JP2018123349A - Screw joint for tube and manufacturing method of screw joint for tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screw joint for tube having excellent seizure resistance and corrosion resistance.SOLUTION: The screw joint for tube has a pin, a box, a Ni-W alloy plating layer and a solid lubrication film. The pin and the box have contact surfaces containing screw parts, metal seal parts and shoulder parts respectively. The Ni-W alloy plating layer contains 35 to 45 mass% or W. Thickness of the Ni-W alloy plating layer is 1 to 20 μm. The Ni-W alloy plating layer is arranged on the contact surfaces of both the pin and the box. The screw joint for tube has further the solid lubrication film on the Ni-W alloy plating layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a threaded joint for pipes and a method for producing a threaded joint for pipes, and more particularly relates to a threaded joint for oil well pipes and a method for producing a threaded joint for oil well pipes.

  Oil well pipes are used to mine oil and natural gas fields. The oil well pipe is formed by connecting a plurality of steel pipes according to the depth of the well. The steel pipes are connected by screwing pipe threaded joints formed at the ends of the steel pipes. The steel pipe is pulled up for inspection or the like, unscrewed, inspected, screwed again, and used again.

  The threaded joint for pipes includes a pin and a box. The pin includes a male screw portion and an unthreaded metal contact portion formed on the outer peripheral surface of the tip portion of the steel pipe. The box includes an internal thread portion and an unthreaded metal contact portion formed on the inner peripheral surface of the distal end portion of the steel pipe. Each of the unthreaded metal contact portions includes a metal seal portion and a shoulder portion. When the steel pipes are screwed together, the male screw part and the female screw part, the metal seal parts of the pin and the box, and the shoulder parts of the pin and the box are in contact with each other.

  The threaded part of the pin and the box and the unthreaded metal contact part are repeatedly subjected to strong friction when the steel pipe is screwed and unscrewed. If these parts do not have sufficient durability against friction, goling (seizure that cannot be repaired) occurs when screwing and unscrewing are repeated. Therefore, the threaded joint for pipes is required to have sufficient durability against friction, that is, excellent seizure resistance.

  Conventionally, in order to improve seizure resistance, compound grease containing a heavy metal called a dope has been used. However, the dope (Pb, Zn, Cu, etc.) contained in the compound grease may affect the environment. For this reason, the development of a threaded joint for pipes that suppresses the use of compound grease is desired.

  International Publication No. 2009/072486 (Patent Document 1) proposes a threaded joint for pipes that is excellent in seizure resistance even without compound grease.

  The threaded joint for pipes described in Patent Document 1 includes a pin and a box each having a contact surface having a threaded portion and an unthreaded metal contact portion. The contact surface of the box has as a top layer a solid lubricating coating having a plastic or viscoplastic rheological behavior. The contact surface of the pin has a solid anticorrosive coating composed mainly of an ultraviolet curable resin as the uppermost layer. This eliminates the use of compound grease, suppresses the generation of rust, exhibits excellent seizure resistance and airtightness, and provides a threaded joint for pipes that has no stickiness on the surface and excellent appearance and inspection. , And Patent Document 1.

  Other seizure resistance improving techniques different from compound greases and solid lubricating films have been proposed in Japanese Patent Application Laid-Open No. 2003-074763 (Patent Document 2) and Japanese Patent Application Laid-Open No. 2008-215473 (Patent Document 3). In these documents, the seizure resistance of a threaded joint for pipes is enhanced by forming a Cu alloy plating layer on the threaded joint for pipes.

  Specifically, the threaded joint for pipes described in Patent Document 2 includes a pin portion and a coupling. At both ends of the coupling, a box portion having a female screw and a metal-metal seal portion is provided. A Cu—Sn alloy layer is disposed on the surface of the female screw and the metal-metal seal portion of the coupling. Patent Document 2 describes that when this threaded joint for pipes is used, even when green dope (a lubricant containing no Pb) is used, sealing performance is better than before and goling can be remarkably suppressed. ing.

  The threaded joint for pipes described in Patent Document 3 includes a pin and a box. At least one contact surface of the pin and the box has a first plating layer made of a Cu—Zn alloy. Thus, it is described in Patent Document 3 that the threaded joint for pipes exhibits sufficient leakage resistance and seizure resistance even when green dope is applied or even when undoped.

