OA16982A - Tubular threaded joint having improved high torque performance. - Google Patents
Tubular threaded joint having improved high torque performance. Download PDFInfo
- Publication number
- OA16982A OA16982A OA1201400208 OA16982A OA 16982 A OA16982 A OA 16982A OA 1201400208 OA1201400208 OA 1201400208 OA 16982 A OA16982 A OA 16982A
- Authority
- OA
- OAPI
- Prior art keywords
- lubricating coating
- coating
- pin
- box
- lubricating
- Prior art date
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Abstract
A tubular threaded joint which is free from harmful heavy metals, which has excellent galling resistance, gas tightness, and rust-preventing properties and which does not readily undergo yielding of shoulder portions even when subjected to makeup with a high torque is constituted by a pin 1 and a box 2 each having a contact surface comprising an unthreaded metal contact portion including a seal portion 4a or 4b and a shoulder portion 5a or 5b and a threaded portion 3a or 3b. Of the contact surface of at least one of the pin and the box, the surfaces of the seal portion and the shoulder portion has a first lubricating coating 10 in the form of a solid lubricating coating, and the surface of the threaded portion or the entire surface of the contact surface has a second lubricating coating 11 selected from a viscous liquid lubricating coating and a solid lubricating coating. The first lubricating coating has a coefficient of friction which is higher than that of the second lubricating coating, and the second lubricating coating is positioned on top in a portion where both the first lubricating coating and the second lubricating coating are present.
Description
Tubuiar Threaded Joint Having Improved High Torque Performance
Technical Field
This Invention relates to a tubuiar threaded joint used for connecting steel pipes and particularly oil country tubuiar goods and to a surface treatment method therefor. A tubuiar threaded joint according to the présent invention can reliably exhibit excellent galling résistance without the application of a lubricating grease such as compound grease which In the past has been applied to threaded joints each time when makeup of oil country tubuiar goods Is carried out. Therefore, a tubuiar threaded joint according to the présent Invention can avold the adverse effects on the global environment and humans caused by compound grease. In addition, the joint does not readily yield even if makeup is carried out with a high torque, thereby making it possible to realize a stable metal-to-métal seal with an adéquate operating margin.
Background Art
Oil country tubuiar goods such as tubing and casing used for excavation of oil wells for exploitation of crude oil or gas oil are usually connected with each other (made up) using tubuiar threaded joints. In the past, the depth of oil wells was 2,000 - 3,000 meters, but in deep wells such as recent oil fields in the sea, the depth sometimes reaches 8,000 -10,000 meters or larger. The length of oil country tubuiar goods Is typically 10 some meters, and tubing through which a fluid such as crude oil flows is surrounded by a plurality of casings. Therefore, the number of oil country tubuiar goods which are connected by threaded joints reaches a huge number.
Since tubuiar threaded joints for oil country tubuiar goods are subjected in their environment of use to loads in the form of tensile forces in the axial direction caused by the mass of oil country tubuiar goods and the joints themselves, compound pressures such as internai and extemal pressures, and geothemnal heat, they need to maintain gas tightness without being damaged even In such severe environments.
Typical tubuiar threaded joints used for connecting oil country tubuiar goods (also referred to as spécial threaded joints) hâve a pin-box structure. A pin, which is a joint component having male (extemal) threads, is typically formed on the outer surface of both ends of an oil country tubular good, and a box, which Is a counterpart joint component having female (internai) threads which engage with the male threads, Is typically formed on the Inner surface of both sides of a coupling, which Is a separate member. As shown In Figure 1, the pin has a shoulder portion (also referred to as a torque shoulder) formed on the end surface at the tip of the pin and a seal portion formed between the end surface and the male threads. Correspondingly, the box has a seal portion and a shoulder portion located in the rear of the female threads and adapted to contact the seal portion and the shoulder portion of the pin, respectively. The seal portions and the shoulder portions of the pin and the box constitute unthreaded métal contact portions of a tubular threaded joint, and the unthreaded métal contact portions and the threaded portions of the pin and the box constitute contact surfaces of a tubular threaded joint. Below-described Patent Document 1 discloses an example of such a spécial threaded joint.
In order to perform makeup of this tubular threaded joint, one end (the pin) of an oil country tubular good Is Inserted Into a coupling (box), and the male threads and the female threads are tightened until the shoulder portions of the pin and the box contact each other and interfère with a suitable torque. As a resuit, the seal portions of the pin and the box Intimately contact each other to form a metai-to-metai seal which guarantees the gas tightness of the threaded joint.
Due to various troubles occumng during the process of lowering tubing or casing into an oil well, it Is sometimes necessary to ioosen a threaded joint which has been made up, raise the joint from the oil well, retighten It, and again lower it Into the well. API (American Petroleum Institute) requires galling résistance such that unrepairable seizing referred to as galling does not take place and gas tightness is maintained even if tlghtenïng (makeup) and loosening (breakout) are carried out 10 times on a joint for tubing and 3 times on a joint for casing.
In order to increase galling résistance and gas tightness, a viscous liquid lubricant (lubricating grease) referred to as compound grease or dope and containing heavy métal powder has been previously applied to the contact surfaces of a threaded joint each time makeup Is carried out. Such compound grease Is prescribed by API BUL 5A2.
With the object of Increaslng the rétention of compound grease and Improving sliding properties, it has been proposed to subject the contact surfaces of a threaded joint to various types of surface treatment to form one or more layers such as nitride treatment, various types of plating Including galvanizing and dispersion plating, and phosphate chemical conversion treatment. However, as stated below, the use of compound grease may hâve adverse effects on the environment and humans.
Compound grease contains large amounts of powder of heavy metals such as zinc, lead, and copper. At the time of makeup of a threaded joint, the applied grease ls washed off or overflows to the outer surface, and it can hâve an adverse effect on the environment and especially on sea life particularly due to harmful heavy metals such as lead. In addition, the process of applying compound grease worsens the work environment and the work efficiency, and there ls also a concem of harm to humans.
In recent years, as a resuit of the enactment In 1998 of the OSPAR Convention (OsloParis Convention) aimed at preventing marine pollution in the Northeast Atlantic, strict environmental régulations are being enacted on a global scale, and In some régions, the use of compound grease ls already being regulated. Accordingly, In order to avoid harmful effects on the 10 environment and humans during the excavation of gas wells and oil wells, a demand has developed for threaded joints which can exhiblt excellent galling résistance without using compound grease.
As a threaded joint which can be used to connect oil country tubular goods without application of compound grease, the présent applicant proposed In Patent Document 2 a threaded 15 joint for steel pipes having a viscous liquid or semisolid lubricating coating and In Patent Document 3 a threaded joint for steel pipes having a solid lubricating coating.
Patent Document 1: JP 5-87275 A
Patent Document 2: JP 2002-173692 A
Patent Document 3: WO 2009/072486
Summary of the Invention
As stated above, with a spécial threaded Joint like that shown In Figure 1 constituted by a pin and a box each with a seal portion, the seal portions of the pin and the box form a metal-to25 métal seal to guarantee gas tightness at the end of makeup.
Figure 2 shows a torque chart at the time of makeup of this type of threaded Joint (ordinate: torque, absdssa: number of tu ms). As shown In this figure, as rotation takes place, the threaded portions of the pin and the box Initially contact and torque gradually increases. Subsequently, the seal portions of the pin and the box contact, and the rate of Increase of torque Increases.
Eventually, the shoulder portion at the tip of the pin and the shoulder portion of the box contact and begln to Interfère (the torque at the start of this Interférence ls referred to as the shouidering torque
Ts), upon which the torque abruptly Increases. Makeup Is completed when the torque reaches a predetermlned makeup torque. The optimum torque In Figure 2 means the torque that Is optimal for the completion of makeup with achieving an amount of interférence In the seal portions which Is necessary for guaranteelng gas tlghtness. A proper value for the optimum torque Is predetermlned depending on the Internai diameter and the type of a joint.
However, In a spécial threaded joint used In very deep wells In which compressive stresses and bending stresses are applied, makeup Is sometimes carried out with a torque which Is higher than usual to prevent the tightened thread from loosening. In this case, the shoulder portion at the end of the pin and the shoulder portion of the box which It contacts sometimes yield, leadîng to plastic deformation of the shoulder portion of at least one member of the pin and the box. As a resuit, as shown in Figure 2, the rate of increase of torque suddenly decreases. The torque at the time when yielding and plastic deformation occur Is referred to as the yield torque Ty. Yielding of the shoulder portions leads to a failure of gas tightness.
In a threaded joint which Is made up with a high torque, it Is advantageous for the value of [Ty minus Ts] (Ty- Ts « ΔΤ ,or the torque-on-shoulder résistance) to be large. However, In the tubular threaded joints described In Patent Document 2 having a viscous liquid or semisolid lubricating coating, Ty Is low compared to when a conventional compound grease Is applied. As a resuit, ΔΤ becomes small, and the shoulder portions yield at a low makeup torque, so it Is sometimes Impossible to perform makeup with a high torque. In the tubular threaded joints described In Patent Document 3 having a solid lubricating coating as well, ΔΤ becomes smaller than that of a conventional compound grease.
The object of the présent Invention is to provide a tubular threaded joint which does not readily undergo yielding of Its shoulder portions even when it is made up with a high torque and which has a lubricating coating which does not contain harmful heavy metals, which has excellent galling résistance, gas tightness, and rust-preventing properties, and which can afford a large ΔΤ to the joint.
It was found that even If the composition of a lubricating coating Is varied so as to vary Its coefficient of friction, ΔΤ does not greatly change because Ts and Ty typically vary In the same direction. For example, If the coefficient of friction of a lubricating coating increases, Ty Increases, but Ts also increases (a phenomenon referred to as high shouldering). As a resuit, In the worst case, the condition referred to as no-shouldering occurs In which the shoulder portions do not contact at a predetermlned makeup torque and makeup cannot be completed.
The présent Inventors found that with a tubular threaded joint having a viscous liquid or solid lubricating coating which does not contain harmful heavy metals which Impose a burden on the global environment, by fbrmlng a high-friction solid lubricating coating on a portion of the contact surface (the threaded portion and the unthreaded métal contact portion) of at least one of a pin and a box such as on the shoulder portion which Is initially contacted and preferably on the unthreaded métal contact portion induding the seal portion and the shoulder portion, and formlng on at least the remaining portion of the contact surface a lubricating coating selected from a viscous liquid lubricating coating and a solid lubricating coating having a lower coeffident of friction than the high-friction solid lubricating coating, a tubular threaded joint Is obtained which has a large ΔΤ and which does not undergo no-shouldering while having suffirent galling résistance, gas tightness, and rust-preventing properties.
The mechanism by which a large ΔΤ is achieved is thought to be generally as follows.
Makeup of a tubular threaded joint Is carried out by Inserting a pin Into a box and then rotating the pin or the box. Initially only the threaded portions of the pin and the box contact and threadingly engage with each other. ln the final stage of makeup, the seal portions and the shoulder portions begln to contact, and makeup is completed when a predetermined amount of Interférence is obtained between the seal portions and the shoulder portions.
As shown in Figure 5(A), for example, with a tubular threaded joint having a high-friction solid lubricating coating on the seal portions and the shoulder portions ofthe contact surfaces of both a pin and a box and a lubricating coating having a lower coefficient of friction on the remaining portion (primarily the threaded portions), while only the threaded portions of the pin and the box Initially contact, a low friction state is achieved by the lubricating coating having a low coeffident of friction which covers the threaded portions, so Ts becomes low. In the final stage of makeup, when the seal portions and the shoulder portions start to contact, the high-friction solid lubricating coatings which cover these portions contact, causing a high-friction state to occur and causing Ty to increase. As a resuit, ΔΤ Is Increased.
The présent invention, which is based on this knowledge, is a tubular threaded joint constituted by a pin and a box each having a contact surface comprising an unthreaded métal contact portion induding a seal portion and a shoulder portion and a threaded portion, characterized ln that the contact surface of at least one of the pin and the box has a first lubricating coating and a second lubricating coating, the first lubricating coating being a solid lubricating coating formed on a portion of the contact surface Induding the shoulder portion, the second lubricating coating being selected from a viscous liquid lubricating coating and a solid lubricating coating and formed on at least the portion of the contact surface where the first lubricating coating is not présent, the first lubricating coating having a coefficient of friction which 1s higher than that of the second lubricating coating, the second lubricating coating being positioned on top ln a portion where both the first lubricating coating and the second lubricating coating are présent.
