Threaded ends of tubular elements having coatings containing zinc-chromium alloys

Abstract

The invention relates in particular to a threaded end 1,2 of a tubular element for drilling and / or working hydrocarbon wells, transporting oil and gas, transporting or storing hydrogen, recovering carbon or recovering geothermal energy. It comprises at least one thread 3,4 extending on its outer or inner circumferential surface. This thread is coated with a layer 15 comprising a zinc-chromium (Zn-Cr) alloy, where zinc (Zn) is the predominant element in weight % with respect to the total weight of the alloy. The invention also relates to a process for preparing such a threaded end 1,2 of a tubular element for drilling and / or working hydrocarbon wells, transporting oil and gas, transporting or storing hydrogen, recovering carbon or recovering geothermal energy. This process comprises at least one electrodeposition step on at least the surface of the thread 3,4 of the end of an aqueous composition comprising one or more zinc salts, one or more chromium salts, one or more electrolytes and one or more surfactants.

Description

[Technical Field]

[0001] The present invention relates to a threaded end of a tubular element for drilling and / or working hydrocarbon wells, transporting oil and gas, transporting or storing hydrogen, capturing carbon or recovering geothermal energy, the threaded end comprising at least one thread, the surface of which is provided with a zinc and chromium-based coating as described below.

[0002] The present invention also relates to a process for preparing a threaded end of a tubular element, comprising at least one electrodeposition step onto the surface of the threads of said threaded end of an aqueous composition based on one or more zinc salts, one or more chromium salts, one or more surfactants, and one or more electrolytes.

[0003] The invention also relates to a tubular threaded joint comprising at least one threaded end of a tubular element, the surface of the threads of which is covered with a zinc and chromium based coating as described below. [Background technology]

[0004] It is noted that for the purposes of the present invention, a tubular element means any element or accessory having a substantially tubular shape, optionally joinable to another element of the same type, for drilling and / or working hydrocarbon wells, for transporting oil and gas, for transporting and / or storing hydrogen, for carbon recovery or for geothermal energy recovery.

[0005] Also, for the purposes of the present invention, a threaded end of a tubular element means any end element of a tubular element, as defined above, having at least one threaded portion or thread on its surface, by means of which the tubular element can be joined or connected, optionally to another element of the same type, to form a joint or connection.

[0006] Thus, within the meaning of the present invention, a threaded end of a tubular element corresponds to an end element of the tubular element that is provided with at least one threaded surface, which is involved in the connection of the tubular element with other similar or different elements.

[0007] Each of the tubular elements has at least one externally threaded region, i.e., an end provided with threads extending on its outer circumferential surface, and / or at least one internally threaded region, i.e., an end provided with threads extending on its inner circumferential surface, which are intended to be joined by being screwed onto a corresponding end of a similar or different element to form a joint or connection.

[0008] Tubular threaded elements of connections are typically joined under defined constraints, specifically defined torque targets, to meet tightening and sealing requirements imposed by the conditions of use, and may need to be threaded and unthreaded multiple times, especially during use.

[0009] The conditions of use of such tubular threaded elements give rise to various types of stresses which can be reduced or minimized by the use of films or greases, especially in the sensitive areas used to connect these elements, such as threaded areas, abutment areas or metal-to-metal sealing surfaces.

[0010] The stresses induced include, in particular, storage safety stresses, which require the application of a storage grease (as opposed to a thread grease that is applied before use), however, there are also solutions using organic or metallic coatings.

[0011] Screwing and unscrewing operations are generally carried out under high axial loads, for example, under the weight of pipes several meters long, typically 10 to 13 meters, that are joined vertically by the threaded joint, which can be exacerbated by slight misalignment of the axes of the threaded elements being joined. This poses a risk of adhesive wear occurring in the pipe connection elements, especially in the threaded and abutting areas and / or metal-to-metal sealing surfaces. It is therefore important to protect these connection elements, especially the threaded areas, from adhesive wear, especially by covering them with a lubricant.

[0012] Additionally, tubular thread elements are often stored and used in harsh environments, such as "offshore" where salt spray is present or "onshore" where sand, dust, and / or other contaminants are present. Therefore, various types of corrosion-resistant coatings are typically applied to threaded areas, intimate contact surfaces, metal-to-metal sealing surfaces, and surfaces that are subject to thread loads in the abutment area.

[0013] However, their use may not be a long-term solution in terms of environmental standards, since greases complying with the API RP5A3 (American Petroleum Institute) standard can be extruded from the tubular elements and released into the environment or, for example, into the wellbore, causing blockages that require specific cleaning operations.

[0014] To address the issues of sustained corrosion and adhesive wear resistance and environmental friendliness, grease substitutes have been used in the prior art.

[0015] Therefore, zinc (Zn) and nickel (Ni) based metallic coatings have been developed to protect the connecting elements of tubular elements, especially the threaded areas, from corrosion and adhesive wear.

[0016] However, while this metal coating offers excellent performance in terms of corrosion resistance and adhesive wear resistance, it has a major drawback in that it is prepared from nickel salts, which are chemicals that are harmful to the human body. Specifically, nickel salts are classified as "CMR" substances, i.e., substances that are known to be carcinogenic, mutagenic, and reproductively toxic.

[0017] Thus, although zinc and nickel based metal coatings are commonly used in industry due to their corrosion and adhesive wear resistance properties, their toxicity has always resulted in serious long-term risks to the health of many workers.

[0018] Other zinc-based metallic coatings have also been developed to protect the connecting elements of tubular elements from corrosion and condensation wear.

[0019] However, such envisioned metal coatings have proven to be a non-viable solution for a variety of reasons.

[0020] For example, zinc (Zn) and cobalt (Co) coatings, typically containing about 1% cobalt by weight, are toxic because their preparation process is based on the use of cobalt salts classified as "CMR" materials.

[0021] Similarly, zinc (Zn) and cadmium (Cd) coatings have the drawback of using cadmium salts, which are substances that are harmful to the human body.

[0022] Tin (Sn) and zinc (Zn)-based coatings, especially those with a tin content of 70% to 80% by weight and a zinc content of 20% to 30% by weight, offer favorable corrosion resistance, but suffer from poor heat resistance, especially at high temperatures, and high manufacturing costs. These drawbacks are particularly related to the high tin content used in the preparation of this type of coating.