International Publication No. 2009/072486 JP 2003-074763 A JP 2008-215473 A

  By the way, after the threaded joint for pipes is manufactured, it is transported by a ship or the like and stored for a certain period until it is used. Transportation and storage of pipe threaded joints may take a long time. Furthermore, the threaded joint for pipes may be stored outdoors. Long-term transportation and storage may cause rust to occur in the threaded joint for pipes, and may reduce the airtightness and seizure resistance of the threaded joint for pipes. Accordingly, the threaded joint for pipes is required to have excellent corrosion resistance in addition to the above-mentioned seizure resistance.

  However, even if the techniques disclosed in Patent Documents 1 to 3 described above are used, it may be difficult to achieve both seizure resistance and corrosion resistance of the threaded joint for pipes.

  An object of the present invention is to provide a threaded joint for pipes having excellent seizure resistance and corrosion resistance and a method for producing the same.

  The threaded joint for pipes of this embodiment includes a pin and a box, a Ni—W alloy plating layer, and a solid lubricating coating. Each pin and box has a contact surface including a threaded portion, a metal seal portion and a shoulder portion. The Ni—W alloy plating layer contains 35 to 45% by mass of W, with the balance being Ni and impurities. The thickness of the Ni—W alloy plating layer is 1 to 20 μm. The Ni—W alloy plating layer is disposed on the contact surfaces of both the pin and the box. The threaded joint for pipes further includes a solid lubricant film on at least one Ni—W alloy plating layer of the pin and the box.

  The manufacturing method of the threaded joint for pipes of this embodiment is a manufacturing method of the threaded joint for pipes provided with a pin and a box. Each pin and box has a contact surface including a threaded portion, a metal seal portion and a shoulder portion. The manufacturing method of this embodiment includes a Ni—W alloy plating layer forming step and a solid lubricant film forming step. In the Ni—W alloy plating layer forming step, a Ni—W alloy plating layer made of a Ni—W alloy is formed on the contact surfaces of both the pin and the box. The Ni—W alloy plating layer contains 35 to 45% by mass of W, with the balance being Ni and impurities. The thickness of the Ni—W alloy plating layer is 1 to 20 μm. In the solid lubricant film forming step, a solid lubricant film is formed on at least one of the Ni-W alloy plating layers of the pin and the box.

  The threaded joint for pipes of this embodiment has excellent seizure resistance and corrosion resistance.

FIG. 1 is a diagram showing a configuration of a threaded joint for pipes according to the present embodiment. FIG. 2 is a cross-sectional view of the threaded joint for pipes according to the present embodiment. FIG. 3 is a cross-sectional view of an example of the contact surface of the threaded joint for pipes according to the present embodiment.

  Hereinafter, this embodiment will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  The present inventors have made various studies on the seizure resistance and corrosion resistance of the threaded joint for pipes. As a result, the following knowledge was obtained.

  In order to increase the seizure resistance of the threaded joint for pipes during screw tightening and unscrewing, it is effective to form a plating layer having a high hardness and a high melting point on the contact surface having a thread portion, a metal seal portion and a shoulder portion. is there. If the hardness of the plating layer is high, the plating layer is less likely to be damaged when the screw joint for pipes is tightened and unscrewed. Furthermore, if the melting point of the plating layer is high, a decrease in the hardness of the plating layer can be suppressed even when the plating layer locally becomes hot during screw tightening and unscrewing of the pipe threaded joint. As a result, the seizure resistance of the threaded joint for pipes is increased.

  On the other hand, in order to improve the corrosion resistance of the threaded joint for pipes, it is effective to form a plating layer with few cracks and defects. When the plating layer includes defects such as cracks and pinholes, a corrosion factor enters from the cracks and defects. Therefore, the corrosion resistance of the threaded joint for pipes decreases.

  If the hardness of the plating layer is increased, the internal stress of the plating layer increases, so that cracks are likely to occur in the plating layer. Therefore, if the hardness of the plated layer is increased to increase the seizure resistance of the threaded joint for pipes during screw tightening and unscrewing, cracks may occur in the plated layer, which may reduce the corrosion resistance of the threaded joint for pipes. . In this case, it becomes difficult to achieve both seizure resistance and corrosion resistance.