The portion of the contact surface having the first lubricating coating may be just the shoulder portion, but preferably it is the entirety ofthe unthreaded métal contact portion, namely, the seal portion and the shoulder portion.
The second lubricating coating may be provided just on the portion of the contact surface which does not hâve the first lubricating coating, or It may be provided on the entire contact surface having the first lubricating coating. In the latter case, the second lubricating coating Is positioned on top of the first lubricating coating.
Preferred coating thicknesses of each coating are as follows.
The coating thickness of the first lubricating coating is 5 - 40 pm.
The coating thickness of the viscous liquid lubricating coating as a second lubricating coating is 5 - 200 pm. However, when this viscous liquid lubricating coating is positioned on top of the first lubricating coating, the total of the coating thickness of the first lubricating coating and that of the viscous liquid lubricating coating is at most 200 pm.
The coating thickness of the solid lubricating coating as a second lubricating coating is 5 150 pm. However, when this solid lubricating coating Is positioned on top of the first lubricating coating, the total of the coating thickness of the first lubricating coating and that of the second solid lubricating coating is at most 150 pm.
When the contact surface of only one of the pin and the box has the first lubricating coating and the second lubricating coating as described above, there are no particular limitations conceming the contact surface of the other member of the pin and the box, and It may be in an untreated state (for example, it may be in a state after the below-described preparatory surface treatment). Preferably, however, at least a portion of the contact surface of the other member and preferably the entirety of the contact surface has any of the following surface treatment coatings formed thereon:
1) a lubricating coating selected from a viscous liquid lubricating coating and a solid lubricating coating,
2) a solid anticorrosive coating, or
3) a lower layer ln the form of a lubricating coating selected from a viscous liquid lubricating coating and a solid lubricating coating, and an upper layer ln the form of a solid anticorrosive coating.
The solid anticorrosive coating is preferably a coating based on an ultraviolet curing resin. The lubricating coating may be either the above-described first lubricating coating or the second solid lubricating coating.
The contact surface of at least one and preferably both of the pin and the box can be previously subjected to surface treatment by a method selected from one or more of blasting treatment, pickling, phosphate chemical conversion treatment, oxalate chemical conversion treatment, borate chemical conversion treatment, electroplatîng, and impact plating in order to Increase the adhesion and the rétention of a coating formed atop the contact surface and/or to Increase the galiing résistance of the threaded joint.
ln a tubular threaded joint according to the présent invention, a lubricating coating which Is formed on Its contact surfaces exhibits a large ΔΤ as observed with a coating made of a conventional lubricating grease such as compound grease which contains harmful heavy metals. Therefore, even at the time of makeup with a high torque, It Is possible to perform makeup without the occurrence of yielding or galiing of the shoulder portions. In addition, galling can be suppressed even under severe conditions such as during unstable excavation operations ln the sea. Furthermore, since the lubricating coating contains substantially no harmful heavy metals such as lead, It poses almost no burden on the global environment. A tubular threaded joint according to the présent Invention suppress the occurrence of rust, and it can continue to exhibit a lubricating function even when subjected to repeated makeup and breakout, so It can guarantee gas tightness after makeup.
Brief Explanatlon ofthe Drawings
Figure 1 schematicaliy shows the unthreaded métal contact portions (the shoulder portions and seal portions) of a spécial threaded joint.
Figure 2 Is a typical torque chart at the time of makeup of a spécial threaded joint.
Figure 3 schematicaliy shows the assembled structure of a steel pipe and a coupling at the time of shipment of the steel pipe.
Figure 4 schematicaliy shows a cross section of a spécial threaded joint.
Figures 5(A) - 5(C) show examples of the structure of coatings on a tubular threaded joint according to the présent invention.
Figures 6(A) · 6(C) show examples ofthe structure of different coatings on a tubular threaded joint according to the présent invention.
Modes for Carrying Out the Invention
Below, embodiments of a tubular threaded joint according to the présent Invention will be explalned in detail by way of example. The présent invention Is not limited to the below-mentïoned embodiments.
Figure 3 schematically shows the state of a typical tubular threaded joint at the time of shipment. A pin 1 having a male threaded portion 3a Is formed on the outer surface of both ends of a steel pipe A, and a box 2 having a female threaded portion 3b is formed on the inner surface of both sides of a coupling B. The coupling B Is previously connected to one end of the steel pipe A. Although not shown In the drawing, a protector for protecting the threaded portions Is previously mounted on the unconnected pin ofthe steel pipe A and the unconnected box ofthe coupling B before shipment These protectors are removed from the threaded joint before use.
As shown in the drawing, In a typical tubular threaded joint, a pin Is formed on the outer surface of both ends of a steel pipe and a box Is formed on the inner surface of a coupling, which is a separate member. There are also intégral tubular threaded joints which do not utilize a coupling and In which one end of a steel pipe is made a pin and the other end is made a box. A tubular threaded joint according to the présent invention can be of either type.
Figure 4 schematically shows the structure of a spécial threaded joint (refened to below simply as a threaded joint), which Is a typical tubular threaded joint used for connecting oil country tubular goods. This threaded joint is constituted by a pin 1 formed on the outer surface of an end of a steel pipe A and a box 2 formed on the inner surface of a coupling B. The pin 1 has a male threaded portion 3a, a seal portion 4a located near the tip of the steel pipe, and a shoulder portion 5a at its end surface. Correspondingly, the box 2 has a female threaded portion 3b, and a seal portion 4b and a shoulder portion 5b on its Inner side.
The seal portions and the shoulder portions of the pin 1 and the box 2 are unthreaded métal contact portions, and the unthreaded métal contact portions (namely, the seal portions and the shoulder portions) and the threaded portions are the contact surfaces of the threaded joint. These contact surfaces need to hâve galiing résistance, gas tightness, and rust-preventing properties. in the past, to provide these properties, (a) a compound grease containing heavy métal powder has been applied to the contact surface of at least one of the pin and the box, or (b) a viscous liquid, semisolid, or solid lubricating coating has been formed on the contact surface. However, as stated above, (a) has the problem that it has an adverse effect on huma ns and the environment, and (b) has the problem of a small ΔΤ whereby when makeup Is carried out with a high torque, there is the possibility of yielding of the shoulder portions occurring before completion of makeup.
A threaded joint according to the présent Invention has a first lubiicating coating and a second lubiicating coating on the contact surface of at least one member of the pin and the box. The first lubiicating coating Is a solid lubiicating coating formed on a portion of the contact surface 10 including at least the shoulder portion. The second lubiicating coating Is selected from a viscous liquid lubiicating coating and a solid lubiicating coating and formed on at least the portion of the contact surface where the first lubiicating coating Is not présent. The first lubiicating coating Is a coating having relatively high friction with a coefficient of friction which Is higher than the coefficient of friction of the second lubiicating coating.
Below, the first lubiicating coating will be referred to as a high-friction solid lubiicating coating, and when the second lubricating coating Is a solid lubiicating coating, that solid lubricating coating will sometimes be referred to as a second solid lubricating coating.
In the locations dose to the threaded portions between the threaded portions and the seal portions of the pin and the box of a threaded joint, a portion where the pin and the box do not 20 contact each other when the threaded joint is made up Is provided with the object of preventing lubricating components from oozing out at the time of makeup of the threaded joint. In some threaded joints, a non-contacting région where the pin and the box Intentîonally do not contact Is provided. Such portions where the pin and the box do not contact each other at the time of makeup are not part of the contact surfaces, and It does not matter whether a coating according to 25 the présent Invention is applied to these portions.
A high-friction solid lubricating coating which Is the first lubricating coating is formed on just a portion of the contact surface of one or both of the pin and the box which Includes the shoulder portion. The portion of the contact surface having the high-friction solid lubricating coating may be just the shoulder portion, but preferably It 1s the entire unthreaded métal contact portion Induding 30 the seal portion and the shoulder portion. Namely, the high-friction solid lubricating coating is preferably formed on the seal portion and the shoulder portion of the contact surface of at least one of the pin and the box. At least the remaining portion of the contact surface which does not hâve the high-friction solid lubricating coating has a second lubricating coating selected from a viscous liquid lubricating coating and a solid lubricating coating formed thereon. The second lubricating coating may be formed on the entire contact surface, In which case the second lubricating coating is positioned on top of the high-friction solid lubricating coating (namely, it forms an upper layer). It Is also possible for the second lubricating coating to be formed just on the portion where the high5 friction solid lubricating coating Is not présent (e.g., just on the threaded portion).
When the contact surface of only one member of the pin and the box has the high-friction solid lubricating coating and the second lubricating coating, there is no particular limitation on surface treatment of the contact surface of the other member of the pin and the box. For example, a high-friction solid lubricating coating which may be the same as or different from the first lubricating coating, a viscous liquid lubricating coating or a solid lubricating coating which may be the same as or different from the second lubricating coating, a solid anticorrosive coating, and a combination of a lower layer In the form of a lubricating coating and particularly a viscous liquid lubricating coating and an upper layer in the form of a solid anticorrosive coating can be formed on at least a portion of the contact surface and preferably on the entire contact surface of the other member. Altematively, the contact surface of the other member can be left untreated, or it can be subjected to just the beiow-described preparatory surface treatment for surface roughening (such as phosphate chemical conversion treatment).
Figures 5(A) - (C) and Figures 6(A) - (B) show various possible embodiments of combinations of the first and second lubricating coatings. In these figures, of the male threads of 20 the threaded portion of the pin 1, the thread 3a* at the extreme end and closest to the seal portion 4a are formed with an incomplète shape which is observed at the start of thread cutting. By making the thread at the extreme end of the pin incomplète threads, stabbing of the pin becomes easler, and the possibility of damage to the threaded portion of the box at the time of stabbing of the pin is decreased.
Figure 5(A) shows an embodiment in which the unthreaded métal contact portions (the seal portions and the shoulder portions) of the contact surfaces of both the pin and the box hâve a high-friction solid lubricating coating 10, and the remainder of each contact surface, which is primarily the threaded portion, has a second lubricating coating 11.
Figure 5(B) shows an embodiment In which the unthreaded métal contact portions of the contact surfaces of both the pin and the box hâve a high-friction soiid lubricating coating 10, and a second lubricating coating 11 which covers the entirety each contact surface is formed atop each high-friction solid lubricating coating 10.
Figure 5(C) shows an embodiment in which one of the pin and the box (the pin in the figure) has a high-friction solid lubricating coating 10 which covers the unthreaded métal contact portion and atop It a second lubricating coating 11 which covers the entire contact surface in the same manner as in Figure 5(B), and the entire contact surface of the other member (the box in the figure) is coated with a second lubricating coating 11.
Figure 6(A) shows an embodiment in which one of the pin and the box (the pin in the figure) has a high-friction solid lubricating coating which covers the unthreaded métal contact portion and a second lubricating coating 11 which covers the remainderofthe contact surface in the same manner as in Figure 5(A), and the entire contact surface of the other member (the box in the figure) is covered by a second lubricating coating 11.
Figure 6(B) shows an embodiment in which one of the pin and the box (the box in the figure) has a high-friction solid lubricating coating 10 which covers the unthreaded métal contact portion and a second lubricating coating 11 which covers the remainder of the contact surface in the same manner as in Figure 5(A), and the entire contact surface ofthe other member (the pin in the figure) is covered by a solid anticorTosive coating 12.
Figure 6(C) shows an embodiment in which one ofthe pin and the box (the pin in the figure) has a high-friction solid lubricating coating 10 which covers the unthreaded métal contact portions and atop It a second lubricating coating 11 which covers the entire contact surface in the same manner as in Figure 5(B), and the entire contact surface of the other member (the box in the figure) is covered by a high-friction solid lubricating coating 10.
