EA047428B1 - METAL PIPE FOR OIL WELL - Google Patents

Description

Field of technology

The present invention relates to a metal pipe for an oil well.

Prior art

The metal pipe for oil well is used for drilling in oil and natural gas fields (hereinafter collectively referred to as oil wells). The metal pipe for oil well has a threaded joint. At the drilling site of the oil well, according to the depth of the oil well, several metal pipes for oil well are connected to form a combined body of oil well tubular goods. The combined body of oil well tubular goods is obtained by screwing the metal pipes for oil wells together. The combined body of oil well tubular goods is taken out and unscrewed for inspection etc., and after the inspection, the combined body of oil well tubular goods is screwed again and reused.

A metal pipe for an oil well comprises a nipple and a coupling. The nipple comprises a contact surface of the nipple, containing a part with an external thread, formed on the outer peripheral surface of the end part of the metal pipe for an oil well. The coupling comprises a contact surface of the coupling, containing a part with an internal thread, formed on the inner peripheral surface of the end part of the metal pipe for an oil well.

The contact surface of the nipple and the contact surface of the coupling repeatedly experience strong friction when screwing and unscrewing the metal pipe for oil wells. If the contact surface of the nipple and the contact surface of the coupling do not have sufficient friction resistance, repeated screwing and unscrewing will cause scoring (unremovable seizure). Therefore, the metal pipe for oil wells should have sufficient friction resistance, i.e., high resistance to scoring.

Generally, compound greases containing heavy metals, called additives, are used to improve the scuffing resistance. Applying compound grease to the contact surface of the pin and/or the contact surface of the box can improve the scuffing resistance of the metal pipe for oil wells. However, heavy metals such as Pb, Zn and Cu contained in compound greases may affect the environment. Therefore, it is necessary to develop a metal pipe for oil wells that has high scuffing resistance without using compound grease. Therefore, methods have been proposed in which a solid lubricating coating is used instead of compound grease. For example, in the threaded joint for pipes proposed in International Publication No. WO2009/072486 (Patent Document 1), a solid lubricating coating is formed on the contact surface of the coupling, and a solid anticorrosive coating consisting of a polymer curable by ultraviolet radiation is formed on the contact surface of the pin. Patent Document 1 states that the solid lubricating coating can prevent the formation of scoring even when repeatedly screwed and unscrewed. In this regard, when a combined body of oil well tubular goods in which several metal pipes for an oil well are screwed together is advanced into an oil well, the combined body of the oil well tubular goods is advanced with rotation. The layers in which oil lies (oil layers) extend in a horizontal direction rather than a vertical direction. Therefore, such oil well drilling methods as directional drilling or horizontal drilling are increasingly used to cover a wide oil reservoir and improve the efficiency of oil production. In directional drilling and horizontal drilling, the combined body of oil field tubular goods is bent underground, and the lower end of the combined body of oil field tubular goods is directed in a diagonal or horizontal direction. If the oil well is oriented in a horizontal or inclined direction, then with an increase in the length in the horizontal or inclined direction, the torque required to advance the combined body of oil field tubular goods increases. If the metal pipe for the oil well is subjected to plastic deformation when such a high torque is applied, it may be impossible to maintain a high level of tightness in some cases. Thus, there is a need for a metal pipe for oil well which will not undergo plastic deformation even when a high torque is applied, in other words, a metal pipe for oil well having high yield torque.

In this regard, the yield torque is defined as follows. Fig. 1 is a graph illustrating the relationship between the number of revolutions of a metal pipe for an oil well and the torque when screwing the metal pipe for an oil well. As shown in Fig. 1, when screwing the metal pipes for an oil well together, the torque initially increases moderately and proportionally to the number of revolutions. As screwing continues, the abutment sections of the metal pipes for an oil well come into contact with each other. The torque that occurs at this time is called the torque

- 1 047428 volume Ts of the stop. After reaching the torque Ts of the stop, with continued make-up, the torque quickly increases in proportion to the number of revolutions. Make-up is completed at the point in time when the torque reaches a predetermined value (tightening torque To). At the tightening torque To, the contact surfaces of the pin and the coupling interact with each other with a corresponding pressure between the surfaces. In this case, the tightness of the combined body of the oil field tubular goods formed by screwing together several metal pipes for an oil well will be high. However, with a further increase in the torque applied to the metal pipe for an oil well, in some cases, a part of the pin and the coupling goes into a fluid state, which leads to plastic deformation. The torque at this time is called the torque Tu at the yield point.

In this connection, if the metal pipe for an oil well does not have a stop section, that is, in the case of a metal pipe for an oil well having a so-called wedge-shaped thread profile, the relationship between the number of turns of the metal pipe for an oil well and the torque is also shown in Fig. 1, similar to the metal pipe for an oil well having a stop section. Thus, in the case of a wedge-shaped thread profile, in the direction of screwing the nipple, the width of the thread crest on the external thread portion gradually decreases along the helical thread line, and the width of the thread groove on the external thread portion gradually increases along the helical thread line. In addition, in the direction of screwing the nipple, the width of the thread groove on the internal thread portion gradually decreases along the helical thread line, and the width of the thread crest on the external thread portion gradually increases along the helical thread line.

In the case of a metal pipe for an oil well with a wedge-shaped thread profile and without a thrust section, as they are screwed together, the bearing sides of the external threaded part and the internal threaded part come into contact with each other, the insertion sides of the external threaded part and the internal threaded part also come into contact with each other, and a locking (pressure fit) occurs. The locking torque is called a counter torque. The counter torque is equivalent to the thrust torque in a metal pipe for an oil well containing a thrust section. Therefore, in the present disclosure, unless otherwise specified, no distinction is made between the counter torque and the thrust torque, and the term thrust torque is used to refer to them. In the case of a metal pipe for oil wells having a wedge-shaped threaded profile, similar to a metal pipe for oil wells having a thrust section, after the thrust torque Ts is reached, if make-up is continued, the torque will increase rapidly in proportion to the number of turns. In addition, if make-up is continued after this, a yield torque Ty occurs.

As disclosed above, recently there has been a demand for a metal pipe for an oil well with a high yield torque which is not subject to plastic deformation even when a high torque is applied. International Patent Application Publication No. 2013/176281 (Patent Document 2) proposes a threaded joint in the form of a nipple characterized by excellent make-up performance under a high torque. In the threaded joint in the form of a nipple disclosed in Patent Document 2, a first solid lubricating coating is formed on a portion including a stop portion of a contact surface of a pin and/or a box. Further, a second solid lubricating coating is formed on at least that portion of the entire contact surface on which the first solid lubricating coating is absent. The Knoop hardness of the first solid lubricating coating is higher than the Knoop hardness of the second solid lubricating coating. During make-up, until the stop portion of the pin and the stop portion of the coupling come into contact, the second solid lubricating coating, which has a lower Knoop hardness, acts and thereby reduces the friction coefficient during make-up. Therefore, the stop torque remains low. After the stop portion of the pin and the stop portion of the coupling come into contact, the first solid lubricating coating, which has a higher Knoop hardness, acts and thereby increases the friction coefficient. Thus, the yield torque increases.

List of cited materials

Patent documents.

Patent Document 1: International Application Publication No. 2009/072486.

Patent Document 2: International Application Publication No. 2013/176281.

The essence of the invention

Technical challenge.

The yield torque can be increased by using the method disclosed in Patent Document 2. However, the yield torque can also be increased by other methods. In addition, as disclosed above, the metal pipe for an oil well also needs to have a scuffing resistance. Therefore, it is desirable to be able to combine a high yield torque and high scuffing resistance.

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The objective of the present invention is to develop a metal pipe for an oil well that can combine high yield torque with high resistance to scuffing.

Solution to the problem.

A metal pipe for an oil well according to the present invention comprises: a pipe main body comprising a first end portion and a second end portion, wherein the pipe main body comprises a nipple formed on the first end portion and a coupling formed on the second end portion;

the nipple comprises a nipple contact surface comprising at least a portion with an external thread formed on the outer peripheral surface of the first end portion of the main body of the pipe;

The coupling contains:

a coupling contact surface comprising at least a portion with an internal thread formed on the inner peripheral surface of the second end portion of the main body of the pipe;

a metallized layer is formed on the first contact surface, wherein the first contact surface is one surface of the contact surface of the nipple and the contact surface of the coupling;

a layer of solid lubricant is formed on the metallized layer;

the arithmetic mean value of the roughness Ra of the second contact surface is from 0.5 to 10.0 μm, wherein the second contact surface is the other surface of the contact surface of the nipple and the contact surface of the coupling; and a semi-solid or liquid anti-corrosion coating is formed on the second contact surface.

Technical results of the invention.

The metal pipe for an oil well according to the present invention makes it possible to simultaneously realize both a high yield torque and high resistance to scuffing.

Brief description of the drawings

Fig. 1 is a graph illustrating the relationship between the number of revolutions of a metal oil well pipe and the torque when screwing the metal oil well pipe.

Fig. 2 is a diagram illustrating one example of a metal pipe for an oil well with a thread and a coupling according to this embodiment of the invention.

Fig. 3 shows a partial sectional view (longitudinal section) parallel to the axis direction of the coupling of the metal pipe for the oil well shown in Fig. 2.

Fig. 4 is a sectional view parallel to the axis direction of the metal pipe for an oil well shown in Fig. 3, illustrating a portion of the metal pipe for an oil well located near the nipple.

Fig. 5 is a sectional view parallel to the axis direction of the metal pipe for an oil well shown in Fig. 3, illustrating a portion of the metal pipe for an oil well located near the coupling.

Fig. 6 is a diagram illustrating another example of a metal pipe for an oil well with a thread and a coupling, different from Fig. 2.

Fig. 7 is a diagram illustrating an integral type metal pipe for an oil well according to this embodiment of the invention.

Fig. 8 is a sectional view for explaining the structure on the first contact surface in the case where the first contact surface is a coupling contact surface.

Fig. 9 is a sectional view for explaining the structure on the second contact surface in the case where the second contact surface is a contact surface of a nipple.

Fig. 10 shows, on an enlarged scale, a part near the second contact surface (in Fig. 9 - the contact surface of the nipple), depicted in Fig. 9.

Fig. 11 is a sectional view for explaining the structure on the first contact surface in the case where the first contact surface is a contact surface of a nipple.

Fig. 12 is a sectional view for explaining the structure on the second contact surface in the case where the second contact surface is a coupling contact surface.

Fig. 13 is a view illustrating the structure of a second contact surface containing a coating obtained by chemical treatment, in the case where the second contact surface is a contact surface of a nipple.

Fig. 14 shows a torque diagram for explaining the yield torque measurement test according to the examples.

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Description of embodiments of the invention

Below, an embodiment of the invention will be described in detail with reference to the drawings. In the drawings, the same reference signs will be used for the same or similar parts, and their disclosure will not be repeated.

The present inventors have carried out several studies on a metal pipe for an oil well that can simultaneously realize both high yield torque and high resistance to scuffing. As a result, the present inventors have come to the following conclusions.

In order to increase the resistance to scuffing during screwing of a metal pipe for an oil well, it is preferable to form a metallized layer on the contact surface (hereinafter referred to as the first contact surface) of a pin (hereinafter referred to as the contact surface of the pin) or on the contact surface of a coupling (hereinafter referred to as the contact surface of the coupling), and to form a solid lubricant layer on the metallized layer. The resistance to scuffing is increased due to the lubricating effect of the solid lubricant layer. The metallized layer also increases the resistance to scuffing, and the metallized layer having high hardness and high melting point further increases the resistance to scuffing during screwing. Therefore, the inventors of the present invention decided that, taking into account the resistance to scuffing, it is preferable to form a metallized layer and a solid lubricant layer in a multilayer manner on the first contact surface, which is the contact surface of the pin or the contact surface of the coupling.

In the case where a metallized layer and a solid lubricant layer are successively applied to a first contact surface, which is a contact surface of a pin or a contact surface of a coupling, the authors of the present invention also carried out studies on the structure of a second contact surface, which is another contact surface of the contact surface of a pin and a contact surface of a coupling, in order to increase the torque while maintaining resistance to scuffing.

In this case, the metal pipes for oil wells after manufacturing are stored outdoors in a site located near the oil well drilling site until they are actually used for drilling the oil well. Therefore, the metal pipes for oil wells must have a certain corrosion resistance, not just the resistance to scoring. Therefore, in a conventional metal pipe for oil wells having a pin contact surface and a coupling contact surface, in some cases, the outermost upper layer of the first contact surface is a solid lubricant layer, and the outermost upper layer of the second contact surface is a known hard anticorrosive coating consisting of a polymer cured by ultraviolet radiation. However, the hard anticorrosive coating does not have the effect of increasing the yield torque.