  Therefore, the present inventors have further studied a plating layer suitable for a threaded joint for pipes. As a result, the inventors of the present invention include screwing and screwing if a Ni-W alloy plating layer containing 35 to 45% by mass of W and the balance being Ni and impurities is formed on the contact surface of the threaded joint for pipes. It has been found that the seizure resistance of the threaded joint for pipes at the time of return is increased and excellent corrosion resistance is obtained. Hereinafter, this point will be described.

  The hardness and melting point of Ni-W alloys containing Ni and W are higher than the hardness and melting point of Cu plating layers that have been conventionally used as plating layers for threaded joints for pipes. Therefore, the Ni—W alloy plating layer made of Ni—W alloy has high hardness (Hv 600 or more) and high melting point (1455 ° C. or more). As a result, if the Ni—W alloy plating layer is used, the seizure resistance of the threaded joint for pipes can be improved.

  The Ni—W alloy plating layer can further improve not only the seizure resistance of the threaded joint for pipes but also the corrosion resistance of the threaded joint for pipes. The Ni—W alloy plating layer has an amorphous structure. Therefore, the Ni—W alloy plating layer does not have structural defects such as pinholes as seen in crystalline metals, and is chemically extremely uniform. For this reason, the Ni—W alloy plating layer has few defects and is difficult for a corrosion factor to enter, and thus exhibits high corrosion resistance.

  However, as described above, since the Ni—W alloy plating layer has high hardness, the Ni—W alloy plating layer may crack. If a crack occurs in the Ni—W alloy plating layer, a corrosion factor enters from the crack and corrodes the base material (metal). With corrosion of the base material, the Ni—W alloy plating layer may peel off. In this case, the corrosion resistance is lowered, and it becomes difficult to achieve both seizure resistance and corrosion resistance.

  Therefore, the present inventors paid attention to the W content in the Ni—W alloy plating layer, and further examined the relationship between the W content, seizure resistance, and corrosion resistance. As a result, when the chemical composition of the Ni—W alloy plating layer is 100% by mass, if the W content is 35 to 45% by mass, generation of cracks can be suppressed, and the Ni—W alloy plating layer is excellent. The present inventors have found for the first time that it is possible to achieve both seizure resistance and excellent corrosion resistance.

  The reason for this is not clear, but the following can be considered. As described above, cracks in the plating layer are caused by internal plating stress. If the amorphous volume ratio in the plating layer is increased, the plating internal stress is lowered. If the W content in the Ni—W alloy plating layer increases, the volume ratio of amorphous in the plating layer increases. Thereby, internal stress falls. On the other hand, if W in the plating layer becomes supersaturated, the influence of amorphous becomes too strong, and the internal stress increases. If the W content in the Ni—W alloy plating layer is 35 to 45 mass%, the generation of cracks due to internal stress can be suppressed. Therefore, the seizure resistance and corrosion resistance of the threaded joint can be improved.

  The threaded joint for pipes of this embodiment completed based on the above knowledge is provided with a pin and a box, a Ni-W alloy plating layer, and a solid lubricating film. Each pin and box has a contact surface including a threaded portion, a metal seal portion and a shoulder portion. The Ni—W alloy plating layer contains 35 to 45% by mass of W, with the balance being Ni and impurities. The thickness of the Ni—W alloy plating layer is 1 to 20 μm. The Ni—W alloy plating layer is disposed on the contact surfaces of both the pin and the box. The threaded joint for pipes further includes a solid lubricant film on at least one Ni—W alloy plating layer of the pin and the box.

  The threaded joint for pipes of this embodiment has the above-mentioned Ni-W alloy plating layer on the contact surfaces of both the pin and the box. Therefore, it has excellent seizure resistance and corrosion resistance.

  The manufacturing method of the threaded joint for pipes of this embodiment is a manufacturing method of the threaded joint for pipes provided with a pin and a box. Each pin and box has a contact surface including a threaded portion, a metal seal portion and a shoulder portion. The manufacturing method includes a Ni—W alloy plating layer forming step and a solid lubricant film forming step. In the Ni—W alloy plating layer forming step, a Ni—W alloy plating layer made of a Ni—W alloy is formed on the contact surfaces of both the pin and the box. The Ni—W alloy plating layer contains 35 to 45% by mass of W, with the balance being Ni and impurities. The thickness of the Ni—W alloy plating layer is 1 to 20 μm. In the solid lubricant film forming step, a solid lubricant film is formed on at least one of the Ni-W alloy plating layers of the pin and the box.