It is understood by those skilled in the art that a tubular threaded Joint according to the présent Invention can hâve a coating structure which Is a combination of coatings other than the combinations described above. For example, the second lubricating coating 11 on one of the pin and the box in Figure 5(A) or on the pin ln Figure 6(A) can be replaced by a solid anticorrosive coating. In this case, the second lubricating coating 11 which is présent on only one member covers the portion on which the high-friction solid lubricating coating is not formed including at least the threaded portion as shown in Figure 6(B).
Next, various coatings which cover the contact surfaces of a tubular threaded joint according to the présent invention will be explained. Unless otherwise specified, % with respect to the content of components of the coatings means mass %. This content is substantially the same as the content based on the total solids content (the total content of nonvolatile components) of a coating composition for forming a lubricating coating.
[Hîgh-Friction Solid Lubricating Coating]
The high-friction solid lubricating coating is a solid lubricating coating having a relatively high coefficient of friction compared to the second lubricating coating. It produces a high-friction state In the final stage of makeup of a threaded joint (starting when the shoulder portions of the pin 5 and the box contact until the seal portions Intimately contact with a predetermined amount of interférence), thereby Increasing ΔΤ by increasing Ty and making It difficult for yielding of the shoulder portions to take place even when makeup Is carried out with a high torque.
In the présent invention, a high-friction solid lubricating coating which has such an effect is provided so as to cover a portion of the contact surface including at least the shoulder portion of at to least one of a pin and a box. Preferably, the entirety of the unthreaded métal contact portion including the seal portion and the shoulder portion is covered by the high-friction solid lubricating coating. When a threaded Joint has a plurality of seal portions and shoulder portions, It Is préférable to cover the entirety of the seal portions and the shoulder portions with a high-friction solid lubricating coating. However, the objective of increasing ΔΤ can be achieved even if only the 15 shoulder portions where contact initially takes place in the final stage of makeup of a threaded joint are covered with a high-friction solid lubricating coating. The location where a high-friction solid lubricating coating Is formed can be suitably set in accordance with the shape of a Joint and the required performance.
Even when a second lubricating coating 11 is formed atop the high-friction solid lubricating 20 coating 10 such as on the pin 1 and the box 2 as shown in Figure 5(B) or on the pin 1 as shown In Figure 5(C), a high-friction state is achieved by the high-friction solid lubricating coating 10 In the final stage of makeup, and a desired effect of increasing ΔΤ can be achieved. The high-friction solid lubricating coating needs to hâve a higher coefficient of friction than the second lubricating coating 11. A certain degree of adhesion to the substrate (the contact surfaces of the pin and the 25 box, which may be in an as-machined state or may hâve a preparatory surface treatment coating such as one formed by phosphate chemical conversion treatment or métal plating) is necessary.
An example of a high-friction solid lubricating coating which is suitable for use in the présent invention is a coating comprising an organic resin or inorganic polymer which contains little or no solid lubricating particles (such as In an amount of at most 5 mass %, preferably at most 3 30 mass %, and more preferably at most 1 mass % based on the total solids content).
A particularly preferred high-friction solid lubricating coating is a solid lubricating coating which is formed from a film-forming composition which is used for lubricating treatment before hydroforming of steel. Spécifie examples of such a composition are Surflube C291 manufactured by Nippon Paint Co., Ltd. (based on a water-soluble resin) and Gardolube L6334 and L6337 manufactured by Chemetali GmbH. A solid lubricating coating formed from this type of composition has a higher coefficient of friction than a lubricating coating used for lubricating threaded joints (such as a lubricating coating selected from a viscous liquid lubricating coating and a second solid lubricating coating used In the présent invention), and it forms a solid lubricating coating having good adhesion and affinity to a lubricating coating. However, the solid lubricating coating which is formed stiii has good lubricating properties and sliding properties, so as shown in Figure 5(A) and Figure 6(B), for example, even if a second lubricating coating having a low coefficient of friction is not présent on the unthreaded métal contact portion including the shoulder portion, galiing résistance necessary for makeup and suffident gas tightness after makeup are obtained if a second lubricating coating is présent on the threaded portions of at least one of the pin and the box.
Another high-friction solid lubricating coating which can be used is a coating comprising the same components as the beiow-described second solid lubricating coating but which has a reduced content of a solid lubricant (lubricating powder).
The coefficient of friction of a solid lubricating coating or a viscous liquid lubricating coating can be measured In accordance with ASTM D2625 (load carrying capadty and lifespan of solid film lubricants) or ASTM D2670 (wear properties of fluid lubricants) by the Falex pin and Vee block method (referred to below as the Falex method) using a Falex pin and Vee block machine. In the Falex method, biocks (Vee blocks) having a tip with a V-shaped opening are disposed fadng opposite sides of a pin, and the pin Is rotated while applying a predetermined pressure loading to the blocks to measure the coefficient of friction.
Measurement ofthe coefficient offriction can be carried out using test pièces constituted by blocks and a pin which are taken from a steel billet made of the same material as used in a tubular threaded joint and which hâve undergone the same preparatory surface treatment and surface coating treatment. Measurement is carried out at around 1 GPa, which corresponds to the maximum pressure of the seal portions at the time of makeup of a tubular threaded joint, and the average coefficient of friction in a steady frictions! state before the occurrence of galiing can be compared. Of course, a high-friction solid lubricating coating according to the présent invention can be selected based on the coefficient of friction measured using another friction measuring apparatus normaliy used in a laboratory. Whatever the measurement method, it is suffident for the coeffident of friction of the high-friction solid lubricating coating to be higher than the coeffident of friction of the second lubricating coating when measurement is carried out under the same conditions.
As long as the high-friction solid lubricating coating according to the présent Invention has a higher coefficient of friction than the viscous liquid lubricating coating or the second solid lubricating coating used as the second lubricating coating, there is no particular lower limit on the coefficient of friction of the high-friction solid lubricating coating. However, in order to adequately achieve the objective of increasing Ty and Increasing ΔΤ, the coefficient of friction of the highfriction solid lubricating coating ls preferably larger by a certain extent than the coefficient of friction of the second lubricating coating. Preferably, the coefficient of friction of the high-friction solid lubricating coating is at least 1.5 times, more preferably at least 2 times, and most preferably at least 2.5 times the coefficient of friction ofthe second lubricating coating.
The coefficient of friction of the high-friction solid lubricating coating as measured by the above-stated Falex method is preferably at least 0.06, more preferably at least 0.08, and most preferably at least 0.1. Since an extremely high coefficient of friction has an adverse effect on the galling résistance of a threaded joint, the coefficient of friction of the high-friction solid lubricating coating ls preferably at most 0.25 and more preferably at most 0.20.
The thickness of the high-friction solid lubricating coating ls preferably 5-40 pm. If it is less than 5 pm, the effect of producing a high level of friction at the time of contact and galling résistance may be inadéquate. On the other hand, if it exceeds 40 pm, not only does the frictionincreaslng effect reach a limit but an adverse effect on the properties of the seal portion may develop.
The high-friction solid lubricating coating can be formed by coating methods well known to those skilled in the art. ln order to form a high-friction solid lubricating coating on a portion of the contact surface of the pin and/or the box, namely, on only the shoulder portion or on the unthreaded métal contact portion Including the seal portion and the shoulder portion, spray coating can be carried out while shielding with a suitable means the portions where it ls not desired to form the high-friction solid lubricating coating. Upon drying to evaporate solvents after application, a high-friction solid lubricating coating ls formed.
[Viscous Uquid Lubricating Coating]
A viscous liquid lubricating coating can be formed using a lubricating grease which has been conventionally used to improve the galling résistance of the contact surfaces of a threaded joint. It ls préférable to use a lubricating grease referred to as green dope which has little adverse effect on the environment and contains no or little heavy métal powder.
A preferred example of such a viscous liquid lubricating coating ls a coating comprising a suitable amount of a base oil and at least one material selected from a rosin-based material, wax, métal soap, and a basic métal sait of an aromatic organic acid. Of these components, a rosin5 based material is effective primarily at increasing the coefficient of friction of a lubricating coating, namely, at increasing ΔΤ, while wax, métal soap, and a basic métal sait of an aromatic organic acid are effective primarily at preventing gailing of a lubricating coating. Therefore, it is possible for a coating to exhibit adéquate lubricating performance even if it does not contain a powder of a soft heavy métal such as lead or zinc. A particularly préférable viscous liquid lubricating coating to comprises ali of a rosin-based material, wax, métal soap, and a basic métal sait of an aromatic organic acid.
A rosin-based material ls selected from rosin and its dérivatives. When it is contained in a lubricating coating, it becomes highly viscous when it undergoes a high pressure in a frictional interface. As a resuit, it is effective at increasing ΔΤ of the coating. The rosin which ls used may t5 be any of tail rosin, gum rosin, and wood rosin, and various rosin dérivatives such as rosin esters, hydrogenated rosins, polymerized rosins, and disproportionated rosins can also be used. The content of the rosin-based material in the lubricating coating is preferably 5 - 30% and more preferably 5 - 20%.
Wax not only has the effect of preventing gailing by decreasing the friction of a lubricating 20 coating, it also decreases the fluidity of the coating and Increases the coating strength. Any of animal, vegetable, minerai, and synthetic waxes can be used. Examples of waxes which can be used are beeswax and whale tallow (animal waxes); Japan wax, camauba wax, candelilla wax, and rice wax (vegetable waxes); paraffin wax, microcrystalline wax, petrolatum, montan wax, ozokerite, and ceresine (minerai waxes); and oxide wax, polyethylene wax, Fischer-Tropsch wax, amide wax, 25 and hardened castor oil (castor wax) (synthetic waxes). Of these, paraffin wax with a molecular weight of 150 - 500 is preferred. The wax content of a lubricating coating is preferably 2-20 %.
A métal soap, which ls a sait of a fatty acid with a métal other than an alkali métal, is effective at Increasing the galling-preventing effect and the rust-preventing effect of a coating. Its content is preferably 2-20 %.
The fatty acid of a métal soap is preferably one having 12-30 carbon atoms from the standpoint of lubricating properties and rust prévention. The fatty acid can be either saturated or unsaturated. Mixed fatty acids derived from natural oils and fats such as beef tallow, lard, wooi fat, palm oil, rapeseed oil, and coconut oil, and single compounds such as lauric acid, tridecyclic add, myristic add, palmitic add, lanopalmitic add, stearic add, Isostearic add, oleic add, elaidic add, arachlc add, behenic add, erudc add, lignoceric add, lanoceric add, a sulfonic add, salicylic add, and a carboxylic add may be used. The métal sait is preferably in the form of a calcium sait, but it may also be a sait of another alkaline earth métal or a zinc sait. The sait may be either a neutral sait or a basic sait.
A viscous liquid lubricating coating may contain a basic métal sait of an aromatic organic add selected from basic sulfonates, basic salicylates, basic phenates, and basic carboxylates as a rust-preventing agent. Each of these basic métal salts of an aromatic organic acid is a sait of an aromatic organic add with excess alkali (an alkali métal or an alkaline earth métal) in which the excess alkali is présent as colliodal fine particles dispersed in oil. These basic métal salts are a grease or a semisolid substance at room température, and exhibit a lubricating action In addition to a rust-preventing action. The alkali which constitutes the cation part of a basic métal sait of an aromatic organic add may be an alkali métal or an alkaline earth métal, but preferably It Is an alkaline earth métal and particularly caldum, barium, or magnésium, each providing the same effect. Its content In the lubricating coating is preferably 10 to 70%.
The higher the base number of the basic métal sait of an aromatic organic add used as a rust-preventing agent, the greater the amount of the fine particles of the sait which function as a solid lubricant, and the better the lubricating properties (galling résistance) which can be imparted by the lubricating coating. When the base number exceeds a certain level, the sait has the effect of neutralizing add components, and the rust-preventing effect of the lubricating coating is increased. For these reasons, it is préférable to use one having a base number (JIS K 2501) of 50 - 500 mgKOH/g. A preferred base number is 100 - 500 mg KOH/g, and more preferably it Is In the range of 250 - 450 mg KOH/g.
