Threaded joint for steel pipes

Technical field

The present invention relates to a threaded joint for steel pipes with improved resistance to friction corrosion, which is applicable for connecting tubular products to oil-bearing areas.

State of the art

Tubular products for oil-based areas (OCTG) used on oil fields and in natural gas fields can have a total length of up to several thousand meters. Such long tubular products for oil-bearing areas are usually assembled by combining a huge number of steel pipes with a piece length of about ten to twelve meters by means of couplings that are short cylindrical elements. The materials used for steel pipes and fittings are usually carbon steel, stainless steel or high alloy steel depending on the application environment.

Such steel pipes are connected by a threaded connection of a mandrel provided with a male threaded portion on its outer peripheral surface and a socket provided with a female threaded portion on its inner peripheral surface. Typically, the mandrel is formed at each end of the steel pipe, and the muff is formed inside the coupling. The connecting part formed by the pin and sleeve is a threaded joint.

In the case of a threaded joint for steel pipes, for which a high degree of gas tightness is required, both the tip of the male threaded part of the spindle and the base part of the female threaded socket are equipped with a thread-free metal contact part formed thereon. By inserting one end of the steel tube into the coupling and twisting the male threaded portion of the mandrel and the female threaded portion of the muff until the unthreaded metal contact portions of the mandrel and the joint come into contact with each other, a metalmetal seal is obtained to ensure gastightness.

Figure 9 schematically illustrates a threaded joint having a pin-like design of this type. On its outer peripheral surface, the pin 1 has a male threaded portion 1 a and at its end has a non-threaded metal contact portion 1b. Correspondingly, on its inner circumferential surface, the joint 2 has a female threaded portion 2 a and a non-threaded metal contact portion 2 b inside it. The joining, i.e. the OCTG joining, is carried out by interconnecting the threaded parts of the spindle 1 and the muff 2 and screwing the threaded portions until the unthreaded metal contact portions of the rod 1 and the sleeve 2 meet each other.

For periodic inspections and similar operations, OCTG is extracted from the well and disconnected, i.e. the threaded portions of the threaded joint are loosened and the steel tubes are separated from the coupling. After completion of the inspection, the OCTG joining is carried out again by screwing the threaded parts of the spindle and the muff and they are lowered

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EP 1 920 180 B1 again to the wellbore. When connecting and disconnecting the OCTG, the sliding contact surfaces of the threaded portions 1a and 2a of the rod 1 and the muff 2 and the threaded metal contact portions 1b and 2b will experience a high friction force many times. Therefore, if the threaded joint does not have sufficient resistance to friction forces, when torsion and loosening are carried out repeatedly, incomplete sealing (poor leakage resistance) and seizing (irreparable severe jamming) of threaded parts 1a and 2a, especially non-threaded metal contact parts 1b and 2b.

Therefore, threaded joints for steel pipes intended for use in OCTG joining must be able to: (a) withstand the tensile forces in the axial direction due to the weight of steel pipes, (b) withstand the pressure of internal and external fluids and (c) maintain good leakage resistance and resistance to galling when repeatedly used (subjected to repeated connection and disconnection) at least four times in the case of housings (large diameter pipes) and at least ten times in the case of pipes (small diameter pipes). In recent years, there has been a trend that the depth of oil wells is increasing, and OCTG is increasingly used in difficult conditions, eg in polar regions, which is why more and more demands are placed on the quality of threaded joints.

In the past, as proposed for example in Japanese Patent No. H0112995B, to provide a contact surface (including the surface of threaded portions 1a, 2a and threaded metal contact portions 1b, 2b) of the mandrel 1 or socket 2 of a threaded joint with improved resistance to friction corrosion, the surface was subjected to a surface treatment, such as copper plating or phosphating, and a complex lubricant (also called a smear) containing heavy metals, such as Pb, was applied to the threaded surface for lubrication.

Today, however, in connection with the prevention of global environmental pollution, which becomes an urgent problem, the use of Pb-containing synov is limited. A heavy mash, which does not contain heavy metals such as Pb, Zn and Cu (called organic mash) has been developed and used, but its lubricating action is improper and the occurrence of mashing can not be prevented, especially when the threaded joint is made of a material relatively susceptible to scuffing, such as stainless steel or high alloy steel.

Other methods to improve the leakage resistance and frictional corrosion resistance which are proposed include (1) a method in which a fluoro resin powder is dispersed in the coating coating, (2) a method in which a protective lubricating coating is produced by a sputtering process and (3) a method in which instead of a compound grease a solid lubricating coating is used, but none of these methods provided adequate leakage resistance and frictional corrosion resistance.

European patent application EP-A1-0246387 discloses a threaded joint defined by the preamble of claim 1.

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U.S. Patent No. 4,513,995 discloses electroless nickel plating of a tubular thread followed by electrolytic tinning.

US patent application 2003/0094810 discloses a threaded joint for steel pipes comprising a mating surface coated with a lower porous layer of zinc.

Disclosure of the invention

The object of the present invention is to provide a threaded joint for steel pipes that can exhibit sufficient leakage resistance and resistance to galling corrosion when used with or without an organic rust.

The threaded joint for steel pipes according to the present invention comprises a pin and a socket, each of which has a contact surface including a threaded portion and a non-threaded metal contact portion, characterized in that it has a first covering layer formed by coating with Sn-Bi-Cu alloy on at least a part of the contact surface. at least one element from the spindle and the sleeve.

