OA17797A - Connecting element for a tubular component overlaid with a metallic composite deposit and method of obtaining such element. - Google Patents

Abstract

The invention concerns a connecting element for a tubular component, said connecting element being overlaid with a coating comprising a principal layer constituted by a nickelphosphorus alloy. The invention also concerns a tubular component comprising one or more such connecting elements, as well as a method for producing such a connecting element.

Description

CONNECTING ELEMENT FOR A TUBULAR COMPONENT OVERLAID WITH A METALLIC COMPOSITE DEPOSIT AND METHOD OF OBTAINING SUCH ELEMENT

The présent invention relates to a connecting element for a tubular component, said connecting element being overlaid with a particular metallic composite coating.

The term “tubular component” as used in the présent invention means any element or accessory used to drill or operate a well.

The term “connecting element” as used in the context of the présent invention means any end element of a tubular component which participâtes in connecting the tubular component with another tubular component.

A tubular component is intended to be connected, via one or more connecting éléments, in particular a threading, a sealing surface and an abutment shoulder, to another tubular component in order to constitute a threaded tubular connection with that other tubular component. The tubular component may, for example, be a relatively great-length tube (in particular approximately ten métrés in length), a tubular coupling a few tens of centimètres in length, an accessory for such tubes (a suspension device or hanger, a part for adapting cross-sections, or cross-over, a safety valve, a drill pipe connector or tool joint, a sub, and the like).

The tubular components are generally connected one with another for dropping into the hydrocarbon well or similar well and to constitute a drill stem, a casing string or a liner or tubing string, or indeed an operating string.

API spécification 5CT issued by the American Petroleum Institute (API), équivalent to ISO standard 11960 : 2004 issued by the International Standardisation Organisation (ISO) govems the spécifications for tubes used as casing or tubing, and API spécification 5B defines standard threadings for such tubes. API spécification 7 defines threaded connectors with a shoulder for rotary drill pipes.

The manufacturers of tubular components with threaded connections hâve also developed threaded connections known as premium connections which hâve threadings with spécifie geometries and spécifie means for providing better performance in service, in particular in the matter of mechanical strength and sealing. Examples of such premium threaded connections and those spécifie means are described, for example, in patent documents EP 1 631 762, US 7 334 821, US 7 997 627, US 7 823 931, US-2010/301603, US-2011/0025051, US 7 900 975, US 8 038 179, US-2011/241340, EP 0 488 912, EP 0 767 335, EP 1 269 060 and US 4 494 777, EP 2501 974 and WO-2012/025461.

These threaded ends, as well as the bearing surfaces and abutment shoulders, are machined very precisely in order to comply with the profiles and geometries required to reach the requisite performances.

Thus, it is vital that these ends, which hâve been very finely and carefully machined, are damaged, polluted and deteriorate as little as possible between the time they leave their production line and the time they are put into use, but also between two successive uses. It will be understood that it is in fact necessary to protect not only the threading, but also any bearing surface(s) and abutment shoulder(s) which each hâve functions which are spécifie and complementary to those of the threadings and which together provide an effective seal when in use against shocks (knocks), corrosion and dust.

The first desired quality for the connecting éléments is hardness.

In particular, the abutment shoulders are exposed to knocks and impacts generated during handling of tubular components in particular when being stored on the drilling platform (rig) or on a base or during the operation when the male portion and the female portion, in particular the threadings, of the tubular components are brought into contact before makeup (stabbing operation).

In addition, the abutment shoulders hâve to be capable of tolerating mechanical loads in terms of compression, tension and torsion during operation.

Thus, hardness is an essential property for abutment shoulders.

The threadings must also hâve good properties in tenus of hardness. In fact, the threadings must hâve good galling protection properties. Increasing the surface hardness allows to protect the threading from galling.

In addition, increasing the hardness allows to prevent the transfer of material from one surface to another.

Finally, the threadings must not wear during makeup and breakout operations.