[0023] Zinc (Zn) and magnesium (Mg) based coatings are themselves obtained by electrodeposition of zinc and magnesium salts in the presence of solvents at high temperatures, typically around 100°C, a preparation process that is difficult to carry out on an industrial scale.

[0024] Zinc (Zn) and iron (Fe) based coatings, especially those with an iron content above 10% by weight, have the disadvantage of oxidizing to form red rust that can be confused with the red oxidation of the iron substrate.

[0025] Generally, zinc (Zn) and magnesium (Mg), zinc (Zn) and iron (Fe), or zinc (Zn) and manganese (Mn) based coatings offer less cathodic protection and therefore less corrosion protection than zinc (Zn) and nickel (Ni) based coatings, because the standard redox potentials of the alloying elements (magnesium, manganese, iron) are lower than that of nickel.

[0026] There is therefore a real need to provide a coating that can effectively protect the threaded ends of tubular elements for drilling and / or working hydrocarbon wells, for oil and gas transportation, for hydrogen transportation or storage, for carbon recovery or for geothermal energy recovery from corrosion and adhesive wear, while overcoming the above-mentioned drawbacks, i.e., with reduced or minimized toxicity. Summary of the Invention [Problem to be solved by the invention]

[0027] It is therefore an object of the present invention to provide a coating that has reduced or no toxicity and does not adversely affect the corrosion and adhesive wear resistance performance due to the nature of the alloying elements, thereby effectively protecting the threaded elements of a tubular element that is used to join the tubular element to another similar or dissimilar tubular element. [Means for solving the problem]

[0028] The present invention therefore relates in particular to a threaded end of a tubular element for drilling and / or working hydrocarbon wells, transporting oil and gas, transporting or storing hydrogen, recovering carbon, or recovering geothermal energy, which has at least one thread extending on its outer or inner circumferential surface, and which is coated with a layer containing a zinc-chromium (Zn-Cr) alloy, in which zinc (Zn) is the predominant element in weight percent relative to the total weight of the alloy.

[0029] That is, a coating comprising a zinc-chromium (Zn-Cr) alloy, in which zinc (Zn) is the predominant metallic element in weight percent relative to the total weight of the alloy, covers at least one thread of the threaded end of the tubular element as described above.

[0030] Preferably, the threaded end of the tubular element as described above comprises at least one thread extending on its outer or inner circumferential surface and at least one non-threaded portion, preferably including a stop and / or a sealing seat. The thread and the non-threaded portion are covered with a coating comprising a zinc-chromium (Zn-Cr) alloy, where zinc (Zn) is the predominant metallic element in weight percent relative to the total weight of the alloy.

[0031] That is, the zinc-chromium (Zn-Cr) coating according to the present invention covers at least one thread of the threaded end of the tubular element as described above, and preferably covers at least the thread of the threaded end of the tubular element and at least one non-threaded portion, preferably including a stop and / or sealing seat.

[0032] In the remainder of the text, within the meaning of the present invention, a layer comprising a zinc-chromium (Zn-Cr) alloy corresponds both to a coating comprising a zinc-chromium (Zn-Cr) alloy and to a zinc-chromium (Zn-Cr) coating. Thus, in this specification, the terms "layer" and "coating" may be used interchangeably to denote a zinc-chromium alloy deposit according to the present invention, covering at least the threads of the threaded end of a tubular element.

[0033] According to the present invention, the layer containing a zinc-chromium (Zn-Cr) alloy is different from a superposition of a zinc (Zn) layer and a chromium (Cr) layer.

[0034] It should be noted that for purposes of this invention, "zinc-chromium (Zn-Cr)" alloy refers to a mixture containing zinc and chromium, where zinc represents the base metal, i.e., the metallic element predominantly present in the mixture, and chromium represents the alloying metallic element, i.e., the metallic element intentionally present in or added to the mixture.

[0035] In other words, the chromium in zinc-chromium (Zn-Cr) alloys is not an impurity or an unnecessary metallic element in the alloy.

[0036] That is, chromium represents the predominant alloying metal element, by weight percent, of all alloying metal elements believed to be present in the mixture.

[0037] The zinc-chromium (Zn-Cr) coating of the present invention has the advantage that the chromium salts used in the preparation process are not classified as "CMR" substances, making them non-toxic and reducing the exposure of workers to serious health risks.

[0038] The chromium present in zinc-chromium (Zn-Cr) alloys corresponds to or is trivalent chromium Cr(III).

[0039] Furthermore, the zinc-chromium (Zn-Cr) coating according to the invention can ensure effective protection against corrosion and adhesive wear of the threaded ends of tubular elements, including in very harsh environments such as marine environments, industrial environments, environments subject to heavy precipitation, and / or environments experiencing large temperature changes.

[0040] Thus, the zinc-chromium (Zn-Cr) coating used in accordance with the present invention effectively provides cathodic protection for the substrate, imparting a good level of corrosion resistance.

[0041] Specifically, the chromium contained in the zinc-chromium metal coating of the present invention naturally passivates to form chromium oxide, which ensures effective protection against corrosion. Therefore, the natural formation of chromium oxide allows for the omission of an additional passivation step aimed at strengthening the corrosion protection performance of the substrate, which offers time savings from an industrial perspective.

[0042] In addition, the zinc-chromium (Zn-Cr) coating has excellent lubricating properties and can ensure effective protection against adhesive wear of the threaded ends during the continuous operation of screwing in and out of tubular elements.

[0043] The zinc-chromium (Zn-Cr) coating used in accordance with the present invention also has the advantage of being resistant to wear during continuous screwing operations, ensuring corrosion and adhesive wear resistance even after several screwing / unscrewing cycles without the need for additional corrosion and adhesive wear protection.

[0044] This means that the zinc-chromium (Zn-Cr) coating according to the invention can provide protection against corrosion and adhesive wear over long periods of time, including multiple screwing and unscrewing of tubular elements in harsh environments.

[0045] In particular, the abrasion resistance may be determined by an indentation test, such as a scratch test, in which a load, in particular a ball, is moved with increasing pressure on the surface of the coating until delamination of the coating, i.e., adhesive failure of the coating, occurs, and in particular the critical load at which adhesive failure occurs is measured.