Bi (bismuth) is known as a material exhibiting low friction. It has been found that when Bi melts with Sn (tin), Bi has the effect of lowering the low-temperature brittleness of Sn known as tinfoil and the effect of significantly improving resistance to galling corrosion at the time of multiple connection and disconnection of OCTG using threaded joints. Because of Bi's effect on lowering Sn low-temperature brittleness, Sn-Bi alloy has the tin blasting effect so that Sn no longer converts to powder due to transformation at low temperatures. The SnBi-Cu alloy is somewhat harder compared to the Sn-Bi alloy, and the addition of Cu to the Sn-Bi alloy not only gives the advantage of tin blast prevention, but also increases wear resistance.

The Bi content in the Sn-Bi-Cu alloy is preferably in the range of 0.5-10% by weight, more preferably 1-5% by weight. The content of Cu in the Sn-Bi-Cu alloy is preferably in the range of 2-15% by weight, more preferably 5-10% by weight. The remaining part of these alloys is generally Sn and impurities, but it is also possible that the alloys further contain Zn and / or Pb in an amount of up to 5% by weight of each.

The threaded joint for steel pipes of the present invention may have a second coating layer formed by coating Sn, coating Cu or coating Ni between the first coating layer and the contact surface of the threaded joint. When this second covering layer is formed under the first covering layer, galling can be sufficiently prevented even if the first coating layer of the Sn-Bi-Cu alloy formed on the second covering layer is relatively thin.

The frictional corrosion resistance can be further improved by forming on the first covering layer at least one lubricating coating layer. The lubricating coating may be a single layer of a viscous liquid or a semi-solid lubricating coating, or it may be a single layer of a solid lubricating coating. In another embodiment, the lubricating coating has a lower layer of solid lubricating coating and a higher layer of a viscous liquid or semi-solid lubricating coating.

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The solid lubricating coating preferably contains a solid lubricating powder in the binder to enhance the lubricating properties of the coating. Due to the pressure applied during repeated connection and disconnection of the OCTG, the solid lubricating powder sticks into the first coating layer of the Sn-Bi-Cu alloy. The amount of solid lubricating powder that sticks is increased in proportion to the pressure and the number of connections and disconnections made. Therefore, even if the pressure becomes high or the threaded joint is used repeatedly, the lubricating effect is maintained due to the embedded solid lubricating powder, and the galling prevention effect on the threaded joint of the present invention is enhanced.

The effect of improving the galling resistance with the solid lubricant powder driven into the first coating layer can be achieved in a similar manner when the lubricating coating is a viscous liquid or a semi-solid coating comprising a solid lubricating powder.

When a solid lubricating coating containing a solid lubricating powder is made directly on the surface of the base metal because the base metal is too hard, the solid lubricant easily falls off without penetrating into the base metal at the time of connection and disconnection, therefore the effect described above can not be achieved.

The threaded joint for steel pipes according to the present invention has improved leakage resistance and resistance to friction corrosion compared to conventional products and exhibits adequate leakage resistance and frictional corrosion resistance without the use of a composite grease that presents many environmental problems. Therefore, the occurrence of mashing can be effectively eliminated, whether it is using organic mash, or without using any mash.

The present invention further provides a threaded rod connector for steel pipes having a contact surface including a threaded portion and a non-threaded metal contact portion characterized in that it has a first coating layer formed by coating with Sn-Bi-Cu alloy on at least a portion of the contact surface.

The present invention further provides a threaded joint for steel pipes having a contact surface comprising a threaded portion and a non-threaded metal contact portion characterized in that it has a first covering layer formed by coating with Sn-Bi-Cu on at least a portion of the contact surface.

A brief description of the figures

Figure 1 schematically shows a cross-sectional view of the contact surface of a threaded joint for steel pipes according to the first embodiment of the present invention.

Figure 2 schematically shows a cross-sectional view of the contact surface of a threaded joint for steel pipes according to the second embodiment of the present invention.

Figure 3 schematically shows a cross-sectional view of the contact surface of a threaded joint for steel pipes according to the third embodiment of the present invention.

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Figure 4 schematically shows a cross-sectional view of the contact surface of a threaded joint for steel pipes according to a fourth embodiment of the present invention.

Figure 5 schematically shows a cross-sectional view of the contact surface of a threaded joint for steel pipes according to a fifth embodiment of the present invention.

Figure 6 is a schematic view of a cross-sectional view of the contact surface of a threaded joint for steel pipes according to a sixth embodiment of the present invention.

Figure 7 is a photograph showing the degree of wettability of the Cu-coated surface.

Figure 8 is a photograph showing the degree of wettability of the surface coated with the Sn-Bi alloy.

Figure 9 schematically shows a cross-sectional view of the mandrel and socket of a typical threaded joint for steel pipes.

The best way to implement the invention

The present invention will be explained below with reference to various embodiments and with reference to the accompanying drawings. In the explanation below, unless otherwise stated, "%" means "% by weight".

