METODO PER ACCRESCERE LA SOLLECITAZIONE DI COMPRESSIONE RESIDUA IN TUBI METALLICI DOPPI

摘要

A method of enhancing residual compressive stress in a horizontal double metallic pipe which includes an outer pipe and an inner pipe fitted into the outer pipe. Cooling water is introduced into both the inner pipe and an annular space defined between the inner pipe and the outer pipe. Further, cooling water is injected into the annular space to form a partial cooling water flow through the cooling water in the annular space. During the injection of cooling water, the outer pipe is heated from the outside thereof to generate a temperature difference between inner and outer faces of the outer pipe to such a degree that thermal stress larger than a yield point is produced in the outer pipe. Then, the heating of the outer pipe is stopped to allow the outer pipe to stand, whereby residual compressive stress is provided to a radially inner portion of the outer pipe.