Agent for forming solid lubricating coating film, oil country tubular goods, and threaded joint for oil country tubular goods

Abstract

It is possible to provide a solid lubricating coating film capable of imparting excellent corrosion resistance as well as lubricity to a connection for oil country tubular goods even when a solid lubricating coating film is adopted for lubrication. An agent for forming a solid lubricating coating film on a thread portion of oil country tubular goods, in which a binder resin contains a prepolymer and a curing agent, the prepolymer is formed of one or more epoxy resins, 70 parts by weight or more of the prepolymer is contained with respect to 100 parts by weight of the binder resin, the epoxy resin constituting the prepolymer has an epoxy equivalent of 100 or more and 500 or less, the solid lubricant contains boron nitride (BN) in an amount of 80% by weight or more, BN has an average particle size of 10 μm or less, and a total weight of the solid lubricant is 0.1 times or more and two times or less a total weight of the binder resin. Figure 1

Description

Agent for forming solid lubricating coating, oil well pipe, and oil well pipe thread joint

[0001] The present disclosure relates to technology related to the lubrication and corrosion resistance of oil country tubular goods (OCG) pipes and oil country tubular goods threaded joints. The present disclosure relates to technology related to oil country tubular goods (OCG) pipes and oil country tubular goods threaded joints in which a solid lubricating coating is formed on the thread surface (including the metal seal surface) instead of a wet lubricating compound. In this specification, the fastening surface of the threaded portion includes the metal seal surface. Here, a solid lubricating coating refers to a coating composed of a binder resin as a matrix component, a solid lubricant dispersed and distributed within the binder resin, and additives added as needed. The present disclosure also aims to provide corrosion resistance while improving lubrication through a solid lubricating coating that realizes lubrication of the oil country tubular goods threads.

[0002] In this specification, the terms "lubricity" and "high lubricity" refer, in a broad sense, to a phenomenon of low friction and easy slippage. In a narrow sense, high lubricity means that the number of times that a thread can be tightened and untightened (also referred to as M / B number) is greater than or equal to a specified number. For example, the seizure resistance of oil country pipe threaded joints is described in the API 5C5 standard. The API 5C5 standard requires that casing sizes can be tightened up to three times. Furthermore, the API 5C5 standard requires that tubing sizes can be tightened up to ten times. In this specification, pipes with female threads may be collectively referred to as boxes. That is, couplings are also described as a type of box.

[0003] In conventional oil country pipe threaded joints, lubrication of the threads has been achieved by forming a coating on the fastening surfaces (sealing surfaces) (hereinafter simply referred to as "fastening surfaces"), which are the surfaces of the threads of at least one of the components on the male and female threads, using a manganese phosphate conversion coating or electroplating with Cu or the like. Lubrication has then been achieved by applying a lubricating compound containing Pb, Zn, or the like onto the coating. In this specification, when a coating is formed on the fastening surfaces (sealing surfaces) of the threads, the coating is also referred to as the fastening surface.

[0004] In response to this, in recent years, attention has been focused on "dry, dope-free" non-wet lubrication technology. "Dry, dope-free" means that the film itself is not a viscous liquid like API-mod compounds, and does not contain harmful heavy metals. One such "dry, dope-free" lubrication technology is one that forms a solid lubricating film on the fastening surfaces to achieve lubrication. This disclosure is about technology related to this "dry, dope-free" lubrication.

[0005] Here, there are various inventions related to solid lubricant coatings in past patent documents. A solid lubricant coating is composed of a lubricant component responsible for lubrication and a solid film as a matrix component that holds the lubricant component within the film. A solid film is a non-viscous, non-liquid film, meaning that it completes lubrication by itself during screw tightening and loosening. Conventional manganese phosphate films and copper electroplating films are solid films themselves. However, since they are based on the assumption that lubrication is achieved by applying a grease-like compound, they are not included in the category of solid lubricant coatings. In this disclosure, lubrication is achieved as a solid film, and an organic resin film is assumed as the solid film. For this reason, in the following description, such solid films will also be referred to as binder resins.

[0006] Conventional lubricating coatings used in oil country tubular goods threaded joints are described in, for example, Patent Documents 1 to 9. In the field of oil country tubular goods threads, BN is widely cited as one of the candidate solid lubricants and is exemplified in many patent documents. For example, Patent Documents 1 and 2 exemplify BN as a solid lubricant present in a solid lubricant coating. Epoxy resins have also been exemplified in previous patent documents. However, few previous patent documents clearly define epoxy resins and their chemical composition. Furthermore, many previous patent documents appear to specify a technology, but do not fully identify it.

[0007] The definition of epoxy resin is very broad. Epoxy resin is generally a general term for thermosetting resins formed by crosslinking and bonding a chemical substance having epoxy groups as a prepolymer (a precursor to the epoxy resin) with a curing agent. However, in academic and commercial contexts, as well as in patent documents, the term "epoxy resin" can refer to either the prepolymer's epoxy group-containing chemical substance itself, or to an epoxy resin produced by copolymerizing the prepolymer with a curing agent. However, these terms are often used interchangeably. In past patent documents, the term "epoxy resin" generally refers to the latter. In essence, past patent documents simply refer to the use of epoxy resin in a broad sense (see Patent Documents 3 to 8).

[0008] In the following description of the present disclosure, the epoxy resin agent used as the base material (prepolymer) for making the epoxy resin film will be referred to as a "prepolymer" or an "epoxy resin in the narrow sense." Finally, the epoxy resin (film) formed by polymerizing the prepolymer and the curing agent will be referred to as an "epoxy resin film."

[0009] Next, Patent Documents 3 to 9 will be explained. Patent Document 3 is an invention in which a solid lubricant coating is formed on a Cu-Sn-Zn plated substrate. Patent Document 3 describes selecting one or both of epoxy resin and polyamide-imide resin as the binder resin for the solid lubricant coating. Patent Documents 4 to 6 exemplify epoxy resin as an ingredient of a solid lubricant coating that has excellent heat resistance and lubricity. Patent Documents 4 to 6 do not specify the heat resistance of the epoxy resin, specifically the temperature limit at which the material can withstand, making it difficult to grasp the properties of the epoxy resin used.

[0010] Patent Document 7 clearly describes the formation of a two-component epoxy on a Zr-based plating substrate. However, two-component epoxy is not new; as mentioned above, epoxy resins are composed of a prepolymer and an epoxy resin curing agent in the narrow sense. The term "two-component" simply refers to a type in which two components are mixed on-site. Even one-component resins contain a prepolymer and a curing agent, so there is nothing new about them. Patent Document 8 describes an invention in which an acrylic silicone resin is formed on an ultraviolet-curable resin. Patent Document 8 cites acrylic acid-modified epoxy resin as one of the candidate compounds, and describes a resin with an epoxy resin main chain and acryloylated terminals.

[0011] Patent Document 9 describes a photocurable acrylic resin coating. Patent Document 9 describes a photocurable (meth)acrylate resin and specifies a film formed by copolymerization of (meth)acrylate monomers triggered by a photopolymerization initiator or other trigger. It lists polyester, polyether, polyurethane, and epoxy as candidates for the main chain structure forming the acrylate side chain. Furthermore, Non-Patent Document 1, although not an evaluation example of a solid lubricant coating, describes a tightening test method using a vertical power tong with a short pin, in which tightening and loosening are performed with a 5 kN weight (510 kg) constantly applied to the top end of the short pin. However, Non-Patent Document 1 evaluates a conventional grease-like compound as a means of determining the suitability of a new thread design.

[0012] Japanese Patent Publication No. 2017-110686 WO2017-110685 Japanese Patent Publication No. 2018-216497 Special Publication No. 2015-501906 Special Publication No. 2015-198557 Special Publication No. 2017-110685 Japanese Patent Publication No. 2017-71844 Japanese Patent Publication No. 2013-183634 Japanese Patent Publication No. 2011-12251

[0013] Tsutome et al.: Journal of the Japan Petroleum Technology Association, Vol. 61, No. 6 (1996), pp. 527-536.

[0014] The lubrication of oil well pipe threads, which is the subject of this disclosure, is performed under special sliding conditions. That is, at the site (actual well), a pin with an actual length of approximately 8 m or more but less than 15 m is tightened and loosened against a box set below. At this time, the pin is lifted by a crane and tightened and loosened using power tongs, but the full load of the pin can be applied to the box thread. In other words, lubrication is performed under a heavy load.

[0015] Furthermore, the pin is not necessarily tightened or loosened in an ideal state. In other words, during tightening, the pin thread is inserted into the box thread or set slightly hand-tightened. However, the pin is not set upright and immovable relative to the box thread. The pin is also not set in a straight, upright position, tilted diagonally. That is, while the lower part of the pin is constrained by the box thread, the upper end (the tip opposite the tightening end) is slightly bent depending on the elastic modulus (Young's modulus) of the material and the actual pin length. Especially for pins longer than 8 m, when viewed from below, the pin appears to be set straight into the box but bent. Since the pin is tightened or loosened from this state, the box thread and pin thread are never tightened or loosened with a uniform and symmetrical load. This results in a situation where parts of the thread surface are in strong localized contact. In other words, lubrication occurs under an unbalanced load. Furthermore, the locations where the bolts make strong contact also change depending on whether the bolts are tightened or loosened.

[0016] With conventional lubrication technology using grease-like compounds, the compound moves in tandem with the tightening and unthreading process. Therefore, even if there are slight fluctuations in lubrication conditions, the lubricant (lubricating compound) functions to converge the tightening and unthreading process in a favorable direction. Therefore, in evaluation tests (also known as laboratory tests) for the tightening and unthreading of threaded joints, it is possible to grasp the lubrication status of a full-size pin by evaluating it using a short-length pin, without relying on an evaluation using a full-size pin. However, according to the inventor's research, with lubrication technology for OCTG threads using solid lubricating coatings, the solid lubricating coating inevitably wears off to some extent. Therefore, it was necessary to devise a way to prevent this shavings from clogging the thread gap. Furthermore, secondary products derived from the worn solid lubricating coating do not always move in tandem with the tightening and unthreading process. The above is what happens in actual wells, and it is a significant difference between solid lubricating coatings and lubrication using lubricating compounds.

[0017] When evaluating solid lubricating coatings in laboratory tests, evaluations using short pins, as in the case of lubrication using lubricating compounds, do not necessarily simulate the effects of large or unbalanced loads for the reasons described above. It was found that evaluations using short pins shorter than the conditions in an actual well make it difficult to scrape the solid lubricating coating, making it impossible to create conditions that simulate the seizure behavior in an actual well. Thus, evaluations using conventional short pins cannot simulate conditions such as secondary products made from shavings of the solid lubricating coating clogging and seizing, or secondary products being pressed against the fastening surface to maintain the lubricating film effect. In other words, conventional evaluations using short pins are simply inefficient in their evaluation of solid lubricating coatings, and when determining the physical property parameters of a solid lubricating coating, areas that actually fail the test are erroneously evaluated as suitable. For these reasons, the inventors have come to the realization that the descriptions in conventional prior art often contain suitable ranges based on the above-mentioned overly lenient evaluations.

[0018] The inventors have come to the realization that it is necessary to define a group of parameters related to the solid lubricant coating by evaluating them under conditions similar to those experienced when OCTG threads are tightened and tightened in an actual well, i.e., assuming that tightening and tightening are performed under a heavy load and an unbalanced load. To achieve this, it is necessary to ensure lubricity in accordance with the conditions of use in an actual well and to clarify the meaning of the upper and lower limits of the parameters before setting each specification. In other words, it is important to define the upper and lower limits of the parameters through evaluations that are in line with conditions in an actual well. As mentioned above, evaluations of the lubrication behavior of OCTG threads have traditionally been conducted by evaluating the tightening and tightening behavior and the number of tightening and tightening operations using power tongs with short pins.

[0019] When a grease-like compound is used as a lubricant, the compound moves in conjunction with the tightening and unwinding of the screw. Therefore, there is no particular problem with evaluating lubrication using either horizontal or vertical tongs with a short pin. In other words, conventional grease-like compounds can be evaluated using laboratory tests with a short pin, including thread design, the presence or absence of undercoatings such as chemical conversion coatings and electroplating, and comparative evaluation of the compound itself. However, as mentioned above, evaluation of the lubrication of solid lubricant coatings presents challenges. Simply evaluating the lubrication using a short pin in a laboratory test does not simulate the behavior in an actual well, resulting in a rather lenient assessment of lubrication. Therefore, a "pass" evaluation using a short pin in a conventional laboratory test does not necessarily mean that the result will be "pass" when tightening and unwinding the screw in an actual well.

[0020] Furthermore, the lubrication of oil well pipe threads differs from other lubrication behaviors, which means that regulations based on evaluations of other lubrication conditions cannot be applied. Generally, when considering the lubrication behavior between two rubbing objects, a situation is assumed in which one object is fixed and the other is moving. For the moving object, it is assumed that lubrication begins when the object is in close contact with the fixed object. Even when both objects are moving, lubrication usually begins when they are in contact with each other.

