Application of induction heating stress improvement to pipe branches

The intergranular stress corrosion cracking (IGSCC) have been found in the heat affected zones of the girth weld of SS 304 pipings in BWR plants. The weld residual stresses are considered to be a big contributor to the IGSCC, since the pipe size dependency of the IGSCC occurrence and that of weld residual stresses are very much alike. The IHSI (Induction Heating Stress Improvement) is a method to lower or change this welding tensile residual stresses on pipe inner surface to compressive ones. The IHSI had been qualified and implemented successfully, as an IGSCC countermeasure, to many weld joints, except pipe to branch joints. The weld residual stresses in branch joints are also concerned to be enough high to cause the IGSCC, therefore, it is strongly requested to make IHSI applicable to such joints. Based upon the preliminary studies, mock-up tests and a three dimensional elasto-plastic analysis were conducted to demonstrate the validity of IHSI to pipe branches. This report describes the results of these experiment and analysis. (orig./HP)