TUBULAR THREADED JOINT HAVING IMPROVED HIGH-TORQUE MAKEUP PROPERTIES.

摘要

In a tubular threaded joint composed of a pin 1 and a box 2 each having a contact surface comprising a threaded portion and an unthreaded metal contact portion including a seal portion and a shoulder portion, a solid lubricating coating 10 having a relatively high Knoop hardness is formed on a portion including the shoulder portion of the contact surface (such as the unthreaded metal contact portion including the shoulder portion and the seal portion) of at least one of the pin and the box, and a solid lubricating coating 11 having a relatively low Knoop hardness is formed at least on the remaining portion of the contact surface (such as the threaded portion). The tubular threaded joint has excellent galling resistance, gas tightness, and rust preventing properties, and since it has a large ?Τ, it does not readily undergo yielding of shoulder portions even when it is made up with a high torque, thereby making it possible to perform makeup in a stable manner.