Patent ID: 9719617
Date: 2017-08-01
CPC Classifications: E21B,F16L

Claim:
1. A threaded joint for steel pipes comprising a pin and a box in which the pin has male threads and a lip portion having a sealing surface and a shoulder surface, and the box has female threads, a sealing surface, and a shoulder surface, wherein at the time of make-up, the male threads engage with the female threads, the sealing surface of the pin sealingly contacts the sealing surface of the box, and the shoulder surface of the pin abuts the shoulder surface of the box, wherein the sealing surface of the pin is constituted solely by a tapered surface portion, the sealing surface of the box comprises, in a direction from the female threads towards the shoulder surface, a first curved surface having a radius of curvature from 15 mm to 120 mm, a tapered surface, and a second curved surface having a radius of curvature from 15 mm to 120 mm, the tapered surface is a surface produced by rotating a straight line which is sloped with respect to a joint axis about the joint axis, and a part of the sealing surface of the box between the first curved surface and the second curved surface is constituted solely by the tapered surface.