THREADED END OF A TUBULAR COMPONENT PROVIDED WITH A COATING COMPRISING A ZINC-CHROMIUM ALLOY

Description

The present invention relates to a threaded end of a tubular component for drilling and/or operating a hydrocarbon well, transporting oil and gas, transporting or storing hydrogen, carbon capture or geothermal energy, comprising at least one thread, the surface of which is provided with a zinc and chromium-based coating as described below.

The invention also relates to a process for preparing a threaded end of a tubular component comprising at least one electrodeposition 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, on the surface of the thread of said end.

The present invention also relates to a tubular threaded joint comprising at least one threaded end of a tubular component, for which the surface of the thread is covered with a zinc and chromium-based coating as described below.

For the purposes of the present invention, a tubular component is understood to mean any element or accessory having a substantially tubular shape capable of being joined to another element, optionally of the same type, which is intended for drilling and/or operating a hydrocarbon well, for transporting oil and gas, for transporting and/or storing hydrogen and for carbon capture or geothermal energy capture.

For the purposes of the present invention, a threaded end of a tubular component is understood to mean any end element of a tubular component, as defined above, the surface of which is provided with at least one threaded portion, i.e. with a thread, which makes it possible to join or connect the tubular component to another component, optionally of the same type, in order to form a joint or connection.

Thus, within the meaning of the invention, the threaded end of a tubular component corresponds to any end element of a tubular component comprising at least one threaded surface and participating in the connection of the tubular component to another similar or different component.

Each tubular component has an end provided with at least one male threaded area, i.e. the thread of which extends over the outer peripheral surface, and/or an end provided with at least one female threaded area, i.e. the thread of which extends over the inner peripheral surface, which are each intended to be joined by screwing together with the corresponding end of a similar or different component to form a joint or connection.

The threaded tubular components of a connection are usually joined under defined constraints in order to meet the tightening and sealing requirements imposed by the conditions of use, more precisely a defined torque is targeted. In addition, the threaded tubular components may have to undergo several screwing and unscrewing cycles, in particular in service.

The conditions of use of these threaded tubular components give rise to various types of stress which can be reduced or even minimized, in particular by the use of films or greases on sensitive parts used to connect these components, such as threaded areas, abutting areas, or metal/metal sealing surfaces.

The stresses induced include, in particular, storage stability stresses requiring the application of storage greases (different from the screwing greases applied before being put into service). However, there are other solutions that consist in using organic or metallic coatings.

Screwing and unscrewing operations are generally carried out under high axial load, for example under the weight of a pipe several metres in length, typically from 10 to 13 metres, to be joined by the threaded joint vertically, possibly aggravated by a slight misalignment of the axis of the threaded elements to be joined. This leads to risks of galling at the connecting elements of the pipe, notably at the threaded areas but also at the abutting areas and/or on the metal/metal sealing surfaces. Consequently, it is important to protect these connecting elements, in particular the threaded areas, against galling by covering them, notably with lubricants.

In addition, threaded tubular components are often stored, and then screwed together, in a harsh environment. This is particularly the case for an “offshore” situation in the presence of saline mist or an “onshore” situation in the presence of sand, dust, and/or other pollutants, leading to risks of corrosion. It is therefore common to use various types of anticorrosion coating on surfaces subjected to screwing, which is the case for threaded areas, or else surfaces in tight contact, which is the case for metal/metal sealing surfaces and abutting areas.

However, in view of environmental standards, it appears that the use of greases meeting the API (American Petrol Institute) RP 5A3 standard is not a viable long-term solution, in so far as these greases are extruded out of the tubular components and released into the environment or, for example, into a well, leading to blockages that require special cleaning operations.

In order to address the problems of lasting resistance to corrosion and galling, and also environmental prerogatives, alternatives to greases have already been used in the prior art.

For this purpose, a metallic coating based on zinc (Zn) and nickel (Ni) was developed in order to protect the connection elements, notably the threaded areas, of a tubular component against corrosion and galling.

However, despite good performance in terms of resistance to corrosion and galling, this metallic coating has the major drawback of being prepared from nickel salts which are chemicals that have harmful effects on human health. Specifically, nickel salts are classified as “CMR” substances, i.e. substances considered to be carcinogenic, mutagenic and reprotoxic.

The metallic coating based on zinc and nickel is thus commonly used in industry because of its properties against corrosion and galling, but its toxicity has at the same time the consequence of regularly exposing a very large number of operators to health risks that may prove to be serious in the long term.

Other zinc-based metallic coatings have also been developed to protect against corrosion and galling of the connecting elements of a tubular component.

However, it has been observed that the metallic coatings thus envisaged do not constitute a viable solution for various reasons.

By way of example, zinc (Zn) and cobalt (Co) coatings, typically those with a content of around 1% by weight of cobalt, are also toxic because their preparation process is based on the use of cobalt salts which are themselves also classified as “CMR” substances.

Similarly, zinc (Zn) and cadmium (Cd) coatings have the disadvantage of being obtained with cadmium salts which are also substances that are toxic to human health.

Coatings based on tin (Sn) and zinc (Zn), in particular those comprising from 70% to 80% by weight of tin and from 20% to 30% by weight zinc, offer advantageous corrosion protection but have a low thermal resistance, in particular to high temperatures, and also high manufacturing costs. These disadvantages are in particular linked to the high tin content used to prepare coatings of this type.