Therefore, the inventors of the present invention have an idea of increasing the friction coefficient and increasing the yield torque during make-up by giving the second contact surface a shape (texture) different from the surface shape of a known metal pipe for an oil well, without using a hard anti-corrosion coating. Further, as a result of further consideration, the inventors of the present invention have an idea that, with a certain roughness of the second contact surface, close contact of the first contact surface and the second contact surface during make-up will make it possible to obtain a high friction coefficient due to the metallized layer under the solid lubricant layer of the first contact surface and the unevenness of the second contact surface, as a result, the yield torque will increase.

On the other hand, it is preferable to ensure a certain corrosion resistance of the second contact surface. However, if a conventional known hard anticorrosive coating is formed on the second contact surface whose surface is rough, the unevenness of the second contact surface will not be transferred to the surface of the hard anticorrosive coating, and therefore the surface of the hard anticorrosive coating will not be roughened to the degree of unevenness of the second contact surface.

Therefore, the inventors of the present invention conceived of forming a semi-solid or liquid anticorrosive coating on the second contact surface, which is a rough surface, rather than a solid coating. When a semi-solid or liquid anticorrosive coating is formed on the rough second contact surface, the anticorrosive properties of the second contact surface are provided by the anticorrosive coating, and when the first contact surface and the second contact surface are tightly contacted during screwing, the anticorrosive coating on the contact portion is easily squeezed out from the gap between the first contact surface and the second contact surface. Thus, using a metallized layer under the solid lubricant layer of the first contact surface and the unevenness of the second contact surface, the friction coefficient is increased and, as a result, the yield torque is increased.

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A metal pipe for an oil well according to the present invention, made on the basis of the above results, has the following structure:

1. A metal pipe for an oil well, comprising:

a main body of a pipe comprising a first end portion and a second end portion, wherein the main body of the pipe comprises a nipple formed on the first end portion and a coupling formed on the second end portion;

the nipple comprises a nipple contact surface comprising at least a portion with an external thread formed on the outer peripheral surface of the first end portion of the main body of the pipe;

The coupling contains:

a coupling contact surface comprising at least a portion with an internal thread formed on the inner peripheral surface of the second end portion of the main body of the pipe;

a metallized layer is formed on the first contact surface, wherein the first contact surface is one surface of the contact surface of the nipple and the contact surface of the coupling;

a layer of solid lubricant is formed on the metallized layer;

the arithmetic mean value of the roughness Ra of the second contact surface is from 0.5 to 10.0 μm, wherein the second contact surface is the other surface of the contact surface of the nipple and the contact surface of the coupling; and a semi-solid or liquid anti-corrosion coating is formed on the second contact surface.

2. A metal pipe for an oil well according to item 1, in which:

on the second contact surface, a coating obtained by chemical treatment is additionally formed, and an anti-corrosion coating is formed on the coating obtained by chemical treatment.

3. A metal pipe for an oil well according to claim 1 or 2, wherein the second contact surface is subjected to jet processing.

4. A metal pipe for an oil well according to any one of claims 1 to 3, in which the metallized layer is made of a Zn-Ni alloy.

Next, a metal pipe for an oil well according to the present embodiment of the invention will be described in detail.

Construction of metal pipe for oil well.

First, before describing the metal pipe for an oil well according to the present embodiment, the structures of the metal pipes for an oil well, which are the subject of the present embodiment, will be described. The available types of metal pipes for an oil well are a threaded and coupling type metal pipe for an oil well and an integral type metal pipe for an oil well. Each type of metal pipe for an oil well will be explained in detail below. The embodiment in which the metal pipe 1 for an oil well is a threaded and coupling type.

Fig. 2 is a diagram illustrating one example of a metal pipe 1 for an oil well according to the present embodiment of the invention. Fig. 2 is a diagram illustrating a metal pipe 1 for an oil well of a so-called threaded and coupling type. As shown in Fig. 2, the metal pipe 1 for an oil well has a pipe main body 10.

The main body 10 of the pipe extends in the direction of the pipe axis. The cross-section perpendicular to the direction of the pipe axis of the main body 10 of the pipe has a circular shape. The main body 10 of the pipe includes a first end portion 10A and a second end portion 10B. The first end portion 10A is an end portion on the side opposite to the second end portion 10B. In the metal pipe 1 for an oil well of the type with a thread and a coupling shown in Fig. 2, the main body 10 of the pipe includes a tubular body 11 of the nipple and a coupling 12. The coupling 12 is connected to one end of the tubular body 11 of the nipple. In particular, the coupling 12 is screwed onto a thread at one end of the tubular body 11 of the nipple.

Fig. 3 is a partial sectional view (longitudinal section) parallel to the pipe axis direction of the coupling coupling 12 of the metal pipe 1 for an oil well shown in Fig. 2. As shown in Fig. 2 and Fig. 3, the pipe main body 10 includes a nipple 40 and a coupling 50. The nipple 40 is formed on the first end portion 10A of the pipe main body 10. When screwing, the nipple 40 is inserted into the coupling of another metal pipe for an oil well (not shown in the figure) and screwed into the coupling of another metal pipe for an oil well. The coupling 50 is formed on the second end portion 10B of the pipe main body 10. When screwing, the nipple of another metal pipe 1 for an oil well is inserted into the coupling 50, and the coupling 50 is screwed onto the nipple of another metal pipe 1 for an oil well.

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Nipple design 40.

Fig. 4 is a sectional view of a portion located near the nipple 40 of the metal pipe 1 for an oil well shown in Fig. 3, which is a sectional view parallel to the axis direction of the metal pipe 1 for an oil well. The dotted line in Fig. 4 indicates a structure of a coupling 50 of another metal pipe for an oil well in the case of screwing the metal pipe 1 for an oil well with another metal pipe 1 for an oil well. As shown in Fig. 4, the nipple 40 has a nipple contact surface 400 on an outer peripheral surface of the first end portion 10A of the pipe main body 10. The nipple contact surface 400 comes into contact with the contact surface 500 of the coupling 50 of the other metal pipe 1 for an oil well when screwing with another metal pipe 1 for an oil well.

The contact surface 400 of the pin comprises at least a portion 41 with an external thread formed on the outer peripheral surface of the first end portion 10A. The contact surface 400 of the pin may further comprise a sealing surface 42 of the pin and a stop surface 43 of the pin. In Fig. 4, on the outer peripheral surface of the first end portion 10A, the sealing surface 42 of the pin is located further on the front end side of the first end portion 10A than the portion 41 with an external thread. In other words, the sealing surface 42 of the pin is located between the portion 41 with an external thread and the stop surface 43 of the pin. The sealing surface 42 of the pin has a conical shape. In particular, the outer diameter of the sealing surface 42 of the nipple gradually decreases from the part 41 with the external thread to the thrust surface 43 of the nipple in the longitudinal direction (the direction of the pipe axis) of the first end part 10A.

When screwing with another metal pipe 1 for an oil well, the sealing surface 42 of the nipple comes into contact with the sealing surface 52 (to be explained below) of the coupling 50 of the other metal pipe 1 for an oil well. More specifically, during screwing, when the nipple 40 is inserted into the coupling 50 of the other metal pipe 1 for an oil well, the sealing surface 42 of the nipple comes into contact with the sealing surface 52 of the coupling. Therefore, when the nipple 40 continues to be screwed into the coupling 50 of the other metal pipe 1 for an oil well, the sealing surface 42 of the nipple comes into close contact with the sealing surface 52 of the coupling. Due to this, during screwing, the sealing surface 42 of the nipple comes into close contact with the sealing surface 52 of the coupling, thereby forming a seal based on direct metal contact. This makes it possible to improve the tightness of screwed metal pipes 1 for oil wells.

In Fig. 4, the thrust surface 43 of the nipple is located on the front end surface of the first end portion 10A. In other words, in the nipple 40 shown in Fig. 4, the externally threaded portion 41, the sealing surface 42 of the nipple, and the thrust surface 43 of the nipple are sequentially arranged in the specified order from the center of the main body 10 of the pipe toward the front end of the first end portion 10A. When screwing with another metal pipe 1 for an oil well, the thrust surface 43 of the nipple is located opposite the thrust surface 53 (to be disclosed below) of the coupling 50 of the other metal pipe 1 for an oil well and contacts it. More specifically, during make-up, the thrust surface 43 of the pin comes into contact with the thrust surface 53 of the coupling as a result of the insertion of the pin 40 into the coupling 50 of another metal pipe 1 for an oil well. This makes it possible to obtain a high torque during make-up. In addition, the positional relationship between the pin 40 and the coupling 50 in the make-up state can be stabilized. It should be noted that the contact surface 400 of the pin 40 includes at least a portion 41 with an external thread. In other words, the contact surface 400 of the pin includes a portion 41 with an external thread and does not necessarily include a sealing surface 42 of the pin and the thrust surface 43 of the pin. The contact surface 400 of the pin may include a portion 41 with an external thread and the thrust surface 43 of the pin and does not necessarily include a sealing surface 42 of the pin. The contact surface 400 of the nipple may comprise a portion 41 with an external thread and a sealing surface 42 of the nipple and does not necessarily comprise a thrust surface 43 of the nipple. In the case of the metal pipe for an oil well with a wedge-shaped thread profile disclosed above, the nipple 40 does not have a thrust surface 43 of the nipple. In this case, if the nipple 40 does not have a thrust surface 43 of the nipple, the coupling 50 does not have a thrust surface 53 of the coupling.

Coupling design 50.

Fig. 5 is a sectional view of a portion of the metal pipe 1 for an oil well shown in Fig. 3 that is located near the coupling 50, which is a sectional view parallel to the axis direction of the metal pipe 1 for an oil well. The dotted line in Fig. 5 indicates the structure of the nipple 40 of another metal pipe 1 for an oil well in the case of screwing the metal pipe 1 for an oil well with another metal pipe 1 for an oil well. As shown in Fig. 5, the coupling 50 has a coupling contact surface 500 on the inner peripheral surface of the second end portion 10B of the pipe main body 10. When screwing with another metal pipe 1 for an oil well, the coupling contact surface 500 comes into contact

- 6 047428 with the contact surface 400 of the nipple 40 of another metal pipe 1 for an oil well, when the nipple 40 is screwed into the coupling 50. The contact surface 500 of the coupling comprises at least a portion 51 with an internal thread formed on the inner peripheral surface of the second end portion 10B. When screwed together, the portion 51 with an internal thread engages with the portion 41 with an external thread of the nipple 40 of another metal pipe for an oil well. The contact surface 500 of the coupling may further comprise a sealing surface 52 of the coupling and a thrust surface 53 of the coupling. In Fig. 5, on the inner peripheral surface of the second end portion 10B, the sealing surface 52 of the coupling is located further from the center of the main body 10 of the pipe than the portion 51 with an internal thread. In other words, the sealing surface 52 of the coupling is located between the portion 51 with the internal thread and the thrust surface 53 of the coupling. The sealing surface 52 of the coupling has a conical shape. In particular, the inner diameter of the sealing surface 52 of the coupling gradually decreases from the portion 51 with the internal thread to the thrust surface 53 of the coupling in the longitudinal direction (the direction of the pipe axis) of the second end portion 10B. When screwing with another metal pipe 1 for an oil well, the sealing surface 52 of the coupling comes into contact with the sealing surface 42 of the nipple 40 of the other metal pipe 1 for an oil well. More specifically, during make-up, when the nipple 40 of another metal pipe 1 for an oil well is screwed into the coupling 50, the sealing surface 52 of the coupling comes into contact with the sealing surface 42 of the nipple, and when the nipple 40 continues to be screwed in, the sealing surface 52 of the coupling comes into close contact with the sealing surface 42 of the nipple. Due to this, during make-up, the sealing surface 52 of the coupling comes into close contact with the sealing surface 42 of the nipple, thereby forming a seal based on direct metal contact. This makes it possible to improve the sealability in the screwed metal pipes 1 for an oil well. The thrust surface 53 of the coupling is located closer to the center of the main body 10 of the pipe in the axial direction of the pipe than the sealing surface 52 of the coupling. In other words, in the coupling 50, the thrust surface 53 of the coupling, the sealing surface 52 of the coupling and the portion 51 with the internal thread are arranged sequentially in the specified order from the center of the main body 10 of the pipe to the front end of the second end portion 10B in the axial direction of the pipe. When screwing with another metal pipe 1 for an oil well, the thrust surface 53 of the coupling is located opposite the thrust surface 43 of the nipple 40 of the other metal pipe 1 for an oil well and comes into contact with it. More precisely, during screwing, the thrust surface 53 of the coupling comes into contact with the thrust surface 43 of the nipple as a result of inserting the nipple 40 of the other metal pipe 1 for an oil well into the coupling 50. This makes it possible to obtain a high torque during screwing. In addition, the positional relationship between the nipple 40 and the coupling 50 in the screwing state can be stabilized.

