TUBULAR THREADED JOINT HAVING IMPROVED HIGH-TORQUE MAKEUP PROPERTIES

摘要

A tubular threaded joint has a pin and a box. 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 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. A solid lubricating coating having a relatively low Knoop hardness is formed at least on the remaining portion of the contact surface, such as the threaded portion. The threaded joint has excellent galling resistance, gas tightness, and rust preventing properties. The joint does not readily undergo yielding of shoulder portions even when made up with a high torque, thereby making it possible to perform makeup in a stable manner.

主权项

1. A tubular threaded joint comprised of a pin and a box each having a contact surface comprising a threaded portion and an unthreaded metal contact portion which includes a seal portion and a shoulder portion, characterized in that a first solid lubricating coating is present on a portion including the shoulder portion of the contact surface of at least one of the pin and the box, a second solid lubricating coating is present on at least a portion of the contact surface of the at least one of the pin and the box not having the first solid lubricating coating, the Knoop hardness of the first solid lubricating coating is higher than the Knoop hardness of the second solid lubricating coating, and when a portion exists where both the first and the second solid lubricating coatings are present, the second solid lubricating coating is positioned below the first solid lubricating coating.