Agent, oil country tubular goods, and threaded joint for oil country tubular goods

Abstract

The present disclosure realizes seizure resistance (galling resistance) equal to or higher than that of a dope compound method of the prior art in terms of lubrication properties during make-up and break-out of oil country tubular goods by using a solid lubricating coating film (10A). An agent for forming a solid lubricating coating film (10A) on a tightening surface of a thread portion, in which a solid lubricant is dispersed in a binder resin as a matrix component, a main component of the solid lubricant is melamine cyanurate, and an average particle diameter of the melamine cyanurate is 0.1 μm or more and 10.0 μm or less, the binder resin contains an alkyd resin and nitrocellulose, and the alkyd resin and nitrocellulose are contained in an amount of 85 wt% or more of the total binder resin component weight, and a total weight of the solid lubricant is 10 parts by weight or more and 100 parts by weight or less based on 100 parts by weight of a total weight of the binder resin.

Description

Chemicals, oil well pipes, and oil well pipe threaded joints

[0001] This disclosure relates to technology related to the lubrication and corrosion resistance of oil country tubular goods threaded joints. This disclosure relates to technology related to a coating structure and an oil country tubular goods threaded joint in which a solid lubricating coating is formed on the fastening surface (including the metal seal surface) of the threaded portion instead of a wet lubricating compound. In this specification, the fastening surface, which is the 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. This disclosure 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 loosened (also referred to as the number of tightening and loosening operations) 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, the lubrication of the threads has been achieved by forming a coating on the fastening surfaces (sealing surfaces) of the threads of at least one of the male and female threaded components (hereinafter also simply referred to as "fastening surfaces") by surface treatment such as a manganese phosphate conversion coating or electroplating using 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 when tightening and loosening a screw. 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, this solid film will also be referred to as a binder resin.

[0006] This disclosure utilizes MCA as the main component of a solid lubricant and a hard film composed of alkyd resin, cellulose, and its derivatives as the binder resin component. This disclosure particularly utilizes cellulose and its derivatives as nitrocellulose. Furthermore, among commercially available paints, there is a group called lacquers, and the majority of these lacquers are made up of alkyd resin and nitrocellulose. These paints are not particularly excellent in terms of lubrication. These are generally used as general-purpose paints and quick-drying paints for plastic models and other hobby applications. While these paints are optimized for rust prevention and decoration, their lubrication properties are not necessarily guaranteed. Therefore, to achieve this lubrication, it is necessary to optimize the composition of the alkyd resin and nitrocellulose components, as well as the selection of a lubricant and its component content range. However, although there are no patent documents that match the above, previous literature has been published that discusses individual components such as alkyd resins and nitrocellulose.

[0007] Patent documents that cite MCA as a solid lubricant include, for example, Patent Documents 1 to 4. Patent Documents 1 to 3 exemplify MCA as one of the candidates for solid lubricant powders for oil country tubular goods threads. Patent Document 4 also describes the use of MCA as one of the essential components for the solid lubricant coating of oil country tubular goods. Patent Document 5 also describes alkyd resins. Patent Document 5 proposes a surface layer with dispersed inorganic silica particles as a treatment that replaces conventional chromate treatments for the surfaces of a wide range of metal materials. Patent Document 5 also lists alkyd resin as one of the candidates for resins that bind silica.

[0008] Patent Document 6 describes the use of nitrocellulose, and lists cellulose as one of the candidate carbohydrates that may be incorporated into lubricating coatings. Patent Document 6 also lists materials, either alone or in blends, from a group of candidates, including cellulose, acrylic resin, vinyl chloride resin, polyvinyl butyral, rubber, and fluororesin, as examples of materials for forming a film that retains lubricating powder. Patent Document 7 also lists nitrocellulose as an example. Patent Document 7 describes a liquid lubricating layer as the lower layer, on which a solid lubricating coating is formed. Nitrocellulose is listed as one of the candidate binder resins for the solid lubricating coating. Patent Document 7 assumes that air drying is required to form the upper layer while protecting the lower liquid lubricating layer. Nitrocellulose is listed as one of the candidate binder resins for the upper layer, which can be formed by air drying.

[0009] Furthermore, although not an example of evaluation of solid lubricant coatings, Non-Patent Document 1 describes a make-up test method using a vertical power tongs with a short pin. Non-Patent Document 1 describes a method in which a 5 kN weight (510 kg weight) is constantly applied during make-up and loosening, regardless of the outer diameter or wall thickness of the OCTG being evaluated. Non-Patent Document 1 describes pins of 7"29# and 7"35#. If the pin length is 40 feet (≈12 m), which is close to the actual length of Range-3, the pin load is approximately 520 kg or 630 kg. Therefore, it is believed that the weight of one evaluation-sized pin is applied during both make-up and loosening. Furthermore, judging from the torque-turn chart, since make-up is completed in half a turn (see Fig. 5 in Non-Patent Document 1, etc.), it can be seen that the initial setting position of the coupling and pin when made by hand just before the start of make-up begins with the threads almost completely engaged with each other.

[0010] International Publication No. 2018 / 216416 JP 2008-069883 A JP 2008-537062 A International Publication No. 2014 / 024755 International Publication No. 2009 / 057754 JP 2017-110685 A JP 2004-053013 A

[0011] Tsutome et al.: Journal of the Japan Petroleum Technology Association, Vol. 61, No. 6 (1996), pp. 527-536. (Fig. 1)

[0012] The inventors conducted research into solid lubricant coatings, referencing the solid lubricant coating materials described in the above-mentioned patent documents and other well-known prior art. Specifically, the inventors optimized the blending ratio of cellulose and its derivatives to alkyd resin to adjust the hardness of the binder resin, and then investigated the lubricity of a film structure in which the amount of MCA (melamine cyanurate) added as a solid lubricant was optimized to further enhance lubricity. Furthermore, they investigated whether corrosion resistance could be maintained. Furthermore, in this research, cellulose and its derivatives were primarily investigated using nitrocellulose. However, previous patent documents have not shown any examples of using this combination to improve lubrication or corrosion resistance. In other words, previous patent documents only specify the preferred ranges for each individual component, although the conditions of use and other factors may vary.

[0013] Examples of using MCA as a solid lubricant are described in Patent Documents 1 to 4. However, MCA is merely listed as one of the candidate solid lubricants. Furthermore, Patent Documents 1 to 3 do not specify alkyd resin as the binder resin for holding the solid lubricant. Even if alkyd resin is broadly considered to be polyester resin, polyester resin is not listed as a candidate binder resin. Patent Document 4 describes a semi-solid to viscous film containing oils and fats, rather than a hard resin film, and therefore its application differs from that of the present disclosure. Furthermore, Patent Documents 1 to 4 only cite MCA as an example, and do not provide detailed information such as the preferred size range or concentration range.

[0014] Furthermore, Patent Document 5 also provides an example of using an alkyd resin as a binder resin. However, Patent Document 5 does not provide an example of application to oil well pipe threads, but rather targets metal materials in general. Furthermore, Patent Document 5 does not primarily focus on alkyd resin. In the context of an invention using silica particles as an anti-corrosion coating layer, alkyd resin is only listed as one possible binder among a group of coating film candidates using silica particles as a binder to fix the particles. This does not particularly match the field targeted by the present disclosure.

[0015] Nitrocellulose is described in Patent Documents 6 and 7. Patent Document 6 lists carbohydrates as an example of an additive to be contained in a lubricating coating. It also lists carbides as an example of a material that changes the film's properties to a high viscosity at high temperatures. While this disclosure uses nitrocellulose as a binder resin, Patent Document 7 presents an application example based on a different concept from using nitrocellulose as a binder resin. Specifically, it is an application example of a solid layer in a two-layer lubricating film structure consisting of a liquid layer and a solid layer. Patent Document 7 lists nitrocellulose as one of the candidate resins that harden at room temperature to retain solid lubricants. However, unlike this disclosure, polymerization with alkyd resins is not anticipated.

[0016] As described above, none of the patent documents describe a solid lubricating coating based on nitrocellulose and alkyd resin that provides both lubrication and corrosion protection. Lubricating coatings using cellulose and cellulose derivatives, or nitrocellulose, are inherently brittle. This renders them unusable for lubrication purposes. Optimizing the blend with alkyd resin, adding an appropriate amount of solid lubricant, and balancing the binder resin and solid lubricant are necessary. In other words, simply mixing these components together is difficult to achieve the desired lubrication. It would be necessary to clearly specify the detailed conditions for each component and to add appropriate additives separately. However, none of the patent documents mention these points.

[0017] Furthermore, 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, the lubrication is performed under a heavy load.

[0018] 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 (without deflection) position while 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 deflected depending on the elastic modulus (Young's modulus) of the material and the actual pin length. In particular, for pins longer than 8 m, when viewed from below, the pin appears to be set straight into the box but bent. The pin is tightened or loosened from this state. Therefore, the box thread and pin thread are never tightened or loosened under a uniform and symmetrical load. This results in a situation where parts of the thread surface are in strong localized contact (lubrication under an unbalanced load). Furthermore, the locations where the bolts make strong contact also change depending on whether the bolts are tightened or loosened.

[0019] With conventional lubrication technology that uses a grease-like compound, the compound moves along with the tightening and loosening process. Therefore, even if there are slight fluctuations in the lubrication conditions, the lubricant (lubricating compound) functions to converge the tightening and loosening process in a favorable direction. Therefore, in evaluation tests (also called laboratory tests) for the tightening and loosening of threaded joints, it is possible to understand the lubrication status of the full-size pin by evaluating it using a short-length pin, without relying on evaluations using full-size pins.

