[0001]The present invention relates to a method of manufacturing a pipe thread fittings and tube or pipe threaded joint.
Background technique
[0002]For mining oil and natural gas fields, oil well pipe is used. Depending on the depth of the well, used by connecting a plurality of steel pipes. Coupling of the steel pipe is performed by screwing the formed pipe thread joint between the ends of the steel pipe. Steel tube, raised for the inspection, is unscrewing, after being examined, is again screwing, is used again.
[0003]
　Pipe thread joint comprises a pin and box. Pin, the outer peripheral surface of the distal end portion of the steel pipe, having a contact surface comprising external threads and an unthreaded metal contact portion. Box, the inner peripheral surface of the distal end portion of the steel pipe, having a contact surface comprising a female threaded portion and an unthreaded metal contact portion. Threaded portion and unthreaded metal contact surfaces of the pin and box, repeatedly subjected to strong friction at the time of the return screw tightening and screw of the steel pipe. These sites, if there is sufficient resistance to friction, galling when repeated back screw tightening and screw (with irreparable shrink) occurs. Therefore, the Pipe threaded joint, sufficient durability against the friction, i.e., is required to have excellent seizure resistance.
[0004]
　Conventionally, in order to improve the seizure resistance, heavy metal containing the compound grease called dope have been used. By applying a compound grease on the surface of the pipe thread joint can improve the galling resistance of the pipe thread fittings. However, heavy metals Pb, Zn and Cu or the like contained in the compound grease is likely to affect the environment. Therefore, development of a pipe thread joint not using compound grease is desired.
[0005]
　JP 2002-221288 (Patent Document 1) and WO 2009/072486 (Patent Document 2) proposes a pipe thread joint having excellent galling resistance without the compound grease.
[0006]
　The pin or the box of the contact surface of the pipe thread joint disclosed in Patent Document 1, at least one of the threaded portion and the unthreaded metal contact portions of the pin or box of the pipe threaded joint, Zn porous by impact plating or forming a Zn alloy layer, thereon a solid lubricating coating or a heavy metal powder does not contain a liquid lubricating coating (eg, coatings and main agent highly basic organic metal salts such as highly basic sulfonates) are formed. Accordingly, without using a liquid lubricant containing heavy metal powder such compounds grease, it has high corrosion resistance, it is possible to suppress the seizure generation and airtightness deterioration due to rust generation at the time of repeated tightening and loosening , and it is described in Patent Document 1.
[0007]
　Pipe threaded joint described in Patent Document 2, the contact surface of the box has a solid lubricating coating having plastic or viscoplastic rheological behavior as an uppermost layer, the contact surface of the pin, an ultraviolet curable resin as an uppermost layer characterized in that it has a solid corrosion protective coating composed mainly of. Thus, without using a compound grease, suppressing the occurrence of rust, it showed excellent galling resistance and airtightness, and no stickiness on the surface, the pipe threaded joint having excellent appearance and inspection can be obtained, It is described in Patent Document 2.
CITATION
Patent Document
[0008]
Patent Document 1: JP 2002-221288 Patent Publication
Patent Document 2: WO 2009/072486
Summary of the Invention
Problems that the Invention is to Solve
[0009]
　Evaluation of seizure resistance is usually performed in a state of being matched core steel pipes for screwing. However, if indeed the pipe thread joint for screwing, which may lead between steel pipe screwing (or steel pipe and coupling) is shifted. This is called misalignment. If misalignment occurs, the pin and box of the contact surface (threaded portion and unthreaded metal contact portion) is subjected to strong shear stress to the strong friction. This shear stress, than in the case of no misalignment, significantly large. Therefore, when misalignment occurs, the seizure is more likely to occur. Therefore, the Pipe threaded joint, suppressing performance seizure even if misalignment occurs, i.e., resistance to misalignment is required.
[0010]
　On the other hand, the unthreaded metal contact portions of the above, comprises a metal seal portion and the shoulder portion. When screwing the pipe thread joint, shoulder portions of the pin and box are in contact. The torque generated at this time that the shoulder ring torque. The pipe thread fitting when screwing, after reaching shouldering torque, for further screwing until the fastening is complete. Thus, it increases airtightness of pipe thread fittings. Further performing screw tightening, the metal constituting at least one of the pin and box begin to undergo plastic deformation. The torque generated at this time that the yield torque.
[0011]
　Engagement completion time of the torque (that engaging torque) regardless of the magnitude of the thread interference is set such that a sufficient seal surface pressure can be obtained. The difference between the shouldering torque and yield torque, that is, is sufficiently large torque on shoulder value, can afford the range of fastening torque. As a result, it becomes easy to adjust the fastening torque. Therefore, the Pipe threaded joint, in addition to the resistance to misalignment of the above is required to have excellent torque characteristics.
[0012]
　On the other hand, OCTG, after being manufactured, transported by ship or the like, is stored a certain period until used. Transport and storage of oil country tubular goods, there is a case in which over a long period of time. Furthermore, storage of oil well pipes might be carried out outdoors. If long term stored outdoors, rust is generated in the threaded joint for oil well pipes, galling resistance and gas tightness of the threaded joint for oil well pipes is reduced in some cases. Therefore, the threaded joint for an oil well pipe is added to the seizure of the above, temperature -20 ℃ ~ + 50 ℃ about not only cold-warm-tropical regions, also be a temperature such as -60 ° C. ~ -20 ° C. even when used in very cold areas, it is required to have excellent corrosion resistance.
[0013]
　The contact surface (threaded portion and unthreaded metal portion), a lubricating film is formed for the purpose of improving the seizure resistance. If oil well pipe as described above are stored outdoors, OCTG sometimes repeated exposure to high temperatures and low temperatures. When repeatedly exposed to high temperature and low temperature, the adhesion of the lubricating coating decreases. A decline in adhesion of the lubricating coating, when carrying out the screwing, lubricating coating may peel off. If the lubricant film is peeled off, and reduced resistance to misalignment of the pipe thread joint further shouldering torque increases. Therefore, the Pipe threaded joint, even when subjected to temperature changes in the repetitive, the high adhesion of the solid lubricating coating is required.
[0014]
　Pipe threaded joint disclosed in Patent Document 1, Zn or Zn alloy layer is porous. Therefore, adhesion between the solid lubricating coating is good, with sufficient seizure resistance. However, because it is porous, the void between the Zn or Zn alloy layer and the base material occurs. Therefore, the base metal of the resulting void portion, which may corrode during long-term course.