The contact surface 500 of the coupling comprises at least a part 51 with an internal thread. When screwed together, the part 51 with an internal thread of the contact surface 500 of the coupling 50 comes into contact with the part 41 with an external thread of the contact surface 400 of the nipple 40 in such a way that the part 51 with an internal thread corresponds to the part 41 with an external thread. The sealing surface 52 of the coupling comes into contact with the sealing surface 42 of the nipple in such a way that the sealing surface 52 of the coupling corresponds to the sealing surface 42 of the nipple. The thrust surface 53 of the coupling comes into contact with the thrust surface 43 of the nipple in such a way that the thrust surface 53 of the coupling corresponds to the thrust surface 43 of the nipple. If the contact surface 400 of the pin contains the portion 41 with the external thread and does not contain the sealing surface 42 of the pin and the thrust surface 43 of the pin, the contact surface 500 of the coupling contains the portion 51 with the internal thread and does not contain the sealing surface 52 of the coupling and the thrust surface 53 of the coupling. If the contact surface 400 of the pin contains the portion 41 with the external thread and the thrust surface 43 of the pin and does not contain the sealing surface 42 of the pin, the contact surface 500 of the coupling contains the portion 51 with the internal thread and the thrust surface 53 of the coupling and does not contain the sealing surface 52 of the coupling. If the contact surface 400 of the nipple comprises a portion 41 with an external thread and a sealing surface 42 of the nipple and does not comprise a thrust surface 43 of the nipple, the contact surface 500 of the coupling comprises a portion 51 with an internal thread and a sealing surface 52 of the coupling and does not comprise a thrust surface 53 of the coupling.

The contact surface 400 of the nipple may comprise several parts 41 with external thread, several sealing surfaces 42 of the nipple and several thrust surfaces 43 of the nipple. For example, the thrust surface 43 of the nipple, the sealing surface 42 of the nipple, the part 41 with external thread, the sealing surface 42 of the nipple, the thrust surface 43 of the nipple, the sealing surface 42 of the nipple and the part 41 with external thread may be arranged in the specified order on the contact surface 400 of the nipple 40 in the direction from the front end of the first end part 10A to the center of the main body 10 of the pipe. In this case, the portion 51 with internal thread, the sealing surface 52 of the coupling, the thrust surface 53 of the coupling, the sealing surface 52 of the coupling, the portion 51 with internal thread, the sealing surface 52 of the coupling and the thrust surface 53 of the coupling will be located in the specified order on the contact surface 500 of the coupling 50 in the direction from the front

- 7 047428 end of the second end part 10B to the center of the main body 10 of the pipe.

In Fig. 4 and Fig. 5, a so-called best connection is shown, in which the pin 40 comprises a portion 41 with an external thread, a sealing surface 42 of the pin and a thrust surface 43 of the pin, and the coupling 50 comprises a portion 51 with an internal thread, a sealing surface 52 of the coupling and a thrust surface 53 of the coupling. However, according to the above disclosure, the pin 40 may comprise a portion 41 with an external thread and does not necessarily comprise a sealing surface 42 of the pin and a thrust surface 43 of the pin. In this case, the coupling 50 comprises a portion 51 with an internal thread and does not comprise a sealing surface 52 of the coupling and a thrust surface 53 of the coupling. In Fig. 6 is a view illustrating one example of a metal pipe 1 for an oil well, in which a nipple 40 includes a portion 41 with an external thread and does not include a sealing surface 42 of the nipple and a thrust surface 43 of the nipple, and a coupling 50 includes a portion 51 with an internal thread and does not include a sealing surface 52 of the coupling and a thrust surface 53 of the coupling.

A variant in which the metal pipe 1 for an oil well is an integral type.

The metal pipe 1 for an oil well shown in Fig. 2, Fig. 3 and Fig. 6 is a so-called threaded and coupling type metal pipe 1 for an oil well, in which the pipe main body 10 comprises a nipple tubular body 11 and a coupling 12. However, the metal pipe 1 for an oil well according to this embodiment of the invention may be an integral type instead of the threaded and coupling type.

Fig. 7 is a diagram illustrating a metal pipe 1 for an integral type oil well according to the present embodiment of the invention. As shown in Fig. 7, the metal pipe 1 for an integral type oil well includes a pipe main body 10. The pipe main body 10 includes a first end portion 10A and a second end portion 10B. The first end portion 10A is located on a side opposite to the second end portion 10B. As disclosed above, in the metal pipe 1 for an oil well of the threaded coupling type, the pipe main body 10 includes a nipple tubular body 11 and a coupling 12. In other words, in the metal pipe 1 for an oil well of the threaded coupling type, the pipe main body 10 is formed by screwing together two separate members (the nipple tubular body 11 and the coupling 12). On the contrary, in the metal pipe 1 for an integral type oil well, the main body 10 of the pipe is formed in a non-detachable manner.

The nipple 40 is formed on the first end portion 10A of the main body 10 of the pipe. When screwing, the nipple 40 is inserted and screwed into the coupling 50 of another metal pipe 1 for an integral type oil well and thus screwed into the coupling 50 of another metal pipe 1 for an integral type oil well. The coupling 50 is formed on the second end portion 10B of the main body 10 of the pipe. When screwing, the nipple 40 of another metal pipe 1 for an integral type oil well is inserted and screwed into the coupling 50 to thus screw the coupling 50 with the nipple 40 of another metal pipe 1 for an oil well. The structure of the nipple 40 of the metal pipe 1 for an oil well of an integral type is similar to the structure of the nipple 40 of the metal pipe 1 for an oil well of a threaded type with a coupling shown in Fig. 4. Similarly, the structure of the coupling 50 of the metal pipe 1 for an oil well of an integral type is similar to the structure of the coupling 50 of the metal pipe 1 for an oil well of a threaded type with a coupling shown in Fig. 5. It should be noted that in Fig. 7, in the nipple 40, the thrust surface of the nipple, the sealing surface of the nipple, the portion with an external thread, the sealing surface of the nipple, the thrust surface of the nipple, the sealing surface of the nipple and the portion with an external thread are arranged in the specified order from the front end of the first end portion 10A to the center of the main body 10 of the pipe in the direction of the axis of the pipe. Thus, in the coupling 50, the internally threaded portion, the coupling sealing surface, the coupling thrust surface, the coupling sealing surface, the internally threaded portion, the coupling sealing surface, and the coupling thrust surface are arranged in this order from the front end of the second end portion 10B to the center of the pipe main body 10 in the direction of the pipe axis. However, similarly to Fig. 4, it is sufficient that the contact surface 400 of the nipple 40 of the integral-type metal pipe 1 for an oil well comprises at least the externally threaded portion 41. Furthermore, similarly to Fig. 5, it is sufficient that the contact surface 500 of the coupling 50 of the integral-type metal pipe 1 for an oil well comprises at least the internally threaded portion 51. In short, the metal pipe 1 for an oil well according to this embodiment may be a threaded-and-coupled type or an integral type.

The metal pipe 1 for an oil well may be a Fe-based alloy steel pipe or an alloy pipe such as a Ni-based alloy pipe. The steel pipe refers to, for example, a low-alloy steel pipe, a martensitic stainless steel pipe, and a duplex stainless steel pipe.

Structure on the contact surface 400 of the nipple or the contact surface 500 of the coupling.

- 8 047428

In the metal pipe 1 for an oil well according to the present embodiment, a metallized layer 60 is formed on the first contact surface which is the contact surface 400 of the pin or the contact surface 500 of the coupling, and further, a solid lubricant layer 70 is formed on the metallized layer 60. In addition, the arithmetic mean value of the roughness Ra of the second contact surface which is the other surface of the contact surface 400 of the pin and the contact surface 500 of the coupling is from 0.5 to 10.0 μm, and a semi-solid or liquid anticorrosive coating 80 is formed on the second contact surface. Next, the structure on the first contact surface and the structure on the second contact surface will be described in the case where the first contact surface is the contact surface 500 of the coupling and the second contact surface is the contact surface 400 of the pin. However, the structure on the first contact surface and the structure on the second contact surface in the case where the first contact surface is the pin contact surface 400 and the second contact surface is the coupling contact surface 500 are similar to the case disclosed below.

Structure on the first contact surface.

Fig. 8 is a sectional view for describing a structure on the first contact surface in the case where the first contact surface is the coupling contact surface 500. As shown in Fig. 8, a metallized layer 60 is formed on the first contact surface. In addition, a solid lubricant layer 70 is formed on the metallized layer 60. Next, the metallized layer 60 and the solid lubricant layer 70 will be disclosed.

Structure of metallized layer 60.

The type of the metallized layer 60 is essentially not limited. For example, the metallized layer 60 may be a zinc metallized layer, a nickel metallized layer, a copper metallized layer, a Zn-Ni alloy metallized layer, a Zn-Co alloy metallized layer, a Ni-W alloy metallized layer, or a Cu-SnZn alloy metallized layer. In addition, the metallized layer 60 may be formed by several metallized layers applied to each other. For example, a nickel metallized layer may be formed on the first contact surface, after which a Zn-Ni metallized layer may be applied and formed on the nickel metallized layer. If the metallized layer 60 is a Cu-Sn-Zn alloy metallized layer, the chemical composition of the Cu-Sn-Zn alloy metallized layer includes, for example, Cu in an amount of 40 to 70 weight %, Sn in an amount of 20 to 50 weight %, and Zn in an amount of 2 to 20 weight %, the remainder being impurities. If the metallized layer 60 is a copper metallized layer, the chemical composition of the copper metallized layer includes, for example, Cu and impurities.

Preferably, the metallized layer 60 is made of a zinc alloy containing one or more types of elements from the group consisting of Ni, Fe, Mg and Mn, and Zn. Such zinc alloy coatings have high hardness and a high melting point. Therefore, such zinc alloy coatings are characterized by high resistance to scuffing. In addition, since zinc is a less noble metal than steel, which serves as the base metal of the main body 10 of the pipe, zinc provides sacrificial protection against corrosion. Therefore, if the metallized layer 60 is made of a zinc alloy, the metallized layer 60 will be characterized by high corrosion resistance, and not only by resistance to scuffing.

In a more preferred embodiment, the metallized layer 60 is a metallized layer of Zn-Ni alloy. The metallized layer of Zn-Ni alloy contains Zn-Ni alloy. The Zn-Ni alloy contains zinc (Zn) and nickel (Ni). Sometimes, the Zn-Ni alloy may contain impurities. In this case, impurities with respect to the Zn-Ni alloy are understood to mean substances other than zinc and nickel that enter the metallized layer of Zn-Ni alloy during the production or other processing operations of the metal pipe for an oil well, and the content of such substances is in a range that does not affect the effects of the present embodiment of the invention. The Zn-Ni alloy not only has excellent corrosion resistance, but, as disclosed above, also has high hardness and a high melting point, that is, has high resistance to scoring.

In the metallized layer of Zn-Ni alloy, the total content of zinc and nickel is preferably 100% by weight, the proportion of nickel contained is from 10 to 20% by weight. A preferred lower limit of the nickel content in the metallized layer of Zn-Ni alloy is 11% by weight, more preferably 12% by weight. A preferred upper limit of the nickel content in the metallized layer of Zn-Ni alloy is 18% by weight, more preferably 16% by weight, even more preferably 15% by weight.

Method for measuring the chemical composition of a metallized layer of Zn-Ni alloy.

If the metallized layer 60 is a Zn-Ni alloy metallized layer, the chemical composition of the metallized layer 60 can be measured on the cross section of the metallized layer using an energy-dispersive X-ray spectroscope. As for the control of the operation

- 9 047428 radios during production, then non-destructive and simple measurement is preferable. Therefore, the chemical composition of the metallized layer of Zn-Ni alloy can be measured, for example, from the surface of the metallized layer by means of a fluorescent X-ray analyzer. In this case, the correction is carried out accordingly using a reference sample with a known chemical composition.

The thickness of the metallized layer is 60.

The thickness of the metallized layer 60 is not limited in principle. The thickness of the metallized layer 60 is, for example, 1 to 20 μm. If the thickness of the metallized layer 60 is 1 μm or more, sufficient resistance to scuffing can be obtained. On the other hand, if the thickness of the metallized layer 60 exceeds 20 μm, the above-mentioned effects will reach a limit. The lower limit of the thickness of the metallized layer 60 is preferably 3 μm, more preferably 5 μm. The upper limit of the thickness of the metallized layer 60 is preferably 18 μm, more preferably 15 μm.

The thickness of the metallized layer 60 can be measured in the following way. A sample is taken, which includes a cross-section of the metallized layer 60. Then, the thickness of the metallized layer 60 is measured at three arbitrary points of the cross-section of the metallized layer 60. The arithmetic mean of the measured thickness is considered the thickness (μm) of the metallized layer 60. In addition to the above-mentioned method, the thickness of the metallized layer 60 can also be measured from the surface of the metallized layer by means of a fluorescent X-ray analyzer, similar to the measurement of the chemical composition of the metallized layer, disclosed above. In this case, the correction is performed accordingly using a reference sample with a known chemical composition.

