| 摘要 |
PURPOSE: To improve seizure resistance in a screw part and in a seal part between metal materials by heating the screw part and the metal seal part in an atmosphere with a specific oxygen concentration so as to generate an oxide scale and forming a chromate coating film on the oxide scale when surface treatment is carried out on an oil well steel pipe joint. CONSTITUTION: When surface treatment is carried out on an oil well steel pipe joint 1 provided with a screw part 3 and a metal seal part 4, heating is carried out in the screw part 3 and the metal seal part 4 at a heating temperature of 400-700 deg.C in an atmosphere with oxygen concentration of 3-18% for 5 minutes or more for generating an oxide scale, on which a chromate coating film with thickness of 0.3μm or more is formed. The chromate treatment is carried out, for example, by performing electrolysis for a fixed time while using a joint 1 side as a negative electrode and using a platinum as a positive electrode in an acid liquid consisting of chromic anhydride and sulfuric acid. In this way, the oil well steel pipe joint 1 is coated by means of the oxide scale treatment and the chromate treatment, so that seizure resistance can be greatly improved.
|
