US Patent 8038179 Threaded joint for steel pipes

A threaded joint for steel pipes comprising a pin 1 having a tapered male thread 11, a tapered sealing surface 13, and an end shoulder surface 14 and a box 2 having correspondingly a tapered female thread 21, a tapered sealing surface 23, and a shoulder surface 24 which is capable of easy tightening and has improved air tightness by the sealing surfaces is arranged such that the pin and the box each have a noncontacting region B where the peripheral surfaces of the pin and the box do not contact each other between the sealing surfaces 13, 23 and the shoulder surfaces 14 and 24. At least a portion of the noncontacting region of the pin adjoining the to end of the pin is a tapered surface portion 18 having substantially the same angle of slope as the tapered sealing surface 13, and the noncontacting region of the box is a substantially cylindrical surface.