[0021] On the other hand, when lubricating OCTG threads, the pin thread (male thread) starts out with some backlash relative to the box thread (female thread) at the beginning of make-up. Therefore, the threads do not always maintain stable contact until they are fully engaged. In other words, the lubrication of OCTG threads involves periods of strong contact and periods of almost no contact, and strong contact poses a high risk of damaging the lubricant film. Furthermore, the lubrication after the threads are engaged is affected by the lubrication conditions at the time. In particular, when there is backlash before the threads are engaged, the conventional method using a grease-like compound moves in conjunction with the tightening of the threads during the initial and final stages of make-up when there is backlash. Therefore, there is little impact from this backlash. On the other hand, with a solid lubricant coating, the solid lubricant coating is easily damaged by the unbalanced load caused by backlash.

[0022] In actual wells, the total weight of the pin threads is applied to the box threads during tightening and loosening. Furthermore, due to the backlash mentioned above, the load is not uniformly distributed, and the pin tends to rotate eccentrically until the threads engage. Therefore, the solid lubricant coating must be able to withstand the large loads applied as an eccentric load. A coating that is easily torn off or completely destroyed is not sufficient. In actual wells, OCTG is often used at lengths of approximately 12 to 16 meters. For example, a 9-5 / 8" outer diameter OCTG approximately 12 meters (approximately 40 feet) long can support a dead weight of approximately 1 ton. On offshore rigs, three pre-connected pin threads are often tightened, creating a severe load of approximately 3 tons on the box side when using 9-5 / 8" outer diameter OCTG.

[0023] When lubricating oil country pipe threads, it is necessary to consider lubrication that can withstand such heavy loads and unbalanced loads. After extensive consideration, the inventors have come to the conclusion that the key is to devise a solid lubricant and binder resin that takes into account how to minimize damage to the solid lubricant coating under conditions of heavy loads and when there is backlash before the threads engage. However, it is difficult to say that solid lubricant coatings have been designed from this perspective in previous literature.

[0024] The inventors have now come to the realization that the above findings are specific to solid lubricant coatings. In conventional lubrication, in which a grease-like compound is applied, the viscous liquid grease-like compound moves in conjunction with tightening and loosening, significantly mitigating the effects of large loads and uneven loads. For this reason, referring to previous literature, the lubrication behavior can be evaluated without any particular problems whether evaluation is performed using horizontal tongs with a short pin or vertical tongs with a short pin.

[0025] On the other hand, in the case of the lubrication behavior of OCTG threads using a solid lubricant coating as disclosed herein, the solid lubricant coating is damaged and peels off or is inevitably gradually worn away, even during tightening until the threads engage or after they are tightened. Unlike grease-like compounds, the peeled slag does not necessarily move in conjunction with tightening and loosening. Furthermore, it has been discovered that the secondary products (slag) derived from the scraped-off solid lubricant coating are released into the gap between the pin thread and the box thread, significantly affecting lubrication. In other words, if the gap is blocked by slag, it can directly lead to seizure. On the other hand, the slag can be reconstituted by being pressed down by a heavy load, and can reattach as a film to one of the threads, improving lubrication.

[0026] The inventors then discovered that laboratory tests using short pins are unable to simulate the heavy load and unbalanced load conditions that occur in actual wells. In other words, evaluations using simple short pins result in little secondary product generation from the solid lubricant coating. This often leads to erroneous judgments of lubrication behavior as acceptable, and it is only after application to an actual well that the solid lubricant coating's design is often discovered to be poor. Furthermore, laboratory tests cannot simulate what actually occurs in a well unless a "backlash" is intentionally created before the threads engage. On the other hand, it is also unrealistic to use full-size pins to conduct tests in actual wells or simulated wells (experimental sites where full-size pins are used for tightening and tightening tests). This would require enormous experimental costs and be unrealistic. For example, the latter requires rental fees of over 10 million yen per day, and even in solid lubrication tests, the maximum number of tightening and tightening cycles is estimated to be 20 to 30, resulting in enormous costs.

[0027] However, most past literature does not take this into consideration when evaluating solid lubricant coatings. In other words, there is no specific information about the lubrication evaluation of threads, and many applications involve horizontal tongs, as is common in laboratory tests, or vertical tongs using simple short pins. Because these conventional evaluations eliminate the effects of the large and unbalanced loads mentioned above, they generally produce favorable results. Therefore, even if these evaluation methods specify the optimum upper and lower limits for lubrication using solid lubricant coatings, they do not represent the ideal range in the true sense. Thus, even under conditions selected by conventional short pin evaluations in laboratory tests, actual wells may experience conditions that do not result in good lubrication, and the technology cannot be considered specific.

[0028] Although this is not an investigation into the lubrication behavior of a solid lubricant coating, Non-Patent Document 1 describes the constant application of a load of 510 kgf to the top end of the pin, both when tightening and loosening the screw. The application of a load of 510 kgf may have been intended to apply a weight equivalent to that of a full-scale 7-inch pin. As mentioned above, when evaluating a solid lubricant coating, it is important to simulate the large loads and unbalanced loads that occur in an actual well. This is because secondary phenomena caused by secondary products derived from the solid lubricant coating have a significant effect on lubrication.

[0029] However, there are two problems with applying the method disclosed in Non-Patent Document 1 to laboratory testing. First, while loads equivalent to one to three full-size pins connected in an actual well are applied in actual wells, the application of a 510 kg load is only possible in certain cases where the pins are light. In other words, depending on the pin size, it cannot necessarily be said to simulate a large load. Second, it is not possible to simulate an unbalanced load. Judging from Figure 5 and other figures in Non-Patent Document 1, especially for premium joints, which require less than one full rotation before tightening, Non-Patent Document 1 intends to test lubrication from the initial tightening position (tightening start point) when the threads are engaged by hand. Furthermore, although it is often overlooked, continuing to tighten the screw while the weight load is applied can lead to the following problem.

[0030] In other words, when tightening the screw, the weight acts as a balancer, allowing the screw to loosen straight from the tightened position without any rattle. This prevents the pin from swinging around, making it impossible to properly simulate the seizure that occurs during tightening in an actual well. This can lead to situations that give the wrong impression that the lubrication properties are good, depending on the situation. Therefore, the researchers learned that the condition parameters related to the solid lubricant coating need to be simulated taking into account the lubrication state when the screws are not fully engaged, as well as the lubrication after engagement, in order to prove that the film has excellent lubrication properties.

[0031] As mentioned above, in the fields targeted by this disclosure, BN has been widely cited in many patent documents as an example of a group of solid lubricant candidates. For example, Patent Documents 1 and 2 exemplify BN as a solid lubricant present in a solid lubricant coating. However, from the perspective of ensuring lubricity that can withstand the lubrication behavior in actual wells, as mentioned above, simply defining BN as a broad term does not necessarily ensure lubrication. Furthermore, although previous patent documents have exemplified the use of epoxy resins as binder resins, very few clearly define the binder resin in accordance with the quality of the epoxy resin.

[0032] Patent Documents 3 to 8 only refer to a mixture of a prepolymer and a curing agent as an epoxy resin, or to the epoxy resin coating produced by this, and only cite it as one of the candidate materials. The definition of epoxy resin is broad, and it remains unclear what exactly it specifically refers to. Here, the epoxy group is a three-membered ring containing oxygen in oxycyclopropane (oxirane). To become a resin, an appropriate curing agent is selected to cause a crosslinking reaction. This means that the three-membered ring opens and polymerizes. In essence, the epoxy group does not exist in the epoxy resin state, but rather in the final form, such as polyether (containing R-O-R'), polyester (containing R-COO-R'), polyhydroxyether (containing -OH and ether groups), or polyhydroxyamine (containing -OH and amine groups).

[0033] The film properties also inherit those of the narrowly defined epoxy resin and the curing agent. Therefore, referring to epoxy resin broadly does not necessarily specify any specific technology. The properties of the epoxy resin coating are determined by the combination of the "narrowly defined epoxy resin" agent as a prepolymer and the curing agent, so mentioning only the narrowly defined epoxy resin agent does not necessarily specify the properties of the epoxy resin coating. Reading past patent documents, one might interpret them as being broadly applicable to any epoxy group, but in reality, this is not necessarily the case. Most do not guarantee the high lubricity that is the objective of this disclosure. To achieve this objective, it is necessary to select an epoxy resin coating that has excellent lubricity, even in its final form.

[0034] Furthermore, past patent documents also ambiguously express expressions such as "contains XX% epoxy resin" (presumably referring to the final epoxy resin film composed of epoxy resin and curing agent). As mentioned above, the combination of a narrowly defined epoxy resin and a curing agent results in polymerization in the order ABABA..., where A is the epoxy resin and B is the curing agent. The general rule for formulating epoxy resins is to combine the epoxy group equivalent of the narrowly defined epoxy resin with the amine equivalent if the curing agent is amine-based, or the active hydrogen equivalent if the curing agent contains an amine. Therefore, even when expressing the weight of the epoxy resin coating, the value can vary considerably depending on the selection of prepolymer and curing agent. Simply limiting a product to "contains XX% epoxy resin" does not clearly identify the epoxy resin, nor does it specify the technology.

[0035] In other words, even if we simply refer to it as epoxy resin, it is just using an epoxy resin agent as the base material (prepolymer), and depending on the choice of hardener, it will become a polymeric substance with a completely different structure. Therefore, unless we specify the physical properties of the "epoxy resin" itself as the final hardened object, the physical properties of the agent containing the epoxy group of the prepolymer, or the hardener, and clarify the range of the parameters that secondarily define these, it does not constitute a definition of the technology.

[0036] Furthermore, Patent Document 3 selects one or both of epoxy resin and polyamide-imide resin as the material to be formed on a Cu-Sn-Zn plated substrate. It is unclear what the term "epoxy resin" refers to. In other words, it broadly encompasses epoxy resins that do not necessarily have good lubricity. Patent Documents 4 to 7 only cite epoxy resin as an example of a solid lubricant coating, and it is difficult to identify this epoxy resin. Patent Document 8 is an invention in which an acrylic silicone resin is formed on a UV-curable resin. Regarding the binder resin for UV-curable resin, this example cites acrylic acid-modified epoxy resin as one of the candidate organic and inorganic resins. Furthermore, the main chain skeleton is an epoxy resin, with its terminals acryloylated. Only examples are given, and no information about the curing agent or properties of the epoxy resin coating is specified.

[0037] On the other hand, Patent Document 9 describes a photocurable acrylic resin coating. It defines a film formed by copolymerizing a photocurable (meth)acrylate resin with a (meth)acrylate monomer group using a trigger such as a photopolymerization initiator. Epoxy, along with polyester, polyether, and polyurethane, is listed as a candidate for the main chain structure forming the acrylate side chain. This invention uses the unit system of parts by weight (PHR: per hundred resin) to express the acrylate (corresponding to the prepolymer in the present disclosure) and the polymer (corresponding to the curing agent in the present disclosure). When an epoxy resin has a main chain structure, the proportion and weight of the epoxy resin can be accurately expressed. The description in Patent Document 9 is clearer than the definitions in Patent Documents 3 to 7. However, since this disclosure is intended to produce a film by curing, not photopolymer resin, Patent Document 9 differs in technology from the present disclosure.

[0038] The present invention has been made in consideration of the above points, and has as its object to provide a solid lubricating coating that can impart excellent corrosion resistance as well as lubricity to oil country pipe threads, even when a solid lubricating coating is used for lubrication.

[0039] In contrast to the conventional situation where lubricating materials are selected based on such lenient evaluations, the inventors have developed a method for producing oil well pipes, oil well pipe threaded joints, and chemicals for making them that combine excellent lubrication and corrosion prevention properties. The method targets a binder resin primarily made of epoxy resin, containing an appropriate proportion of BN as a solid lubricant component, with other additives added as appropriate. These films are constructed with specified parameters to withstand the harsh lubrication conditions encountered in the lubrication of actual oil well pipe threads, which are subject to the heavy and unbalanced loads described above.

[0040] That is, one aspect of the present invention is an agent for forming a solid lubricant coating on the threads of oil country tubular goods, the agent comprising a solid lubricant dispersed in a binder resin, the binder resin including a prepolymer and a curing agent, the prepolymer being made of one or more types of epoxy resin, the prepolymer being contained in an amount of 70 parts by weight or more per 100 parts by weight of the binder resin, the epoxy equivalent of the epoxy resin constituting the prepolymer being in the range of 100 to 500, 80% by weight or more of the solid lubricant being BN (boron nitride) and the average particle size of the BN being 10 μm or less, and the total weight of the solid lubricant being 0.1 to 2 times the total weight of the binder resin.

[0041] Another aspect of the present invention is an oil country tubular good having a lubricating coating formed on a thread portion, the solid lubricating coating being constituted by dispersing a solid lubricant in a binder resin, the binder resin including an epoxy resin cured with a curing agent, the binder resin containing 70 parts by weight or more of the epoxy resin per 100 parts by weight of the binder resin, the epoxy equivalent of the epoxy resin being in the range of 100 to 500, 80% by weight or more of the solid lubricant being BN (boron nitride) with an average particle size of 10 μm or less, and the total weight of the solid lubricant being 0.1 to 2 times the total weight of the binder resin.

