RU2802489C1 - Threaded connection for pipe and method for manufacturing threaded connection for pipe - Google Patents

Abstract

FIELD: threaded connections for pipes.

SUBSTANCE: method for manufacturing a threaded connection for pipes is also described. The threaded connection for pipes comprises a nipple (3), a sleeve (4) and a metallized layer (100) made of Zn-Ni alloy. The nipple (3) comprises a contact surface (34) containing a part (31) with an external thread. The sleeve (4) comprises a contact surface (44) containing a part (41) with an internal thread. The metallized layer (100) of the Zn-Ni alloy is located on at least one surface of the contact surface of the nipple (34) and the contact surface (44) of the sleeve. The metallized layer (100) of the Zn-Ni alloy comprises graphite.

EFFECT: invention has excellent galling resistance and can prevent loosening when used in a horizontal wellbore.

10 cl, 12 dwg, 1 tbl

Description

TECHNICAL FIELD

[0001] The present description of the invention relates to a threaded connection for pipes and a method for manufacturing a threaded connection for pipes.

BACKGROUND ART

[0002] For drilling in oil or natural gas fields, oilfield tubular products are used. Oilfield tubular products are made by connecting several pipes in accordance with the depth of the well. Pipes are connected by screwing together threaded pipe connections made at the end parts of the pipes. Oilfield tubular products are tightened and loosened for inspection or other operations, and after inspection are tightened and reused.

[0003] A threaded pipe connection includes a nipple and a coupling. The nipple comprises a nipple contact surface comprising a male threaded portion formed on an outer peripheral surface of the end portion of the pipe. The pin contact surface may include a metal pin seal portion and a pin thrust portion. The coupling contains a coupling contact surface containing a part with an internal thread made on the inner peripheral surface of the end part of the pipe. The coupling contact surface may comprise a metal coupling sealing portion and a coupling thrust portion. In the following, the pin contact surface and the coupling contact surface will be referred to simply as the “contact surface.”

[0004] When fixing the pipes, the contact surface of the nipple and the contact surface of the coupling are in contact with each other. Accordingly, the pin contact surface and the coupling contact surface repeatedly experience strong friction when fixing and loosening the pipes. If such areas are not sufficiently resistant to friction, repeated fixing and loosening will lead to the formation of scoring (seizing that cannot be removed). Consequently, threaded connections for pipes must have sufficient resistance to friction, in particular high resistance to galling.

[0005] To improve resistance to scuffing, the prior art uses a compound lubricant containing heavy metals. Applying a compound grease to the surface of a pipe threaded joint can improve the galling resistance of the pipe threaded joint. However, heavy metals such as Pb contained in compound lubricants may have an environmental impact. Therefore, there is a need to develop a threaded connection for pipes that does not require the use of compound lubricant.

[0006] Japanese Patent Application Published No. 05-149485 (Patent Document 1) proposes a threaded joint technology for pipes having excellent scuffing resistance. The threaded pipe connection disclosed in Patent Document 1 forms a dispersed metallized layer on the surface of a pin or coupling, wherein one or more kinds of non-metallic phases and one additional metallic phase are dispersed in the dispersed metallized layer, which become a eutectoid state in a metal matrix. According to Patent Document 1, the result is a pipe thread connection having excellent scuffing resistance even when fixed and loosened using a heavy metal-free compound lubricant.

[0007] A number of studies, including Patent Document 1, consider improving sliding ability by dispersing a non-metallic material in a metallized layer to improve scuffing resistance or reduce the coefficient of friction. Specifically, Japanese Patent Application Published No. 2008-214666 (Patent Document 2) proposes a pipe thread joint with improved scuff resistance for dispersing a non-metallic material in a metallized layer.

[0008] The threaded pipe connection disclosed in Patent Document 2 forms a low friction composite coating layer on the surface of a base material, wherein the low friction composite coating layer contains a carbon nanomaterial and a zinc component. According to Patent Document 2, the result is a threaded pipe connection that exhibits significant friction reduction under heavy loads and locking properties that enable the threaded member to withstand harsh environmental conditions.

LIST OF MATERIALS CITED

PATENT DOCUMENTS

[0009]

Patent Document 1: Japanese Patent Application Published No. 05-149485

Patent Document 2: Japanese Patent Application Published No. 2008-214666

SUMMARY OF THE INVENTION

TECHNICAL PROBLEM

[0010] Currently, in order to increase the production of oil or natural gas, oil wells continue to be deepened. In addition to increasing the depth of oil wells, the number of horizontal wells is expected to increase in the future. A well with a horizontal end is a well drilled vertically down to a formation containing oil or natural gas (oil formation), as well as drilled along an oil formation in the horizontal direction or at an angle from the horizontal direction. In recent years, there has been a tendency to increase the length of horizontal trunks. In a well with a horizontal end, the well trajectory changes from vertical to horizontal in the middle of the well. Therefore, in the curved part, where the well trajectory changes from vertical to horizontal, all oil tubular products experience high loads. Therefore, the pipe threaded connection in the curved part is also subject to high stress. In addition, when drilling a well with a horizontal end, it is necessary to push oil-grade tubular products into the well while simultaneously rotating such products in the circumferential direction. When rotating under heavy load, the threaded pipe connection may become loose. A loose threaded connection for pipes leads to a decrease in the tightness of petroleum tubular products. Therefore, the threaded connection for pipes must be made in such a way that it is difficult to loosen even in a well with a horizontal end.

[0011] The methods disclosed in Patent Documents 1 or 2 can improve the galling resistance of a pipe threaded connection. However, Patent Documents 1 or 2 do not mention reducing the looseness of a pipe thread connection even if it is used for a horizontal well.

[0012] It is an object of the present disclosure to provide a pipe threaded joint that is highly resistant to galling and can prevent loosening even when used in a horizontal well, and to provide a method for producing a pipe threaded joint.

THE SOLUTION OF THE PROBLEM

[0013] The threaded connection for pipes according to the present description of the invention contains a nipple, a coupling and a metallized layer of a Zn-Ni alloy. The nipple includes a contact surface including a male thread portion. The coupling includes a contact surface containing a portion with an internal thread. A metallized Zn-Ni alloy layer is placed on or above at least one surface of a pin contact surface and a coupling contact surface. The metallized layer of Zn-Ni alloy contains graphite.

[0014] A method for manufacturing a threaded connection for pipes in accordance with the present description of the invention comprises a preparation step and a metallized layer formation step. At the preparation stage, the nipple, coupling and solution are prepared for applying the metallized layer. The nipple includes a contact surface containing a male thread portion. The coupling includes a contact surface containing a portion with an internal thread. The solution for applying the metallized layer contains zinc ions, nickel ions and graphite. At the stage of forming the metallized layer, at least one surface of the pin contact surface and the coupling contact surface is brought into contact with the solution for applying the metallized layer and coated by electrolytic deposition, resulting in at least one surface of the pin contact surface and A metallized layer of Zn-Ni alloy is formed on the contact surface of the coupling.

TECHNICAL RESULT OF THE INVENTION

[0015] The threaded pipe connection according to the present disclosure has high galling resistance and can prevent loosening when used in a horizontal wellbore. The method for manufacturing a threaded pipe connection in accordance with the present description of the invention makes it possible to obtain the above-disclosed threaded pipe connection.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In FIG. Figure 1 shows a diagram illustrating the results of the Bowden sliding test for samples Nos. 1, 3 and 7 in the Example.

In FIG. Figure 2 shows an illustration of the configuration of an example threaded connection for coupling-type pipes.

In FIG. Figure 3 illustrates the configuration of an example threaded connection for continuous type pipes.

In FIG. Figure 4 shows a cross-section of an example of a threaded connection for pipes.

