Internal Mechanical Stress Improvement Method for Mitigating Stress Corrosion Cracking in Weld Areas of Nuclear Power Plant Piping

Abstract

Method for mitigating stress corrosion cracking at an internal (i.e., welled-side) weld area in piping of a nuclear power plant includes the steps of actuating a radially movable tool to produce a radial bad against the internal (i.e., normally wetted) surfaces at or near the weld area to create a deep residual compressive stress state at the wetted surface of the weld. The method permits post-process verification by physical measurements of surface distortion.

What is claimed is: 
     
         1 . An internal, wetted side, mechanical method for mitigating stress corrosion cracking at an internal weld area in piping in a nuclear power plant comprising the steps of
 inserting a tool internally to the piping, the tool having an operating end with a radially movable member;   positioning the operating end adjacent the weld area;   actuating the operating end to more the radially movable member to produce a radial load on the internal surface of the piping near the weld area; and   removing the tool to create, when the tool is removed, a deep residual compressive stress state at the weld area.   
     
     
         2 . The method for mitigating stress corrosion cracking at an internal weld area as recited in  claim 1  wherein said actuating step includes mechanically moving a plurality of wedges radially outwardly. 
     
     
         3 . The method for mitigating stress corrosion cracking at an internal weld area as recited in  claim 1  wherein said actuating step includes supplying fluid to a bladder to radially expand the bladder. 
     
     
         4 . The method for mitigating stress corrosion cracking at an internal weld area as recited in  claim 1  wherein the radially movable member exerts the radially outward displacement of the pipe at one or more axial locations adjacent the weld area to create a desired magnitude, depth and orientation of the residual compressive stress field. 
     
     
         5 . The method for mitigating stress corrosion cracking at an internal weld area as recited in  claim 1  wherein the weld area is on the inner diameter of a nozzle, safe end or pipe. 
     
     
         6 . The method for mitigating stress corrosion cracking at an internal weld area as recited in  claim 1  wherein the weld is a J-groove weld in an internal surface of a reactor vessel wall adjacent piping penetrating the reactor vessel wall. 
     
     
         7 . An internal, wetted side, mechanical method for mitigating stress corrosion cracking at an internal weld area in a nuclear power plant including a reactor vessel having a wall with piping penetrating therethrough with the weld area surrounding the piping and disposed within a J-weld groove comprising the steps of
 inserting a tool internally to the piping, the tool having an operating end with a radially movable member;   positioning the operating end adjacent the J-groove weld area;   actuating the operating end to move the radially movable member to produce a radial bad on the internal surface of the piping near the J-groove weld area, and   removing the tool to create, when the tool is removed, a deep residual compressive stress state at the J-groove weld area and the internal surface of the piping.