METHOD FOR MEASURING RESIDUAL STRESS OF CURVED PIPE

PURPOSE:To measure the residual stress of a curved pipe by removing the surface of the curved tube in order and detecting the strain of the opposite surface from each removed surface at every time the surface is removed. CONSTITUTION:When discharge working is carried out, a controller 24 supplies a current to an electrode 16 the material 10 to be inspected from a power source 22 and while an arm part 20 is rotated around an axis 14 and moved in the direction of a pipe axis 10A along the tube-axial vertical section of the material 10 to be inspected, the internal surface of the object material 10 is fused by the discharge working, thereby removing a specific thickness part of the internal surface. Then the electrode 16 is varied in size after the discharge working and he discharge working operation is repeated to reduce the thickness of the object material 10 stepwise. Then a strain measuring instrument measures the strain value of the object material 10 before the discharge working and then measures the strain value after the discharge working. This operation is repeated specific times to obtain measured strain values of the object material 10. The measured strain values are substituted in a specific expression to fine the residual stress.