Solid lubricant for Zn-Ni coating on a threaded tubular element

Abstract

A tubular threaded element for the drilling, the operation of hydrocarbon wells, the transport of oil and gas, the transport or the storage of hydrogen, the carbon capture or the geothermal energy, including a metal body and at least one threaded end including at least one threaded portion, the threaded end including a multilayer coating on at least one portion of the surface of the threaded end wherein the multilayer coating includes a first layer including a solid coating including Zinc-Nickel electrodeposited on the at least one portion of the surface of the threaded end, a second oxalation-type conversion layer above the first layer, a third layer including a polyurethane or epoxy matrix loaded with solid lubricant particles above the second layer.

Claims

1. A tubular threaded element, comprising: a metal body and at least one threaded end comprising at least one threaded portion, said threaded end comprising a multilayer coating on at least one portion of the surface of the threaded end wherein said multilayer coating comprises: a first layer comprising a solid coating comprising Zinc-Nickel electrodeposited on said at least one portion of the surface of the threaded end; an oxalation conversion layer formed on the first layer; and a layer of a polyurethane or epoxy matrix comprising solid lubricant particles formed on the second oxalation conversion layer, wherein a porosity of the oxalation conversion layer is from 5% to 35%.

2. The tubular threaded element according to claim 1, wherein the oxalation conversion layer comprises nickel oxalate and/or zinc oxalate.

3. The tubular threaded element according to claim 1, wherein the oxalation conversion layer has a layer weight per unit area from 0.1 g/m.sup.2 to 20 g/m.sup.2.

4. The tubular threaded element according to claim 3, wherein the layer weight per unit area of the oxalation conversion layer is from 0.5 g/m.sup.2 to 10 g/m.sup.2.

5. The tubular threaded element according to claim 1, wherein the porosity of the oxalation conversion layer is from 10% to 25%.

6. The tubular threaded element according to claim 1, wherein the oxalation conversion layer has a thickness from 0.5 m to 30 m.

7. The tubular threaded element according to claim 6, wherein the thickness of the oxalation conversion layer is from 1 m to 20 m.

8. The tubular threaded element according to claim 1, wherein the oxalation conversion layer comprises a microcracked polyhedron type texture with edges of from 1 m to 30 m in width.

9. The tubular threaded element according to claim 1, wherein the at least one threaded end further comprises a stop surface and a sealing surface, wherein the multilayer coating covers the stop surface and/or the sealing surface.

10. A method for manufacturing the tubular threaded element according to claim 1, comprising: electrodepositing a zinc-nickel layer on a metal surface of a threaded end; an oxalation conversion treatment of the surface of the zinc-nickel layer to obtain the oxalation conversion layer; and covering the oxalation conversion layer with a layer comprising a polyurethane or epoxy matrix loaded with solid lubricant particles.

11. The method for manufacturing a tubular threaded element according to claim 10, wherein the oxalation conversion treatment is carried out at a temperature from 25 C. to 90 C.

12. The method for manufacturing a tubular threaded element according to claim 10, wherein the oxalation conversion treatment comprises treatment with oxalic acid solution having a concentration of from 1 g/L to 75 g/L.

13. The method for manufacturing a tubular threaded element according to claim 12, wherein the oxalic acid solution further comprises an additive selected from the group consisting of a nitrate, a chloride, a thiocyanate, a thiosulphate and a combination thereof.

Description

BRIEF DESCRIPTION OF FIGURES

(1) The invention will be better understood, and other aims, details, features and advantages thereof will appear more clearly during the following description of several particular embodiments of the invention, given only for illustrative and non-limiting purposes, with reference to the appended drawings.

(2) FIG. 1 schematically shows, in a partial view in longitudinal section, a joint resulting from the assembly of two male and female tubular threaded elements according to the invention.

(3) FIG. 2 schematically shows, in a longitudinal section, a section of the multilayer coating according to the invention.

