Weld Residual Stress Analysis and the Effects of Structural Overlay on Various Nuclear Power Plant Nozzles

Author:

Zhang Tao1,Brust Frederick W.,Wilkowski Gery2,Huang Chin-Cheng,Liu Ru-Feng3,Ranganath Sam4,Wang Lihua,Tsai Yao Long5

Affiliation:

1. e-mail:

2. 3518 Riverside Drive, Suite 202, Columbus, OH 43221

3. Mechanical and System Engineering Program (MSEP), Institute of Nuclear Energy Research, 1000 Wenhua Road, Jiaan Village, Longtan, Taoyuan 32546, Taiwan (R.O.C)

4. XGEN Engineering, 7173 Queensbridge Way, San Jose, CA 95120-4081

5. Material and Chemical Research Laboratories, Industrial Technology Research Institute, Building 52, 195 Chung-Hsing Road, Section 4, Chutung, Hsinchu 31040, Taiwan (R.O.C)

Abstract

Welding is a commonly used and one of the most important material-joining processes in industry. The incidences of defects had been located by ultrasonic testing in various pressurizer nozzle dissimilar metal welds (DMW) at nuclear power plants. In order to evaluate the crack propagation, it is required to calculate the stress distribution including weld residual stress and operational stress through the wall thickness in the weld region. The analysis procedure in this paper included not only the pass-by-pass welding steps but also other essential fabrication steps of surge, safety/relief, and spray nozzles. In this paper, detailed welding simulation analyses have been conducted to predict the magnitude of these stresses in the weld material. To prevent primary water stress corrosion cracking (PWSCC) in pressurized water reactors (PWR) on susceptible welded pipes with dissimilar metal welds, the weld overlay process has been applied to repair nuclear reactor pipe joints in plants. The objectives of such repairs are to induce compressive axial residual stresses on the pipe inside surface, as well as increase the pipe thickness with a weld material that is not susceptible to stress corrosion cracking. Hence, understanding the residual stress distribution is important to evaluate the reliability of pipe joints with weld overlay repairs. The finite element results in this paper showed that, after deposition of the DMW nozzle and stainless steel welds, tensile weld residual stresses still exist at regions of the DMW through the thickness. This tensile weld residual stress region was significantly reduced after welding the overlay. The overlay weld also provides a more uniform and large compressive region through the thickness, which has a beneficial effect on the structural integrity of the DMW in the plant.

Publisher

ASME International

Subject

Mechanical Engineering,Mechanics of Materials,Safety, Risk, Reliability and Quality

Reference19 articles.

1. Boggs, R., Joseph, M., and Hall, J., 1996, “Experience With Detection and Disposition of PWSCC Flaws in PWR Pressurizer and Reactor Coolant System Loop Alloy 600 Penetrations,” Service Experience and Design in Pressure Vessels and Piping (Including High Pressure Technology), ASME Pressure Vessel and Piping Conference, Montreal QC, Canada, July21–26.

2. Zhang, T., Wilkowski, G., Rudland, D., Brust, F., Mehta, H. S., Sommerville, D. V., and Chen, Y., 2008, “Weld—Overlay Analyses—An Investigation of the Effect of Weld Sequencing,” ASME Pressure Vessel and Piping Conference, Chicago, IL, July27–31.

3. Bamford, W., Newton, B., and Seeger, D., 2006, “Recent Experience With Weld Overlay Repair of Indications in Alloy 182 Butt Welds in Two Operating PWRs,” ASME Pressure Vessel and Piping Conference, Vancouver, BC, Canada, July23–27.

4. Wang, Y.-Y., Feng, Z., Cheng, W., and Liu, S., 1998, “Residual Stress Effects on Crack Driving Force in Multipass Welds,” ASME Pressure Vessel and Piping Conference, San Diego, CA, July26–30.

5. Rudland, D., Chen, Y., Zhang, T., Wilkowski, G., Broussard, J., and White, G., 2007, “Comparison of Welding Residual Stress Solutions for Control Rod Drive Mechanism Nozzles,” ASME Pressure Vessel and Piping Conference, San Antonio, TX, July22–26.

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