In FIG. 5 is a sectional view of an example of a threaded connection for pipes according to the present embodiment of the invention.

In FIG. 6 is a cross-sectional view of an example of a pipe threaded connection according to another embodiment of the invention, the pipe threaded connection being different from that shown in FIG. 5.

In FIG. 7 is a sectional view of an example of a pipe threaded connection according to a further embodiment of the invention, the pipe threaded connection being different from that shown in FIG. 5 and 6.

In FIG. 8 is a sectional view of an example of a threaded connection for pipes according to the present embodiment, in which a lubricating coating is provided on the pin and the coupling.

In FIG. 9 is a sectional view of an example of a pipe thread according to another embodiment of the invention, the pipe thread being different from that shown in FIG. 8.

In FIG. 10 is a sectional view of an example of a pipe threaded connection according to a further embodiment of the invention, the pipe threaded connection being different from that shown in FIG. 8 and 9.

FIG. 11 is a diagram illustrating the results of the Bowden sliding test for samples Nos. 2, 4 and 5 in the example.

FIG. 12 is a diagram illustrating the results of the Bowden sliding test for specimens Nos. 6 and 8 in the example.

DISCLOSURE OF OPTIONS FOR IMPLEMENTING THE INVENTION

[0017] Below, embodiments of the invention will be described in detail with reference to the drawings. Identical or comparable elements will have the same reference designations and the description of the elements will not be repeated.

[0018] The inventors of the present invention primarily focused on the coefficient of friction and investigated the resistance to galling and loosening of a tubular connection that occurs when using a tubular connection in a horizontal wellbore. As a result, the following results were obtained.

[0019] The threaded connection for pipes is fixed and loosened with a prescribed torque. When locked and loosened as described above, the contact surfaces of the pin and coupling slide against each other with a high boundary pressure, for example 1.0 GPa or more, applied to the contact surfaces. In other words, the contact surfaces experience strong friction when fixed and loosened. Accordingly, when the coefficient of friction between the contact surfaces is high, the frictional heat generated during fixation and loosening increases, which facilitates sticking or scoring. In metal-to-metal contact, the likelihood of scoring is high when the coefficient of friction between metals, for example, exceeds 0.4. Therefore, usually an attempt is made to reduce the coefficient of friction between the contact surfaces by applying a lubricant or forming a metallized layer with a low coefficient of friction on the contact surfaces. For example, when using a conventional anti-corrosion additive API, the friction coefficient of contact surfaces becomes approximately 0.05 - 0.2. In this case, the formation of scoring on the contact surfaces is prevented.

[0020] At the same time, the inventors of the present invention have discovered that reducing the coefficient of friction makes it easier to loosen a threaded connection for pipes. The torque required for locking and loosening is proportional to the coefficient of friction between the contact surfaces. In particular, the higher the coefficient of friction between the contact surfaces, the higher the locking and loosening torque. A pipe threaded connection that is not subject to loosening can be obtained if the pipe threaded connection maintains a high torque when loosened. Hereinafter, the ability to maintain high torque when weakened will be referred to as high torque maintaining ability.

[0021] Accordingly, as the coefficient of friction decreases, the galling resistance of the pipe threaded joint increases, but the loosening of the pipe threaded joint becomes easier. In this case, with an increase in the coefficient of friction, loosening of the threaded connection for pipes is prevented, however, the resistance of the threaded connection for pipes to the formation of scoring is reduced. As stated above, it has been found difficult to achieve high galling resistance of a pipe threaded connection while still being able to maintain high torque.

[0022] Meanwhile, detailed studies by the inventors of the present invention have shown that in the case where said layer formed on or above the contact surfaces contains graphite, the galling resistance of the pipe threaded connection is improved, as well as the ability to maintain high torque. moment. In this regard, a detailed description will be given with reference to the drawing.

[0023] FIG. 1 is a diagram illustrating the results of the Bowden slip test of an example. FIG. 1 shows sample No. 1 showing the result of the Bowden sliding test of a metallized layer of Zn-Ni alloy containing no graphite. Sample No. 3 shows the result of the Bowden sliding test of a metallized layer of a Zn-Ni alloy containing graphite. Sample No. 7 shows the result of the Bowden sliding test on a metallized Cu layer containing graphite.

[0024] For samples No. 1 and No. 3 shown in FIG. 1, the number of slides until the coefficient of friction exceeds 0.4 for the metallized layer of Zn-Ni alloy containing graphite (sample No. 3) is greater than for the metallized layer from a Zn-Ni alloy that does not contain graphite (sample No. 1). As described above, if the coefficient of friction of a pipe threaded connection exceeds 0.4, the likelihood of scoring increases significantly. Accordingly, FIG. 1 shows that the scoring resistance of the Zn-Ni alloy metallized layer was increased due to the graphite content.

[0025] Further, sample No. 3 shown in FIG. 1, in the Zn-Ni alloy metallized layer containing graphite, had a high friction coefficient exceeding 0.2 after more than 50 slides. After the number of slips exceeded 200, the friction coefficient exceeded 0.4. Accordingly, the coefficient of friction of the Zn-Ni alloy metallized layer containing graphite was maintained at approximately 0.2 - 0.4 for 150 slides. In short, for the Zn-Ni alloy metallized layer containing graphite, the number of slips before scoring was large, as was the number of slips with a high coefficient of friction. Thus, it has become clear that a Zn-Ni alloy metallized layer containing graphite is capable of providing both excellent scuffing resistance and high torque capability.

[0026] Meanwhile, for sample No. 7 shown in FIG. 1, the friction coefficient of the Cu metallized layer containing graphite was about 0.1 until the number of slips exceeded 250. After the number of slips exceeded 300, the friction coefficient immediately exceeded 0.4. Accordingly, for a metallized layer of Cu containing graphite, the number of slips with a friction coefficient of approximately 0.2 - 0.4 turned out to be small. Thus, the Cu metallized layer containing graphite had excellent scuffing resistance and was not capable of supporting high torque.

[0027] As described above, the inventors' studies have shown that both the galling resistance and the high-torque capability of a pipe threaded connection are increased by incorporating graphite into said coating, that is, a Zn- alloy metallized layer. Ni formed on or above contact surfaces. However, the reason why the galling resistance and high-torque capability of a pipe threaded connection increases when graphite is introduced into the metallized Zn-Ni alloy layer has not yet been clarified. The inventors of the present invention believe that the reason is as follows.

[0028] The hardness of the Zn-Ni alloy coating is higher than that of conventional Cu coating. The higher the hardness, the higher the resistance to the load applied by sliding during fixation under very high boundary pressure (eg, 1.0 GPa or more). In addition, in the following example, on samples in which the coefficient of friction exceeded 0.4 in the Bowden sliding test, peeling of the metallized layers from the steel sheet was tested for each sample after the Bowden sliding test. In this case, the amount of the remaining metallized layer of the Zn-Ni alloy containing graphite (samples Nos. 2 - 5) turned out to be greater than the amount of the remaining metallized layer of the Zn-Ni alloy not containing graphite (sample No. 1). Accordingly, the graphite contained in the Zn-Ni alloy metallized layer can prevent the Zn-Ni alloy metallized layer from peeling off.

[0029] Thus, the inventors of the present invention assume that the friction coefficient of the Zn-Ni alloy metallized layer is increased by peeling off a portion of the metallized layer according to the amount of sliding. It is believed that in a partially exfoliated metallized Zn-Ni alloy layer, the friction coefficient increases to a level of 0.2 to 0.4. In addition, the graphite content of the Zn-Ni alloy metallized layer prevents the Zn-Ni alloy metallized layer from peeling off, that is, the friction coefficient can be maintained at 0.2 to 0.4. In addition, this trend is not confirmed for the metallized Cu layer containing graphite. Thus, the metallized layer of the Zn-Ni alloy is characterized in that the graphite prevents the metallized layer from peeling off, which makes it possible to maintain the coefficient of friction at a level of 0.2 to 0.4.