Coatings based on zinc (Zn) and magnesium (Mg) are themselves notably obtained by electrodeposition of zinc salts and magnesium salts in the presence of solvents at elevated temperatures, typically at temperatures of around 100° C., which makes the preparation process difficult to implement on an industrial scale.

Coatings based on zinc (Zn) and iron (Fe), in particular those with the content of more than 10% by weight of iron, have the disadvantage of oxidizing by forming a red rust that can be confused with the red oxidation of the iron of the substrate.

In general, coatings of zinc (Zn) and magnesium (Mg), zinc (Zn) and iron (Fe) or else zinc (Zn) and manganese (Mn) provide lower cathodic protection to the substrate than a coating based on zinc (Zn) and nickel (Ni), therefore lower corrosion protection, due to the fact that the alloying elements (magnesium, manganese and iron) have standard redox potentials lower than that of nickel.

Thus, there is a real need to provide a coating capable of overcoming the abovementioned drawbacks, that is to say which has a reduced or even minimized toxicity, while being able to effectively protect the threaded ends of a tubular component intended for drilling and/or operating a hydrocarbon well, transporting oil and gas, transporting or storing hydrogen, carbon capture or geothermal energy, against corrosion and galling.

One of the objectives of the present invention is thus to provide a coating that has reduced toxicity or is non-toxic, and the anticorrosion and anti-galling performance of which is not adversely affected by the nature of the alloying elements, so as to effectively protect the threaded elements of a tubular component used to join it to another similar or different tubular component.

The present invention therefore relates in particular to a threaded end of a tubular component for drilling and/or operating a hydrocarbon well, transporting oil and gas, transporting or storing hydrogen, carbon capture or geothermal energy, comprising at least one thread extending over its outer or inner peripheral surface, the thread of which is coated with a layer comprising a zinc-chromium (Zn—Cr) alloy in which zinc (Zn) is the predominant element by weight, relative to the total weight of the alloy.

In other words, the coating comprising a zinc-chromium (Zn—Cr) alloy in which zinc (Zn) is the predominant metal element by weight, relative to the total weight of the alloy, covers at least one thread of the threaded end of the tubular component, as defined above.

Preferentially, the threaded end of the tubular component, as defined above, comprises at least one thread extending over its outer or inner peripheral surface and at least one non-threaded portion, preferably containing a stop and/or a sealing seat; the thread and the non-threaded portion being covered by a coating comprising a zinc-chromium (Zn—Cr) alloy in which zinc (Zn) is the predominant metal element by weight, relative to the total weight of the alloy.

In other words, the zinc-chromium (Zn—Cr) coating according to the invention covers at least one thread of the threaded end of the tubular component, as defined above, and preferably at least said thread and at least one non-threaded portion, preferably containing a stop and/or a sealing seat, of the threaded end of the tubular component.

Within the meaning of the invention, in the remainder of the text, the layer comprising the 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 the description, the terms “layer” and “coating” may be used interchangeably to denote the zinc-chromium alloy deposit, as defined according to the invention, covering at least the thread of the threaded end of the tubular component.

In accordance with the present invention, the layer comprising the zinc-chromium (Zn—Cr) alloy is different from the superposition of a zinc (Zn) layer and a chromium (Cr) layer.

For the purposes of the present invention, a “zinc-chromium (Zn—Cr)” alloy is understood to mean a mixture comprising zinc and chromium, in which zinc represents the base metal, i.e. the metal element present predominantly in the mixture, and chromium represents an alloying metal element, i.e. a metal element that is intentionally present in or added to the mixture.

In other words, the chromium in the zinc-chromium (Zn—Cr) alloy is not an impurity or an unwanted metal element in the alloy.

In yet other words, chromium represents the predominant alloying metal element by weight among all the alloying metal elements likely to be present in the mixture.

The zinc-chromium (Zn—Cr) coating according to the invention has the advantage of not being toxic because the chromium salts used during the preparation process are not classified as “CMR” substances, which reduces the exposure of the operators to serious heath risks.

The chromium present in the zinc-chromium (Zn—Cr) alloy corresponds/is trivalent chromium Cr (III).

Furthermore, the zinc-chromium (Zn—Cr) coating in accordance with the invention makes it possible to guarantee effective protection against corrosion and galling of a threaded end of a tubular component, including in very harsh environments such as marine and industrial environments, and environments subject to heavy precipitation and/or that experience large temperature ranges.

The zinc-chromium (Zn—Cr) coating used according to the invention thus confers a good level of corrosion resistance by providing effective cathodic protection of the substrate.

Specifically, the chromium contained in the zinc-chromium metallic coating according to the invention passivates naturally, forming chromium oxide, which makes it possible to guarantee effective protection against corrosion. Thus, the natural formation of chromium oxide makes it possible to dispense with the implementation of an additional passivation step aimed at reinforcing the corrosion protection of the substrate, providing a time saving from an industrial point of view.

The zinc-chromium (Zn—Cr) coating also has excellent lubrication properties guaranteeing effective protection of the threaded end against galling during successive operations of screwing and unscrewing the tubular component.

The zinc-chromium (Zn—Cr) coating used according to the invention also has the advantage of being resistant to wear during successive screwing operations, which allows it to continue to guarantee anti-corrosion and anti-galling performance even after several screwing/unscrewing cycles without requiring additional anti-corrosion and anti-galling protection.

In other words, the zinc-chromium (Zn—Cr) coating according to the invention is capable of providing protection against corrosion and galling over the long term, including after several screwing and unscrewing operations of the tubular component in a harsh environment.