[0020] On the other hand, according to the inventor's research, when using lubrication technology for oil well pipe threads that use a solid lubricant coating, the solid lubricant coating is inevitably worn away to some extent. It was necessary to devise a way to prevent this shavings from clogging the thread gap. Furthermore, the secondary formations resulting from the worn-off solid lubricant coating do not always move in tandem with tightening and loosening. This is what happens in actual wells, and is a major difference from lubrication using a wet lubricant compound.

[0021] Furthermore, we have found that evaluations of OCTG threaded joints using the same lubrication technology as that using conventional grease-like compounds cannot evaluate the lubrication technology of OCTG threads using solid lubricating coatings, resulting in a lenient evaluation. In other words, in conventional patent documents, evaluations of make-up and unmake-up of OCTG threaded joints often use lubrication using wet lubricating compounds, even when evaluating solid lubricating coatings. Therefore, we have found that the conditions for solid lubricating coating lubrication (such as the preferred ranges of components) described in previous patent documents cannot be adopted as is. In other words, 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 loads and unbalanced loads for the reasons mentioned above. We have found that evaluations using short pins that are shorter than the conditions in an actual well make it difficult to scrape off the solid lubricating coating, making it impossible to create conditions that can simulate the seizure behavior in an actual well.

[0022] As described above, conventional evaluations using short pins cannot simulate situations where secondary products made from shavings of the solid lubricating coating clog and cause seizure, or where the secondary products are pressed against the fastening surfaces again to maintain the lubricating film effect. In other words, conventional evaluations using short pins are simply unavoidably lenient in their evaluation of the solid lubricating coating, and when determining the physical property parameters of the solid lubricating coating, they erroneously evaluate a range that would actually be unacceptable as being within a suitable range. For these reasons, the inventors have come to the realization that the reality is that conventional prior art documents often describe suitable ranges based on lenient evaluations such as those described above.

[0023] As described above, it was discovered that the following (1) and (2) must be taken into consideration as peculiarities of the lubrication of oil country pipe threads. (1) There is structural play (play) in the initial stage of thread make-up and in the later stage of unmake-up. (2) The target is lubrication and friction under a heavy weight applied from above. In other words, it is necessary to create conditions similar to those that oil country pipe threads are exposed to when make-up and unmake-up in an actual well. In other words, it is necessary to specify a group of parameters related to the solid lubricant coating on the premise that make-up and unmake-up are performed under heavy and unbalanced loads. It was discovered that the invention must be completed after guaranteeing lubricity in accordance with these actual conditions of use and clarifying the meaning of the upper and lower limits of the parameters.

[0024] Thus, it is important to define upper and lower limits for parameters based on actual well conditions. The lubrication behavior of OCTG threads has traditionally been evaluated using short pins and power tongs to measure the tightening and untightening behavior and the number of tightening and untightening operations. With conventional grease-like compounds, the compound moves in conjunction with the tightening and untightening operations. Therefore, there are no particular issues with evaluating lubrication behavior, whether using horizontal or vertical tongs with short pins. In other words, conventional grease-like compounds can be evaluated using short pins to compare thread design, the presence or absence of base layers such as chemical treatments or electroplating, and the compound itself.

[0025] However, this is not the case with solid lubricant coatings. Evaluations using short pins do not simulate actual well conditions and result in a rather lenient assessment of lubrication. A "fail" rating using short pins corresponds to a "fail" rating in actual well tightening. However, a "pass" rating using short pins does not necessarily mean a "pass" rating in actual well tightening. The problem is that a "pass" rating using short pins includes a "fail" rating in actual well tightening. Furthermore, because the lubrication behavior of OCTG threads differs from other lubrication behaviors, it is difficult to apply standards based on other lubrication conditions. Generally, when considering the lubrication behavior between two rubbing objects, one is assumed to be fixed and the other is moving. For moving objects, lubrication is assumed to begin when the moving 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.

[0026] On the other hand, when lubricating oil well pipe 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, when lubricating oil well pipe threads, there are uneven periods of strong contact and periods of almost no contact. Strong contact increases the risk of damaging the lubricant film. Furthermore, after the threads are engaged, the lubrication is affected by the lubrication conditions at the time. In particular, in situations where there is backlash before the threads are fully engaged, a solid lubricant coating is susceptible to damage due to the uneven load caused by backlash. In particular, in the case of lubricant coatings made of cellulose and cellulose derivatives, or nitrocellulose and alkyd resins, as targeted in this disclosure, the inherent brittleness of the binder resin is a key issue. Under actual conditions of use in wells, particularly when there is backlash before the threads mesh, the coating can peel off completely or crack. It is necessary to design a solid lubricating coating so that this phenomenon does not cause a loss of lubrication.

[0027] 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. Offshore rigs often use three pre-connected pin threads for tightening. Therefore, when using 9-5 / 8" outer diameter OCTG, the box side experiences a severe load of approximately 3 tons.

[0028] The lubrication of oil country pipe threads must be such that it can withstand such heavy loads and uneven loads. After extensive investigation, the inventors have come to the realization that the key is to devise a solid lubricant and binder resin that takes into consideration how to minimize damage to the solid lubricant coating under heavy load conditions and when there is backlash before the threads engage.

[0029] On the other hand, it is difficult to say that past patent documents have designed solid lubricant coatings based on this perspective. For example, Patent Document 1 states that the screw threads are hand-tightened until they engage in the initial tightening process, clearly ignoring backlash. Furthermore, the fact that the screw threads are tightened until they engage indirectly indicates that this is a laboratory evaluation using a short pin. In actual wells, it is rare for the screw threads to be tightened to the point where they engage. It is almost impossible to set full-size pin threads in an ideal upright position. The pin flexes to a certain extent during tightening. For this reason, hand tightening is almost always completed before the pin threads are fully seated in the coupling. Patent Documents 2, 3, 4, and 6 state that the tightening speed is 10 rpm. Patent Document 7 describes a tightening test at a tightening speed of 20 rpm, followed by a tightening and tightening back test, simulating operation in an actual pipe. These documents do not disclose information about the initial tightening position. However, since there is no specific mention that the tightening was performed in an actual well, it is assumed that the results were obtained using a short pin in a laboratory. Furthermore, the screw instruction manuals provided by the applicants of these patent documents instruct that the tightening should be performed at 1 rpm or less. This also suggests that the tightening and tightening tests in these patent documents are likely laboratory tests. Since there is no specific mention of this, it does not appear that when starting to tighten with power tongs, the tightening begins from a part where there is play when setting the pin and box screws by hand.

[0030] Here, when applying a grease-like compound, the viscous liquid grease-like compound moves in conjunction with the tightening and loosening of the fasteners. This significantly reduces the effects of large loads and uneven loads. Therefore, whether evaluating with horizontal tongs using short pins or vertical tongs, there are no particular problems and the lubrication behavior can be evaluated.

[0031] In contrast, in the case of oil well pipe threads using a solid lubricant coating, the solid lubricant coating, which is equivalent to a viscous liquid grease-like compound, is damaged and peels off during tightening, both before and after the threads engage. Alternatively, the solid lubricant coating is inevitably gradually worn away. Unlike grease-like compounds, the peeled off slag does not necessarily move in conjunction with tightening and loosening. The release of secondary products from the scraped-off solid lubricant coating into the gap between the pin thread and the box thread significantly affects lubrication. Closing the thread gap directly leads to seizure. Alternatively, when pressed down by a heavy load, these secondary products can move in conjunction with tightening and loosening. When pressed down, they can reconstitute and reattach as a film to one of the threads, improving lubrication.

[0032] Conventional testing using short pins is unable to simulate the heavy loads and unbalanced loads that occur in actual wells. Consequently, conventional laboratory tests often produce only a small amount of secondary products derived from the solid lubricant coating, resulting in a false pass / fail judgment of the lubrication behavior. Consequently, it is often the case that the solid lubricant coating design is poorly designed only after the pipe is applied to an actual well. Furthermore, unless a "backlash" is intentionally created before the threads engage, it is impossible to simulate what actually occurs in a well. On the other hand, it is not practical to use full-size pins to test in actual wells or simulated wells (laboratory sites where full-size pins are used for tightening and tightening tests). This would require enormous experimental costs, making it unrealistic. The latter method requires rental fees of over 10 million yen per day, and even for solid lubrication tests, the maximum number of tightening and tightening cycles for small diameter pipes is estimated to be 10 to 20, which would be extremely expensive.

[0033] Most past patent documents do not take such considerations into account when evaluating solid lubricant coatings. Furthermore, there is no specific information about the lubrication evaluation of threads, and many applications involve horizontal tongs, as is common in laboratories, or vertical tongs using short pins. Evaluations using these methods eliminate the effects of the large and unbalanced loads mentioned above, so generally, most results are favorable. Therefore, even if these evaluation methods define favorable upper and lower limits, they do not represent truly favorable ranges. Even under conditions selected in laboratory short pin evaluations, actual wells may experience conditions that do not result in favorable lubrication, and so the technology cannot be considered specific.

[0034] Although this is not an investigation into the lubrication behavior of a solid lubricant coating, in Non-Patent Document 1, a load of 510 kg is continuously applied throughout the entire process, both when tightening and loosening a screw. This may mean applying 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 uneven loads that occur in actual wells. This is because secondary phenomena caused by secondary products derived from the solid lubricant coating have a significant effect on lubrication. However, in Non-Patent Document 1, depending on the size, it is difficult to say that a large load was necessarily simulated.