(4) FIG. 3 shows a graph representing the evolution of the screwing torque at each end of screwing for different types of coatings on tubular threaded elements, for different connections including either oxalation or passivation.

(5) FIG. 4 shows a graph representing the evolution of the screwing torque at each end of screwing for different types of coatings on tubular threaded elements, for one of the connections different from that of FIG. 3 and comprising either oxalation or passivation.

(6) FIG. 5 shows a graph representing the number of steps required during a BOWDEN test depending on a layer weight for different types of conversion, in particular to reach 0.2 of coefficient of friction relative to the layer weight.

(7) FIG. 6 shows an image taken by SEM (Scanning Electron Microscope) observation, according to a longitudinal sectional view, of a multilayer coating according to the invention.

(8) FIG. 7 shows an image taken by SEM (Scanning Electron Microscope) observation, according to a longitudinal sectional view, of a multilayer coating according to the state of the art.

(9) FIG. 8 shows an image taken by SEM (Scanning Electron Microscope) observation according to a top view of the surface of an oxalation-type conversion layer according to the invention at 5000 magnification.

(10) FIG. 9 describes an image taken by SEM (Scanning Electron Microscope) observation according to an elevated view of the surface of an oxalation-type conversion layer according to the invention at 20000 magnification.

DESCRIPTION OF THE EMBODIMENTS

(11) In the remainder of the description, the terms longitudinal, transverse, vertical, front, rear, left and right are defined according to a usual orthogonal reference frame as represented in the drawings, which comprises:

(12) A horizontal longitudinal axis X, and from left to right of the sectional views;

(13) Moreover, in the description and the claims, the terms external or internal and the axial and radial orientations will be used to designate, according to the definitions given in the description, elements of the tubular threaded joint. The longitudinal axis X determines the axial orientation. The radial orientation is directed orthogonally to the longitudinal axis X.

(14) FIG. 1 shows a joint or a connection, along the longitudinal axis X, of a first male tubular threaded element (1) according to the invention, comprising a metal body (5) and a male threaded end (3), said male threaded end (3) comprising a male stop surface (6), a male sealing surface (8) and a male threaded portion (14), the first male tubular threaded element (1) being represented assembled with a second tubular threaded element (2) according to the invention, comprising a metal body (5) and a female threaded end (4), said female threaded end (4) comprising a female stop surface (7), a female sealing surface (9), and a female threaded portion (15).

(15) Each of the male (3) and female (4) threaded ends consist of a metal substrate (20) and a multilayer coating (10) on this metal substrate (20).

(16) The threaded tubular elements (1, 2) are represented in the screwed state, but the invention does not exclude that they can be in the unscrewed unitary state.

(17) The multilayer coating (10) can be on one or the other of the male (3) and female (4) threaded ends or even on both at the same time. In particular, said multilayer coating (10) can be on a male (6) or female (7) stop surface, on a male (8) or female (9) sealing surface, or even on a male (14) female (15) threaded portion, on several of these surfaces or all these surfaces. Concerning FIG. 1, the multilayer coating (10) is on the male threaded end (3).

(18) FIG. 2 shows a longitudinal sectional view of a multilayer coating (10) on the metal substrate (20) of a male threaded end (3). However, said coating (10) may just as well be on the metal substrate of a female threaded end. Thus, all developments concerning the multilayer coating (10) on the male threaded end (3) apply analogously to a multilayer coating (10) on the female threaded end.

(19) In particular, the figure shows the multilayer coating (10) comprising a first layer (11) of a solid coating comprising Zinc-Nickel electrodeposited on the surface of the male threaded end (3), that is to say on the metal substrate (20) which constitutes said male threaded end (3).

(20) Said multilayer coating (10) comprises a second oxalation-type conversion layer (12) above the first layer (11).

(21) The second conversion layer (12) of the oxalation type can comprise nickel oxalate and/or zinc oxalate (not shown in the Figure). These two elements can originate from the oxalation layer, by reaction between oxalic acid and the zinc-nickel layer.