Layer 70 of solid lubricant.

In addition, a solid lubricant layer 70 is formed on the metallized layer 60. During screwing, the solid lubricant layer 70 increases the lubrication of the coupling 50 and the nipple 40 of the metal pipe 1 for an oil well. The solid lubricant layer 70 is a solid coating at a normal temperature (20°C±15°C).

The terms solid, semi-solid and liquid used in the present description are defined as follows. The term solid means a state in which the shape is constant at normal temperature, and even when an external force is applied, the shape does not change, or at least one part is destroyed. The term semi-solid means a state in which, although a certain shape is maintained at normal temperature, when an external force is applied, at least the part to which the external force is applied easily changes shape without being destroyed. In the present description, the state of grease and the semi-dry state are included in the definition of a semi-solid substance. The term liquid means the state of a liquid. Note that the state in the case where the volatile components of the liquid evaporate and the non-volatile viscous components remain also corresponds to semi-solid or liquid.

The solid lubricant layer 70 contains, for example, a solid lubricant powder and a binder serving as a matrix. In other words, the solid lubricant layer 70 is a coating layer in the form of a heterogeneous system in which the solid lubricant powder is bound to a binder.

Solid lubricant powder.

The solid lubricant powder is a powder that exhibits a lubricating effect. A known material commonly used as a solid lubricant can be used as the solid lubricant powder. It is preferable to use a material that does not have a negative impact on the environment as the solid lubricant powder.

Preferably, the solid lubricant powder comprises one or more substances from the group consisting of molybdenum sulfide ( _MoS2 ), tungsten disulfide (WS2), graphite or boron nitride (BN), carbon black, polytetrafluoroethylene powder (PTFE) and graphite fluoride (CFX). Molybdenum sulfide (MoS2) and tungsten disulfide (WS2) are inorganic powders with a graphite crystal structure. The average particle diameter of the solid lubricant powder is essentially unlimited. The average particle diameter of the solid lubricant powder is, for example, from 0.5 to 15 μm.

In the solid lubricant layer 70, the mass ratio of the total amount of solid lubricant powder to the total amount of binder is preferably 0.3 to 0.9. If the mass ratio of the total amount of solid lubricant powder to the total amount of binder is 0.3 or more, the scuff resistance of the solid lubricant layer 70 is further increased. If the mass ratio of the total amount of solid lubricant powder to the total amount of binder is 0.9 or less, the adhesiveness and strength of the solid lubricant layer 70 are further increased.

The solid lubricant layer 70 may further comprise a powder other than the solid lubricant powder. For example, the solid lubricant layer 70 comprises a solid lubricant powder.

- 10 047428 of a non-organic material and silica. The other powder is, for example, an inorganic powder that does not have a graphite crystal structure. If the solid lubricant layer 70 contains a solid lubricant powder and another powder, the preferred mass ratio of the total amount of the solid lubricant powder and the other powder to the total amount of the binder is 0.9 or less.

Connecting.

The binder in the solid lubricant layer 70 contains an organic polymer and/or an inorganic macromolecular compound.

The organic polymer as a binder is preferably an organic polymer characterized by heat resistance, moderate hardness and moderate abrasiveness. The organic polymer as a binder contains, for example, one or more types from the group consisting of a thermosetting polymer and a thermoplastic polymer. The organic polymer contains one or more substances from the group consisting of an epoxy resin, a polyimide resin, a polyamide-imide resin, a polycarbodiimide resin, a polyethersulfone, a polyetheretherketone, a phenolic resin and a furan resin, a polyvinyl resin, an acrylic resin and a polyurethane resin, a polyethylene resin, a silicone resin and a fluororubber.

From the viewpoint of improving the adhesiveness of the solid lubricant layer 70, the solid lubricant layer 70 can be formed by heat-curing a liquid composition serving as a raw material for the solid lubricant layer 70 and containing a solid lubricant powder and a binder (hereinafter referred to as an organic liquid composition). The heat-curing temperature is preferably 80°C or more, more preferably 150 to 380°C. The processing time is preferably 5 minutes or more, more preferably 20 to 60 minutes. The heat-curing process may include a pre-drying process and a sintering process. In the pre-drying process, the temperature is maintained in the range of 80 to 100°C for a period of 2 to 15 minutes. The sintering process is performed after the pre-drying. In the sintering process, the temperature is maintained in the range of 150 to 380°C for a period of 10 to 50 minutes.

The inorganic macromolecular compound as a binder is, for example, a compound with a structure with three-dimensionally crosslinked metal-oxygen bonds, such as TiO, Si-O, Zr-O, Mn-O, Ce-O or Ba-O. Such inorganic macromolecular compounds can be obtained by hydrolysis and condensation of a hydrolyzable metal compound such as a metal alkoxide or a metal chloride. The inorganic macromolecular compound can be obtained using a hydrolyzable metal compound containing a functional group such as an amino group or an epoxy group. The hydrolyzable metal compound containing a functional group such as an amino group or an epoxy group is, for example, a silane coupling agent or a titanate coupling agent.

If the binder is an inorganic macromolecular compound, the solid lubricant layer 70 is formed, for example, in the following manner. A liquid composition containing a solvent of a hydrolyzable metal compound or its partial hydrolyzate and a solid lubricant powder (hereinafter referred to as the inorganic liquid composition) is applied to the metallized layer 60. The applied liquid composition is treated by moistening and/or heating. As a result of the above-described processes, a solid lubricant layer 70 is obtained containing an inorganic macromolecular compound as a binder. As disclosed above, moistening treatment can be performed to promote the hydrolysis of the compound of the hydrolyzable metal compound. During moistening treatment, the applied liquid composition is left in atmospheric air, preferably in a humidified atmosphere with a relative humidity of 70% or more for a given period of time. Preferably, heating is performed after moistening treatment. Condensation of the hydrolyzate obtained by hydrolysis of the metal compound and the release of a by-product (water) of condensation of the by-product (alcohol in case the metal compound is a metal alkoxide) of hydrolysis are stimulated by heating. As a result, the solid lubricant layer 70 can be formed in a short period of time. Further, due to heating after the humidification treatment, the adhesion of the formed solid lubricant layer 70 is fixed. Heating after the humidification treatment is preferably performed after evaporation of the solvent remaining in the coating film. The heating temperature after the humidification treatment is preferably set in the range of 50 to 200°C, close to the boiling point of the alcohol obtained as a by-product. In addition, heating in an air heater is effective.

The thickness of the solid lubricant layer 70 is 3 to 50 μm. The preferred thickness of the solid lubricant layer 70 is 10 to 40 μm. If the thickness of the solid lubricant layer 70 is 10 μm or more, high lubricity can be obtained while maintaining consistency. On the other hand, if the thickness of the solid lubricant layer 70 is 40 μm or less, the adhesiveness of the solid lubricant layer 70 will be more constant. In addition, if the thickness of the solid lubricant layer 70 is 40 μm or less, the thread tolerance (thread clearance) between the sliding surfaces widens. In this case, the interfacial pressure during sliding decreases. Therefore, it is possible to prevent

- 11 047428 excessive increase in tightening torque. Accordingly, the thickness of the solid lubricant layer 70 is preferably 10 to 40 μm. A more preferable lower limit of the thickness of the solid lubricant layer 70 is 15 μm, even more preferable 20 μm. A more preferable upper limit of the thickness of the solid lubricant layer 70 is 35 μm, even more preferable 30 μm.

The thickness of the solid lubricant layer 70 is measured in the following manner. A sample is taken that contains the first contact surface on which the solid lubricant layer 70 is formed. One of the surfaces of the sample corresponds to a cross-section made perpendicular to the axial direction (longitudinal direction) of the metal pipe for an oil well. Hereinafter, such a cross-section is called the observation surface. On the observation surface, the area containing the solid lubricant layer 70 is examined under a microscope. The magnification during examination under a microscope is set to 500x. The thickness of the solid lubricant layer 70 is determined in 10 arbitrary observed areas. In each observed area, the thickness of the solid lubricant layer 70 is measured in three arbitrary places. The arithmetic mean value of the thickness of the solid lubricant layer 70 in 10 observed areas (a total of 10x3=30 thickness values) is determined as the thickness (μm) of the solid lubricant layer 70.

Structure on the second contact surface.

Fig. 9 is a sectional view for explaining the structure on the second contact surface in the case where the second contact surface is the pin contact surface 400. As shown in Fig. 9, the arithmetic mean value of the roughness Ra of the second contact surface is 0.5 to 10.0 μm. In addition, a semi-solid or liquid anticorrosive coating 80 is formed on the second contact surface (in Fig. 9, on the pin contact surface 400). Next, the arithmetic mean value of the roughness Ra and the anticorrosive coating 80 of the second contact surface will be disclosed.

The arithmetic mean value of roughness Ra of the second contact surface.

The arithmetic mean value of roughness Ra of the second contact surface (in Fig. 9, the contact surface 400 of the nipple) is measured by the method for measuring the arithmetic mean value of roughness specified in JIS B 0601 (2013). In particular, 10 arbitrary points in the direction of the thread top (thread cutting direction) of the threaded portion on the second contact surface are taken as measurement points. At each measurement point, the arithmetic mean value of roughness Ra is measured over the evaluation length oriented in the direction of the pipe axis. The evaluation length is set to a multiple of five times the sampling length (limit wavelength). The arithmetic mean value of roughness Ra is measured using a roughness probe, and the measurement speed is set to 0.5 mm/s. The arithmetic mean value of roughness Ra is taken as the arithmetic mean value of roughness at six points out of 10, excluding the largest arithmetic mean value of roughness Ra, the next largest arithmetic mean value of roughness Ra, the smallest arithmetic mean value of roughness Ra and the next smallest arithmetic mean value of roughness Ra. For example, a surface roughness tester with the trade name SURFTEST SJ-301 manufactured by Mitutoyo Corporation is used as a contact roughness meter.

The arithmetic mean value of the roughness of the second contact surface after thread cutting is less than 0.1 μm. If the arithmetic mean value of the roughness Ra of the second contact surface is from 0.5 to 10.0 μm, the roughness of the second contact surface is adjusted by a certain treatment of the second contact surface. The surface treatment is, for example, blasting. Preferably, the second contact surface is subjected to blasting. Blasting is understood to mean treatment in which a shot blasting device is used, ensuring the collision of an abrasive material (abrasive) with the second contact surface. Blasting is, for example, sand blasting, shot blasting or grit blasting. Blasting is treatment in which an abrasive material (abrasive) is mixed with compressed air, and the resulting mixture is fed to the second contact surface. The roughness of the second contact surface can be adjusted accordingly by selecting the abrasive material used in blasting, as well as the advancement speed, etc.

Anti-corrosion coating 80.

Anti-corrosion coating 80 is formed on the second contact surface. Anti-corrosion coating 80 is semi-solid or liquid at normal temperature (20°C±15°C).

Fig. 10 shows an enlarged view of the part near the second contact surface shown in Fig. 9 (in Fig. 9, the contact surface 400 of the nipple). As shown in Fig. 10, a slight unevenness is formed on the second contact surface (in this case, the contact surface 400 of the nipple) to such an extent that the arithmetic mean value of the roughness Ra is from 0.5 to 10 μm. Due to this unevenness, the coefficient of friction between the contact surface 400 of the nipple and the contact surface 500 of the coupling during screwing increases, and the

- 12 047428 yield point torque is calculated.

Types of anti-corrosion coating 80.

Anti-corrosion coating 80 can be one of the following two types.

(A) Liquid anti-corrosion coating.

(B) Semi-hard anti-corrosion coating.

The following describes liquid anti-corrosion coating and semi-solid anti-corrosion coating.

(A) Structure of liquid anti-corrosion coating.

A liquid anti-corrosion coating is an anti-corrosion coating in a liquid state. The term liquid means the state of a liquid. Note that the state in which the volatile components of the liquid evaporate and the non-volatile viscous components remain also corresponds to a semi-solid or liquid. A liquid anti-corrosion coating can be obtained, for example, by applying a commercially available anti-corrosion lubricant, which is also called a light oil, such as WD-40 (trade name). The chemical composition of the liquid anti-corrosion coating includes, for example, white spirit in an amount of 50 to 75 weight % and mineral oil in an amount of 25 weight % or less.

White spirit.

White spirit is a solvent equivalent to industrial gasoline No. 4 specified in JIS K 2201 (1991). A preferred lower limit of the content of white spirit is 52% by weight, more preferably 54%, still more preferably 56%, and still more preferably 58%. A preferred upper limit of the content of white spirit is 70% by weight, more preferably 68%, more preferably 66%, still more preferably 64%, and still more preferably 62%.

Mineral based oil.

The mineral oil is obtained by refining crude oil. The mineral oil is one or more types from the group consisting of paraffinic oil, naphthenic oil and aromatic oil. The preferred lower limit of the mineral oil content is 2% by weight, more preferably 4%, even more preferably 6%, and even more preferably 8%. The preferred upper limit of the mineral oil content is 22% by weight, more preferably 20%, even more preferably 18%, and even more preferably 16%.

