Tubular threaded joint having improved high torque performance

摘要

A tubular threaded joint which is free from harmful heavy metals, which has excellent galling resistance, gas tightness, and rust-preventing properties and which does not readily undergo yielding of shoulder portions even when subjected to makeup with a high torque is constituted by a pin 1 and a box 2 each having a contact surface comprising an unthreaded metal contact portion including a seal portion 4a or 4b and a shoulder portion 5a or 5b and a threaded portion 3a or 3b. Of the contact surface of at least one of the pin and the box, the surfaces of the seal portion and the shoulder portion has a first lubricating coating 10 in the form of a solid lubricating coating, and the surface of the threaded portion or the entire surface of the contact surface has a second lubricating coating 11 selected from a viscous liquid lubricating coating and a solid lubricating coating. The first lubricating coating has a coefficient of friction which is higher than that of the second lubricating coating, and the second lubricating coating is positioned on top in a portion where both the first lubricating coating and the second lubricating coating are present.