[0030] The inventors of the present invention believe that, due to the above mechanism, a threaded connection for pipes having a metallized layer of Zn-Ni alloy containing graphite is characterized by both excellent resistance to galling and increased ability to maintain high torque. It should be noted that when using a mechanism different from the above mechanism, there is a possibility that the Zn-Ni alloy metallized layer containing graphite will improve the scoring resistance and high torque supporting ability of the pipe threaded connection. However, the examples described below have shown that excellent pipe thread galling resistance and increased high torque capability can be achieved by containing graphite in the Zn-Ni alloy metallized layer.

[0031] A threaded pipe connection according to the present embodiment of the invention based on the above includes a nipple, a coupling and a metallized layer of a Zn-Ni alloy. The nipple includes a contact surface including a male thread portion. The coupling includes a contact surface containing a portion with an internal thread. A metallized Zn-Ni alloy layer is placed on or above at least one surface of a pin contact surface and a coupling contact surface. The metallized layer of Zn-Ni alloy contains graphite.

[0032] The threaded pipe connection according to the present embodiment includes a metallized layer of Zn-Ni alloy containing graphite. Thus, the threaded pipe connection according to the present embodiment has excellent scuffing resistance and high torque supporting ability. Thus, the pipe threaded connection has excellent resistance to galling and is likely to be difficult to loosen even if used in a horizontal wellbore. The metallized layer of Zn-Ni alloy, graphite and impurities will hereinafter be referred to as the metallized Zn-Ni alloy layer.

[0033] Preferably, if the chemical composition of the Zn-Ni alloy metallized layer is taken to be 100.0 atomic %, the Ni content of the Zn-Ni alloy metallized layer will be from 5.0 to 35.0 atomic %.

[0034] In this case, the hardness of the metallized Zn-Ni alloy layer is increased.

[0035] Preferably, if the chemical composition of the Zn-Ni alloy metallized layer is taken to be 100.0 atomic %, the graphite content of the Zn-Ni alloy metallized layer will be from 30.0 to 60.0 atomic %.

[0036] In this case, the ability to maintain high torque is further increased, reducing the likelihood of loosening of the pipe threaded connection even when used in a horizontal wellbore.

[0037] The thickness of the Zn-Ni alloy metallized layer described above can be from 1.0 to 50.0 μm.

[0038] Preferably, the threaded pipe connection may further comprise a lubricant coating on or above the pin contact surface and/or the coupling contact surface and/or a Zn-Ni alloy metallized layer.

[0039] In this case, the wear resistance of the threaded pipe connection is improved.

[0040] A method for manufacturing a threaded joint for pipes according to the present embodiment of the invention comprises a preparation step and a metallized layer forming step. At the preparation stage, the nipple, coupling and solution are prepared for applying the metallized layer. The nipple includes a contact surface containing a male thread portion. The coupling includes a contact surface containing a portion with an internal thread. The solution for applying the metallized layer contains zinc ions, nickel ions and graphite. In the step of forming the metallized layer, at least one surface of the pin contact surface and the coupling contact surface is brought into contact with the metallized layer solution so as to form a metallized layer of Zn-Ni alloy on at least one surface of the pin contact surface and contact surface of the coupling by electrolytic deposition.

[0041] A threaded pipe connection according to the present embodiment and a manufacturing method thereof will be described in detail below. In the following description, atomic % means atomic percentage.

[0042] Threaded connection for pipes

The pipe threaded connection is a coupling type pipe threaded connection or a continuous type pipe threaded connection. In fig. Figure 2 shows an illustration of the threaded connection configuration for coupling-type pipes. As shown in FIG. 2, a threaded connection for pipes includes a pipe 1 and a coupling 2. At both ends of the pipe 1, nipples 3 are formed, on the outer surface of each of which a part with an external thread is provided. At both ends of the coupling 2, couplings 4 are formed, on the inner surfaces of which a part with an internal thread is provided. The coupling 2 is attached to the end of the pipe 1 by screwing the nipple 3 and the coupling 4 together.

[0043] In FIG. 3 is a diagram illustrating the configuration of an example threaded connection for continuous type pipes. As shown in FIG. 3, the threaded connection for pipes contains a pipe 1. At one end of the pipe 1, a nipple 3 is formed, on the outer surface of which a part with an external thread is provided. At the other end of the pipe 1, a coupling 4 is formed, on the inner surface of which a part with an internal thread is provided. Pipes 1 can be connected to each other by screwing nipple 3 and coupling 4 together. The pipe threaded connection according to the present embodiment can be used for both the coupling type pipe threaded connection and the continuous type pipe threaded connection.

[0044] The portions that come into contact with each other when screwing together the pin 3 and the coupling 4 are called the pin contact surface 34 and the coupling contact surface 44. In fig. Figure 4 shows a cross-section of an example of a threaded connection for pipes. In the example of a threaded pipe connection shown in FIG. 4, the nipple 3 includes a male thread portion 31, a metal sealing portion 32 on the nipple side, and a nipple thrust portion 33. The coupling 4 includes an internal thread portion 41, a metal sealing portion 42 on the coupling side, and a coupling thrust portion 43.

[0045] When screwing together the pin 3 and the coupling 4, the threaded parts (male thread part 31 and the female thread part 41), metal sealing parts (metal sealing part 32 on the pin side and metal sealing part 42 on the couplings) and thrust parts (thrust part 33 of the nipple and thrust part 43 of the coupling). That is, if the pin contact surface 34 includes a male thread portion 31, a pin-side metal sealing portion 32, and a pin thrust portion 33, then the coupling contact surface 44 includes an internal thread portion 41, a coupling-side metal sealing portion 42, and a thrust portion 43 couplings. It should be noted that the threaded pipe connection according to the present embodiment need not include a metal sealing portion and an abutment portion if it includes a threaded portion.

[0046] In short, the nipple 3 includes a contact surface 34 containing a male thread portion 31. As described above, the pin contact surface 34 may further comprise a pin-side metal sealing portion 32 and a pin abutment portion 33. Therefore, the pin contact surface 34 may not include a pin-side metal sealing portion 32 and a pin thrust portion 33 as long as it includes a male thread portion 31. The pin contact surface 34 may comprise a male thread portion 31 and a nipple-side metal sealing portion 32, a male thread portion 31 and a nipple thrust portion 33, or a male thread portion 31, a nipple-side metal sealing portion 32, and a nipple thrust portion 33 .

[0047] Thus, the coupling 4 includes a contact surface 44 containing a portion 41 with internal threads. As described above, the coupling contact surface 44 may further comprise a coupling-side metal sealing portion 42 and a coupling abutment portion 43. Therefore, the coupling contact surface 44 may not include the coupling-side metal sealing portion 42 and the coupling thrust portion 43 as long as it includes an internal thread portion 41. The coupling contact surface 44 may comprise an internal thread portion 41 and a coupling-side metal sealing portion 42, an internal thread portion 41 and a coupling thrust portion 43, or an internal thread portion 41, a coupling-side metal sealing portion 42, and a thrust portion 43 couplings.

[0048] An embodiment will be described below in which the pin contact surface 34 includes a male thread portion 31, a pin side metal sealing portion 32, and a nipple thrust portion 33, and the coupling contact surface 44 includes an internal thread portion 41, a metal seal portion 42 on the coupling side and the coupling thrust portion 43 as one example of a threaded connection for pipes according to the present embodiment.