[0015]
　Pipe threaded joint described in Patent Document 2, in the normal temperature of the use environment, having adhesion and lubrication performance superior solid lubricating coating. Therefore, with sufficient seizure resistance in a normal temperature. However, the ambient temperature used in the pipe thread joints may of hot or cold. And the base material of the pipe thread joint, the thermal expansion coefficient between the solid lubricant film is different. Therefore, use environmental temperatures of the pipe thread joint if a high temperature, adhesion of the solid lubricating coating decreases. Further, if high-temperature use environment temperature of pipe thread joint, a solid lubricating coating is softened and oxidation. Thereby, adhesion of the solid lubricating coating is further reduced. On the other hand, the ambient temperature of the pipe thread joint if cryogenic, solid lubricating coating is hardened and embrittled. Thereby, adhesion of the solid lubricating coating decreases. A decline in adhesion of a solid lubricating coating, peeling and some damage to the solid lubricating coating to occur, seizure resistance of pipe thread joint is reduced. Additionally, threaded joint for pipes, at the time of transportation is exposed to high temperatures, which may in use be exposed to cryogenic temperatures. Therefore, the Pipe threaded joint, even if repeatedly exposed to high temperatures and cryogenic temperatures is required to have a high adhesion to the solid lubricating coating.
[0016]
　An object of the present invention has excellent seizure resistance, torque characteristics, and has a corrosion resistance, high temperature and repeated exposed pipe thread joint and a manufacturing method thereof having contact with the superior lubricating coating be cryogenically it is to provide.
Means for Solving the Problems
[0017]
　Pipe thread joint of the present embodiment includes a pin and box. Each pin and box has a contact surface including a threaded portion and an unthreaded metal contact portion. Pipe thread joint includes a first plating layer, the second plating layer, and a lubricating coating. The first plating layer is formed on at least one of the contact surfaces of the pin and box, made of Zn-Ni alloy. The second plating layer is formed on the first plating layer is a plating layer of porous made of Zn or Zn alloy. Lubricating coating is formed on the second plated layer. Contact surface side, a first plating layer made of Zn-Ni alloy, the second plating layer consisting of Zn or Zn alloy, and are laminated in this order lubricating coating.
[0018]
　Method for manufacturing a pipe thread joint of the present embodiment, each of which is the manufacturing method of the pipe thread joint comprising a pin and box has a contact surface including a threaded portion and an unthreaded metal contact portion. The manufacturing method of this embodiment is provided with the electroplating process, and impact plating step, a lubricant film formation step. The electroplating process, on at least one of the contact surfaces of the pin and box to form a first plating layer made of Zn-Ni alloy was carried out electroplating treatment. The impact plating process, after forming the first plating layer, an impact plating treatment was performed to form the second plating layer consisting of Zn or Zn alloy. The lubricating coating step, on the second plating layer to form a lubricating coating.
Effect of the invention
[0019]
　Pipe thread joint of the present embodiment has excellent seizure resistance, torque characteristics, and has a corrosion resistance, the adhesion between the repetition exposed excellent lubricating coating be a high temperature and a cryogenic temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020]
[1] Figure 1 is a case where misalignment has occurred, a schematic diagram of a screwing of the steel pipe.
FIG. 2 is a diagram showing the rotational speed of the pipe thread joint, the relationship between the torque.
FIG. 3 is a diagram showing a configuration of a pipe thread joint of the present embodiment.
[4] FIG. 4 is a cross-sectional view of a pipe thread joint according to the present embodiment.
FIG. 5 is a cross-sectional view of the contact surface of the pipe thread joint according to the present embodiment.
DESCRIPTION OF THE INVENTION
[0021]
　Hereinafter, with reference to the accompanying drawings, the present embodiment will be described in detail. Its description will not be repeated the same reference numerals designate like or corresponding parts in FIG.
[0022]
　The present inventor has seizure resistance pipe thread joint having a pin and box were studied the relationship between the adhesion of the torque characteristic, corrosion resistance, and lubricating coating. As a result, the present inventors have obtained the following findings.
[0023]
　As an indication of seizure resistance, there is a high temperature resistance and misalignment resistance. In conventional pipe thread fittings, high temperature resistance can be sufficient, in some cases anti-misalignment resistance is insufficient. Figure 1 is a schematic view for explaining a misalignment. Referring to FIG. 1, the steel pipe 100, steel body (hereinafter, simply referred to as body) provided with a 101 and a coupling 102. Coupling 102 is fixedly screwing the upper end of the body 101. Steel tube 100 has a pin 103 on the outer circumferential surface of the lower end (lower end of the body 101) has a box 104 on the inner peripheral surface of the upper end (the upper end of the coupling 102). As shown in FIG. 1, the steel pipe 100 which is vertically aligned, the pin 103 of the upper steel tube 100 is inserted in the box beneath the steel pipe 100, it is screwed. Thus, coupling is arranged steel pipes 100 to each other up and down.
[0024]
　When screwing, the upper steel pipe 100, preferably screwing and disposed below the steel pipe 100 coaxially. However, in practice, during the screwing, the central axis of the upper of the steel pipe 100, not aligned and the central axis of the lower of the steel pipe 100, which may intersect. This is called misalignment. By carrying out screwing in a state in which misalignment has occurred, as compared with the case of no misalignment, more likely to occur seizure.
[0025]
　To increase the resistance to misalignment of the pipe thread joint, a plating layer having a high hardness and high melting point, it is effective to form a contact surface including a threaded portion and an unthreaded metal contact portion. The higher the hardness of the plating layer, the plating layer on the contact surface during the return screw tightening and screw is less likely to be damaged. Furthermore, the higher the melting point of the plating layer, during the return screw tightening and screw, locally plated layer even when heated to a high temperature is hard to put to melt.
[0026]
　Therefore, pipe threaded joint according to the present embodiment, to form the first plating layer made of Zn-Ni alloy on the contact surface. The first plating layer is preferably a porosity of less than 5%. The first plating layer porosity is less than 5%, it can be formed by electroplating treatment. Thus, first plating layer is electroplated layer.
[0027]
　Hardness and the melting point of Zn-Ni alloy constituting the first plating layer is high. Therefore, it is possible to increase the resistance to misalignment of the pipe thread fittings. Zinc (Zn) is lower hardness and melting point as compared with copper which have been used in a conventional plating layer (Cu). However, Zn-Ni alloy is Zn alloys have a sufficiently high hardness and high melting point. Therefore, the first plating layer, it is possible to improve the resistance to misalignment resistance.
[0028]
　Furthermore the use of the Zn-Ni alloy, it is possible to improve the corrosion resistance of the pipe thread fittings. Zinc (Zn) is iron (Fe), a base metal as compared with nickel (Ni) and chromium (Cr). Therefore, zinc by forming a first plating layer comprising (Zn) on the contact surface, preferentially plating layer is corroded than steel (sacrificial protection). Thus, it increases corrosion resistance of the pipe thread fittings.
[0029]
　On the other hand, to increase the lubricity, usually lubricating coating is formed on the contact surface of the pipe thread fittings. Lubricating coating may be either a solid lubricating coating and a liquid lubricating coating. Lubricating coating, by repeated exposure to high temperatures and low temperatures, the adhesion is lowered. Lubricating coating adhesion is lowered, peeling the pipe thread joint when returning screwing and screw. In particular, when the screwing in situations where misalignment occurs is performed easily lubricating coating peeled off. If the lubricant film is peeled off, the lubricity of the threaded portion of the pipe thread joint is reduced.
