Joint for steel pipe having high galling resistance and surface treatment method thereof

A method of conducting surface treatment on a joint of a steel pipe comprising the steps of:

• providing a manganese phosphate chemical formation coating layer of 5 to 30 .mu.m thickness on at least one of a threaded portion and a metallic sealing portion of the joint of the steel pipe;
• and coating thereon a solid lubricant containing at least one powder selected from the group consisting of molybdenum disulfide and tungsten disulfide and also containing at least one of epoxy resin, furan resin and polyamideimide resin, the composition of which satisfies the following expression,
• 0.2.ltoreq.(quantity of said at least one powder selected from the group consisting of molybdenum disulfide and tungsten disulfide)/(quantity of said at least one of epoxy resin, furan resin and polyamideimide resin).ltoreq.9.0 (weight ratio);
• and conducting heat treatment on the thus provided layer so as to form a solid lubricant coating layer of 10 to 45 .mu.m thickness.

A method of conducting surface treatment on a joint of a steel pipe for providing a three layer type coating layer comprising the steps of:

• providing a nitriding layer, the thickness of which is 1 to 20 .mu.m, on at least one of a thread portion and a metal seal portion of the joint of an oil well steel pipe made of alloy steel, said oil well steel pipe being formed from an alloy steel having a Cr content which is not less than 10 weight %;
• providing a surface treatment layer having a thickness of 0.5 to 15 .mu.m selected from one of an iron plating layer and an iron alloy plating layer containing not more that 10% by weight of at least one element selected from the group consisting of Ni and Co, and also providing a manganese phosphate chemical formation coating layer, the thickness of which is 5 to 30 .mu.m;
• and coating thereon a solid lubricant containing at least one powder selected from the group consisting of molybdenum disulfide and tungsten disulfide and also containing at least one of epoxy resin, furan resin and polyamideimide resin, the composition of which satisfies the following expression,
• 0.2.ltoreq.(quantity of at least one powder selected from the group consisting of molybdenum disulfide and tungsten disulfide)/(quantity of at least one of epoxy resin, furan resin and polyamideimide resin).ltoreq.9.0 (weight ratio);
• and conducting heat treatment to form a solid lubricant coating layer of 10 to 45 .mu.m thickness.

A method of conducting surface treatment on a joint of a steel pipe comprising the steps of:

• providing a nitriding layer of 1 to 20 .mu.m thickness in combination with a manganese phosphate chemical formation coating layer of 5 to 30 .mu.m thickness on at least one of a threaded portion and a metallic sealing portion of the joint of the steel pipe;
• and coating thereon a solid lubricant containing at least one powder selected from the group consisting of molybdenum disulfide and tungsten disulfide and also containing at least one of epoxy resin, furan resin and polyamideimide resin, the composition of which satisfies the following expression,
• 0.2.ltoreq.(quantity of said at least one powder selected from the group consisting of molybdenum disulfide and tungsten disulfide)/(quantity of said at least one of epoxy resin, furan resin and polyamideimide resin).ltoreq.9.0 (weight ratio);
• and conducting heat treatment on the thus provided layer so as to form a solid lubricant coating layer of 10 to 45 .mu.m thickness.