[0049] In a pipe threaded joint comprising metal sealing parts and thrust parts, arrangements of the threaded parts, metal sealing parts and thrust parts are not substantially limited. In particular, FIG. 4 shows a nipple 3 in which the nipple thrust part 33, the metal sealing part 32 on the nipple side and the male thread part 31 are arranged in that order from the end of the pipe 1. In addition, FIG. 4 shows a coupling 4 , in which the internal thread portion 41, the coupling-side metal sealing portion 42, and the coupling thrust portion 43 are arranged in that order from the end of the pipe 1 or coupling joint 2. However, their arrangement is not limited to the arrangement shown in FIG. 4 and may be changed if necessary.

[0050] For example, as shown in FIG. 3, the male thread portion, the metal pin sealing portion, the nipple thrust portion, the metal pin sealing portion, and the male thread portion may be arranged on the nipple 3 in that order from the end of the pipe 1. Likewise, as shown in FIG. Thus, on the coupling 4, the internal thread part, the metal coupling sealing part, the coupling thrust part, the metal coupling sealing part and the internal thread part can be arranged in this order from the end of the pipe 1 or the coupling joint 2.

[0051] Therefore, the contact surface 34 of the pin 3 may include a plurality of male thread portions 31, a plurality of pin-side metal sealing portions 32, and a plurality of nipple thrust portions 33. Likewise, the contact surface 44 of the coupling 4 may include a plurality of internally threaded portions 41, a plurality of coupling-side metal sealing portions 42, and a plurality of coupling abutment portions 43.

[0052] Zn-Ni alloy metallized layer

A threaded pipe connection according to the present embodiment includes a nipple 3, a coupling 4, and a Zn-Ni alloy metallized layer. A metallized Zn-Ni alloy layer is placed on or above at least one surface of the pin contact surface 34 and the coupling contact surface 44.

[0053] In FIG. 5 is a cross-sectional view of a threaded pipe connection according to the present embodiment of the invention. As shown in FIG. 5, metallized Zn-Ni alloy layers 100 are located on both the pin contact surface 34 and the coupling contact surface 44. In fig. 6 is a sectional view of a threaded pipe connection according to another embodiment of the invention, the threaded pipe connection being different from that shown in FIG. 5. As shown in FIG. 6, the metallized Zn-Ni alloy layers 100 can only be placed on the coupling contact surface 44. In fig. 7 is a cross-sectional view of a pipe threaded connection according to a further embodiment of the invention, the pipe threaded connection being different from that shown in FIG. 5 and 6. As shown in FIG. 7, the Zn-Ni alloy metallized layers 100 can only be placed on the pin contact surface 34.

[0054] The Zn-Ni alloy metallized layer 100 must be placed on or above at least one of the pin contact surface 34 and the coupling contact surface 44. In addition, the Zn-Ni alloy metallized layer 100 may be placed on or over at least one surface of the entire pin contact surface 34, the entire coupling contact surface 44, a portion of the pin contact surface 34, and a portion of the coupling contact surface 44. In particular, the pin-side metal sealing portion 32 and the coupling-side metal sealing portion 42, as well as the nipple thrust portion 33 and the coupling thrust portion 43 are under high boundary pressure, especially in the final fixing step. Therefore, in the case where the pipe threaded connection includes a metal nipple sealing portion 32, a metal coupling sealing portion 42, a nipple thrust portion 33, and a coupling thrust portion 43, a metallized layer of Zn-Ni 100 alloy may be placed on or over at least one partly consisting of a metal sealing portion 32 on the nipple side, a metal sealing portion 42 on the coupling side, a nipple thrust portion 33, and a coupling thrust portion 43. In contrast, if the Zn-Ni alloy metallized layer 100 is placed entirely on or above at least one contact surface of the contact surfaces 34 and 44, the manufacturing efficiency of a pipe thread joint is improved.

[0055] As described above, the Zn-Ni alloy metallized layer 100 contains a Zn-Ni alloy, graphite and impurities. In this case, the Zn-Ni alloy contains zinc (Zn) and nickel (Ni). In addition, the Zn-Ni alloy may contain impurities. Here, impurities in the Zn-Ni alloy metallized layer 100 and impurities in the Zn-Ni alloy mean substances other than Zn, Ni and graphite and contained in the Zn-Ni alloy metallized layer 100 or Zn-Ni alloy during the manufacture of the thread pipe connections to the extent that impurities do not interfere with the effects of the present disclosure.

[0056] The Ni content of the Zn-Ni alloy metallized layer 100 is not limited to the specified content. However, if the entire chemical composition of the Zn-Ni alloy metallized layer 100 is taken to be 100.0 atomic %, a Ni content of 5.0 to 35.0 atomic % in the Zn-Ni alloy metallized layer 100 will result in an increase hardness of the metallized layer of 100 Zn-Ni alloy.

[0057] Thus, if the chemical composition of the Zn-Ni alloy metallized layer 100 is taken to be 100.0 atomic %, the Ni content of the Zn-Ni alloy metallized layer 100 is preferably 5.0 to 35.0 atomic %. %. More preferably, the lower limit of Ni content in the Zn-Ni alloy metallized layer 100 is 10.0 atomic %. More preferably, the upper limit of Ni content in the Zn-Ni alloy metallized layer 100 is 30.0 atomic %.

[0058] It should be noted that zinc (Zn) contained in the Zn-Ni alloy metallized layer 100 is a more active metal compared to iron (Fe), which is the main component of the pipe. Thus, Zn provides sacrificial protection, increasing the corrosion resistance of the threaded connection for pipes.

[0059] Graphite

Graphite is a substance consisting of layered sheets (graphenes), each of which is a hexagonal lattice in which carbon atoms are connected. Graphite contains carbon (C) and the remainder is due to impurities. Since the bond strength between layers in graphene is weak, graphenes are prone to delamination. Therefore, graphite is commonly used as a lubricant. However, according to the present embodiment, the metallized Zn-Ni alloy layer 100 containing graphite increases the galling resistance of the pipe threaded connection and improves the ability to support high torque. As a result, the pipe threaded connection can prevent loosening even when used in a horizontal well.

[0060] Graphite content

The content of graphite in the Zn-Ni alloy metallized layer 100 is not limited to the specified content. However, if the entire chemical composition of the Zn-Ni alloy metallized layer 100 is taken to be 100.0 atomic %, a graphite content of 30.0 atomic % or more will further enhance the ability of the Zn-Ni alloy metallized layer 100 to maintain high torque. moment. In this case, loosening of the pipe thread will be prevented with increased reliability even if the pipe thread is used in a well with a horizontal end. In contrast, if the entire chemical composition of the Zn-Ni alloy metallized layer 100 is taken to be 100.0 atomic %, a conventional Zn-Ni alloy metallized layer 100 can be formed in a stable manner when the graphite content is 60.0 atomic % or less. Thus, if the chemical composition of the Zn-Ni alloy metallized layer 100 is taken to be 100.0 atomic %, the graphite content of the Zn-Ni alloy metallized layer 100 is preferably 30.0 to 60.0 atomic %. More preferably, the lower limit of the graphite content in the Zn-Ni alloy metallized layer 100 is 40.0 atomic %. More preferably, the upper limit of the graphite content of the Zn-Ni alloy metallized layer 100 is 55.0 atomic %.