The wear resistance may notably be determined by means of an indentation test, such as a scratch test. This test consists notably in applying a load, in particular a ball, which is moved at increasing pressure over the surface of the coating until peeling, i.e. adhesive failure of the coating, occurs. In particular, the critical load for which adhesive failure occurs is measured.

Thus, the threaded end according to the invention exhibits increased resistance to corrosion and galling, including after several screwing and unscrewing cycles of the tubular component provided with said end, even in harsh environments mentioned above.

Furthermore, the zinc-chromium (Zn—Cr) coating according to the invention has a performance at least as good as that of a zinc-nickel (Zn—Ni) coating with respect to the appearance of red rust.

Moreover, the zinc-chromium (Zn—Cr) coating according to the invention has a performance better than that of a zinc-nickel (Zn—Ni) coating with respect to the appearance of white rust.

In particular, salt spray tests, carried out without passivation of the coating, reveal a rapid appearance of white rust on zinc-nickel (Zn—Ni) coatings and a much slower appearance of this white rust for a zinc-chromium (Zn—Cr) coating according to the invention, even for a halved thickness.

Within the meaning of the present invention, the expression “zinc (Zn) is the predominant element by weight relative to the total weight of the alloy” means that zinc has the highest content by weight among the elements of the alloy.

According to one embodiment, the thread is coated with a layer consisting of a binary zinc-chromium (Zn—Cr) alloy in which zinc (Zn) is the predominant element by weight, relative to the total weight of the alloy.

In accordance with the present invention, the term “content” corresponds to the concentration by weight of the metal element in question relative to the concentration of all the elements present in the alloy.

In other words, the “content” is the concentration by weight of the metal element in question relative to the total concentration of the mixture.

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

Preferably, the content of zinc (Zn) varies from 70% to 80% by weight, more preferentially from 70% to 75% by weight, relative to the total weight of the zinc-chromium alloy.

According to a preferred embodiment, the content of chromium (Cr) is greater than or equal to 3% by weight, preferably greater than or equal to 20% by weight, relative to the total weight of the zinc-chromium alloy.

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

Preferably, the zinc-chromium (Zn—Cr) alloy is a mixture comprising zinc, representing the predominant metal element by weight relative to the total weight of the alloy, chromium, which is an alloying metal element, preferably the only alloying metal element, and optionally one or more metallic or nonmetallic impurities.

For the purposes of the invention, an “alloying metal element” is understood to mean an alloying element intentionally present in or added to the alloy.

In other words, an alloying metal element is not an impurity.

In yet other words, the chromium present in the alloy according to the invention is not an impurity.

Specifically, the zinc-chromium (Zn—Cr) coatings according to the invention having a chromium content greater than or equal to 3% by weight comprise at least one crystalline phase of the Cr—Zn-17 phase type, which notably has an increased corrosion resistance compared with a coating consisting solely of zinc.

According to one embodiment of the invention, the content of chromium (Cr) varies from 20% to 30% by weight, relative to the total weight of the zinc-chromium alloy.

The zinc-chromium coatings according to the invention having a chromium content ranging from 20% to 30% by weight, relative to the total weight of the zinc-chromium (Zn—Cr) alloy, have the advantage of being particularly adherent to the surface, coherent and homogeneous while having excellent anticorrosion properties, in particular anticorrosion properties equal to or better than those of zinc-based coatings, in particular coatings based on zinc and nickel.

The quality of the coating according to the invention is thus significantly improved, in particular in terms of adherence, coherence and wear resistance, for chromium contents ranging from 20% to 30% by weight, relative to the total weight of the alloy, compared to coatings based on zinc and chromium having a chromium content strictly less than 20% by weight (<20% by weight) or strictly greater than 30% by weight (>30% by weight).

In particular, zinc-chromium (Zn—Cr) coatings having a chromium content ranging from 20 to 30% by weight comprise at least one crystalline phase of the gamma phase type conferring an anticorrosion property five times greater than that of a coating consisting solely of zinc (i.e. a coating whose zinc content is 100% by weight relative to the total weight of the coating).

The advantage of this crystalline phase lies in the fact that it has a centred cubic structure and thus possesses certain elements of symmetry in common with the crystal lattice of austenite of certain steels used as substrate, which promotes epitaxial growth and leads to better adhesion of the coating to the substrate.

Thus, zinc-chromium coatings according to the invention having a chromium content ranging from 20% to 30% by weight exhibit better adhesion to the substrate than coatings based on zinc and chromium having a chromium content strictly less than 20% by weight (<20% by weight) or strictly greater than 30% by weight (>30% by weight).

In other words, the zinc-chromium (Zn—Cr) coatings according to the invention having a chromium content ranging from 20% to 30% by weight have a better quality structure and an increased strength.

Furthermore, zinc-chromium (Zn—Cr) coatings with a chromium content ranging from 20% to 30% by weight, relative to the total weight of the alloy, have anticorrosion properties 14 times better than those of a zinc-nickel (Zn—Ni) coating for white rust.

According to one embodiment of the invention, the chromium (Cr) content varies from 25% to 30% by weight relative to the total weight of the zinc-chromium alloy.

The zinc-chromium (Zn—Cr) coatings according to the invention having a chromium content ranging from 25% to 30% by weight, relative to the total weight of the zinc-chromium alloy, withstand loads at least as high as coatings based on zinc and nickel, while having excellent anticorrosion properties, especially in harsh environments.