[0046] The threaded end according to the invention therefore exhibits increased resistance to corrosion and adhesive wear, even in the harsh environments mentioned above, including after several screwing-in and screwing-out cycles of the tubular element provided with said end.

[0047] Furthermore, the zinc-chromium (Zn-Cr) coating of the present invention performs at least as well as zinc-nickel (Zn-Ni) coatings against the appearance of red rust.

[0048] Furthermore, the zinc-chromium (Zn-Cr) coating of the present invention has superior performance against the appearance of white rust compared to zinc-nickel (Zn-Ni) coating.

[0049] In particular, salt spray tests performed without passivation of the coating revealed that the zinc-nickel (Zn-Ni) coating showed early appearance of white rust, while the zinc-chromium (Zn-Cr) coating of the present invention showed delayed appearance of white rust even when the coating thickness was halved.

[0050] In the sense of the present invention, the expression "zinc (Zn) is the predominant element in % by weight relative to the total weight of the alloy" means that zinc has the highest content in % by weight among the elements of the alloy.

[0051] According to one embodiment, the threads are coated with a layer comprising a binary zinc-chromium (Zn-Cr) alloy, where zinc (Zn) is the predominant element in weight percent relative to the total weight of the alloy.

[0052] According to the present invention, the term "content" corresponds to the weight concentration of the metallic element in question relative to the concentrations of all elements present in the alloy.

[0053] In other words, the "content" is the weight concentration of the target metal element relative to the total concentration of the mixture.

[0054] According to one embodiment, the zinc (Zn) content is greater than 50% by weight, preferably greater than or equal to 60% by weight, more preferably greater than or equal to 65% by weight, relative to the total weight of the zinc-chromium alloy.

[0055] Preferably, the zinc (Zn) content is 70% by weight to 80% by weight, more preferably 70% by weight to 75% by weight, based on the total weight of the zinc-chromium alloy.

[0056] According to a preferred embodiment of the present invention, the chromium (Cr) content is 3% by weight or more, preferably 20% by weight or more, based on the total weight of the zinc-chromium alloy.

[0057] Preferably, chromium is the only alloying metal element present in the zinc-chromium (Zn-Cr) alloy.

[0058] Preferably, the zinc-chromium (Zn-Cr) alloy is a mixture comprising zinc as the predominant metallic element in weight percent relative to the total weight of the alloy, and chromium as an alloying metallic element, preferably chromium as the only alloying metallic element, and optionally one or more metallic or non-metallic impurities.

[0059] It should be noted that for purposes of this invention, "alloying metal element" means an alloying element that is intentionally present in or added to the alloy.

[0060] That is, the alloying metal elements are not impurities.

[0061] That is, the chromium present in the alloy according to the present invention is not an impurity.

[0062] In particular, zinc-chromium (Zn-Cr) coatings according to the invention, which contain a chromium content of 3% by weight or more, contain at least one crystalline phase of the Cr-Zn-17 type and have significantly improved corrosion resistance compared to coatings consisting of zinc alone.

[0063] According to one embodiment of the present invention, the chromium (Cr) content is 20% by weight to 30% by weight based on the total weight of the zinc-chromium alloy.

[0064] The zinc-chromium (Zn-Cr) coating according to the invention, which has a chromium content of 20% to 30% by weight based on the total weight of the Zn-Cr alloy, has excellent corrosion resistance properties, comparable to or even superior to zinc-based coatings, especially zinc- and nickel-based coatings, while having the advantage of being particularly adherent and consistently homogeneous on the surface.

[0065] The quality of the coating according to the invention is therefore significantly improved, especially in terms of adhesion, cohesion and wear resistance, when the chromium content is between 20% and 30% by weight relative to the total weight of the alloy, compared to zinc and chromium-based coatings with a chromium content strictly less than 20% by weight (<20% by weight) or strictly more than 30% by weight (>30% by weight).

[0066] In particular, zinc-chromium (Zn-Cr) coatings with a chromium content of 20% to 30% by weight contain at least one crystalline phase of the gamma type, which confers corrosion resistance properties five times greater than those of coatings consisting solely of zinc (i.e., coatings with a zinc content of 100% by weight relative to the total weight of the coating).

[0067] The advantage of this crystalline phase lies in the fact that it is cubic-centred and therefore shares an element of symmetry with the austenitic crystal lattice of some steels used as substrates, which promotes epitaxial growth and improves adhesion of the coating to the substrate.

[0068] Thus, zinc-chromium coatings according to the invention having a chromium content of 20% to 30% by weight exhibit better adhesion to the substrate than zinc- and chromium-based coatings having a chromium content strictly less than 20% by weight (<20% by weight) or strictly more than 30% by weight (>30% by weight).

[0069] In other words, the zinc-chromium (Zn-Cr) coating according to the present invention, which has a chromium content of 20% to 30% by weight, has a better structure and improved strength.

[0070] Furthermore, zinc-chromium (Zn-Cr) coatings, which contain 20% to 30% chromium by weight relative to the total weight of the alloy, have corrosion resistance properties 14 times better than zinc-nickel (Zn-Ni) coatings against white rust.

[0071] According to one embodiment of the present invention, the chromium (Cr) content is 25% by weight to 30% by weight based on the total weight of the zinc-chromium alloy.

[0072] The zinc-chromium (Zn-Cr) coatings according to the invention, which have a chromium content of 25% to 30% by weight relative to the total weight of the zinc-chromium alloy, withstand loads at least as well as zinc- and nickel-based coatings and at the same time have excellent corrosion resistance properties, especially in harsh environments.

[0073] The zinc-chromium coating according to the invention, which has a chromium content of 25% to 30% by weight based on the total weight of the zinc-chromium alloy, has better long-term wear resistance than zinc- and nickel-based coatings and at the same time has excellent corrosion resistance properties.

[0074] Advantageously, the chromium (Cr) content is 27% by weight relative to the total weight of the zinc-chromium alloy.

[0075] According to a preferred embodiment of the present invention, the zinc (Zn) content is 70% to 80% by weight and the chromium (Cr) content is 20% to 30% by weight, based on the total weight of the zinc-chromium alloy.