[0061] Method for measuring Ni and graphite content in a metallized layer of Zn-Ni alloy

The Ni content and graphite content in the Zn-Ni alloy metallized layer 100 can be measured by the following method. First, a pipe threaded joint sample is prepared on which or above which a metallized Zn-Ni alloy layer 100 is formed. The surface of the Zn-Ni alloy metallized layer 100 as a sample is subjected to elemental analysis by energy dispersive X-ray spectroscopy using an electron probe microanalyzer (FE-EPMA: JXA-8530F manufactured by JEOL Ltd.). The sample is irradiated with an electron beam at an accelerating voltage of 15-30 kV and an irradiation current of 1 nA at maximum, and the X-ray intensity, including the C-kα line, the Zn-kα line and the Ni-kα line, is measured at a magnification of 1500x to 5000x. Based on the X-ray line intensities of the corresponding elements, the C content (in atomic %), Zn content (in atomic %) and Ni content (in atomic %) are calculated. The value obtained by dividing the Ni content by the total content of C, Zn and Ni is considered the Ni content (in atomic %). The value obtained by dividing the C content by the total content of C, Zn and Ni is considered the graphite content (in atomic %). Elemental analysis is performed at three specified points on the surface of the Zn-Ni alloy metallized layer 100, and the average of the resulting contents is used.

[0062] Thickness of Zn-Ni alloy metallized layer

The thickness of the Zn-Ni alloy metallized layer 100 is not limited to the specified thickness. The thickness of the Zn-Ni alloy metallized layer 100 is, for example, from 1.0 to 50.0 μm. When the thickness of the Zn-Ni alloy metallized layer 100 is 1.0 μm or more, sufficient scuffing resistance can be stably obtained. When the thickness of the Zn-Ni alloy metallized layer 100 exceeds 50.0 μm, the above effect reaches a maximum. Thus, the thickness of the Zn-Ni alloy metallized layer 100 is preferably from 1.0 to 50.0 μm. More preferably, the upper limit of the thickness of the Zn-Ni alloy metallized layer 100 is 20.0 μm.

[0063] Method for measuring the thickness of a metallized layer of a Zn-Ni alloy

The thickness of the Zn-Ni alloy metallized layer 100 can be measured in the following manner. The thickness of the Zn-Ni alloy metallized layer 100 is measured at four random points on the pin contact surface 34 and the coupling contact surface 44 on which or above which the Zn-Ni alloy metallized layer 100 is formed using PHASCOPE PMP10, a phase sensitive eddy current thickness gauge from Helmut Fischer GmbH. Measurements are performed in a manner consistent with International Organization for Standardization (ISO) 21968(2005). The measuring points are taken to be four points on the pipe threaded connection in the circumferential direction (four points including 0°, 90°, 180° and 270°). The arithmetic mean value of the measurement results is taken as the thickness of the metallized layer 100 of the Zn-Ni alloy.

[0064] Vickers hardness of the Zn-Ni alloy metallized layer

The galling resistance of a pipe thread connection increases as the hardness of the Zn-Ni alloy metallized layer 100 increases. Therefore, the lower limit of the Vickers hardness (Hv) of the Zn-Ni alloy metallized layer 100 is preferably 150, more preferably 250. The upper limit of the Vickers hardness (Hv) of the Zn-Ni alloy metallized layer 100 is preferably maximum high. The upper limit of the Vickers hardness (Hv) of the Zn-Ni alloy metallized layer 100 is, for example, 600.

[0065] Method for measuring the Vickers hardness of a metallized Zn-Ni alloy layer

The Vickers hardness of the Zn-Ni alloy metallized layer 100 can be measured by the following method. Nipple 3 or coupling 4 is prepared, depending on which of them contains the metallized layer 100 of the Zn-Ni alloy. The nipple 3 or coupling 4, at least one of which contains a metallized layer 100 of a Zn-Ni alloy, is cut perpendicular to the axial direction. At predetermined five points on the open cross-section of the Zn-Ni alloy metallized layer 100, the Vickers hardness is measured in a manner consistent with JIS Z2244(2009). When measuring, a Fischer scope HM2000 microhardness tester from Fischer Instruments K. K. is used. The test temperature is set to normal temperature (25°C), and the test force (F) is 5 - 100 mN. Of the five measurement results, the maximum and minimum values are eliminated, and the arithmetic average of the three results is taken as the Vickers hardness (Hv) of the Zn-Ni alloy metallized layer 100.

[0066] Lubricating coating

The threaded pipe connection according to the present embodiment is characterized by excellent galling resistance and high ability to maintain high torque in the absence of lubricant, as well as preventing loosening. However, the pipe threaded connection may further comprise a lubricant coating 200 on or above at least one of the pin contact surface 34, the coupling contact surface 44, and the Zn-Ni alloy metallized layer 100. In this case, the wear resistance of the threaded connection for pipes increases. In fig. 8 is a sectional view of an example of a threaded connection for pipes according to the present embodiment, in which a lubricating coating is provided on the nipple 3 and the coupling 4. Referring to FIG. 8, the lubricating coating 200 can be applied to both the Zn-Ni alloy metallized layer 100 formed on the pin contact surface 34 and the Zn-Ni alloy metallized layer 100 formed on the clutch contact surface 44. The arrangement of the lubricating coating 200 is not limited to that shown in FIG. 8.

[0067] The lubricating coating 200 may be located only on or above the Zn-Ni alloy metallized layer 100 formed on or above the pin contact surface 34. Thus, the lubricating coating 200 may be located only on or above the Zn-Ni alloy metallized layer 100 formed on or above the coupling contact surface 44. Alternatively, the lubricating coating 200 may be located directly on at least one surface of the pin contact surface 34 and the coupling contact surface 44. In fig. 9 is a sectional view of an example of a pipe thread according to another embodiment of the invention, the pipe thread being different from that shown in FIG. 8. As shown in FIG. 9, the lubricating coating 200 may be located directly on the pin contact surface 34, which does not have a metallized Zn-Ni alloy layer 100. In fig. 10 is a sectional view of an example of a pipe threaded connection according to a further embodiment of the invention, the pipe threaded connection being different from that shown in FIG. 8 and 9. As shown in FIG. 10, the lubricating coating 200 may be located directly on the clutch contact surface 44, which does not have a metallized Zn-Ni alloy layer 100.

[0068] Alternatively, the lubricating coating 200 may be located entirely on or above at least one of the pin contact surface 34, the coupling contact surface 44, and the Zn-Ni alloy metallized layer 100. The lubricating coating 200 may be located only partially on or above at least one surface selected from the pin contact surface 34, the coupling contact surface 44, and the Zn-Ni alloy metallized layer 100.

[0069] The lubricating coating 200 may be solid, semi-solid, or liquid. Semi-solid form means a state in which fluidity is lost in a static state, but when force (pressure, heat, etc.) is applied from outside, fluidity can be acquired. Liquid form means a state in which there is a certain volume, but no certain form. The liquid or semi-solid form is a highly viscous substance such as a lubricant. The lubricating coating 200 may be a known material having lubricating properties. The choice of known material having lubricating properties is essentially unlimited; for example, such material may be particulate lubricants or non-particulate lubricants. In addition, the lubricating coating 200 may contain a binder to form the coating. The lubricant coating 200 may optionally include a lubricant, solvent, or other component.

[0070] Lubricating particles are not limited to a particular type of particles, as long as the particles have lubricating properties. The lubricating particles are one or more types selected from the group consisting of, for example, graphite, molybdenum disulfide (MoS2), tungsten disulfide (WS2), boron nitride (BN), polytetrafluoroethylene (PTFE), graphite fluoride (CFx) and carbonate calcium (CaCO3). An example of a non-particulate lubricant is SEAL-GUARD (trade mark) ECF (trade mark) from JET-LUBE Inc. In other examples, the other lubricant contains rosin, metallic soap, and wax.

[0071] Examples of the binder are one or two types selected from the group consisting of an organic binder and an inorganic binder. Examples of the organic binder include one or two types selected from the group consisting of a thermosetting resin and a thermoplastic resin. Examples of the thermosetting resin include one or more types selected from the group consisting of polyethylene resin, polyimide resin and polyamide-imide resin. Examples of the inorganic binder include one or two types selected from the group consisting of compounds containing an alkoxysilane bond and a siloxane bond.

