To prevent occurrence of seizure during tightening and loosing up to at least 10 times, without having to apply grease, even for a high alloy coupling, for an oil well pipe having a large inside diameter, for a coupling having high interference amount in its screw part, or an oil well pipe screw coupling apt to cause the seizure, by improving the seizure resistance of the screw coupling for the oil well pipe constituted of a pin and box, that have a contact surface comprising a screw part and a no-screw metal contact part.
A solid lubricating coating, having M47 or larger for of Rockwell hardness, preferably 500 N/m or higher of adhesion strength determined by SAICAS method (surface-interface cutting method) is formed on a contact surface of at least either the box and the pin. When oil is applied to one or both metal contact parts of the box and the pin, in which the solid lubricating coating has been formed or not been formed, the seizure resistance is further improved.
GOTO KUNIO
ANRAKU TOSHIRO
NAGASAKU SHIGEO