(22) Finally, a third lubricating layer (13) comprising a polyurethane or epoxy matrix loaded with solid lubricant particles is deposited above the second layer (12). The solid lubricant particles are selected, without limitation, from PTFE, talc, chromium oxide, alumina.

(23) Advantageously, the first solid deposition layer (11) comprising zinc-nickel confers improved lubricating properties, whose effects are preserved from delamination, lineage and galling. Indeed, the second oxalation layer acts on the first layer as a solid lubricant. The latter allows giving the first solid deposition layer (11) comprising ZnNi to have a much more stable and durable coefficient of friction. Said coefficient of friction being less than 0.2. Indeed, beyond 0.2 there is a risk of galling.

(24) The applicant has indeed demonstrated by comparison that this stability and this durability were not found with a passivation layer (see FIG. 3 and FIG. 4). The second oxalation layer (12) also allows conferring a chemical or mechanical insulating barrier effect for the sub-layer or first layer (11) of solid deposition comprising ZnNi. The second oxalation layer (12) amplifies the effects provided by the third layer (13). The latter conferring an additional lubricating effect in synergy with the lubricating effect conferred by the second layer (12) thus increasing the screwing capacities of a connection (see FIG. 3).

(25) Moreover, the use of oxalic acid is less restrictive relative to the regulations in force and is not classified as CMR, that is to say it is not carcinogenic, mutagenic or reprotoxic.

(26) Advantageously, the second oxalation layer (12) comprises nickel oxalate and zinc oxalate and allows delaying the metal/metal contact and storing a portion of the dissipation energy emitted during screwing the connection.

(27) Indeed, during the crushing of the coating (10) under the action of the screwing of the threaded ends, the functional surfaces of the ends come into contact with very high contact pressures. The second layer (12) will be crushed first by undergoing the effects of stresses and pressures before the first solid layer (11), which preserves said first layer (11) and improves the overall endurance of the coating (10). In addition, surprisingly, it has been found that the addition of a nickel oxalate allows improving the anti-corrosion resistance of the conversion layer.

(28) FIG. 3 shows, in a comparative manner, the evolution of the screwing torque at each end of screwing for different types of coatings on tubular threaded elements, either according to the state of the art with a passivation type layer, or according to the invention with an oxalation-type layer. The term end of screwing means the moment when the two stops of a male tubular threaded element and of a female tubular threaded element are in contact during a screwing/unscrewing cycle (M&B).

(29) One method used to ensure that the connections are assembled correctly and to determine the end of screwing time consists in monitoring the torque applied by a collet against the number of revolutions. The term collet means a high-capacity self-locking wrench used to grip the male and female components of the connection and apply a clamping/unclamping torque. By connecting a computer to the load cell on the collet and an electronic revolution counter, a graph can be plotted showing the torque on the vertical axis and the number of revolutions on the horizontal axis. By collecting each of the performed ends of screwing, a new graph can be replotted as represented in FIG. 3.

(30) FIG. 3 also shows a dashed line located approximately at 70,000 N.Math.m which represents the PLT, that is to say the capacity of the maximum wrench. When the curve approaches or reaches this maximum wrench capacity, there is a high probability that the galling of the connection occurs and to limit the number of maximum clamping/unclamping or screwing/unscrewing possibilities (M&B).

(31) All connections used in this FIG. 3, without taking into account the coating, are identical, that is to say that they correspond to tubular threaded elements of the VAM SLIJ-II type. These types of tubes are tested and validated according to the API RP 5C5: 2017 CAL II standard.

(32) Each curve represents a coating comprising a first layer of electrodeposited zinc-nickel, as well as a second passivation-type or oxalation-type conversion layer according to the invention and a third lubricating layer. Therefore, only the nature of the second conversion layer is varied from one curve to another.

(33) The curves 1 and 2 represent a coating comprising a chromium III passivation layer. The presence of two curves corresponds to two screwing tests with an identical coating.