[0072] The chemical composition of the lubricating coating 200 located on or above the pin contact surface 34, the chemical composition of the lubricating coating 200 located on or above the coupling contact surface 44, and the chemical composition of the lubricating coating 200 located on or above the Zn alloy metallized layer 100 -Ni, may be the same or different from each other.

[0073] The thickness of the lubricating coating 200 is not limited to the specified thickness. The thickness of the lubricating coating 200 is, for example, from 30 to 300 microns. If the thickness of the lubricating coating 200 is 30 μm or more, when the pipe thread is fixed, the torque reduction effect is enhanced when the thrust portions (nipple thrust portion 33 and coupling thrust portion 43) come into contact with each other. This makes it easy to adjust the amount of torque when locking. If the thickness of the lubricating coating 200 exceeds 300 μm, the above-mentioned effect is canceled out because excess lubricating coating 200 is removed from the pin contact surface 34 and the clutch contact surface 44 upon locking.

[0074] If the lubricating coating 200 is solid, the thickness of the lubricating coating 200 can be measured in the following way. A nipple 3 or coupling 4 is prepared, one of which contains a lubricating coating 200. The nipple 3 or coupling 4 is cut perpendicular to the axial direction. The cross section containing the lubricant coating 200 is examined under a microscope. The magnification for microscopic examination is set to 500x. This method determines the thickness of the lubricating coating 200.

[0075] If the lubricating coating 200 is liquid or semi-solid, the thickness of the lubricating coating 200 can be measured in the following way. An arbitrary location for measuring nipple 3 or coupling 4 in a threaded connection for pipes is determined. For example, an arbitrary measurement location is determined on the metal sealing part 32 of the nipple or the metal sealing part 42 of the coupling. The identified measurement location (area: 5 mm × 20 mm) is wiped with an absorbent cloth moistened with ethanol. The amount of lubricant is calculated as the difference between the mass of the absorbent napkin before wiping and the mass of the absorbent napkin after wiping. Based on the amount of lubricant applied, the density of the lubricant and the area of the measuring point, the average thickness of the lubricant coating 200 is calculated.

[0076] Arrangement of Zn-Ni alloy metallized layer and lubricant coating

As noted above, the location of the lubricating coating 200 is substantially unlimited. Accordingly, provided that the Zn-Ni alloy metallized layer 100 is disposed on or above at least one surface of the pin contact surface 34 and the coupling contact surface 44, and the lubricant coating 200 is disposed on or above at least one surface of the contact surface 34 nipples, a coupling contact surface 44 and a metallized Zn-Ni alloy layer 100, the combination of arrangement options is not limited. The case in which only the Zn-Ni alloy metallized layer 100 is formed is called structure 1. The case in which the Zn-Ni alloy metallized layer 100 is formed, and a lubricating coating 200 is further formed on or above the Zn-Ni alloy metallized layer 100 , is called structure 2. The case in which only the lubricating coating 200 is formed is called structure 3. The case in which neither the Zn-Ni alloy metallized layer 100 nor the lubricating coating 200 is provided is called structure 4. For the pin contact surface 34 and Any of the structures 1–4 is possible on the coupling contact surface 44 if the above condition is met. In particular, if the pin contact surface 34 corresponds to structure 1 or 2, the coupling contact surface 44 may correspond to any of the structures 1 to 4. If the pin contact surface 34 corresponds to structure 3 or 4, the coupling contact surface 44 corresponds to structure 1 or 2. Conversely, if the lock contact surface 44 corresponds to structure 1 or 2, the coupling contact surface 34 may correspond to any of structures 1 - 4. If the coupling surface 44 corresponds to structure 3 or 4, the pin contact surface 34 corresponds to structure 1 or 2.

[0077] Base metal of pipe threaded connection

The chemical composition of the base metal of a pipe threaded connection is not limited to the specified chemical composition. Examples of base metal include carbon steels, stainless steels and alloy steels. Among alloy steels, high alloy steels such as duplex stainless steels containing alloying elements such as Cr, Ni and Mo, and Ni alloys have high corrosion resistance. Accordingly, if high-alloy steel is used as the base metal, the corrosion resistance of the pipe thread connection can be increased.

[0078] Manufacturing method

The method for manufacturing a threaded pipe joint according to the present embodiment is the above-disclosed method for manufacturing a threaded pipe joint. A method for manufacturing a threaded connection for pipes contains a preparation stage and a stage of forming a metallized layer.

[0079] Preparation stage

At the preparation stage, nipple 3, coupling 4 and solution are prepared for applying the metallized layer. The nipple 3 includes a contact surface 34 containing a male thread portion 31 as described above. The coupling 4 includes a contact surface 44 containing an internally threaded portion 41 as described above. At least one surface of the pin contact surface 34 and the coupling contact surface 44 may be subjected to known preparation. Preparation may involve defatting. During degreasing, oil, oil stains and other similar contaminants are removed from at least one surface of the pin contact surface 34 and the coupling contact surface 44. Degreasing may be, but is not limited to, solvent degreasing, alkaline degreasing, and electrolytic degreasing. As a preparation, additional etching can be performed. Etching removes rust, oxidized machining coating, and other similar contaminants from at least one surface of the pin contact surface 34 and the coupling contact surface 44.

[0080] The solution for applying the metallized layer contains zinc ions, nickel ions and graphite. The plating solution contains zinc ions obtained by dissolving a zinc salt (eg, zinc sulfate) in the plating solution. The plating solution contains nickel ions produced by dissolving a nickel salt (eg, nickel sulfate) in the plating solution. The zinc salt and nickel salt anion is in particular a sulfuric acid ion and/or a chloride ion and/or a pyrophosphate ion. Preferably, the solution for applying the metallized layer contains zinc ions in a concentration of 1 to 100 g/l and nickel ions in a concentration of 1 to 100 g/l.

[0081]

In addition, the solution for applying the metallized layer contains graphite. Thus, the Zn-Ni alloy metallized layer 100 contains graphite. As a result, the galling resistance of the Zn-Ni alloy metallized layer 100 and the ability to support high torque are increased, which can prevent the pipe thread from loosening even when the pipe thread is used in a horizontal wellbore. In the manufacturing method according to the present embodiment, powdered graphite is preferably used. The particle size of graphite is not limited to the specified particle size. The graphite particle size is, for example, from 0.01 to 30 μm. Taking into account the dispersion in the solution for applying the metallized layer and the balance between particle size and layer thickness, the more preferred graphite particle size is from 0.01 to 10 microns. The size of the graphite particles can be suitably set in a range allowing the graphite particles to be dispersed in the metallized layer deposition solution and the graphite to be captured by the Zn-Ni alloy metallized layer 100.

[0082] When the graphite content in the metallized layer deposition solution is 3 g/L or more, the graphite can be stably entrained by the Zn-Ni alloy metallized layer 100. This can stably improve the ability of the Zn-Ni alloy metallized layer 100 to maintain high torque. On the contrary, when the graphite content of the metallized layer coating solution is 20 g/L or less, it is possible to prevent graphite from being deposited in the metallized layer coating bath. Thus, the graphite content in the solution for applying the metallized layer is preferably from 3 to 20 g/l. More preferably, the lower limit of graphite content in the solution for applying the metallized layer is 5 g/l. More preferably, the upper limit of the graphite content in the solution for applying the metallized layer is 10 g/l.

[0083] Dispersant

Preferably, the solution for applying the metallized layer further contains a dispersant. The dispersant increases the dispersion of graphite in the solution for applying the metallized layer. Preferably, the dispersant is polyacrylic acid and/or 1-butyl-1-methylpyrrolidinium chloride.