In order to suppress the fluldity of a viscous liquid lubricating coating at high températures and further increase Its galling résistance, the lubricating coating may contain a lubricating powder. The lubricating powder can be any harmless one which Is not toxic and which does not overly decrease the coeffident of friction. A preferred lubricating powder is graphite. Amorphous graphite which produces little decrease in the coeffident of friction is more preferred. The content of a lubricating powder is preferably 0.5 - 20%.
In order to Increase the uniformity of dispersion of a solid lubricating powder in the lubricating coating or to improve the properties of the lubricating coating, the lubricating coating may include components other than those described above, such as one or more components selected from organic resins and various oils and additives normally used in lubricating oils (such as an extreme pressure agent).
Oils refer to lubricating components which are liquid at room température and which can be used In lubricating oils. Oils themselves hâve lubricating properties. Examples of oils which can be used include synthetic esters, natural oils, and minerai oils. The above-described rustpreventing agents (basic salts of aromatic organic acids) also hâve lubricating properties, so they also function as oils. The properties of a lubricating coating vary with the content of oil. If a coating does not contain an oil or if the oil content Is too low, the lubricating coating does not become a vis cou s liquid lubricating coating and Instead becomes a solid lubricating coating. In the présent Invention, such a lubricating coating can also be used as a solid lubricating coating.
An organic resin and particularly a thermoplastic resin suppresses tackiness of the lubricating coating and increases the thickness of the coating, and when it is introduced Into a frictional Interface, it Increases galling résistance and decreases friction between contacting métal portions even when a high makeup torque (a high pressure) is applied. Therefore, it may be contained in a lubricating coating. In such cases, it Is préférable to use a resin in powder form having a particle diameter in the range of 0.05 - 30 pm and more preferably in the range of 0.07 20 pm.
Some examples of thermopiastic resins are polyethylene resins, polypropylene resins, polystyrène resins, poly(methyl acrylate) resins, styrene-acrylic acid ester copolymer resins, polyamide resins, and polybutene (poiybutyiene) resins. A copolymer or blend or of these resins or of these resins and other thermoplastic resins can also be used. The density of the thermopiastic resin (JIS K 7112) is preferably in the range of 0.9 -1.2. In addition, In view of the necessity for the resin to readily deform on a frictional surface in order to exhibit lubricating properties, the thermal deformation température (JIS K 7206) of the resin Is preferably 50-150’ C.
When the lubricating coating contains a thermopiastic resin, the content thereof In the coating is preferably at most 10 % and more preferably in the range of 0.1 - 5 %. The total content of the above-described rosin-based material and the thermopiastic resin Is preferably at most 30 %.
Examples of natural oils and fats which can be used as an oil include beef tallow, lard, wool fat, palm oil, rapeseed oil, and coconut oil. A minerai oil (including a synthetic minerai oil) having a viscosity at 40’ C of 10 - 300 cSt can also be used as an oii.
A synthetic ester which can be used as an oil can increase the plastidty of the thermopiastic resin and at the same time can Increase the fluïdity of the lubricating coating when subjected to hydrostatic pressure. In addition, a synthetic ester with a high melting point can be used to adjust the melting point and hardness (softness) of the lubricating coating. Examples of a synthetic ester are fatty acid monoesters, dîbaslc acid diesters, and fatty acid esters of trimethylolpropane or pentaerythritol.
Examples of fatty acid monoesters are monoesters of carboxylic acids having 12-24 carbon atoms with higher alcohols having 8-20 carbon atoms. Examples of dibasic add diesters are diesters of dibasic acids having 6-10 carbon atoms with higher alcohols having 8-20 carbon atoms. Examples of fatty acids which constitute a fatty acid ester of trimethylolpropane or pentaerythritol are ones having 8-18 carbon atoms.
When a lubricating coating contains at least one ofthe above oils, the content of the oil Is preferably made at least 0.1 mass % in order to obtain an increase in gaîllng résistance. The content Is preferably made at most 5 mass % in order to prevent a decrease in the coating strength.
An extreme pressure agent has the effect of increasing the galling résistance ofthe lubricating coating when added in a small amount. Nonlimiting examples of an extreme pressure agent are vulcanized oils, polysulfides, and phosphates, phosphites, thiophosphates, and dithiophosphoric add métal salts. When an extreme pressure agent Is contained ln a lubricating coating, its content is preferably in the range of 0.05 - 5 mass %.
Examples of preferred vulcanized oils are compounds which contain 5-30 mass % of sulfur and are obtained by adding sulfur to unsaturated animal or vegetable oils such as olive oil, castor oil, rice bran oil, cottonseed oil, rapeseed oil, soy bean oil, corn oil, beef tallow, and lard and heating the mixture.
Examples of preferred polysulfides are polysulfides of the formula Rr(S)c-R2 (wherein Rt and R2 may be the same or different and are an alkyl group having 4-22 carbon atoms, an aryl group, an alkylaryl group, or an arylalkyl group, and c is an integer from 2 to 5) and olefin sulfides containing 2-5 sulfur bonds per molécule. Dibenzy! disulfide, di-tert-dodecyl poiysulfide, and ditert-nonyl poiysulfide are particularly preferred,
Phosphates, phosphites, thiophosphates, and dithiophosphoric add métal salts may be of the following general formulas.
phosphates: (R3O)(R4O)P(=O)(ORS) phosphites: (RsOXR^JPfORs) thiophosphates: (R3O)(R4O)P(=S)(OR3) dithiophosphoric add métal salts: [(R3O)(ReO)P(=S)-S]2-M
In the above formulas, R3 and Re are each an alkyl group having 1 to 24 carbon atoms, a cycloalkyl group, an alkylcycloalkyl group, an aryl group, an alkyïaryl group, or an arylalkyï group, Re and Rs are each a hydrogen atom, an alkyl group having 1 to 24 carbon atoms, a cycloalkyl group, an alkylcycloalkyl group, an aryl group, an alkyïaryl group, or an arylalkyï group, and M is molybdenum (Mo), zinc (Zn), or barium (Ba).
In addition to the above-described components, the viscous liquid lubricating coating may contaln an antioxldant, a preservative, a colorant, and the like.
A viscous liquid lubricating coating can be formed by applylng a coating composition to the contact surfaces of at least one of the pin and the box of a threaded joint, and drying the coating if necessary. Depending on the coating method, the composition which is used may contain a volatile organic solvent in addition to the above-described components.
When the coating composition Is a solid orsemisolid at room température, it may be applied after being heated to lower its viscosity (for example, it may be applied with a spray gun in the form of a hot melt).
When heating is not employed, a solvent is contained in the coating composition to decrease the viscosity of the composition to a viscosity sufficient for application. As a resuit, the coating thickness and the composition of the lubricating coating which is formed are made uniform and coating formation can be carried out efficiently. Examples of preferred solvents are petroleum solvents such as solvents corresponding to Industrial gasoline près cri bed by JIS K 2201, minerai spirits, aromatic petroleum naphtha, xylene, and Cellosolves. Two or more of these may be used in combination. A solvent having a flash point of at least 30° C, an initial boiling point of at least 150e C, and a final boiling point of at most 210° C is preferred because it is relatively easy to handle and it rapidly evaporates, so the drying time can be short.
A preferred coating thickness of the viscous liquid lubricating coating Is 5 - 200 pm and more preferably 15 - 200 pm. The lubricating coating is preferably sufficiently thick to fiil minute interstices In the contact surfaces such as the spaces between threads. If the coating thickness Is too small, the effects of components such as a rosin-based material, wax, métal soap, or lubricating powder being supplied to the frictional surface from the interstices due to the action of hydrostatic pressure which develops at the time of makeup can no longer be expected, and the galling résistance of a threaded joint worsens. Furthermore, when the lubricating coating contains a rustpreventing agent, the rust-preventing effect becomes Inadéquate. On the other hand, making the coating thickness too large is not only wasteful, but It runs counter to preventlng environmental pollution, which is one of the objects of the présent invention. When a viscous liquid lubricating coating is formed atop a high-friction solid iubricating coating 10 as a second iubricating coating 11 as shown in Figures 5(B) and 5(C), the total coating thickness of the high-friction solid lubricating coating and the viscous liquid iubricating coating is preferably at most 200 pm.
[Second Solid Lubricating Coating]
A solid lubricating coating which is used to form the second lubricating coating ln the form of the second solid lubricating coating ln the présent Invention ls baslcally constituted by a powder having a solid lubricating action (referred to as a iubricating powder) and a binder. This coating can be formed by applying a dispersion having a lubricating powder dispersed in a bindercontaining solution. The lubricating powder is strongly adhered to the surface of a threaded joint ln a state ln which It ls dispersed in the binder in the coating, and at the time of makeup, It ls stretched by the makeup pressure to a reduced thickness. As a resuit, it increases the galling résistance of a threaded joint.
Examples of a lubricating powder include but not limited to moiybdenum disulfide, tungsten disulfide, graphite, fluorinated graphite, zinc oxide, tin sulfide, bismuth sulfide, organomolybdenum compounds (e.g., a moiybdenum dialkyfthlophosphate or a moiybdenum dialkylthiocarbamate), PTFE (polytetrafluoroethylene), and BN (boron nitride). One or more of these can be used.
From the standpoints ofthe adhesion and rust-preventing properties ofthe solid iubricating coating, graphite is a particularly preferred iubricating powder, and from the standpoint of filmforming properties, amorphous graphite ls more preferred. A preferred content of lubricating powder in the solid lubricating coating is 2 -15 mass %. In the présent invention, It is necessary for the coefficient of friction of the second solid lubricating coating to be lower than the coefficient of friction of the high-friction solid lubricating coating. The coefficient of friction of the second solid lubricating coating can be adjusted by the content of the lubricating powder. Accordingly, as stated above, If the content of a lubricating powder ls made small, this type of solid iubricating coating can also be used as a high-friction solid lubricating coating.
The binder can be an organic resin or an inorganic polymer.
The organic resin ls preferably one having heat résistance and suitable hardness and wear résistance. Examples of such a resin are thermosetting resïns such as epoxy resins, polylmide resins, polycarbodiïmide resins, phenolic resins, furan resins, and silicone resins; and thermoplastic resins such as polyolefins, polystyrènes, polyuréthanes, polyimides, polyesters, polycarbonates, acrylic resins, thermoplastic epoxy resins, polyamide-lmide resins, polyether ether ketones, and polyether sulfones. The resin which is used may be a copolymer or a blend of two or more resins.
When the binder is a thermosetting resin, from the standpolnts of adhesion and wear résistance of a thermosetting solid lubricating coating, It ls préférable to perform heat setting treatment. The température of this heat setting treatment ls preferably at least 120° C and more preferably 150 - 380’ C, and the treatment time îs preferably at least 30 minutes and more preferably 30 - 60 minutes.
When the binder is a thermoplastic resin, it is possible to employ a coating composition using a solvent, but it ls also possible to form a thermoplastic solid lubricating coating without a solvent using the hot melt method. In the hot melt method, a coating composition containing a thermoplastic resin and a lubricating powder ls heated to melt the thermoplastic resin, and the composition which has become a low viscosity fluid ls sprayed from a spray gun having a température maintainlng ability which maintains a constant température (normally a température which ls around the same as the température of the composition in a molten state). The heating température of the composition is preferably 10 - 50’ C higherthan the melting point ofthe thermoplastic resin (the melting température or the softening point). In this method, It is suitable to use a thermoplastic resin having a melting point of 80 - 320’ C and preferably 90 - 200’ C.
The substrate which ls coated (namely, the contact surface of the pin and/or the box) is preferably preheated to a température higher than the melting point of the thermoplastic resin. As a resuit, it ls possible to obtain good coating properties. When the coating composition contains a small amount (such as at most 2 mass %) of a surface active agent such as polydimethyl siloxane, it is possible to form a good quality coating even if the substrate ls not preheated or even if the preheating température is lower than the melting point of the base resin. After coating, the thermoplastic resin is solidified by cooling the substrate by air cooling or natural cooling to form a solid lubricating coating atop the substrate.