[0042] According to one aspect of the present invention, the physical parameters of the binder resin (main component: epoxy resin) and solid lubricant (main component: BN) constituting the solid lubricant coating are comprehensively defined, taking into account evaluations from newly devised laboratory tests that can reproduce behavior in actual wells. As a result, according to one aspect of the present invention, it is possible to provide a chemical capable of forming a solid lubricant coating (lubricant coating) that, even when using a solid lubricant coating for lubrication, has lubricity equivalent to or better than that of conventionally used grease-like lubricating compounds, and lubrication and corrosion resistance comparable to that of anti-rust grease-like compounds and oil-like anti-rust agents for storage. For example, according to one aspect of the present invention, an oil well pipe threaded joint that exhibits lubrication performance and corrosion resistance during make-up is obtained, taking into account conditions equivalent to those that may occur in an actual well environment. Note that conditions equivalent to those in an actual well include conditions such as a pin weight being applied from above to the box, conditions in which a load is applied obliquely due to misalignment of the axis, and conditions in which the load is applied locally rather than uniformly.

[0043] FIG. 1 is a diagram showing an oil country pipe and an oil country pipe threaded joint. FIG. 2 is a diagram (a) of a tightening chart in an actual well, and a diagram (b) showing the initial set position at that time. FIG. 3 is a diagram (a) of a tightening chart in a conventional laboratory test, and a diagram (b) showing the initial set position at that time. Schematic diagrams of tightening charts, where (a) is for an actual well and (b) is for a conventional laboratory test. FIG. 4 is a diagram explaining a new laboratory test (weight-tongs test). FIG. 5 is a diagram showing an example of weight placement in the new laboratory test (weight-tongs test). FIG. 6 is a diagram illustrating a coating structure.

[0044] Next, an embodiment of the present invention will be described with reference to the drawings. Conventionally, to achieve both the objectives of lubrication and rust prevention during storage, different or similar grease-like compounds have been used for lubrication during make-up and loosening, and for long-term outdoor storage (rust prevention). In contrast, the thread structure of this embodiment uses an epoxy resin coating with appropriately defined parameters as the binder resin on one or both of the contact areas between the male thread metal and the female thread metal of the thread material, or on a portion of these areas. Furthermore, a solid lubricating coating with appropriately defined parameters, in which BN is dispersed as a solid lubricant, is employed within this coating. This embodiment is intended to improve lubrication and impart corrosion resistance.

[0045] The present invention also covers chemicals for forming this solid lubricant coating. It also covers a lubricant coating that combines the coating of this embodiment with a base layer, and a film structure suitable for lubrication of oil country tubular goods threads, including the film hardness of the other side where the coating is not formed. This embodiment can also be applied to a wide range of uses for this lubricant coating, including improving the lubrication and rust prevention of metal materials. In light of the above-mentioned problems, the inventors have conducted research and found that the above problems can be solved through the formulation of chemicals, the development of solid lubricant coatings on oil country tubular goods threads, and methods for verifying this. The solid lubricant coating of this embodiment was developed using an epoxy resin cured with a curing agent as the main component of the binder resin and boron nitride (BN) as the main component of the solid lubricant.

[0046] (Configuration) This embodiment is an invention relating to a coating structure formed on the fastening surface of the threaded portion of an oil country tubular good and an oil country tubular good threaded joint used in actual oil / gas applications, and a structure having this coating structure as a lubricating coating. This embodiment is characterized by a lubricating coating comprising a solid lubricating coating formed on the threaded portion of the oil country tubular good, and there are no particular limitations on the thread structure itself of the oil country tubular good and its threaded joint. The thread structure of the oil country tubular good and its threaded joint may be any known or novel thread structure.

[0047] <Oil country tubular goods and oil country tubular goods threaded joint> An oil country tubular goods is composed of, for example, a box 2 such as a coupling, and a pin 1, as shown in Fig. 1. An oil country tubular goods threaded joint is composed of a box 2 such as a coupling having a female thread 2a, and a pin 1 having a male thread 1a, as shown in Fig. 1. A lubricating coating comprising a solid lubricating coating is formed on the contact surface (fastening surface 10) of the threaded portion of at least one of the box 2 and the pin 1.

[0048] <Chemical Agent> The chemical agent used to form a solid lubricant coating in this embodiment will now be described. The chemical agent in this embodiment is composed of a solid lubricant dispersed in a binder resin as a matrix component. The chemical agent includes a binder resin, a solid lubricant, and a solvent component. The binder resin includes a prepolymer and a curing agent. The prepolymer is made of one or more epoxy resins. The prepolymer is contained in an amount of 70 parts by weight or more per 100 parts by weight of the binder resin. The epoxy equivalent of the epoxy resin that constitutes the prepolymer is in the range of 100 to 500. It is preferable that the glass transition temperature Tg of the epoxy resin that constitutes the prepolymer is 100°C or higher.

[0049] The solid lubricant contains 80% or more by weight of BN (boron nitride). The average particle size of the BN is 10 μm or less. The total weight of the solid lubricant is 0.1 to 2 times the total weight of the binder resin. The solvent component is preferably contained in an amount of 30 to 80 parts by weight per 100 parts by weight of the sum of the total weight of the solid lubricant and the total weight of the binder resin excluding the curing agent. In addition, the agent may contain a curing accelerator in an amount of 0 to 10 parts by weight per 100 parts by weight of the total weight of the epoxy resin constituting the prepolymer. The curing agent is, for example, a curing agent that cures the epoxy resin, and is composed of an amine-based curing agent, an acid anhydride-based curing agent, a phenol-based curing agent, or a latent curing agent.

[0050] In this case, the epoxy resin that constitutes the prepolymer preferably has more than two epoxy groups (a multifunctional epoxy resin). The epoxy resin that constitutes the prepolymer preferably has six or fewer epoxy groups. More preferably, the epoxy resin that constitutes the prepolymer has four or fewer epoxy groups. The viscosity of the agent having the above configuration is preferably 20 mPa·sec or more and 2,000 mPa·sec or less. The agent of this embodiment is applied to the fastening surface of the thread and dried to form a solid lubricating coating 10A (see FIG. 7(a)).

[0051] <Lubricating coating comprising solid lubricating coating 10A> The solid lubricating coating 10A is composed of a solid lubricant dispersed in a binder resin as a matrix component. The binder resin contains a prepolymer and a curing agent, and the prepolymer is cured by polymerizing with the curing agent. The prepolymer is made of one or more types of epoxy resin. The prepolymer contains 70 parts by weight or more of prepolymer per 100 parts by weight of the binder resin. The epoxy equivalent of the epoxy resin that makes up the prepolymer is in the range of 100 to 500. It is preferable that the glass transition temperature Tg of the epoxy resin that makes up the prepolymer is 100°C or higher.

[0052] The solid lubricant contains 80% by weight or more of BN (boron nitride). The average particle size of the BN is 10 μm or less. The total weight of the solid lubricant is 0.1 to 2 times the total weight of the binder resin. The curing agent is, for example, a curing agent that hardens the epoxy resin, and is composed of an amine-based curing agent, an acid anhydride-based curing agent, a phenol-based curing agent, or a latent curing agent. In this case, the epoxy resin constituting the prepolymer preferably has more than two epoxy groups (a multifunctional epoxy resin). The epoxy resin constituting the prepolymer preferably has six or fewer epoxy groups. More preferably, the epoxy resin constituting the prepolymer has four or fewer epoxy groups.

[0053] The solid lubricating coating 10A of this embodiment has a hardness of, for example, 3H or greater. The thickness of the solid lubricating coating 10A is, for example, 10 μm or greater and 150 μm or less. The lubricating coating of this embodiment may have a base layer 10B between the fastening surface of the threaded portion and the solid lubricating coating 10A (see FIG. 7( b)). The base layer 10B may be, for example, a chemical conversion coating layer or an electroplated layer. The above lubricating coating is formed on the fastening surface of the threaded portion of at least one of the box and the pin.

[0054] <Regarding the determination of each provision> The inventors have come to the realization that the key to solving the above problems is to control the following four points ((a) to (d)) and related matters within preferred ranges. (a) Devise an appropriate new laboratory test that simulates tightening and tightening in an actual well, and use the new laboratory test method to specify the upper and lower limits of each parameter for the solid lubricant coating and clarify their preferred ranges. (b) Specify the optimum range for BN by referring to the evaluation by the laboratory test in (a). (c) Specify the optimum range for the physical properties of the epoxy resin using the provision in (b). (d) Furthermore, specify the preferred ranges related to these.

[0055] Here, an appropriate method for simulating make-up and make-back in an actual well is a method for simulating the make-up behavior that occurs when an OCTG thread is made up in an actual well. This method is used to confirm the upper and lower limits of the parameters of this embodiment and determine suitable ranges. The lubrication state of an OCTG thread can be divided into two phases, whether in a laboratory test or in an actual well. Phase 1 is lubrication during make-up and make-back when the threads are not engaged, and Phase 2 is lubrication during make-up and make-back when the threads are engaged. Phase 1 corresponds, for example, to the area (x) in the torque-turn chart of FIG. 4. Phase 2 corresponds, for example, to the areas (y) and (z) in FIG. 4.

[0056] Regarding the former (Phase 1), if the screw is tightened by hand or other means until it meshes, this step is not necessary (see Figure 3 for example). However, in many actual wells, the tightening start position is simply to insert the pin into the box and set it in place. Alternatively, the tightening start position is to tighten it a few times thereafter to loosely secure it so that cross-threading does not occur. In other words, in many actual wells, it is common to start tightening and unfastening when the screw does not mesh (see Figure 2 for example). Note that cross-threading refers to a situation where the screw threads are tightened with an uneven level, or slip into the correct thread position while being tightened.

[0057] In Phase 1, the tongs are used to tighten and loosen the screws at a high speed of 5 to 20 rpm. Meanwhile, as the screws continue to be tightened, the screws begin to mesh, transitioning to Phase 2. This transition causes a slight increase in torque, and from this point on, the screw is slowly tightened at a speed of approximately 0.5 to 2.0 rpm. The reverse procedure is followed when loosening. These procedures are the same whether a conventional grease-like compound is used as lubrication or a solid lubricant coating is applied as in this embodiment. The conditions for setting the screws in the initial position are important for determining their behavior when creating backlash. When considering the behavior of the joint, it is important that the pin thread is exposed more than one to three threads from the box thread during initial tightening.

[0058] <About Figure 2> Figure 2 is an example that directly simulates an actual well. That is, Figure 2 shows a tightening chart (torque turn chart) when a tightening test was conducted using a pin with an actual length of 40 feet (≒12 m) and a solid lubricant coating for lubrication. The test conditions for Figure 2(a) will be explained. As an example, the solid lubricant coating is made of a PAI (polyamideimide) binder resin and MoS as a solid lubricant. ２ The dispersed material was used.

[0059] Also, Figure 2 is an example that simulates a situation that often occurs in actual oil and gas fields. That is, this is an example where tightening was started from a state where the initial set position at the start of tightening was not a state where the threads were fully engaged with each other, as shown in Figure 2(b). In other words, this is an example where tightening was started from a state where the pin thread was about half exposed at the start of initial tightening, as shown in Figure 2(b). The threads were not engaged with each other because the tightening was not intentionally stopped by hand. Even if you try to set the pin thread into the box screw by hand, it will inevitably stop halfway. This means that it cannot be tightened any further by hand. A long and heavy full-length pin does not stand strictly perpendicular to the box screw, as theoretically depicted. When viewed from below, it is slightly bent, and it is very common for it to be unable to be tightened any further by hand. The pin used was a 9-5 / 8" 53.5#Q125 JFELION ＴＭ The pin was about 40 feet long with a screw. Figure 2(a) shows the torque-turn chart for the pin when the entire length was being tightened while the pin was suspended by a crane from above the rig. The torque-turn chart example in Figure 2(a) can be seen as a situation that often occurs in actual wells.

[0060] What is noteworthy in Figure 2(a) is the region just before the point where torque continuously increases (from zero to approximately 6.3 revolutions: corresponding to Phase 1). In principle, torque should not be generated in this region. However, in reality, as shown in Figure 2(a), spike-like torque tends to be generated irregularly and frequently. This suggests that the pin thread is in irregular, localized contact with the box thread as it rotates. This is the situation that occurs during actual tightening. This means that, depending on the design and optimization of the solid lubricant coating, destruction and peeling of the solid lubricant coating are unavoidable to some extent. It is important to note here that the chart in Figure 2(a) was not created under the worst-case conditions intentionally; it is a torque-turn chart for a sample with a solid lubricant coating.