[0084] Polyacrylic acid is a polymer of acrylic acid. When polyacrylic acid or a salt of polyacrylic acid (for example, sodium polyacrylate) is dissolved in the solution for applying the metallized layer, the polyacrylic acid is included in the solution for applying the metallized layer. Preferably, the polyacrylic acid has a low molecular weight. Low molecular weight polyacrylic acid can further increase the dispersion of graphite. The upper limit of the molecular weight of the polyacrylic acid is preferably 10,000, more preferably 2,000, based on the average molecular weight. The lower limit of the molecular weight of polyacrylic acid is not limited to the specified molecular weight. The lower limit of the molecular weight of polyacrylic acid is, for example, 1000 based on average molecular weight.

[0085] 1-Butyl-1-methylpyrrolidinium chloride is a compound expressed by the chemical formula C9H20ClN and is classified as a quaternary ammonium salt. 1-Butyl-1-methylpyrrolidinium chloride is a compound containing a five-membered ring (an N+-containing heterocycle). 1-Butyl-1-methylpyrrolidinium chloride is also used as an ionic liquid.

[0086] The content of the dispersant in the solution for applying the metallized layer is not limited to the specified content. A small amount of dispersing agent contained in the solution for applying the metallized layer increases the dispersion of graphite. The content of dispersant in the solution for applying the metallized layer is, for example, from 1 × 10 ^-6 to 1 × 10 ^-4 mol/l. If the solution for applying the metallized layer contains both polyacrylic acid and 1-butyl-1-methylpyrrolidinium, the content of each of them is preferably from 1 × 10 ^-6 to 1 × 10 ^-4 mol/l. The content of polyacrylic acid (mol/l) means the molar ratio to its average molecular weight.

[0087] The solution for applying the metallized layer may contain a conductive salt and/or an anodic dissolution promoter and/or a complexing agent and/or a pH buffer and/or a surfactant and/or a reducing agent and/or a stabilizer and/or other additives as necessary.

[0088] Metallized layer formation step

In the metallization layer forming step, at least one surface of the pin contact surface 34 and the coupling contact surface 44 is subjected to electrolytic deposition by being brought into contact with the above-disclosed metallization layer solution so as to form a Zn-Ni alloy metallization layer 100 .

[0089] A device for applying a metallized layer contains, for example, a bath for applying a metallized layer, a stirring device, a filter, a temperature controller, an anode plate and a washing device. The above plating solution is poured into the plating bath, and at least one of the nipple 3 and/or coupling 4 as well as the anode plate are immersed in the plating solution. In this case, pipe 1 or coupling connection 2 can be completely immersed in the solution for applying a metallized layer. The pin 3 may be completely immersed in the plating solution, or only the contact surface 34 of the pin 3 may be immersed in the plating solution. The coupling 4 may be completely immersed in the plating solution, or only the contact surface 44 of the coupling 4 may be immersed in the plating solution. When a voltage is applied to at least one surface of the pin contact surface 34 and the coupling contact surface 44 and the anode plate, a metallized Zn-Ni alloy layer 100 is formed on or over at least one surface of the pin contact surface 34 and the coupling contact surface 44 .

[0090] Conditions including plating bath temperature, current density, pH, stirring speed can be set accordingly. Electrical deposition conditions assume, for example, pH of the solution for applying the metallized layer: 1–10, temperature of the solution for applying the metallized layer: 10–60 °C, current density: 1–100 A/dm2, stirring speed: 0.1–1 m /s, processing period: 1—100 minutes. Upon completion of the metallized layer forming step, at least one surface of the pin contact surface 34 and the coupling contact surface 44 is washed and dried if necessary. The method of washing and drying is not limited to the above method.

[0091] Lubricating coating forming step

The manufacturing method according to the present embodiment may further comprise the step of forming a lubricating coating. Specifically, after the above-mentioned step of forming the metallized layer, that is, after forming the above-described Zn-Ni alloy metallized layer 100 on or above at least one surface of the pin contact surface 34 and the coupling contact surface 44, the step of forming a lubricating coating can be performed. In the lubricating coating forming step, a lubricating coating 200 is formed on or over at least one surface of a pin contact surface 34, a coupling contact surface 44, and a Zn-Ni alloy metallized layer 100.

[0092] The lubricating coating 200 is formed by applying the above-described lubricant to at least one of the pin contact surface 34, the coupling contact surface 44, and the Zn-Ni alloy metallized layer 100. The application method is not limited to the specified method. The application method may be spraying, brushing or dipping. In the case of a spray method, the lubricant may be sprayed when heated to improve fluidity. The lubricating coating 200 may be formed only partially on or over at least one surface of the pin contact surface 34, the coupling contact surface 44, and the Zn-Ni alloy metallized layer 100. However, the lubricating coating 200 is preferably formed completely and uniformly on or above the pin contact surface 34, the coupling contact surface 44, and the Zn-Ni alloy metallized layer 100.

[0093] The steps described above make it possible to obtain a threaded connection for pipes in accordance with the present embodiment of the invention.

EXAMPLES

[0094] An example will be described below. Unless otherwise noted, the symbol "%" in the example indicates mass percentage.

[0095] Preparation stage

In the present example, a commercially available cold-rolled steel sheet was used, which was assumed to be the base metal of the threaded connection. The cold-rolled steel sheet had a length of 150 mm × a width of 100 mm (coating surface of a length of 100 mm × a width of 100 mm). The cold rolled steel sheet was made from low carbon steel. Chemical composition of steel sheet: C: 0.19%, Si: 0.25%, Mn: 0.8%, P: 0.02%, S: 0.01%, Cu: 0.04%, Ni: 0 .1%, Cr: 13%, Mo: 0.04%, and the rest: Fe and impurities.

[0096] The bath for applying the metallized layer for sample No. 1-5 had the following composition:

- solution for applying the metallized layer: DAIN Zinalloy alloy (manufactured by Daiwa Fine Chemicals Co., Ltd.),

- graphite: TIMREX (trade mark) KS6 (IMERYS GRAPHITE & CARBON companies) 1-10 g/l, particle size < 100 nm (D90),

- polyacrylic acid (Sigma-Aldrich company), 2 × 10 ^-5 mol/l, average molecular weight (Mw) 1800,

- 1-butyl-1-methylpyrrolidinium chloride (Merck KGaA) 2 × 10 ^-5 mol/l.

[0097] The bath for applying the metallized layer for sample No. 6-8 had the following composition:

- solution for applying the metallized layer: copper sulfate pentahydrate 200 g/l, and sulfuric acid 50 g/l (KISHIDA CHEMICAL Co., Ltd.),

- graphite: TIMREX (trade mark) KS6 (IMERYS GRAPHITE & CARBON companies) 1-10 g/l, particle size < 100 nm (D90),

- polyacrylic acid (Sigma-Aldrich company), 2 × 10 ^-5 mol/l, average molecular weight (Mw) 1800,

- 1-butyl-1-methylpyrrolidinium chloride (Merck KGaA) 2 × 10 ^-5 mol/l.

[0098] Metallized layer formation step

A metallized layer was formed on the surface of the steel sheet of each sample under the following conditions:

- temperature in the bath for applying the metallized layer: 25°C,

- coating current density: 2 A/dm ² ,

- coating thickness (specified value): 5—10 microns,

- mixing speed: 0.4 m/s,

- anode for applying a metallized layer (counter electrode): insoluble anode (Ti plate coated with iridium oxide).