  By the manufacturing method of the present embodiment, a threaded joint for pipes having a Ni—W alloy plating layer on both contact surfaces of the pin and the box can be manufactured. Therefore, the threaded joint for pipes has excellent seizure resistance and corrosion resistance.

  Hereinafter, the threaded joint for pipes and the manufacturing method thereof according to the present embodiment will be described in detail.

[Screw joint for pipes]
The threaded joint for pipes includes a pin and a box. FIG. 1 is a diagram showing a configuration of a threaded joint for pipes according to the present embodiment. Referring to FIG. 1, the threaded joint for pipe includes a steel pipe 1 and a coupling 2. At both ends of the steel pipe 1, pins 3 having male thread portions on the outer surface are formed. At both ends of the coupling 2, boxes 4 having internal thread portions on the inner surface are formed. The coupling 2 is attached to the end of the steel pipe 1 by screwing the pin 3 and the box 4 together.

  The threaded joint for pipes of this embodiment may be an integral-type threaded joint for oil well pipes in which one end of the steel pipe 1 is a pin 3 and the other end is a box 4 without using the coupling 2. . That is, the threaded joint for pipes of this embodiment may be the coupling system shown in FIG. 1 or the integral type described above.

  Each of the pin 3 and the box 4 includes a contact surface having a threaded portion, a metal seal portion, and a shoulder portion. FIG. 2 is a cross-sectional view of the threaded joint for pipes according to the present embodiment. With reference to FIG. 2, the pin 3 includes a male screw portion 31, a metal seal portion 32, and a shoulder portion 33. The box 4 includes a female screw part 41, a metal seal part 42, and a shoulder part 43. The portions that come into contact when the pin 3 and the box 4 are screwed together are referred to as contact surfaces 34 and 44. Specifically, when the pin 3 and the box 4 are screwed together, the screw parts (male screw part 31 and female screw part 41), the metal seal parts (metal seal parts 32 and 42), and the shoulder parts (shoulder part). 33 and 43) contact each other. That is, the contact surfaces 34 and 44 include screw portions 31 and 41, metal seal portions 32 and 42, and shoulder portions 33 and 43.

  FIG. 3 is a cross-sectional view of an example of the contact surfaces 34 and 44 of the threaded joint for pipes according to the present embodiment. In FIG. 3, the threaded joint for pipes includes a Ni—W alloy plating layer 100 on the contact surface 34 of the pin 3 and the contact surface 44 of the box 4. The threaded joint for pipes may further include a solid lubricating coating 200 on the Ni—W alloy plating layer 100. If the solid lubricating coating 200 is provided on the Ni—W alloy plating layer 100, the lubricity is enhanced and the seizure resistance of the threaded joint for pipes is further enhanced.

  The arrangement of the alloy plating layer of this embodiment is not limited to FIG. A Ni—W alloy plating layer 100 is provided on both the contact surface 34 of the pin 3 and the contact surface 44 of the box 4, and a solid lubricating film is formed on at least one Ni—W alloy plating layer 100 of the pin 3 and the box 4. 200 and the solid lubricant film 200 may not be provided on the other Ni—W alloy plating layer 100.

[Ni-W alloy plating layer 100]
The Ni—W alloy plating layer 100 is disposed on the contact surfaces 34 and 44 of both the pin 3 and the box 4. The Ni—W alloy plating layer 100 is made of a Ni—W alloy. The Ni-W alloy contains Ni and W, and the balance consists of impurities. Here, the impurities are substances other than Ni and W, which are contained in the Ni-W alloy plating layer 100 during the manufacture of the threaded joint for pipes and contained in a content that does not affect the effects of the present invention. Including. Impurities are, for example, Fe, S, O, C and the like. The hardness and melting point of the Ni—W alloy plating layer 100 are high. Therefore, the seizure resistance of the pipe threaded joint is increased.

  When the chemical composition of the Ni—W alloy plating layer 100 is 100 mass%, the Ni—W alloy plating layer 100 contains 35 to 45 mass% W. In this case, the generation of cracks in the Ni—W alloy plating layer can be suppressed, and the Ni—W alloy plating layer exhibits high corrosion resistance. As a result, the threaded joint for pipes can achieve both excellent seizure resistance and excellent corrosion resistance.