[0030]
　Since the first plating layer is an electrical plating layer has a flat surface. Therefore, when the solid lubricant film is formed on the first plating layer, the adhesion of the lubricating coating tends to decrease.
[0031]
　Therefore, on the first plating layer, forming a second plating layer of porous made of Zn or Zn alloy, to form a lubricating coating on the second plating layer. In this case, adhesion of the lubricating coating is increased. The second plating layer, than the first plating layer porous: a (porous Porous). Preferably, the porosity of the second plating layer is 5 to 80%. Second plating layer of porous than the first plating layer can be formed by impact plating. Therefore, the second plating layer is an impact plating layer. Second plating layer is an impact plating layer has an uneven surface. If it is a lubricating coating is formed on a surface having irregularities, a so-called anchor effect, the adhesion is improved. The higher the adhesion of the lubricating coating, even if it is repeatedly exposed to high temperature and low temperature, separation of the lubricant film is suppressed. If it is peeled off the lubricant film suppressed, lubricity is maintained high during the return screw tightening and screw. Therefore, further increases the resistance to misalignment of the pipe thread fittings.
[0032]
　Further if it is maintained high lubricity of pipe thread joint, yield torque when the screw tightening is increased. Figure 2 is a diagram showing the relationship between the rotational speed and torque of the threaded portion of the pipe thread fittings. Referring to FIG. 2, when the pin and box screwing, shoulder portions of the pin and box are in contact. The torque generated at this time that the shoulder ring torque. The threaded portion of the pipe thread joint when screwing, after reaching shouldering torque, for further screwing until the fastening is complete. Thus, it increases airtightness of the threaded portion of the pipe thread fittings. Further performing screw tightening, the metal constituting at least one of the pin and box begin to undergo plastic deformation. The torque generated at this time that the yield torque.
[0033]
　Engagement completion time of the torque (fastening torque) regardless of the magnitude of the thread interference is set such that a sufficient seal surface pressure can be obtained. If is sufficiently large torque on shoulder value is the difference between the shouldering torque and yield torque, can afford the range of fastening torque. As a result, it becomes easy to adjust the fastening torque. Thus, yield torque, it is preferable not become too low. It shows sufficient adhesion of the lubricating coating, even after repeated back screw tightening and screw, yield torque is kept high. That is, after repeated use also, it is easy to adjust the fastening torque, excellent torque characteristics.
[0034]
　Pipe thread joint of the present embodiment has been completed based on the above findings, having a pin and box. Each pin and box has a contact surface including a threaded portion and an unthreaded metal contact portion. Pipe thread joint, the pin and box of at least one contact surface on the Zn-Ni first plating layer made of an alloy, and a second plating layer of porous made of Zn or Zn alloy on the first plating layer, the and a lubricant film on the second plating layer. These are from the contact surface side, the first plating layer are laminated in this order in the second plating layer and the lubricating coating.
[0035]
　Pipe thread joint of the present embodiment includes a first plating layer on the contact surface. Zn-Ni alloy constituting the first plating layer is a high hardness and high melting point. Therefore, excellent resistance to misalignment resistance. In addition, Zn-Ni alloy has a sacrificial protection effect. Therefore, pipe thread joint of the present embodiment is also excellent in corrosion resistance. Pipe thread joint of the present embodiment further between the first plating layer and the lubricating coating, a second coating layer consisting of Zn or Zn alloy. The second plating layer is porous than the first plating layer. Therefore, as compared with the case of forming a direct lubricating coating on the first plating layer, the adhesion of the lubricating coating is increased with respect to the pipe threaded joint. Since the second plating layer is a porous, it shows a sufficient torque on shoulder value, shows excellent torque characteristics.
[0036]
　Second plating layer is formed by impact plating treatment, a shock-plated layer. Impact plating treatment, for example, a blast treatment of the metal particles to be plated. In this case, the second plating layer formed is porous and its surface has irregularities. Therefore, adhesion of the lubricating coating is increased by an anchor effect. Impact plating can be other similar known method other than blasting of the metal particles.
[0037]
　The porosity of the second plating layer is preferably 5 to 80%, more preferably 10 to 60%.
[0038]
　The thickness of the first plating layer is 1 ~ 20 [mu] m, the thickness of the second plating layer is 2 ~ 30 [mu] m, the thickness of the lubricant film is preferably 5 ~ 50 [mu] m.
[0039]
　Method for manufacturing a pipe thread joint of the present embodiment is a method for producing a pipe thread joint described above. The method provides a electroplating process, and impact plating step, a lubricant film formation step. The electroplating process, by carrying out electroplating treatment, on at least one of the contact surfaces of the pin and the box, forming a first plating layer made of Zn-Ni alloy. The impact plating step, after forming the first plating layer, an impact plating treatment was performed to form the second plating layer consisting of Zn or Zn alloy. The lubricating film forming step, the lubricant film on the second plating layer.
[0040]
　It will be described in detail a method for manufacturing a pipe thread fittings and pipe thread joint of the present embodiment.
[0041]
　[Pipe thread fittings]
　pipe thread joint comprises a pin and box. Figure 3 is a side view with a partial cross-section of the pipe thread joint 50 according to this embodiment. Referring to FIG. 3, the pipe threaded joint 50, the steel pipe body (hereinafter, simply referred to as body) a 1 and a coupling 2. At both ends of the main body 1, pin 3 having an externally threaded portion on an outer surface is formed. At both ends of the coupling 2, box 6 having a female screw portion on an inner surface is formed. By screwing the pin 3 and the box 6, to the end of the body 1, it is mounted coupling 2. On the other hand, without using a coupling 2, a pin 3 to one end of the body 1, and the other end with the box 6, there is also a threaded joint for oil well pipes of the integral type. Pipe thread joint of the present embodiment can be used in the coupling method and the integral form of both pipe thread fittings.
[0042]
　Figure 4 is a cross-sectional view of the pin and box of pipe thread joint 50 according to this embodiment. Referring to FIG. 4, the pin 3 has a contact surface. Contact surface, a pin 3 and box 6 is a portion in contact when screwing. Contact surface includes a threaded portion (male thread) 4 and an unthreaded metal contact portion. Unthreaded metal contact portion is formed at the tip of the pin 3, and a metal sealing portion 8 and the shoulder portion 9. Similarly, box 6 has a contact surface. Contact surface comprises threaded portion (female screw) 5, unthreaded metal contact portion (metal seal part 10 and the shoulder portion 11). When the pin 3 and the box 6 screwing, shoulder portions (shoulder portions 9 and 11), the metal seal portions (metal seal portion 8 and 10), and, threaded portions (male screw portion 4 and the female threaded portion 5) in contact with each other.
