método para produzir tubo/cano de aço sem costura

When performing piercing-rolling by use of a plug with a protection film on its surface, applying a lubricant made of an aqueous solution containing a total of 5 to 30% mass% of one or more of boron oxide, boric acid, and amine borate to the protection film on the plug surface, and using this plug for piercing-rolling makes it possible to realize the increase of the life of plug for piecing-rolling without reducing the efficiency of piercing-rolling, consequently allowing the efficient production of a seamless steel tube/pipe. Moreover, it is preferable that the plug is cooled after the piecing-rolling, the application of the above described lubricant is performed when the surface temperature of the front edge of plug decreases to 100°C or less, and the plug is reused for the piercing-rolling. In this occasion, it is preferable that the protection film on the plug surface is formed by arc spraying iron wire material onto the surface of the base metal of plug, and comprises oxides and Fe.