[0076] According to a preferred embodiment of the invention, the layer comprising a zinc-chromium alloy as described above is a layer made of a binary zinc-chromium alloy.

[0077] According to a preferred embodiment of the present invention, the threads are coated with a layer consisting of a binary zinc-chromium (Zn-Cr) alloy, in which zinc (Zn) is the predominant element in weight percent relative to the total weight of the alloy, and the chromium (Cr) content is between 20% and 30% by weight relative to the total weight of the alloy.

[0078] According to a preferred embodiment of the present invention, a layer comprising a zinc-chromium (Zn-Cr) alloy is electrodeposited.

[0079] Advantageously, zinc and chromium can be deposited on the substrate by electroplating at very high current densities, particularly at deposition rates of around 7 μm per minute, which is three times faster than the deposition rate of layers made from zinc-nickel alloys.

[0080] According to one embodiment, the layer containing the zinc-chromium (Zn-Cr) alloy has a thickness of 4 μm to 20 μm. Such a thickness allows the zinc-chromium layer to be more optimally applied at least to the threads of the threaded end of the tubular element. In other words, the deposition of the zinc-chromium (Zn-Cr) layer according to the invention, when applied in a thickness range of 4 μm to 20 μm, is better distributed in the threads and provides improved protection against corrosive and adhesive wear. Such a thickness allows for optimal adaptation to the shape of the threads of the end of the tubular element.

[0081] Advantageously, from 4 μm onwards the corrosion protection is fully achieved, and up to 20 μm the layer remains dense without allowing for brittleness. Above 20 μm the layer may become too thick for the machining clearances of the connections.

[0082] Advantageously, the layer comprising a zinc-chromium (Zn-Cr) alloy has a chromium content of 20% to 30% by weight, preferably 25% to 30% by weight, relative to the total weight of the zinc-chromium alloy, and a thickness of 4 μm to 20 μm, preferably 10 μm to 20 μm.

[0083] Zinc-chromium (Zn-Cr) coatings with a chromium content of 20% to 30% by weight, preferably 25% to 30% by weight, relative to the alloy layer weight and a thickness of 4 μm to 20 μm, preferably 10 μm to 20 μm, have the advantage of being optimally distributed on the thread, having particularly good adhesion, being consistently homogeneous and wear-resistant while having excellent corrosion properties.

[0084] Advantageously, the layer comprising a zinc-chromium (Zn-Cr) alloy is not coated with a passivation layer comprising trivalent chromium (Cr(III)).

[0085] In particular, the chromium contained in the coating naturally forms chromium oxide, eliminating the need for an additional passivation step to enhance corrosion protection.

[0086] Advantageously, therefore, zinc-chromium coatings are not covered with a passivation layer containing trivalent chromium (Cr(III)).

[0087] Preferably, the threaded end of the tubular element further comprises at least one non-threaded portion coated with a layer comprising a zinc-chromium (Zn-Cr) alloy according to the invention.

[0088] Preferably, the non-threaded portion comprises a stop.

[0089] Preferably, the non-threaded portion comprises a sealing seat.

[0090] According to a preferred embodiment of the invention, the non-threaded part coated with the layer comprising a zinc-chromium (Zn-Cr) alloy according to the invention comprises a stop and / or a sealing seat.

[0091] Preferably, the threaded end of the tubular element is made of steel.

[0092] Preferably, the steel threaded end of the tubular element as described above comprises at least one thread extending on its outer or inner peripheral surface, the thread being coated with at least one layer comprising a zinc-chromium (Zn-Cr) alloy, the Zn-Cr alloy having a chromium content of 20% to 30% by weight, preferably 25% to 30% by weight, relative to the total weight of the Zn-Cr alloy.

[0093] Preferably, the steel threaded end of the tubular element as described above comprises at least one thread extending on its outer or inner circumferential surface, the thread being coated with at least one layer comprising a zinc-chromium (Zn-Cr) alloy, the chromium content of which is 20% to 30% by weight, preferably 25% to 30% by weight, relative to the total weight of the zinc-chromium alloy, and the thickness of which is 4 μm to 20 μm.

[0094] According to one embodiment, the surface of the thread as described above, and optionally the surface of the non-threaded portion, coated with the zinc-chromium (Zn-Cr) coating according to the invention may have a surface roughness (Ra) of 1.6 μm to 3.2 μm.

[0095] According to one embodiment, the surfaces of the threads and the surfaces of the non-threaded parts, preferably provided with a stop and / or sealing seat, and coated with a zinc-chromium (Zn-Cr) coating according to the invention, may have a surface roughness (Ra), in particular a surface roughness (Ra) of 1.6 μm to 3.2 μm.

[0096] The surface roughness can be achieved by sandblasting.

[0097] That is, the surface of the thread, and possibly the surface of the non-threaded portion, may be pre-treated with a mechanical treatment, preferably sandblasting.

[0098] Surface roughening can improve the adhesion and wear resistance of zinc-chromium (Zn-Cr) coatings.

[0099] According to a preferred embodiment of the present invention, the surface of the thread, preferably including the stop and / or sealing seat, and optionally the non-threaded parts, are pretreated by sandblasting and coated with a zinc-chromium (Zn-Cr) coating having a chromium content of 20% to 30% by weight and preferably a thickness of 4 μm to 20 μm.

[0100] The present invention also relates to the use of a layer comprising a zinc-chromium (Zn-Cr) alloy as described above for protecting at least one threaded end of a tubular element as described above against corrosion and adhesive wear.

[0101] The present invention also relates to a process for preparing a threaded end, as described above, of a tubular element for drilling and / or working hydrocarbon wells, for oil and gas transportation, for hydrogen transportation or storage, for carbon recovery or for geothermal energy recovery, which process comprises at least one step of electrodepositing, onto at least the surface of the threads of the end, an aqueous composition comprising one or more zinc salts, one or more chromium salts, one or more electrolytes, and one or more surfactants, preferably non-ionic surfactants.

[0102] The process according to the invention allows for the deposition of a layer comprising at least one zinc-chromium (Zn-Cr) alloy as described above, which is homogeneous, compact and can be evenly distributed over the threads of the threaded end.

[0103] According to one embodiment, the process according to the invention may include a step of preparation of the surface to be coated by mechanical treatment, more preferably by sandblasting.