The inorganic polymer ls a compound having a three-dimensionally crosslinked structure of metal-oxygen bonds such as Ti-O, Si-O, Zr-O, Mn-O, Ce-O, or Ba-O. This compound can be formed by hydrolysis and condensation of a hydrolyzable organometallic compound typified by a métal alkoxide, although hydrolyzable inorganic compound such as titanium tetrachloride can also be used. A preferred métal alkoxide which can be used ls one having lower alkoxy groups such as methoxy, ethoxy, isopropoxy, propoxy, isobutoxy, butoxy, or tert-butoxy groups. A preferred métal alkoxide is an aikoxide of titanium or silicon, and a titanium alkoxide is particularly préférable. Among these, titanium Isopropoxide is preferred due to its excellent film-forming properties.
The Inorganic polymer may contain an alkyl group which may be substituted with a functional group such as an amine or an epoxy group. For example, it is possible to use an organometallic compound in which some ofthe alkoxygroups are replaced by an alkyl group containing a functional group as is the case with silane coupling agents and titanate coupling agents.
When the binder is an inorganic polymer, a lubricating powder is added to a solution of a métal alkoxide or a partial hydrolysate thereof and dispersed therein, and the resulting composition is applied to the contact surface of at least one of a pin and a box. The resulting coating may be subjected to humidifylng treatment and then heated if necessary, thereby allowing hydrolysis and condensation ofthe métal alkoxide to proceed andforming a solid lubricating coating inwhich a lubricating powder is dispersed in a coating formed from an inorganic polymer having metal-oxygen bonds.
Even when using any of the above-described binders, when the coating composition contains a solvent, the solvent may be any of water, a water-miscible organic solvent such as an alcohol, or a water-lmmiscible organic solvent such as a hydrocarbon or an ester. Two or more types of solvents may be used in combination.
In addition to a lubricating powder, various additives such as a rust-preventing agent can be added to the solid lubricating coating within a range that does not impair the galling résistance of the coating. For example, the rust-preventing properties of the solid lubricating coating itself can be improved by adding one or more of zinc powder, a chromium pigment, silica, and an alumina pigment. A particularly preferred rust-preventing agent Is calcium ion exchanged silica. A solid lubricating coating may also contain an inorganic powder in order to adjust the siiding properties of the coating. Examples of such an inorganic powder are titanium dioxide and bismuth oxide. These rust-preventing agents, Inorganic powders, and the like (nameiy, powder components other than a lubricating powder) can be présent in a total amountof up to 20% ofthe solid lubricating coating.
In addition to the above components, the solid lubricating coating may contain auxiliary additives selected from a surface active agent, a colorant, an antioxidant, and the like In an amount of at most 5%, for example. It is also possible to contain an extreme pressure agent, a liquid lubricant, or the like in a very small amount of at most 2 %.
For the same reasons as given for the viscous liquid lubricating coating, the thickness of the solid lubricating coating Is preferably 5 -150 pm and more preferably 20 -100 pm. When the solid lubricating coating is formed atop a high-friction solid lubricating coating, the total thickness of the high-friction soiid lubricating coating and the solid lubricating coating is preferably at most 150 pm.
[Solid Anticorrosive Coating]
As stated above with respect to Figure 4, during the time until actual use of a tubular threaded joint, a protector is often mounted on a pin or box which has not been connected to another member. It Is necessary for a solid anticorrosive coating not to be destroyed under at least a force applied during mounting of a protector, not to be dissolved even when exposed to water which condenses below the dew point during transport or storage, and not to easily soften at high températures exceeding 40e C. Any coating which can satisfy such properties can be used as a solid anticorrosive coating. For example, a solid anticorrosive coating may be a thermosetting resin coating optionally containing a rust-preventing component.
A preferred solid anticorrosive coating is a coating based on an ultraviolet curing resin. Known resin compositions comprising at least a monomer, an oligomer, and a photopolymerization Initiator can be used as an ultraviolet curing resin.
Examples of monomers include but are not Iimited to polyvalent (di-, tri-, or higher) esters of a polyvalent alcohol with a (meth)acryllc add, various (meth)acrylate compounds, Nvinylpyrrolidone, N-vinylcaproiactam, and styrene. Examples of oligomers indude but are not Iimited to epoxy (meth)acrylates, urethane (meth)acrylates, polyester (meth)acrylates, polyester (meth)acrylates, polyether (meth)acrylates, and silicone (meth)acrylates,
Usefui photopolymerization initiators are compounds having absorption In the wavelength range of 260 - 450 nm, induding benzoin and its dérivatives, benzophenone and Its dérivatives, acetophenone and its dérivatives, Michlerts ketone, benzil and its dérivatives, tetraikylthiuram monosulfide, thioxanes, and the like. It is partîcularly preferred to use a thioxane.
From the standpolnts of coating strength and sliding properties, a solid anticorrosive coating formed from an ultraviolet curing resin may contain an additive selected from a lubricant and/or a fibrous fiiter and a rust-preventing agent. Examples of a lubricant are métal soaps such as caldum stéarate and zinc stéarate, and polytetrafluoroethylene (PTFE) resin. An example of a fibrous Aller is adcular calcium carbonate such as Whiskal sold by Maruo Caldum Co„ Ltd.. One or more of these additives can be added in an amount of 0.05 - 0.35 parts by mass with respect to
1 part by mass of the ultraviolet curing resin. Examples of a rust-preventing agent are aluminum tripolyphosphate and aluminum phosphite. It can be added in a maximum amount of around 0.10 parts by mass with respect to 1 part by mass of the ultraviolet curing resin.
A solid anticorrosive coating which is formed from an ultraviolet curing resin is often transparent. From the standpoint of facilitating quality inspection of the resulting solid anticorrosive coating either visually or by image processing (investigating whether there is a coating and the uniformityornonuniformityofthe coating thickness), the solid anticorrosive coating may contain a colorant. The colorant which is used can be selected from pigments, dyes, and fluorescent materials. The amount of a colorant is preferably a maximum of 0.05 parts by mass with respect to one part by mass ofthe ultraviolet curing resin.
A preferred colorant Is a fluorescent material. A fluorescent material may be any of fluorescent pigments, fluorescent dyes, and fluophors used in fluorescent paints, but preferably It Is a fluorescent pigment. A solid anticorrosive coating which contains a fluorescent material Is colorless or transparent with a color under visible light, but when it Is irradiated with a black light or ultraviolet rays, It fluoresces and becomes colored, making It possible to ascertaln the presence of a coating or whether there Is unevenness of the coating. Furthermore, as it Is transparent under visible light, the material undemeath the solid anticorrosive coating, namely, the surface ofthe substrate can be observed. Accordingly, inspection for damage to the threaded portions of the threaded joint Is not impeded by a solid anticorrosive coating.
After a composition based on an ultraviolet curing resin is applied to a contact surface of a threaded joint, it Is Irradiated with ultraviolet light to cure the coating, resulting in the formation of a solid anticorrosive coating based on an ultraviolet curing resin. Irradiation with ultraviolet light can use a usual commercialiy available ultraviolet light irradiation apparatus having an output wavelength in the range of 200 - 450 nm. Examples of a source of ultraviolet light are a high pressure mercury vapor lamp, an ultrahlgh pressure mercury vapor lamp, a xénon lamp, a carbon arc lamp, a métal hallde lamp, and sunlight.
The coating thickness of a solid anticorrosive coating (the overall coating thickness when there are two or more layers of an ultraviolet curing resin) is preferably in the range of 5 - 50 pm and more preferably ln the range of 10 - 40 pm. If the coating thickness of the solid anticorrosive coating is too small, it does not adequately fonction as a anticorrosive coating. On the other hand, if the coating thickness of the solid anticorrosive coating is too large, the solid anticorrosive coating Is sometimes destroyed under the force of mounting when Installing a protective member such as a protector, and corrosion prévention ends up being Inadéquate.
A solid anticorrosive coating based on an ultraviolet curing resin is a transparent coating, so the condition of the substrate can be observed through the coating without removing It, and It is possible to Inspect the threaded portions before makeup from atop the coating. Accordingly, by forming the solid anticorrosive coating on the contact surface of a pin, it is possible to easily inspect for damage of the threaded portion of the pin which is typically formed on the outer surface of an end of a steel pipe and which is easily damaged.
As stated above with respect to the high-friction solid lubricating coating, each of the above-described viscous liquid lubricating coating, solid lubricating coating, and solid anticorrosive coating is preferably applied by spray coating. Spray coating Includes hot melt coating.
As shown In Figure 5(A), when a high-friction solid lubricating coating is formed on the unthreaded métal contact portion of a contact surface and a second lubricating coating Is formed on the threaded portion which is the remainlng portion of the contact surface, either the high-friction solid lubricating coating or the second lubricating coating may be formed first. In this case, particularly when the second lubricating coating Is a solid lubricating coating, it is préférable to make the thicknesses of the high-friction solid lubricating coating and the solid lubricating coating approximately the same (for example, within ± 15 pm) so that a large step does not develop at the border between the two types of coatings. When the second lubricating coating is a viscous liquid lubricating coating, it has a large ability to deform at the time of makeup, so the second lubricating coating and the high-friction solid lubricating coating may hâve a large différence In their thicknesses. Normally, the viscous liquid lubricating coating has a larger coating thickness than the high-friction solid lubricating coating.
[Preparatory Surface Treatmentj
In a tubular threaded joint according to the présent invention In which a high-friction solid lubricating coating and a second lubricating coating and In some cases also a solid anticorrosive coating are formed on the contact surfaces of a pin and/or a box, if preparatory surface treatment for surface roughening Is carried out on the contact surfaces which are the substrate for the coatings so that the surface roughness Is greater than 3-5 pm, which Is the surface roughness after machinlng, the coating adhesion increases, and there Is a tendency for the desired effects of the coatings to be enhanced. Accordingly, before forming a coating, It is préférable to carry out preparatory surface treatment on the contact surfaces to roughen the surfaces.
When a coating is formed atop a contact surface having a large surface roughness, the thickness of the coating is preferably larger than Rmax of the contact surface so as to completely cover the contact surface. When the contact surface is rough, the thickness of a coating Is the average value of the overall coating thickness which Is calculated from the area, the mass, and the density of the coating.
Exarnples of preparatory surface treatment for surface roughening are blasting treatment by projecting a blasting material such as spherical shot or angular gril, pickling by Immersion in a strang add such as sulfuric acid, hydrochloric acid, nitric acid, or hydrofluoric acid to roughen the surface, chemical conversion treatment such as phosphate treatment, oxalate treatment, or borate treatment (as the resulting crystals grow, the roughness of the crystal surface increases), electroplating with a métal such as Cu, Fe, Sn, orZn or an alloy of these metals (projections are selectively plated, so the surface is slightly roughened), and Impact plating which can form a porous plated coating. As one type of electroplating, composite plating which forms a plated coating In which minute solid particles are dispersed In métal Is possible as a method of imparting surface roughness because the minute solid particles project from the plated coating. Preparatory surface treatment may use two or more methods In combination. Treatment can be carried out In accordance with known methods.
Whichever preparatory surface treatment method Is used for the contact surfaces, the surface roughness Rmax produced by preparatory surface treatment for surface roughening Is preferably 5-40 pm. If Rmax Is less than 5 pm, adhesion of a lubricating coating formed thereon and rétention of the coating may become Inadéquate. On the other hand, if Rmax exceeds 40 pm, friction increases, the coating may be unable to withstand shearing forces and compressive forces at the time of a high pressure, and the coating may be easily destrayed or peeled off.
From the standpointof the adhesion ofthe lubricating coating, preparatorysurface treatment which can form a porous coating, namely, chemical conversion treatment and Impact plating are preferred. With these methods, In order to make Rmax of the porous coating at least 5 pm, the coating thickness is preferably made at ieast 5 pm. There Is no particular upper limit on the coating thickness, but normally at most 50 pm and preferably at most 40 pm is sufficient. If a lubricating coating is formed atop a porous coating which is formed by preparatory surface treatment, the adhesion of the lubricating coating Is Increased by the so-called anchor effect. As a resuit, it becomes difficult for peeling of the solid lubricating coating to take place under repeated makeup and breakout, contact between metals is effectively prevented, and galling résistance, gas tightness, and corrosion résistance are further Increased.