(34) The curves 3 and 4 represent a coating comprising an oxalation layer for which an iron nitrate accelerator was used during the deposition of the layer. The presence of two curves corresponds to two screwing tests with an identical coating.

(35) The curves 5 and 6 represent a coating comprising an oxalation layer without accelerator. The presence of two curves corresponds to two screwing tests with an identical coating.

(36) FIG. 3 shows that all the curves representative of the passivation, namely the curves 1 and 2, show an increase in the torque for each screwing/unscrewing operation and come dangerously close to the PLT as the screwing/unscrewing revolutions progress. The opposite is observed with the curves representative of oxalation, namely the curves 3, 4, 5 and 6. Indeed, these curves are substantially flat, resulting in stable torques as the screwing/unscrewing operations progress. Although the curves 3, 4, 5 and 6 show a stability up to 5 revolutions of screwing/unscrewing, the applicant has been able to demonstrate that this stability can go up to 15 revolutions of screwing/unscrewing when the second layer (12) is an oxalation layer according to the invention.

(37) In addition, it was noted for the coatings of curves 1 and 2, as the revolutions of screwing/unscrewing progress, the appearance of galling, lineage at the bottoms of the threads, the top of the threads and thread seat, and therefore a damage to the electrodeposited zinc-nickel layer.

(38) With regard to the oxalation-type coatings, the applicant found no form of galling, un absence of damage to the first zinc-nickel layer and the formation of a tribofilm which confers effects of insulating barrier to the entire multilayer coating.

(39) The results of the comparative analysis are not limited and remain valid for any type of tubes in the field of oil and gas, energy or storage, for a use such as the exploitation of wells or the transport of hydrocarbons, the transport or the storage of hydrogen, the geothermal energy or the carbon capture.

(40) FIG. 4 describes similarly to FIG. 3, a comparison of the evolution of the screwing torque at each end of screwing in the same manner as for the tests in FIG. 3, and for different types of coatings, on another type of connection, namely VAM SLIJ-III.

(41) The curves 1, 2 and 3 correspond to threaded ends coated with a coating comprising a second passivation-type layer. The coating is on the entire threaded end, namely the threading or a threaded portion, the stop surface and the sealing seat. There are 3 curves because they correspond to the number of tests carried out with the same coating. The curves 4 and 5 correspond to threaded ends with a multilayer coating according to the invention comprising a second oxalation-type layer.

(42) The comparative analysis and the resulting results are similar to those developed for FIG. 3.

(43) The curves 1, 2, 3 show an increase in the torque from the second screwing/unscrewing. The curve 1 shows an impossibility of performing a fifth screwing/unscrewing for the corresponding joint due to galling, while the curves 4 and 5 show a torque stability for all screwing/unscrewing.

(44) The applicant demonstrates that the conclusions of the superior effects in terms of stability and reliability of the oxalation according to the invention relative to the passivation are not limited to VAM SLIJ-II alone and can therefore be transposed from one type connection to another.

(45) FIG. 5 shows a graph of the required number of steps, that to say the number of round trips of a steel ball, depending on the layer weight of a second conversion layer, during a BOWDEN test to reach 0.2 of coefficient of friction depending on the type of coatings.

(46) Each tested sample has a coating which comprises identically at least one first ZnNi layer and a lubricant layer, the variable between the samples is the presence and/or the nature of the second layer.

(47) There is a comparison of 3 types of coatings, namely a coating without a conversion layer, that is to say neither passivation nor oxalation, the layer weight will therefore be 0 g/m.sup.2 (represented by a square on the graph). A coating with a second passivation-type layer with two examples of layer weights set respectively at 0.1 g/m.sup.2 and 0.15 g/m.sup.2 (represented by a circle on the graph). Indeed, for the passivation, it is difficult or even impossible to find layer weight values which are greater than 0.2 g/m.sup.2. Finally, a multilayer coating, according to the invention, with a second oxalation-type layer (represented by a triangle on the graph), numerous tests have been carried out with this type of coating with different layer weight values.