The sealing surfaces must also hâve sufficient hardness, in particular because the sealing surfaces are responsible for the seal of the connection for the tubular components. In fact, a sealing surface is a surface which is generally tapered in shape, located on the end of a first tubular component which, when two tubular components are connected together via their respective ends, is caused to exert a pressure on the sealing surface of the end of a second component. These two tapered surfaces in contact and under pressure can be used to create a seal and prevent the passage of fluids between a zone termed an internai zone of the connected tubular components and a zone which is external of the connected tubular components. These components may be used when connected to participate in extracting oil from a well, and inside these wells, and thus inside the components, there may be a column of liquid under very high pressure.

The connecting éléments must also perform well in tenus of corrosion résistance and lubricating properties.

In particular, the éléments of the connection can be stored for several years before being used, sometimes in highly aggressive environments.

Lubricating properties are particularly important for the threadings. The abutment shoulders also hâve to be lubricated, but to a lesser extent than the threadings.

The threadings should also be protected against galling, in particular during makeup and breakout operations. In fact, at the well, the threadings hâve to be able to undergo several makeup and breakout cycles. Makeup operations are carried out vertically under a high axial load, for example the weight of a tube several métrés in length (typically 10 to 13 métrés) to be connected vertically via the threaded connection, which gives rise to galling risks, in particular in the threadings. This load may also be localized due to a slight misalignment in the axes ofthe threaded éléments to be connected because the tube to be connected is suspended vertically, increasing the risks of galling.

The connecting éléments for the tubular components cited above are generaliy coated with an anti-corrosion grease which is removed just before they are connected. Before such connection, the anti-corrosion grease is removed and a lubricating grease is added (the operation is known as rig préparation). However, prior art greases suffer from a certain number of disadvantages linked to their amount of toxic constituents, to the pollution they generate and to the number of prior steps necessary before being able to drop a component into the well. In particular, cleaning of the anticorrosion grease (also known as storage grease) is traditionally carried out with a high pressure water jet. The operation is lengthy, dirty, might contaminate other connections in the vicimty and nécessitâtes using holding and re-processing tanks for the effluents in order to comply with environmental standards.

Patent documents US 6 027 145, EP 1 211 451 and EP 1 934 508 disclose that it is known to apply a dry lubricant comprising solid lubricant particles at the factory. In these cases when a dry lubricant is used at the factory, it is then necessaiy to protect the layer of lubricating product with which the ends of the components is coated as much as possible, both from mechanical removal and from pollution (sand, débris) which could hâve a detrimental effect on the efficacy of the lubricating product.

To this end, it is also known that these layers of product, which are applied at the factory as soon as the threaded end has been manufactured, are aimed at providing both anti-corrosion protection of the end during the storage period and lubrication for subséquent makeup of that end, as taught in particular in documents WO 2004/033951 or WO 2008/125740. In particular, lubrication must be able to control the characteristic curve of the makeup torque of the connection in order to guarantee the final seal.

The compositions used may be composed of a multi-functional coating which is both anticorrosive and lubricating, as described in WO 2008/125740 applied to each end to be connected, or to superimposed layers as described in WO 2004/033951, where some are fabricants and others protect against corrosion.

Whatever they are, during makeup, the anti-corrosion éléments are mixed with the lubricating éléments and will modify the lubricating behaviour which would be observed without them. It has frequently been demonstrated that coupling between these functions is very strong and contradictory. An improvement in the anti-corrosion behaviour of a design generally results in détérioration in the lubricating power and vice versa, an improvement in the lubricating power reduces the corrosion behaviour during storage. The performance of the compromises proposed by the prior art solutions is limited.

Further, the dry anti-corrosion coatings normally used cannot guarantee very long période of corrosion résistance, in particular in highly aggressive environments (marine environment, industrial environment, high précipitation environment and/or large température ranges, for example).

Thus, there is a need for the provision of connecting éléments which hâve good properties in terms of hardness, corrosion résistance and fabrication which do not suffer from the disadvantages of the prior art.

Thus, the invention provides a connecting element for a tubular component, said connecting element being overiaid with a coating comprising a principal layer constituted by a nickelphosphorus alloy.

The phosphorus generally represents 5% to 13%, preferably 8% to 13%, more preferably 10% to 12%, even more preferably 10.5% to 11.5% by weight of the total weight of the nickelphosphorus alloy.