[0099] Measuring the composition of the metallized layer

For the steel sheet in each sample on which a metallized layer was formed, the contents of Ni (atomic %) and graphite (atomic %) were measured in the manner described above. In samples 6–8, elemental analysis was performed by EDS, and the proportion of C content was determined as the graphite content (atomic %), taking the total content of Cu and C as 100.0 atomic %. The measurement results are shown in Table 1.

[0100]

[0101] Measuring the thickness of the metallized layer

For the steel sheet in each sample on which a metallized layer was formed, the thickness of the metallized layer was measured in the manner described above. The measurement results are shown in Table 1.

[0102] Vickers hardness measurement of metallized layer

For the steel sheet in each sample on which a metallized layer was formed, the Vickers hardness (Hv0.005) of the metallized layer was measured in the manner described above. The measurement results are shown in Table 1.

[0103] Bowden Slip Test

For the steel sheet in each specimen on which a metallized layer was formed, a Bowden slip test was performed under the following conditions. In addition, changes in the coefficient of friction during the test are shown in FIG. 1, FIG. 11 and FIG. 12. The test conditions are as follows:

- steel ball: 3/16''SUJ2,

- load: 3 kgf (Hertzian contact pressure: average 1.5 GPa),

- sliding width: 10 mm,

- sliding speed: 4 mm/s,

- lubricant: absent (without lubrication),

- test temperature: room temperature (25°C).

[0104] FIGS. 11 and 12 are diagrams each illustrating the results of the Bowden slip test performed in the Example. As shown in FIG. 1, FIG. 11 and FIG. 12, if the number of slides from the start of sliding to the point at which the friction coefficient (μ) exceeds 0.4 is large, the scuffing resistance of the steel sheet can be considered excellent. In addition, if the number of slips in which the friction coefficient (μ) remained between 0.2 and 0.4 is large, the high torque maintaining ability can be considered excellent. Thus, in the present example, the number of slips from the start of sliding to the point at which the coefficient of friction (μ) exceeds 0.4 without scoring was defined as the “total number of slips.” In addition, the number of slides in which the coefficient of friction (μ) remained between 0.2 and 0.4 without scoring was defined as the “number of slides with a high friction coefficient.” The resulting number of high-friction slips (slips) and the total number of slips for the steel sheet of each sample are shown in Table 1.

[0105] Evaluation results

According to Table 1, FIG. 1, FIG. 11 and FIG. 12, the steel sheets of samples Nos. 2-5 contained a metallized layer of Zn-Ni alloy containing graphite. As a result, the total number of slips until the coefficient of friction (μ) exceeds 0.4 exceeded 90, and the steel sheets showed excellent resistance to scoring. In addition, the number of high-friction sliding events in which the friction coefficient maintained a value of 0.2 to 0.4 without scuffing exceeded 60, and the steel sheets exhibited excellent high-torque ability. Thus, a pipe threaded connection comprising a Zn-Ni alloy metallized layer containing graphite can be considered to have excellent galling resistance and resistance to loosening even when used in a horizontal wellbore.

[0106] The steel sheets of samples 3 to 5 had a graphite content of 30.0 to 60.0 atomic %. As a result, the total number of slips increased compared to the steel sheet of sample No. 2, in which the graphite content was 2.7 atomic%, that is, the steel sheets showed improved resistance to scuffing. In addition, the steel sheets showed an increased number of high friction slides compared to the steel sheet of sample No. 2, that is, an improved ability to maintain high torque. Thus, a threaded pipe connection containing a metallized layer of Zn-Ni alloy with a graphite content of 30.0 to 60.0 atomic % can be considered to have increased resistance to galling and resistance to loosening, even when used in a horizontal well. trunk

[0107] In contrast, the steel sheet of sample No. 1 contained a metallized layer of Zn-Ni alloy containing no graphite. As a result, the total number of slips was 90 or less, which means that the steel sheet did not demonstrate excellent scuffing resistance. In addition, the number of high-friction slides was 60 or less, meaning the steel sheet did not show excellent ability to maintain high torque.

[0108] The steel sheet of sample No. 6 contained a metallized layer of Cu containing no graphite. As a result, the total number of slips was 90 or less, which means that the steel sheet did not demonstrate excellent scuffing resistance. In addition, the number of high-friction slides was 60 or less, meaning the steel sheet did not show excellent ability to maintain high torque.

[0109] The steel sheets of samples 7 and 8 contained a metallized layer of Cu containing graphite. As a result, the total number of slips exceeded 90 and the steel sheets showed excellent resistance to scoring. In addition, the number of high-friction slips was 60 or less, meaning the steel sheets did not show excellent ability to maintain high torque.

[0110] As can be seen from the above, an embodiment according to the present invention has been described. However, the above embodiment serves only as an example of the implementation of the present specification. Therefore, the present specification is not limited to the previously mentioned embodiment, and the previously mentioned embodiment can be modified and implemented as appropriate without departing from the spirit of the present specification.

LIST OF REFERENCE SYMBOLS

[0111] 1 steel pipe

2 coupling connection

3 nipple

31 parts with external thread

32 metal nipple sealing part

33 nipple thrust part

34 nipple contact surface

4 coupling

41 parts with internal thread

42 metal sealing part of the coupling

43 thrust part of the coupling

44 contact surface of the coupling

100 metallized layer of Zn-Ni alloy

200 lubricating coating

Claims (10)

1. A threaded connection for pipes, comprising a nipple comprising a pin contact surface comprising a male threaded portion, a coupling comprising a coupling contact surface comprising an internal threaded portion, and a metallized Zn-Ni alloy layer located on at least one surface from the contact surface of the nipple and the contact surface of the coupling, while the metallized layer of the Zn-Ni alloy contains graphite. 2. A threaded connection for pipes according to claim 1, in which, if the entire chemical composition of the metallized layer of the Zn-Ni alloy is taken to be 100.0 atomic%, the Ni content in the metallized layer of the Zn-Ni alloy ranges from 5.0 to 35 .0 atomic %. 3. Threaded connection for pipes according to claim 1, in which, if the entire chemical composition of the metallized layer of the Zn-Ni alloy is taken to be 100.0 atomic%, the graphite content in the metallized layer of the Zn-Ni alloy is from 30.0 to 60 .0 atomic %. 4. Threaded connection for pipes according to claim 2, in which, if the entire chemical composition of the metallized layer of the Zn-Ni alloy is taken as 100.0 atomic %, the graphite content in the metallized layer of the Zn-Ni alloy ranges from 30.0 to 60 .0 atomic %. 5. Threaded connection for pipes according to claim 1, in which the thickness of the metallized layer of the Zn-Ni alloy ranges from 1.0 to 50.0 microns. 6. Threaded connection for pipes according to claim 2, in which the thickness of the metallized layer of the Zn-Ni alloy ranges from 1.0 to 50.0 microns. 7. Threaded connection for pipes according to claim 3, in which the thickness of the metallized layer of the Zn-Ni alloy ranges from 1.0 to 50.0 microns. 8. Threaded connection for pipes according to claim 4, in which the thickness of the metallized layer of the Zn-Ni alloy ranges from 1.0 to 50.0 microns. 9. Threaded connection for pipes according to any one of paragraphs. 1-8, further comprising a lubricating coating on at least one surface of a pin contact surface, a coupling contact surface and a Zn-Ni alloy metallized layer. 10. A method for manufacturing a threaded connection for pipes, including the following steps: preparing a nipple containing a contact surface of the nipple containing a part with an external thread; a coupling comprising a coupling contact surface comprising an internally threaded portion; and a solution for applying a metallized layer containing zinc ions, nickel ions and graphite; and forming a metallized layer of the Zn-Ni alloy on at least one surface of the pin contact surface and the coupling contact surface by electrolytic deposition by bringing at least one surface of the pin contact surface and the coupling contact surface into contact with the solution for applying the metallized layer.