[0043]
　Figure 5 is a cross-sectional view of the contact surface of the pipe thread joint 50 according to this embodiment. Referring to FIG. 5, the pipe threads joint 50, on at least one contact surface of the pin 3 and box 6, in order from the contact surface side, the first plating layer 21, the second plating layer 22, and a lubricating coating 23 provided.
[0044]
　[First plating layer 21]
　The first plating layer 21 is formed on at least one contact surface of the pin 3 and box 6. The first plating layer 21 is electroplated layer consisting of Zn-Ni alloy. Hardness and melting point of the first plating layer 21 is high. Thus, it increases resistance to misalignment of the pipe thread joint 50. Furthermore, Zn contained in the first plating layer 21 is for a base metal, it is increased corrosion of the pipe thread joint 50.
[0045]
　Zn-Ni alloy constituting the first plating layer 21 contains Zn and Ni, the balance being impurities. Impurity is, for example, Fe, S, O, C or the like. Preferred Zn content of Zn-Ni alloy is 85 wt%, more preferably from 90 mass%. Preferred Ni content of Zn-Ni alloy is 10-15 wt%. The first plating layer 21 has a large Zn content. Therefore, a large effect of sacrificial protection.
[0046]
　Zn and Ni content of the first plating layer 21 is measured by the following method. Measurement of Zn and Ni content, for example, performed using a hand-held X-ray fluorescence analyzer (Olympus DP2000 (trade name DELTA Premium)). Zn-Ni arbitrary points 4 of alloy plating alms metal seal portion surface (circumferential direction of the pipe of any 0 °, 90 °, 180 °, 270 ° positions) to the composition analysis. Obtaining measured content of Zn and Ni by the measurement mode of the alloy.
[0047]
　The preferred thickness of the first plating layer 21 is 1 ~ 20 [mu] m. When the thickness of the first plating layer 21 is 1μm or more, it is possible to improve the resistance to misalignment resistance and corrosion resistance of the pipe thread joint 50 further stably. When the thickness of the first plating layer 21 is 20μm or less, the adhesion of the first plating layer 21 is further stabilized. Therefore, preferred thickness of the first plating layer 21 is 1 ~ 20 [mu] m.
[0048]
　The thickness of the first plating layer 21 is measured by the following method. The contact surfaces forming the first plating layer 21, ISO (International Organization for Standardization) 21968 contacting a probe of overcurrent phase type film thickness measuring device that conforms to the (2005). A high frequency magnetic field on the input side of the probe, thereby measuring the phase difference between the overcurrent on the first plating layer 21 which is excited. Converting the phase difference in the thickness of the first plating layer 21. A thickness measurement at the screw joint, any portions 4 of the metal seal part (circumferential direction of the pipe of any 0 °, 90 °, 180 °, 270 ° position) is measured.
[0049]
　It is preferable porosity of the first plating layer 21 is less than 5%. Case of forming a plating layer in an electroplating process, the porosity of the plating layer is less than 5%. The porosity of the electroplated layer, constitutes a space or a plating layer such as a pinhole, including air gap between particles, and the opening of the fine aggregate.
[0050]
　The porosity of the first plating layer 21 can be measured by known methods.
[0051]
　[Second plating layer 22]
　The second plating layer 22 is formed on the first plating layer 21. Second plating layer 22 is made of a Zn or Zn alloy. That is, the second plating layer 22 contains a Zn or Zn alloy, the balance being impurities. Impurity is, for example, Fe, S, O, C or the like. Zn alloy, Zn content is meant more than 50% of the alloy. Zn alloy, for example, a Zn-Fe alloy. Second plating layer 22 may be a plating layer made of pure Zn and impurities, may be a plated layer consisting of Zn alloy and impurities. Zn content in the Zn alloy can be measured similarly to the Zn content in the first plating layer 21.
[0052]
　The second plating layer 22 is porous in comparison with the first plating layer (porous), having an uneven surface. For curing by lubricating coating 23 is entered into the unevenness, by a so-called anchor effect, increases the adhesion of the lubricating coating 23, the durability of the lubricating coating is increased. Therefore, even when performed repeatedly back screwing and screws pipe thread joint 50, peeling of the lubricating coating 23 is suppressed. Furthermore, even if the lubricating coating 23 is worn, part or abrasion powder of the lubricant film 23 within (hole) of the second plating layer 22 remains by repeating the back screw tightening and screw the pipe thread joint 50. Therefore, pipe threaded joint 50 maintains the high lubricity.
[0053]
　Second plating layer 22 is impact plating layer formed by impact plating. Impact plating layer is porous than electroplated layer. The porosity of the second plating layer 22 formed by impact plating treatment, for example, 5 to 80%. The porosity of the second plating layer 22 can be measured in the same manner as the porosity of the first plating layer 21.
[0054]
　The preferred thickness of the second plating layer 22 is 2 ~ 30 [mu] m. When the thickness of the second plating layer 22 is 2μm or more, adhesion and proper torque on shoulder value of the lubricating coating 23 is obtained by more stable. On the other hand, the effect is saturated when the thickness of the second plating layer 22 is greater than 30 [mu] m. Thus, the preferred thickness of the second plating layer 22 is 2 ~ 30 [mu] m. The thickness of the second plating layer 22 is measured at a thickness similar to the method of the first plating layer 21 described above.
[0055]
　Lubricating coating 23]
　lubricating coating 23 is formed on the second plating layer 22. The lubricant film 23, increases the lubricity of the pipe thread joint 50. Lubricating coating 23 may be a solid lubricating coating, or a liquid lubricating coating. Preferably, the lubricant film 23 is a solid lubricating coating. Lubricating coating 23 may use well known. Lubricating coating 23, for example, it contains the lubricating particles and a binder. Lubricating coating 23, if desired, it may contain a solvent and other ingredients.
[0056]
　Lubricating particles decreases the friction coefficient of the surface of the lubricant film 23. Lubricating particles is not particularly limited as long as a particle having a lubricating property. Lubricating particles, for example, graphite, MoS 2 (molybdenum disulfide), WS 2 (tungsten disulfide), BN (boron nitride), PTFE (polytetrafluoroethylene), CFx (graphite fluoride), CaCO 3 (calcium carbonate ) or may be combined thereof. Preferably, graphite, graphite fluoride, MoS 2 and PTFE is used. If the lubricant film 23 is 100 mass%, preferably the content of the lubricant particles is 5 to 40 mass%.
[0057]
　Binding agent binds the lubricating particles in the lubricating coating 23. The binder may be used organic resins, inorganic resins, or mixtures thereof. When using an organic resin, it is possible to use a thermosetting resin or a thermoplastic resin. Thermosetting resins such as epoxy resins, polyimide resins, polycarbodiimide resins, polyether sulfone resins, polyether ether ketone resins, phenolic resins, furan resins, urea resins, acrylic resins. Thermoplastic resins such as polyamide-imide resins, polyethylene resins, polypropylene resins, polystyrene resins and ethylene-vinyl acetate resin.