In accordance with a first embodiment of the invention, the thickness of the principal layer constituted by the nickel-phosphorus alloy is advantageously in the range 5 to 10 pm. Said thickness allows to provide the hardness required for the connecting element.

In accordance with a second embodiment of the invention, the thickness of the principal layer constituted by the nickel-phosphorus alloy is advantageously 15 to 35 ,um, preferably 20 to 35 pm, more preferably 25 to 30 pm. Such a thickness not only allows to provide the hardness required for the connecting element, but also allows to provide protection against corrosion.

Such a nickel-phosphorus alloy layer has been proposed by the company MACDERMID under the trade name NIKLAD XD7647.

In accordance with a preferred embodiment, the coating further comprises an additional layer constituted by a nickel-phosphorus alloy comprising the particles of one or more solid lubricant compounds, said additional layer being disposed on said principal layer.

A solid lubricant is a solid and stable substance which is inteiposed between two friction surfaces in order to reduce the coefficient of friction and to reduce wear and damage to the surfaces.

These substances can be classifïed into various categories defined by their functional mechanism and their structure. These categories are described, for example, in the hand-outs entitled “Les lubrifiants solides [Solid lubricants]” issued by Mr Eric Gard at the École Nationale Supérieure des Pétroles et Moteurs (France):

• class 1 : solid substances owing their lubricating properties to their crystalline structure, for example graphite, boron nitride BN or zinc oxide ZnO;

• class 2: solid substances owing their lubricating properties on the one hand to their crystalline structure and on the other hand to a reactive chemical element in their composition, for example molybdenum disulphide MoS₂, graphite fluoride, tin sulphides or bismuth sulphides;

• class 3: solid substances owing their lubricating properties to their chemical reactivity, for example certain chemical compounds of the thiosulphate type (for example Desilube 88 marketed by Desilube Technology Inc.);

• class 4: solid substances owing their lubricating properties to a plastic or viscoplastic behaviour under frictional load, for example polytetrafluoroethylene (PTFE) or polyamides.

Silicon carbide and tungsten carbide may also be cited.

The particles of one or more solid lubricant compounds are advantageously selected from particles of polytetrafluoroethylene, talc, mica, boron nitride, silicon carbide, tungsten carbide, tungsten sulphide, molybdenum sulphide and mixtures thereof.

Preferably, the particles of one or more solid lubricant compounds are selected from polytetrafluoroethylene particles.

Advantageously, the phosphorus of the nickel-phosphorus alloy comprising the particles of one or more solid lubricant compounds represents 5% to 13%, preferably 8% to 13%, more preferably 10% to 12% by weight of the total weight of the nickel-phosphorus alloy comprising the particles of one or more solid lubricant compounds.

The particles of one or more solid lubricant compounds advantageously represent 20% to 35% by volume, preferably 25% to 30% by volume with respect to the total volume of the nickelphosphorus alloy comprising the particles of one or more solid lubricant compounds.

The thickness of said additional layer constituted by a nickel-phosphorus alloy comprising the particles of one or more solid lubricant compounds may be in the range 3 to 13 pm, preferably 5 to 10 pm

A layer of nickel-phosphorus alloy of this type comprising polytetrafluoroethylene particles has been proposed by the company MACDERMID under the trade name NIKLAD ICE Ultra.

Furthermore, the coating may comprise a lubricant layer disposed on. said principal layer or on said additional layer when the coating comprises said additional layer.

The lubricant layer may be selected from a grease, a semi-solid lubricant layer or a solid, dry lubricant layer comprising one or more solid lubricant particles in a resin.

The semi-solid lubricant layer generally comprises one or more extreme pressure additives, one or more solid lubricant particles, one or more metallic soaps and one or more low melting point waxes. Such semi-solid lubricant layers are described, for example, in patent application FR 2 937 046.

The solid, dry lubricant layer generally comprises one or more solid lubricant particles for reducing friction in a resin binder such as an organic or inorganic polymer, selected from heat curable epoxy, polyuréthane, unsaturated polyester, polyphenylsulphone, polyimide and silicone resins; thermoplastic polyolefin, olefin copolymer, polyamide, polyamide-imide, polyaryletherketone resins; alkaline polysilicates with a SiCh/MxO ratio of more than 2, where M=Na, K or Li; organometallics such as alkoxy-titanates or ethyl silicate.