Anti-corrosion additive.

The anticorrosive coating 80 may also contain an anticorrosive additive in addition to white spirit and mineral oil. The term anticorrosive additive is a general term for additives that have corrosion resistance. The anticorrosive additive is, for example, one or more of the following substances: aluminum tripolyphosphate, aluminum phosphite and calcium ion-exchange silicon dioxide. Preferably, the anticorrosive additive is calcium ion-exchange silicon dioxide and/or aluminum phosphite. Other known (commercially available) reactive water-repellent agents can also be used as an anticorrosive additive.

The content of the anticorrosive additive in the anticorrosive coating 80 is preferably 10% or less by weight. A preferable upper limit of the content of the anticorrosive additive in the anticorrosive coating 80 is 9%, more preferably 8%, and even more preferably 5%. A preferable lower limit of the content of the anticorrosive additive in the anticorrosive coating 80 is 2%, more preferably 3%. It should be noted that the anticorrosive coating 80 does not necessarily have to contain the anticorrosive additive. In other words, the chemical composition of the anticorrosive coating 80 may include white spirit and mineral oil, and the rest may be impurities. It should be noted that the anticorrosive coating 80 essentially does not contain a heavy metal powder. In other words, in the anticorrosive coating 80, the heavy metal is an impurity. The heavy metal powder is, for example, a powder or particles of Pb, Cu, Zn or other similar substances. The anticorrosive coating 80 also does not contain chlorine compounds. Therefore, the metal pipe for an oil well according to this embodiment of the invention can be used in an offshore oil well in which the use of a lubricant containing a heavy metal, a chlorine compound or other such substances is prohibited.

(B) Structure of semi-solid anti-corrosion coating.

A semi-solid anticorrosive coating is an anticorrosive coating in a state in which, although the coating retains a certain shape at normal temperature, when an external force is applied, at least the part that experiences the external force easily changes its shape without destruction (without cracking). A semi-solid anticorrosive coating may be in a state of consistent lubrication or a semi-dry state.

The chemical composition of the semi-solid anti-corrosion coating includes, for example, in weight %, purified mineral oil in an amount of 20 to 30%, mineral-based wax in an amount of 8

- 13 047428 up to 13%, graphite in an amount of 3 to 5%, and rosin in an amount of 5 to 10%, the rest is calcium sulfonate and impurities.

Refined mineral oil is a hydrocarbon compound obtained by processing mineral oil, natural gas, etc. Mineral wax is wax obtained from mineral oil. Wax is an organic substance that is solid at normal temperatures and turns into a liquid when heat is applied to it. Rosin is a resin obtained by distilling rosin with water vapor to remove turpentine oil from it.

It should be noted that the semi-solid anticorrosive coating may be a known yellow additive or a known green additive. The anticorrosive coating 80 is in a semi-solid or liquid state. Therefore, compared with the case of forming a solid coating, when forming the anticorrosive coating 80 on the second contact surface, a special device is usually not required. Depending on the properties of the anticorrosive coating 80 and the technical conditions, drying by heating can be performed.

The anticorrosive coating 80 formed on the second contact surface is in a semi-solid or liquid state. When screwing the metal pipe for an oil well, the semi-solid or liquid anticorrosive coating 80 changes shape or flows, accompanying the screwing. As a result, the surface roughness of the anticorrosive coating 80 formed on the second contact surface is substantially equal to the roughness of the second contact surface.

Note that a metallized layer is not formed on the second contact surface. If a metallized layer is formed on the second contact surface, which is a rough surface, and an anticorrosive coating 80 is formed on the formed metallized layer, the unevenness of the second contact surface will not transfer to the surface of the metallized layer. In other words, the surface roughness of the metallized layer will be less than the roughness of the second contact surface. Therefore, it is impossible to adequately increase the torque at the yield point when screwing. In addition, if a metallized layer is formed on the second contact surface, after which the surface of the metallized layer is roughened and then the anticorrosive coating 80 is formed, the production costs increase. Therefore, in the metal pipe for an oil well according to the present embodiment of the invention, a metallized layer is not formed on the second contact surface.

A case in which the contact surface of the nipple is considered the first contact surface and the contact surface of the coupling is considered the second contact surface.

In the previous description of the structure of the first and second contact surfaces, the coupling contact surface 500 was considered as the first contact surface, and the pin contact surface 400 was considered as the second contact surface. However, as disclosed above, the pin contact surface 400 may serve as the first contact surface, and the coupling contact surface 500 may serve as the second contact surface. In this case, as shown in Fig. 11, the metallized layer 60 is formed on the pin contact surface 400 (the first contact surface), and the solid lubricant layer 70 is formed on the metallized layer 60. In addition, as shown in Fig. 12, the roughness of the coupling contact surface 500 (the second contact surface) is adjusted, and the arithmetic mean value of the roughness Ra of the coupling contact surface 500 is from 0.5 to 10.0 μm. In addition, an anti-corrosion coating 80 is formed on the contact surface 500 of the coupling.

As disclosed above, in the metal pipe 1 for an oil well according to the present embodiment, the metallized layer 60 is formed on the first contact surface which is the contact surface 400 of the pin or the contact surface 500 of the box, and a solid lubricant layer 70 is formed on the metallized layer 60. In addition, the second contact surface located opposite the first contact surface during make-up has roughness, and the arithmetic mean value of the roughness Ra of the second contact surface is from 0.5 to 10.0 μm. In addition, a semi-solid or liquid anticorrosive coating is formed on the second rough contact surface. The resistance to scuffing during make-up can be improved by the metallized layer 60 and the solid lubricant layer 70 of the first contact surface. In addition, if the semi-solid or liquid anti-corrosion coating 80 is formed on the second contact surface, which is a rough surface, a high friction coefficient is achieved due to the metallized layer 60 under the solid lubricant layer 70 on the first contact surface and the unevenness of the second contact surface. As a result, the torque at the yield point increases.

A chemically treated 90 coating formed on the second contact surface.

In the metal pipe 1 for an oil well according to the present embodiment, a chemically treated coating may be further formed on the second contact surface, and an anticorrosive coating 80 may be formed on the chemically treated coating. Fig. 13 is a view illustrating the structure of the second

- 14 047428 contact surface containing a coating 90 obtained by chemical treatment, in the case where the second contact surface is a contact surface 400 of a nipple. As shown in Fig. 13, a chemically treated coating 90 is formed on the second contact surface, the roughness of which has been adjusted so that the arithmetic mean value of the roughness Ra is from 0.5 to 10.0 μm, and an anticorrosive coating 80 is formed on the chemically treated coating 90. In this case, the chemically treated coating 90 is formed in contact with the second contact surface, and the anticorrosive coating 80 is formed in contact with the chemically treated coating 90. The chemically treated coating 90 is, for example, one or more types of coating from the group consisting of phosphate chemically treated, oxalate chemically treated or borate chemically treated coatings. Preferably, the chemically treated coating 90 is a phosphate chemically treated coating.

The chemically treated coating 90 is porous. Therefore, when the anticorrosive coating 80 is formed on the chemically treated coating 90, the adhesion (holding ability) of the second contact surface of the anticorrosive coating 80 increases due to the so-called anchor effect. In this case, the corrosion resistance of the second contact surface increases. The thickness of the chemically treated coating 90 is essentially not limited. The preferred thickness of the chemically treated coating 90 is from 5 to 40 μm. If the thickness of the chemically treated coating 90 is 5 μm or more, the corrosion resistance is further increased. If the thickness of the chemically treated coating is 40 μm or less, the adhesion of the anticorrosive coating 80 increases while maintaining the consistency. It should be noted that Fig. 13 shows a case in which the second contact surface is the contact surface 400 of the pin. However, even if the second contact surface is the coupling contact surface 500, the chemically treated coating 90 may be similarly formed on the second contact surface, and the anti-corrosion coating 80 may be formed on the chemically treated coating 90.

It should be noted that the anticorrosive coating 80 may be formed in direct contact with the second contact surface, and the chemically treated coating 90 may be absent on the second contact surface. Preferably, in the case where the chromium content is 1.00% by weight or less in the chemical composition of the metal pipe 1 for an oil well, the chemically treated coating 90 is formed on the second contact surface, and the anticorrosive coating 80 is formed on the chemically treated coating 90. If the chromium content is 1.00% by weight or less in the chemical composition of the metal pipe 1 for an oil well, the corrosion resistance of the base metal of the metal pipe 1 for an oil well will not be high. If the chromium content is 1.00 weight % or less in the chemical composition of the metal pipe 1 for an oil well, the chemically treated coating 90 is formed on the second contact surface, and the anticorrosive coating 80 is formed on the chemically treated coating 90, the corrosion resistance of the second contact surface can be increased.

Manufacturing process.

An example of a method for manufacturing a metal pipe for an oil well according to the present embodiment of the invention having the above-disclosed structure will be disclosed below. It should be noted that the disclosed manufacturing method is one example of a method for manufacturing a metal pipe for an oil well according to the present embodiment of the invention. Accordingly, the choice of the manufacturing method is not limited as long as the manufacturing method can manufacture the metal pipe for an oil well according to the present embodiment of the invention. The disclosed manufacturing method is a preferable example of a method for manufacturing a metal pipe for an oil well according to the present embodiment of the invention.

The method for manufacturing a metal pipe for an oil well according to the present embodiment comprises a step of preparing a hollow shell with a threaded connection (a step of preparing a hollow shell with a threaded connection), a step of forming a metallized layer 60 on the first contact surface (a step of forming a metallized layer), a step of forming a layer 70 of a solid lubricant on the metallized layer 60 (a step of forming a layer of a solid lubricant), a step of adjusting the roughness of the second contact surface (a step of adjusting the roughness of the second contact surface), and a step of forming an anti-corrosion coating on the second contact surface whose roughness has been adjusted (a step of forming an anti-corrosion coating). Each of these steps is described in detail below.

Stage of preparation of a hollow shell with a threaded connection.

At the stage of preparing a hollow shell with a threaded connection, a hollow shell with a threaded connection is prepared. In this case, a hollow shell with a threaded connection is understood as the main

- 15 047428 pipe body 10. If the metal pipe for an oil well is of the threaded and coupling type, the main body 10 of the pipe comprises a nipple tubular body 11 and a coupling 12. If the metal pipe for an oil well is of the integral type, the main body 10 of the pipe is formed in a non-detachable manner.

A product supplied by a third party may be used as the pipe main body 10, or the pipe main body 10 may be prepared by manufacturing the pipe main body 10. In the case of manufacturing the pipe main body 10, the pipe main body 10 is manufactured, for example, in the following manner.

Molten steel is used to obtain the starting material. In particular, a casting (slab, bloom or billet) is produced in a continuous casting process using molten steel. An ingot can also be produced using an ingot manufacturing process using molten steel. If necessary, a slab, bloom or ingot can be subjected to blooming to obtain a cast product (billet). The starting material (slab, bloom or billet) is produced in the above-described manner. The prepared starting material is subjected to hot working to obtain a hollow shell. The hot working method can be piercing rolling according to the Mannesmann process, or a hot extrusion process. The hollow shell after hot working is subjected to known hardening and tempering processes to regulate the strength of the hollow shell. The hollow shell is obtained in the above-described manner. Note that if the metal pipe for an oil well is of the threaded and coupling type, a hollow shell for the coupling 12 is also obtained. The method for manufacturing the hollow shell for the coupling 12 is similar to the method for manufacturing the hollow shell disclosed above.

If the metal pipe for an oil well is of the threaded and coupling type, the thread is cut relative to the outer surface of both end portions of the hollow shell for the tubular body 11 of the nipple to obtain the nipple contact surface 400. In addition, the thread is cut relative to the inner surface of both end portions of the hollow shell for the coupling 12 to obtain the coupling contact surface 500. The nipple of one end of the hollow shell for the tubular body 11 of the nipple is inserted and screwed into the coupling of one end of the hollow shell for the coupling 12. The main body of the pipe comprising the tubular body 11 of the nipple and the coupling 12 (hollow shell with a threaded connection) is manufactured in the above-described manner.

If the metal pipe for an oil well is of the integral type, the thread is cut relative to the outer surface of the first end portion 10A of the hollow shell corresponding to the main body 10 of the pipe, to obtain the contact surface 400 of the nipple. In addition, the thread is cut relative to the outer surface of the second end portion 10B of the hollow shell corresponding to the main body 10 of the pipe, to obtain the contact surface 500 of the coupling. The main body 10 of the pipe containing the nipple and the coupling (hollow shell with a threaded connection) is manufactured in the above-described manner.

Stage of metallized layer formation.