The zinc-chromium coatings according to the invention having a chromium content ranging from 25% to 30% by weight relative to the total weight of the zinc-chromium alloy have better long-term abrasion resistance than coatings based on zinc and nickel, while having excellent anticorrosion properties.

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

According to a preferred embodiment, the zinc (Zn) content varies from 70% to 80% by weight and the chromium (Cr) content varies from 20% to 30% by weight, relative to the total weight of the zinc-chromium alloy.

According to a preferred embodiment, the layer comprising a zinc-chromium alloy, as defined above, is a layer consisting of a binary zinc-chromium alloy.

According to a preferred embodiment, the thread is coated with a layer consisting of a binary zinc-chromium (Zn—Cr) alloy in which zinc (Zn) is the predominant element by weight, relative to the total weight of the alloy and the chromium (Cr) content varies from 20% to 30% by weight relative to the total weight of the alloy.

According to a preferred embodiment, the layer comprising zinc-chromium (Zn—Cr) alloy is deposited electrolytically.

Advantageously, electrodeposition, or electroplating, makes it possible to deposit zinc and chromium on the substrate at a very high current densities, in particular at a deposition rate of the order of 7 μm/min. This deposition rate is three times higher than that of the deposition of a layer made of a zinc-nickel alloy.

According to one embodiment, the layer comprising a zinc-chromium (Zn—Cr) alloy has a thickness ranging from 4 to 20 μm. Such a thickness makes it possible to apply the zinc-chromium layer more optimally to at least the thread of a threaded end of a tubular component. In other words, the deposition of the zinc-chromium (Zn—Cr) layer according to the invention is better distributed over the thread for thicknesses ranging from 4 to 20 μm, providing improved corrosion and galling protection. Such a thickness thus makes it possible to optimally match the geometry of the threads of the end of the tubular component.

Advantageously, from 4 μm corrosion protection is fully achieved, and up to 20 μm the layer remains dense without allowing any brittleness. Above 20 μm, there is a risk of having a layer that may be too thick for the machining clearance of the connection.

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

Zinc-chromium (Zn—Cr) coatings having a chromium content ranging from 20% to 30% by weight, preferably ranging from 25% to 30% by weight, based on the total weight of the alloy and having a thickness ranging from 4 to 20 μm, preferably ranging from 10 to 20 μm, have the advantage of being optimally distributed over the thread and of being particularly adherent, have the advantage of being particularly adherent, homogeneous, coherent and wear resistant while having excellent corrosion properties.

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

Specifically, the natural formation of chromium oxide from the chromium contained in the coating makes it possible to dispense with an additional passivation step aimed at reinforcing the corrosion protection.

Thus, the zinc-chromium coating is advantageously not covered by a passivation layer comprising trivalent chromium (Cr(III)).

Preferentially, the threaded end of the tubular component further comprises at least one non-threaded part coated with the layer comprising a zinc-chromium (Zn—Cr) alloy according to the invention.

Preferably, the non-threaded portion comprises a stop.

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

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

Preferentially, the threaded end of the tubular component is made of steel.

Preferably, the threaded steel end of the tubular component as described above comprises at least one thread extending over its outer or inner peripheral surface, the thread of which is coated with at least one layer comprising a zinc-chromium (Zn—Cr) alloy having a chromium content ranging from 20% to 30% by weight, preferably ranging from 25% to 30% by weight, relative to the total weight of the zinc-chromium (Zn—Cr) alloy.

Preferably, the threaded steel end of the tubular component as described above comprises at least one thread extending over its outer or inner peripheral surface, the thread of which is coated with at least one layer comprising a zinc-chromium (Zn—Cr) alloy having a chromium content ranging from 20% to 30% by weight, preferably ranging from 25% to 30% by weight, relative to the total weight of the zinc-chromium alloy, and a thickness ranging from 4 to 20 μm.

According to one embodiment, the surface of the thread and optionally of the non-threaded part, as defined above, coated with a zinc-chromium (Zn—Cr) coating according to the invention, may have a surface roughness, in particular a surface roughness (Ra) ranging from 1.6 to 3.2μ m.

According to one embodiment, the surface of the thread and of the non-threaded portion preferably comprising a stop and/or a sealing seat, coated with a zinc-chromium (Zn—Cr) coating according to the invention, may have a surface roughness, in particular a surface roughness (Ra) ranging from 1.6 to 3.2 μm.

The surface roughness can be obtained by a sandblasting process.

In other words, the surface of the thread, and possibly the surface of the non-threaded portion, can be treated beforehand by a mechanical treatment, preferably a sandblasting process.

The roughness of the surface makes it possible to improve the adhesion of the zinc-chromium (Zn—Cr) coating and the wear resistance thereof.

According to a preferred embodiment, the surface of the thread, and optionally of the non-threaded portion preferably comprising a stop and/or a sealing seat, is pretreated by a sandblasting process, and the zinc-chromium (Zn—Cr) coating has a chromium content ranging from 20% to 30% by weight and, preferably, a thickness ranging from 4 to 20 μm.

The invention also relates to the use of a layer comprising a zinc-chromium (Zn—Cr) alloy, as defined above, to protect at least one threaded end of a tubular component as defined above from corrosion and galling.

The present invention also relates to a process for preparing a threaded end, as defined above, of a tubular component intended for drilling and/or operating a hydrocarbon well, transporting oil and gas, transporting or storing hydrogen, carbon capture or geothermal energy, comprising at least one electrodeposition, on at least the surface of the thread of said 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, preferably nonionic surfactants.