In accordance with a first embodiment, the connecting element of the invention may be a threading.

In accordance with a second embodiment, the connecting element of the invention may be a sealing surface.

In accordance with a third embodiment, the connecting element of the invention may be an abutment shoulder.

The invention also concerns a tubular component comprising one or more connecting éléments in accordance with the invention.

More particularly, the tubular component of the invention is produced from steel, in particular steels such as those described in API 5CT standards, for example those comprising carbon in a proportion of less than 0.25%, and/or preferably, steels with a grade such as those defined in the standards ISO11960 and ISO13680 and/or a H40, J55, K55, M65, L80, C90, C95,

T95, PI 10, Q125, carbon steel or a 13Cr or S13Cr or Duplex 22Cr + 25Cr or Super-Duplex 25Cr martensitic steel, or a Fe 27Cr austenitic steel.

In accordance with a first embodiment, the tubular component of the invention comprises a threading which is a connecting element in accordance with the invention. In this embodiment, the tubular component ofthe invention may also comprise an abutment shoulder which is a connecting element in accordance with the invention.

In a second embodiment, the tubular component of the invention comprises an abutment shoulder which is a connecting element in accordance with the invention.

In a third embodiment, the tubular component in accordance with the invention comprises a sealing surface which is a connecting element in accordance with the invention. In this embodiment, the tubular component in accordance with the invention may also comprise a threading which is a connecting element in accordance with the invention and/or an abutment shoulder which is a connecting element in accordance with the invention.

A tubular component of the invention may be connected via one or more connecting éléments, which may or may not be in accordance with the invention, in particular a threading, a sealing surface and an abutment shoulder, to another tubular component which may or may not be in accordance with the invention, to form a threaded tubular connection.

In particular, at one of its ends, the tubular component has a threading formed on its outer or inner peripheral surface depending on whether the threaded end is male or female in type, this threading allowing the component to be connected to a complementary component.

A female tubular component of the invention comprising one or more connecting éléments overlaid with a coating constituted by the principal layer and the optional additional layer as defined above may be connected with a male tubular component which is not in accordance with the invention and which comprises one or more connecting éléments overlaid only with a lubricant layer as defined above.

A female tubular component in accordance with the invention comprising one or more connecting éléments overlaid with a coating constituted by the principal layer, the optional additional layer and the lubricant layer as defined above may be connected with a male tubular component in accordance with the invention and which comprises one or more connecting éléments overlaid with a principal layer and an optional additional layer as defined above.

A female tubular component in accordance with the invention comprising one or more connecting éléments overlaid with a coating constituted by the principal layer, the optional additional layer and the lubricant layer as defined above may be connected with a male tubular component in accordance with the invention and which comprises one or more connecting éléments overlaid with a principal layer, an optional additional layer and a lubricant layer as defined above.

Using the connecting éléments in accordance with the invention and tubular components in accordance with the invention means that the steps for cleaning and lubrication of the connections before use can be dispensed with (rig ready solution). The coating used in accordance with the invention is highly adhesive and not déformable, and so avoids using spécifie protectors specially designed to limit damage to the coatings (for example contactless protectors on the threads or a sealed protector).

Protectors are in fact devices which are becoming more and more complicated in order to protect the threads and the connection against corrosion and damage to the coatings. The présent invention means that simplified protectors can be used, for example non-sealing protectors or even protectors the manufacturing spécifications for which no longer need to be too severe in order to ensure that the contact between the surfaces of the protector and the surfaces of the connection is very good.

The coating used in accordance with the invention has a good level of corrosion résistance by providing cathodic protection of the substrate. The optional presence of particles of lubricant compounds as defined above and which hâve a low wettability also mean that corrosion résistance is improved.