The metallized layer 60 is formed on the first contact surface, which is the contact surface 400 of the nipple or the contact surface 500 of the coupling of the prepared main body of the pipe. The metallized layer 60 can be formed by a known method. The metallized layer 60 can be formed by the method of electrodeposition or chemical deposition.

For example, in the case of forming the metallized layer 60 from the Zn-Ni alloy by the electrodeposition method, the galvanic bath contains zinc ions and nickel ions. The galvanic bath composition preferably includes zinc ions in an amount of 1 to 100 g/l; and nickel ions in an amount of 1 to 50 g/l. The conditions for the electrodeposition method are, for example, the following: the pH of the galvanic bath in the range of 1 to 10, the temperature in the galvanic bath in the range of 25 to 80 °C, the current density in the range of 1 to 100 Adm ² and the duration of treatment in the range of 0.1 to 30 min. For example, in the case of forming the metallized layer 60 from the Cu-Sn-Zn alloy by the electrodeposition method, the galvanic bath contains copper ions in an amount of 1 to 50 g/l, tin ions in an amount of 1 to 50 g/l, and zinc ions in an amount of 1 to 50 g/l. The electrodeposition conditions can be similar to the above-mentioned conditions for forming the metallized layer 60 made of the Zn-Ni alloy. If the metallized layer 60 is made of copper or a copper alloy, the metallized layer 60 can be obtained by a known method.

The stage of formation of a solid lubricant layer.

At the stage of forming a solid lubricant layer, a solid lubricant layer 70 is formed on a metallized layer 60. The stage of forming a solid lubricant layer comprises an application stage and a curing stage.

Application stage.

At the application stage, the composition for forming the solid lubricant layer 70 on the metallized layer 60 is applied to the metallized layer 60 in a known manner.

For example, if the composition is an organic liquid composition disclosed

- 16 047428 above, the organic liquid composition is applied to the first contact surface by spraying. In this case, the viscosity of the organic liquid composition is adjusted so that it can be applied by spraying at normal temperature and pressure. Instead of spraying, another application method can be used, for example, by brushing or dipping. The same applies to the case in which the composition is an inorganic liquid compound.

Curing stage.

If the composition is an organic liquid composition, the applied organic liquid composition is cured in the curing step to form a solid lubricant layer 70. The solid lubricant layer 70 is formed by drying and/or thermal curing of the polymer solution for application, which has been applied to the metallized layer 60. Drying and/or thermal curing can be performed in a known manner in accordance with the type of binder. Preferred conditions and similar parameters of this process are disclosed above. If the composition is an inorganic liquid composition disclosed above, the applied inorganic liquid composition is treated by moistening and/or heating in the curing step.

The solid lubricant layer 70 is formed on the metallized layer 60 by performing the above-mentioned application and curing steps.

Stage of adjusting the roughness of the second contact surface.

At the stage of adjusting the roughness of the second contact surface, the roughness of the second contact surface, which is the contact surface 400 of the nipple or the contact surface 500 of the coupling of the main body 10 of the pipe, is adjusted in such a way that the arithmetic mean value of the roughness Ra of the second contact surface is from 0.5 to 10.0 μm.

Surface roughness adjustment is performed, for example, by means of blasting. Blasting.

Blasting is a process in which a shot blasting device is used to impinge on an abrasive material (abrasive) with a second contact surface in order to roughen the second contact surface. Blasting is, for example, sand blasting. Sand blasting is a process in which an abrasive material (abrasive) is mixed with compressed air and the resulting mixture is supplied to the second contact surface. Examples of an abrasive material include a material in the form of spherical shot and angular fine particles. Sand blasting can be performed in a known manner. For example, air is compressed by a compressor and an abrasive material is mixed with the compressed air. The abrasive material can be, for example, stainless steel, aluminum, ceramic material, or aluminum oxide. The sand blasting conditions, such as the advance speed, can be set appropriately. By appropriately selecting the abrasive material used for blasting and appropriately adjusting the advance speed, etc. in the blasting step, the arithmetic mean value of the roughness Ra of the second contact surface can be adjusted in the range of 0.5 to 10.0 μm.

Stage of formation of anti-corrosion coating.

In the step of forming the anti-corrosion coating, the anti-corrosion lubricant for forming a semi-solid or liquid anti-corrosion coating is applied to the second contact surface of the main body 10 of the pipe after the step of adjusting the roughness of the second contact surface. The anti-corrosion coating is not in a solid state, but in a semi-solid or liquid state. Therefore, if a semi-solid or liquid anti-corrosion lubricant is applied to the second contact surface, a semi-solid or liquid anti-corrosion coating can be easily formed. The choice of the method for applying the semi-solid or liquid anti-corrosion lubricant is essentially not limited, provided that it allows the anti-corrosion coating to be formed on the second contact surface. For example, the anti-corrosion lubricant can be applied by a spraying method. The anti-corrosion lubricant can also be applied with a brush. Another known method can be used to apply the anti-corrosion lubricant to the second contact surface to form the anti-corrosion coating.

Optional stage.

The stage of formation of the coating obtained by chemical treatment.

In the case of forming the chemically treated coating 90 on the second contact surface, the step of forming the chemically treated coating may be performed after the step of adjusting the roughness of the second contact surface and before the step of forming the anti-corrosion coating. In other words, the step of forming the chemically treated coating is optional and does not have to be performed.

In the case of performing the stage of forming the coating obtained by chemical treatment, the known chemical treatment is performed at the stage of forming the coating obtained by chemical treatment, which allows forming the coating obtained by chemical treatment 90 on the second contact surface after adjusting the roughness of the second contact surface. Chemical treatment can be performed in a known manner. As a solution for treatment, one can use

- 17 047428 use a known chemical solution. For example, if the chemically treated coating 90 is formed by a phosphate chemical treatment, in one example, the solution that can be mentioned is a zinc phosphate chemical treatment solution containing 1 to 150 g/L of phosphate ions, 3 to 70 g/L of zinc ions, 1 to 100 g/L of nitrate ions, and 0 to 30 g/L of nickel ions. A manganese phosphate solution can also be used for the chemical treatment. The temperature of the solution is, for example, from normal temperature to 100°C. The treatment time can be appropriately set depending on the desired coating thickness, and is, for example, 5 to 20 minutes. In order to facilitate the formation of the chemically treated coating, surface modification can be performed before the chemical treatment. Surface modification refers to a treatment involving immersion in an aqueous solution containing colloidal titanium to modify the surface. After chemical treatment, rinsing with water or warm water before drying is preferred.

The metal pipe for an oil well according to this embodiment can be manufactured using the above-described production processes.

Examples

Examples are disclosed below. However, the metal pipe for an oil well according to the present embodiment is not limited to the examples. The symbol % used in the examples means weight % unless otherwise specified.

Example 1.

Metallic oil well pipes of various designs were prepared. The following test was performed using the metal oil well pipes thus prepared, and the yield torque (ft-lbs) was measured. First, the metal oil well pipes shown in Table 1 were prepared.

Table 1

Test No. Outside Diameter (inch) Wall thickness, (mm) Steel grade Second contact surface First contact surface Yield point torque coefficient Metalized layer Solid lubricant layer Blasting Ra (µm) Zinc Phosphate Anti-corrosion coating Type 11 7 10.36 L80 - <0.5 Yes Liquid anti-corrosion coating Zn-Ni Yes 100% 12 7 10.36 L80 - <0.5 - Semi-hard anti-corrosion coating Zn-Ni Yes 102% 13 7 10.36 L80 Yes 2,5 Yes Liquid anti-corrosion coating Zn-Ni Yes 122% 14 7 10.36 L80 Yes 2,4 - Semi-hard anti-corrosion coating Zn-Ni Yes 122% 15 7 10.36 L80 Yes 2,5 Yes Yellow additive Zn-Ni Yes 134% 16 7 10.36 L80 Yes 2.7 - Yellow additive Zn-Ni Yes 168%

The outside diameter of the metallic oil well tubular goods in Tests Nos. 11-16 was 7 inches (177.80 mm) and the wall thickness was 10.36 mm. The chemical composition of each metallic oil well tubular goods was L80 as defined in API-5CT.

In tests Nos. 11 to 16, the first contact surface was considered to be the coupling contact surface, and the second contact surface was considered to be the nipple contact surface. A metallized layer of Zn-Ni alloy was formed on the first contact surface for each test number. Specifically, the first contact surface was dipped in a plating solution and plated by electrodeposition to form a metallized layer of Zn-Ni alloy on the first contact surface. DAIN Zinalloy N2-PL (trade name) produced by Daiwa Fine Chemicals Co., Ltd. was used as the plating solution for the metallized layer of Zn-Ni alloy. In each test, the chemical composition of the metallized layer of Zn-Ni alloy formed in the above-mentioned manner contained nickel in an amount of 10 to 16 weight %, with the remainder being zinc. Note that the thickness of the metallized layer of Zn-Ni alloy for each test number was 5 to 15 μm. In addition, a solid lubricant layer was formed on the metallized layer of the Zn-Ni alloy. Specifically, an organic liquid composition was applied to the metallized layer of the Zn-Ni alloy. The organic liquid composition contained epoxy resin, pure water, ethylene glycol mono-n-butyl ether, isopropyl alcohol, 1-butanol and PTFE particles. After applying the organic liquid composition to the metallized layer of the Zn-Ni alloy by spraying, a known curing procedure was performed, thereby obtaining a solid lubricant layer. Specifically,

- 18 047428 were pre-dried (at 85°C for 10 min) and sintered (at 210°C for 20 min) for curing. The average thickness of the obtained solid lubricant layer was 20 to 30 μm in each test. The second contact surface was sandblasted in tests Nos. 13 to 16. The arithmetic mean roughness value Ra of the second contact surface after sandblasting was measured according to the method for measuring the arithmetic mean roughness value specified in JIS B 0601 (2013). Specifically, 10 arbitrary points on the second contact surface were taken as the measurement points. At each measurement point, the arithmetic mean roughness value Ra was measured along the evaluation length oriented in the direction of the pipe axis. The evaluation length was set to a multiple of five times the sampling length (limit wavelength). The arithmetic mean value of roughness Ra was measured using a probe roughness meter, and the measurement speed was set to 0.5 mm/s. The arithmetic mean value of roughness Ra was taken as the arithmetic mean value of roughness at six of 10 points, excluding the highest arithmetic mean value of roughness Ra, the next highest arithmetic mean value of roughness Ra, the lowest arithmetic mean value of roughness Ra, and the next lowest arithmetic mean value of roughness Ra. A surface roughness tester with the trade name SURFTEST SJ-301 manufactured by Mitutoyo Corporation was used as a contact roughness meter. The obtained arithmetic mean value of roughness Ra (μm) is given in Table 1. 1. Note that the second contact surface in tests No. 11 and 12 was not subjected to sandblasting (marked with the symbol - in the Blasting column of Table 1). The arithmetic mean value of the roughness Ra of the second contact surface of the metal pipe for an oil well in tests No. 11 and 12, in which sandblasting was not carried out, was approximately 0.2 μm, respectively, that is, it was below 0.5 μm. The arithmetic mean value of the roughness Ra of the second contact surface of the metal pipe for an oil well in tests No. 13-16 was 2.7, that is, each of these values was in the range from 0.5 to 10.0 μm.

In addition, in Tests No. 11, 13 and 15, the second contact surface (the contact surface of the nipple) was dipped into a zinc phosphate chemical treatment solution (PALBOND 181X (trade name), manufactured by Nihon Parkerizing Co., Ltd.) at a temperature of 75 to 85°C for 10 min, which formed a zinc phosphate chemical treatment layer. The thickness of the zinc phosphate chemical treatment layer was 12 μm. Note that the zinc phosphate chemical treatment layer was not formed on the second contact surface in Tests No. 12, 14 and 16 (marked with the symbol - in the Zinc Phosphate column of Table 1).

In tests No. 11 and 13, an anticorrosive coating was formed on the layer obtained by chemical treatment with zinc phosphate. In particular, a liquid anticorrosive coating was formed on the layer obtained by chemical treatment with zinc phosphate in tests No. 11 and 13. In addition, a semi-solid (in the state of consistent grease) anticorrosive coating was formed on the second contact surface in tests No. 12 and 14. A semi-solid anticorrosive coating containing a yellow additive was formed on the second contact surface in tests No. 15 and 16. In each of the tests, a liquid or semi-solid anticorrosive lubricant was sprayed onto the surface of the layer obtained by chemical treatment with zinc phosphate or the second contact surface from a distance of 300 mm to form a liquid or semi-solid anticorrosive coating. Alternatively, a liquid or semi-solid anticorrosive lubricant was applied by a brush to the surface of the layer obtained by chemical treatment with zinc phosphate or the second contact surface to form a liquid or semi-solid anticorrosive coating. In the spray coating, the metal pipe for an oil well was rotated around its central axis, and a liquid or semi-solid anticorrosive coating was formed on the entire surface of the layer obtained by chemical treatment with zinc phosphate or the entire second contact surface.