[0058]
　When using the inorganic resin as the binder, it is possible to use polymetalloxane. The polymetalloxane, metal - repetition of oxygen bond refers to a polymeric compound is a main chain skeleton. Preferably, polytitanoxane (Ti-O) and polysiloxane (Si-O) is used. These inorganic resin is obtained by allowing a metal alkoxide hydrolysis and condensation. Alkoxy group of the metal alkoxide, for example, methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, an isobutoxy group, a lower alkoxy group such as butoxy and tert- butoxy. If the lubricant film 23 is 100 mass%, preferably the content of the binder is 60 to 95 mass%.
[0059]
　If it is necessary to dissolve or disperse the lubricating particles and binder, a solvent. Solvent, as long as it can disperse or dissolve the components contained in the lubricating coating 23 is not particularly limited. The solvent may be an organic solvent or water. The organic solvent for example, toluene and isopropyl alcohol.
[0060]
　Lubricating coating 23, if desired, it may contain other ingredients. Other ingredients, for example, rust inhibitors, corrosion inhibitors, surfactants, waxes, friction modifiers and pigments. Lubricating particles, a binder, the content of each of the solvent and other components are appropriately set.
[0061]
　Lubricating coating 23, the above-mentioned composition to at least one contact surface of the pin 3 and box 6 is applied, it is formed by solidifying.
[0062]
　Referring to FIG. 3, the pipe threaded joint 50 fastening the pin 3 and the box 6 at the time of shipment, the lubricating coating 23 is formed only on one of the contact surfaces of the pin 3 and the box 6 may be subsequently fastened. In this case, than the body 1 having a length dimension, towards the coupling 2 of the short dimensions, it is easy coating work of the composition. Therefore, it is preferable to form a lubricating coating 23 on the contact surface of the box 6 of the coupling 2. Of pipe thread fitting 50, the tube end of the pin 3 and the box 6 are not fastened at the factory, to form a lubricating coating 23 on both the contact surface of the pin 3 and box 6, lubricity and simultaneously corrosion resistance it may have been granted. Further, a lubricating coating 23 is formed on only one of the contact surfaces of the pin 3 and box 6, on the other contact surface may be formed solid corrosion protective coating to be described later. In either case, galling resistance to the screw, the airtightness and corrosion resistance can be imparted.
[0063]
　Lubricating coating 23 to cover all of the at least one contact surface of the pin 3 and box 6 are preferred. Lubricating coating 23, part of the contact surface only (e.g., the seal portion 8 and 10 only) may be coated.
[0064]
　Lubricating coating 23 may be a single layer or a multilayer. The multilayer, refers to a state in which the lubricant film 23 are stacked two or more layers from the contact surface side. By repeating the solidified coating composition, the lubricant film 23 can be formed of two or more layers. Lubricating coating 23 may be directly formed on the contact surface may be formed after the surface treatment to be described later.
[0065]
　The preferred thickness of the lubricant film 23 is 5 ~ 50 [mu] m. When the thickness of the lubricant film 23 is 5μm or more, it is possible to stably obtain a high lubricity. On the other hand, the thickness of the lubricant film 23 is equal to 50μm or less, adhesion of the lubricating coating 23 is stabilized. Further, the thickness of the lubricant film 23 is equal to 50μm or less, the thread tolerance of the sliding surface (clearance) widens, surface pressure during sliding is low. Therefore, it is possible to suppress the fastening torque becomes excessively high. Thus, the preferred thickness of the lubricant film 23 is 5 ~ 50 [mu] m.
[0066]
　The thickness of the lubricant film 23 is measured by the following method. Under the same conditions as in the case of applying a lubricating coating 23 on the pipe thread joints, applying a lubricating coating on a flat plate. Among the coating conditions of the threaded joint and the flat plate for tube, the distance between the object to be coated and the nozzle tip, the injection pressure, to match the conditions such as the rotational speed of the viscosity and the coating object of the composition. To match the viscosity of the composition, the tank, the temperature of the piping and the nozzle outlet, to match with the threaded joint and the flat plate for tube. And weight before plating of applying the composition, the difference between the weight of the plate after application of the composition, and calculates the application amount of the composition per unit time. Solidifying the composition on plates, to form a lubricating coating 23. The thickness of the lubricating coating 23 is measured using a film thickness meter. And weight before plating of applying the composition, the difference between the weight of the plate after forming a lubricating coating 23, which calculates the weight of the lubricant film 23. From the film thickness of the lubricating film 23 and weight and to calculate the density of the lubricating coating 23. Next, the screw shape and size from the (inner diameter and thickness, etc.), and calculates the application target area of ​​pipe thread fittings. The application target area corresponds to the area when expanding thread forming surface having irregularities in the plane. Application time of the composition to the pipe thread joint, the density of the coating target area and the lubricant film 23, for pipe threaded joint, and calculates an average film thickness of the lubricant film 23.
[0067]
　[Solid corrosion protective coating]
　screw aforementioned pipe joint 50 is provided with a lubricating coating 23 on one of the contact surfaces of the pin 3 and box 6, on the other contact surface of the pin 3 and box 6 may comprise a solid corrosion protective coating . As described above, until the pipe thread joint 50 is actually used, it may be stored for a long period of time. In this case, if the solid corrosion protective coating is formed, corrosion resistance of the pin 3 or box 6 is increased.
[0068]
　Solid corrosion protective coating, for example, a chromate coating of chromate. Chromate film is formed by a known trivalent chromate treatment.
[0069]
　Solid corrosion protective coating is not limited to the chromate film. Other solid corrosion protective coating, for example, containing an ultraviolet curable resin. In this case, having an intensity not destroyed by the force the solid corrosion protective coating is applied during protector mounting. Moreover, during transport or storage, the solid corrosion protective coating is not dissolved even when exposed to condensed water from the relationship between the dew point. Furthermore, the solid corrosion protective coating even at high temperatures exceeding 40 ° C. is not easy to softening. UV-curable resins are known resin compositions. UV-curable resin, a monomer, containing oligomer and a photopolymerization initiator, as long as it causes a photopolymerization reaction to form a cured coating film by being irradiated with ultraviolet rays is not particularly limited.
[0070]
　The other contact surface of the pipe thread joint 50, the plating layer is formed, may be the above-mentioned solid corrosion protective coating to the plating layer is formed, be directly solid corrosion protective coating is formed on the other contact surface good.
[0071]
　[Preform pipe thread joint 50]
　The composition of the base material of the pipe thread joint 50 is not particularly limited. Preform pipe thread fitting 50, for example, a carbon steel, stainless steel and alloy steel. Among alloy steels, Cr, high-alloy steel such as duplex stainless steels and Ni alloy containing alloy elements such as Ni and Mo are high corrosion resistance. Therefore, the use of these high alloy steel base material of the pipe thread joint 50, in a corrosive environment containing hydrogen sulfide and carbon dioxide, excellent corrosion resistance is obtained.