Finally, the coating used in accordance with the invention does not wear during successive makeup operations. Thus, it can continue to guarantee the anti-corrosion behaviour quality even after several makeup/breakout cycles without necessitating supplémentai anti-corrosion protection. In addition, its high wear résistance means that débris or dust which can be observed upon breakout is not generated.

The invention also concems a method for producing a connecting element as defined above, in which the principal layer and optional additional layer are deposited by autocatalytic déposition.

The principal layer constituted by a nickel-phosphorus alloy used in accordance with the invention may be deposited on the connecting element by autocatalytic déposition. Autocatalytic deposits of nickel-phosphorus alloy are described in NF standard EN ISO 4527, as well as in the document by Louis LACOURCELLE - Nickelage chimique [Chemical nickeling], Techniques de l’ingénieur, Metallic materials essay.

Autocatalytic deposits of nickel-phosphorus alloy are proposed by the company MACDERMID under the trade name NiKlad™ELV.

The additional layer optionally used in accordance with the invention, constituted by a nickel-phosphorus alloy comprising particles of one or more lubricant compounds, may be obtained by autocatalytic déposition.

Autocatalytic deposits of nickel-phosphorus alloy containing particles of polytetrafluoroethylene hâve been proposed by the company MACDERMID under the trade name NiKlad™ ICE ULTRA.

Déposition of the principal layer used in accordance with the invention and of the possible additional layer used in accordance with the invention may be carried out using an autocatalytic method comprising the following steps:

• cleaning the surface of the connecting element; cleaning may be carried out by alkaline degreasing, then rinsing, then electrolytic degreasing, then rinsing, then acid stripping, then rinsing; then:

• depositing the nickel-phosphorus, then depassivating the surface, then optional déposition of nickel-phosphorus supplemented with particles of lubricant compound, then rinsing; then • oven drying, for example at a température of the order of 70°C; then • a degassing treatment in an oxidizing atmosphère, typically for 2h at 220°C.

In accordance with a first embodiment, this method may also include a posterior heat treatment at a température which is preferably in the range 250°C to 300°C, for example for a period of 3 to 5 h.

This posterior heat treatment allows to increase the hardness of the coating and thus of the threading, and to improve the anti-galling performances without, however, deteriorating the corrosion protection performances.

In accordance with a second embodiment, this method may also comprise a posterior heat treatment step carried out at a température which is preferably in the range 300°C to 600°C, for example for a period of 3 to 5 h. In this case, the hardness of the coating is substantially increased, for example from 500 Hk when the method does not comprise this posterior heat treatment step to 800 Hk when it comprises this step, but the corrosion protection performances deteriorate.

Some features of the invention are disclosed in more detail in the following description made with reference to the accompanying drawings:

Figure 1 is a diagrammatic view of a connection resulting from connecting two tubular components by makeup.

Figure 2 is an enlarged view ofthe zone in box A of Figure 1.

Figure 3 is a detailed view of the coopération between the threads of two connected tubular components.

Figure 4 is a detailed view of a connecting element (threading) of the invention overlaid with a coating.

The threaded connection shown in Figure 1 comprises a first tubular component with an axis of révolution 9 provided with a male end 1 and a second tubular component with an axis of révolution 9 provided with a female end 2. The two ends 1 and 2 each end in a terminal surface orientated radially with respect to the axis 9 of the threaded connection and are respectively provided with threaded portions 3 and 4 which cooperate together for mutual connection by makeup of the two components. The threaded portions 3 and 4 may be of the trapézoïdal or other thread type. In the example shown, the threaded portions hâve threads with a vanishing profile at the respective ends ofthe threaded portions. These vanishing profiles extend over a portion of the axial extent of the threaded portion. In particular, a portion of the threaded portion with a vanishing profile 10 does not cooperate with a complementary threading.

In addition, as can be seen in Figure 2, metal/metal sealing surfaces (bearing surfaces) 5, 6 intended to corne into an interférence sealing contact one against the other after connection of the two threaded components by makeup are respectively provided on the male and female ends close to the threaded portions 3, 4. Finally, the male end 1 ends in a terminal surface 7 which abuts against a corresponding surface 8 provided on the female end 2 when the two ends are made up one into the other. The surfaces 7 and 8 are termed abutment shoulders.