  W increases the amorphous volume ratio of the Ni—W alloy plating layer 100. If the amorphous volume ratio increases, the internal stress decreases and cracks are suppressed. As a result, the corrosion resistance of the pipe threaded joint is increased. If the W content is less than 35% by mass, this effect cannot be obtained. If the W content is less than 35% by mass, the hardness of the Ni—W alloy plating layer 100 is further lowered and seizure resistance is lowered. On the other hand, if the W content exceeds 45% by mass, the amorphous volume ratio in the Ni—W alloy plating layer 100 is too high. In this case, cracks are generated in the Ni—W alloy plating layer 100 and the corrosion resistance is lowered. If the W content exceeds 45% by mass, the hardness will be too high, and the seizure resistance will be lowered. Therefore, the W content in the Ni—W alloy plating layer 100 is 35 to 45 mass%. The minimum with preferable W content in the Ni-W alloy plating layer 100 is 38 mass%. The upper limit with preferable W content in the Ni-W alloy plating layer 100 is 42 mass%.

  The W content of the Ni—W alloy plating layer 100 is measured by the following method. The W content is measured using, for example, a hand-held X-ray fluorescence analyzer (Olympus DP2000 (trade name DELTA Premium)). Composition analysis is performed at any four locations (any 0 °, 90 °, 180 °, and 270 ° locations in the tube circumferential direction) on the surface of the metal seal portion subjected to Ni-W. The measured content of Ni and W is determined according to the measurement mode of the alloy. The W content (mass%) is obtained by dividing the measured content of Ni and W by the measured content of W.

  The thickness of the Ni—W alloy plating layer 100 is 1 to 20 μm. If the thickness of the Ni—W alloy plating layer 100 is less than 1 μm, the seizure resistance and the corrosion resistance decrease. If the thickness of the Ni—W alloy plating layer 100 exceeds 20 μm, the adhesion of the plating is lowered.

  The thickness of the Ni—W alloy plating layer 100 is measured by the following method. The contact surface on which the Ni—W alloy plating layer 100 is formed is brought into contact with an overcurrent phase film thickness measuring instrument probe conforming to ISO (International Organization for Standardization) 21968 (2005). The phase difference between the high frequency magnetic field on the input side of the probe and the overcurrent on the Ni—W alloy plating layer 100 excited thereby is measured. This phase difference is converted into the thickness of the Ni—W alloy plating layer 100. In the film thickness measurement at the threaded joint, any four locations (any 0 °, 90 °, 180 °, 270 ° locations in the pipe circumferential direction) of the metal seal portion are measured.

[Solid lubricating coating 200]
Referring to FIG. 3, the threaded joint for pipes preferably further includes a solid lubricating coating 200 on at least one Ni—W alloy plating layer 100 of pin 3 and box 4. In this case, the lubricity of the threaded joint for pipes is further enhanced. A well-known solid lubricant film 200 can be used. The solid lubricating coating 200 contains, for example, lubricating particles and a binder. The solid lubricating coating 200 may contain a solvent and other components as necessary.

The lubricating particles reduce the friction coefficient of the surface of the solid lubricating coating 200. The lubricating particles are not particularly limited as long as they have lubricating properties. Lubricating particles include, for example, graphite, MoS ₂ (molybdenum disulfide), WS ₂ (tungsten disulfide), BN (boron nitride), PTFE (polytetrafluoroethylene), CF _x (graphite fluoride) and CaCO ₃ (carbonic acid). One or more selected from the group consisting of calcium). Preferably, graphite, graphite fluoride, MoS ₂ and PTFE are used. When the solid lubricating coating is 100% by mass, the preferred content of the lubricating particles is 5 to 40% by mass.

  The binder binds the lubricating particles into the solid lubricating coating 200. The binder is, for example, one or two selected from the group consisting of organic resins and inorganic resins. When using organic resin, 1 type selected from the group which consists of a thermosetting resin and a thermoplastic resin can be used. The thermosetting resin is, for example, one or two selected from the group consisting of epoxy resin, polyimide resin, polycarbodiimide resin, polyether sulfone, polyether ether ketone resin, phenol resin, furan resin, urea resin, and acrylic resin. More than a seed. The thermoplastic resin is, for example, one or more selected from the group consisting of polyamideimide resin, polyethylene resin, polypropylene resin, polystyrene resin, and ethylene vinyl acetate resin. When the solid lubricant film is 100% by mass, the preferable content of the binder is 60 to 95% by mass.

