THREADED JOINT FOR STEEL PIPES

摘要

A screw-threaded joint for a steel pipe includes a pin (1) and a box (2). The pin (1) has a tapered male screw thread (11), a tapered seal surface (13), and an end shoulder surface (14), while the box (2) has, in a corresponding manner, a tapered female screw thread (21), a tapered seal surface (23), and a shoulder surface (24). The pin (1) and the box (2) can be easily fastened together, and the screw-threaded joint has improved tightness at seal surfaces. The pin and the box have a contactless region (B) between the seal surfaces (13, 23) and the shoulder surfaces (14, 24), and the peripheral surfaces of the pin and the box do not make contact with each other in the contactless region (B). At least that portion of pin which is in the contactless region and adjacent the front end of the pin is a tapered surface portion (18) having substantially the same inclination angle as the tapered seal surface (13). Also, that portion of the box which is in the contactless region is substantially a circular cylindrical surface.