(48) When two rough movable parts are in contact, a wear mechanism can lead to a shrinkage of the material with generation of debris which is the consequence of a plastic deformation. The value of the coefficient of friction depends on the composition and the structure of the surface, its roughness and its mechanical properties such as plasticity, ductility and surface resistance to shear stresses. In the case of a coating on a connection, the value of a coefficient of friction must be less than 0.2. Indeed, beyond 0.2, there is a risk of galling.

(49) In order to evaluate the lubricating properties (coefficient of friction) of the coating surface, a commercially available Bowden Friction Tester (Shinko Engineering Co., Ltd.) was used. In the Bowden Friction Tester, a steel ball (100CR6) was displaced back and forth in a straight line over 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.

(50) A commercially available steel ball made of steel (100CR6) with an outer diameter of 10 mm (Amatsuji Steel Ball Manufacturing Co., Ltd.) which is previously degreased is used as the steel ball in the Bowden friction test.

(51) The steel ball is applied to the evaluated coatings and moved with a pressing load of 300 N.

(52) FIG. 5 shows that the coating without a conversion layer reaches the critical threshold of 0.2 of friction before reaching 150 steps.

(53) The coating with passivation confers a lubrication which is substantially greater than that of a layer without conversion and allows reaching the critical threshold of 0.2 of coefficient of friction at about 200 steps.

(54) The coating with oxalation confers a superior lubrication to the two previous types of coatings with a critical threshold of 0.2 of coefficient of friction reached between 400 and 600 steps depending on the value of the layer weight. The oxalation therefore allows conferring on the solid deposition layer comprising ZnNi to have a much more stable and durable coefficient of friction.

(55) Indeed, the applicant has determined that the oxalate layer specifically improves the plastic deformation of ZnNi on the surface thereof even under a high contact pressure improving the atomic dislocation, the grain rotation and the stability of the system before the flacking of large blocks and the appearance of large-scale defects.

(56) It has been observed that even with a lower layer weight, the oxalate layers produce a longer lasting lubricating film, chemically or physically improving the lubrication efficiency.

(57) According to a variant of the invention, the layer weight of the second layer (12) is comprised between 0.1 g/m.sup.2 and 20 g/m.sup.2.

(58) According to another variant of the invention, the layer weight of the second layer (12) is comprised between 0.5 g/m.sup.2 and 10 g/m.sup.2.

(59) Advantageously, it has been determined that the endurance is proportional to layer weight, the greater the layer weight the greater the endurance.

(60) However, when the layer weight exceeds a certain threshold, the result is problems of cohesive failure in the oxalation layer. The layer ends up breaking on its own when subjected to external stresses. Consequently, there will be risks of delamination and flaking for the oxalation layer which will lead therewith to the delamination of the third lubricating layer. The applicant has determined that when up to 10 g/m.sup.2, there is a better compromise between a good endurance and a reduced risk of cohesive failure.

(61) FIG. 6 describes an image taken by SEM (Scanning Electron Microscope) observation, according to a longitudinal sectional view, of a multilayer coating (10) according to the invention, on the metal substrate (20) of a male threaded end (3).

(62) The multilayer coating (10) comprises a first layer (11) of a solid coating comprising electrodeposited Zinc-Nickel. Said coating also comprises an oxalation-type conversion layer 12. The third lubricating layer comprising a polyurethane or epoxy matrix loaded with solid lubricant particles is not observable as it is, and a plastic coating resin (22) is used for the preparation of the sample for metallographic observation. This resin (22) is only useful to obtain the image of FIG. 6 and therefore does not form part of the invention.

(63) FIG. 7 describes an image taken by SEM (Scanning Electron Microscope) observation, according to a longitudinal sectional view; of a multilayer coating (100) comprising a passivation layer (102), according to the state of the art, on the metal substrate (120) of a male threaded end (103).

