Abstract
A method of utilizing the principle of magnetostriction to perform non-destructive diagnosis to determine whether or not there is residual stress produced by an earthquake in a bent pipe has been developed. The method is used to measure total stress of the principal stress difference. Because large stress produced during the manufacture of a bent pipe remains in the pipe, an effort was made to separate the residual stress from the measured value by regressing the measured value to a theoretical stress calculation equation for bent pipe by Rodabaugh and George. As a result, only the stress produced by external force was precisely obtained divided into longitudinal and circumferential stress. Because the upper limit stress value that can be diagnosed by the method is approximately 55% of the yield stress, it has been proposed as a method to be used to make a primary judgment of whether or not stress produced by an earthquake remains.