Similar to the conventional steel tube threaded connection shown in Figure 9, the steel tube threaded connector of the present invention consists of a spindle having, on its outer peripheral surface, a male threaded portion and a non-threaded metal contact portion and a muff having a female threaded portion on its inner peripheral surface. and a non-threaded metal contact part. The surfaces of the threaded and non-threaded metal contact portions of the mandrel and sleeve are contact surfaces that come into contact with each other during the OCTG joining by screwing the threaded portions. In the present invention, at least a portion of the contact surface of at least one member from the mandrel and the muff has formed on it a first coating layer with a Sn-Bi alloy coating or a Sn-Bi-Cu alloy coating.

Typically, the mandrel is formed at both ends of the steel tube, and the muff is formed inside the connector, which is a short element separate from the steel tube. Other threaded joints known as threaded joints are known and used, in which a mandrel is formed at one end of the steel tube and a sleeve is formed at the other end, such that the steel pipes are joined together without the use of a connector. In principle, a threaded joint is also feasible, in which the mandrel is formed on the outer peripheral surface of the coupling and the muff is formed on the inner peripheral surface of both ends of the steel tube. The present invention can be applied to any of these types of threaded joints.

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The effects of the present invention can be achieved when the first covering layer according to the present invention and optionally the second covering layer and / or the lubricating coating are placed on the contact surface of only one of the spindle and the muff. For example, in the case of a typical threaded joint having a spindle at both ends of a steel pipe, the treatment of the present invention can only be carried out on the contact surface of the muff which is easier to process. In this case, the contact surface of the second element, here the muffs, may not be machined (left in the machined condition) or may be subjected to a suitable conventional lubricating treatment.

Non-limiting examples of materials that can be used to make a threaded joint for steel pipes of the present invention, and therefore, respectively, a steel tube and couplers are carbon steel, stainless steel and high alloy steel. Prior to coating according to the present invention, the contact surface of the threaded joint may be subjected to surface roughening by the method of sandblasting, shot peening or other.

Each of Figs. 1-6 schematically shows a cross-section of a contact surface of a threaded joint mandrel or socket in accordance with various embodiments of the present invention in which at least one layer has been formed on the contact surface, including a first covering layer.

In the case of the threaded joint shown in FIG. 1, the contact surface of the base metal of the mandrel or muff has only the first covering layer 6 formed thereon by Sn-Bi alloying (not part of the invention) or the Sn-Bi-Cu alloying (part of the invention). The first coating layer can be formed both by Sn-Bi alloy coating and Sn-Bi-Cu coating.

It is usually advantageous if the thickness of the first cover layer 6 is in the range of 330 μm, more preferably 5-25 μm. When the second coating layer described below is not produced under the first cover layer, the first layer preferably has a greater thickness in the above-mentioned range, e.g. between 10 and 30 .mu.m. On the other hand, when a second covering layer is produced and / or a subsequently described solid lubricating coating is also produced, the thickness of the first covering layer can be only 15 μm or less. In this case, the thickness of the first coating layer is preferably in the range of 3-20 [mu] m, more preferably 5-15 [mu] m.

The Sn-Bi alloying can be done by electropinating (Sn plating) using, for example, an alkaline plating bath or an acid galvanic bath. When compound Bi is added to the Sn compound in the electroplate bath to perform Sn-Bi alloy coating in which Bi co-precipitates with Sn, the hardness of the resulting galvanic coating significantly increases compared to that of the pure Sn coating (Hv: 8-10 ). For example, the galvanic coating of a Sn-Bi alloy containing 0.5% -10% Bi has a hardness of 2-3 times greater than that obtained from coating pure Sn and therefore has an increased resistance to wear. At the same time, due to Bi co-precipitation, the low temperature brittleness of the Sn (Snap Plasma) coverage is reduced.

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Similarly, Sn-Bi-Cu coating can be performed by performing galvanic coating using a galvanizing bath containing, in addition to Sn, Bi compound and compound

Cu. The Sn-Bi-Cu alloy coating gives the effects described above for Bi and results in a higher hardness of the coating, which is why its resistance to wear is even greater.

An exemplary Alkaline galvanic coating for Sn-Bi coating contains 100110 g / l of potassium stannate, 35-60 g / l of potassium hydroxide and 0.5-1.5 g / l based on the metallic Bi of Bi. Typical coating conditions for this electroplating bath include a bath temperature of 75-85 ° C and a current density of 0.5-3 A / dm².

An exemplary acidic galvanic bath for Sn-Bi coating contains 130 g / l of organic acid, 10 g / l based on Sn metal compound Sn and 3 g / l based on the metallic Bi of Bi. Typical coating conditions for this galvanic bath are the temperature^Kapie^{li 30}-⁴⁰°^{C and gę}hundred^pr^ADat ^0.3-9^{5 A / d}m².

An exemplary acidic galvanic bath for coating with Sn-Bi-Cu alloy contains 130180 g / l of organic acid, 15 g / l based on metal Sn compound Sn, 1.5 g / l based on the metallic Bi compound Bi and 1 g / l in terms of metallic Cu compound. Typical coating conditions for this galvanic bath are 15-30 ° C bath temperature and density^pr^ADat ^0.5-9^{5 A / d}m².

For each of these galvanic baths, the source of each of the metals can be selected from the corresponding metal soluble electrode compounds.

In the case of a steel threaded connector shown in figure 2, a second galvanic layer is formed on the surface of the base metal by covering Sn, Cu coating or Ni coating, and a first cover layer 6 is formed on top of the second covering layer 7 by coating with Sn-Bi alloy or coating with Sn-Bi-Cu alloy. The second covering layer can also be formed by coating with two or more layers (such as a Ni electroplating layer and a Cu galvanic layer).