Figure 3 shows a detail of a thread of a threaded portion. Each thread thus comprises a load flank 11 forming an angle 12 in the range -5° to +5° with respect to the normal N to the connection axis 10. The load flank is connected via a crest 13 to a stabbing flank 14. In particular, the connection shown is such that in the final position of the connection, the load flanks of the male threaded portion 3 are in contact with the corresponding load flanks of the female threaded portion

4.

Figure 4 shows the male end 1 of a tubular component in which the threaded portion 3 and the sealing surface 5 (bearing surface) are overlaid with a coating 15 as defined in the invention. Example

A metallic coating of a principal layer of a nickel-phosphorus alloy comprising 11% by weight of phosphorus, and an additional layer of a nickel-phosphorus alloy comprising polytetrafluoroethylene (PTFE) particles in an amount of 25% by volume with respect to the volume of the alloy, was produced on a L80 grade carbon steel threading.

The principal layer was deposited using the autocatalytic method proposed by the company MACDERMID with the trade name NiKlad™ ELV.

The additional layer was deposited using the autocatalytic method proposed by the company MACDERMID with the trade name NiKlad™ ICE ULTRA.

The principal nickel-phosphorus layer was 29 gm thick. The additional nickel-phosphorusPTFE layer was 7.4 gm thick.

The metallic composite deposit obtained had a hardness of at least 550 Hk under 10 g.

The metallic composite deposit had very good corrosion résistance.

Tests were carried out on the shore at a marine industrial exposure site (port of Dunkirk) classed as level 4 (high) on a scale of up to C5 (see “Corrosivity Class” in accordance with ISO standard 9223).

After 12 months exposure in Dunkirk with a protector, no signs of rust were observed.

After 12 months exposure in Dunkirk without a protector, a few rare spots of corrosion were observed (Re 1 on the European scale for degree of rusting, ISO 4628-3).

After 24 months exposure in Dunkirk with a protector, no signs of rust were observed.

The metallic composite deposit was not damaged during a scratch test type test where it was subjected to an increasing load from ION to 300N provided by a tungsten carbide bead with a diameter of 5 mm. In contrast to other metallic deposits (Cu-Sn-Zn alloy type), the deposit does not crack; no detachment or délamination of the coating was observed.

The metallic composite deposit had excellent anti-galling performances.

Laboratory tests (Vee block test with a constant 785N load, équivalent to a contact pressure of 500-600 MPa, characteristic ofthe contact pressures occurring during makeup of a connection at the threads) exhibited highly progressive wear during use of nickel-phosphorus supplemented with PTFE compared with a metallic deposit of a temary Cu-Sn-Zn alloy.

Makeup curves veiy similar to those obtained with an API grease were obtained: highly regular slopes (not bumpy), with clearly identifiable changes in the slope.

Corrosion tests according to ISO Standard 9227 - Corrosion tests in artificiai atmosphères or sait spray tests - hâve been carried out on a sample corresponding to the example described 5 above (noted with sample reference “D”) and was compared to samples with various thicknesses of constituting layers. AU the samples are L80 grade carbon steel threaded éléments overlaid with a principal layer of a nickel-phosphorus alloy comprising 11% by weight of phosphorus, and an optional additional layer of a nickel-phosphorus alloy comprising polytetrafluoroethylene (PTFE) particles in an amount of 25% by volume with respect to the volume of the alloy.

Ail those samples hâve been exposed to neutral spray test (NSS) for at least 1000 hours,

Results are given according to ISO standard 9227, on a European scale with levels of rust ranging from ReO to Re9; level ReO corresponding to a 0% rusted surface; Re3 corresponding to a 1% rusted surface; Re5 corresponding to a 8% rusted surface; Re6 corresponding to a 40%-50% rusted surface.