[0035] Furthermore, Non-Patent Document 1 fails to simulate an unbalanced load. Judging from Figure 1 in Non-Patent Document 1 and other figures, especially for premium joints, less than one full rotation is required before tightening. This poses a problem in that the initial tightening position (tightening start point) by hand is intended to test lubrication from a state where the threads are fully engaged. While it may be difficult to notice, continuing the above load during tightening can lead to the following problem. Specifically, while this is a pitfall in laboratory evaluation, we discovered that during tightening, the weight acts as a balancer, allowing the screw to loosen straight from the initial tightening position without any rattle. This prevents the pin from swinging, making it impossible to properly simulate the seizure that occurs during tightening in an actual well. Depending on the circumstances, this could lead to a false impression that the lubrication properties are good. Therefore, the condition parameters for the solid lubricating coating must be determined by taking into account both the lubrication conditions when the threads are not fully engaged and the lubrication conditions after engagement to demonstrate superior lubrication properties.

[0036] For the lubrication of oil well pipe threads that use solid lubricant coatings, it is necessary to achieve a level of lubrication equivalent to that achieved by conventional compounds by specifying and optimizing the binder resin and the solid lubricant used as an additive within the binder resin. However, conventional evaluations of solid lubricant coatings have not been conducted under the conditions encountered in actual wells, as described above. In other words, it is necessary to specify the optimum range for solid lubricant coatings using a test method that reflects the above points. However, such laboratory testing has not been conducted to date.

[0037] The present invention has been made in light of the above-mentioned points, and aims to achieve, using a solid lubricating coating, seizure resistance (galling resistance) that is equivalent to or better than that achieved by the conventional dope compound method, with regard to the lubrication characteristics during make-up and make-back of oil country tubular goods.

[0038] The present disclosure relates to a method that has not received much attention in the past, in which a solid lubricant coating is formed using MCA (melamine cyanurate) as the main component, with a binder resin consisting primarily of nitrocellulose and alkyd resin. Furthermore, in light of the above-mentioned problems, the inventors conducted research and discovered that the above-mentioned problems can be solved by compounding the agent, developing a solid lubricant coating on oil country pipe threads, and developing a method for verifying this.

[0039] We have learned that the key points are to control the following four conditions and related factors within the optimum ranges: (a) To specify the upper and lower limits of each parameter and clarify the optimum ranges by confirming them through actual well tightening or by using an appropriate test method that simulates tightening and tightening back in an actual well; (b) To use the above (a) to specify the optimum range for the main solid lubricant, MCA (melamine cyanurate); (c) To use the above (b) to specify the optimum ranges for the main nitrocellulose and alkyd resin; (d) To specify other additives, plasticizers, solvents, etc.

[0040] Based on the above findings, and in order to solve the problems, 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 main component of the solid lubricant being melamine cyanurate, the melamine cyanurate having an average particle size of 0.1 μm or more and 10.0 μm or less, the binder resin containing an alkyd resin and nitrocellulose, the alkyd resin and nitrocellulose comprising 85 wt % or more of the total binder resin component weight, and the total weight of the solid lubricant being 10 parts by weight or more and 100 parts by weight per 100 parts by weight of the total binder resin weight.

[0041] Another aspect of the present invention is an oil country tubular good having a lubricating coating formed on a thread portion thereof, wherein the lubricating coating is formed on a fastening surface of the thread portion of at least one of the box and the pin, the solid lubricating coating being constituted by dispersing a solid lubricant in a binder resin, the main component of the solid lubricant being melamine cyanurate, the melamine cyanurate having an average particle size of 0.1 μm or more and 10.0 μm or less, the binder resin containing an alkyd resin and nitrocellulose, the alkyd resin and nitrocellulose comprising 85 wt % or more of the total binder resin component weight, and the total weight of the solid lubricant being 10 parts by weight or more and 100 parts by weight or less, relative to 100 parts by weight of the total binder resin weight.

[0042] According to an aspect of the present invention, it is possible to provide a solid lubricating coating that uses MCA as a solid lubricant and is capable of imparting good lubricity and corrosion resistance to oil country pipe threads. For example, according to an aspect of the present invention, it is possible to obtain an oil country pipe threaded joint that has lubrication performance and corrosion resistance during make-up, 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 in which the weight of the pin is applied from above to the box, a load is applied obliquely due to misalignment of the axis, and there are many situations 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. After extensive research, the inventors have found that make-up and loosening with a solid lubricating coating can be divided into two lubrication phases, and that the conditions occurring in each phase must be taken into consideration.

[0045] <About Figure 2> Figure 2(a) is an example of a torque turn chart generated in an actual well. The conditions in Figure 2(a) are a simulation of an actual well, and are a torque turn chart (tightening chart) obtained when a tightening test was conducted using a pin with an actual length of 40 feet (≒12 m). In actual oil and gas fields, tightening often begins when the threads are not fully engaged with each other. In consideration of this situation, Figure 2(a) shows an example in which tightening was started from an initial set position where the pin thread was exposed to about half its full length at the start of initial tightening, as shown in Figure 2(b). The pin used was a 9-5 / 8" 53.5 #Q125 JFELION ＴＭ In order to simulate an actual well, a pin with a length of about 40 feet (a pin with the length of Range-3) was used.

[0046] Figure 2(a) shows the chart when the entire length of the pin is being tightened with vertical tongs while being suspended from above the rig by a crane. Figure 2(a) can be considered to represent the situation that often occurs in actual wells. This torque-turn chart can be interpreted by dividing it into two phases. "Phase 1" refers to the region of tightening and loosening when the threads of the box and pin are not fully engaged. "Phase 2" refers to the region where the threads engage and a steady torque begins to build up, and the torque increases in response to tightening.

[0047] What is noteworthy about Figure 2(a) is that, in principle, torque should not be generated before the point where torque continuously increases (in Figure 2(a) the region where the rotation speed is 6.3 rpm or less: Phase 1). However, in reality, spike-like torque tends to be generated irregularly and frequently in Phase 1. This suggests that in the Phase 1 region, the pin threads are in irregular and localized contact with the box threads as they rotate. This is the situation that occurs during actual tightening in wells. This also means that, depending on the design and optimization of the solid lubricant coating, it is inevitable to some extent that the solid lubricant coating will be destroyed and peeled off in Phase 1. It should be emphasized here that the condition in Figure 2(a) was not intentionally created to be the worst case scenario; rather, it is a perfectly normal torque-turn chart of a sample with a solid lubricant coating.

[0048] <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 Figure 2. Figure 3 uses a pin with the same outer diameter, wall thickness, and thread type as Figure 2, but a short pin approximately 1 m long. In this case, the weight of the short pin, equivalent to 100 kg, is applied to the box thread. Figure 3(a) is also a torque turn chart for when tightening is initiated after the threads are fully engaged. That is, it is a torque turn chart for when the pin threads are exposed approximately 1 to 3 threads at the start of initial tightening, as shown in Figure 3(b). The conditions shown in Figure 3(a) are also commonly used in conventional laboratory tightening tests, and represent an example in which the screw is tightened by hand until it engages. In short, compared to the case in Figure 2, this is a case where the load is small (no effect of a large load) and there is no initial screw runout (no effect of an unbalanced load).

[0049] It should be noted that the units on the horizontal axis are different in Figure 3(a) compared to Figure 2(a). In Figure 3(a), tightening with the tongs begins after the threads have been hand-tightened until they are fully engaged, so the spike-like torque seen in Figure 2(a) is not observed. As can be seen from Figure 3, in conventional laboratory tests, the position at which the threads are hand-tightened until they engage is often used as the initial position for tightening with the power tongs. As a result, there is no behavior in Phase 1 until the threads engage. For this reason, conventional laboratory tests are conducted under conditions that do not cause breakdown of the solid lubricating coating, which would occur before the threads engage (conditions without Phase 1), in other words, tests that only evaluate tightening and loosening in the region of Phase 2 after engagement.

[0050] <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) is the example of Figure 2, and Figure 4(b) is the example of Figure 3. According to the inventors' studies, when considering use in actual 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, some spikes are acceptable. This is a situation in which the solid lubricant coating is damaged. In this case, it is preferable to design the solid lubricant coating so that secondary products from broken or peeled solid lubricant coatings do not clog the thread gap during the make-up and unmake-up process, but rather adhere well to the threads and assist lubrication.

[0051] Judging from the results of make-up and tightening tests, many previous documents appear to focus on lubrication after the threads engage (Figures 4(b) and 3(a)). This appears to be related to the lubrication that occurs after the threads engage, i.e., the lubrication properties of the solid lubricant coating itself. For this reason, it is assumed that a short pin and horizontal or vertical tongs are used to manually tighten the threads until they engage, and then the screw is tightened and tightened. Among patent documents that specify the number of times the screw is tightened and tightened, some state that small diameter sizes can be tightened and tightened up to 10 times in actual wells. This appears to be a reasonable number, both in evaluations using short pins and in actual wells. On the other hand, there are also occasional statements 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 tightened and tightened up to 15-20 times. However, this is almost never the case in actual well tightening and tightening, especially in large diameter cases where solid lubricant coatings are used.

[0052] Furthermore, large-diameter oil well pipe threads generally have higher tightening torque values ​​and more play (backlash) between the box thread and the pin thread. This inevitably leads to some degree of breakdown and peeling of the solid lubricant coating before the threads are fully engaged. Furthermore, at the beginning of the test, when the pin thread is set into the box thread, the pin is heavy and difficult to handle. For this reason, there is a certain frequency of the pin thread accidentally hitting the box thread, which also breaks and peels off the solid lubricant coating. This embodiment was developed by devising a new laboratory test with an eye to the actual tightening and tightening conditions in wells and by referring to the evaluations obtained from that new laboratory test.

