Residual stress improvement by means of induction heating

A new method for improving residual stresses in pipe weldment has been proposed. This method, named IHSI (Induction Heating Stress Improvement), has been developed to improve residual stresses by creating local plastic flows through the application of high thermal stresses induced when a pipe is heated from the outside by an induction coil and cooled simultaneously from the inside by water. To obtain a better heating condition and to make a demonstration test, some basic studies were conducted on 304 type austenitic stainless steel pipes. The residual stresses with and without IHSI were measured by the conventional strain gage method. A cracking test was also conducted for demonstration by boiling 42% MgCl2 solution. The following experimental results were obtained, showing that IHSI is capable of satisfactory improvement of the residual stresses in pipe weldment. 1. High tensile residual stresses were lowered or shifted to the compressive side 2. No cracks were observed on the inside surface near the pipe weldment after the application of IHSI 3. Little variation was observed on microstructure and mechanical properties. (auth.)