Note that the liquid anticorrosive lubricant contained white spirit in an amount of 50 to 75% by weight and mineral oil in an amount of 25% by weight or less. The semi-solid anticorrosive lubricant contained (in weight %) purified mineral oil in an amount of 20 to 30%, mineral wax in an amount of 8 to 13%, graphite in an amount of 3 to 5%, and rosin in an amount of 5 to 10%, the rest being calcium sulfonate. As disclosed above, in Tests No. 15 and 16, yellow additive (BoL4010NM (trade name) manufactured by Bestolife Corporation) was used as the semi-solid anticorrosive lubricant.

The metal pipes for oil well testing No. 11-16 were manufactured using the manufacturing process disclosed above.

Measurement of yield torque.

The yield torque was measured in the following manner using a pair (two) of metal oil well pipes (metal oil well pipes with a wedge-shaped thread profile and no thrust surface) in each test. Specifically, the tightening torque value was gradually increased at a tightening speed of 0.5 rpm, and the test was completed

- 19 047428 was at the point where the material acquired yield properties. The torque during make-up was measured and the torque graph shown in Fig. 14 was plotted. The reference symbols Ts in Fig. 14 denote the torque at the stop. The line segment L is a straight line that has the same slope as the slope of the linear region of the torque graph after the stop and for which the number of turns is 0.2% greater than the number in the linear region. In the present example, the torque value at which the line segment L and the torque graph intersect was defined as the torque Ty at the yield point. The ratio (%) of the yield torque Ty in each test to the yield torque Ty in test No. 11, in which the second contact surface was not sandblasted, was defined as the yield torque coefficient. The yield torque coefficient is shown in Table 1.

Evaluation results.

As shown in Table 1, in Tests No. 13-16, a Zn-Ni alloy metallized layer and a solid lubricant layer were deposited on the first contact surface, the second contact surface was sandblasted, the surface roughness was 0.5 to 10.0 μm, and a semi-solid or liquid anticorrosive coating was formed on the second contact surface. Therefore, the yield torque coefficient was high compared with Tests No. 11 and 12 in which the second contact surface was not sandblasted. In other words, excellent high torque was obtained.

Example 2.

Metal pipes for oil wells were prepared, shown in Table 2.

Table 2

Test No. Outside Diameter (in.) Wall thickness (mm) Steel grade Second contact surface First contact surface Yield point torque coefficient Metalized layer Solid lubricant layer Blasting Ra (µm) Zinc Phosphate Anti-corrosion coating Type 21 7 10.36 L8013CR - <0.5 - Liquid anti-corrosion coating Zn-Ni Yes 100% 22 7 10.36 L8013CR - <0.5 - Semi-hard anti-corrosion coating Zn-Ni Yes 94% 23 7 10.36 L8013CR Yes 2,4 - Liquid anti-corrosion coating Zn-Ni Yes 146% 24 7 10.36 L8013CR Yes 2.7 - Semi-hard anti-corrosion coating Zn-Ni Yes 131%

The outside diameter of the metallic oil well tubular goods in Tests No. 21-24 was 7 inches (177.80 mm) and the wall thickness was 10.36 mm. The chemical composition of each metallic oil well tubular goods conformed to L80-13CR as defined in API-5CT.

In tests No. 21-24, the first contact surface was considered to be the coupling contact surface, and the second contact surface was considered to be the nipple contact surface. The metallized layer of Zn-Ni alloy was formed on the first contact surface for each test number in the same manner as in Example 1. In each of the tests, the chemical composition of the metallized layer of Zn-Ni alloy contained nickel in an amount of 10 to 16 weight %, with the remainder being zinc. The thickness of the metallized layer of Zn-Ni alloy for each test number was from 5 to 15 μm.

In addition, a solid lubricant layer of the same type as in Example 1 was formed on the metallized layer of Zn-Ni alloy. In each test, the average thickness of the resulting solid lubricant layer was 20 to 30 μm.

On the other hand, the second contact surface in Tests Nos. 23 and 24 was subjected to sandblasting in the same manner as in Example 1. The arithmetic mean value of roughness Ra of the second contact surface after sandblasting was measured in the same manner as in Example 1. The obtained arithmetic mean value of roughness Ra (μm) is given in Table 2. Note that the second contact surface in Tests Nos. 21 and 22 was not subjected to sandblasting (marked with the symbol - in the Blasting column of Table 2). The arithmetic mean value of roughness Ra of the second contact surface of the metal pipe for oil wells in Tests Nos. 21 and 22, in which sandblasting was not performed, was approximately 0.2 μm, respectively, that is, it was lower than 0.5 μm.

The anticorrosive coating was formed on the second contact surface in each test. Specifically, the liquid anticorrosive coating was formed on the second contact surface in Tests Nos. 21 and 23. In addition, the semi-solid anticorrosive coating was formed on the second contact surface in Tests Nos. 22 and 24. The forming methods are similar to Example 1. The metal pipes for oil wells for Tests Nos. 21-24 were manufactured by the above-described production process.

Measurement of yield torque.

The yield torque coefficient of the metal pipe for an oil well in each test number was determined similarly to Example 1.

Evaluation results.

As shown in Table 2, in Tests No. 23 and 24, a Zn-Ni alloy metallized layer and a solid lubricant layer were deposited on the first contact surface, the second contact surface was sandblasted, the surface roughness was 0.5 to 10.0 μm, and a liquid or semi-solid anticorrosive coating was formed on the second contact surface. Therefore, the yield torque coefficient was high compared with Tests No. 21 and 22 in which the second contact surface was not sandblasted. In other words, excellent high torque was obtained.

Example 3.

Metal pipes for oil well were prepared, shown in Table 3.

Table 3

Test No. Outside Diameter (in.) Wall thickness (mm) Steel grade Second contact surface First contact surface Yield point torque coefficient Metalized layer Solid lubricant layer Blasting Ra (µm) Zinc Phosphate Anti-corrosion coating Type 31 9-5/8 13.84 P110 - <0.5 - Liquid anti-corrosion coating Zn-Ni Yes 100% 32 9-5/8 13.84 P110 Yes 2,4 - Liquid anti-corrosion coating Zn-Ni Yes 121%

The outside diameter of the metallic oil well tubular goods in Tests No. 31-32 was 9-5/8 inches (244.475 mm) and the wall thickness was 13.84 mm. The chemical composition of each metallic oil well tubular goods was P110 as defined in API-5CT.

In tests No. 31 and 32, the first contact surface was considered to be the coupling contact surface, and the second contact surface was considered to be the nipple contact surface. The metallized layer of Zn-Ni alloy was formed on the first contact surface for each test number in the same manner as in example 1. In each of the tests, the chemical composition of the metallized layer of Zn-Ni alloy contained nickel in an amount of 10 to 16 weight %, with the remainder being zinc. The thickness of the metallized layer of Zn-Ni alloy for each test number was from 5 to 15 μm.

In addition, a solid lubricant layer of the same type as in Example 1 was formed on the metallized layer of Zn-Ni alloy. In each test, the average thickness of the obtained solid lubricant layer was 20 to 30 μm. On the other hand, the second contact surface in Test No. 32 was sandblasted in the same manner as in Example 1. The arithmetic mean roughness value Ra of the second contact surface after sandblasting was measured in the same manner as in Example 1. The obtained arithmetic mean roughness value Ra (μm) is given in Table 3. Note that the second contact surface in Test No. 31 was not sandblasted (marked with the symbol - in the Blasting column of Table 3). The arithmetic mean value of the roughness Ra of the second contact surface of the metal pipe for oil well in test No. 31, in which sandblasting was not carried out, was approximately 0.2 μm, respectively, that is, it was lower than 0.5 μm.

The anticorrosive coating was formed on the second contact surface in each test. Specifically, the semi-solid anticorrosive coating was formed on the second contact surface in Tests No. 31 and 32. The forming methods were similar to Example 1. The metal pipes for oil wells for Tests No. 31 and 32 were manufactured by the above-described manufacturing process.

Measurement of yield torque and evaluation results.

The yield torque coefficient of the metal oil well pipe in each test number was determined similarly to Example 1. As shown in Table 3, in test No. 32, a Zn-Ni alloy metallized layer and a solid lubricant layer were applied to the first contact surface, the second contact surface was sandblasted, the surface roughness was from 0.5 to 10.0 μm, and a liquid anticorrosive coating was formed on the second contact surface. Therefore, the yield torque coefficient

- 21 047428 yield was high compared to test No. 31, in which the second contact surface was not sandblasted. In other words, excellent high torque was obtained.

Example 4.

Metal pipes for oil wells were prepared, shown in Table 4.

Table 4

Test No. Outside Diameter (in.) Wall thickness (mm) Steel grade Second contact surface First contact surface Yield point torque coefficient Metalized layer Solid lubricant layer Blasting Ra (µm) Zinc Phosphate Anti-corrosion coating Type 41 7 11.51 SM13CRS- 110 - <0.5 - Semi-hard anti-corrosion coating Zn-Ni Yes 100% 42 7 11.51 SM13CRS- 110 - <0.5 - Liquid anti-corrosion coating Zn-Ni Yes 99% 43 7 11.51 SM13CRS- 110 Yes 2,5 - Semi-hard anti-corrosion coating Zn-Ni Yes 118%

The outside diameter of the metal oil well pipe in Test No. 41-43 was 7 inches (177.80 mm) and the wall thickness was 11.51 mm. The material with the trade name SM13CRS-110 manufactured by Nippon Steel Corporation was used to manufacture the metal oil well pipe.

In tests No. 41-43, the first contact surface was considered to be the coupling contact surface, and the second contact surface was considered to be the nipple contact surface. The metallized layer of Zn-Ni alloy was formed on the first contact surface for each test number in the same way as in example 1. In each of the tests, the chemical composition of the metallized layer of Zn-Ni alloy contained nickel in an amount of 10 to 16 weight %, with the remainder being zinc. The thickness of the metallized layer of Zn-Ni alloy for each test number was from 5 to 15 μm.

In addition, a solid lubricant layer of the same type as in Example 1 was formed on the metallized layer of Zn-Ni alloy. In each test, the average thickness of the obtained solid lubricant layer was 20 to 30 μm. On the other hand, the second contact surface in Test No. 43 was sandblasted in the same manner as in Example 1.

The arithmetic mean value of the roughness Ra of the second contact surface after sandblasting was measured in the same manner as in Example 1. The obtained arithmetic mean value of the roughness Ra (μm) is given in Table 4. Note that the second contact surface in tests No. 41 and 42 was not subjected to sandblasting (marked with the symbol - in the Blasting column of Table 4). The arithmetic mean value of the roughness Ra of the second contact surface of the metal pipe for an oil well in tests No. 41 and 42, in which sandblasting was not carried out, was approximately 0.2 μm, respectively, that is, it was below 0.5 μm.

The anticorrosive coating was formed on the second contact surface in each test. Specifically, the semi-solid anticorrosive coating was formed on the second contact surface in Tests No. 41 and 43. In addition, the liquid anticorrosive coating was formed on the second contact surface in Test No. 42. The forming methods are similar to Example 1. The metal pipes for oil wells for Tests No. 41-43 were manufactured by the above-described production process.

Measurement of Yield Torque and Evaluation Results The yield torque coefficient of the metal pipe for oil well in each test number was determined similarly to Example 1. As shown in Table 4, in Test No. 43, a Zn-Ni alloy metallized layer and a solid lubricant layer were applied to the first contact surface, the second contact surface was sandblasted, the surface roughness was 0.5 to 10.0 μm, and a semi-hard anticorrosive coating was formed on the second contact surface. Therefore, the yield torque coefficient was high compared with Tests No. 41 and 42 in which the second contact surface was not sandblasted. In other words, excellent high torque was obtained. Example 5

Metal pipes for oil wells were prepared, shown in Table 5.

- 22 047428

Table 5

Test No. Outside Diameter (in.) Wall thickness (mm) Steel grade Second contact surface First contact surface Yield point torque coefficient Metalized layer Solid lubricant layer Blasting Ra (µm) Zinc Phosphate Anti-corrosion coating Type 51 4-1/2 6.88 L80- 13CR - <0.5 - Liquid anti-corrosion coating Zn-Ni Yes 100% 52 4-1/2 6.88 L80- 13CR - <0.5 - Semi-hard anti-corrosion coating Zn-Ni Yes 95% 53 4-1/2 6.88 L80- 13CR Yes 2.7 - Liquid anti-corrosion coating Zn-Ni Yes 149% 54 4-1/2 6.88 L80- 13CR Yes 2,5 - Semi-hard anti-corrosion coating Zn-Ni Yes 136%

The outside diameter of the metallic oil well tubular goods in Tests No. 51-54 was 4.5 inches (114.3 mm) and the wall thickness was 6.88 mm. The chemical composition of each metallic oil well tubular goods was L80-13CR as defined in API-5CT.