[0053] Here, an appropriate method for simulating the make-up and make-back behavior of OCTG threads in an actual well is to simulate the make-up behavior that occurs when OCTG threads are made in an actual well. This method is used to confirm the upper and lower limits of the parameters disclosed herein and determine suitable ranges. The lubrication of OCTG threads must be evaluated based on what will occur in an actual well. To do this, the only options are to simulate what may occur in an actual well or to evaluate using an actual full-length pin. The make-up and make-back process of OCTG threads can be divided into two stages. The pin thread is inserted into the box thread and turned as is, or, to avoid cross-threading, the threads are turned by hand until they are sufficiently engaged. However, there are two stages: one where the threads are not fully engaged and torque is generated, i.e., until the threads are fully engaged, and another stage after the threads are fully engaged. The former is not a common situation when considering normal friction and sliding. The latter, where a constant load is not applied, is a commonly assumed situation when it comes to friction. In the former case, tightening and loosening are performed at 5 to 25 rpm. After torque builds up, tightening and loosening are performed at a slower speed of less than 1 rpm to a maximum of around 3 rpm. In actual wells, the pin is set suspended from above, so the pin's own weight is applied to the box screw at most. This is called a heavy load. Also, while the pin appears upright when tightened and loosened from a distance, in reality, due to thread play, it is tightened and loosened eccentrically until the threads are fully engaged. This is called an unbalanced load. In particular, in areas where the threads do not mesh, the solid lubricant coating is easily damaged, causing parts to peel off. For this reason, the solid lubricant coating itself is designed based on solid lubricants, binder resins, and other specifications to prevent the peeled pieces from clogging the gaps in the threads or becoming seized.

[0054] The present invention was completed by defining suitable ranges for each of the above-mentioned components. Furthermore, the film evaluation was based on the situations that may occur in an actual well, taking into account backlash (play) and heavy load application conditions, and evaluating and judging the lubrication.

[0055] (Configuration) This embodiment is an invention relating to a coating structure formed on the fastening surfaces of oil country tubular goods threads actually used in oil and gas, and a threaded joint having that coating structure as a lubricating coating. This embodiment is characterized by a lubricating coating comprising a solid lubricating coating formed on the fastening surfaces of a threaded joint, and there are no particular limitations on the thread structure of the threaded joint itself. The thread structure of the threaded joint may be any known or novel thread structure.

[0056] <Oil country tubular goods and oil country tubular goods threaded joints> Oil country tubular goods (OCG) are composed of a box 2, such as a coupling, and a pin 1, as shown in Figure 1. As shown in Figure 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. 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. The following explanation will focus on the box thread (female thread side) and the pin thread (male thread side). This includes both T&C (Threaded & Coupled) type joints for oil country tubular goods and integral type joints.

[0057] <Chemicals> The chemicals used to form a solid lubricant coating in this embodiment will now be described. The chemicals in this embodiment are composed of one or more solid lubricants dispersed in a binder resin as a matrix component. The main component of the solid lubricant is melamine cyanurate, and the average particle size of the melamine cyanurate is 0.1 μm or more and 10.0 μm or less. A solid lubricant whose main component is melamine cyanurate means that, for example, 80 wt % or more, preferably 90 wt % or more of the total weight of the solid lubricant is melamine cyanurate.

[0058] The total weight of the solid lubricant is 10 parts by weight or more and 100 parts by weight or less, when the total weight of the binder resin is 100 parts by weight. The binder resin contains an alkyd resin and nitrocellulose. The alkyd resin and nitrocellulose account for 85% by weight or more of the total binder resin component weight. The weight of the nitrocellulose is preferably 0.5 times or more and 3 times or less the weight of the alkyd resin.

[0059] The solvent contained in the agent is one or more materials selected from mineral spirits, aromatics, alcohols, ester solvents, and ketone solvents. Examples of aromatics include mineral spirits, toluene, xylene, naphtha, and benzene. Examples of alcohols include ethanol, propanol, isopropanol, and butanol. Examples of ester solvents include butyl acetate, methyl acetate, and isobutyl acetate. Examples of ketone solvents include methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and acetone.

[0060] The weight of the solvent is, for example, 20% to 80% of the total weight of the solid lubricant and the binder resin. The oil length of the alkyd resin is, for example, 10 to 60. The agent may also contain a plasticizer. The plasticizer is, for example, one or more materials selected from dibutyl phthalate (DBP), dimethyl phthalate (DMP), and diethyl phthalate (DEP). When a plasticizer is contained, it is, for example, contained in an amount of 10 parts by weight to 20 parts by weight per 100 parts by weight of nitrocellulose.

[0061] <Coating Structure of Oil Well Tubular Goods Thread> The coating structure of an oil well tubular good thread in this embodiment will now be described. A lubricating coating comprising a solid lubricating coating is formed on the fastening surface of the threaded portion of at least one of the box and the pin. The solid lubricating coating is constituted by a solid lubricant dispersed in a binder resin as a matrix component. The main component of the solid lubricant is melamine cyanurate, and the average particle size of the melamine cyanurate is 0.1 μm or more and 10.0 μm or less. The binder resin contains an alkyd resin and nitrocellulose. The alkyd resin and nitrocellulose account for 85 wt % or more of the total weight of the binder resin components.

[0062] The total weight of the solid lubricant is 10 to 100 parts by weight per 100 parts by weight of the total weight of the binder resin, and the thickness of the solid lubricant coating is 10 to 150 μm. The lubricant coating may have an underlayer 10B between the fastening surface and the solid lubricant coating ( FIG. 7( b) ). The underlayer 10B may be, for example, a manganese phosphate chemical conversion coating, a zinc phosphate chemical conversion coating, or an electroplated film containing one or more metals selected from Cu, Sn, and Zn. The solid lubricant coating has, for example, a pencil hardness of 2B or greater.

[0063] <Oil country tubular goods threaded joint> A lubricating coating comprising the above-mentioned solid lubricating coating is formed on the fastening surface of the threaded portion of at least one of the box and the pin. Alternatively, a lubricating coating comprising the above-mentioned solid lubricating coating is formed on the fastening surface of the threaded portion of one of the box and the pin. Meanwhile, a second solid lubricating coating softer than the above-mentioned solid lubricating coating is formed on the fastening surface of the threaded portion of the other of the box and the pin.

[0064] The second solid lubricating coating is formed, for example, by dispersing a second solid lubricant in a second binder resin as a matrix component. The second binder resin is primarily composed of a fluorine-based organic compound. The second solid lubricant component is composed of one or more compounds using a material selected from the fatty acids in the following Group X and a material selected from the metal elements in the following Group Y. Group X: stearic acid, isostearic acid, behenic acid, lauric acid, 12-hydroxystearic acid Group Y: Li, Na, Mg, Al, Ca, Zn, Ba The solvent contained in the agent for forming the second solid lubricating coating is, for example, a fluorine-containing solvent in the following Group Z, which accounts for 90% or more of the solvent component weight. Group Z: HFC, HFE, HFO The second solid lubricating coating preferably has a pencil hardness of 3B or less.

[0065] Here, the inventors simply selected MCA as the solid lubricant and a binder resin consisting of nitrocellulose and alkyd resin as the binder resin, and created a solid lubricant coating using these as the main components. In this case, they discovered that when they actually performed a tightening / untightening test, some components seized and some did not, resulting in completely unpredictable results. In other words, simply combining materials based on published inventions did not necessarily achieve the lubrication achieved by conventional lubricating compounds. Therefore, even if they used previous inventions as an analogy, it was not necessarily possible to reproduce good lubrication.

[0066] In this embodiment, a new laboratory testing evaluation method was devised that allows evaluation under conditions equivalent to those of an actual well, as will be described later, and tests were carried out using this evaluation method. Referring to the test results, the inventors discovered a solid lubricating coating with improved seizure resistance that can withstand use in an actual well, as well as suitable ranges for each agent, covering an expanded range that also includes oil well pipe threaded joints and metallic materials, and thus completed the present invention. This will be explained in further detail.

[0067] <Basic Structure and Film Thickness of the Solid Lubricant Coating> The solid lubricant coating of this embodiment is composed of a solid lubricant primarily composed of MCA (melamine cyanurate) dispersed in a binder resin consisting of alkyd resin and nitrocellulose. The suitability of this combination was determined through numerous experiments using newly devised laboratory tests. The reasons for selecting MCA as the primary component of the solid lubricant are as follows: It is an excellent lubricant that provides high lubrication, and it can maintain high lubrication even when there is some seizure and localized high temperatures. During tightening and loosening, the pin thread and box thread may rub against each other, generating frictional heat to some extent, but this is to maintain sufficient lubrication even during such times.

[0068] The binder resin consisting of alkyd resin and nitrocellulose was selected for the following reasons. The selection of alkyd resin and nitrocellulose represents a horizontal expansion of technology from lacquer paint. Lacquer paint has the advantage that it can be cured at room temperature and pressure without heat treatment if an alkyd resin with the appropriate oil length is selected. This makes film formation easy and allows for multiple coats. Furthermore, there are no particular problems with mixing the above-mentioned MCA into lacquer paint.

[0069] It is desirable to obtain a binder resin film that is as hard as possible. A pencil hardness of approximately HB to 2H is desirable. Furthermore, the binder resin must be brittle enough to prevent peeling that involves the removal of most of the resin (complete peeling), rather than gradual chipping. The solid lubricating coating must be formed to a minimum thickness of 10 μm. A thickness of 10 μm or more can maintain both lubrication properties and corrosion resistance. It is difficult to generalize the upper limit of the film thickness because the gap between the box thread and the pin thread varies depending on the type and design of the oil well pipe thread. In this embodiment, the upper limit is set to 150 μm, for example. Since many oil well pipe threads are designed with a gap between the threads of approximately 100 to 200 μm, the upper limit is set to 150 μm. A film thickness of 10 to 50 μm is more preferable.