The thickness of the second covering layer 7 in the case of Sn coating is preferably 1-15 [mu] m, more preferably 2-10 [mu] m or, in the case of Ni or Cu coating, 1-15 [mu] m, more preferably 1-10 [mu] m.

The coating of the Sn can be carried out, for example, using a galvanic bath, which contains 200 g / l tin fluoroborate, 125 g / l fluoroboric acid, 25 g / l boric acid, 2 g / l gelatin and 1 g / l β-naphthol, by electroplating at a bath temperature of 20-25 ° C and a current density of 1-5 A / dm2. Sn coating is typically carried out from such a fluoroborate bath, but considering the ease of wastewater treatment, a commercially available organic sulfonate based Sn bath can also be used.

The Cu coating and Ni coating can be carried out by a conventional Ni or Cu plating method. Galvanic baths useful for coating Cu include copper cyanide bath, copper sulphate bath and copper pyrophosphate bath. Of these, copper cyanide bath and copper sulfate bath are preferred. Galvanic baths useful for

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The Ni coatings include a Watts nickel bath, a nickel chloride bath, a nickel sulfamate bath and an ammonium chloride bath (low temperature nickel bath). Of these, Watts nickel bath and nickel chloride bath are preferred.

In the embodiment shown in figure 1, the first layer 6 of the Sn-Bi-Cu alloy is formed on the contact surface of the threaded joint. In the embodiment shown in figure 2, a second covering layer 7 is pre-formed on the contact surface by coating Sn, Cu or Ni, and then a first covering layer 6 is produced.

When the base metal is carbon steel, it is possible to form the first cover layer 6 (figure 1) or the second cover layer 7 (figure 2) with good adhesion, even if it is produced directly on the surface of the steel.

On the other hand, in a situation where the base metal 5 is stainless steel or high alloy steel, if the first coating layer from the Sn-Bi-Cu coating is formed directly on the steel surface, the resulting galvanic coating will have poor surface adhesion and tendency to easily peel-off. Therefore, the contact surface of the threaded joint is preferably galvanized against Cu or Ni before coating it with a Sn-Bi-Cu alloy layer to form the first covering layer. In this case, a first coating layer with good adhesion can be formed on the contact surface by means of impact galvanizing.

Similarly, when a second cover layer 7 is pre-formed on the contact surface as shown in figure 2, if the base metal 5 is stainless steel or high alloy steel, it is preferable to carry out Ni or Cu impact galvanisation beforehand. However, in a situation where the second covering layer is a thin Ni or Cu layer, for example, on the order of 1-3 μm, on the surface of stainless steel or high alloy steel, it is possible to produce a second coating layer with good adhesion even if pre-galvanizing is omitted.

Ni or Cu electroplating may be carried out in a conventional manner. In general, Ni Ni electroplating is carried out using a nickel chloride bath, whereas Cu galvanizing is carried out using a copper cyanide bath. In any case, the galvanizing time is short enough to produce a galvanic coating with a thickness of less than 1 [mu] m, and preferably at most 0.5 [mu] m.

In the case of the threaded joint for steel pipes shown in figure 3, the surface of the first covering layer 6 of the Sn-Bi-Cu alloy is covered by a lubricating coating 8. In figure 3 and figure 4, the structure underneath the first cover layer 6 is not shown, but maybe be the same as in figure 1 or figure 2.

Examples of a lubricating coating are solid lubricating coatings such as those described in Japanese Patent Applications Nos. 2001-6575 IA, 2002-221288A, 2002-327875A or 2002348587A (baked coating containing solid lubricant dispersed in a binder) or

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A viscous or semi-solid coating such as described in Japanese Patent Applications Nos.

2002-173692A or 2004-53013A (coating containing various lubricating components in the base oil).

Examples of the preferred solid lubricating powder present in the solid lubricating coating include, but are not limited to, graphite, MoS2 (molybdenum disulphide), WS2 (tungsten disulfide), BN (boron nitride), PTFE (polytetrafluoroethylene), CF (carbon fluoride) and CaCO3 (calcium carbonate) . Of these, graphite and MoS2 are preferred. They have a stratified crystalline structure characterized by significant strength of bonds in the plane and low strength of inter-plane interactions and they are prone to delamination of the crystalline surfaces, which leads to slip effect and makes them suitable for improving resistance to friction corrosion.

As a binder for use in the preparation of a solid lubricating coating, various materials capable of forming an organic or inorganic film may be used. Examples of material capable of forming an organic film are organic resins with good heat resistance, such as epoxy resins, polyamide resins and polyimide-amide resins. Examples of a material capable of forming an inorganic membrane are organic or inorganic substances, such as silica sol, alkoxysilanes and titanium alkoxides, from which a metal oxide coating may be formed.

The solid lubricating coating can be made by mixing a solid lubricating powder with a binder solution to form a coating composition, applying a coating composition to the contact surface of a threaded joint to steel pipes, and drying the coating preferably by heating to coat the coating. The annealing temperature depends on the type of binder and when the binder is an epoxy resin, it is preferably about 150-250 ° C.

