Weld repair of Heavy Section Steel Technology program vessel V-7. Final report

Abstract

The in situ repair of a flaw in a large nuclear pressure vessel is likely to be a complex undertaking. Normally, a thermal stress relief is required to reduce peak welding stresses; however, accomplishing this task under field conditions can result in difficulties related to warpage of the vessel. Consequently, Section XI of the ASME Boiler and Pressure Vessel Code has provided guidelines for making major repairs without a subsequent thermal stress relief. The Heavy Section Steel Technology (HSST) Program has been pressure-testing intermediate sized vessels roughly scaled to nuclear reactor pressure vessels. One such vessel - ITV-7, intentionally flawed in the axial direction, was hydraulically pressurized to failure - leakage occurred when the vessel was pressurized to 2 1/2 times the design pressure. Arrangements were made with the HSST Program Office to use this vessel for the purpose of repairing the thru wall flaw according to Section XI procedures. The repair was performed to demonstrate the utility of such a weld repair. This report documents details of the procedures used with that repair. (GRA)