TECHNICAL FIELD
[0001]
The present disclosure relates to an oil-well metal pipe.
BACKGROUND ART
[0002]
An oil-well metal pipe is used for drilling in oil fields and natural gas fields
(hereinafter, oil fields and natural gas fields are collectively referred to as "oil
wells"). An oil-well metal pipe has a threaded connection. At the oil well drilling
site, in accordance with the depth of the oil well, a plurality of oil-well metal pipes
are connected to form an oil country tubular goods connected body. The oil country
tubular goods connected body is formed by fastening oil-well metal pipes to each
other. The oil country tubular goods connected body is lifted up and loosened for
the purpose of inspection and the like, and after being inspected, the oil country
tubular goods connected body is refastened and reused.
[0003]
An oil-well metal pipe includes a pin and a box. The pin has a pin contact
surface including an external thread part on an outer peripheral surface of an end
portion of the oil-well metal pipe. The box has a box contact surface including an
internal thread part on an inner peripheral surface of an end portion of the oil-well
metal pipe.
[0004]
The pin contact surface and the box contact surface repeatedly experience
strong friction during fastening and loosening of the oil-well metal pipe. Unless
there is sufficient durability with respect to friction at the pin contact surface and the
box contact surface, galling (uncorrectable seizure) will occur during repeated
fastening and loosening. Therefore, an oil-well metal pipe is required to have
2
- 2 -
sufficient durability with respect to friction, that is, to have excellent galling
resistance.
[0005]
Conventionally, heavy metal-containing compound greases, which are
referred to as "dopes", have been used to improve the galling resistance.
Application of a compound grease to the pin contact surface and/or the box contact
surface can improve the galling resistance of an oil-well metal pipe. However,
heavy metals contained in compound greases, such as Pb, Zn, and Cu, may affect the
environment. For this reason, the development of an oil-well metal pipe that is
excellent in galling resistance without the use of a compound grease is desired.
[0006]
Therefore, techniques have been proposed that employ a solid lubricant
coating instead of a compound grease. For example, in a threaded connection for
pipes proposed in International Application Publication No. WO2009/072486 (Patent
Literature 1), a solid lubricant coating is formed on a box contact surface, and a solid
anticorrosive coating composed of a UV curable resin is formed on a pin contact
surface. It is described in Patent Literature 1 that by means of the solid lubricant
coating, the occurrence of galling can be suppressed even when fastening and
loosening are repeated..

We claim:
1. An oil-well metal pipe, comprising:
a pipe main body including a first end portion and a second end portion,
wherein:
the pipe main body includes:
a pin formed at the first end portion, and
a box formed at the second end portion;
the pin includes:
a pin contact surface which at least has an external thread part formed on an
outer peripheral surface of the first end portion of the pipe main body;
the box includes:
a box contact surface which at least has an internal thread part formed on an
inner peripheral surface of the second end portion of the pipe main body;
a plating layer is formed on a first contact surface, the first contact surface
being one of the pin contact surface and the box contact surface;
a solid lubricant layer is formed on the plating layer;
an arithmetic average roughness Ra of a second contact surface is within a
range of 0.5 to 10.0 m, the second contact surface being the other of the pin contact
surface and the box contact surface; and
a semi-solid or liquid anti-rust coating is formed on the second contact
surface.
2. The oil-well metal pipe according to claim 1, wherein:
a chemical treatment coating is further formed on the second contact surface,
and
the anti-rust coating is formed on the chemical treatment coating.
3. The oil-well metal pipe according to claim 1 or claim 2, wherein:
the second contact surface is subjected to a blasting treatment.