  When an inorganic resin is used, polymetalloxane can be used. The polymetalloxane refers to a polymer compound in which a repeating metal-oxygen bond is a main chain skeleton. Preferably, polytitanoxane (Ti—O) and polysiloxane (Si—O) are used. These inorganic resins are obtained by hydrolyzing and condensing metal alkoxide. The alkoxy group of the metal alkoxide is, for example, a lower alkoxy group such as a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, an isobutoxy group, a butoxy group and a tert-butoxy group.

  When it is necessary to dissolve or disperse the lubricating particles and the binder, a solvent is used. The solvent is not particularly limited as long as it can disperse or dissolve the components contained in the solid lubricating coating 200. As the solvent, one or two selected from the group consisting of an organic solvent and water can be used. The organic solvent is, for example, one or two selected from the group consisting of toluene and isopropyl alcohol.

  The solid lubricating coating 200 can contain other components as necessary. Other components are, for example, rust inhibitors, corrosion inhibitors, surfactants, waxes, friction modifiers, pigments and the like. The respective contents of the lubricating particles, the binder, the solvent and other components are appropriately set.

[Base material for threaded joints for pipes]
The chemical composition of the base material of the threaded joint for pipes is not particularly limited. Examples of the base material include carbon steel, stainless steel, and alloy steel. Among alloy steels, the corrosion resistance of duplex stainless steels containing alloy elements such as Cr, Ni and Mo and high alloy steels such as Ni alloys is high. Therefore, if these high alloy steels are used as the base material, the corrosion resistance of the threaded joint for pipes is increased. The base material of the threaded joint for pipes is, for example, 13% Cr steel (C: 0.18%, Si: 0.23%, Mn: 0.8%, P: 0.02%, which is a kind of high alloy steel, S: 0.01%, Cu: 0.04%, Ni: 0.1%, Cr: 13%, Mo: 0.04%, balance: Fe and impurities).

[Production method]
The manufacturing method of the threaded joint for pipes of this embodiment is a manufacturing method of the above-mentioned threaded joint for pipes. The manufacturing method includes a Ni—W alloy plating layer forming step and a solid lubricant film forming step.

[Ni-W alloy plating layer forming step]
In the Ni—W alloy plating layer forming step, the Ni—W alloy plating layer 100 made of the Ni—W alloy is formed on the contact surfaces 34 and 44 of both the pin 3 and the box 4 of the prepared pipe thread joint. The Ni—W alloy plating layer 100 is formed by electroplating. The electroplating is performed by immersing the contact surfaces 34 and 44 of the pin 3 or the box 4 as the material to be plated in a plating bath containing Ni ions and W ions, and applying current. The plating bath preferably contains Ni ions: 0.13-0.3 mol / L and W ions: 0.3-0.42 mol / L. The conditions for electroplating can be set as appropriate. The electroplating conditions are, for example, plating bath pH: 1 to 10, plating bath temperature: 10 to 60 ° C., current density: 1 to 100 A / dm ² , and processing time: 0.1 to 30 minutes.

[Solid lubricating film forming process]
A solid lubricating coating 200 is formed on the Ni—W alloy plating layer 100 of at least one of the pin 3 and the box 4. In the solid lubricant film forming step, first, a solid lubricant film composition (hereinafter also referred to as a composition) is prepared. The composition is formed by mixing the lubricating particles and binder described above. The composition may further contain the above-described solvent and other components.

  The obtained composition is applied onto the Ni—W alloy plating layer 100. The method of application is not particularly limited. For example, the composition is sprayed onto the Ni—W alloy plating layer 100 using a spray gun. The pin 3 or the box 4 to which the composition is applied is heated and dried. As a result, the composition is cured, and the solid lubricating coating 200 is formed on the Ni—W alloy plating layer 100. The conditions for the heat drying can be appropriately set in consideration of the boiling point and melting point of each component contained in the composition. For compositions that do not use a solvent, the hot melt method can be used. In the hot melt method, the composition is heated to a fluid state. The composition in a fluidized state is sprayed using, for example, a spray gun having a temperature holding function. The pin 3 or the box 4 coated with the composition is cooled by air cooling or the like. As a result, the composition is cured, and the solid lubricating coating 200 is formed on the Ni—W alloy plating layer 100.

[Ground treatment process]
This manufacturing method may implement a base treatment process before a Ni-W alloy plating layer formation process as needed. The ground treatment process is, for example, pickling and alkali degreasing. In the base treatment step, oil and the like attached on the contact surface forming the Ni—W alloy plating layer is washed. The ground treatment step may further include grinding such as sand blasting and mechanical grinding. Only one type of these base treatments may be performed, or a plurality of base treatments may be combined.

