals Park, OH, ASM, pp. 380–392.
14.
Koistinen, D. P., and Marburger, R. E., 1964, ASM Trans. Q., 67.
15.
Moore
,
M. G.
, and
Evans
,
W. P.
,
1958
, “
Mathematical Correction for Stress in Removed Layers in X-Ray Diffraction Residual Stress Analysis
,”
SAE Trans.
,
66
, pp.
340
345
.
16.
Preve´y
,
P. S.
,
1977
, “
A Method of Determining Elastic Properties of Alloys in Selected Crystallographic Directions for X-Ray Diffraction Residual Stress Measurement
,”
Adv. X-Ray Anal.
,
20
, pp.
345
354
, Plenum Press, New York.
17.
Preve´y
,
P. S.
,
1986
, “
The Use of Pearson VII Functions in X-Ray Diffraction Residual Stress Measurement
,”
Adv. X-Ray Anal.
,
29
, pp.
103
112
, Plenum Press, New York.
18.
Prevey, P. S., 1987, “The Measurement of Residual Stress and Cold Work Distributions in Nickel Base Alloys,” Residual Stress in Design, Process and Material Selection, ASM, Metals Park, OH.
19.
Alloy Digest, 1972, Inconel Alloy 600 Spec. Sheet Ni-176, Eng. Alloys Dig., Upper Montclair, NJ, July.
20.
Woldman’s Engineering Alloys, 1979, 6th Edition, ed., R. C. Gibbons, American Society for Metals, p. 747.
21.
Diffraction Notes, Residual Stress Contour Mapping, No. 19, Summer 1997.
22.
Hill, R., 1950, The Mathematical Theory of Plasticity, Oxford at the Clarendon Press, pp. 19–23.
23.
Chen, W. F., and Zhang, H., 1991, Structural Plasticity, pp. 129–130.
24.
Cook, R. D., and Young, W. C., 1985, Advanced Mechanics of Materials, pp. 21–26.
25.
Lissenden
,
C. J.
,
Gil
,
C. M.
, and
Lerch
,
B. A.
,
1999
, “
A Methodology for Determining Rate-Dependent Flow Surfaces for Inconel 718
,”
J. Test. Eval.
,
27
, No. 6, Nov. pp.
402
411
.
You do not currently have access to this content.