[0104] Preparing the surface to be coated by mechanical treatment, preferably sandblasting, can improve adhesion of the zinc-chromium (Zn-Cr) coating and minimize the risk of embrittlement.

[0105] According to one embodiment, the process according to the invention may comprise a step of preparation of the surface of the thread and of the non-threaded part, preferably comprising the stop and / or sealing seat, by mechanical treatment, preferably sandblasting.

[0106] According to one embodiment, the process according to the invention may comprise a step of sandblasting the surface to be coated of the threaded end, preferably the surface of the thread comprising the stop and / or sealing seat and the surface of the non-threaded part.

[0107] According to one embodiment, the process according to the invention comprises the steps of sandblasting the surface to be coated and electrodepositing the aqueous composition as described above onto at least the sandblasted surface of the thread, preferably onto the sandblasted surface of the thread and preferably onto the sandblasted surface of the non-threaded part comprising the stop and / or sealing seat.

[0108] Furthermore, the resulting zinc-chromium coating has a surface with a homogeneous aesthetic appearance.

[0109] According to a preferred embodiment of the present invention, the deposition rate of the aqueous composition on the surface to be coated is between 4 μm and 20 μm per minute, preferably between 5 μm and 7 μm per minute.

[0110] The zinc and chromium salts are soluble in aqueous compositions.

[0111] According to the present invention, the chromium (Cr) salt is a trivalent chromium Cr(III) salt.

[0112] Preferably, the electrodeposition is at least 30 amps / dm 2 This is done at a current density of .

[0113] In particular, a sufficient stirring speed of the aqueous composition, for example a speed of 0.23 m / s at the cathode, allows advantageously to increase the current density without the risk of causing seizing, which would likely result in a deterioration in the appearance of the zinc-chromium (Zn-Cr) coating according to the invention.

[0114] More preferably, the electrodeposition is carried out at a current of 30 amps / dm 2 ~50 amps / dm 2The current density is

[0115] 30 amps / dm 2 Below this, chromium incorporation is reduced or inhibited and the resulting coating has dark grey specks representing chromium-free areas.

[0116] According to one embodiment, the weight ratio of the chromium salt to the zinc salt is between 0.8 and 1.4.

[0117] Preferably, the surfactant is selected from the group consisting of non-ionic surfactants.

[0118] Preferably, the nonionic surfactant is a (poly)alkoxylated fatty alcohol, in particular a (poly)alkoxylated C-C 40 It is selected from the group consisting of fatty alcohols, in particular poly(ethylene glycol) octyl ether, and oxirane, 2-methyl-, oxirane and polymer, mono(2-naphthonyl) ether.

[0119] The presence of a surfactant in the aqueous composition allows for the deposition of chromium along with the zinc.

[0120] In fact, it has been found that without surfactants, the deposit obtained does not contain chromium. This is especially because the pH of the cathode increases due to the release of dihydrogen, resulting in the formation of zinc hydroxide, which inhibits the diffusion of chromium to the cathode. This absence of chromium deposition can be explained by the presence of a shift in the reduction potential (chromium becomes lower than the zinc reduction potential and / or water reduction potential).

[0121] Thus, the presence of at least one surfactant can facilitate the diffusion of chromium in the diffusion layer and / or reduce the cathodic overpotential of chromium and / or increase the cathodic overpotential of water electrolysis, thereby minimizing the release of dihydrogen and the formation of zinc hydroxide.

[0122] Preferably, the concentration of the surfactant is 0.3 mmol / l to 3 mmol / l.

[0123] The brightness of the zinc-chromium (Zn-Cr) coating of the present invention can be adjusted by adjusting the surfactant concentration.

[0124] Preferably, the brightness of the zinc-chromium (Zn-Cr) coating according to the present invention can be increased by increasing the concentration of the surfactant.

[0125] Preferably, the zinc salt may be selected from zinc sulfate, zinc chloride, and zinc sulfamate. Preferably, the zinc salt is zinc sulfate.

[0126] Preferably, the chromium salt may be selected based on the properties of the zinc salt: if zinc sulfate is preferred, then chromium sulfate is preferentially selected.

[0127] The conductive salt / carrier salt may be selected from the group consisting of sodium sulfate, potassium sulfate, and ammonium sulfate, and mixtures thereof, and is preferably sodium sulfate. The conductive salt / carrier salt can ensure conductivity during the process.

[0128] Preferably, the aqueous composition further comprises one or more amino acids, preferably glycine.

[0129] Glycine can impart a gloss, semi-gloss, or matte finish to the zinc-chromium (Zn-Cr) coating of the present invention.

[0130] The content of glycine in the aqueous composition may be between 50 g / l and 75 g / l relative to the total concentration of the composition.

[0131] The glycine content allows the matte appearance of the zinc-chromium (Zn-Cr) coating according to the invention to be adjusted.

[0132] Preferably, increasing the glycine content and decreasing the surfactant content results in a matte appearance of the zinc-chromium (Zn-Cr) coating.

[0133] Preferably, the zinc-chromium (Zn-Cr) coating has a glossy appearance when the glycine content is decreased and the surfactant content is increased.

[0134] When zinc-chromium (Zn-Cr) coatings are shiny on non-sandblasted surfaces or semi-gloss on sandblasted surfaces, the mechanical properties of the zinc-chromium (Zn-Cr) coatings are superior to zinc-chromium (Zr-Cr) coatings with a matte appearance.

[0135] The pH of the aqueous composition may be from 1.5 to 3.5, preferably from 2 to 2.5.

[0136] In fact, if the pH of the aqueous composition exceeds 3.5 in particular, the risk of precipitation of chromium salts in the bath increases, and if the pH is between 1.5 and 3.5, this risk can be minimized.

[0137] The process according to the invention is carried out at a temperature of 35° C. to 45° C. Below 35° C., the effectiveness of the composition may be insufficient, and above 45° C., the chemical components may deteriorate.

[0138] Preferably, the aqueous composition comprises: one or more zinc salts, one or more chromium salts, one or more conductive / carrier salts, preferably sodium sulfate; one or more surfactants, preferably nonionic surfactants, and Optionally, one or more amino acids, preferably glycine Includes.