[0061] <About Figure 3> Figure 3(a) is a torque turn chart for a screw tightened with vertical power tongs using the same solid lubricant coating as in Figure 2. Figure 3 uses a pin with the same outer diameter, wall thickness, and thread type as in Figure 2, but a short pin approximately 1 m long. Figure 3(a) also shows a torque turn chart for when tightening is initiated after the threads are fully engaged. That is, it shows a torque turn chart for when the pin threads are exposed by approximately 1 to 3 threads at the start of initial tightening, as in Figure 3(b). The conditions in Figure 3(a) are also commonly used for tightening in conventional laboratory tests, and represent an example in which a tightening test was conducted after the threads were manually tightened until they were engaged.

[0062] It should be noted that the units on the horizontal axis in Figure 3(a) are different from those in Figure 2. In Figure 3(a), tightening with tongs begins after the threads have been hand-tightened to the point of meshing, so the spike-like torque seen in Figure 2(a) is not observed. In other words, it can be understood that investigating the lubrication properties of the solid lubricant coating only in Phase 2, without going through Phase 1, is equivalent to conventional laboratory testing. As can be seen from Figure 3, in conventional laboratory testing, breakdown of the solid lubricant coating, which often occurs in Phase 1, does not occur, and tightening occurs when the threads are fully meshed, that is, from the region where both surfaces of the threads begin to come into contact.

[0063] <About Figure 4> Figure 4 illustrates Figures 2(a) and 3(a) in a manner that makes it easier to compare them. Figure 4(a) shows the example of Figure 2, and Figure 4(b) shows the example of Figure 3. According to the inventors' investigations, when considering actual use in wells, the ideal solid lubricant coating is one that does not break down in the region (x) of Figure 4(a) and minimizes the risk of breakage or peeling. Alternatively, a small amount of spikes may be acceptable. Furthermore, even in situations where the solid lubricant coating is damaged, it is preferable to design it so that secondary products from the broken or peeled solid lubricant coating do not clog the thread gap during the make-up and unmake-up process, but rather adhere well to the threads and assist lubrication.

[0064] To achieve this, it is important to control the film quality of the solid lubricating coating so that it is hard enough to exceed a predetermined hardness. Pencil hardness, which is a hardness index based on the scratch resistance, can be used as an example of a method for evaluating hardness. However, it is preferable that the viscosity of the solid lubricating coating agent be kept low enough to allow spray coating or brush coating when forming the lubricating coating, and that the coating be applied evenly. Furthermore, it is preferable that the constituent components of the solid lubricating coating behave like rubber or liquid during the curing process, forming a single, smooth film due to the surface tension of the components.

[0065] Furthermore, in the laboratory test evaluation method of this embodiment, it is preferable to evaluate a new laboratory test having the following conditions (1) to (6) for the purpose of simulating the tightening and tightening behavior in an actual well. An example of the actual laboratory test device configuration will be described later. (1) A weight equivalent to the weight of one to three full-size pins is set on top of the short pin. (2) The initial set position of the short pin screw and box screw is stopped at about halfway of the pin thread, for example, so that half is exposed, that is, the threads of the short pin are loosely fastened, and then the tightening and tightening test is started. (3) From the state in "(2)," tightening is started at a high speed of 15 rpm, and tightening is continued until a torque equal to or greater than the predetermined value is detected.

[0066] (4) Once the torque has been reached, stop and tighten at a slow speed of 1 rpm (tightening complete). (5) To untighten, follow the steps in reverse. (6) Once the short pin screw has been completely removed, observe the pin thread surface and the box screw surface (you may need to use an air blower to observe) to determine whether any abnormal events such as seizure have occurred. If there are no problems, repeat steps (2) and onwards. If there is slight seizure in the threaded portion (seizure in the sealing portion is not acceptable regardless of the degree of seizure), make any necessary adjustments, apply a repair solid lubricant if necessary, and then repeat steps (2) and onwards.

[0067] In this embodiment, a new evaluation of the lubrication properties of a solid lubricant coating was conducted based on this evaluation method, and optimal conditions for the solid lubricant coating were selected (see Examples). Judging from the results of numerous make-up and loosening tests (laboratory tests) in previous literature, it is recognized that conventional laboratory tests focus on lubrication after thread engagement (the conditions in regions (y) and (z) in Figures 4(a) and (b)). It appears that conventional laboratory tests evaluate the lubrication properties of a solid lubricant coating under the assumption that it is in a healthy state, without taking into account the condition in region (x), i.e., the torque spike condition. In other words, conventional laboratory tests use a short pin and horizontal or vertical tongs for evaluation, and appear to involve tightening and loosening from a position where the threads are fully tightened by hand until they engage. Among the patent documents that specify the number of times that tightening and loosening can be done, some state that tightening in an actual well is possible up to 10 times for small diameter sizes, but whether evaluating with a short pin or in an actual well, this appears to be a plausible number of times if the initial set position (the tightening start position) begins from a position where the screws are fully engaged with each other.

[0068] On the other hand, previous literature has occasionally stated that for large diameter sizes such as 9-5 / 8" and 13-3 / 8", make-up and tightening based on a solid lubricant coating can be performed up to 15-20 times. However, in actual well make-up and tightening, that is, when the actual size pin has its own weight and the threads are not yet engaged, this is thought to be almost impossible in large diameter cases using a solid lubricant coating. It goes without saying that simulating actual make-up and tightening conditions is important in evaluating the lubricity of a solid lubricant coating. It is necessary to evaluate the condition in which the solid lubricant coating is peeled off or damaged in a situation where there is play before the threads engage. In this embodiment, various specifications have been established with reference to the results of new laboratory tests that enable evaluation taking such conditions into account. The solid lubricant coating of this embodiment is based on the premise that the solid lubricant coating is a solid lubricant coating in which BN, the main component of the solid lubricant, is dispersed in a binder resin whose main component is an epoxy resin coating, and the various conditions have been determined by referring to the results of new laboratory tests.

[0069] Each of these specifications will be explained in more detail. <Basic Structure, Film Thickness, and Film Structure of the Solid Lubricant Coating> In this embodiment, the solid lubricant coating is formed by dispersing a solid lubricant primarily composed of BN in a cured epoxy resin coating. It is particularly preferable to obtain a pencil hardness of 3H or higher. In this embodiment, BN was selected as the primary component of the solid lubricant in order to obtain a film that can achieve high lubrication and maintain high lubrication even at high temperatures. In other words, when tightening and loosening, the pin thread and box thread rub against each other to some extent, generating frictional heat. This is to maintain sufficient lubrication even at that time.

[0070] In this embodiment, an epoxy resin coating was selected as the binder resin. The reason for using an epoxy resin coating is that it is easy to handle and is less expensive than other chemicals. Furthermore, in addition to being a well-balanced material, by selecting the appropriate "narrowly defined epoxy resin chemical" and curing agent, it is easy to obtain a hard film and a film with excellent heat resistance, as is the focus of this embodiment. Furthermore, epoxy resin coatings have many advantages, such as excellent adhesion and bonding properties, the possibility of forming a film without a base layer (such as a manganese phosphate conversion coating or an electroplating film), and the lack of significant shrinkage upon curing.

[0071] Regarding the coating thickness, a minimum thickness of 10 μm is required to maintain lubrication properties and corrosion resistance. The upper limit is difficult to generalize because the gap between the box thread and the pin thread varies depending on the type and design of the OCTG thread, but we set it at 150 μm. Here, since most OCTG threads are designed with an upper limit of 100 to 200 μm between the threads, we set an upper limit of 150 μm or less. A film thickness of 10 to 50 μm is more preferable. As mentioned above, the gap between the crest and root of a male or female thread may be 100 to 200 μm. However, the gap between the stabbing flanks and the load flanks of a male or female thread also changes depending on whether the thread is tightened or loosened. When the gap narrows, the threads are almost completely in contact with each other. Therefore, a smaller film thickness is preferable, with a film thickness of 10 to 50 μm being the preferred range.

[0072] However, these film thicknesses refer to the film thickness in the as-formed state before the first tightening. When tightening and untightening, some of the binder resin is scraped off, and the film applied at room temperature is actually crushed and becomes thinner. Therefore, even if the thickness of the thread flank exceeds the expected gap, problems such as seizure do not occur. Furthermore, the epoxy resin may be formed directly on the thread flank, or a base layer may be formed between the thread flank and the epoxy resin. Examples of the base layer include a manganese phosphate conversion coating layer and a metal plating layer such as copper plating. Although there are various theories and it is difficult to say that a theoretical consensus has been reached, the OH groups in the epoxy resin can form hydrogen bonds with the metal surface to form a film with strong adhesion. The above OH groups are those found in epoxy resin films such as polyhydroxyethers and polyhydroxyamines. For this reason, adhesion is thought to be minimal even without a base surface treatment layer, or even with a surface treatment layer (which may be expected to utilize anchoring effects, etc.).

[0073] <Solid Lubricant> In this embodiment, a solid lubricant containing boron nitride (BN) as a main component is dispersed in a binder resin.

[0074] [Solid Lubricant] Using the new laboratory testing method described above, we clarified the range in which the solid lubricant BN significantly improves lubrication. Specifically, by using the new laboratory testing method described above to examine various lubricating coatings in which BN is dispersed in an epoxy resin binder, we clarified the range in which BN significantly improves lubrication. However, using BN (boron nitride) as a solid lubricant does not always produce a highly lubricating state. It was found that a BN-based component system containing 80% or more of BN when the total weight of the solid lubricant is used as the denominator and having an average particle size of 0.1 to 10 μm produces significant benefits. While the finer the BN, the better, since the lower limit of the average particle size of commercially available BN is 0.1 μm, we set this value as the lower limit. The upper limit was determined experimentally, and it was confirmed that excellent lubricity was achieved up to the 10 μm range.

[0075] In the case of a lubricant formed by stacking two-dimensional crystal structures such as BN, when the average particle size exceeds 10 μm, the plate-like structures slide to achieve lubrication. In this case, adjacent plate-like structures are stretched to overlap each other. This results in the formation of white tape-like secondary products. As these are formed thicker, they tend to clog the thread gap, increasing the risk of seizure. Generally, smaller average particle sizes result in less overlapping, suppressing the formation of these white tape-like secondary products, and therefore achieving high lubrication. For this reason, the elements of the invention require that BN account for 80% or more by weight of the total weight of the solid lubricant and that the BN have an average particle size of 10 μm or less.

[0076] The meaning of these definitions is as follows. BN (boron nitride) in a broad sense cannot always create a highly lubricating state. In order to achieve high lubricity in the usage environment of oil country pipe threads, and in this embodiment, BN dispersed in the epoxy resin used as the binder resin, is used within this range, it is expected that optimal and significantly high lubricity can be achieved. Here, BN is MoS ２ Like graphite, BN has a strong crystalline structure in the two-dimensional plate direction, and in the Z-axis direction, the two-dimensional plate faces are connected by weak intermolecular forces. When force is applied, BN achieves lubrication by sliding between the plate faces.

[0077] In this embodiment, "80% or more BN" means that BN is the main component of the solid lubricant. The definition of "80% or more BN" means that even if other solid lubricants are included at a rate of 20% or less, there will be no adverse effects on a BN-based design. In this embodiment, the more BN there is as a material constituting the solid lubricant, the better. Since the inclusion of other components can sometimes deteriorate lubricity, the range in which BN can be the main component is set to 80% or more. Preferably, it is 90% or more. The smaller the average particle size of BN, the better. The average particle size is a parameter that refers to the particle size at 50% of the cumulative value in the particle size distribution determined by laser diffraction / scattering method or the like.

[0078] The reason for limiting the average particle size of BN to 10 μm is that a particle size exceeding 10 μm is likely to destroy the binder resin film and trigger complete peeling. In other words, the particles peeled off from the solid lubricant coating are pressed together during tightening and loosening, forming secondary products. However, as individual plate-like BN structures deform and slide along the plate surface, adjacent plate-like BN structures overlap, ultimately forming a strong white tape-like secondary product. As these become thicker, they are unable to move with tightening and loosening, increasing the risk of seizure. Generally, the smaller the average particle size of BN, the less overlap there is, and the less likely the white tape-like secondary product is to form. This is believed to result in high lubrication. Currently, the lower limit of the average particle size of commercially available BN is 0.1 μm, so the lower limit is likely to be around that range. However, with technological advances, BN with an average particle size of 0.1 μm or less is also included in this embodiment.

[0079] Furthermore, industrial types of BN include flake-like and particulate types. In this embodiment, either form is acceptable. It is preferable to use finely granulated BN. Solid lubricants other than BN may be mixed in under the condition of 20% or less, as described above. The other solid lubricants may be of any type, and may include PTFE (Teflon (registered trademark): polytetrafluoroethylene), graphite, graphite fluoride, MoS ２ , W.S. ２Examples of such solid lubricants include melamine cyanurate (MCA), mica, and talc. Oil-based substances may also be mixed in as a type of solid lubricant, provided that the amount is 20% or less of the solid lubricant. For example, carnauba wax, perfluoropolyether (PFPE) oil, and low-molecular-weight chlorotrifluoroethylene (CTFE) oil may be mixed in. The lubrication of BN can be maintained or improved.