[0070] As mentioned above, the gap between the crest and valley of male and female threads may be 100 to 200 μm. However, the gap between the stabbing flanks and the load flanks of male and female threads changes when tightening and loosening. When the gap narrows, the threads are almost tightly fitted. Therefore, a smaller film thickness is preferable, with a preferred range of 10 μm to 50 μm. However, these film thicknesses refer to the film thickness in the as-formed state before the first tightening. When tightening and loosening, some of the binder resin is scraped off, and the film thickness applied at room temperature is actually crushed and becomes a thin film. Therefore, even if the gap is thicker than expected in an actual well, this does not cause problems such as seizure.

[0071] <About the Solid Lubricant> The solid lubricant contains one or more solid lubricants. The solid lubricant contains 80% by weight or more of melamine cyanurate (MCA). The average particle diameter of the melamine cyanurate is 0.1 to 10.0 μm. In this embodiment, a solid lubricant composed primarily of MCA is dispersed within a binder resin. The elements of the present disclosure are that MCA accounts for 80% of the total weight of the solid lubricant as the denominator, and that the average particle diameter of the MCA is 0.1 μm or more and 10.0 μm or less. These specifications mean that a broad range of MCA cannot always achieve a highly lubricating state. Therefore, in order to achieve high lubricity in the operating environment of oil country pipe threads, and for the MCA dispersed in the epoxy resin, which is the binder resin used in the present disclosure, using it within this range is optimal, and significantly high lubricity can be expected.

[0072] The smaller the average particle size of the MCA, 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 or the like. A more preferable range is preferably 2 μm or less. When an MCA with an average particle size of 2 μm or less is selected, coarse MCA particles of approximately 10 to 20 μm may be included in rare cases. The reason for specifying a more preferable range is to eliminate concerns about seizure caused by the inclusion of coarse MCA particles. The term "80 wt % or more of the solid lubricant" means that MCA constitutes the majority of the solid lubricant. Furthermore, this definition means that, when the total weight of the solid lubricant is used as a modulus, even if less than 20% of other solid lubricants are included, there is no adverse effect in an MCA-based design.

[0073] In the present disclosure, the higher the proportion of MCA in the solid lubricant, the better. Since the lubricity may be impaired by the addition of other components to MCA, the range in which MCA can be the main component is set to 80% or more. Other solid lubricants that can be expected to be mixed at a maximum of less than 20% include, for example, BN, which has the same white tone, and PTFE, which has excellent lubricity. Other solid lubricants include graphite, graphite fluoride, and MoS. ２ , W.S. ２Examples of the lubricant include cellulose, mica, and talc. An oil-based substance may also be mixed in as a type of solid lubricant. For example, carnauba wax, PFPE oil (perfluoropolyether), CTFE oil (low polymer of chlorotrifluoroethylene), etc. may be mixed in. By mixing in an oil-based substance, the lubrication of the MCA can be maintained or improved.

[0074] <Binder Resin Component> The binder resin component includes an alkyd resin and nitrocellulose, with this combination comprising 85% or more by weight of the total binder resin component. Preferably, the proportion of nitrocellulose is 0.5 to 3 times the weight of the alkyd resin. Preferably, the oil length of the alkyd resin is 10 to 60. For example, one or more types of phthalate esters may be mixed as a plasticizer. In this case, it is preferable to contain 10 to 20 parts by weight of phthalate esters per 100 parts by weight of nitrocellulose. Examples of suitable phthalate esters include dibutyl phthalate (DBP), dimethyl phthalate (DMP), and diethyl phthalate (DEP).

[0075] In this embodiment, so-called nitrocellulose lacquer was used as a binder resin component. Nitrocellulose lacquer is a compound made by dissolving compatible nitrocellulose and alkyd resin in a fast-drying solvent. When applied, the solvent evaporates from the surface, resulting in a hard film. Although nitrocellulose lacquer films are hard, they are also brittle and require a certain degree of flexibility. Adding alkyd resin improves film quality. In this case, the alkyd resin is between 0.5 and 3 times the weight of the nitrocellulose component. If it is less than 0.5 times, the brittleness becomes pronounced. Furthermore, when tightening and loosening oil well pipe threads, they are prone to peeling, resulting in a high tendency for seizure. If it exceeds 3 times, small cracks are more likely to occur in the binder resin film.

[0076] In this embodiment, the primary usage scenario is assumed to be that the agent will form a film upon natural drying after application. Therefore, it is preferable for the alkyd resin to have an oil length of 10 or more but less than 60. If the oil length is less than 10, heat treatment is required to form a film. If the oil length exceeds 60, the viscosity will be too high, potentially causing clumping and uneven application when brushed or sprayed. Furthermore, a long oil length is undesirable because it directly reduces the strength of the alkyd resin. As mentioned above, nitrocellulose is hard but also brittle. For this reason, an alkyd resin is mixed to form a resin film. Furthermore, to overcome this brittleness, it is preferable to incorporate one or more types of phthalate esters as a plasticizer. The plasticizer should be present in an amount of 10 to 20 parts by weight per 100 parts by weight of nitrocellulose. Even at this level, surface cracking can be minimized.

[0077] On the other hand, nitrocellulose is susceptible to ultraviolet light. Therefore, it is preferable to avoid direct sunlight on the surface coated with a solid lubricant coating. Therefore, it is preferable to form the solid lubricant coating on the box thread side. When applying the solid lubricant coating of this embodiment to the pin thread side, it is recommended to use it with a protector attached. In either case, it is also acceptable to add a trace amount of an oxybenzone-based ultraviolet absorbing agent, of 5 parts by weight or less per 100 parts by weight of nitrocellulose, to protect against ultraviolet light. In addition, additives for adjusting the drying properties and liquid viscosity of the agent as a whole and for adjusting the hardness of the solid lubricant coating, as well as solvents that do not remain in the solid lubricant coating after drying, may be added.

[0078] <About the Solvent> The chemical agent contains a solvent. The solvent may be, for example, one or more of mineral spirits or alcohols such as toluene, xylene, naphtha, benzene, ethanol, propanol, isopropanol, or butanol. In this embodiment, the intended drying property of the applied chemical agent is rapid. For this reason, it is preferable to dissolve the coating components (nitrocellulose, alkyd resin, MCA, etc.) in a highly volatile organic solvent. Rapid drying here refers to the ability of the film to harden after approximately five minutes of natural exposure. Depending on the circumstances, air blowing or other methods may be used during film formation. The weight of the solvent is preferably 20% to 80% of the total weight of the binder resin, primarily composed of nitrocellulose and alkyd resin, and the total weight of the solid lubricant, primarily composed of MCA. If the weight exceeds 80%, the chemical solution itself becomes thin, making it difficult to apply, and the drying time is excessive. This makes it difficult to use. If the concentration is less than 20%, the viscosity of the liquid will be too high, making it difficult to apply the liquid evenly.

[0079] <Composition ratio of solid lubricant and binder resin> When the total weight of the binder resin is 100 parts by weight, the total weight of the solid lubricant is 10 parts by weight or more and 100 parts by weight or less. When the total weight of the binder resin, primarily composed of nitrocellulose and alkyd resin, is 100 parts by weight, the solid lubricant primarily composed of MCA must be specified as described above. If the solid lubricant is less than 10 parts by weight, the amount of lubricant is too small, resulting in insufficient lubrication and early seizure. Conversely, if the solid lubricant is more than 100 parts by weight, the amount of solid lubricant is too large. In other words, if too much solid lubricant is embedded in the binder resin composed of nitrocellulose and alkyd resin, the binder resin itself becomes brittle. This also results in excessive peeling of the coating during fastening, increasing the risk of seizure. Therefore, it is necessary to adjust the solid lubricant content within the above range.

[0080] <Film Hardness of Solid Lubricant Coating> The solid lubricant coating preferably has a pencil hardness of 2B or higher. Considering the lubrication behavior of a solid lubricant coating in an actual well, the solid lubricant coating is prone to damage during the behavior until the threads engage, i.e., when the OCTG threads are tightened with backlash present. However, by increasing the film hardness, damage can be minimized. Specifically, a hard film of 2B or higher prevents the solid lubricant coating from being scraped off. In this embodiment, the solid lubricant coating is made hard. This ensures that the film is not brittle and maintains lubrication so that it does not break down completely during tightening. Therefore, it is recommended to use nitrocellulose and alkyd resin as the main components and adjust the hardness of the binder resin to 2B or higher. As described above, this hardness can be adjusted by adjusting the ratio of nitrocellulose to alkyd resin and the particle size and concentration of MCA.

[0081] The pencil hardness evaluation is measured according to the method specified in JIS K 5600-5-4 (1999). The JIS standard 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 film hardness was evaluated by pencil hardness is that the pencil hardness test method evaluates "scratching" with a pencil, and this film hardness evaluation method is caused by "scratching," similar to the behavior of solid lubricant coating peeling between the male and female threads of oil country pipe threads. Indentation-based film hardness measurement methods such as Rockwell, Vickers, Shore, and Knoop, which are sometimes used for coatings, are used in this disclosure because coatings are thin and are affected by the substrate.