[0139] Advantageously, the process according to the invention does not include the additional step of forming a passivating corrosion-resistant layer containing trivalent chromium (Cr(III)).

[0140] That is to say, advantageously, the process according to the invention does not include a step of forming a passivating corrosion-resistant chemical layer comprising trivalent chromium (Cr(III)) after the deposition of the layer comprising a zinc-chromium alloy.

[0141] Another subject of the present invention relates to a tubular element for drilling and / or working hydrocarbon wells, transporting oil and gas, transporting or storing hydrogen, recovering carbon, or recovering geothermal energy. It has a threaded end according to the present invention, which includes at least one thread extending on its outer or inner surface. The thread is covered with a layer containing a zinc-chromium (Zn-Cr) alloy according to the present invention, where zinc (Zn) is the predominant element in terms of weight percent relative to the total weight of the alloy.

[0142] The threaded end is as described above.

[0143] The layer containing the zinc-chromium (Zn-Cr) alloy is as described above.

[0144] The tubular elements have improved corrosion resistance and adhesive wear resistance.

[0145] Preferably, the tubular element is male and has at least one thread extending on its outer circumferential surface.

[0146] More preferably, the tubular element is male and has at least one thread extending on its outer circumferential surface and at least one non-threaded portion, preferably selected from a stop and / or a sealing seat.

[0147] Preferably, the tubular element is female and has at least one thread extending on its inner circumferential surface.

[0148] More preferably, the tubular element is female and has at least one thread extending on its inner circumferential surface and at least one non-threaded portion, preferably selected from a stop and / or a sealing seat.

[0149] According to the invention, the tubular element is provided with an axis of rotation.

[0150] The tubular element according to the invention is made in particular of steel, in particular of a steel as specified in the API 5CT standard, for example a steel containing less than 0.25% carbon, and / or preferably a steel having a grade defined in accordance with the ISO 11960 and ISO 13680 standards, and / or H40, J55, K55, M65, L80, C90, C95, T95, P110 or Q125 carbon steel, or a martensitic 13Cr or S13Cr steel, or a duplex 22Cr+25Cr steel, or a superduplex 25Cr steel, or an austenitic Fe27Cr steel.

[0151] The invention also relates to the use of a tubular element as described above for drilling and / or working hydrocarbon wells, transporting oil and gas, transporting or storing hydrogen, capturing carbon or capturing geothermal energy.

[0152] Preferably, the invention relates to the use of a tubular element as described above for drilling and / or working a hydrocarbon well.

[0153] The present invention also relates to a tubular threaded joint for drilling and / or operating hydrocarbon wells, transporting oil and gas, transporting or storing hydrogen, recovering carbon, or recovering geothermal energy. The tubular threaded joint comprises a threaded end of a male tubular element having at least one thread extending on its outer circumferential surface and a threaded end of a female tubular element having at least one thread extending on its inner circumferential surface. These are threaded together. At least one threaded end is as described above. In particular, the thread is covered with a layer including a zinc-chromium (Zn-Cr) alloy as described above.

[0154] In particular, the tubular threaded joint according to the invention has excellent corrosion resistance and adhesive wear resistance, especially in harsh environments such as those mentioned above.

[0155] Preferably, the two threaded ends are as described above.

[0156] According to one aspect of the present invention, the threaded end of the male tubular element has at least one thread extending on its outer circumferential surface, which is coated with a layer comprising a zinc-chromium (Zn-Cr) alloy according to the present invention as described above.

[0157] According to one aspect of the invention, the threaded end of the female tubular element has at least one thread extending on its inner circumferential surface, which is coated with a layer comprising a zinc-chromium (Zn-Cr) alloy according to the invention as described above. According to yet another aspect of the present invention, the threaded end of the male tubular element has at least one thread extending on its outer circumferential surface, which is coated with a layer comprising a zinc-chromium (Zn-Cr) alloy according to the present invention, and the threaded end of the female tubular element has at least one thread extending on its inner circumferential surface, which is coated with a layer comprising a zinc-chromium (Zn-Cr) alloy according to the present invention.

[0158] Preferably, the tubular threaded joint comprises a threaded end of a male tubular element having at least one non-threaded portion with at least one thread and metallic interference extending on its outer circumferential surface, and a threaded end of a female tubular element having at least one non-threaded portion selected from a stop and / or sealing seat with at least one thread and metallic interference extending on its inner circumferential surface, wherein the thread and non-threaded portion are covered with a layer comprising a zinc-chromium (Zn-Cr) alloy according to the invention as described above.

[0159] In the context of this specification, range terms are intended to include the values ​​in the stated range unless otherwise expressly stated.

[0160] Additionally, as used herein, the phrase "at least one" is equivalent to "one or more." [Brief explanation of the drawings]

[0161] The features of the present invention will now be described in detail with reference to the accompanying drawings. [Figure 1] FIG. 1 is a schematic diagram of a joint resulting from threaded joining of two tubular elements. [Figure 2] FIG. 2 is an enlarged view of the boxed area A in FIG. [Figure 3] FIG. 10 shows in detail the cooperation of the threads of the two assembled tubular elements. [Figure 4] FIG. 2 shows in detail a connecting element (thread) according to the invention, which is covered with a zinc-chromium coating according to the invention. [Figure 5] FIG. 1 is a diagram comparing the time to appearance of white rust layers of strength 2 and strength 3 on the surface of a zinc-nickel (Zn-Ni) coating and a zinc-chromium (Zn-Cr) coating according to the present invention after exposure to a salt spray test. [Figure 6] FIG. 1 is a graph comparing the time it takes for a zinc-nickel (Zn-Ni) coating surface and a zinc-chromium (Zn-Cr) coating surface according to the present invention to be completely covered with a white rust layer of strength 2 after exposure to a salt spray test. DETAILED DESCRIPTION OF THE INVENTION

[0162] The threaded joint shown in FIG. 1 comprises a first tubular element having a rotation axis 9 and a male end 1, and a second tubular element having a rotation axis 9 and a female end 2. Each of the two ends 1 and 2 terminates in an end face oriented radially relative to the axis 9 of the threaded joint and has a threaded portion 3 and 4, respectively, that cooperate with each other for threaded assembly of the two elements. The threaded portions 3 and 4 may have trapezoidal threads or other types of threads. In the illustrated embodiment, the threaded portions have tapered threads at each end of the threaded portion. These tapered threads extend over a portion of the axial extent of the threaded portion. In particular, the portion 10 of the threaded portion having a tapered thread does not cooperate with a complementary thread.