[0080] <Epoxy Resin Constituting the Binder Resin> In this embodiment, an epoxy resin was selected as the binder resin. In this embodiment, a binder resin containing 70 or more parts by weight of epoxy resin was selected, assuming that the total of the other resins constituting the binder resin and the epoxy resin as a prepolymer was 100 parts by weight. Furthermore, an epoxy resin with an epoxy equivalent of 100 to 500 was selected. Furthermore, in this embodiment, it is preferable that the solid lubricant coating be a hard film. To achieve this, a curing agent is selected to create an epoxy resin coating with a strong three-dimensional network structure. For example, an epoxy resin as a prepolymer was selected that has more than two epoxy groups (multifunctional epoxy), or the curing agent has more than two functional groups, or both have more than two functional groups. This enables the creation of a three-dimensional copolymerized film and provides heat resistance.

[0081] Here, heat resistance refers to preventing the epoxy resin from being destroyed by heat generated in areas where strong friction occurs, even if slight seizure occurs during screw tightening. The epoxy equivalent range of 100 to 500 was selected to increase crosslink density and harden the material. It also means increasing the concentration of epoxy groups, which, in other words, keeps the epoxy equivalent low. Here, if the epoxy equivalent exceeds 500, the film inevitably becomes soft. It also becomes difficult to provide heat resistance sufficient for tightening and loosening. The lower limit of the epoxy equivalent of 100 is specified as the approximate limit for commercially available epoxy resins. If a lower epoxy equivalent is available, the epoxy equivalent is not limited to 100, and selecting a lower epoxy material is considered within the scope of this embodiment.

[0082] The term "epoxy resin" used here refers to an epoxy resin coating formed by copolymerizing a "narrowly defined epoxy resin" as a prepolymer with a curing agent. The reason for selecting epoxy resin is its excellent adhesion and bonding properties, water and moisture resistance, heat resistance, and lack of significant shrinkage upon curing. Furthermore, it is a well-balanced material, being easy to handle and inexpensive compared to other chemicals. In particular, among binder resins, this embodiment aims for a hard film, and an appropriate curing agent was selected to produce an epoxy resin coating with a pencil hardness of 3H or higher. The binder resin is the matrix that holds the BN-based solid lubricant and, together with the BN, forms the main component of the solid lubricant coating.

[0083] The reason why a hard epoxy resin film provides good lubrication (make-up and unmake-up characteristics) is as follows. When lubricating oil country pipe threads using a solid lubricating coating, the solid lubricating coating tends to be damaged to some extent when there is backlash before the threads engage. However, it tends to withstand this damage. Furthermore, even after the threads engage, the weight of a typical oil country pipe thread, which is approximately 8 to 12 meters long, continues to be applied as it tightens. This inevitably results in a structure in which the solid lubricating coating is slightly worn away while maintaining lubrication. Therefore, unless the pencil hardness is 3H or higher, damage is significant and the coating can only be made up to a few times.

[0084] For the above reasons, in this embodiment, when the sum of the "narrowly defined epoxy resin" group, excluding the weight of the curing agent component, and other lubricant components is taken as 100 parts by weight, the "narrowly defined epoxy resin" is 70 parts by weight or more, making the component primarily epoxy resin. Also, an epoxy equivalent of 100 to 500 was selected. This is to increase the number of crosslinking points (increase the crosslinking density) and create a strong coating.

[0085] A "narrowly defined" prepolymer epoxy resin can form a three-dimensional structure even with two epoxy groups. However, a more preferred range is a multifunctional epoxy resin with more than two epoxy groups. "Multifunctional" epoxy means that the average number of epoxy groups per molecule exceeds two. This means that there are more epoxy groups than in a "normal epoxy resin" composed of two epoxy groups. Multifunctional epoxies can form more three-dimensional crosslinks in the reaction with a curing agent, so when (co)polymerized, the crosslinked network becomes stronger, resulting in a harder film (even a harder pencil hardness).

[0086] At the same time, the Tg (glass transition temperature) is high, resulting in excellent heat resistance. It is preferable to achieve a Tg above 100°C for excellent heat resistance. The epoxy groups in one molecule are preferably between two and six, with a more preferable range being between two and four. This is because the hardening of the solid lubricating coating reduces peeling and eliminates complete failure during the initial and final stages of tightening and unfastening. During these stages, the threads are not engaged, creating a backlash that makes the solid lubricating coating susceptible to failure. With epoxy groups exceeding six, there is a high risk of steric hindrance occurring during the reaction between the epoxy groups and the curing agent. In this case, copolymerization of the epoxy resin and the curing agent may take too long, or a hard film may not necessarily be obtained. For this reason, the limit is six or less. On the other hand, even when a bifunctional epoxy resin and a curing agent with more than two functional groups form a three-dimensional network structure, allowing the film to harden. It is preferable that both the epoxy resin and the curing agent are multifunctional, since this results in a harder, three-dimensional network.

[0087] The epoxy equivalent is defined as a preferred range of 100 to 500. The epoxy equivalent is the molecular weight of the epoxy resin in the narrow sense as a prepolymer divided by the number of epoxy groups. The epoxy equivalent can be considered as the molecular weight bound by crosslinking points. The above range is defined because a smaller epoxy equivalent increases the crosslink density and thus the hardness. Examples of prepolymers include bifunctional epoxy resins such as bisphenol A epoxy resins, bisphenol F epoxy resins, and bisphenol C epoxy resins. Examples of multifunctional epoxy resins with more than two functionalities include phenol novolac compounds, cresol novolac epoxy compounds, aliphatic epoxy compounds, glycidyl ester epoxy resins, glycidyl amine epoxy resins, multifunctional phenol epoxy resin compounds, and derivatives thereof. These may be used alone or in combination.

[0088] In this embodiment, the "narrowly defined epoxy resin" is defined as the component that constitutes the binder resin, and when the sum of the "narrowly defined epoxy resin" group and other lubricant components, excluding the weight of the curing agent component, is taken as 100 parts by weight, the epoxy resin accounts for 70 parts by weight or more. In other words, the component is primarily composed of epoxy resin. As a more preferred range, when the total weight of the "narrowly defined epoxy resin" is taken as 100 parts by weight, it is desirable that the polyfunctional epoxy resin accounts for 70 parts by weight or more.

[0089] The former phrase "70 parts by weight or more of epoxy resin" refers to the following: As described above, this embodiment targets a hard film with a pencil hardness of 3H or more. However, when a hard film is selected using epoxy resin, it often becomes brittle. For this reason, it means that other binder resin components may be added under the condition of less than 30 parts by weight. To obtain a hard film, it is preferable to strengthen the three-dimensional network structure. For this reason, the amount of polyfunctional epoxy resin (more than two epoxy groups) is specified as 70 parts by weight or more. Under the condition of less than 30 parts by weight, a thermoplastic resin may be selected as the other binder resin component to prevent the epoxy resin from becoming too hard and brittle.

[0090] Epoxy resin coatings, which are final materials composed of (co)polymerized prepolymers and curing agents, inevitably become brittle when adjusted to a hardness. To avoid this brittleness, suitable agents are prepared for the monopolymer epoxy resin. Alternatively, epoxy resins with strong skeletons or molecular chains, such as benzene rings, introduced into the main chain may be used. In some cases, the epoxy resin itself may be modified with rubber, fluorene, or urethane to introduce flexible chains. This is intended to improve toughness by incorporating points that reduce internal stress within the epoxy resin coating. Alternatively, a thermoplastic polymer may be incorporated in an amount of less than 30 parts by weight. The incorporation of a thermoplastic polymer into the epoxy resin coating is intended to improve toughness through cavitation effects, etc. The thermoplastic polymer referred to here is not particularly limited. The thermoplastic polymer may contain, for example, POM (polyacetal), PC (polycarbonate), PPS (polyphenylene sulfide), PTFE (Teflon (registered trademark): polytetrafluoroethylene), or the like.

[0091] The weight blending amount of epoxy resin is expressed in parts by weight rather than percent by weight for the following reason. Basically, one active hydrogen reacts with one epoxy group for each agent in the prepolymer epoxy resin. When the curing agent is an amine, one active hydrogen is roughly equivalent to the amine equivalent. Therefore, the weight blending ratio is determined by the epoxy equivalent of each prepolymer and the active hydrogen equivalent of the curing agent. Therefore, there are an infinite number of combinations of epoxy resin and curing agent. In contrast, the weight blending amount of epoxy resin is proportional to the amount of epoxy resin after curing. For this reason, the blending ratio cannot be clearly determined unless it is expressed in terms of the weight blending amount of the prepolymer epoxy resin. For this reason, parts by weight are used to define it.

[0092] However, in the case of latent curing agents, the curing agent itself is not truly necessary. For example, this occurs when the prepolymer epoxy resin itself self-polymerizes due to the anionic polymerization catalytic reaction of the latent curing agent. Examples of latent curing agents include imidazole, tertiary amine, dicyandiamide, and low-temperature, fast-curing polymercaptan. When using these latent curing agents, polymerization does not necessarily occur in a 1:1 ratio. However, in this specification, the weight parts of the prepolymer epoxy resin are used as a parameter to narrow down the characteristics of the epoxy resin. Here, the film is preferably formed by brushing or mechanically applying the agent at room temperature. For this reason, the agent must be liquid at room temperature. Furthermore, for convenience, a one-component agent is preferable to a two-component agent. Furthermore, after application to the thread surface, it is preferable for the agent to copolymerize and form a film by heat treatment rather than immediately solidifying.

[0093] Regarding the viscosity of the agent, if the viscosity is too low, the agent will drip down the threads from the point where it is applied to the threaded portion. In the case of female threads, the agent will accumulate and pool at the 6 o'clock position, increasing the concern that the film thickness will increase in that area. Even in the case of male threads, the agent may fall in the form of droplets at the 6 o'clock position, making it difficult to achieve a homogeneous state before heat treatment. On the other hand, if the viscosity of the agent is too high, it cannot be applied by brushing. Furthermore, spraying is not suitable due to clogging and other problems. Therefore, the preferred range of agent viscosity is 200 cps or more and 900 cps or less (0.2 Pa·sec or more and 0.9 Pa·sec or less). However, even if the viscosity of the agent itself is too high beyond this range, adding a reactive diluent to reduce the viscosity of the agent is considered to be included in this embodiment.

[0094] <Regarding Epoxy Resin Curing Agent> In this embodiment, the curing agent refers to an agent that contributes to the crosslinking reaction between crosslinking groups of the "narrowly defined epoxy resin" of the prepolymer. There are no particular limitations on the curing agent, and any agent generally known as an epoxy resin curing agent can be used. There are no particular restrictions on the curing agent as long as the selection of the narrowly defined epoxy resin and the selection of this curing agent achieves the conditions for realizing a hard epoxy resin coating having a pencil hardness exceeding 3H as described above.

[0095] Examples of curing agents include amine-based curing agents such as aliphatic amines, polyether amines, alicyclic amines, and aromatic amines. Epoxy resins prepared with these curing agents become polyhydroxyamines. Examples of acid anhydride-based curing agents include dodecenyl succinic anhydride, polyadipic anhydride, tetrahydrophthalic anhydride, trialkyltetrahydrophthalic anhydride, and phthalic anhydride. Epoxy resins prepared with these curing agents become polyesters. Examples of phenol-based curing agents include dihydroxyphenyls, and epoxy resins prepared with these curing agents become polyhydroxyethers. Examples of latent curing agents include amine-based curing agents such as tertiary amines and aromatic amines, imidazoles, and boron halide amine complexes, and examples of epoxy resins include polyethers.

[0096] The amount of curing agent, excluding latent curing agents, is basically mixed with the amount defined by the active hydrogen equivalent of each curing agent and the epoxy equivalent of the epoxy agent in the narrow sense. The active hydrogen equivalent of each curing agent is approximately equivalent to the amine equivalent when the curing agent is an amine. On the other hand, the amount of latent curing agent added is linked to the reaction rate, so the amount can be determined appropriately each time. This embodiment is based on forming a hard coating with a pencil hardness of 3H or higher. For this reason, it is preferable to use a heat-curing curing agent rather than a room-temperature curing type. The former curing agent has a low glass transition temperature (Tg) and produces a soft film. The latter curing agent often has a high glass transition temperature (Tg) and is excellent in heat resistance and mechanical strength.

[0097] <About Epoxy Resin Curing Accelerators> A curing accelerator may be used during the reaction between a narrowly defined epoxy resin and a curing agent. While there are exceptions, when the curing agent is an aromatic amine, heating will accelerate the curing reaction. However, for many curing agents, heating often does not accelerate the reaction. In such cases, a curing accelerator may be used. When an acid anhydride curing agent, a phenolic curing agent, or a dicyandiamide-based latent curing agent is selected as the curing agent, curing is almost always impossible without the use of a curing accelerator. Examples of curing accelerators include tertiary amines and tertiary amines such as DBU (diazabicyclononene) and DBN (diazabicycloundecene), imidazole-based agents, and TPP (triphenylphosphine) such as phosphine and phosphonium salts. The amount of these curing accelerators added is, for example, 0.01 to 10 parts by weight per 100 parts by weight of a narrowly defined epoxy resin (the epoxy resin that constitutes the prepolymer). However, the amount added may need to be adjusted depending on the situation. The amount is preferably 0.1 to 3 parts by weight.