[0082] <Other Provisions> The solid lubricating coating 10A may be formed directly on the substrate steel (fastening surface) (see FIG. 7(a)). Alternatively, as shown in FIG. 7(b), the solid lubricating coating may be formed after forming a base layer 10B. The presence of such a base layer can improve the adhesion of the solid lubricating coating. Examples of base layer 10B include a manganese phosphate conversion coating, a zinc phosphate conversion coating, and an electroplated film containing at least one of Cu, Sn, and Zn.

[0083] <When the above solid lubricating coating is formed on only one of the opposing fastening surfaces> The above solid lubricating coating may be formed on both the pin thread and the box thread of an oil country pipe thread, or on only one of them. When the above solid lubricating coating is formed on only one side, the fastening surface of the other thread may be left as machined or may have a shot-blasted texture. Alternatively, a second soft solid lubricating coating may be formed on the fastening surface of the other thread.

[0084] [Second Solid Lubricant Coating] The second solid lubricant coating is formed, for example, by dispersing a second solid lubricant in a second binder resin as a matrix component. The second binder resin is primarily composed of a fluorine-based organic compound. The second solid lubricant component is made up of one or more compounds using a material selected from the fatty acids in the following Group X and a material selected from the metal elements in the following Group Y. Group X: stearic acid, isostearic acid, behenic acid, lauric acid, 12-hydroxystearic acid Group Y: Li, Na, Mg, Al, Ca, Zn, Ba The solvent of the agent used to form the second solid lubricant coating is, for example, a fluorine-containing solvent in the following Group Z, which accounts for 90% or more of the solvent weight. Group Z: HFC, HFE, HFO

[0085] The second solid lubricating coating is preferably soft, with a pencil hardness of 3B or less. While the aforementioned solid lubricating coating has a pencil hardness of 2B or more, it is preferable that the second solid lubricating coating be softer for the following reasons: That is, contact between hard and soft films can achieve more favorable friction than contact between hard objects. Specifically, as the soft film is scraped away, the solid lubricant can be expected to be constantly and gradually exposed and supplied, making it easier to achieve low friction.

[0086] <Lubrication Property Evaluation Method> In this embodiment, each material is specified from the perspective of achieving lubrication properties that can withstand the environment likely to occur in an actual well. Furthermore, the upper and lower limits were determined through confirmation (testing) under conditions that correspond to the tightening and tightening conditions in an actual well. The tightening and tightening conditions in a typical laboratory test, using horizontal and vertical power tongs with short pins, do not correspond to the actual conditions, and in the case of a solid lubricant coating, the conditions are too lenient. Therefore, it is meaningless to explain the upper and lower limits of each material based on evaluation using a typical laboratory test. Unless the conditions are extremely challenging, the number of tightening and tightening times will be judged as passing. In this disclosure, a new laboratory test that can simulate the conditions in an actual well was devised, and the new laboratory test was used to evaluate the material under conditions that correspond to those in an actual well. This new laboratory test is also called a deadweight tong test.

[0087] <Test method simulating actual well test conditions (new laboratory test (weight-tong test)> In this embodiment, as explained using Figures 2 to 4, the phenomenon that occurs in the lubrication of oil country pipe threads is considered to be divided into two stages: before the threads engage (Phase 1) and after (Phase 2). Then, a method was devised to comprehensively evaluate thread lubrication, taking into account the make-up and retightening (lubrication) in the first stage (Phase 1) and including the lubrication in the second stage (Phase 2). If this evaluation is not performed, it is very likely that frequent problems will occur in an actual well, even if the evaluation in the laboratory test is OK. In an actual well, a large load and an unbalanced load are applied before the threads engage. This can cause the solid lubricant coating to be damaged or peel off, and in severe cases, it may even be completely peeled off. Taking this into consideration, upper and lower limits of preferred ranges were selected for the parameters of this embodiment.

[0088] As mentioned above, damage to solid lubricating coatings is unavoidable during tightening until the threads engage. Secondary products are then formed based on the peeled off 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 parameters related to the solid lubricating coating and the selection of optimal ranges meaningless. In other words, accurate solid lubricating coatings cannot be achieved without considering whether the secondary products, or the reconstituted "secondary products," that are generated based on damage and peeling of the solid lubricating coating affect lubrication. In this embodiment, evaluation is performed using a new laboratory test that takes these findings into account.

[0089] 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 achieve 15-20 tightening and loosening cycles, even for large diameters such as 9-5 / 8" and 13-3 / 8". While these results show that the lubrication is slightly inferior to that of grease-like compounds, such a high number of tightening and loosening cycles is virtually impossible with solid lubricant coatings. These results are likely due to evaluations using horizontal or vertical power tongs with short pins, which are commonly seen in traditional laboratory testing. In actual well tightening and loosening tests using large diameter solid lubricant coatings, it is rare to see a tightening and loosening cycle of 15-20 cycles.

[0090] In this embodiment, testing was conducted 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 a large load during tightening and an offset load during tightening and loosening. For example, a large load equivalent to a full-size pin is applied to the joint, and the rattle that occurs before the threads engage during the tightening process is taken into consideration. Furthermore, the rattle that occurs during the loosening process due to the disengagement of the threads is also taken into consideration. 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 allow for the application and removal of a load from the weight 3 on top of the pin 1. The short screw 1 and box screw 2 are then tightened using the pin thread portion 1a and the box thread portion 2a.

[0091] 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 pins' outer diameter and thickness as the load equivalent to one to three actual size pins. For a 9-5 / 8" 53.5#, this is about a 1 ton load (2,200 lbs) per pin, and about 3 tons (6,600 lbs) for three pins connected together.

[0092] The weight 3 illustrated in FIG. 5 comprises 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 symbol 1c indicates the inner diameter surface of the pin 1. When the weight 3 is attached as described above, holes 1d and 13a are drilled in the bayonet rod 13 and the pin 1 to penetrate the pin 1 and the bayonet rod 13. Then, as shown in FIG. 6, a piercing rod 12 is inserted into the holes 1d and 13a to integrate the weight 3 and the pin 1. A swivel-type hook 11 is welded to the center of the weight body 3's upper shaft, and the weight 3 is suspended from a ceiling suspension device 20 via a hanging chain 21. This makes it possible to adjust the magnitude of the load of the weight on the pin by adjusting the degree to which the weight is lifted by the hanging device 20.

[0093] When tightening, the hanging chain 21 is loosened, the weight load is applied to the box screw, and the tightening is performed at 5 to 20 rpm until the torque is established (Phase 1). This is a simulation of backlash. Once the torque is established, the rotation speed is reduced to 0.5 to 2 rpm, and the tightening is performed to the tightened position (Phase 2). On the other hand, when loosening (re-tightening), the weight 3 is lifted by the hanging device 20, and the re-tightening is performed without applying the weight 3 load. As for the rotation speed, when the torque is established, loosening begins at a rotation speed of 0.5 to 2 rpm, and when the torque reaches about 1 / 10 of the tightening torque value, loosening is performed at a high speed of 5 to 20 rpm.

[0094] Here, not applying a load during loosening provides conditions closer to the environment of an actual well. This finding is based on experimental data showing that the lubrication characteristics were evaluated better when the load of the weight 3 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, allowing the pin to loosen straight and without rattle from the tightening completion position. On the other hand, consider a case where the weight was reduced, that is, a case where the load was lifted to bring the weight load to zero. In this case, they found that loosening the threaded joint with the load reduced, including cases where the load did not reach zero completely, allowed for testing under conditions that caused more rattle and were more likely to damage the solid lubricant coating.

[0095] In the new laboratory tests under the above conditions, it is possible to simulate a situation in which secondary products from solid lubricant coating-derived components, which are released into the thread gap due to unavoidable spalling, do not move with the tightening / retraction but instead become stuck in a certain location, causing seizure. It is also possible to simulate other situations in which the coating itself is completely peeled off. As a result, upper and lower limits for parameters related to the solid lubricant coating can be specified in accordance with actual well conditions. After retraction, the pin screw and box screw were separated, and debris from the solid lubricant coating on the surface was blown away with an air blower. The surface was then inspected and the retraction was resumed. This embodiment specifies the components and other factors to achieve lubrication properties that can withstand the conditions 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.

[0096] (Effects) In the field of lubrication using a solid lubricant coating for oil well pipe threads, this embodiment can simultaneously achieve high lubricity and corrosion resistance sufficient to withstand actual make-up in a well. This embodiment aims to simultaneously achieve high lubricity and corrosion resistance by using MCA as the main component of the solid lubricant and nitrocellulose and alkyd resin as the main components of the binder resin component. The solid lubricant coating of this embodiment can achieve lubrication properties and corrosion resistance comparable to those of conventional grease-like compounds for lubrication, anti-rust grease-like compounds for storage, and oil-like rust inhibitors. Furthermore, by specifying the molecular weights of the binder resin and solid lubricant that make up the solid lubricant coating, this embodiment can achieve lubrication performance during make-up comparable to that of conventional oil well pipe threads without using conventional compounds.

[0097] In this embodiment, for example, an oil well pipe threaded joint is obtained that has lubrication performance during make-up, taking into account actual well-equivalent conditions that may occur in an actual well environment. Note that actual well-equivalent conditions refer to conditions such as the pin weight being applied from above to the box (heavy load), a load being applied obliquely (unbalanced load) due to misalignment of the axis, and many situations in which the load is applied locally rather than uniformly. Furthermore, the application may be expanded beyond the lubrication of oil well pipe threads to other metal materials. Furthermore, the target is not only the film, but also the agent used to create the film.