The preferred solid lubricating coating has a coating thickness of 5-30 pm and contains 10% -50% solid lubricating powder. The Sn-Bi-Cu alloy coating being the cover layer in contact with the solid lubricating coating is characterized by good affinity for the liquid, therefore the solid lubricating coating produced on this coating has good adhesion.

The lubricating or viscous lubricating coating preferably does not contain a significant amount of heavy metal powder, such as Pb, Zn and Cu, which is harmful to the environment and humans. Such a lubricating coating contains a significant amount of one or more lubricating components (such as waxes, metal ion soaps, and various types of alkali metal and organic acid salts including basic calcium or barium sulfonates, phenolate, salicylate and carboxylate) in the base oil (such as oil a mineral, ester or fat based on a higher fatty acid). The form of the lubricating coating, i.e. whether it is a viscous liquid or semi-solid, depends on the viscosity of the base oil and the amount of lubricating ingredients. The preferred thickness of the viscous or semi-solid coating is 10-200 μm.

Figure 4 shows an embodiment in which the lubricating coating consists of a lower layer in the form of a solid lubricating coating 8a and a top layer in the form of a lubricating coating of a viscous liquid or semi-solid 8b. The lower solid lubricating coating and the upper coating

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The viscous or semi-solid lubricating fluid constituting the two layers 8a and 8b, respectively, may be the same as described above.

Figure 5 shows an embodiment in which a first coating layer 6 is formed on the surface of the base metal 6 by coating with a Sn-Bi-Cu alloy and a solid lubricating coating 8a1 containing MoS2 is formed on top of the first cover layer 6. The solid lubricating coating 8a1 containing MoS2 can be prepared as described above by applying a coating composition containing MoS2 powder dispersed in a binder, such as an epoxy resin, followed by baking. The thickness of the coating is preferably about 330 μm for the first covering layer 6 and about 5-30 μm for a solid lubricating coating with a total thickness of the two layers of about 10-45 μm.

Figure 6 shows an embodiment the same as that shown in Figure 5 except that the solid lubricating coating is a solid lubricating coating 8a2 containing graphite.

When a solid lubricating coating is formed on top of the first coating layer 6 of the Sn-Bi-Cu alloy, as shown in Figure 5 and Figure 6, it may be advantageous to form, as a bottom second covering layer, a thin, uncoated Cu-layer of thickness 1- 3 pm When such a thin Cu coating layer is formed under the first cover layer 6, because of the heat at the time of baking the solid lubricating coating 8a1 or 8a2 (usually carried out at 150-250 ° C), a layer of compound is formed between the first cover layer 6 and the base metal 5 intermetallic Sn-Bi-Cu with a gentle concentration gradient, whereby the adhesion force of the first coating layer 6 increases.

It is possible to produce one or more first and second coating layers and electroplating layers by electroless plating or a gas phase coating instead of electroplating. However, electroplating is preferred because of its efficiency and economy.

The threaded joint for steel pipes according to the present invention is preferably used for combining OCTG without applying a mash or after applying an organic mucus. Very good lubricating properties have a particularly threaded connection having a solid lubricating coating 8a, 8a1 or 8a2 formed on the first covering layer 6 of the Sn-Bi or Sn-Bi-Cu alloy, as shown in Figures 4 to 6, due to the ability of solid lubricating powder in a lubricating coating for pressing under pressure into a first covering layer that is relatively soft and provides good resistance to frictional corrosion even when used to connect OCTG without applying a mash. When a lubricating coating of a viscous liquid or a semi-solid lubricant is formed on top of the solid lubricating coating, the galling resistance increases additionally. Similarly,

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In the case of a threaded joint according to the present invention shown in figure 1 or figure 2 in which no lubricating coating is formed, so that the first coating layer of the Sn-Bi-Cu alloy is exposed, in general it is preferred to use such a threaded joint for combining OCTG with applying ecological sponge.

Generally, the ointment is a semi-solid or solid composition comprising one or more thickeners and optionally other solid particles dispersed in the lubricating oil. Suitable thickening agents include soaps with metal ions, Ca complexes, urea derivatives, metal salts and bentonite derivatives. The type of ointment, which is essentially free of heavy metal powder and is characterized by good biodegradability, is called ecological mash. Although there is no specific definition of ecological mazy, under the general standard, an organic mast should have a BOD value of at least 60%. Ecological musk is distinguished in terms of biodegradability from a semi-solid lubricating coating that can be produced on top of the first coating layer according to the present invention. The consistency of the smears is measured by the penetration ability, as defined in JIS K 2220 5.3, in the same way as for lubricants. The viscous lubricating coating has a much thinner consistency that can be measured with a standard viscometer, such as a Brookfield viscometer. Its viscosity is usually at most 10,000 cSt at 40 ° C.

Examples

The following examples are intended to show the effects of the present invention, but are not intended to limit the present invention in any way. In the examples, the contact surface including the threaded portion and the non-threaded metal contact portion of the spindle will be referred to as the "spindle surface" and the contact surface including the threaded portion and the non-threaded metal contact portion of the muff will be referred to as the "muff face".

The threaded joints for steel pipes prepared in the examples consisted of a mandrel formed at each end of a seamless test tube steel, the outer diameter of 244.5 mm, wall thickness 13.84 mm, and length 1200 mm and the muffs of the connector formed inside. Each mandrel had a male threaded portion and a non-threaded metal contact portion formed on its outer peripheral surface, and each socket had a female threaded portion and a non-threaded metal contact portion formed on its inner peripheral surface. The steel pipe and coupling were made of 13 Cr steel, which is a high alloy steel containing 13% Cr, 0.1% Ni and 0.04% Mo.