The process according to the invention makes it possible to deposit a layer comprising at least one zinc-chromium (Zn—Cr) alloy, as defined above, which is homogeneous, compact and capable of being uniformly distributed over the threads of the threaded end.

According to one embodiment, the process according to the invention may also comprise a preparation of the surface to be coated, preferably by a mechanical treatment, more preferentially a sandblasting process.

The preparation of the surface to be coated by a mechanical treatment, preferably a sandblasting process, makes it possible to improve the adhesion of the zinc-chromium (Zn—Cr) coating and minimizes the risks of brittle behaviour of the coating.

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

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

According to one embodiment, the process according to the invention comprises sandblasting the surface to be coated and the electrodeposition of the aqueous composition defined above on at least the sandblasted surface of the thread, preferably the sandblasted surface of the thread and of the non-threaded portion preferably comprising a stop and/or a sealing seat.

Furthermore, the zinc-chromium coating obtained has a surface with a homogeneous aesthetic appearance.

According to a preferred embodiment, the rate of deposition of the aqueous composition on the surface to be coated is between from 4 to 20 μm/min, preferably 5 to 7 μm/min.

The zinc salts and the chromium salts are soluble in the aqueous composition.

In accordance with the invention, the chromium (Cr) salt(s) are trivalent chromium Cr(III) salts.

Preferably, the electrodeposition is carried out at a current density greater than at least 30 amperes/dm².

In particular, a sufficient stirring speed of the aqueous composition, for example a speed of 0.23 m/s at the cathode, makes it possible to advantageously increase the current density without the risk of causing burn marks which are likely to give rise to a degradation of the appearance of the zinc-chromium (Zn—Cr) coating according to the invention.

More preferentially, the electrodeposition is carried out at a current density ranging from 30 amperes/dm² to 50 amperes/dm².

Below 30 amperes/dm² the incorporation of chromium is reduced or even inhibited and the coating obtained has dark gray spots, representing chromium-free areas.

According to one embodiment, the weight ratio of the chromium salt(s) to the zinc salt(s) varies from 0.8 to 1.4.

Preferably, the surfactant(s) is/are chosen from the group consisting of nonionic surfactants.

Preferably, the nonionic surfactant is chosen from the group consisting of (poly)alkoxylated fatty alcohols, notably (poly)alkoxylated C₈-C₄₀ fatty alcohols, in particular poly(ethylene glycol) octyl ether, and oxirane, 2-methyl-, polymer with oxirane, mono(2-naphthonyl) ether.

The presence of the surfactant in the aqueous composition makes it possible to deposit the chromium together with the zinc.

Indeed, it has been observed that in the absence of surfactant, the deposit obtained does not contain chromium. This is due in particular to the formation of zinc hydroxides, resulting from the increase in pH at the cathode due to the release of dihydrogen, which can block the diffusion of chromium to the cathode. This lack of chromium deposit can also be explained by the existence of a shift in reduction potentials (chromium becoming lower than zinc reduction potential and/or water reduction potential).

The presence of at least one surfactant thus makes it possible to facilitate the diffusion of chromium in the diffusion layer and/or to reduce the cathode overpotential of chromium and/or to increase the cathode overpotential of the electrolysis of water, which makes it possible to minimize the release of dihydrogen and the formation of zinc hydroxides.

Preferably, the surfactant is present in a concentration ranging from 0.3 to 3 mmol/l.

The surfactant concentration makes it possible to adjust the brightness of the zinc-chromium (Zn—Cr) coating according to the invention.

Preferably, increasing the surfactant concentration makes it possible to increase the brightness of the zinc-chromium (Zn—Cr) coating according to the invention.

Preferably, the zinc salts may be chosen from zinc sulfate, zinc chloride and zinc sulfamate, preferentially the zinc salt will be zinc sulfate.

Preferably, the chromium salts can be chosen on the basis of the nature of the zinc salt. If zinc sulfate is preferred, then chromium sulfate will preferentially be chosen.

The conductive salts/carrier salts can be chosen from the group consisting of sodium sulfate, potassium sulfate and ammonium sulfate and mixtures thereof, preferably sodium sulfate. The conductive salts/carrier salts make it possible to ensure electrical conductivity during the process.

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

Glycine makes it possible to result in bright, semi-bright or matte zinc-chromium (Zn—Cr) coatings according to the invention.

The glycine content in the aqueous composition may vary from 50 to 75 g/l relative to the total concentration of the composition.

The glycine content makes it possible to adjust the matte appearance of the zinc-chromium (Zn—Cr) coating according to the invention.

Preferably, when the glycine content is increased and the surfactant content is decreased, the zinc-chromium (Zn—Cr) coating has a matte appearance.

Preferably, when the glycine content is decreased and the surfactant content is increased, the zinc-chromium (Zn—Cr) coating has a bright appearance.

When the zinc-chromium (Zn—Cr) coating is bright on a non-sandblasted surface or semi-bright on a sandblasted surface, the mechanical properties of the zinc-chromium (Zn—Cr) coating are better than those of a zinc-chromium (Zn—Cr) coating with a matte appearance.

The pH of the aqueous composition may range from 1.5 to 3.5, preferably from 2 to 2.5.

In fact, when the pH of the aqueous composition is in particular greater than 3.5, the risks of precipitation of the chromium salts are increased in the bath, thus between pH 1.5 and pH 3.5 the risks are minimized.