[0098] <Regarding Other Additives> In this embodiment, the film is formed by dispersing a solid lubricant mainly composed of BN in a cured epoxy resin coating. However, it is preferable to obtain a hard film (pencil hardness of 3H or more). Therefore, the main objective is to obtain a hard epoxy resin coating. Glass fiber or carbon fiber may also be added to harden the film. The resin composition of this embodiment may further contain surfactants, emulsifiers, elasticity reducing agents, diluents, antifoaming agents, ion trapping agents, etc.

[0099] <Method for Analyzing Film Hardness> In this embodiment, the pencil hardness of the hard film was evaluated. Specifically, the hardness was measured according to the method specified in JIS K 5600-5-4 (1999). The JIS clearly states that this standard is a translation of "ISO / DIS 15184, Paints and Varnishes - Determination of Film Hardness by Pencil Test." However, the pencil hardness test method itself was evaluated based on the JIS standard. Furthermore, the reason for evaluating film hardness by pencil hardness is that it is an evaluation of "scratching" with a pencil, and this film hardness evaluation method is caused by "scratching," which is similar to the behavior of solid lubricant coatings peeling off between the male and female threads of oil country pipe threads. The film hardness measurement methods that are sometimes used for coatings, such as Rockwell, Vickers, Shore, and Knoop, which are based on indentation, are not suitable for thin coatings and are affected by the base, so in this embodiment, pencil hardness was used.

[0100] <Surface on which the solid lubricating coating is formed> The solid lubricating coating of this embodiment is used by forming the coating on either the coupling side (female thread side) or the pin side (male thread side), or both, of an oil country pipe thread. Alternatively, it is preferable that the solid lubricating coating of this embodiment is formed on either the coupling side (female thread side) or the pin side (male thread side), and a softer film different from the coating coating is formed on the other side. In the latter case, it is even more preferable that the softer film hardness formed on the side not coated with the coating coating of this embodiment has a pencil hardness of 4B or less. Since the epoxy resin coating of this embodiment is a hard film with a pencil hardness of 3H or more, a film structure with a hardness difference provides preferable lubrication properties.

[0101] The former is a method of utilizing the lubricating properties of a solid lubricating coating, as originally intended by this embodiment. The latter is a method of further improving the lubricating properties. Rather than achieving lubrication by opposing two films with good lubricating properties, even greater improvements in lubricating properties can be expected by opposing two films, one of which is harder or softer than the film of this embodiment. As pointed out using Figure 2, when tightening and loosening screws in a state with backlash until the screws engage, a spike-like torque occurs (phase 1), and the soft coating can be expected to deform itself and reduce the surface pressure. Furthermore, the hard coating of this embodiment, which is mainly composed of BN and epoxy resin, can be expected to provide high lubrication throughout the entire tightening and loosening process of the screw.

[0102] <Method for Manufacturing Solid Lubricant Coatings> A film can be formed by applying a coating agent to the desired thickness in one go and then forming it into a film by baking or other methods. Preferably, instead of repeatedly baking the coating in multiple steps, a pre-heat treatment (pre-drying) is performed at least once at a temperature lower than the baking temperature, followed by baking and film formation. In this case, the solid lubricant coating thickness is set to 50 μm or less after one application, and a pre-drying step is inserted between the coatings, followed by film formation and pre-drying. These steps are performed two or more times, including the initial film formation, and the pre-drying is stopped for the final film formation and a main drying step is performed. Examples of the main drying step include baking, infrared irradiation, ultraviolet irradiation, hot air, or other drying methods, or leaving the coating in the air or natural drying. The final coating thickness is preferably adjusted to a total thickness of 10 to 150 μm. Pre-drying refers to drying in which only a portion of the solvent (e.g., 30% to 70%) is removed.

[0103] In this embodiment, the film is formed using a chemical based on a solvent containing a solid lubricant primarily composed of BN and a binder resin primarily composed of epoxy resin. The chemical preferably has a high viscosity, with a high film component content relative to the solvent. In this case, if the film is formed all at once, the surface tension along the thread structure of the oil well pipe will tend to pull the liquid along the corners of the threads, resulting in a thinner film, while the liquid will tend to pool in the corners of the thread roots. Therefore, it is better to perform the baking process in multiple stages.

[0104] However, multiple main baking processes tend to weaken the adhesion between films, making them more susceptible to peeling. Therefore, it is better to pre-bake the film after removing some of the solvent components, then repeat the coating and pre-baking process to form a film with the required thickness by pre-baking, and then perform the main baking. This is because it effectively ensures uniformity in film quality and thickness. Furthermore, from the perspective of corrosion resistance, film formation by multiple coating processes is less likely to result in pinholes penetrating the entire film. This is also effective. Furthermore, performing the main baking process in two stages is preferable to strengthen the cross-linked structure of the epoxy resin. Performing a primary curing process below the Tg temperature to gel the film, followed by a secondary curing process above the Tg temperature is expected to result in a complete cross-linked structure.

[0105] This section will provide a detailed explanation of the solid lubricant primarily composed of BN, the binder resin primarily composed of epoxy resin, and other additives, as well as a detailed explanation and clarification of the preferred ranges for an evaluation method simulating actual well conditions. This embodiment is not limited to the solid lubricant coating formed on oil well pipe threaded joints, but can also be used for the agents used to create such coatings and for lubrication of items other than oil well pipe threads. The following explanation will focus on box threads (female thread side) and pin threads (male thread side). However, this section also includes threaded and coupled (T&C) type joints and integral type joints for oil well pipes.

[0106] <Test Method (New Laboratory Test) Simulating Actual Well Test Conditions> In this embodiment, as explained using Figures 2 to 4, the phenomenon occurring in the lubrication of OCTG threads was considered to be divided into two phases: the lubrication before the threads engage (Phase 1) and the lubrication after the threads have fully engaged (Phase 2). Then, taking into account the make-up and back-tightening (lubrication) in the first phase (Phase 1), the thread lubrication was comprehensively evaluated, including the lubrication in the second phase (Phase 2). Without this evaluation, frequent problems in actual wells could occur, even if the laboratory test evaluation was satisfactory. In actual wells, large loads and unbalanced loads are applied before the threads engage, which can damage or peel off the solid lubricant coating. In severe cases, the solid lubricant coating can peel off completely. Taking this into consideration, the upper and lower limits of the preferred ranges of the parameters in this embodiment were selected.

[0107] As mentioned above, damage to solid lubricating coatings is unavoidable during tightening until the threads engage. Secondary products are then formed based on the spalled material. If these products clog the thread gap, seizure occurs. Therefore, unless lubrication evaluation is performed under conditions that closely resemble actual well conditions, there is a risk that solid lubricating coatings that actually fail the test may be erroneously judged as passing. Such a lenient evaluation renders the upper and lower limits of solid lubricating coating parameters and the selection of preferred ranges meaningless. In other words, accurate solid lubricating coating specifications cannot be established without considering whether the secondary products, or the reconstituted "secondary products," that are generated based on damage and spalling of the solid lubricating coating affect lubrication. In this embodiment, evaluation is performed using a new laboratory test that takes these findings into account.

[0108] Furthermore, relying on evaluations using horizontal power tongs with short pins or vertical power tongs with short pins (traditional laboratory testing) would be meaningless when evaluating solid lubricant coatings. Past patent documents sometimes state that lubrication tests based on solid lubricant coatings can be performed up to 15-20 times, even on large diameters such as 9-5 / 8" and 13-3 / 8". While these results compare favorably with those of grease-like compounds, such a high number of times is practically impossible with solid lubricant coatings. With solid lubricant coatings, the main lubricant layer is inevitably worn away. With grease-like compounds, on the other hand, the surface must be cleaned and reapplied after each tightening and loosening process, meaning that heavy metals such as Pb and Zn, which are the main lubricants, are resupplied each time. Therefore, in actual well tightening and untightening cases where a solid lubricant coating is used for a large diameter well, it is rare to see a tightening and untightening cycle of 15 to 20 times. Also, when it is said that a solid lubricant coating can be tightened and untightened 15 to 20 times, it is thought that this is because the lubrication of the threads is evaluated only in Phase 2, when the threads are fully engaged, without going through Phase 1, when the threads are not engaged. In other words, this is thought to be based on evaluations using horizontal or vertical power tongs using short pins, which are commonly seen in conventional laboratory tests.

[0109] In this embodiment, testing was performed using the equipment configuration shown in Figure 5 based on the new laboratory test conditions described above. The new laboratory test is based on evaluation under conditions that allow for the application of a large load during tightening and the application of an unbalanced load during tightening and loosening. In the new laboratory test, a large load equivalent to that of a full-size pin is applied, for example, and the rattle that occurs before the threads engage during the tightening process is taken into account. Furthermore, the rattle that occurs when the threads disengage during the loosening process is also taken into account. The new laboratory test uses a vertical power tong 4. A short pin 1 is used as the test pin. However, the pin 1 is designed to be able to apply and remove a load using a weight 3 from above. The short pin 1 and box screw 2 are then tightened via the pin thread portion 1a and the box thread portion 2a.

[0110] At that time, in order to simulate a situation where the threads do not mesh, the initial temporary tightening position is set so that half of the total number of threads of the pin threads 1a are exposed from the box screw 2 (see Figure 2 (b)). This is one of the causes of rattle. Tightening begins from this state. When tightening, a weight 3 is attached to the upper end of the pin 1, which is the end opposite the tightening screw of the box screw 2. The weight of the weight 3 is calculated based on the actual size pin's outer diameter and thickness as a load equivalent to one to three actual size pins. For a 9-5 / 8" 53.5#, the weight is approximately 1 ton load (2,200 lb) per pin, and approximately 3 tons (6,600 lb) for three pins connected together.

[0111] The weight 3 shown in Fig. 5 is composed of a weight body 3A and a bayonet rod 13, as shown in Fig. 6. The bayonet rod 13 is welded to the underside of the weight body 3A and is positioned axially symmetrically to the weight 3. The weight is attached to the pin 1 by loosely inserting the bayonet rod 13 into the pin 1. Reference numeral 1c denotes the inner diameter surface of the pin 1. When the weight 3 is attached as described above, holes 1d and 13a that pass through the pin 1 and bayonet rod 13 are drilled in the bayonet rod 13 and the pin 1. Then, as shown in Fig. 6, the weight 3 and the pin 1 are integrated by inserting a piercing rod 12 into the holes 1d and 13a.

[0112] A swivel-type hook 11 is welded to the center of the shaft at the top of the weight 3, and the weight is suspended from a hanging device 20 on the ceiling via a hanging chain 21. This makes it possible to adjust the load of the weight on the pin by adjusting the degree to which the hanging device 20 lifts the weight. When tightening, the hanging chain 21 is loosened so that the weight load is applied to the box screw, and the screw is tightened at 5 to 20 rpm until a torque is generated (Phase 1). This simulates wobble. Once the torque is generated, the rotation speed is reduced to 0.5 to 2 rpm, and the screw is tightened to the tightened position (Phase 2).

[0113] On the other hand, when loosening (re-tightening), the weight 3 is lifted by the hanging device 20, and re-tightening is performed without applying the weight 3's load. The rotation speed is 0.5 to 2 rpm when torque is high, and when the torque reaches approximately 1 / 10 of the tightening torque value, loosening is performed at a high speed of 5 to 20 rpm. Here, not applying a load from the weight 3 during loosening provides conditions closer to the actual well environment. This is based on experimental findings, based on data showing that the lubrication characteristics were evaluated better when the weight 3's load was applied than when it was not applied. That is, the inventors observed actual experiments and found that when loosening was performed with the weight applied, the weight acted as a balancer, and the pin loosened straight from the tightening completion position without any rattle. On the other hand, when the weight is reduced, that is, when the load is lifted to make the weight load zero and testing is performed, it has been found that, even when the load does not become completely zero, the situation in which the load is reduced and the joint is loosened allows testing under conditions that cause severe pin rattle and are more likely to damage the solid lubricant coating.

[0114] In the new laboratory tests under the above conditions, it was possible to simulate situations in which secondary products from solid lubricant coating-derived components released into the thread gap due to unavoidable spalling or other reasons do not move with the tightening / retraction process but instead become stuck in a certain location, causing seizure, or other situations in which the coating itself peels off completely. As a result, upper and lower limits for parameters related to the solid lubricant coating could be specified in accordance with actual well conditions. After retraction was completed, the pin screw and box screw were separated, and debris from the solid lubricant coating on the screw surface was blown away with an air blower. The surface was then inspected and the retraction was continued. This embodiment specifies the components and other factors to achieve lubrication properties that can withstand the environments likely to occur in an actual well. Furthermore, the upper and lower limits were determined by checking conditions that corresponded to the tightening / retraction conditions in an actual well.

