BENT PIPE AND A METHOD FOR ITS MANUFACTURE

摘要

A bend pipe that realizes not only simultaneous possession of high streng th and excellent toughness by its base metal but also possession of excellen t toughness by its weld metal, for example, API Standard X100-grade or highe r. A thick steel sheet is produced by hot rolling followed by, at 700° to 50 0°C, cooling at a cooling rate of less than 5°C/sec at its central part in t he direction of thickness. A bend stock pipe being a weld steel pipe using t he above thick steel sheet as a raw material is produced, heated to 900° to 1100°C, and subjected to bend working. The resultant pipe at 700° to 500°C i s cooled at a cooling rate of 5°C/sec or higher at its central part in the d irection of thickness to a temperature zone of 300°C or below. Thereafter, t empering at 300° to 500°C is carried out to thereby attain production of a b end pipe of API Standard X100-grade equivalent or higher.