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

Preferably, the aqueous composition comprises:

• • one or more zinc salts,
  • one or more chromium salts,
  • one or more conductive salts/carrier salts, preferably sodium sulfate,
  • one or more surfactants, preferably nonionic surfactants, and
  • optionally one or more amino acids, preferably glycine.

Advantageously, the process according to the invention does not include an additional step of forming a passivation anti-corrosion conversion layer comprising trivalent chromium (Cr(III)).

In other words, advantageously, the process according to the invention does not include a step of forming a passivation anti-corrosion conversion layer comprising trivalent chromium (Cr(III)) after the deposition of the layer comprising a zinc-chromium alloy.

Another subject of the invention is a tubular component for drilling and/or operating a hydrocarbon well, transporting oil and gas, transporting or storing hydrogen, carbon capture or geothermal energy, comprising a threaded end according to the invention containing at least one thread extending over its outer or inner peripheral surface, which is covered with a layer comprising a zinc-chromium (Zn—Cr) alloy, in accordance with the invention, in which zinc (Zn) is the predominant element by weight, relative to the total weight of the alloy.

The threaded end is as defined above.

The layer comprising a zinc-chromium (Zn—Cr) alloy is as defined above.

The tubular component exhibits improved corrosion resistance and galling resistance.

Preferentially, the tubular component is of the male type and has at least one thread extending over its outer peripheral surface.

More preferentially, the tubular component is of the male type and has at least one thread extending over its outer peripheral surface and at least one non-threaded portion, preferably chosen from a stop and/or a sealing seat.

Preferentially, the tubular component is of the female type and has at least one thread extending over its inner peripheral surface thereof.

More preferentially, the tubular component is of the female type and has at least one thread extending over its inner peripheral surface and at least one non-threaded portion, preferably chosen from a stop and/or a sealing seat.

According to the invention, the tubular component is provided with an axis of revolution.

The tubular component according to the invention is more particularly made of steel, and in particular the steels as described in the API SCT standards, for example those comprising carbon in a proportion of less than 0.25%, and/or preferentially steels having a grade as defined according to the ISO11960 and ISO13680 standards, and/or else an H40, J55, K55, M65, L80, C90, C95, T95, P110 or Q125 carbon steel, or else a martensitic 13Cr or S13Cr steel, or Duplex 22Cr+25Cr steel, or Super-Duplex 25Cr steel, or austenitic Fe 27Cr steel.

The invention also relates to the use of a tubular component as defined above for drilling and/or operating a hydrocarbon well, transporting oil and gas, transporting or storing hydrogen, carbon capture or geothermal energy.

Preferably, the invention relates to the use of the tubular component as defined above for drilling and/or operating a hydrocarbon well.

The present invention also relates to a tubular threaded joint for drilling and/or operating a hydrocarbon well, transporting oil and gas, transporting or storing hydrogen, carbon capture or geothermal energy, comprising a threaded end of a male-type tubular component having at least one thread extending over its outer peripheral surface and a threaded end of a female-type tubular component having at least one thread extending over its inner peripheral surface, which are screwed into one another, at least one of said ends being as defined above, in particular the thread of which is covered by a layer comprising a zinc-chromium (Zn—Cr) alloy as defined above.

The tubular threaded joint according to the invention notably has a better resistance to corrosion and to galling, including in harsh environments as defined above.

Preferably, the two threaded ends are as defined above.

According to one aspect of the invention, the threaded end of the male-type tubular component has at least one thread, which extends over its outer peripheral surface, covered by a layer comprising a zinc-chromium (Zn—Cr) alloy according to the invention as described above.

According to one aspect of the invention, the threaded end of the female-type tubular component has at least one thread, which extends over its inner peripheral surface, covered by a layer comprising a zinc-chromium (Zn—Cr) alloy according to the invention as described above.

According to yet another aspect of the invention, the threaded end of the male-type tubular component has at least one thread, which extends over its outer peripheral surface, covered by a layer comprising a zinc-chromium (Zn—Cr) alloy according to the invention, and the threaded end of the female-type tubular component has at least one thread, which extends over its inner peripheral surface, covered by a layer comprising a zinc-chromium (Zn—Cr) alloy according to the invention.

Preferably, the tubular threaded joint comprises a threaded end of a male-type tubular component having at least one thread extending over its outer peripheral surface and at least one non-threaded portion with metal/metal interference, and a threaded end of a female-type tubular component having at least one thread extending on its inner peripheral surface and at least one non-threaded portion chosen from a stop and/or a sealing seat with metal/metal interference; the thread and the non-threaded portion being covered with a layer comprising a zinc-chromium (Zn—Cr) alloy according to the invention as described above.

In the text of the description, and unless otherwise indicated, the limits of a range of values are included in this range, in particular in the expressions “between” and “ranging from . . . to . . . ”.

Moreover, the expression “at least one” used in this description is equivalent to the expression “one or more”.

Features of the invention are explained in greater detail in the following description, with reference to the appended drawings.

FIG. 1 is a schematic view of a joint resulting from the joining, by screwing together, of two tubular components.

FIG. 2 is an enlarged view of the boxed area A from FIG. 1.

FIG. 3 is a detailed view of the cooperation between the threads of two assembled tubular components.

FIG. 4 is a detailed view of a connection element (thread) according to the invention covered with a zinc-chromium coating in accordance with the invention.

FIG. 5 is a diagram comparing the appearance time of a layer of white rust of intensity 2 and intensity 3, after exposure to a salt spray test, on the surface of a zinc-nickel (Zn—Ni) coating and the surface of a zinc-chromium (Zn—Cr) coating in accordance with the invention.