[0163] Additionally, as shown in Figure 2, metal-to-metal sealing surfaces (seats) 5, 6 intended to form a fluid-tight seal with one another after the two threaded elements are threaded together and assembled are formed on the male and female ends, respectively, near the threaded portions 3, 4. Finally, the male end 1 terminates in an end face 7 that abuts a corresponding surface 8 formed on the female end 2 when the two ends are threaded together. Surfaces 7 and 8 are called stops.

[0164] 3 shows the threads of the threaded portion in detail. Each of the threads has a load flank 11 that forms an angle 12 ranging from −5° to +5° with respect to the normal N of the connection axis 10. The load flanks are connected to assembly flanks 14 via apexes 13. In particular, as shown in the figure, the load flanks of the male threaded portion 3 are connected to contact corresponding load flanks of the female threaded portion 4 in the final assembled position.

[0165] Figure 4 shows the male end 1 of a tubular element, where the threaded portion 3 and the sealing surface 5 (seat) are covered with a coating 15 according to the invention, i.e. a zinc-chromium coating comprising a zinc-chromium (Zn-Cr) alloy in which zinc (Zn) is the predominant element in weight percent relative to the total weight of the alloy.

[0166] Preferably, coating 15 has a chromium content of 20% to 30% by weight, more preferably 25% to 30% by weight, and a zinc content of 70% to 80% by weight, more preferably 70% to 75% by weight, based on the total weight of the alloy.

[0167] Exemplary Embodiments L80 grade carbon steel threads were electroplated with a semi-bright metallic coating containing a zinc-chromium (Zn-Cr) alloy with a chromium content of 27 wt.% based on the total weight of the alloy, as described above.

[0168] Semi-bright zinc-chromium coatings were obtained from aqueous compositions containing 75 g / l of glycine.

[0169] Zinc-chromium coatings were compared with zinc-nickel (Zn-Ni) coatings, where zinc was the predominant element by weight percent. The nickel content ranged from 10 wt% to 18 wt%. The weight percent was calculated relative to the total weight of the alloy.

[0170] Tribological tests (scratch and Bowden tests) were performed on the coatings to determine the critical load at which delamination (plastic deformation) of the coating was observed, the initial coefficient of friction, and the number of cycles the coating could withstand.

[0171] Salt spray tests were also conducted on the coatings to determine the corrosion resistance performance of the coatings.

[0172] [Scratch test] The experimental conditions were as follows: a tungsten carbide ball was used, and the load was increased from 10N to 260N while the ball travel speed was 4.20mm / s, the travel time was 2.38 seconds, the ball size was 5mm, and the track length was 10mm.

[0173] The results of the scratch test are shown in Table 1.

[0174] [result] [Table 1]

[0175] The scratch test results, shown in Table 1, indicate that the semi-bright zinc-chromium coating withstood loads at least as great as those withstood by zinc-nickel coatings with nickel contents ranging from 10% to 18% by weight relative to the total weight of the alloy.

[0176] [Bowden test] To evaluate the lubrication properties (friction coefficient) of the coating surface, a commercially available Bowden friction tester (Shinko Engineering Co., Ltd.) was used. The Bowden friction tester applies a load to a tungsten carbide ball while it moves back and forth linearly over a coating formed on a steel plate.

[0177] The coefficient of friction was measured by the friction force and pressure load.

[0178] [procedure] A tungsten carbide ball was applied to the coating and moved under pressure loads of 30N and 100N with a ball speed of 4.20mm / s, a duration of 2.38 seconds, a ball size of 5mm, and a track length of 10mm.

[0179] To evaluate the lubrication properties of the coatings, the initial coefficient of friction was determined.

[0180] To evaluate the abrasion resistance of each coating, the number of cycles (number of times the ball passes over the surface) was measured for each coating.

[0181] The results are shown in Tables 2 and 3.

[0182] [Bowden test results with a load of 30N] [Table 2]

[0183] The Bowden test results shown in Table 2 show that for a load of 30 N, the zinc-chromium coating according to the present invention has a lower initial coefficient of friction than the zinc-nickel coating.

[0184] Furthermore, the zinc-chromium coating showed the same level of durability as the zinc-nickel coating under a load of 30N.

[0185] [Bowden test results with a load of 100N] [Table 3]

[0186] The results of the Bowden test carried out at a load of 100 N, shown in Table 3, show that the zinc-chromium coating according to the present invention is more durable than the zinc-nickel coating.

[0187] As a result, the zinc-chromium coating according to the present invention had better wear resistance than the zinc-nickel coating with a nickel content of 10 wt% to 18 wt%.

[0188] That is, as the load increased, the zinc-chromium (Zn-Cr) coating of the present invention showed improved durability, i.e., higher wear resistance, compared to the zinc-nickel (Zn-Ni) coating.

[0189] [Salt spray test] For the corrosion tests, neutral salt spray tests were carried out in a climate chamber under the following conditions: 35°C, 50 g / l saline solution with a density of 1.029–1.036 at 25°C and a pH of 6.5–7.2 at 25°C, collected at an average rate of 1.5 ml / h.

[0190] This test evaluated the appearance of red rust and white rust.

[0191] [Corrosion resistance: Appearance of red rust] The appearance of red rust was evaluated by determining the degree of rust, Re, corresponding to the ratio of the rusted surface area to the total surface area, in ascending order.

[0192] In this case, an intact sample without red rust must meet class Re0 of the ISO 9227 standard.

[0193] The results are shown in Table 4.

[0194] [Table 4]

[0195] The degree of rust after the test is in ascending order from Re0 to Re2, which corresponds to the rusted surface area relative to the total surface area.

[0196] According to the degree of rust, Re0 = rust on 0% of the total surface area; Re1 = 0.05% of the total surface area of ​​rust; Re2 = 0.5% of the total surface area rust, Re6 = 40% to 50% of the total surface area is rusted This is what happened.