[0072]
　[Manufacturing Method]
　Hereinafter, a method for manufacturing a pipe thread joint 50 according to this embodiment.
[0073]
　Method for manufacturing a pipe thread joint 50 according to this embodiment is provided with the electroplating process, and impact plating step, a lubricant film formation step.
[0074]
　[Electroplating process]
　In the electroplating process, by carrying out electroplating treatment, on at least one contact surface of the pin 3 and box 6, to form the first plating layer 21. Electroplating process is carried out in a known manner. For example, the plating bath containing zinc ions and nickel ions, and immersing at least one contact surface of the pin 3 and box 6, carried out by energizing. The plating bath can be used commercially available ones. Bath, preferably, zinc ion: 1 ~ 100 g / L and nickel ions: containing 1 ~ 50g / L. Processing conditions of the electroplating process can be appropriately set. Electroplating process conditions, for example, plating bath pH: 1 ~ 10, the plating bath temperature: 10 ~ 60 ° C., a current density: 1 ~ 100A / dm 2 , and the processing time: 0.1-30 minutes. As described above, the preferred thickness of the first plating layer 21 is 1 ~ 20 [mu] m.
[0075]
　[Impact plating process]
　The impact plating process, to implement a dry impact plating treatment to form a second plating layer 22 is impact plating layer on the first plating layer 21. Dry impact plating method is a projection plating method of colliding a plating object particles by using, for example, blasting device. In the present embodiment may be subjected to plating only on the contact surface. Therefore, localized plating is possible projection plating method is suitable.
[0076]
　Particles used in the dry impact plating method such as a projection plating method is a metal particle having a Zn or Zn alloy at least on the surface. Whole may be metal particles made of Zn or Zn alloy. Preferred projection material used in Patent Document 1, a Fe or Fe alloy as the core (core), on the surface thereof, through a Fe-Zn alloy layer, consisting of particles coated with Zn or Zn alloy layer. Particles, for example, the product name Z Iron manufactured by Dowa Iron Powder Co., Ltd. can be used. The preferred particle size of the particles is 0.2 ~ 1.5 mm.
[0077]
　When projecting the Fe or Fe metal particles the surface of the core coated with Zn or Zn alloy of alloy pipe thread joint 50, only Zn or Zn alloy is a coating layer of the particles adheres to the steel tube. Thereby, the second plated layer 22 is impact plating layer consisting of Zn or Zn alloy is formed on the first plating layer 21. Impact plating layer is porous porosity of 5 to 80%. Therefore, by forming the lubricating coating 23 and a solid corrosion protective coating on the second plating layer 22, by a so-called "anchor effect", further enhanced adhesion of the lubricating coating 23 and a solid corrosion protective coating. As described above, the preferred thickness of the second plating layer 22 is 2 ~ 30 [mu] m.
[0078]
　Lubricating coating formation process]
　After the impact plating process, implementing the lubricating coating process. The lubricating coating step, first, a lubricating coating composition (hereinafter, also referred to. As composition) is prepared. Composition is formed by mixing the lubricating particles and a binder described above. The composition may further contain a solvent and other components described above.
[0079]
　The resulting composition is coated on the second plating layer 22. The method of application is not particularly limited. For example, a composition with a solvent, using a spray gun, sprayed on the second plating layer 22. In this case, the composition is uniformly coated on the second plating layer 22. Pins 3 or box 6 composition has been applied, drying or heat drying. Heat drying for example, can be carried out using a commercially available hot-air drying apparatus. Thus, the composition is cured, the solid lubricating coating 23 is formed on the second plating layer 22. Conditions of heat drying, taking into account the boiling point and melting point of each component contained in the composition can be appropriately set.
[0080]
　When forming the lubricating coating 23 using a composition without solvent, for example, it can be used a hot-melt method. The hot melt method is in a fluid state by heating the composition. The composition was in a fluid state for example, spraying with a spray gun having a temperature maintaining function. Thus, uniformly applying the composition on the second plating layer 22. The heating temperature of the composition can be appropriately set in consideration of the melting point and softening temperature of the binder and other components described above. Pins 3 or box 6 was applied composition is cooled by air cooling or the like. Thus, the composition is cured, the lubricant film 23 is formed on the second plating layer 22.
[0081]
　[Formation of a solid corrosion protective coating (trivalent chromate treatment)
　as described above, on one of the contact surfaces of the pin 3 and box 6, the electroplating process, an impact plating process, and, by implementing a lubricating coating step, first plated layer 21 to form the second plating layer 22 and the lubricating coating 23.
[0082]
　On the other hand, for the other contact surface of the pin 3 and box 6, first plating layer 21 may be formed a second plating layer 22 and the lubricating coating 23, the plating layer and / or the solid corrosion protective coating formed it may be. Hereinafter, the other contact surface, the case of forming a solid corrosion protective coating consisting of a first plating layer 21 and the chromate film.
[0083]
　In this case, to implement the above-described electroplating process, to form the first plating layer 21. After the electroplating process, to implement a trivalent chromate treatment to form a solid corrosion protective coating. The trivalent chromate treatment, is a film (chromate film) chromate trivalent chromium. Chromate film formed by the trivalent chromate treatment suppresses white rust on the surface of the Zn alloy plating layer. Thus, product appearance is improved (however, rusty white Zn alloy plating layer, not rust pipe thread joint 50. Therefore, no influence on the seizure resistance and corrosion resistance of the pipe thread joint 50). Trivalent chromate treatment can be carried out in a known manner. For example, at least one contact surface of the pin 3 and box 6 is immersed in a chromate treatment solution, or sprayed coating the chromate treatment solution to contact the surface. Washed with water then contacting surface. The contact surface was immersed in a chromate treatment solution may be washed with water after the energization. The chromating solution is applied to the contact surface, it may be dried by heating. Processing conditions trivalent chromate can be appropriately set.
[0084]
　[Pretreatment step]
　above manufacturing process, if necessary, may include a pretreatment step before the electroplating process. Pretreatment process, for example, a pickling and alkaline degreasing. The pretreatment step, cleaning the oil or the like adhering on the contact surface. Pretreatment step may further comprise a grinding such as mechanical grinding finishing.
[0085]
　With the above-described manufacturing process, to produce a pipe thread joint 50 of the present embodiment.
Example
[0086]
　Hereinafter, the embodiment will be described. However, the invention is not intended to be limited by the examples. In embodiments, the contact surface of the pin the pin surface, the contact surface of the box as the box surface. The% in the examples means mass% unless otherwise specified.
[0087]
　In this example, called the made Nippon Steel Sumitomo Metal Co. VAM21 (registered trademark) was used threaded steel pipe. VAM21 (R) outer diameter: 24.448cm (9-5 / 8 inch), was a steel pipe wall thickness of 1.199cm (0.472 inches). Steel is carbon steel, the chemical composition, C: 0.21%, Si: 0.25%, Mn: 1.1%, P: 0.02%, S: 0.01%, Cu: 0 .04%, Ni: 0.06%, Cr: 0.17%, Mo: containing 0.04%, the balance being Fe and impurities.