In tests No. 51-54, the first contact surface was considered to be the coupling contact surface, and the second contact surface was considered to be the nipple contact surface. A metallized layer of Zn-Ni alloy was formed on the first contact surface for each test number in the same manner as in Example 1. In each of the tests, the chemical composition of the metallized layer of Zn-Ni alloy contained nickel in an amount of 10 to 16 weight %, with the remainder being zinc. The thickness of the metallized layer of Zn-Ni alloy for each test number was from 5 to 15 μm.

In addition, a solid lubricant layer of the same type as in Example 1 was formed on the metallized layer of Zn-Ni alloy. In each test, the average thickness of the obtained solid lubricant layer was 20 to 30 μm. On the other hand, the second contact surface in Tests No. 53 and 54 was sandblasted in the same manner as in Example 1. The arithmetic mean roughness value Ra of the second contact surface after sandblasting was measured in the same manner as in Example 1. The obtained arithmetic mean roughness value Ra (μm) is given in Table 5. Note that the second contact surface in Tests No. 51 and 52 was not sandblasted (marked with the symbol - in the Blasting column of Table 5). The arithmetic mean value of the roughness Ra of the second contact surface of the metal pipe for oil well in tests No. 51 and 52, in which sandblasting was not carried out, was approximately 0.2 μm, respectively, that is, it was lower than 0.5 μm.

The anticorrosive coating was formed on the second contact surface in each test. Specifically, the liquid anticorrosive coating was formed on the second contact surface in Tests No. 51 and 53. In addition, the semi-solid anticorrosive coating was formed on the second contact surface in Tests No. 52 and 54. The forming methods are similar to Example 1. The metal pipes for oil wells for Tests No. 51-54 were manufactured by the above-described production process.

Measurement of Yield Torque and Evaluation Results The yield torque coefficient of the metal pipe for oil well in each test number was determined similarly to Example 1. As shown in Table 5, in Tests No. 53 and 54, a Zn-Ni alloy metallized layer and a solid lubricant layer were deposited on the first contact surface, the second contact surface was sandblasted, the surface roughness was 0.5 to 10.0 μm, and a semi-solid or liquid anticorrosive coating was formed on the second contact surface. Therefore, the yield torque coefficient was high compared with Tests No. 51 and 52 in which the second contact surface was not sandblasted. In other words, excellent high torque was obtained.

Example 6.

Metal pipes for oil wells were prepared, shown in Table 6.

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Table 6

Test No. Outside Diameter (in.) Wall thickness (mm) Steel grade Second contact surface First contact surface Yield point torque coefficient Metalized layer Solid lubricant layer Blasting Ra (µm) Zinc Phosphate Anti-corrosion coating Type 61 4-1/2 6.88 SM13CRS- 110 - <0.5 - Liquid anti-corrosion coating Zn-Ni Yes 100% 62 4-1/2 6.88 SM13CRS- 110 - <0.5 - 11 semi-hard anti-corrosion coating Zn-Ni Yes 108% 63 4-1/2 6.88 SM13CRS- 110 Yes 2,4 - Liquid anti-corrosion coating Zn-Ni Yes 154% 64 4-1/2 6.88 SM13CRS- 110 Yes 2.6 - 11 semi-hard anti-corrosion coating Zn-Ni Yes 138%

The outside diameter of the metal oil well pipe in Test No. 61-64 was 4.5 inches (114.3 mm) and the wall thickness was 6.88 mm. The material with the trade name SM13CRS-110 manufactured by Nippon Steel Corporation was used to manufacture the metal oil well pipe.

In tests No. 61-64, the first contact surface was considered to be the coupling contact surface, and the second contact surface was considered to be the nipple contact surface. The metallized layer of Zn-Ni alloy was formed on the first contact surface for each test number in the same manner as in Example 1. In each of the tests, the chemical composition of the metallized layer of Zn-Ni alloy contained nickel in an amount of 10 to 16 weight %, with the remainder being zinc. The thickness of the metallized layer of Zn-Ni alloy for each test number was from 5 to 15 μm.

In addition, a solid lubricant layer of the same type as in Example 1 was formed on the metallized layer of Zn-Ni alloy. In each test, the average thickness of the obtained solid lubricant layer was 20 to 30 μm. On the other hand, the second contact surface in Tests No. 63 and 64 was sandblasted in the same manner as in Example 1. The arithmetic mean roughness value Ra of the second contact surface after sandblasting was measured in the same manner as in Example 1. The obtained arithmetic mean roughness value Ra (μm) is given in Table 6. Note that the second contact surface in Tests No. 61 and 62 was not sandblasted (marked with the symbol - in the Blasting column of Table 6). The arithmetic mean value of the roughness Ra of the second contact surface of the metal pipe for oil well in tests No. 61 and 62, in which sandblasting was not carried out, was approximately 0.2 μm, respectively, that is, it was lower than 0.5 μm.

The anticorrosive coating was formed on the second contact surface in each test. Specifically, the liquid anticorrosive coating was formed on the second contact surface in Tests No. 61 and 63. In addition, the semi-solid anticorrosive coating was formed on the second contact surface in Tests No. 62 and 64. The forming methods are similar to Example 1. The metal pipes for oil wells for Tests No. 61-64 were manufactured by the above-described production process.

Measurement of yield torque and evaluation results.

The yield torque coefficient of the metal pipe for oil well in each test number was determined similarly to Example 1. As shown in Table 6, in Tests No. 63 and 64, a Zn-Ni alloy metallized layer and a solid lubricant layer were applied to the first contact surface, the second contact surface was sandblasted, the surface roughness was 0.5 to 10.0 μm, and a semi-solid or liquid anticorrosive coating was formed on the second contact surface. Therefore, the yield torque coefficient was high compared with Tests No. 61 and 62 in which the second contact surface was not sandblasted. In other words, excellent high torque was obtained.

Example 7.

Oil well metal pipes of various designs were prepared. Using the prepared oil well metal pipes, the following cyclic make-up tests were performed and the galling resistance was evaluated. First, the oil well metal pipes shown in Table 7 were prepared.

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Table 7

Test No. Outside Diameter (inch) Wall thickness (mm) Steel grade Second contact surface First contact surface Number of screwing cycles Blasting Zinc Phosphate Anti-corrosion coating Metalized layer Solid lubricant 71 7 11.51 SM13CRS- 110 - - Liquid anti-corrosion coating Zn-Ni Yes 10 72 7 11.51 SM13CRS- 110 - - 11 semi-hard anti-corrosion coating Zn-Ni Yes 10 73 7 11.51 SM13CRS- 110 Yes - Liquid anti-corrosion coating Zn-Ni Yes 7 74 7 11.51 SM13CRS- 110 Yes - 11 semi-hard anti-corrosion coating Zn-Ni Yes 6 75 7 11.51 SM13CRS- 110 Yes - Liquid anti-corrosion coating Zn-Ni Yes 10 76 7 11.51 SM13CRS- 110 Yes - 11 semi-hard anti-corrosion coating Zn-Ni Yes 10 77 7 11.51 SM13CRS- 110 Yes - Liquid anti-corrosion coating Zn-Ni Yes 10 78 7 11.51 SM13CRS- 110 Yes - 11 semi-hard anti-corrosion coating Zn-Ni Yes 10 79 7 12.65 SM13CRS- 110 - - Liquid anti-corrosion coating Zn-Ni Yes 10 80 7 12.65 SM13CRS- 110 - - 11 semi-hard anti-corrosion coating Zn-Ni Yes 10 81 7 12.65 SM13CRS- 110 Yes - Liquid anti-corrosion coating Zn-Ni Yes 10 82 7 12.65 SM13CRS- 110 Yes - 11 semi-hard anti-corrosion coating Zn-Ni Yes 10 83 7 11.51 SM13CRS- 110 Yes - Yellow additive Zn-Ni Yes 10

The outside diameter of the metallic oil well tubular goods in Test Nos. 71 to 83 was 7 inches (177.80 mm), and the wall thickness was 11.51 mm or 12.65 mm. As for the metallic oil well tubular goods in Test Nos. 71 to 83, the material used for these tests had the trade name SM13CRS-110 manufactured by Nippon Steel Corporation. In Test Nos. 71 to 83, the first contact surface was considered to be the contact surface of the coupling, and the second contact surface was considered to be the contact surface of the pin. A metallized layer of Zn-Ni alloy was formed on the first contact surface for each test number in the same manner as in Example 1. In each of the tests, the chemical composition of the metallized layer of Zn-Ni alloy contained nickel in an amount of 10 to 16 weight %, with the balance being zinc. The thickness of the metallized layer of Zn-Ni alloy for each test number ranged from 5 to 15 µm.

In addition, a solid lubricant layer of the same type as in Example 1 was formed on the metallized layer of Zn-Ni alloy. In each test, the average thickness of the obtained solid lubricant layer was 20 to 30 μm. On the other hand, the second contact surface in Tests Nos. 73 to 78, 81 and 82 was sandblasted in the same manner as in Example 1. The arithmetic mean roughness value Ra of the second contact surface after sandblasting was measured in the same manner as in Example 1. The obtained arithmetic mean roughness value Ra (μm) in each test was approximately 2.5 μm, that is, in the range of 0.5 to 10.0 μm. Note that the second contact surface in tests No. 71, 72, 79 and 80 was not subjected to sandblasting (marked with the symbol - in the Blasting column of Table 7). The arithmetic mean value of the roughness Ra of the second contact surface in tests in which sandblasting was not carried out was approximately 0.2 μm, i.e., it was below 0.5 μm.

An anticorrosive coating was formed on the second contact surface in each test. Specifically, a liquid anticorrosive coating was formed on the second contact surface in Tests Nos. 71, 73, 75, 77, 79, and 81. In addition, a semi-solid anticorrosive coating was formed on the second contact surface in Tests Nos. 72, 74, 76, 78, 80, and 82. The formation methods are similar to Example 1. Note that in Test No. 83, a yellow additive was applied and a semi-solid anticorrosive coating was formed. The metal pipes for an oil well for Tests Nos. 71-83 were manufactured by the above-described production process.

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Claims (1)

Scoring resistance test. The evaluation of the galling resistance was conducted by the repeated make-up test. In Test Nos. 71-83 in Table 7, make-up and loose-fitting were repeated at room temperature (20°C) using a pair (two) of metal oil well pipes in each test, and the galling resistance was evaluated. The tightening torque was set to 24350 N m. After each make-up and loose-fitting cycle, the contact surface of the pin and the contact surface of the box were visually inspected. The occurrence level of galling on the thread parts, the sealing surface of the pin and the sealing surface of the box were checked by visual inspection. As for the sealing surface of the pin and the sealing surface of the box, the test was terminated when the galling occurrence was confirmed. If the galling on the threaded part was insignificant and could be repaired by restoring by filing or the like, the galling was removed and the test was continued. The maximum number of make-up cycles is taken to be 10. The highest number (not more than 10) of make-up cycles without the formation of irreparable burrs on a part of the thread or the formation of burrs on the sealing surface of the pin and the sealing surface of the coupling was taken as an evaluation indicator of the resistance to scuffing. The results are shown in the column Number of Make-up Cycles in Table 7. The API standard specifies that the number of make-up cycles for a 7-inch casing pipe should not be less than three. Thus, it was established that high resistance to scuffing is demonstrated in the case when the number of make-up cycles is three or more. Evaluation results. As shown in Table 7, in each of tests No. 71-83, the number of make-up cycles was three or more, that is, the metal pipes for oil wells that passed these tests have high resistance to scuffing. An embodiment of the present invention has been disclosed above. However, the above embodiment of the invention is only one example of implementing the present invention. Accordingly, the present invention is not limited to the above embodiment, and the above embodiment of the invention can be appropriately changed and implemented within the scope without departing from the essence of the present invention. List of reference designations: 1 - metal pipe for oil well; 10 - main body of the pipe; 10A - first end part; 10B - the second end part; 11 - tubular body of the nipple; 12 - coupling sleeve; 40 - nipple; 50 - coupling; 60 - metallized layer; 70 - solid lubricant layer; 80 - anti-corrosion coating; 90 - coating obtained by chemical treatment; 400 - nipple contact surface; 500 - coupling contact surface. CLAUSE OF THE INVENTION 1. A metal pipe for an oil well, comprising: a main body of a pipe comprising a first end portion and a second end portion, wherein the main body of the pipe comprises a nipple formed on the first end portion and a coupling formed on the second end portion; the nipple comprises a nipple contact surface comprising at least a portion with an external thread formed on the outer peripheral surface of the first end portion of the main body of the pipe; The coupling contains: a coupling contact surface comprising at least a portion with an internal thread formed on the inner peripheral surface of the second end portion of the main body of the pipe; a metallized layer is formed on the first contact surface, wherein the first contact surface is one surface of the contact surface of the nipple and the contact surface of the coupling; a layer of solid lubricant is formed on the metallized layer; -