[0098] (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 main component of the solid lubricant being melamine cyanurate, the melamine cyanurate having an average particle size of 0.1 μm or more and 10.0 μm or less, the binder resin including an alkyd resin and nitrocellulose, the alkyd resin and nitrocellulose comprising 85 wt % or more of the total binder resin component weight, and the total weight of the solid lubricant being 10 parts by weight or more and 100 parts by weight or less, relative to 100 parts by weight of the total binder resin weight.

[0099] (2) The weight of the nitrocellulose is 0.5 to 3 times the weight of the alkyd resin. (3) It contains a solvent, the solvent being one or more materials selected from mineral spirits, aromatics, alcohols, ester solvents, and ketone solvents, and the weight of the solvent is 20 to 80% of the total weight of the solid lubricant and the total weight of the binder resin. (4) The oil length of the alkyd resin is 10 to 60. (5) It contains one or more materials selected from dibutyl phthalate (DBP), dimethyl phthalate (DMP), and diethyl phthalate (DEP) as a plasticizer, and the plasticizer is contained in an amount of 10 to 20 parts by weight based on 100 parts by weight of the nitrocellulose.

[0100] (6) An oil country tubular good having a lubricating coating formed on a thread portion, the lubricating coating comprising a solid lubricating coating being formed on a fastening surface of the thread portion of at least one of the box and the pin, the solid lubricating coating being constituted by dispersing a solid lubricant in a binder resin, the main component of the solid lubricant being melamine cyanurate, the average particle size of the melamine cyanurate being 0.1 μm or more and 10.0 μm or less, the binder resin containing an alkyd resin and nitrocellulose, the alkyd resin and nitrocellulose comprising 85 wt % or more of the total weight of the binder resin components, the total weight of the solid lubricant being 10 parts by weight or more and 100 parts by weight or less per 100 parts by weight of the total weight of the binder resin, and the thickness of the solid lubricating coating (composed of the binder resin, solid lubricant, other additives, etc.) being 10 μm or more and 150 μm or less.

[0101] (7) The lubricating coating has a base layer between the fastening surface of the threaded portion and the solid lubricating coating, and the base layer is made of a manganese phosphate conversion coating, a zinc phosphate conversion coating, or an electroplated film containing one or more metals selected from Cu, Sn, and Zn. (8) The solid lubricating coating has a pencil hardness of 2B or greater. (9) 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 the oil country tubular goods on which the lubricating coating of the present disclosure is formed.

[0102] (10) A lubricating coating comprising the solid lubricating coating is formed on the fastening surface of the threaded portion of one of the box and the pin, and a second solid lubricating coating softer than the solid lubricating coating is formed on the fastening surface of the threaded portion of the other of the box and the pin. (11) The second solid lubricating coating is formed by dispersing a second solid lubricant in a second binder resin, the second binder resin being primarily composed of a fluorine-based organic compound, and the second solid lubricant being composed of one or more compounds using a material selected from the following Group X fatty acids and a material selected from the following Group Y metal elements: - Group X: stearic acid, isostearic acid, behenic acid, lauric acid, 12-hydroxystearic acid - Group Y: Li, Na, Mg, Al, Ca, Zn, Ba (12) The second solid lubricating coating has a pencil hardness of 3B or less.

[0103] Next, examples based on this embodiment will be described. First, the pass / fail criteria for lubrication behavior based on the number of make-up and loosening operations will be described. The criteria are as follows: For casing sizes, three or more make-up and loosening operations were considered pass, and five were considered better. For tubing sizes, five or more were considered pass, and ten or more were considered even better. The casing size specifications are in accordance with ISO 13679. For tubing, five or more operations, which is lower than the ISO 13679 specification, were considered pass. It is clear that the number of make-up and loosening operations tends to be worse due to the solid lubricating coating compared to lubrication using conventional grease-like compounds, and this fact is becoming recognized in the oil and gas industry. As mentioned above, if a short pin were simply used to perform a tightening and loosening test from the point where the threads engage, the requirements of ISO 13679 would be an easy target, but this disclosure uses a new laboratory test (weight-tongs test) to evaluate under conditions of large load and unbalanced load, which are close to the conditions that can actually occur in a well, and to simulate conditions where there is play and the threads do not engage, and therefore this standard was used.

[0104] The load applied by the weight tongs was a 1 ton weight, with 9-5 / 8" being the equivalent of a full-size piece. The weight was attached to the top of the pin screw. The initial tightening position was set to a position where 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, this example was carried out using the device shown in Figures 5 and 6.

[0105] In addition, the weight was applied during tightening. On the other hand, the test was conducted under conditions designed to prevent the weight from being applied during tightening. If a test were conducted under load during tightening, and a pin with an integrated weight and short pin was used, the short pin with the integrated weight would rise straight up from the tightening position, unlike the full-size pins used in actual wells. Because the weight acts as a balancer, there is no rattle. The pins used in actual wells are long and therefore slightly bent. For this reason, as the pin gradually becomes unsteady and the threads no longer mesh, rattle occurs, increasing the likelihood of destroying the solid lubricant coating.

[0106] Therefore, in the lubrication evaluation using weight tongs, no load was applied during unfastening, simulating the rattle that occurs when the threads approach a state where they no longer mesh. Also, not applying a load does not necessarily mean that the load is zero. The test was conducted by lifting the weight using an overhead crane or similar device, so that no load was applied. The test to check the number of times the weight tongs were used to unfasten was conducted more than twice. The pass / fail criteria were then determined by comparing the number of times achieved with the test score.

[0107] Example 1 In Example 1, lubrication property evaluation using weight tongs is described. Tables 1 to 4 show the conditions and evaluation results for each example. Note that a solid lubricating coating is also called a coating film. The second solid lubricating coating is also called a soft film coating.

[0108]

[0109]

[0110]

[0111]

[0112] Nos. 1 to 10 used high-strength carbon steel material: Q125. Nos. 11 to 15 used sour-resistant carbon steel material: C110. All examples use 9-5 / 8" 53.5# oil well pipe coupling threads and pin threads. The thread type is JFELION ＴＭ is.

[0113] <No. 1-10> [No. 1-No. 4] Cases No. 1-No. 4 are comparative evaluation results for different power tongs. Cases No. 1-No. 3 all have the same material parameters within the appropriate range. The only difference is the conditions for tightening and tightening the tongs. No. 1 uses horizontal tongs, No. 2 uses simple vertical tongs, and No. 3 uses vertical tongs but employs a new laboratory test with a weight attached (hereinafter referred to as the weight tong test). Additionally, No. 4 corresponds to the results of a tightening and tightening test using a Range-3 pipe (just over 12 m, approximately 40 ft) in a simulated well.

[0114] No. 1 is a case where more than 10 tightening / loosening cycles were possible (10 was the limit). No. 2 was limited to 7 tightening / loosening cycles. No. 3 was performed twice, with three and four tightening / loosening cycles possible. No. 4 was performed three times, with three, three, and four tightening cycles possible. In No. 1, the weight of the short pin screw is not applied to the coupling screw. At the same time, the axis is adjusted in No. 1, so there is no unbalanced load due to screw backlash. On the other hand, in No. 2, the weight of one short pin is applied to the coupling threads. For the size in this case, the weight of a 1-meter short pin is approximately 100 kg.

[0115] No. 3 simulates a condition in which a force of 1 ton, equivalent to the force of one full-size pin, is applied. Furthermore, in No. 3, as described above, the pin's set position is intentionally set in a partially tightened state, with approximately half of the pin threads exposed to the coupling screw, and tightening begins. This results in a state in which the threads do not mesh with each other, resulting in play, as occurs in actual wells. In other words, the tightening / retraction conditions simulate a condition in which the solid lubricant coating is damaged. No. 4 corresponds to tightening / retraction conditions that closely resemble the tightening conditions in an actual well. Nos. 3 and 4 are examples of the present invention.

[0116] Although Nos. 1 and 2 exceeded the pass mark in the number of tightening and tightening operations, they are comparative examples. Based on their results, Nos. 3 and 4 are examples that can be considered examples of the present invention. What Nos. 1 and 2 mean is that evaluation using a weight-bearing tong, which is similar to an actual well, would result in a lenient evaluation unless the upper and lower limits of the parameters specified in this disclosure are accounted for. In other words, the methods used in numerous patent documents to date result in a lenient evaluation of solid lubricant coatings. This suggests that conventional laboratory testing is not suitable as an evaluation method. It also means that the weight-bearing tongs testing method can simulate the conditions in an actual well.

[0117] As a reference experiment (not listed in the table) not included in this example, the following well experiment, which has been widely conducted, was also conducted under the same tong conditions as Nos. 1 to 4. Specifically, a manganese phosphate coating was formed on the coupling thread, and a grease-like compound, API-mod grade BOL-72733 from Best-O-Life, was applied to the pin threads with a shot-blasted surface, and then a tightening / untightening test was conducted. In this case, five or more tightening / untightening cycles were confirmed in each case, and no significant differences were observed. This indicates that the grease-like compound moves in conjunction with the tightening / untightening of the threads, and therefore is not as affected by the test method conditions (tong conditions) as a solid lubricant coating. Thus, it was found that tests to prove the significance of solid lubricant coating parameters must be conducted in actual wells, simulated well tests, or new laboratory tests (weight-tong tests).

[0118] [No. 5 to No. 8] No. 5 to No. 8 are examples compared under nearly identical conditions. These examples were primarily designed to examine variations in the thickness of the solid lubricant coating, the presence or absence of shot blasting, the presence or absence of plasticizer, and the presence or absence of a different solid lubricant coating on the pin thread side. No. 5 is an example in which the film thickness exceeded the upper limit of the present disclosure, but the other parameters were within the appropriate range. No. 5 is an example in which, due to the thickness of the film, material from the damaged solid lubricant coating clogged the thread gap during tightening and loosening, resulting in early seizure. No. 6 is an example in which the film thickness was within the appropriate range and a plasticizer was also added. No. 5 was one rank softer in pencil hardness, but was able to tighten and loosen more than specified, and therefore qualifies as an example of the present invention.