As shown in Table 1 and Table 2, at least one coating layer and optionally at least one lubricating coating on the top of the cover was formed on the surface of the muff of each connector. Table 1 shows working examples in which no lubricating coating was produced (Examples 1-8) and in which one or two lubricating coatings were produced (Examples 913). Examples 5-8 are within the scope of the present invention. Table 2 shows comparative examples in which the outermost covering layer was not a Sn-Bi or Sn-Bi-Cu alloy coating layer.

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The Sn-Bi alloy coating and the Sn-Bi-Cu alloy coating shown in Table 1 were formed by galvanic coating using the acidic electroplating bath described above (using the appropriate metal sources in the form of the organic acid salt). The alloy composition of these alloy coatings was approximately the following: 3% Bi for Si-Bi alloy coating and approximately 3% Bi and approximately 7.5% Cu for the Sn-Bi-Cu alloy coating. The Sn-Cu coating used in some comparative examples was carried out by galvanic coating using an alkaline electroplate bath. The Cu content in the SnCu alloy coating was approximately 50%.

When a second coating layer was produced before the first covering layer, it was produced by electroplating. The galvanizing bath used was a sulphonate bath for Sn coating, nickel chloride bath for Ni coating and copper cyanide bath for Cu coating.

Although not shown in Tables 1 and 2, since the base metal was a high alloyed steel, before the lowest of the cover layers given in the tables was made, each surface of the muff after degreasing was pre-galvanized with Ni 0.5 μm impact using a bath nickel chloride for impact galvanizing. However, in Examples 4 and 13 and Comparative Examples 1-3 and 5-7, in which the lowest of the coating layers was a 1 μm thick Ni coating layer, Ni NiI was not carried out.

The lubricating coatings used in the examples were solid lubricating coatings and lubricating coatings of a viscous liquid. The solid lubricating coating contained a lubricating powder (graphite or molybdenum disulfide) in an epoxy resin and was produced by applying a coating composition followed by baking at approximately 200 ° C. The content of the lubricating powder in solid lubricating coatings was 30% for graphite and 40% for molybdenum disulphide (MoS2).

The viscous lubricating coating contained wax and basic calcium sulfonate as a lubricating oil in mineral oil as the base oil.

The threaded joints with machined surfaces as shown in Tables 1 and 2 were subjected to the following mashing test.

(Mashing test)

The spigot at the end of the steel pipe was inserted into the coupling sleeve. The surface of the mandrel was pre-peened using glass beads. In some examples, a commercially available ointment was pre-applied to the surface of the muff. In order to simulate the connection and disconnection of the OCTG, for the joining, the threaded parts of the mandrel and muff were meshed and screwed to a torque of 49351,8 Nm (36400 ft-lb) at room temperature until the non-threaded metal contact portions of the mandrel and muff were in contact, and then, for disconnection, they were unscrewed by separating the steel pipe from the coupling. The surface of the joint was then visually observed to determine whether or not there was seizing.

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This connection and disconnection procedure was carried out up to ten times, and the frictional corrosion resistance was evaluated in each connection and disconnection cycle until seizing (irreparable severe jamming) occurred. When a delicate, repetitive jamming was observed, the test was continued after repairing the threaded joint. The results are shown in Tables 1 and 2.

Table 1

<td>Example</td><td>Surface structure of the muff (in the order from top to bottom layer) (w value brackets means coating thickness)</td><td>Application goo ecological</td><td>Test results mashing (number combining cycles and disconnection before occurrence seizure)</td>

<td rowspan="2">Example 1 *</td><td rowspan="2">Sn-Bi alloy coating (15 pm)</td><td>Yes</td><td>8 times</td>

<td>No</td><td>6 times</td>

<td rowspan="2">Example 2 *</td><td rowspan="2">Sn-Bi alloy coating (12 pm); Sn cover (5 pm)</td><td>Yes</td><td>10 times</td>

<td>No</td><td>8 times</td>

<td>Example 3 *</td><td>Sn-Bi alloy coating (14 μm); Cu cover (3 pm)</td><td>Yes</td><td>10 times</td>

<td>Example 4 *</td><td>Sn-Bi alloy coating (25 μm); Ni coating (1 pm)</td><td>Yes</td><td>10 times</td>

<td>Example 5</td><td>alloying Sn-Bi-Cu (12 pm)</td><td>Yes</td><td>8 times</td>

<td>Example 6</td><td>Sn-Bi-Cu alloy coating (10 μm); Sn cover (10 pm)</td><td>Yes</td><td>10 times</td>

<td>Example 7</td><td>Sn-Bi-Cu alloy coating (15 μm); Cu cover (5 pm)</td><td>Yes</td><td>10 times</td>

<td>Example 8</td><td>Sn-Bi-Cu alloy coating (15 μm); Ni coating (5 pm)</td><td>Yes</td><td>10 times</td>

<td>Example 9 *</td><td>solid lubricating coating containing graphite (30 pm); Sn-Bi alloy coating (5 pm)</td><td>No</td><td>8 times</td>