[0088]
　To the pin surface and the box surface using a steel pipe of each test number was performed finished by machine grinding (surface roughness of 3 [mu] m). Thereafter, the plating layer shown in Table 1 (first and second plating layer) or coating (solid corrosion protective coating, lubricating coating) to form, was prepared pin and box of each test number.
[0089]
[Table 1]

[0090]
　Method of forming the plating layer or coating was as follows. In each test number was measured porosity in a known manner. Porosity of electroplated layer is less than 5%, the porosity of the dry impact plating layer was 5 to 80%. The porosity of the manganese phosphate coating was less than 30%.
[0091]
　Test No. 1]
　In Test No. 1, relative to the pin surface by electroplating subjected to Zn-Ni electroplated steel Daiwa Kasei Co., to form a first plating layer having a thickness of 8 [mu] m. Conditions of electroplating, the plating bath pH: 6.5, the plating bath temperature: 25 ° C., a current density: 2A / dm 2 , and processing time were: 18 min. The composition of the first plating layer, Zn: was 15%: 85% and Ni. Furthermore, the first plating layer thus obtained was subjected to trivalent chromate treatment. Trivalent chromate treatment solution, was used trade name dyne chromate TR-02 manufactured by Daiwa Kasei Co., Ltd.. Trivalent chromate treatment conditions, the bath pH: 4.0, bath temperature: 25 ° C., and treatment time was 50 seconds.
[0092]
　To box surface, under the same conditions as the pin surface to form a first plating layer. Then, to form a second plating layer by dry impact plating (projection plating method). The dry impact plating treatment, coating with metal particles is Zn-Fe alloy. The average thickness of the obtained second plating layer was 10 [mu] m. The formed box surface of the first plating layer and the second plating layer was applied to the solid lubricating coating composition. Solid lubricating coating composition may be graphite 5 weight% and contained PTFE4 mass%, and PFPE10 mass%. The solid lubricating coating composition was heated to 130 ° C. and cooled to spray coating, to form an average thickness 30μm solid lubricating coating.
[0093]
　Test No. 2]
　In Test No. 2, with respect to the pin surface was carried out the same processing as in Test No. 1. The resulting film thickness and the chemical composition of the first plating layer was the same as Test No. 1. Coating thickness trivalent chromate was also estimated to be similar. For box surface, after forming the first plating layer and the second plating layer in the same manner as Test No. 1, the solid lubricating coating composition was applied trade name Xylan1425. Trade name Xylan1425 an epoxy-based resin 22 wt%, PTFE particles 9 wt%, the solvent total of 18 wt%, and containing pigment, 40 wt% water. After spraying the solid lubricant coating composition on the box surface (5 minutes at 90 ° C.) heat drying, and to form a solid lubricating coating performs (20 min at 210 ° C.) cured. The average thickness of the obtained solid lubricating coating was 30 [mu] m.
[0094]
　Test No. 3]
　In Test No. 3, with respect to the pin surface and the box surface, as with the box surface Test No. 1, to form a first plating layer and the second plating layer. The resulting film thickness and the chemical composition of the first and second plating layer was the same as Test No. 1. Thereafter, for the pin surface was coated with the solid lubricating coating composition described below. Solid lubricating coating composition, Ltd. Kawa邑Laboratory Ltd., the trade name DEFRIC COAT 405, containing molybdenum disulfide and graphite in an inorganic polymeric binder. After spraying on the box surface of the solid lubricating coating composition was allowed to stand for 3 hours in the atmosphere. Thereafter, the blown hot air humidified 150 ℃ 10 minutes. The average thickness of the obtained solid lubricating coating was 20 [mu] m. For box surface was formed the same solid lubricating coating and the box surface Test No. 2. The resulting thickness and chemical composition of the solid lubricating film was the same as Test No. 2 of the box surface.
[0095]
　[Test No. 4]
　In Test No. 4, with respect to the pin surface, similar to the pin surface of the test number 1, to form a first plating layer and trivalent chromate film. Each plating layer and the thickness of the film formed was the same as Test No. 1. Relative box surface to form a second plating layer similar to the box surface Test No. 1. The average thickness of the obtained second plating layer was 10 [mu] m. To the resulting second plating layer was formed on the same solid lubricating coating and the box surface Test No. 2. The resulting thickness and chemical composition of the solid lubricating film was the same as Test No. 2 of the box surface.
[0096]
　[Test No. 5]
　In Test No. 5, with respect to the pin surface, similar to the pin surface of the test number 1, to form a first plating layer and trivalent chromate film. Each plating layer and the thickness of the film formed was the same as Test No. 1. Relative box surface, similar to the pin surface of the test number 1, to form a first plating layer. The thickness of the first plating layer formed was the same as Test No. 1. The first plating layer obtained to form a similar solid lubricating coating and the box surface Test No. 2. The resulting thickness and chemical composition of the solid lubricating film was the same as Test No. 2 of the box surface.
[0097]
　Test No. 6]
　In Test No. 6, with respect to the pin surface, similar to the pin surface of the test number 1, to form a first plating layer and trivalent chromate film. Each plating layer and the thickness of the film formed was the same as Test No. 1. Relative box surface, similar to the pin surface of the test number 1, to form a first plating layer. The thickness of the first plating layer formed was the same as Test No. 1. The formed box surface of the first plating layer, in a manganese phosphate chemical conversion treatment solution of 80 ~ 95 ° C. was immersed for 10 minutes to form a thick 12μm manganese phosphate coating (surface roughness 10 [mu] m). The formed box surface manganese phosphate coating was formed the same solid lubricating coating and the box surface Test No. 2. The resulting thickness and chemical composition of the solid lubricating film was the same as Test No. 2 of the box surface.
[0098]
　[Fastening Evaluation Test]
　As concluded evaluation test was evaluated seizure resistance and torque characteristics. The seizure resistance was evaluated high temperature resistance and misalignment resistance.
[0099]
　: [Seizing resistance high temperature resistant]
　at high temperature oil well, in order to examine the influence of the layer on the first plating layer, using the pin and box of Test No. 2 and Test No. 6 was carried out repeatedly fastening test. Specifically, while fastening the pin and box fastened to the first, and heated for 6 hours at 200 ° C. The ambient box by a band heater. Loosen then repeated back screw tightening and screw. Tightening rate starts at 10rpm, shoulder ring later was 2rpm. Tightening torque was 42.8kN · m. Return screw tightening and screw the pipe thread joint was carried out at room temperature (20 ° C.). The return screw tightening and screw each performed once, was confirmed visually and the occurrence of seizing by the torque change during fastening. The test was terminated at the time with an unrecoverable burn has occurred. The results are shown in Table 2.