FIG. 6 is a diagram comparing the time for complete coverage by a layer of white rust of intensity 2, after exposure to a salt spray test, of the surface of a zinc-nickel (Zn—Ni) coating and of the surface of a zinc-chromium (Zn—Cr) coating in accordance with the invention.

The threaded joint shown in FIG. 1 comprises a first tubular component with an axis of revolution 9 and a male end 1 and a second tubular component with an axis of revolution 9 and a female end 2. The two ends 1 and 2 each terminate in an end surface oriented radially with respect to the axis 9 of the threaded joint and are respectively provided with threaded portions 3 and 4 which cooperate with each other for mutual assembly by screwing together of the two components. The threaded portions 3 and 4 may be of the trapezoidal thread type or other type. In the example shown, the threaded portions have threads with tapering profiles at the respective ends of the threaded portions. These tapering profiles extend over a part of the axial extent of the threaded portion. In particular, a part of the threaded portion with a tapering profile 10 does not cooperate with a complementary thread.

Furthermore, as shown in FIG. 2, metal/metal sealing surfaces (seats) 5, 6 intended to be in leaktight close contact against one another after assembly by screwing together of the two threaded components, are formed respectively on the male and female ends in the vicinity of the threaded portions 3, 4. Finally, the male end 1 terminates in an end surface 7 which abuts against a corresponding surface 8 formed on the female end 2 when the two ends are screwed into one another, The surfaces 7 and 8 are referred to as stops.

In FIG. 3, the detail of a thread of a threaded portion is shown. Each thread thus comprises a load flank 11 forming an angle 12 of between −5° and +5° relative to the normal N of the connection axis 10. The load flank is connected by a crest 13 to an assembly flank 14. In particular, the connection shown is such that, in the final position of the assembly, the load flanks of the male threaded portion 3 are in contact with the corresponding load flanks of the female threaded portion 4.

FIG. 4 shows the male end 1 of a tubular component, of which the threaded portion 3 and sealing surface 5 (seat) are covered with a coating 15 as defined in the invention, that is to say, a zinc-chromium coating comprising a zinc-chromium (Zn—Cr) alloy in which zinc (Zn) is the predominant element by weight, relative to the total weight of the alloy.

Preferably, the coating 15 has a chromium content ranging from 20% to 30% by weight, more preferentially ranging from 25% to 30% by weight, and a zinc content ranging from 70% to 80% by weight, more preferentially ranging from 70% to 75% by weight, relative to the total weight of the alloy.

Exemplary Embodiment

A thread made of L80 grade carbon steel is electroplated, as described above, with a semi-bright metal coating comprising a zinc-chromium (Zn—Cr) alloy having a chromium content of 27% by weight relative to the total weight of the alloy.

The semi-bright zinc-chromium coating was obtained from an aqueous composition containing 75 g/l of glycine.

The zinc-chromium coating is compared with zinc-nickel (Zn—Ni) coatings, in which zinc is the predominant element by weight, having various weight contents of nickel ranging from 10% to 18% by weight. The percentage by weight is calculated relative to the total weight of the alloy.

The coatings were subjected to tribological tests (scratch test and Bowden test) in order to determine the critical load for which peeling of the coatings (plastic deformation) is observed, the initial coefficient of friction and the number of cycles that the coatings are capable of withstanding.

The coatings were also subjected to a salt spray test to determine their anti-corrosion performance.

Scratch Test

The experimental conditions use a tungsten carbide ball which is applied to the coatings and moved with an increasing load ranging from 10 N to 260 N, with a speed of movement of the ball of 4.20 mm/s, a duration of 2.38 seconds, a ball size of 5 mm and a track length of 10 mm.

The Scratch Test Results are Shown in Table 1

Results

TABLE 1
% by weight	Critical load (N)

of the metal element		ZnCr
X in the alloy (Zn—X)	Zn—Ni	(semi-bright)
10	250
14	209
18	149
27		170

The results of the scratch tests described in Table 1 show that the semi-bright zinc-chromium coating withstands loads at least as high as those withstood by zinc-nickel coatings having a nickel content ranging from 10% to 18% by weight relative to the total weight of alloy.

Bowden Test

In order to evaluate the lubricating properties (coefficient of friction) of the surface of the coating, a commercially available Bowden friction tester (Shinko Engineering Co., Ltd.) was used. In the Bowden friction tester, a tungsten carbide ball was moved back and forth in a straight line on a coating formed on a steel sheet while a load was applied to the ball.

The coefficient of friction was measured from the frictional force and the pressure load at that time.

Procedure

The tungsten carbide ball is applied to the coatings and moved with a pressing load of 30 N and 100 N, with a speed of movement of the ball of 4.20 mm/s, a duration of 2.38 seconds, a ball size of 5 mm and a track length of 10 mm.

The initial coefficient of friction was determined to evaluate the lubricating properties of the coating.

The number of cycles (number of passes of the ball over the surface) was measured for each coating to evaluate their abrasion resistance.

The results are indicated in Tables 2 and 3 below.

Bowden Test—Result for a 30 N Load

TABLE 2
	Initial coefficient	Endurance
% by weight	of friction	(number of cycles)

of the metal element X		ZnCr		ZnCr
in the alloy (Zn—X)	Zn—Ni	(semi-bright)	Zn—Ni	(semi-bright)
10	—
14	0.5-0.6		300
18	0.4-0.5		500
27		0.3-0.4		500

The Bowden test described in Table 2 shows that for a load of 30 N, the initial coefficients of friction are lower for a zinc-chromium coating according to the invention than for zinc-nickel coatings.