(64) The multilayer coating (100) comprises a first layer (101) of a solid coating comprising electrodeposited Zinc-Nickel. The coating also comprises a passivation type conversion layer (102). The third lubricating layer comprising a polyurethane or epoxy matrix loaded with solid lubricant particles is not observable as it is, and a plastic coating resin (22) is used for the preparation of the sample for metallographic observation. This resin (22) is only useful to obtain the image of FIG. 7.

(65) The observation in FIG. 6 shows a thick and textured oxalation layer which measures about 5 m. However, according to other observations, the oxalation layer can be comprised between 0.5 m and 30 m, preferably the layer can be comprised between 1 m and 20 m.

(66) Compared with the image in FIG. 7, the second passivation-type conversion layer is simply not observable because it is less than 100 nm.

(67) This difference in observation is important to the extent that it guarantees a minimum thickness for the oxalation and which remains visible. By comparison, this visibility is not found with the passivation of FIG. 7. This thickness has advantages, such as allowing a better resistance of the material. Indeed, on the one hand, a thickness that exceeds a certain threshold, in particular 30 m, can cause cohesive failure problems. On the other hand, a layer which is less than 0.5 m or 500 nm is insufficient and will necessarily cause problems of insufficient lubrication.

(68) A cohesive failure is an undesirable effect which can degrade or even eliminate the effect of the second layer, the first zinc-nickel layer becoming vulnerable to the environment and the induced stresses.

(69) With regard to the cracks (24) and other fissures observed in the Zinc-Nickel layer in FIGS. 6 and 7, they resulted from the preparation of the samples for the purposes of the metallographic observation.

(70) Advantageously, the applicant has also determined that the thickness of the second oxalation layer has an insulating barrier type effect for the first solid Zinc-Nickel layer.

(71) FIG. 6 also shows a porosity of the second oxalation layer (12), said porosity of the second layer (12) can be comprised between 5% and 35%.

(72) According to a variant of the invention, the second layer (12) can be comprised between 10% and 25%.

(73) The term porosity of the second layer means empty spaces between the base of the crystals, the latter being able to cover said porosity at their height. It is also referred to as open porosity when there are cracks which have a direct path between the Zinc-Nickel layer and the third layer comprising a polyurethane or epoxy matrix loaded with solid lubricant particles.

(74) Advantageously, the porosity allows improving the retention of the upper layer of the multilayer coating thanks to a phenomenon of mechanical anchoring of the upper layer in the empty spaces of the oxalation layer.

(75) By comparison with FIG. 7, this porosity will not be found for a second passivation-type conversion layer according to the state of the art. Indeed, the applicant has determined that a passivation layer is much too thin to admit any porosity.

(76) FIG. 8 describes an image taken by SEM (Scanning Electron Microscope) observation according to an elevated view of the surface of an oxalation-type conversion layer (12) at 5000 magnification.

(77) It is observed in particular that the surface of the layer is textured by microcracked polyhedrons (30).

(78) The term microcracked polyhedron means a 3-dimensional geometric shape having planar polygonal faces which are grouped into segments called edges. The number of faces and edges is random, the length of the edges can range from 0.5 m to 30 m. The layer may have randomly distributed microcracks. The width of the cracks can range from 0.05 m to 1 m wide. Thanks to this feature, a texture of the microcracked polyhedron type gives the upper layer a capacity of retention and attachment to the oxalation layer.

(79) According to a variant of the invention, the second layer (12) can be produced with an accelerator which has the effect of accentuating the homogenisation of the oxalation, and thus of obtaining a thinner and denser layer.

(80) FIG. 9 describes an image taken by SEM (Scanning Electron Microscope) observation according to an elevated view of the surface of an oxalation-type conversion layer according to the invention at 20000 magnification.

(81) The developments of FIG. 8 are valid and applicable to FIG. 9.