[0115] The new laboratory test under the above conditions will be referred to as a weight-tongs test. In this embodiment, as explained using Figures 2 to 4, it is important to consider two types of phenomena that occur during the lubrication of OCTG threads, and to evaluate thread lubrication based on the initial tightening and tightening (lubrication) process. Failure to perform this evaluation can lead to frequent problems occurring in actual wells, even if the laboratory test evaluation is satisfactory. In actual wells, there are two types of tightening and tightening: tightening and tightening, which focus on lubrication while there is still some backlash before the threads engage, and tightening and tightening, which focus on lubrication after the threads are fully engaged. In actual wells, the weight of a single full-size pin, or in some cases the weight of three pins connected together, is applied to the receiving female thread. Furthermore, pins are not tightened perfectly vertically and straight. Pin threads tend to bend in their elastic range and be slightly bent when set. In reality, the pin threads inevitably tighten eccentrically due to the backlash during the initial and final tightening stages. In the horizontal and vertical power tongs using the above-mentioned short pins, a solid lubricating coating is required that can withstand situations where the torque is unstable and spike-like torque occurs at times until the threads engage, as shown in (x) in Figure 4(a).

[0116] (Other) The present disclosure may also have the following configurations: (1) An agent for forming a solid lubricant coating on a threaded portion of an oil country tubular good, the agent comprising a solid lubricant dispersed in a binder resin, the binder resin including a prepolymer and a curing agent, the prepolymer being made of one or more types of epoxy resin, the prepolymer being contained in an amount of 70 parts by weight or more per 100 parts by weight of the binder resin, the epoxy resin constituting the prepolymer having an epoxy equivalent ranging from 100 to 500, 80% by weight or more of the solid lubricant being BN (boron nitride) with an average particle size of 10 μm or less, and the total weight of the solid lubricant being 0.1 to 2 times the total weight of the binder resin.

[0117] (2) The solvent component is contained in an amount of 30 to 80 parts by weight, based on 100 parts by weight of the sum of the total weight of the solid lubricant and the total weight of the binder resin excluding the curing agent. (3) The curing accelerator is contained in an amount of 0 to 10 parts by weight, based on 100 parts by weight of the total weight of the agent. (4) The epoxy resin constituting the prepolymer has more than two epoxy groups (multifunctional epoxy resin). (5) The epoxy resin constituting the prepolymer has six or fewer epoxy groups. (6) The epoxy resin constituting the prepolymer has four or fewer epoxy groups. (7) The curing agent is an agent that cures the epoxy resin and is composed of an amine-based curing agent, an acid anhydride-based curing agent, a phenol-based curing agent, or a latent curing agent. (8) The glass transition temperature Tg of the epoxy resin constituting the prepolymer is 100°C or higher. (9) The viscosity of the agent is 20 mPa·sec or higher and 2,000 mPa·sec or lower.

[0118] (10) An oil country tubular good having a lubricating coating formed on a thread portion, the solid lubricating coating being constituted by dispersing a solid lubricant in a binder resin, the binder resin including an epoxy resin cured with a curing agent, the binder resin containing 70 parts by weight or more of the epoxy resin per 100 parts by weight of the binder resin, the epoxy equivalent of the epoxy resin being in the range of 100 to 500, 80% by weight or more of the solid lubricant being BN (boron nitride), the average particle size of the BN being 10 μm or less, and the total weight of the solid lubricant being 0.1 to 2 times the total weight of the binder resin.

[0119] (11) The epoxy resin has more than two epoxy groups (multifunctional epoxy resin). (12) The epoxy resin has six or fewer epoxy groups. (13) The epoxy resin has four or fewer epoxy groups. (14) The curing agent is a curing agent that cures the epoxy resin and is comprised of an amine-based curing agent, an acid anhydride-based curing agent, a phenol-based curing agent, or a latent curing agent. (15) The glass transition temperature Tg of the epoxy resin is 100°C or higher.

[0120] (16) The solid lubricating coating has a pencil hardness of 3H or greater. (17) The thickness of the solid lubricating coating is 10 μm or greater and 150 μm or less. (18) The lubricating coating is formed on the fastening surface of the threaded portion of at least one of the box and the pin. (19) The lubricating coating has a base layer between the fastening surface of the threaded portion and the solid lubricating coating, the base layer consisting of a chemical conversion treatment layer or an electroplated layer. (20) An oil country tubular goods threaded joint connecting a box having an internal thread and a pin having an external thread, wherein the oil country tubular goods of at least one of the box and the pin is made of oil country tubular goods on which the lubricating coating of the present disclosure is formed.

[0121] Next, examples based on this embodiment will be described. <Regarding Pass Criteria> First, the pass criteria for lubrication behavior based on the number of make-up and loosening attempts will be described. For casing sizes, three or more make-up and loosening attempts were considered pass, and five make-up and loosening attempts were considered better. For tubing sizes, five or more make-up and loosening attempts were considered pass, and ten or more make-up and loosening attempts were considered even better. The casing size specifications are in accordance with ISO 13679. For tubing, on the other hand, five or more make-up and loosening attempts, which is lower than the ISO 13679 specifications, were considered pass. It is clear that the number of make-up and loosening attempts tends to be worse due to the solid lubricant coating compared to lubrication using conventional grease-like compounds. This is becoming recognized in the oil and gas industry.

[0122] As mentioned above, if a short pin were simply used to perform the tightening and loosening test from the point where the threads engage, it would be easy to meet the ISO 13679 regulations. However, in this embodiment, evaluation was performed using a "weight tongs test (a new laboratory test)" to simulate conditions that are close to those that may occur in an actual well, such as a heavy load, an unbalanced load, and a condition where there is play and the threads do not engage. In the following explanation, 9-5 / 8" 53.5#, 9-5 / 8" 43.5#, and 7" 29# were used. Since these sizes are often used for casing, tightening and loosening three or more times is considered to be acceptable, and five times is considered to be even better.

[0123] In the case of the 9-5 / 8" 53.5#, a 3-ton weight was used to test the load of three connected pins. For the 9-5 / 8" 43.5# and 7" 29#, weights of 2.5 ton and 1 ton were used, respectively. The initial tightening position was set so that half of the total number of pin threads were visible from the box screw, meaning that tightening was performed from a state where the threads were not interlocking with each other. In other words, the tests were performed using the equipment shown in Figures 5 and 6. The tests were performed so that a load was applied during tightening, but that no load was applied during untightening.

[0124] If a test is conducted under load conditions using a weight during tightening, using a pin that combines a short pin and a weight, the short pin will rise straight up from the tightening position, unlike the full-size pin in an actual well. Because the weight acts as a balancer, there is no rattle. Because the full-size pin is long and slightly bent, it gradually becomes unstable and the threads no longer engage, causing rattle and increasing the likelihood of destroying the solid lubricant coating. Therefore, in the lubrication evaluation using weight tongs, no load was applied during tightening to simulate the rattle that occurs when the threads approach a state where they no longer engage. Furthermore, applying no load does not necessarily mean that the load is zero. The test was conducted by hoisting the weight using an overhead crane or similar device to avoid applying any load to the weight. The test to check the number of times tightening and loosening using weight tongs was carried out at least twice, and the pass / fail of the parameters was judged by comparing and evaluating whether each number met the pass standard and how the number achieved compared to the test score.

[0125] Example 1 Example 1 based on this embodiment will now be described with reference to the tables. This example is primarily an example in which a lubricating coating comprising a solid lubricating coating is provided on the make-up surface 10 of an oil country pipe threaded joint, and the acceptability of the lubricating coating comprising the solid lubricating coating is evaluated. In this example, a make-up and unmake-up test was carried out under the conditions shown in Tables 1 to 4, and the acceptability of the lubricating coating was determined.

[0126]

[0127]

[0128]

[0129]

[0130] In the table, No. 1 to 4 are steel grade: carbon steel high strength material Q125, screw size is 9-5 / 8" 53.5#, and screw is JFELION ＴＭIn Nos. 1 to 4, a solid lubricating coating was applied to the coupling side threads by forming an epoxy resin mainly made of BN. The pin side was either left as shot blasted or coated with soft lubricating and anti-rust paint.

[0131] The epoxy resin was a cresol novolac epoxy resin with six epoxy groups and an epoxy equivalent of 200. The curing agent was a phenol novolac-based resin with a functional group equivalent, i.e., active hydrogen equivalent, of 195. TPP (triphenylphosphine) was used as the curing promoter, and 2 parts by weight (2 pbr) of the curing promoter was mixed with 100 parts by weight of the epoxy resin and curing agent to promote curing. The heat treatment was performed at 160°C for 2 hours and 180°C for 4 hours. The epoxy resin had a pencil hardness of 3H. In the table, coupling threads are referred to as CPLG threads and pin threads as PIN threads.

[0132] No. 1 is an example in which the BN size of the solid lubricant is 20 μm, exceeding the specified 10 μm, and the film thickness is 45 μm. In No. 1, a tightening and tightening test of an oil well pipe thread was conducted using horizontal tongs. The pin's own weight is not applied to the coupling, and the axis is adjusted, so No. 1 is an example in which the tightening and tightening test was conducted without any particular problems. However, because the test evaluation conditions were lenient compared to the tightening and tightening conditions in an actual well, more than five tightening and tightening cycles were achieved, even though the BN was outside the standard.

[0133] On the other hand, No. 2 is a case where the pin thread side was coated with an acrylate-based fluorine-based paint under the same coupling membrane conditions as No. 1. The results of the tightening / retraction test were conducted under new laboratory test conditions, using a vertical tongs as shown in Figure 5 and a 3-ton weight load. As mentioned at the beginning of the example, tightening / retraction was performed by applying a load during tightening and unloading the load (including loosening the load). Note that the 3-ton load simulates the connection of three full-length pins of the same size. In No. 2, the number of tightening / retraction cycles was less than the required number. In an actual well, the pin's own weight is applied to the coupling thread, and the pin is not set symmetrically or straight relative to the center of the coupling; rather, the pin axis is bent when set. Furthermore, there is "play" before the threads engage with each other, resulting in conditions where large and unbalanced loads are applied to the coupling thread. Under conditions similar to those of an actual well, if the average particle size of the BN solid lubricant exceeds the upper limit of 10 μm, the number of tightening and loosening operations will not satisfy the standard.

[0134] No. 3 is an example in which the average particle size of BN in the solid lubricant coating on the coupling side was changed compared to No. 2. Specifically, the average particle size of BN was 5 μm, within the standard range. Other parameters were also adjusted within the scope of this disclosure. In a weight-tongs test, the number of tightening and loosening cycles met the standard. This demonstrates that sufficient lubrication can be maintained in an actual well. No. 4 is an example under the same conditions as No. 3, except that the tightening test was conducted in a simulated well. In No. 4, three connected full-length pins were used to prevent impact on the box thread when setting the pin thread with the stabbing guide. A compensator was also used to prevent excessive swing of the pin thread. This is a result simulating the conditions in an actual well. No. 4 demonstrated good lubricity, the same results as No. 3. These results show that the weight-tong test, which is a new laboratory testing method, can simulate the conditions in an actual well.

[0135] No. 5 is a case where the film thickness was 8 μm, below the lower limit of 10 μm compared to Nos. 3 and 4. No. 5 was a case where tightening and loosening were difficult and was judged as NG. No. 6 is a case where the film under the conditions of Nos. 1 to 5 was formed on the short pin side with a film thickness of 10 μm, rather than on the coupling thread side. The tongs were simply vertical tongs, and structurally, no weight was applied to the top of the coupling. It was found that even if the coating relationship between the coupling thread and the pin thread was reversed, a sufficient number of tightening and loosening cycles could be ensured as long as it was within the specifications disclosed herein. Nos. 3 and 6 clearly demonstrate good lubrication behavior, even in cases where the coupling side has a BN-based epoxy resin coating and the pin side has a soft paint coating, and conversely, in cases where the pin side has a BN-based epoxy resin coating and the coupling side has a soft paint coating.

[0136] In the case of No. 7, the steel grade is carbon steel sour-resistant material C110, the screw size is 9-5 / 8" 53.5#, and the screw is JFELION ＴＭ This experiment was conducted using a BN-based epoxy resin to form a solid lubricant coating on the coupling side threads. The pin side was an example of a soft lubricant and anti-rust paint applied over a shot-blasted surface. This example of a solid lubricant coating on the coupling side threads was the only two-component system. The epoxy resin was a bisphenol A-based epoxy resin with four epoxy groups and an epoxy equivalent of 220. Modified alicyclic polyamine and polyamidoamine were dissolved in a solvent in a weight ratio of 4:6 as hardeners. The combined functional group equivalent of the hardener, i.e., the active hydrogen equivalent, was 95. Therefore, the bisphenol A-based epoxy resin was formulated to react with an epoxy equivalent of 185. The film hardness was 3B, below the lower limit of the specification, making it soft. Furthermore, because it is a two-component system, it tends to harden quickly upon mixing, becoming syrup-like, with a target film thickness of 50 μm. However, it was far from homogeneous. This is an example (comparison example) where the number of tightening and loosening cycles is not good.