  Examples will be described below. In the embodiment, the contact surface of the pin is referred to as the pin surface, and the contact surface of the box is referred to as the box surface. Moreover,% in an Example means the mass%.

  For the base material, 13% Cr steel (C: 0.18%, Si: 0.23%, Mn: 0.8%, P: 0.02%, S: 0.0. 01%, Cu: 0.04%, Ni: 0.1%, Cr: 13%, Mo: 0.04%, balance: Fe and impurities). Using this 13% Cr steel, seamless steel pipes and couplings were produced. The seamless steel pipe had an outer diameter of 168.28 mm, a wall thickness of 12.1 mm, and a length of 1200 mm. On the outer surface of both ends of the seamless steel pipe, a pin having a male thread part and an unthreaded metal contact part was formed by cutting. Boxes having internal thread portions and unthreaded metal contact portions were formed on the inner surfaces of both ends of the coupling by cutting.

[Ni-W alloy plating layer forming step]
A Ni—W alloy plating layer was formed on the surface of the pin and the box of test number 1 to test number 7. The Ni—W alloy plating layer was formed by electroplating. Specifically, the Ni—W alloy plating layer was formed by immersing the coupling in the plating bath of each test number and energizing it. The plating conditions were plating bath pH: 5, plating bath temperature: 60 ° C., current density: 20 A / dm ² (constant current electrolysis method). The composition of the plating bath for each test number was as shown in Table 1.

  The plating bath was prepared by dissolving commercially available nickel sulfate heptahydrate, disodium tungstate, triammonium citrate: 0.6 mol / L in pure water. The total metal salt concentration was constant at 0.6 mol / L. Several plating baths were constructed by changing the ratio of disodium tungstate concentration to total metal salt concentration.

  A Cu—Sn—Zn alloy plating layer was formed on the surface of the pin and box of test number 8. Specifically, a Cu—Sn—Zn alloy plating layer was formed on the box surface by electroplating using a cyan bath containing copper ions, tin ions and zinc ions. The Cu—Sn—Zn alloy plating layer contained Zn: about 7%, Sn: about 40%, Cu: about 53%.

[Solid lubricating film forming process]
A solid lubricating film was further formed on the surface of the boxes of Test No. 1 to Test No. 8. The composition for forming a solid lubricant film contained polyamideimide resin: 12% by mass, dimethyl sulfoxide: 45% by mass, PTFE particles: 5% by mass, and pure water: the balance. After spraying this composition on the alloy plating layer, preliminary drying (85 ° C., 10 minutes) and main heating (280 ° C., 30 minutes) were performed to form a solid lubricating film having an average film thickness of 30 μm.

  The pin surface was subjected to mechanical grinding finish (surface roughness 3 μm), and then a solid anticorrosive film was formed. The composition for forming a solid anticorrosive film contained an acrylic resin-based ultraviolet curable resin paint, aluminum phosphite, and polyethylene wax. The contents of aluminum phosphite and polyethylene wax were 0.05 and 0.01, respectively, with respect to the acrylic resin ultraviolet curable resin 1. After this composition was applied to the surface of the pin, the composition was cured by irradiating it with ultraviolet rays using a UV lamp (air-cooled mercury lamp, output 4 kW, ultraviolet wavelength: 260 nm). The thickness of the solid anticorrosion coating was 25 μm.

[Measurement of W content in alloy plating layer]
The W content in the alloy plating layer of each test number was measured by the method described above. The results are shown in Table 1.

[Alloy plating layer thickness measurement test]
The thickness of the alloy plating layer of each test number was measured by the method described above. The results are shown in Table 1.

[Evaluation test for seizure resistance]
Seizure resistance was evaluated for the pins and boxes of each test number. Specifically, using a seamless steel pipe having a pin and a box of each test number and a coupling, screw tightening and unscrewing were repeated at room temperature. Screwing and unscrewing was repeated up to 10 times. The tightening torque for screw tightening was 49351.8 N · m (36400 ft · lbs). Each time the screw tightening and screw unwinding were performed once, the pin surface was visually observed. The occurrence of seizure was confirmed by visual observation. The number of times that screw tightening and screw unwinding were observed without causing seizure. The results are shown in Table 1. In Table 1, “> 10” indicates that seizure did not occur even when screw tightening and screw unscrewing were repeated 10 times.