In addition, the zinc-chromium coating exhibits an endurance at least as high as the zinc-nickel coatings for a load of 30 N.

Bowden Test—Result for a 100 N Load

TABLE 3
	Endurance
% by weight	(number of cycles)

of the metal element X		ZnCr
in the alloy (Zn—X)	Zn—Ni	(semi-bright)
10	<100
14	<100
18	100-150
27		250

The Bowden test carried out for a load of 100 N, described in Table 3, shows that the zinc-chromium coating according to the invention has a higher endurance than that of the zinc-nickel coatings.

As a result, the zinc-chromium coating according to the invention has better wear resistance than the zinc-nickel coatings in which the nickel content varies from 10% to 18% by weight.

As a result, the more the load is increased, the more the zinc-chromium (Zn—Cr) coating according to the invention exhibits improved endurance, namely therefore a higher wear resistance, compared with a zinc-nickel (Zn—Ni) coating.

Salt Spray Test

The corrosion tests consisted of a neutral salt spray test carried out in a climatic chamber under the following conditions: 35° C. with a 50 g/l saline solution having a density of between 1.029 and 1.036 at 25° C., a pH of between 6.5 and 7.2 at 25° C. and collected at an average rate of 1.5 ml/h.

During this test, the appearance of red rust and white rust was evaluated.

Anti-Corrosion Performance—Appearance of Red Rust

The appearance of red rust is evaluated by determining, in ascending order, the degree of rusting Re which corresponds to the percentage of rusted surface area relative to the total surface area.

Intact samples without red rusting must then meet class Re0 of the ISO 9227 standard after exposure.

The results are indicated in Table 4 below.

TABLE 4
	Red rust after salt spray test
Coating	over a period of 504 hours
Zn—Ni with 14% nickel - 10 μm	Re1
Zn—Cr (1) with 27% chromium - 5 μm	Re0
Zn—Cr (1) with 27% chromium - 10 μm	Re1
Zn—Cr (1) with 27% chromium - 15 μm	Re1

The degree of rusting, in ascending order from Re0 to Re2 after exposure corresponds to the rusted surface area relative to the total surface area.

In accordance with this degree of rusting:

• • Re0=0% rusting of the total surface area,
  • Re1=0.05% rusting of the total surface area,
  • Re2=0.5% rusting of the total surface area,
  • Re6=40%-50% rusting of the total surface area.

Table 4 thus shows that the zinc-chromium (Zn—Cr) coatings perform at least as well against the appearance of red rust as a zinc-nickel coating.

Anti-Corrosion Performance—Appearance of White Rust

The presence of white rust corresponds to the oxidation of the coating, in particular the oxidation of zinc, and is evaluated by measuring, after exposure to salt spray, its appearance time and its time for total coverage of the surface of the coating.

After exposure to salt spray, the intensity of the layer of white rust covering the coatings classified in the following ascending order:

• • white rust of intensity 1 corresponding to a layer of white rust that is thin and light, which can also be referred to as bloom,
  • white rust of intensity 2 corresponding to a layer of white rust that is in the form of crystals,
  • white rust of intensity 3 corresponding to a layer of white rust that is very dense.

Appearance Time of White Rust

FIG. 5 compares the appearance time of a layer of white rust of intensity 2 and intensity 3 after exposure to the salt spray test, on the surface of a zinc-nickel coating [Zn—Ni with 14% by weight of nickel and a thickness of 10 μm] and on the surface of a zinc-chromium coating [Zn—Cr with 27% by weight of chromium and a thickness of 5 μm].

FIG. 5 shows a rapid appearance of a layer of white rust of intensity 2 on the surface of the zinc-nickel coating [Zn—Ni with 14% by weight nickel and a thickness of 10 μm], starting at 24 hours, whereas a layer of white rust of intensity 2 appears only after 170 hours on the surface of a zinc-chromium coating [Zn—Cr with 27% by weight of chromium and a thickness of 5 μm].

FIG. 5 also shows the rapid appearance of a layer of white rust of intensity 3 on the zinc-nickel coating [Zn—Ni with 14% by weight nickel and a thickness of 10 μm], starting at 24 hours, whereas a layer of white rust of intensity 3 appears only after 336 hours for a zinc-chromium coating [Zn—Cr with 27% by weight of chromium and a thickness of 5 μm].

Time for Total Coverage of the Surface of the Coating by White Rust

FIG. 6 compares the time for complete coverage of the surface of a zinc-nickel coating [Zn—Ni with 14% by weight of nickel and a thickness of 10 μm] and of a zinc-chromium coating [Zn—Cr with 27% by weight of chromium and a thickness of 5 μm] by a layer of white frost of intensity 2.

FIG. 6 shows that the time for complete coverage of the surface of the zinc-nickel coating [Zn—Ni with 14% by weight of nickel and a thickness of 10 μm] by a layer of white rust of intensity 2 is 24 hours, whereas this time for coverage by this same layer is 336 hours for a zinc-chromium coating [Zn—Cr with 27% by weight of chromium and a thickness of 5 μm].

CONCLUSION

The results show that the zinc-chromium (Zn—Cr) coatings according to the invention have better performance in terms of appearance of white rust compared to a zinc-nickel (Zn—Ni) coating.

This results in better adhesion of the layers deposited subsequently on the zinc-chromium coatings.