Particularly preferred types of preparatory surface treatment for forming a porous coating are phosphate chemical conversion treatment (treatment with manganèse phosphate, zinc phosphate, Iron manganèse phosphate, or zinc calcium phosphate) and formation of a zinc or zincIron alloy coating by impact plating. A manganèse phosphate coating Is préférable from the standpoint of adhesion, and a zinc or zinc-iron alloy coating which can be expected to provide a sacrificial corrosion-preventing effect by zinc Is préférable from the standpoint of corrosion résistance.
Phosphate chemical conversion treatment (phosphating) can be carried out by immersion or spraying in a conventional manner. An acldic phosphating soluiton which Is normally used for zinc-plated materials can be used as a chemical conversion treatment solution. For example, a zinc phosphating solution containing 1 -150 g/L of phosphate ions, 3-70 g/L of zinc ions, 1 -100 g/L of nitrate ions, and 0-30 g/L of nickel ions can be used. It is also possible to use a manganèse phosphating solution which Is normally used for threaded joints. The température of 10 the solution can be from room température to 100e C, and the duration of treatment can be up to 15 minutes depending upon the desired coating thickness. In order to promote the formation of a coating, prior to phosphate treatment, an aqueous surface conditioning solution containing colloïdal titanium can be supplied to the surface to be treated. After phosphate treatment, washing is preferably performed with cold or warm water followed by drying.
Impact plating can be carried out by mechanical plating In which particles are impacted with a material to be piated inside a rotating barrel, or by blast plating In which particles are impacted against a material to be piated using a blasting machine. In the présent invention, it is suffïcient to plate just a contact surface, so it is préférable to empioy blast plating which can perform localïzed plating. The thickness of a zinc or zinc alloy layer which is formed by impact plating is preferably 5 - 40 pm from the standpoints of both corrosion résistance and adhesion.
For example, particles having an iron core coated with zinc or a zinc alloy are blasted against the contact surface to be coated. The content of zinc or a zinc alloy In the particles is preferably in the range of 20 - 60 mass %, and the diameter of the particles Is preferably In the range of 0.2 -1.5 mm. As a resuit of blasting, only the zinc or zinc alloy which Is the coating layer 25 of the particles adhères to the contact surface which forms a substrate, and a porous coating made of zinc or a zinc alloy is formed atop the contact surface. This impact plating can form a porous métal piated coating having good adhesion to a steel surface regardiessofthecomposition ofthe steel.
As another type of preparatory surface treatment, aithough it produces almost no surface 30 roughening effect, electroplating In one or more spécifie layers may improve the adhesion of the lubricating coating to the substrate and may improve the galling résistance of a tubular threaded joint.
Examples of such preparatory surface treatment for a lubricating coating are electroplating with a meta! such as Cu, Sn, or Ni or alloys of thèse metals. Plating may be single-layer plating or multiple-layer plating with two or more iayers. Spécifie examples of this type of electroplating are Cu plating, Sn plating, Ni plating, Cu-Sn alioy plating, Cu-Sn-Zn alloy plating, two-layer plating by Cu plating and Sn plating, and three-layer plating by Ni plating, Cu plating, and Sn plating. Particularly a tubular threaded joint made from a steel having a Cr content exceeding 5% is susceptible to galiing, and therefore It Is preferably subjected to preparatory surface treatment In the form of single-layer plating with a Cu-Sn alloy or a Cu-Sn-Zn alloy or multiple-layer plating with two or more layers selected from these alloy platings and Cu plating, Sn plating, and Ni plating such as two-layer plating by Cu plating and Sn plating, two-layer plating by Ni plating and Sn plating, two-layer plating by Ni plating and Cu-Sn-Zn alloy plating, and three-layer plating by Ni plating, Cu plating, and Sn plating are preferred.
These types of plating can be formed by the method described In JP 2003-74763 A. In the case of multiple-layer plating, the lowermost layer of plating (usualiy Ni plating) Is preferably an extremely thin plating layer referred to as strike plating and having a thickness of less than 1 pm. The plating thickness (the overall thickness In the case of multiple-layer plating) is preferably in the range of 5-15 pm.
It Is possible to form a solid anticorrosive coating as another preparatory surface treatment method.
When the second lubricating coating Is a vlscous liquid lubricating coating, in order to reduce the surface tackiness of this coating, a thin, dry solid coating (e.g., having a thickness of 10 - 50 pm) may be formed as an upper layer of the lubricating coating. This dry solid coating can be a usual resin coating (such as a coating of an epoxy resin, a polyamide resin, a polyamide-imide resin, or a vinyl resin) and it can be formed from either a water-based composition or an organic solvent-based composition. The coating may also contain a small amount of wax In order to afford lubricity.
Examples
The effects of the présent invention will be illustrated by the following examples and comparative examples. In the following explanation, the contact surface of a pin Including the threaded portion and the unthreaded métal contact portion will be referred to as the pin surface, and the contact surface of a box Including the threaded portion and the unthreaded métal contact portion will be referred to as the box surface. The surface roughness Is expressed as Rmax.
Unless particularly specified, % means mass %.
The pin surface and the box surface of commercially availabie spécial threaded joints (VAM TOP with an outer diameter of 17.78 cm (7 inches) and a wall thickness of 1.036 cm (0.408 Inches) manufactured by Sumitomo Métal Industries, Ltd.) made from carbon steel A, Cr-Mo steel B, or 13% Cr steel C having the composition shown in Table 1 were subjected to preparatory surface treatment as shown ln Table 2. Then, as shown ln Table 3, a high-friction solid lubricating coating and a second lubricating coating selected from a viscous liquid lubricating coating and a solid lubricating coating and sometimes a solid anticorrosive coating were formed on the pin surface and the box surface.
The details of treatment and the coating composition will be described below. in Table 3, the unthreaded métal contact portion means the seal portion and the shoulder portion, and the threaded portion means the portion of the contact surface other than the seal portion and the shoulder portion. When forming different coatings on the unthreaded métal contact portion and the threaded portion, first the high-friction solid lubricating coating was formed on the unthreaded métal contact portion, and then the indicated lubricating coating was formed on the threaded portion. When forming a lubricating coating on the threaded portion, a shielding plate was used so as not to form the lubricating coating atop the high-friction solid lubricating coating which was formed on the unthreaded métal contact portion. However, the border between these coatings need not be clear, and the effects ofthe présent invention can be obtained even when there Is an overlapping région of around 1 mm.
The coefficients offriction ofthe high-friction solid lubricating coating, the viscous liquid lubricating coating, and the solid lubricating coating which were formed were the maximum coefficients of friction under steady state conditions when the coefficients of friction were measured by the above-mentioned Falex testing method with a pressure of 1 GPa. Measurement was carried out In accordance with ASTM D2670. The pin used for measurement had a diameter of 6.35 mm (1/4 Inch), and 2 Vee blocks had a V-shaped groove with an included angle of 96’ and a groove width of 6.35 mm (1/4 Inch). The pin and the blocks were prepared by cutting them from a billet of the same steel as the threaded joint to be tested, and they underwent the same preparatory surface treatment and coating treatment as the surface of the pin and the box, respectively, of the threaded joint to be tested.
A high torque test ln which makeup was carried out with a high makeup torque was performed on a tubular threaded joint which was prepared in the above-described manner to obtain a torque chart like that shown ln Figure 2. The values for Ts (the shouldering torque), Ty (the yield torque), and ΔΤ (the torque-on-shoulder résistance = Ty - Ts) were measured on the torque chart.
Ts was the torque at the start of Interférence of the shoulder portions. Specifically, Ts was the torque when the change in torque which appeared when the shoulder portions interfered began to enter a linear région (région of elastic deformation). Ty was the torque at the start of 5 plastic deformation. Specifically, Ty was the torque when the torque began to leave the linear région after Ts was reached In which the change in torque with the number of tums was linear. ΔΤ (= Ty - Ts) was made 100 for Comparative Example 1 In Table 3 using a conventional compound grease. Table 4 shows the results of comparison of other examples with this value of ΔΤ.
A repeated makeup and breakout test was carried out on each tubular threaded joint, and 10 galling résistance was evaluated. In the repeated makeup and breakout test, makeup of a threaded joint was carried out with a makeup speed of 10 rpm and a high makeup torque of 20 kNm, and after breakout, the state of galling of the pin surface and the box surface was investigated. In cases In which seizing scratches which developed due to makeup were light and repeated makeup was possible if repalr was performed, repair was carried out and makeup and breakout 15 were continued. Makeup was carried out 10 times (for 10 cycles). Table 4 also shows the results of this test.
Table 1
| Mark | Steel composition of threaded joint (mass %, remainder. Fe and Impurities) | ||||||||
| C | Si | Mn | P | S | Cu | NI | Cr | Mo | |
| A | 0,24 | 0.3 | 1.3 | 0.02 | 0.01 | 0.04 | 0.07 | 0.17 | 0.04 |
| B | 0.25 | 0.25 | 0.8 | 0.02 | 0.01 | 0.04 | 0.05 | 0.95 | 0.18 |
| C | 0.19 | 0.25 | 0.8 | 0.02 | 0.01 | 0.04 | 0.1 | 13 | 0.04 |
Table 2
| No. | Preparatory surface treatment | Steel mark | |
| Pin | Box | ||
| 1 .Machine grinding (R=3) | 1.Machine grinding (R=3) | ||
| Example 1 | 2.Zn phosphating (R=8) (t=12) | 2.Mn phosphating (R=12) (t=15) | A |
| 1.Machine grinding (R=3) | |||
| Example 2 | Sand blasting (R=10) | 2.Ni strike plating + Cu plating | C |
| (R=3) (t=12) | |||
| 1.Machine grinding (R=3) | 1.Machine grinding (R=3) | ||
| Example 3 | 2.Zn phosphating (R=8)( t=12) | 2.Ni strike plating + Cu-Sn-Zn alloy plating (R=2) (t=7) | B |
| 1 .Machine grinding (R=3) | 1.Machine grinding (R=3) | ||
| Example 4 | 2,Zn phosphating (R=8) (t=12) | 2,Ni strike plating + Cu-Sn-Zn | B |
| alloy plating (R=2) (t=7) | |||
| Compar. | 1.Machine grinding (R=3) | 1.Machine grinding (R=3) | A |
| Example 1 | 2.Zn phosphating (R=8) (t=12) | 2,Mn phosphating (R=12) (t=15) | |
| Compar. | 1.Machine grinding (R=3) | 1.Machine grinding (R=3) | B |
| Example 2 | 2.Zn phosphating (R=8)( t=12) | 2.Mn phosphating (R=10) (t=12) | |
| Com par. | 1.Machine grinding (R=3) | 1 .Machine grinding (R=3) | B |
| Example 3 | 2.Zn phosphating (R=8) (t=12) | 2.Mn phosphating (R=10) (t=12) | |
| Com par. | 1.Machine grinding (R=3) | 1 .Machine grinding (R=3) | B |
| Example 4 | 2.Zn phosphating (R=8)( t=12) | 2.Mn phosphating (R=10) (t=12) | |
| Com par. | 1 .Machine grinding (R=3) | 1.Machine grinding (R=3) | B |
| Example 5 | 2.Zn phosphating (R=8) (t=12) | 2.Mn phosphating (R=10) (t=12) |
R: surface roughness (pm); t: coating thickness (pm)
Table 3
| No. | Layer | Pin | Box | ||
| Unthreaded métal contact portion | Threaded portion | Unthreaded métal contact portion | Threaded portion | ||
| Example 1 | — | High-friction solid lubricating coating | Viscous liquid lubricating coating | High-friction solid lubricating coating | Viscous liquid lubricating coating |
| Example 2 | Lower | High-friction solid lubricating coating | Viscous liquid lubricating coating | ||
| Upper | Viscous liquid lubricating coating | ||||
| Example 3 | Lower | High-friction solid lubricating coating | High-friction solid lubricating coating | ||
| Upper | Viscous liquid lubricating coating | ||||
| Example | — | UV curable solid anticorrosive | High-friction | Solid |
| 4 | coating | solid lubricating coating | lubricat-ing coating | |
| Comp. Ex. 1 | — | Compound grease in viscous liquid form according to API BUL 5A2 | ||
| Comp. Ex. 2 | — | Viscous liquid lubricating coating | Viscous liquid lubricating coating | |
| Comp. Ex. 3 | — | UV curable solid anticorrosive coating | Solid lubricating coating | |
| Comp. Ex. 4 | — | High-friction solid lubricating coating | Viscous liquid lubricating coating | |
| Comp. | UV curable solid anticorrosive | High-friction solid lubricating | ||
| Ex. 5 | coating | coating |
Table 4
| ΔΤ ratio (=Ty - Ts)1) | Results of repeated makeup and | |
| No. | (Relative value when the value of | breakout test with a high torque |
| Comparative Example 1 is 100) | for 10 cycles | |
| Example 1 | 125 | no galiing through 10 cycles |
| Example 2 | 112 | no galling through 10 cycles |
| Example 3 | 110 | no galling through 10 cycles |
| Example 4 | 105 | no galling through 10 cycles |
| Compar. Ex. 1 | 100 | no galling through 10 cycles |
| Compar. Ex. 2 | 52 | no galling through 10 cycles |
| Compar. Ex. 3 | 70 | no galling through 10 cycles |
| Compar. Ex. 4 | 61 | galling occuned in the 5th cycle |
| Compar. Ex. 5 | not assessable | galling occurred In the 1st cycle |
1) A value of at least 95 ls acceptable for practical use.