Sample reference	Coating	Rust level after 500h exposure (Re scale)	Rust level after lOOOh exposure (Re scale)
A	One principal layer NiP from 25pm to 31pm	4.5	6
B	One principal layer NiP from 15pm to 20 pm and one additional layer of NiP-PTFE from 5pm to lOpm	3	4.5
C	One principal layer NiP from 20pm to 25 pm and one additional layer of NiP-PTFE from 5pm to lOpm	2.6	4.5

D

One principal layer NiP from 25pm to 30 pm and one additional layer of NiP-PTFE from 5pm to lOpin

2.3

2.8

The sample D with a coating comprising a principal layer of Nickel -Phosphorus alloy having a thickness in the range 25 pm to 30pm and an additional layer of Nickel Phosphorus comprising 5 particles of PTFE lubricant présents an excellent behaviour to corrosion.

Claims (21)

1. A connecting element for a tubular component, characterized in that it is overlaid with a coating comprising a principal layer constituted by a nickel-phosphorus alloy.

2. A connecting element according to claim 1, characterized in that the phosphores represents 5% to 13%, preferably 8% to 13%, more preferably 10% to 12%, even more preferably 10.5% to 11.5% by weight of the total weight of the nickel-phosphorus alloy.

3. A connecting element according to claim 1 or claim 2, characterized in that the thickness of said principal layer constituted by a nickel-phosphorus alloy is in the range 5 to 10 pm.

4. A connecting element according to claim 1 or claim 2, characterized in that the thickness of said principal layer constituted by a nickel-phosphorus alloy is in the range 15 to 35 pm, preferably 20 to 35 pm, more preferably 25 to 30 pm.

5. A connecting element according to any one of the preceding claims, characterized in that the coating further comprises an additional layer constituted by a nickel-phosphorus alloy comprising particles of one or more solid lubricant compounds, said additional layer being disposed on said principal layer.

6. A connecting element according to claim 5, characterized in that the particles of one or more solid lubricant compounds are selected from particles of polytetrafluoroethylene, talc, mica, boron nitride, silicon carbide, tungsten carbide, tungsten sulphide, molybdenum sulphide and mixtures thereof.

7. A connecting element according to claim 5 or claim 6, characterized in that the phosphores of the nickel-phosphorus alloy comprising the particles of one or more solid lubricant compounds represents 5% to 13%, preferably 8% to 13%, more preferably 10% to 12% by weight of the total weight of the nickel-phosphorus alloy comprising the particles of one or more solid lubricant compounds.

8. A connecting element according to any one of claims 5 to 7, characterized in that the particles of one or more solid lubricant compounds represent 20% to 35% by volume, preferably 25% to 30% by volume with respect to the total volume of the mckel-phosphorus alloy comprising the particles of one or more solid lubricant compounds.

9. A connecting element according to any one of claims 5 to 8, characterized in that the thickness of said additional layer constituted by a nickel-phosphorus alloy comprising the particles of one or more solid lubricant compounds is in the range 3 to 13 pm, preferably 5 to 10 pm.

10. A connecting element according to any one of the preceding claims, characterized in that the coating comprises a lubricant layer disposed on said principal layer or on said additional layer when the coating comprises said additional layer.

11. A connecting element according to claim 10, characterized in that that lubricant layer is selected from a grease, a semi-solid lubricant layer or a solid, dry lubricant layer comprising one or more solid lubricant particles in a resin.

12. A connecting element according to any one ofthe preceding claims, characterized in that it is a threading.

13. A connecting element according to any one of the preceding claims, characterized in that it is a sealing surface.

14. A connecting element according to any one of the preceding claims, characterized in that it is an abutment shoulder.

15. A tubular component comprising one or more connecting éléments as defined in any one of the preceding claims.

16. A tubular component according to claim 15, characterized in that it comprises a threading as defined in claim 12.

17. A tubular component according to claim 15 or claim 16, characterized in that it comprises a sealing surface as defined in claim 13.

18. A tubular component according to claim 15, 16 or 17, characterized in that it comprises an abutment shoulder as defined in claim 14.

19. A method for obtaimng a connecting element as defined in any one of claùns 1 to 14, characterized in that the principal layer and the optional additional layer are deposited by autocatalytic déposition.

20. A method according to claim 19, characterized in that it includes a step for posterior

5 treatment at a température in the range 250°C to 300°C.

21. A method according to claim 19, characterized in that it comprises a step for posterior treatment at a température in the range 300°C to 600°C.