SCREW JOINT FOR STEEL PIPE

摘要

In the present invention, a threaded joint for a steel pipe is provided with: a pin having an male thread formed of a two-stage thread, and a sealing surface comprising a tapered surface and curved surface formed at an intermediate part of the two-stage thread; and a box having a female thread formed of a two-stage thread, and a sealing surface comprising a tapered surface and curved surface formed at an intermediate part of the two-stage thread. The taper angle of the tapered surface of the pin and the taper angle of the tapered surface of the box are substantially the same. The threaded joint has a structure in which, in the course of fastening the male thread and the female thread together, the pin and the box interfere with one another in the radial direction while the sealing surface of the pin and the sealing surface of the box are in contact, thereby causing at least some of each of the sealing surfaces to be in close contact across the entire periphery; and is provided with a contact-pressure-increasing mechanism for increasing the contact pressure between the sealing surface of the pin and the sealing surface of the box once fastening has concluded.