[Salt spray test]
The salt spray test was implemented using the test piece which has the same composition as the said coupling. The test piece was provided with the same alloy plating layer and solid lubricant film as the box surface of each test number. The size of the test piece was 70 mm in width, 50 mm in length, and 1 mm in thickness. The salt spray test was performed based on the method described in JIS Z2371 (2000). The test time was a maximum of 1000 hours. The time when rust was generated on the surface of the test piece of each test number was measured by visual observation. The results are shown in Table 1. In Table 1, “> 1000” indicates that rust did not occur even after 1000 hours. In Table 1, “<500” indicates that rusting occurred in less than 500 hours.

[Evaluation results]
Referring to Table 1, the threaded joints for pipes of Test No. 3 to Test No. 5 were provided with Ni—W alloy plating layers on the contact surfaces of both the pin and the box. Furthermore, the W content in the Ni—W alloy plating layer was 35 to 45 mass%. Therefore, excellent seizure resistance and corrosion resistance were exhibited. Specifically, in the threaded joints for pipes of test numbers 3 to 5, no seizure occurred even when the screw tightening and screw return were repeated nine times. Furthermore, the threaded joints for pipes of Test No. 3 to Test No. 5 were not confirmed to rust even after 1000 hours in the salt spray test.

  On the other hand, in the threaded joint for tubes of test number 1, the W content of the Ni—W alloy plating layer was less than 35 mass%. Therefore, seizure occurred in the threaded joint for pipe of test number 1 when the screw tightening and screw unscrewing were repeated four times. Furthermore, the pipe thread joint of test number 1 was confirmed to rust after 650 hours in the salt spray test.

  In the threaded joint for pipes of test number 2, the W content of the Ni—W alloy plating layer was less than 35 mass%. Therefore, seizure occurred in the threaded joint for pipe of test number 2 when the screw tightening and screw unscrewing were repeated three times. Further, rusting was confirmed in the threaded joint for pipe of test number 2 after 750 hours in the salt spray test.

  In the threaded joint for pipe of test number 6, the W content of the Ni—W alloy plating layer exceeded 45 mass%. Therefore, seizure occurred in the threaded joint for pipe of test number 6 when the screw tightening and screw unscrewing were repeated five times. Furthermore, rusting was confirmed in the threaded joint for pipe of test number 6 after 700 hours had passed in the salt spray test.

  In the threaded joint for pipe of test number 7, the thickness of the Ni—W alloy plating layer was as thin as 0.5 μm. Therefore, seizure occurred in the threaded joint for test No. 7 when screw tightening and screw unscrewing were repeated twice. Furthermore, rusting was confirmed in less than 500 hours in the salt spray test.

  The threaded joint for pipes of test number 8 was provided with a conventional Cu—Sn—Zn alloy plating layer. Therefore, seizure occurred in the threaded joint for pipe of test number 8 when screw tightening and screw unscrewing were repeated seven times. Furthermore, rusting was confirmed in the pipe thread joint of test number 8 after 750 hours in the salt spray test.

  The embodiment of the present invention has been described above. However, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately changing the above-described embodiment without departing from the spirit thereof.

3 Pin 4 Box 31, 41 Thread part 32, 42 Metal seal part 33, 43 Shoulder part 34, 44 Contact surface 100 Ni-W alloy plating layer 200 Solid lubricant film

Claims (2)

A pin and a box each having a contact surface including a threaded portion, a metal seal portion and a shoulder portion;
Ni-W alloy plating layer containing 35 to 45% by mass of W on the contact surfaces of both the pin and the box, the balance being Ni and impurities, and having a thickness of 1 to 20 μm;
A threaded joint for pipes, comprising a solid lubricating coating on the Ni-W alloy plating layer of at least one of the pin and the box. Each of which is a method of manufacturing a threaded joint for a pipe comprising a pin and a box having a contact surface including a thread portion, a metal seal portion and a shoulder portion,
On the contact surfaces of both the pin and the box, a Ni-W alloy plating layer containing 35 to 45% by mass of W, the balance being made of Ni and impurities, and having a thickness of 1 to 20 μm is formed. And a process of
Forming a solid lubricant film on the Ni-W alloy plating layer of at least one of the pin and the box.

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