This application is a 371 of PCT/JP2018/038095, filed Oct. 12, 2018.

TECHNICAL FIELD

The present invention relates to a composition, in particular a composition for forming a lubricant coating layer to be used in a threaded connection for oil country tubular goods, and also relates to a threaded connection for pipes or tubes that includes a lubricant coating layer formed from the composition.

BACKGROUND ART

Oil well pipes are used for drilling of oil fields and natural gas fields. Oil well pipes are formed by coupling a plurality of steel pipes in accordance with the depth of the well. Connection of steel pipes can be carried out by fastening threaded connection for pipes or tubes formed at ends of the two steel pipes. When trouble occurs during the course of operations until an oil well is completed or after completion of an oil well, oil country tubular goods may be repeatedly lifted and loosened to inspect the thread faces and the like thereof, and thereafter refastened and lowered for re-use.

The threaded connection for pipes or tubes includes a pin and a box. The pin includes a male threaded portion formed in the outer peripheral surface at the end of the pipe. The box includes a female threaded portion formed in the inner peripheral surface at the end of the pipe. The pin and the box may also include an unthreaded metal contact portion. The threaded portions and unthreaded metal contact portions of the pin and the box repeatedly experience strong friction during fastening and loosening of the pipes. If these portions are not sufficiently resistant to friction, galling (unrepairable seizure) will occur during repeated fastening and loosening. Thus, it is necessary that threaded connection for pipes or tubes have sufficient resistance to friction, i.e., excellent galling resistance.

Heretofore, heavy metal-containing compound greases, referred to as dopes, have been used to improve the galling resistance. Application of a compound grease to the surface of a threaded connection for pipes or tubes can improve the galling resistance of the threaded connection for pipes or tubes. However, heavy metals contained in compound greases, such as Pb, Zn, and Cu, may affect the environment. For this reason, the development of a composition for forming a lubricant coating layer to be used in a threaded connection for pipes or tubes which does not use a compound grease is desired.

International Application Publication No. WO2009/057754 (Patent Literature 1) and International Application Publication No. WO2014/024755 (Patent Literature 2) propose a lubricant coating layer excellent in galling resistance even without using a compound grease, and a composition for forming a lubricant coating layer.

The lubricant coating layer described in Patent Literature 1 includes one of or both of rosin and calcium fluoride, and a metal soap, a wax and a basic metal salt of an aromatic organic acid. It is described in Patent Literature 1 that, as a result, the lubricant coating layer is excellent in anti-galling, gas tightness and anti-rust properties.

A composition for forming a lubricant coating layer on a tube-like threaded connection described in Patent Literature 2 contains melamine cyanurate and a basic metal salt of an aromatic organic acid, and one or more types selected from the group consisting of a pine resin-based material, a wax, a metal soap and a lubricant powder. It is described in Patent Literature 2 that, as a result, the obtained lubricant coating layer is excellent in anti-galling, gas tightness and anti-rust properties.

CITATION LIST

Patent Literature

Patent Literature 1: International Application Publication No. WO2009/057754Patent Literature 2: International Application Publication No. WO2014/024755

SUMMARY OF INVENTION

Technical Problem

In this connection, the threaded portions and unthreaded metal contact portions of the pin and box include metal seal portions and shoulder portions. During fastening of a threaded connection for pipes or tubes that has an unthreaded metal contact portion, the shoulder portions of the pin and box come in contact with each other. Torque that arises at that time is called “shouldering torque”. During fastening of a threaded connection for pipes or tubes, after the shouldering torque is reached, fastening is continued until fastening is completed. By this means, the gas tightness of the threaded connection for pipes or tubes is enhanced. If fastening proceeds further, metal constituting at least one of the pin and the box starts to undergo a plastic deformation. The torque at such time is referred to as “yield torque”.

The torque when fastening is completed (hereunder, referred to as “fastening torque”) is set so that a sufficient seal interfacial pressure is obtained irrespective of the size of the thread interference amount. If there is a sufficient difference between the shouldering torque and the yield torque (hereunder, this difference is referred to as “torque on shoulder resistance ΔT), the range of the fastening torque widens. As a result, the fastening torque is adjusted easily. Therefore, it is necessary that a threaded connection for pipes or tubes has both the aforementioned galling resistance and a high torque on shoulder resistance ΔTthat is, high over-torque performance. This similarly applies with respect to a threaded connection for pipes or tubes which does not have an unthreaded metal contact portion (particularly, a shoulder portion). Even when a threaded connection for pipes or tubes does not have a shoulder portion, if high torque is maintained at a time of high interfacial pressure, it will be easy to adjust the fastening torque.

An objective of the present invention is to provide a composition for obtaining a threaded connection for pipes or tubes having excellent galling resistance and high over-torque performance, and also a threaded connection for pipes or tubes which includes a lubricant coating layer formed from the composition and which has excellent galling resistance and high over-torque performance.

Solution to Problem

The composition according to the present embodiment is a composition for forming a lubricant coating layer on a threaded connection for pipes or tubes, the composition containing Cr2O3, a metal soap, a wax and a basic metal salt of an aromatic organic acid.

The threaded connection for pipes or tubes according to the present embodiment is a threaded connection that is for pipes or tubes and that includes a pin and a box. The pin and the box each include a contact surface that includes a threaded portion. The threaded connection for pipes or tubes includes, as an outermost layer, a lubricant coating layer that is formed from the aforementioned composition on at least one of the contact surfaces of the pin and the box.

Advantageous Effects of Invention

A threaded connection for pipes or tubes according to the present embodiment includes a lubricant coating layer. A composition for forming the aforementioned lubricant coating layer contains Cr2O3. Therefore, the threaded connection for pipes or tubes according to the present embodiment exhibits excellent galling resistance even when fastening is repeated. In addition, the threaded connection for pipes or tubes according to the present embodiment exhibits high over-torque performance.