[0197] Table 4 shows that zinc-chromium (Zn-Cr) coatings can inhibit the appearance of red rust at least as well as zinc-nickel coatings.

[0198] [Corrosion resistance: appearance of white rust] The presence of white rust corresponds to oxidation of the coating, particularly oxidation of the zinc, and was assessed by measuring the time it took to appear and to completely cover the surface of the coating after exposure to salt spray.

[0199] After exposure to salt spray, the strength of the white rust layer over the coating was ranked in ascending order as follows: · White rust intensity 1: corresponds to a thin, light layer of white rust, also known as bloom. White rust intensity 2: corresponds to a layer of white rust in the form of crystals. White rust intensity 3: corresponds to a very dense layer of white rust.

[0200] [White rust appearance time] Figure 5 compares the time it takes for white rust layers of strength 2 and strength 3 to appear on the surface of a zinc-nickel coating [Zn-Ni, nickel content 14 wt%, thickness 10 μm] and a zinc-chromium coating [Zn-Cr, chromium content 27 wt%, thickness 5 μm] after exposure to a salt spray test.

[0201] Figure 5 shows that on the surface of the zinc-nickel coating [Zn-Ni, nickel content 14 wt%, thickness 10 μm], a white rust layer of strength 2 appeared rapidly after 24 hours, whereas on the surface of the zinc-chromium coating [Zn-Cr, chromium content 27 wt%, thickness 5 μm], a white rust layer of strength 2 appeared only after 170 hours.

[0202] Figure 5 also shows that a white rust layer of strength 3 appeared rapidly after 24 hours on the zinc-nickel coating [Zn-Ni, nickel content 14 wt%, thickness 10 μm], whereas a white rust layer of strength 3 appeared only after 336 hours on the zinc-chromium coating [Zn-Cr, chromium content 27 wt%, thickness 5 μm].

[0203] [Time until the coating surface is completely covered with white rust] Figure 6 shows the results of a comparison of the time it takes for a layer of white rust of strength 2 to completely cover the surface of a zinc-nickel coating [Zn-Ni, nickel content 14 wt%, thickness 10 μm] and a zinc-chromium coating [Zn-Cr, chromium content 27 wt%, thickness 5 μm].

[0204] Figure 6 shows that it took 24 hours for a layer of white rust with strength 2 to completely cover the surface of a zinc-nickel coating [Zn-Ni, nickel content 14 wt%, thickness 10 μm], while it took 336 hours for the same layer to completely cover the surface of a zinc-chromium coating [Zn-Cr, chromium content 27 wt%, thickness 5 μm].

[0205] [Conclusion] As described above, it has been shown that the zinc-chromium (Zn-Cr) coating of the present invention has superior performance in terms of the appearance of white rust compared to zinc-nickel (Zn-Ni) coating.

[0206] As a result, the adhesion of the layer deposited after the zinc-chromium coating was improved.

Claims

1. Threaded end (1, 2) of a tubular element for drilling and / or working hydrocarbon wells, transporting oil and gas, transporting or storing hydrogen, recovering carbon or recovering geothermal energy, comprising at least one thread (3, 4) extending on its outer or inner circumferential surface, said thread (3, 4) being coated with a layer (15) comprising a zinc-chromium (Zn-Cr) alloy, wherein zinc (Zn) is the predominant element in weight percent relative to the total weight of said zinc-chromium alloy and represents the alloying metal element as a base metal mainly present in the mixture, and chromium represents the main additional alloying metal element added to the mixture. Threaded end (1, 2) of a tubular element, characterized in that

2. Threaded end portion (1, 2) of a tubular element according to claim 1, characterized in that the zinc (Zn) content is more than 50% by weight, relative to the total weight of the zinc-chromium alloy.

3. 3. The threaded end portion (1, 2) of a tubular element according to claim 1 or 2, characterized in that the chromium (Cr) content is greater than or equal to 3% by weight, relative to the total weight of the zinc-chromium alloy.

4. Threaded end portion (1, 2) of a tubular element according to claim 1, characterized in that the chromium (Cr) content is between 20% and 30% by weight, relative to the total weight of the zinc-chromium alloy.

5. Threaded end portion (1, 2) of a tubular element according to claim 1, characterized in that said layer (15) is electro-deposited.

6. Threaded end portion (1, 2) of a tubular element according to claim 1, characterized in that the thickness of said layer (15) is between 4 μm and 20 μm.

7. Threaded end (1, 2) of a tubular element according to claim 1, characterized in that it further comprises at least one non-threaded portion coated with the layer (15) according to any one of claims 1 to 6.

8. Threaded end portion (1, 2) of a tubular element according to claim 7, characterized in that the non-threaded portion comprises a stop (7, 8) and / or a sealing seat (5, 6).

9. Threaded end (1, 2) of a tubular element according to claim 1, characterized in that it is made of steel.

10. 10. A process for preparing a threaded end (1, 2) of a tubular element according to any one of claims 1 to 9, characterized in that it comprises at least one step of electrodepositing the surface of the threads (3, 4) of said threaded end with an aqueous composition comprising one or more zinc salts, one or more chromium salts, one or more electrolytes and one or more surfactants.

11. 11. The process according to claim 10, characterized in that it includes a step of preparing the surface to be coated by a mechanical treatment.

12. A tubular element for drilling and / or working hydrocarbon wells, for transporting oil and gas, for transporting or storing hydrogen, for carbon recovery or for geothermal energy recovery, the tubular element comprising a threaded end (1, 2) according to any one of claims 1 to 9.

13. 13. A tubular element according to claim 12, characterized in that it is male and has at least one thread (3) extending on the outer circumferential surface of said tubular element.

14. 13. A tubular element according to claim 12, characterized in that it is female and has at least one thread (4) extending on the inner circumferential surface of said tubular element.

15. 10. A tubular threaded joint comprising a threaded end (1) of a male tubular element and a threaded end (2) of a female tubular element, wherein the threaded end (1) of the male tubular element has a thread extending on its outer circumferential surface and the threaded end (2) of the female tubular element has at least one thread extending on its inner circumferential surface, the threads of the threaded end (1) of the male tubular element and the threads of the threaded end (2) of the female tubular element being threaded together, and wherein at least one of the threaded ends is a threaded end according to any one of claims 1 to 9.

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