(Example 1)
The pin surface and the box surface of a spécial threaded Joint made of carbon steel having composition A shown in Table 1 were subjected to preparatory surface treatment and coating treatment as described below to form the coating structure shown In Figure 5(A).
[Box Surface]
After finishing by machine grinding (surface roughness of 3 pm), the box surface underwent preparatory surface treatment by immersion for 10 minutes in a manganèse phosphating solution at 80 - 95° C to form a manganèse phosphate coating having a thickness of 15 pm (surface roughness of 12 pm).
Surflube C291 manufactured by Nippon Paint Co., Ltd. which was diluted with water to a strength of 10% was applied by spray coating to the unthreaded métal contact portion (the seal portion and the shoulder portion) ofthe box surface which had undergone the preparatory surface treatment to form a high-friction solid lubricating coating having a coating thickness of approximately 10 pm after drying, The coefficient of friction of this solid lubricating coating was 0.1. The threaded portion (the portions other than the seal portion and the shoulder portion) of the box surface which had undergone the preparatory surface treatment was treated so as to form a viscous liquid lubricating coating thereon in the following manner.
The composition of the viscous liquid lubricating coating was 15% of a hydrogenated rosin ester (Ester Gum H manufactured by Arakawa Chemical Industries, Ltd.), 48% of a h'ghly basic calcium sulfonate as a basic métal sait of an aromatic organic acid (Calcinate C-400CLR manufactured by Crompton Corporation, base number of 400 mg KOH/g), 17% of calcium stéarate as a métal soap (manufactured by DIC Corporation), 10% of amorphous graphite as a solid lubricant (Blue P manufactured by Nippon Graphite Industries, Ltd.), and 10% of paraffin wax.
After the above-described composition was diluted with 30 parts by mass of an organic solvent (Exxsol D40 manufactured by Exxon Mobil Corporation) per 100 parts by mass of the composition to lower its viscosity, it was applied to the threaded portion of the box surface by spray coating. After évaporation of the solvent, a viscous liquid lubricating coating having a thickness of approximately 50 pm was formed. The coefficient of friction of this lubricating coating was 0.04.
[Pin Surface]
After finishing by machine grinding (surface roughness of 3 pm), the pin surface was subjected to preparatory surface treatment by immersing for 10 minutes in a zinc phosphating solution at 75 - 85 C to form a zinc phosphate coating (surface roughness of 8 pm) with a thickness of 12 pm.
The same treatment as for the box surface to form lubricating coatings was carried out on the pin surface which had undergone the preparatory surface treatment. Namely, the abovedescribed high-friction solid lubricating coating was formed on the unthreaded métal contact portion, and the above-described viscous liquid lubricating coating was formed on the threaded portion. The coating thickness and the coefficient of friction of each coating were the same as for the box surface.
As can be seen from Table 4, the value of ΔΤ in a high torque test was such that the ratio of ΔΤ when the value of ΔΤ for Comparative Example 1 was given a value of 100 (referred to below as the ΔΤ ratio) was 125%. Compared to the ΔΤ ratio of around 50% for Comparative Example 2 which did not hâve a high-friction solid lubricating coating on the seal portion or the shoulder portion (the entirety of the pin surface and the box surface was coated with a viscous liquid lubricating coating), the ΔΤ ratio was greatly increased.
Moreover, ΔΤ in Example 1 was increased by 25% with respect to ΔΤ of the reference example using compound grease (Comparative Example 1 ). Accordingly, it was verified that the threaded joint of Example 1 could be made up with a high torque without the occurrence of yielding of the shoulder portions. In the repeated makeup and breakout test, makeup and breakout could be performed 10 times without the occurrence of galling.
(Example 2)
The pin surface and the box surface of a spécial threaded joint made of the 13% Cr steel having composition C shown in Table 1 were subjected to the below-described preparatory surface treatment and coating treatment to form the coating structure shown In Figure 5(C).
[Box Surface]
After finishing by machine grinding (surface roughness of 3 pm), the box surface underwent NI strike plating and then Cu plating by electroplating to form a plated coating with an overall thickness of 12 pm. The surface roughness after this preparatory surface treatment was 3 pm.
The same viscous liquid lubricating coating as described in Example 1 was formed by spray coating on the entirety of the box surface which had undergone the preparatory surface treatment. The coating thickness of the viscous liquid lubricating coating after évaporation of the solvent was 80 pm, and its coefficient of friction was 0.04.
[Pin Surface]
The pin surface was subjected to preparatory surface treatment by sandblasting with No.
sand to give a surface roughness of 10 pm.
Undiluted Gardolube L6334 manufactured by Chemetall GmbH was applied by spray coating to the unthreaded métal contact portion (the seal portion and the shoulder portion) of the pin surface which had undergone the preliminary surface treatment to form a high-friction solid lubricating coating having a thickness of approximately 15 pm. The coefficient of friction of this 5 high-friction solid lubricating coating was 0.15. The same viscous liquid lubricating coating as was formed on the box surface was formed to the same coating thickness on the entire pin surface including the unthreaded métal contact portion on which the high-friction solid lubricating coating had been formed.
In the high torque test, the ΔΤ ratio was 112%, confirming that ΔΤ was larger than for 10 Comparative Example 1 which used compound grease. Of course, makeup and breakout could be carried out 10 times without any problem in the repeated makeup and breakout test.
(Example 3)
The pin surface and the box surface of a spécial threaded joint made of the Cr-Mo steel having composition B shown in Table 1 were subjected to the below-described preparatory surface treatment and coating treatment to form the coating structure shown ln Figure 6(C).
[Box Surface]
After finishing by machine grinding (surface roughness of 3 pm), the box surface underwent Ni strike plating foilowed by Cu-Sn-Zn alloy plating by electroplating to form a plated 20 coating having an overall thickness of 7 pm. The surface roughness after the preparatory surface treatment was 2 pm.
The unthreaded métal contact portion and the threaded portion of the box surface which had undergone the preparatory surface treatment was coated by spray coating with Surflube C291 manufactured by Nippon Paint Co., Ltd. which was diluted with water to a strength of 10% to form a 25 high-friction solid lubricating coating (coefficient of friction of 0.1 ) having a coating thickness of approximately 10 pm after drying.
[Pin Surface]
After finishing by machine grinding (surface roughness of 3 pm), the pin surface was Immersed for 10 minutes ln a zinc phosphating solution at 75 - 85* C for preparatory surface 30 treatment to form a zinc phosphate coating (surface roughness of 8 pm) having a thickness of 12 pm.
The unthreaded meta! contact portion of the pin surface which had undergone the preparatory surface treatment was coated by spray coating with Surflube C291 manufactured by Nippon Paint Co., Ltd. which was diluted with water to a strength of 10% to form a high-friction solid lubricating coating with a coating thickness of approximately 10 pm (coefficient of friction of 0.1) after drying. Then, the viscous liquid lubricating coating described In Exampfe 1 was formed on the solid lubricating coating and on the threaded portion (namely, on the entire pin surface) by the same method as in Example 1 to a coating thickness of approximately 50 pm.
In the high torque test, the ΔΤ ratio was 110%, confirming that ΔΤ was larger than for the compound grease of Comparative Example 1. In the repeated makeup and breakout test, makeup and breakout were performed 10 times without any problems.
(Example 4)
The pin surface and the box surface of a spécial threaded joint made of the the Cr-Mo steel having composition B shown In Table 1 were subjected to the below-described preparatory surface treatment and coating treatment to form a coating having the structure shown in Figure 6(B).
[Box Surface]
After finishing by machine grinding (surface roughness of 3 pm), the box surface underwent Ni strike plating followed by Cu-Sn-Zn alloy plating by electroplating to form a plated coating having an overall thickness of 7 pm. The surface roughness after the preparatory surface treatment was 2 pm.
The unthreaded metaf contact portion of the box surface which had undergone the preparatory surface treatment was coated by spray coating with Surflube C291 manufactured by Nippon Paint Co., Ltd. which was diluted to a strength of 10% to form a high-friction solid lubricating coating (coefficient of friction of 0.1) having a coating thickness of approximately 50 pm after drying. On the threaded portion of the box surface which had undergone the preparatory surface treatment, a solid lubricating coating was formed in the following manner.
A lubricating coating composition having the below-described composition was heated at 120° C in a tank equipped with a stirrer to maintain a molten state having a viscosity suitable for coating, while the box surface which had undergone the preparatory surface treatment described above was preheated to 120e C by induction heating. Using a spray gun having a spraying head with a heat retaining mechanism, the above-described molten lubricating coating composition was applied to the threaded portion of the preheated box surface. After cooling, a solid lubricating coating having a thickness of 50 pm (coefficient of friction of 0.03) was formed.
The composition ofthe lubricating coating composition was as follows:
15% camauba wax,
15% zinc stéarate,
5% liquid polyalkyl méthacrylate (Viscoplex™ 6-950 manufactured by Rohmax Corporation),
49% corrosion inhibitor (NA-SUL™ Ca/W1935 manufactured by King Industries, Inc.),
3.5% amorphous graphite
1% zinc oxide,
5% titanium dîoxide,
5% bismuth trioxide,
1% silicone (polydimethyl siloxane), and antloxldants (made by Ciba-Geigy Corporation):
0.3% Irganox™ L150 and
0.2% Irgafos™ 168.
[Pin Surface]
After finlshing by machine grinding (surface roughness of 3 pm), the pin surface was immersed for 10 minutes In a zinc phosphating solution at 75 - 85’ C to form a zinc phosphate coating (surface roughness of 8 pm) having a thlckness of 12 pm. On the entire pin surface which had undergone this preparatory surface treatment, a solid anticorrosive coating was formed from an ultraviolet curing resin in the following manner.
A coating composition was prepared by adding aluminum zinc phosphate as a rustpreventing agent and polyethylene wax as a lubricant to an epoxy acrylic resln-based ultraviolet curing resin palnt composition (solventless type) manufactured by Chugoku Marine Paints, Ltd. The resulting coating composition contained 94% resin, 5% rust-preventing agent, and 1% lubricant based on the total solids content. This coating composition was applied by spraying to the entire pin surface and was irradiated with ultraviolet rays (wavelength of 260 nm) from an air-cooled mercury vapor lamp having an output of 4 kW to cure the coating. The resulting coating had a thickness of 25 pm and was colorless and transparent. The male threaded portion of the pin could be Inspected through the coating either with the naked eye or with a magnifying giass.
In the high torque test, the ΔΤ ratio was 105%. The ΔΤ ratio was greatly increased compared to Comparative Example 3 in which a high-friction solid lubricating coating was not formed on the unthreaded métal contact portion (the seal portion and the shoulder portion) of the box surface. In addition, the ΔΤ ratio was Increased compared to Comparative Example 1 which used a conventional compound grease. In the repeated makeup and breakout test, makeup and breakout could be carried out 10 times without any problems.