<td>Example * 10</td><td>solid lubricating coating containing graphite (30 pm); Sn-Bi alloy coating (11 pm); Sn cover (3 pm)</td><td>No</td><td>8 times</td>

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<td>Example * 11</td><td>lubricating coating made of viscous liquid (200 pm); solid lubricating coating containing graphite (10 pm); Sn-Bi alloy coating (10 pm)</td><td>No</td><td>10 times</td>

<td>Example * 12</td><td>lubricating coating made of viscous liquid (200 pm); solid lubricating coating containing graphite (10 pm); Sn-Bi alloy coating (10 pm); Sn cover (5 pm)</td><td>No</td><td>10 times</td>

<td>Example * 13</td><td>lubricating coating made of viscous liquid (200 pm); solid lubricating coating containing graphite (10 pm); Sn-Bi alloy coating (10 pm); Cu coating (5 pm); Ni coating (1 pm)</td><td>No</td><td>10 times</td>

* = not part of the present invention

Table 2

<td>Example comparative</td><td>Surface structure of the sleeve (in order from top to bottom layer) (value in brackets means the thickness of the coating)</td><td>Application goo ecological</td><td>Mash test results (number of joining cycles and disconnection before occurrence of seizure)</td>

<td rowspan="2">Example comparative 1</td><td rowspan="2">Cu coating (10 pm); Ni coating (1 pm)</td><td>Yes</td><td>4 times</td>

<td>No</td><td>1 time</td>

<td rowspan="2">Example comparative 2</td><td rowspan="2">solid lubricating coating containing graphite (25 pm); Cu coating (10 pm); Ni coating (1 pm)</td><td>Yes</td><td>4 times</td>

<td>No</td><td>1 time</td>

<td>Example comparative 3</td><td>solid lubricating coating containing MoS2 (25 pm); Cu coating (10 pm); Ni coating (1 pm)</td><td>Yes</td><td>4 times</td>

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<td>Example comparative 4</td><td>Cu-Sn cover (10 pm)</td><td>Yes</td><td>6 times</td>

<td>Example comparative 5</td><td>Cu coating (8 pm); Ni coating (1 pm)</td><td>No</td><td>2 times</td>

<td>Example comparative 6</td><td>solid lubricating coating containing graphite (25 pm); Cu coating (8 pm); Ni coating (1 pm)</td><td>No</td><td>2 times</td>

<td>Example comparative 7</td><td>solid lubricating coating containing MoS2 (25 pm); Cu coating (9 pm); Ni coating (1 pm)</td><td>No</td><td>2 times</td>

<td>Example comparative 8</td><td>solid lubricating coating containing graphite (25 pm); Cu-Sn cover (12 pm)</td><td>No</td><td>Three times</td>

(Example 1)

The surface of the joint had a 15 μm thick layer of Sn-Bi alloy coating. In the mashing test carried out after the application of organic rust to the surface of the joint, connecting and disconnecting without the occurrence of seizure could be carried out eight times. When the same surface of the joint was subjected to a mash test without applying ecological lye, it was possible to connect and disconnect without the occurrence of galling six times.

(Example 2)

The surface of the joint had a lower layer of the 5 μm thick Sn cover and the upper layer of the 12-μm Sn-Bi alloy cover. In the mashing test carried out after the application of organic rust to the surface of the joint, connecting and disconnecting without the occurrence of seizure could be carried out ten times. When the same surface of the joint was subjected to a mash test without applying organic oily, it was possible to connect and disconnect without the occurrence of seizure eight times.

(Example 3)

The surface of the muff had a lower layer of Cu coating with a thickness of 3 μm and an upper layer of a 14-μm Sn-Bi alloy coating. In the mashing test carried out after the application of organic rust to the surface of the joint, connecting and disconnecting without the occurrence of seizure could be carried out ten times.

(Example 4)

The surface of the joint had a lower Ni coating layer of 1 μm and the upper layer of a 25 μm thick Sn-Bi alloy coating. In the mash test carried out after application

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It was possible to connect and disconnect it without the occurrence of seizure ten times.

(Example 5)

The surface of the joint had a 12 μm thick layer of Sn-Bi-Cu alloy coating. In the mashing test carried out after the application of organic rust to the surface of the joint, connecting and disconnecting without the occurrence of seizure could be carried out eight times.

(Example 6)

The surface of the joint had a 10 μm thick bottom coating layer and a 10 μm thick top layer of the Sn-Bi-Cu alloy coating. In the mashing test carried out after the application of organic rust to the surface of the joint, connecting and disconnecting without the occurrence of seizure could be carried out ten times.

(Example 7)

The surface of the joint had a lower layer of 5 μm thick Cu coating and the upper layer of a 15 μm thick Sn-Bi-Cu alloy coating. In the mashing test carried out after the application of organic rust to the surface of the joint, connecting and disconnecting without the occurrence of seizure could be carried out ten times.

(Example 8)

The surface of the joint had a lower Ni coating layer 5 μm thick and an upper layer of a 15 μm thick Sn-Bi-Cu alloy coating. In the mashing test carried out after the application of organic rust to the surface of the joint, connecting and disconnecting without the occurrence of seizure could be carried out ten times.

(Example 9)

The surface of the muff had a 5 μm thick Sn-Bi coating layer and a solid lubricating coating containing 30 μm thick graphite formed on the cover layer. In the mashing test carried out without applying organic mash, it was possible to combine and disconnect without the occurrence of galling eight times.