[0100]
[Table 2]

[0101]
　[Evaluation Result]
　Referring to Table 2, Test No. 2 did not generate seizure back 10 times repeatedly screwing and screws. On the other hand, in Test No. 6, a manganese phosphate layer of the surface treatment layer 2 is high temperature degradation. This seems to be because of desorption and embrittlement of crystal water. As a result, until the second time, but we were able to conclude without seizure, because it was produced with unrecoverable fired at the third time, the test was terminated.
[0102]
　: [Seizing resistance resistance misalignment resistance]
　using a pin and box of the test Nos. 1 to Test No. 6, returned repeatedly screwing and screw involving misalignment was evaluated resistance to misalignment resistance. The crossing angle θ of misalignment was 5 °. Return screwing and screw was repeated up to 10 times. Tightening rate of return screwing and screw 10 rpm, the tightening torque was 42.8kN · m. The return screw tightening and screw each performed once, it was observed visually pin surface and the box surface. By visual observation, it was confirmed the occurrence of the seizure. It is a very minor seizure, if possible recovery, and continue the test and repair the seizure flaws. Without causing with unrecoverable baked it was measured the number of times that could return screw tightening and screw. The results are shown in Table 2.
[0103]
　[Evaluation Result]
　Referring to Table 2, seizure did not occur due to misalignment in the pin and box of the test Nos. 1 to Test No. 3 and Test No. 6. This adhesion to the solid lubricating coating layer is presumably because the improved by a layer formed on the first plating layer. On the other hand, in Test No. 4 and the test number 5, the fastening count was significantly reduced.
[0104]
　[Torque Characteristics
　using a pin and box of the test Nos. 1 to Test No. 6 was carried out torque characteristic test. Specifically, the torque on shoulder value (difference between yield torque and shouldering torque) was measured as follows. Prepare the pin and box of test numbers 1 to Test No. 6, Weatherford, Inc. of power - has signed with the tongs. By performing even tightening give further torque after engagement, to produce a torque chart as shown in FIG. To measure the torque on the shoulder value on the torque chart. Shouldering torque shoulder is in contact, is a torque value when the torque change began away from the first linear region (elastic deformation range). On the other hand, yield torque, the torque value at which the plastic deformation starts. Specifically, it occurs after reaching the shouldering torque, a torque value when he started away from the second linear region. Here, the ground processing layer 1 and second test numbers 1-6, and using a solid corrosion protective coating layer was prepared pin and box was subjected to treatment by replacing the solid lubricant coating layer to the grease conforming to API standards. A torque on shoulder value in this case 100, to determine the value of the test numbers 1 to Test No. 6. The results are shown in Table 2.
[0105]
　[Evaluation Result]
　Referring to Table 2, in Test Nos. 1 to Test No. 3, the second plating layer is an impact plating layer is formed, the torque on shoulder value exceeds 100, exhibited excellent torque characteristics . On the other hand, the torque on shoulder value In Test No. 4 and the test number 5 is less than 100, the torque characteristic is low. For the Test No. 6 layer on the first plating layer was a manganese phosphate layer, the torque on shoulder value is less than 100, the torque characteristic was low.
[0106]
　: Corrosion resistance evaluation test salt spray test]
　were prepared test specimens in the test Nos. 1 to Test No. 6 and the same composition of carbon steel. The size of the test piece is 70 mm × 150 mm, the thickness was 1 mm. On specimens subjected to the same surface treatment as in Test Nos. 1 to Test No. 6 was to salt spray test. Salt spray test JIS Z2371: it was carried out based on the method described in 2000. Red rust on the surface of the test piece for each test number was measured times caused by visual observation. The results are shown in Table 2.
[0107]
　[Evaluation Result]
　Test No. 1 - test No. 3, Test No. 5 and Test No. 6, since the electroplating layer is formed as a first plating layer, rust did not occur. On the other hand, in Test No. 4, only the second plating layer is a porous impact plating layer immediately above the contact surface is formed, sufficient anticorrosion effect can be obtained, rust occurs on the entire surface at 500 hours.
[0108]
　[Weathering test: (adhesion of the lubricating coating) coating durability test]
　were prepared boxes of test numbers 1 to Test No. 6. Each box was cut from the end of the tube 1 m. The order as a test climatic conditions as described (humidity relative humidity) in Table 3, were performed weathering test simulating all weather from extreme cold to hot. Observing the box surface was visually examined the appearance of a solid lubricating coating (the presence or absence of peeling and rust).
[0109]
[table 3]

[0110]
　[Evaluation Result]
　Test No. 1 - test No. 3, and Test No. 6, since both the first and second plating layer is formed, there is no peeling of the coating, rust did not occur. On the other hand, in Test No. 4, only the second plating layer is an impact plating layer is formed on the surface, low adhesion to the base material, the film was peeled off. Furthermore, sufficient anticorrosion effect can be obtained, rust occurs on the entire surface at 500 hours. In Test No. 5, since only the first plating layer is an electrical plating layer is formed, adhesion of the lubricating coating is low, the film was peeled off.
[0111]
　It has been described an embodiment of the present invention. However, the above-described embodiment is merely an example for implementing the present invention. Accordingly, the present invention is not limited to the embodiments described above, it can be implemented by changing the above-described embodiments without departing from the scope and spirit thereof as appropriate.
DESCRIPTION OF SYMBOLS
[0112]
　3 pins
　4,5 thread section
　6 Box
　8,10-metal seal portion
　9,11 shoulder portion
　21 first plating layer
　22 and the second plating layer
　23 lubricating coating
　50 Pipe threaded joint

claims

Each A pipe thread joint comprising a pin and box has a contact surface including a threaded portion and an unthreaded metal contact portion,
　the pin and at least one of the contact surface of the box, first made of Zn-Ni alloy a first plating layer,
　wherein the first plating layer, and a second plating layer of porous made of Zn or Zn alloy,
　the second plating layer, and a lubricating coating, pipe threaded joint.
[Requested item 2]
　A pipe thread joint according to claim 1, wherein the porosity of the second plating layer is 5 to 80%, Pipe threaded joint.
[Requested item 3]
　A pipe thread joint according to any one of claims 1 and 2, the thickness of the first plating layer is 1 ~ 20 [mu] m, the thickness of the second plating layer is 2 ~ 30 [mu] m, and the thickness of the lubricating coating is 5 ~ 50 [mu] m, pipe threaded joint.
[Requested item 4]
　A pipe thread joint according to any one of claims 1 to 3, wherein the lubricating coating is a solid lubricating coating, pipe threaded joint.
[Requested item 5]
　Each A method of manufacturing a pipe thread joint comprising a pin and box has a contact surface including a threaded portion and the unthreaded metal contact portion,
　the pin and at least one of the contact surface of the box, the electroplating process forming a first plating layer made of Zn-Ni alloy was performed,
　after forming the first plating layer, the impact plating treatment was performed to form the second plating layer consisting of Zn or Zn alloy step and,
　after forming the second plating layer, and forming a lubricant film, method of manufacturing a pipe thread fittings.