(Comparative Example 1)
The pin surface and the box surface of a spécial threaded joint made of the carbon steel having composition A shown In Table 1 were subjected to the below-described preparatory surface treatment and coating treatment, [Box Surface]
After finishing by machine grinding (surface roughness of 3 pm), the box surface underwent preparatory surface treatment by immersion for 10 minutes In a manganèse phosphating solution at 80 - 95° C to form a manganèse phosphate coating having a thickness of 15 pm (surface roughness of 12 pm). A viscous liquid compound grease In accordance with API BUL 5A2 was applied to the box surface which had undergone this preparatory surface treatment to form a lubricating coating. The coated amount of the compound grease was a total of 50 g on the pin and the box. The coated area was a total of roughly 1400 cm2.
[Pin Surface]
After finishing by machine grinding (surface roughness of 3 pm), the pin surface was Immersed for 10 minutes in a zinc phosphating solution at 75 - 85* C to form a zinc phosphate coating (surface roughness of 8 pm) having a thickness of 12 pm. The same compound grease as was used on the box surface was applied to the pin surface which had undergone this preparatory surface treatment.
As shown in Table 3, during 10 cycles of makeup and breakout In the repeated makeup and breakout test, there was no occurrence of galling through the tenth cycle. However, compound grease contains heavy métal such as iead, so It is harmful to humans and the environment.
In the high torque test, the joint exhibited a high value of Ty with a large value of ΔΤ by which yielding of the shoulder portions did not occur even when makeup was carried out with a high torque. The values for ΔΤ ratio in the other examples was calculated with the value of ΔΤ at this time being made 100.
(Comparative Example 2)
The pin surface and the box surface of a spécial threaded joint made of the Cr-Mo steel having composition B in Table 1 were subjected to the following preparatory surface treatment and coating treatment.
[Box Surface]
After finishing by machine grinding (surface roughness of 3 pm), the box surface was immersed for 10 minutes In a manganèse phosphating solution at 80 - 95° C to form a manganèse phosphate coating with a thickness of 12 pm (surface roughness of 10 pm). The viscous liquid lubricating coating described in Example 1 was formed by the same method on the entire box surface which had undergone this preparatory surface treatment. After évaporation of the solvent, a viscous liquid lubricating coating having a thickness of approximately 60 pm was formed. The coefficient of friction of this lubricating coating was 0,04.
[Pin Surface]
After finishing by machine grinding (surface roughness of 3 pm), the pin surface was immersed for 10 minutes in a zinc phosphating solution at 75 - 85’ C to form a zinc phosphate coating (surface roughness of 8 pm) having a thickness of 12 pm. The same viscous liquid lubricating coating as on the box surface was formed to a thickness of 60 pm on the entire pin surface which had undergone the preparatory surface treatment.
In the repeated makeup and breakout test, the results were extremely good with no occurrence of galling in 10 cycles of makeup and breakout. However, In the high torque test, the ΔΤ ratio was an extremely small value of 52% compared to the conventional compound grease (Comparative Example 1 ). Namely, It was agaln confirmed that if the contact surfaces of a tubuiar threaded joint are entirely coated only with a viscous liquid lubricating coating having a low coefficient of friction, the ΔΤ ratio is greatly reduced.
(Comparative Example 3)
The pin surface and the box surface of a spécial threaded joint made ofthe Cr-Mo steel having composition B ln Table 1 were subjected to the following preparatory surface treatment and coating treatment.
[Box Surface]
After finishing by machine grinding (surface roughness of 3 pm), the box surface underwent preparatory surface treatment by immersion for 10 minutes in a manganèse phosphating solution at 80 - 95e C to form a manganèse phosphate coating having a thickness of 12 pm (surface roughness of 10 pm). The same solid lubricating coating as described ln Example 4 was formed by the same method on the entire box surface which had undergone the preparatory surface treatment. After cooling, a solid lubricating coating having a thickness of approximately 50 pm (coefficient of friction of 0.03) was formed.
[Pin Surface]
After finishing by machine grinding (surface roughness of 3 pm), the pin surface was immersed for 10 minutes in a zinc phosphating solution at 75 - 85° C to form a zinc phosphate coating (surface roughness of 8 pm) having a thickness of 12 pm. The same ultraviolet curing resin coating (coating thickness of 25 pm) as described in Example 4 was formed by the same method on the entire pin surface which had undergone the preparatory surface treatment.
ln the repeated makeup and breakout test, the results were extremely good with no occurrence of galling ln 10 cycles of makeup and breakout. However, in the high torque test, the ΔΤ ratio was an extremely small value of 70% compared to conventional compound grease.
(Comparative Example 4)
The pin surface and the box surface of a spécial threaded joint made of the Cr-Mo steel having composition B ln Table 1 were subjected to the following preparatory surface treatment and coating treatment.
[Box Surface]
After finishing by machine grinding (surface roughness of 3 pm), the box surface was immersed for 10 minutes in a manganèse phosphating solution at 80 - 95° C to form a manganèse phosphate coating with a thickness of 12 pm (surface roughness of 10 pm). The same viscous liquid lubricating coating as described in Example 1 was formed by the same method on the entire box surface which had undergone this preparatory surface treatment. After évaporation of the solvent, a viscous liquid lubricating coating having a thickness of approximately 60 pm was formed. The coefficient of friction of this lubricating coating was 0.04.
[Pin Surface]
After finishing by machine grinding (surface roughness of 3 pm), the pin surface was immersed for 10 minutes In a zinc phosphating solution at 75 - 85° C to form a zinc phosphate coating (surface roughness of 8 pm) having a thickness of 12 pm. The same high-friction solid lubricating coating as formed on the unthreaded métal contact portion of the pin surface in Example 1 was formed to a thickness of 10 pm on the entire pin surface which had undergone the preparatory surface treatment.
In the repeated makeup and breakout test, the makeup torque was constantly high from the first cycle, and galling occurred in the fifth cycle maklng it unable to continue the test. In the high torque test, the ΔΤ ratio was a small value of 61% compared to the conventional compound grease (Comparative Example 1 ). Namely, when the entire contact surface of one member of a threaded Joint was coated with a high-friction solid lubricating coating, the galling résistance was greatly impaired, and due to a considérable Increase in the shouldering torque, the ΔΤ ratio was not improved.
(Comparative Example 5)
The pin surface and the box surface of a spécial threaded joint made of the Cr-Mo steel having composition B in Table 1 were subjected to the following preparatory surface treatment and coating treatment.
[Box Surface]
After finishing by machine grinding (surface roughness of 3 pm), the box surface was immersed for 10 minutes in a manganèse phosphating solution at 80 - 95e C to form a manganèse phosphate coating having a thickness of 12 pm (surface roughness of 10 pm). The same highfriction solid lubricating coating as formed on the unthreaded métal contact portion of the box surface In Example 4 was formed to a thickness of about 20 pm on the entire box surface which had undergone the preparatory surface treatment.
[Pin Surface]
After finishing by machine grinding (surface roughness of 3 pm), the pin surface was immersed for 10 minutes in a zinc phosphating solution at 75 - 85° C to form a zinc phosphate coating (surface roughness of 8 pm) having a thickness of 12 pm. The same ultraviolet curing resin coating (coating thickness of 25 pm) as described in Example 4 was formed by the same method on the entire pin surface which had undergone the preparatory surface treatment.
In the repeated makeup and breakout test, galîing occurred In the first cycle, and the test termlnated. This prématuré galling made It unable to evaluate by the high torque test. It was confirmed that the combination of coatings In this example affords poor lubricity leading to a significant worsening in galling résistance, which Is the fondamental performance required for a tubular threaded joint.
(Other Tests) ln order to Investigate the rust-preventing properties of the tubular threaded joints manufactured ln Examples 1-4, the same preparatory surface treatment and formation of lubricating coating or coatings as for the box ln Table 2 were performed on a separately prepared coupon test piece (70 mm x 150 mm x 1.0 mm thick). Each test plece was subjected to a sait spray test (in accordance with JIS Z 2371 (corresponding to ISO 9227) at a température of 35’ C for 1000 hours) or a humidity résistance test (ln accordance with JIS K 5600-7-2 (conesponding to ISO 6270) at a température of 50’ C and a relative humidity of 98% for 200 hours), and the occurrence of rust was Investigated. As a resuit, It was ascertalned that there was no occurrence of rust on the tubular threaded joints of Examples 1 - 4 In either of the tests.
When each of the examples of tubular threaded joints underwent a gas tightness test and an actual use test In an actual excavating apparatus, each joint exhibited satisfactory properties. It was confirmed that makeup could be stably carried out with these joints even when the makeup torque was high due to the values forAT which were larger than with conventionally used compound grease.
Claims (10)
- 46 Claims1. A tubular threaded joint constituted by a pin and a box each having a contact surface comprising an unthreaded métal contact portion including a seal portion and a shoulder portion and a threaded portion, characterized in that the contact surface of at least one of the pin and the box has a first lubricating coating and a second lubricating coating, the first lubricating coating being a solid lubricating coating formed on a portion ofthe contact surface including the shoulder portion, the second lubricating coating being selected from a viscous liquid lubricating coating and a solid lubricating coating and formed on at ieast the portion of the contact surface where the first lubricating coating is not présent, the first lubricating coating having a coefficient of friction which is higherthan that ofthe second lubricating coating, the second lubricating coating being positioned on top If there is a portion of the contact surface in which both the first lubricating coating and the second lubricating coating are présent.
- 2. A tubular threaded joint as set forth in claim 1 wherein the portion of the contact surface including the shoulder portion on which the first lubricating coating is formed is an unthreaded métal contact portion ofthe contact surface.
- 3. A tubular threaded joint as set forth ln claim 2 wherein the unthreaded métal contact portion of the contact surface of at least one of the pin and the box has the first lubricating coating, and the threaded portion of the contact surface has the second lubricating coating.
- 4. A tubular threaded joint as set forth in claim 2 wherein the unthreaded métal contact portion of the contact surface of at least one of the pin and the box has the first lubricating coating, and the entirety of the contact surface has the second lubricating coating formed atop the first lubricating coating.
- 5. A tubular threaded joint as set forth in claim 1 wherein the contact surface of one member of the pin and the box has the first lubricating coating formed on a portion of the contact surface Including the shoulder portion and the second lubricating coating formed on at least the portion of the contact surface where the first lubricating coating is not présent, and the contact surface of the other member of the pin and the box has a coating selected from a lubricating coating which is selected from a viscous liquid lubricating coating and a solid lubricating coating; a solid anticorrosive coating; and a two-layer coating comprising a lower layer in the form of a lubricating coating selected from a viscous liquid iubricating coating and a solid lubricating coating and an upper iayer ln the form of a solid anticorrosive coating.
- 6. A tubular threaded joint as set forth ln claim 5 wherein the solid anticorrosive coating is based on an ultraviolet curing resin.
- 7. A tubular threaded joint as set forth in any one of claims 1 - 6 wherein the contact surface of at leastone ofthe pin and the box is subjected tosurfacetreatment bya method selected from blasting, pickling, phosphate chemical conversion treatment, oxalate chemical conversion treatment, borate chemical conversion treatment, electroplating, impact platïng, and two or more of these methods prior to forming the iubricating coating or anticorrosive coating.
- 8. A tubular threaded joint as set forth in any one of claims 1 - 6 wherein the first lubricating coating has a thickness of 5 - 40 pm.
- 9. A tubular threaded joint as set forth ln claim 8 wherein the second lubricating coating is a viscous liquid lubricating coating having a thickness of 5 - 200 pm, and when this second lubricating coating is positioned atop the first lubricating coating, the total thickness of the first lubricating coating and the second lubricating coating is at most 200 pm.
- 10. A tubular threaded joint as set forth in claim 8 wherein the second lubricating coating is a solid lubricating coating having a thickness of 5 -150 pm, and when this second lubricating coating ls positioned atop the first lubricating coating, the total thickness of the first lubricating coating and the second lubricating coating is at most 150 pm.
Publications (1)
| Publication Number | Publication Date |
|---|---|
| OA16982A true OA16982A (en) | 2016-02-26 |
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