[0119] No. 7 is an example of the present invention, with a solid lubricant coating on the coupling thread under the same conditions as No. 6, but with a soft film formed on the pin thread side. In accordance with the present disclosure, a solid lubricant based on MCA was used, and a film was formed on the threads with a blend of nitrocellulose and alkyd resin within the ranges disclosed herein. By applying a soft solid lubricant coating to the thread surface of the mating material, the number of make-up and unmake cycles increased, which clearly improves the lubrication characteristics. No. 8 is an example of the present invention, with the solid lubricant coating thickness set to the upper limit of 150 μm. While No. 5, with a film thickness of 170 μm, could only be made up and unmake less than three times, No. 8 achieved an acceptable number of make-up and unmake cycles. This shows that the upper limit of film thickness is 150 μm.

[0120] [Nos. 9 and 10] Case No. 9 is an example of a solid lubricant consisting of 80 wt. % MCA and 20 wt. % BN. All parameters for Case No. 9 are within the preferred ranges, making it an example of the present invention. Case No. 10 is an example in which the proportion of MCA in the solid lubricant is lower than the specified ranges disclosed, and the average particle size of the MCA exceeds the specified ranges disclosed. Case No. 10 was an example in which the other specifications were within the preferred ranges, but seizure occurred early in the make-up / make-back test, making it a comparative example.

[0121] <Nos. 11-15> Nos. 12 and 14 were adjusted within a suitable range and are examples of the invention. On the other hand, Nos. 11, 13, and 15 are comparative examples. No. 11 is a case in which 20% melamine resin was added in addition to the components of nitrocellulose and alkyd binder resin, and the nitrocellulose was blended in a quantity exceeding the specified amount. This condition was one of the causes of the film brittleness in No. 11. While there was only one example of No. 11 in which the number of tightening and loosening operations exceeded five, the remaining two examples were less than three and are comparative examples. No. 13 is a case in which the amount of solid lubricant was too small compared to the binder resin, resulting in seizure and inability to maintain lubrication. Conversely, No. No. 15 is a case where the solid lubricant was blended in an amount exceeding the specified range, the blending ratio of nitrocellulose was lower than specified, and the oil length of the alkyd resin was greater than specified. No. 15 is a case where the number of tightening and loosening operations did not reach the specified number.

[0122] Nos. 12 and 14, whose parameters were within the ranges specified in this disclosure, required more tightening and loosening cycles than Nos. 11, 13, and 15. Comparing Nos. 1 to 15 revealed that the average particle size of the melamine cyanurate must be between 0.1 μm and 10.0 μm. It also revealed that the weight of the "alkyd resin and nitrocellulose" binder resin component must be at least 85 wt. % of the total binder resin weight. It also revealed that the total weight of the solid lubricant must be between 10 parts by weight and 100 parts by weight, assuming the total weight of the binder resin is 100 parts by weight. It also revealed that the thickness of the solid lubricant coating must be between 10 μm and 150 μm.

[0123] (Example 2) Several examples from Example 1 were selected and subjected to a salt spray test to confirm corrosion resistance. Among the cases shown in Example 1, Nos. 3, 6, and 14 were selected from the carbon steel-based OCTG screw conditions and subjected to salt spray testing. A new film was formed on the material for this salt spray test on the coupling sample. Furthermore, as a comparative example, a 0.8 mm thick SPCC (a thin steel sheet / cold-rolled annealed sheet of ordinary mild steel) was also used (Condition A).

[0124] The OCTG screw materials were used in two cases: one in which protectors were tightened and loosened once on both ends of the coupling thread (Nos. 3-2, 6-2, and 14-2), and the other with protectors reattached (corresponding to a second tightening: Nos. 3-3, 6-3, and 14-3). The samples were then lined up horizontally. In other words, the samples were lined up, not standing, and a salt spray test was carried out to conduct the corrosion test. For the pin threads, samples with only the threads were used, and the side with the threads was tightened and loosened once with a protector. The outside, where the protectors were not reattached, was covered with imide tape to prevent water from entering the pipe.

[0125] Detailed conditions are as follows. That is, the solid lubricant coating conditions for Nos. 3-2, 3-3, 6-2, 6-3, and 14-2, 14-3 correspond to those for Nos. 3, 6, and 14 in Example 1. The significance of this test method is that oil country pipe threads are shipped after their ends are tightened with protectors and are often stored in this state in a yard near the well. This is because the environment is close to the actual conditions of use. The conditions without a protector represent even more severe conditions when the protector is removed. The example of the SPCC thin plate is an example in which the thread is not tightened or loosened with a protector, and the corrosion resistance of the film itself is observed from the thread shape.

[0126] <Saltwater spray conditions> Spray conditions: JIS K 5600-7-1 Saltwater concentration: 5±0.5 wt% Temperature: 35°C Humidity: 98-99% Spray amount: 1-2 mL / hr / 80 cm ２ pH: 6.5 to 7.2 Time: 24 hours The results are shown in Table 5.

[0127]

[0128] As can be seen from Table 5, all of the comparative examples, including No. A, Nos. 3-2, 3-3, 6-2, 6-3, and 14-2, 14-3, were found to have sufficient corrosion resistance and not corrode in salt spray. The film quality is F or higher, making it hard and protective, and even when tightened and loosened, it does not sustain fatal damage. Furthermore, the main components of MCA, nitrocellulose, and alkyd are water-repellent, preventing water absorption. This is presumably a major factor.

[0129] The entire contents of Japanese Patent Application No. 2021-91464 (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.

[0130] DESCRIPTION OF SYMBOLS 1 Pin 1a Male thread 2 Box (coupling) 2a Female thread 3 Weight 3A Weight body 4 Power tong 10A Solid lubricant coating 10B Base layer 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 main component of the solid lubricant is melamine cyanurate, the average particle diameter of the melamine cyanurate is 0.1 μm or more and 10.0 μm or less, the binder resin includes an alkyd resin and nitrocellulose, and the alkyd resin and nitrocellulose account for 85% by weight or more of the total weight of the binder resin component, and the total weight of the solid lubricant is 10 parts by weight or more and 100 parts by weight or less with respect to 100 parts by weight of the total weight of the binder resin. A chemical characterized by this.

2. The chemical according to claim 1, characterized in that the weight of the nitrocellulose is 0.5 times or more and 3 times or less the weight of the alkyd resin.

3. Containing a solvent, the solvent is composed of one or more materials selected from mineral spirits, aromatics, alcohols, ester solvents, and ketone solvents, and the weight of the solvent is 20% or more and 80% or less of the total weight of the total weight of the solid lubricant and the binder resin. The chemical according to claim 1 or claim 2, characterized by this.

4. The chemical according to any one of claims 1 to 3, characterized in that the oil length of the alkyd resin is 10 to 60.

5. Containing one or more materials selected from dibutyl phthalate (DBP), dimethyl phthalate (DMP), and diethyl phthalate (DEP) as a plasticizer, and when the weight of the nitrocellulose is 100 parts by weight, the plasticizer contains 10 parts by weight or more and 20 parts by weight or less. The chemical according to any one of claims 1 to 4, characterized by this.

6. An oil well pipe having a lubricating coating 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 main component of the solid lubricant is melamine cyanurate, the average particle diameter of the melamine cyanurate is 0.1 μm or more and 10.0 μm or less, the binder resin includes an alkyd resin and nitrocellulose, and the alkyd resin and nitrocellulose account for 85% by weight or more of the total weight of the binder resin components, the total weight of the solid lubricant is 10 parts by weight or more and 100 parts by weight or less with respect to 100 parts by weight of 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. An oil well pipe characterized by the above.

7. The lubricating coating has an underlayer between the fastening surface of the threaded portion and the solid lubricating film, and the underlayer is composed of a manganese phosphate conversion coating, a zinc phosphate conversion coating, or an electroplated film containing one or more metals selected from Cu, Sn, and Zn. The oil well pipe according to claim 6, characterized by the above.

8. The solid lubricating film has a hardness of 2B or more in terms of pencil hardness. The oil well pipe according to claim 6 or claim 7, characterized by the above.

9. An oil well pipe thread joint connecting a box having a female thread and a pin having a male thread, wherein at least one of the oil well pipes of the box and the pin is composed of the oil well pipe with the above lubricating coating described in any one of claims 6 to 8. An oil well pipe thread joint characterized by the above.

10. A lubricating coating with the solid lubricating film is formed on the threaded portion of one of the box and the pin, and a second solid lubricating film softer than the solid lubricating film is formed on the threaded portion of the other of the box and the pin. The oil well pipe thread joint according to claim 9, characterized by the above.

11. The second solid lubricating coating is composed of the second solid lubricant dispersed in the second binder resin. The second binder resin is mainly composed of a fluorine-based organic compound. The second solid lubricant is composed of one or more compounds selected from the materials selected from the fatty acids in the following Group X and the materials selected from the metal elements in the following Group Y. The oil well pipe thread joint according to claim 10, characterized in that: - Group X: stearic acid, isostearic acid, behenic acid, lauric acid, 12-hydroxystearic acid - Group Y: Li, Na, Mg, Al, Ca, Zn, Ba 12. The oil well pipe thread joint according to claim 10 or claim 11, characterized in that the second solid lubricating coating has a pencil hardness of 3B or less.