[0137] No. 8 to 10 are made of carbon steel sour-resistant material C110, with a screw size of 9-5 / 8" 53.5#, and the screws are JFELION. ＴＭ The test was conducted under the following conditions. A solid lubricating coating was formed on the coupling threads using an epoxy resin primarily composed of BN. The pin side was shot-blasted to form a soft lubricating and anti-rust paint. The epoxy resin was a trisphenolmethane-type epoxy resin with three epoxy groups and an epoxy equivalent of 185. The curing agent was a diethylenetriamine-based resin with a functional group equivalent, i.e., an active hydrogen equivalent, of 125, and cured without any lubrication aids. The glass transition temperature (Tg) was 150°C. The film thickness was 55 μm and the pencil hardness was 3H. No. 8 was an example in which the coupling threads were coated with an epoxy resin and the pin side was coated with a soft lubricating and anti-rust paint, and the test was able to be tightened and loosened more than the specified number of times.

[0138] No. 9 is a case in which an epoxy resin coating was applied not only to the coupling thread side but also to the pin thread side, and this case also exceeded the specified number of times. Comparing No. 8 and No. 9, No. 8 had a better number of tightening and loosening operations. This shows that having a hard epoxy resin coating of 3H or higher containing BN as specified in the invention on one side of the thread and a softer coating on the other side provides better lubrication. No. 10 is a case in which there is no coating on the pin side and it has only been shot blasted. It clearly shows that the epoxy resin coating contains BN, a solid lubricant, within the range specified in this embodiment, and has excellent lubrication properties.

[0139] No. 11 to No. 13 are made of carbon steel sour-resistant material C110, with a screw size of 9-5 / 8" 53.5#, and the screws are JFELION. ＴＭThis experiment was carried out using a phenol-novolac-based hardener. The conditions for the solid lubricant BN were changed on the coupling thread, and then an epoxy resin was formed to create a solid lubricant coating. The pin side was shot-blasted to create a soft lubricating and anti-rust paint. The epoxy resin was a tetrakisphenolethane-based epoxy resin with four epoxy groups and an epoxy equivalent of 165. The curing agent was a phenol-novolac-based hardener with a functional group equivalent, or active hydrogen equivalent, of 206. Triphenylphosphine (TPP) was used as a curing aid. The conditions for the solid lubricant BN were changed on the coupling thread, and then an epoxy resin was formed.

[0140] Nos. 11 and 12 are examples where only shot blasting was performed on the pin side. No. 13 is an example where an acrylate-based F paint containing metal soap was applied. The difference between Nos. 11 and 12 is the film thickness and the solvent mixture ratio, but both are examples of good lubrication. No. 13 is an example where no BN was added, and because it does not contain a solid lubricant, the number of tightening and loosening cycles did not meet the pass standard.

[0141] No. 14 is made of carbon steel sour-resistant material C110, with a screw size of 7"29#, and is made of JFELION ＴＭ This was carried out under the following conditions. A solid lubricant coating was formed on the coupling side threads using an epoxy resin containing 85% BN as a solid lubricant and 15% PTFE as another solid lubricant. The pin side was shot-blasted to form a soft lubricating and anti-rust paint. The epoxy resin was a glycidyl ester-type epoxy resin with three epoxy groups and an epoxy equivalent of 190. This is an example of a self-polymerizing epoxy resin coating, in which 5 parts by weight of 1,2,4-triazole was added to a total of 100 parts by weight of the solid lubricant and prepolymer epoxy resin, forming a self-polymerizing epoxy catalyst. No. 14 was a film formed within the parameters formulated within the specifications of this disclosure, and its lubrication was deemed acceptable.

[0142] Nos. 15 and 16 are cases where the viscosity of the agent was outside the preferred range. Both Nos. 15 and 16 are made of carbon steel sour-resistant material C110, with a screw size of 9-5 / 8" 43.5#, and the screw was JFELION. ＴＭ This is a case where a BN-containing epoxy resin coating was formed on the coupling side. For the pin side, No. 15 was shot-blasted as is, while No. 16 was shot-blasted and then coated with an acrylate-based fluororesin. For No. 15, a 1:1 mixture of polyglycerol polyglycidyl ether and polyglycerol polyglycidyl ether was used. The curing agent was phthalic anhydride. DMP-30, i.e., 2,4,6-tris(dimethylaminomethyl)phenol, was used as a curing aid, at 5 parts by weight per 100 parts by weight of the total weight of the solid lubricant and epoxy resin. This example shows a viscosity of 3,500 mPa·sec, significantly exceeding the upper limit of the specification. Because of its high viscosity, it is difficult to apply evenly in a paste form. However, in the case of the coated specimen, the number of times of tightening and loosening equivalent to two times was three times, and therefore this specimen was judged to be an example of the present invention.

[0143] No. 16 uses cyclohexanedimethanol diglycidyl ether as the epoxy resin, dicyandiamide as the curing agent, and imidazole as the curing aid. This example shows a viscosity of 25 mPa·sec, significantly below the lower limit of the specification. No. 16 has a viscosity similar to that of cooking oil, and when applied, it tends to pool at the 6 o'clock position rather than remain in place. Even when attempting to apply the coating while rotating the pipe, it pooled at the 6 o'clock position before baking, resulting in a thin, homogeneous film thickness of 25 μm. This indicates poor lubrication. Furthermore, the Tg of the epoxy resin film was outside the preferred range. Therefore, the tightening / untightening test was attempted three times, but No. 16 failed twice, once, and three times, resulting in results that could hardly be described as excellent. No. 16 is a comparative example.

[0144] Example 2 Example 2 is an evaluation of corrosion resistance by a salt spray test. Salt spray was performed on Nos. 3, 8, 11, and 14, selected from the carbon steel-based oil country pipe thread conditions shown in Example 1. A new coating was formed on the material of the coupling sample for this salt spray test. As a comparative example, a 0.8 mm thick SPCC (a thin steel sheet / cold-rolled annealed sheet of ordinary mild steel) was used (Condition A).

[0145] The OCTG screw material was tightened and loosened once with a protector on both ends of the coupling thread. Then, salt spray was performed on samples in which the material was left as is (Nos. 3-2, 8-2, 11-2, and 14-2) and samples in which the protector was reattached and tightened (corresponding to the second tightening: Nos. 3-3, 8-3, 11-3, and 14-3). The corrosion test was then performed by arranging the samples side by side, i.e., not standing upright, and observing them. The pin threads were samples with only the threads, and the threaded side was tightened and loosened once with a protector. Imide tape was applied to the outside, where the protector was not reattached, to prevent water from entering the inside of the pipe.

[0146] Detailed conditions are as follows: The conditions for the solid lubricating coatings of Nos. 3-2, 3-3, 8-2, 8-3, 11-2, 11-3, and 14-2, 14-3 are the same as those for Nos. 3, 8, 11, and 14 in Example 1.

[0147] <Salt Water Spray Conditions> The salt water spray conditions are as follows: Spray conditions: JIS K 5600-7-1 Salt water concentration: 5±0.5 wt % Temperature: 35°C Humidity: 98 to 99% Spray amount: 1 to 2 mL / hr / 80 cm ２ pH: 6.5-7.2 Time: 24hr

[0148] The significance of this test method is as follows: Oil well pipe threads are shipped after the ends are tightened with protectors, and are often stored in that state in a yard near the well. For this reason, the salt water sprayed condition is an environment close to the actual conditions of use. The condition without a protector means the even more severe conditions when the protector is removed. The example of SPCC thin plate is a case where the protector is not tightened or loosened, and the corrosion resistance of the film itself is observed from the thread shape. The results are shown in Table 5.

[0149]

[0150] As can be seen from Table 5, all of the comparative examples, including No. A, Nos. 3-2, 3-3, 8-2, 8-3, 11-2, 11-3, and 14-2, 14-3, were not corroded in salt spray and were found to have sufficient corrosion resistance. It is believed that this is largely due to the fact that the film quality is 3H hard, the protector, and that even when tightened and loosened, no fatal damage is caused, and the BN itself is water-repellent and does not attract water.

[0151] The entire contents of Japanese Patent Application No. 2021-91463 (filed May 31, 2021), from which this application claims priority, are incorporated herein by reference. While the present invention has been described with reference to a limited number of embodiments, the scope of the invention is not limited thereto, and modifications of each embodiment based on the above disclosure would be obvious to those skilled in the art.

[0152] DESCRIPTION OF SYMBOLS 1 Test pin 1a Male thread 1c Inner diameter surface 1d Through hole 2 Box (coupling) 2a Female thread 3 Weight 4 Power tong 10A Solid lubricant coating 10B Base layer 11 Hook (Swivel type) 12 Piercing rod 13 Insert rod 20 Lifting device (crane) 21 Chain (hanging rope)

Claims

1. A chemical for forming a solid lubricating film on a threaded portion of an oil well pipe, wherein a solid lubricant is dispersed in a binder resin, the binder resin contains a prepolymer and a curing agent, the prepolymer consists of one or more epoxy resins, and the prepolymer is contained in an amount of 70 parts by weight or more based on 100 parts by weight of the binder resin, the epoxy equivalent of the epoxy resin constituting the prepolymer is in the range of 100 or more and 500 or less, 80% by weight or more of the solid lubricant is BN (boron nitride), the average particle diameter of the BN is 10 μm or less, and the total weight of the solid lubricant is 0.1 times or more and 2 times or less the total weight of the binder resin. A chemical for forming a solid lubricating film, characterized by the above.

2. The chemical for forming a solid lubricating film according to claim 1, characterized in that the solvent component is contained in an amount of 30 parts by weight or more and 80 parts by weight or less based on 100 parts by weight of the sum of the total weight of the solid lubricant and the total weight of the binder resin excluding the curing agent.

3. The chemical for forming a solid lubricating film according to claim 1 or claim 2, characterized in that a curing accelerator is contained in an amount of 0 parts by weight or more and 10 parts by weight or less based on 100 parts by weight of the total weight of the epoxy resin constituting the prepolymer.

4. The chemical for forming a solid lubricating film according to any one of claims 1 to 3, characterized in that the epoxy resin constituting the prepolymer has more than two epoxy groups (polyfunctional epoxy resin).

5. The chemical for forming a solid lubricating film according to claim 4, characterized in that the epoxy resin constituting the prepolymer has 6 or less epoxy groups.

6. The chemical for forming a solid lubricating film according to claim 4, characterized in that the epoxy resin constituting the prepolymer has 4 or less epoxy groups.

7. The chemical for forming a solid lubricating film according to any one of claims 1 to 6, characterized in that the curing agent is a curing agent for curing an epoxy resin and consists of an amine-based curing agent, an acid anhydride-based curing agent, a phenol-based curing agent, or a latent curing agent.

8. The chemical for forming a solid lubricating film according to claim 7, characterized in that the glass transition temperature Tg of the epoxy resin constituting the prepolymer is 100 °C or more.

9. The chemical agent for forming a solid lubricating film according to any one of claims 1 to 8, wherein the viscosity of the chemical agent is 20 mPa·sec or more and 2,000 mPa·sec or less.

10. An oil well pipe having a lubricating film provided with a solid lubricating film formed on a threaded portion, wherein the solid lubricating film is composed of a solid lubricant dispersed in a binder resin, the binder resin contains an epoxy resin cured with a curing agent, and the epoxy resin is contained in an amount of 70 parts by weight or more per 100 parts by weight of the binder resin, the epoxy equivalent of the epoxy resin is in the range of 100 or more and 500 or less, 80% by weight or more of the solid lubricant is BN (boron nitride), the average particle diameter of the BN is 10 μm or less, the total weight of the solid lubricant is 0.1 times or more and 2 times or less the total weight of the binder resin, and the thickness of the solid lubricating film is 10 μm or more and 150 μm or less.

11. The oil well pipe according to claim 10, wherein the epoxy resin has more than two epoxy groups (polyfunctional epoxy resin).

12. The oil well pipe according to claim 11, wherein the epoxy resin has 6 or less epoxy groups.

13. The oil well pipe according to claim 11, wherein the epoxy resin has 4 or less epoxy groups.

14. The curing agent is a curing agent for curing an epoxy resin and is composed of an amine-based curing agent, an acid anhydride-based curing agent, a phenol-based curing agent, or a latent curing agent. The oil well pipe according to any one of claims 10 to 13.

15. The oil well pipe according to claim 14, wherein the glass transition temperature Tg of the epoxy resin is 100°C or more.

16. The oil well pipe according to any one of claims 10 to 15, wherein the solid lubricating film has a hardness of 3H or more in terms of pencil hardness.

17. The lubricating film has an underlayer between the surface of the threaded portion and the solid lubricating film, and the underlayer is composed of a chemical conversion treatment layer or an electroplated layer. The oil well pipe according to any one of claims 10 to 16.

18. An oil well pipe thread joint connecting a box having an internal thread and a pin having an external thread, wherein at least one of the oil well pipes of the box and the pin is made of the oil well pipe with the lubricating coating formed as described in any one of claims 10 to 17. This is an oil well pipe thread joint characterized by the above.