(Example 10)

The surface of the sleeve had a 3 μm thick bottom coating layer, an upper layer of a 11 μm thick Sn-Bi alloy cover and a solid lubricating coating containing 30 μm thick graphite formed on top of the cover layer. In the mashing test carried out without applying organic mash, it was possible to combine and disconnect without the occurrence of galling eight times.

(Example 11)

The surface of the muff had a 10 μm thick Sn-Bi alloy coating, a lower solid lubricating coating containing 10 μm graphite and an upper lubricating coating of a 200 μm viscous fluid formed on the cover layer. In the mashing test carried out without applying organic mash, connecting and disconnecting without the occurrence of seizure could be carried out ten times.

(Example 12)

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The surface of the sleeve had a 5 μm thick bottom coating layer and an upper 10 mm thick Sn-Bi alloy layer and a lower solid lubricating coating containing 10 μm graphite and a top lubricating coating of viscous 200 pm thick liquid formed on the coating layers. In the mashing test carried out without applying organic mash, connecting and disconnecting without the occurrence of seizure could be carried out ten times.

(Example 13)

The surface of the joint had the lowest Ni coating layer 1 μm, an intermediate 5 μm thick Cu coating layer and the upper 10 mm thick Sn-Bi coating layer and a lower solid lubricating coating containing 10 μm graphite and an upper lubricating layer of viscous liquid 200 pm thick formed on the coating layers. In the mashing test carried out without applying organic mash, connecting and disconnecting without the occurrence of seizure could be carried out ten times.

(Comparative example 1)

The surface of the joint had a lower Ni coating layer of 1 μm and an upper layer of a 10 μm thick Cu cover. In the mashing test carried out after application to the surface of the muff, ecological fade occurred in the fourth cycle of connection and disconnection. When the same surface of the joint was subjected to a mash test without applying ecological lyric, the seizing took place in the first cycle.

(Comparative example 2)

The surface of the joint had a lower Ni coating layer of 1 μm and an upper layer of a 10 μm thick Cu coating and a solid lubricating coating containing 25 μm thick graphite formed on top of the coating layers. In the mashing test carried out after application to the surface of the muff, ecological fade occurred in the fourth cycle of connection and disconnection. When the same surface of the joint was subjected to a mash test without applying ecological lyric, the seizing took place in the first cycle.

(Comparative example 3)

The surface of the joint had a lower Ni coating layer 1 μm and an upper layer of a 10 μm thick Cu coating and a solid lubricating coating containing 25 μm MoS 2 formed on top of the coating layers. In the mashing test carried out after application to the surface of the muff, ecological fade occurred in the fourth cycle of connection and disconnection.

(Comparative example 4)

The surface of the joint had a 10 μm thick layer of the Sn-Cu alloy coating. In the mashing test carried out after applying ecological slag to the surface of the muff, the seizing took place in the sixth connection and disconnection cycle.

(Comparative example 5)

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The surface of the joint had a lower Ni coating layer of 1 μm and an upper layer of Cu coating with a thickness of 8 μm. In the mashing test carried out without applying an organic rust, the seizing took place in the second connection and disconnection cycle.

(Comparative example 6)

The surface of the joint had a lower Ni coating layer of 1 μm and an upper layer of Cu coating with a thickness of 8 μm and a solid lubricating coating containing 25 μm thick graphite formed on top of the coating layers. In the mashing test carried out without applying an organic rust, the seizing took place in the second connection and disconnection cycle.

(Comparative example 7)

The surface of the joint had a lower Ni coating layer 1 μm and a top layer of a 9 μm thick Cu coating and a solid lubricating coating containing 25 μm MoS 2 formed on top of the coating layers. In the mashing test carried out without applying an organic rust, the seizing took place in the second connection and disconnection cycle.

(Comparative example 8)

The surface of the joint had a 12-μm thick Sn-Cu coating layer and a solid lubricating coating containing 25 μm thick graphite formed on top of the cover layer. In the mashing test carried out without applying the ecological slime, the seizing took place in the third cycle of connection and disconnection.

Based on the results of the examples and comparative examples described above, it can be seen that the steel tube threaded connection according to the present invention was clearly more effective in containing frictional corrosion than the threaded joints of the comparative examples.

(Difference in affinity)

The difference in affinity (wettability) between the Cu coating and the Sn-Bi alloy coating was tested. Figures 7 and 8 show photographs showing the method of liquid (water) decomposition after placing one drop of liquid on the Cu coating surface (Figure 7) and the Sn-Bi alloy coating (Figure 8) formed in the examples. The degree of liquid distribution indicates the wettability of the surface, i.e. its affinity for the liquid. The liquid was better distributed on the Sn-Bi alloy than on the Cu coating, indicating that the Sn-Bi alloy coating had greater affinity for this liquid.

The difference in affinity had its true reflection in the results of the mash test. Examples 9-12, in which there was a solid lubricating coating containing graphite formed on top of the Sn-Bi alloy coating, showed a much higher resistance to friction corrosion than comparative examples 2 and 6 in which the same solid lubricating coating formed on top of the Cu coating was present. One of the reasons for this difference in frictional corrosion resistance is that the affinity and thus the adhesion of the solid lubricating coating to the coating layer was higher in the case of Sn-Bi alloy coating than in the case of Cu coating.

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