Separable Threaded Connection With Asymmetric Coating

Abstract

A screw joint has a tubular element with a female thread and a tubular element with a male thread, wherein the male thread and the female thread have first contact surfaces that cooperate with each other, and the tubular elements optionally have second contact surfaces adjacent to the female thread and/or the male thread, wherein the first contact surfaces and the optional second contact surfaces each have a coating including a first and a second layer, wherein the first layer is formed as a conversion layer in each case, one of the first contact surfaces that cooperate with each other has a second layer made of ceramic material with a friction reducing effect and the other of the two contact surfaces that cooperate with each other has, as a second layer, a varnish layer with a binding agent made of an organic polymer throughout which solid lubricant particles are distributed.

Claims

1. A screw joint comprising a tubular element having a female thread and a tubular element having a male thread, wherein said male thread and said female thread have first contact surfaces that cooperate with each other, and the tubular elements optionally having a second contact surfaces adjacent to said female thread and/or said male thread, wherein said first contact surfaces and, if applicable, said second contact surfaces each having a coating which has at least a first and a second layer, wherein said first layer is formed as a conversion layer in each case, wherein one of said first and, if applicable, second contact surfaces that cooperate with each other has a layer comprised of ceramic material with a friction reducing effect as a second layer and the other of the two contact surfaces that cooperate with each other has a varnish layer with a binding agent comprised of an organic polymer, throughout which solid lubricant particles are distributed, as a second layer.

2. The screw joint according to claim 1, wherein said second layer comprised of a ceramic material is formed on said tubular element with said female thread and said second layer consisting of a varnish layer is formed on said tubular element with said male thread.

3. The screw joint according to claim 1, wherein (a) said ceramic layer has a thickness of less than 1 m, (b) said ceramic layer has a thickness of less than 200 nm, or (c) said said ceramic layer has a thickness of particularly 10 and 100 nm.

4. The screw joint according to claim 1, wherein said ceramic layer includes a resin or a hydrophobing agent, in order to increase corrosion resistance.

5. The screw joint according to claim 1, wherein said ceramic layer comprises titanium, zirconium, niobium, tantalum, molybdenum, chromium, silicon, vanadium, tungsten, germanium oxides and/or combinations thereof.

6. The screw joint according to claim 1, wherein said ceramic layer consists of a wet chemical, a self-depositing precipitate or a ceramic prepolymer with organic components applied by means of coating.

7. The screw joint according to claim 1, wherein (a) said first layer is formed as a phosphate layer, (b) said first layer consists of manganese phosphate, iron phosphate and/or zinc phosphate, and optionally with the addition of nickel salts, (c) said first layer consists of manganese phosphate and zinc phosphate, or (d) said first layer consists of of manganese phosphate.

8. The screw joint according to claim 1, wherein said second contact surfaces comprise sealing surfaces that cooperate with each other to form a sealing seat and further comprise shoulder surfaces that cooperate with each other, wherein said sealing surfaces are optionally conical and are optionally arranged in screw-in direction adjoining to said female and male thread respectively.

9. The screw joint according to claim 1, wherein (a) said varnish layer has a thickness of between 5 and 80 m, in the area of said first contact surfaces, or (b) said varnish layer has a thickness of between 10 and 40 m, in the area of said first contact surfaces.

10. The screw joint according to claim 1, wherein (a) said varnish layer has a thickness of between 10 and 500 m, in the area of said second contact surfaces; or (b) said varnish layer has a thickness of between 40 and 300 m, in the area of said second contact surfaces.

11. The screw joint according to claim 1, wherein said varnish layer has a smaller thickness in the area of said first contact surfaces than in the area of said second contact surfaces.

12. The screw joint according to claim 8, wherein (a) said varnish layer has a thickness of between 10 and 300 m, in the area of said sealing surfaces; or (b) said varnish layer has a thickness of between 40 and 150 m, in the area of said sealing surfaces.

13. The screw joint according to claim 8, wherein (a) said varnish layer has a thickness of between 50 and 500 m, in the area of said shoulder surfaces; or (b) said varnish layer has a thickness of between 150 and 300 m, in the area of said shoulder surfaces.

14. The screw joint according to claim 1, wherein said organic polymer of said binding agent of said varnish layer is a polymer that hardens through cross-linking.

15. The screw joint according to claim 1, wherein said varnish layer consists of a baking varnish with a synthetic resin binding agent, or comprises a two-component system of a synthetic resin and a curing agent as a binding agent.

16. The screw joint according to claim 15, wherein said synthetic resin is an alkyd resin, optionally modified with epoxy resin.

17. The screw joint according to claim 1, wherein aid solid lubricant particles are polymer-based and particularly consist of a synthetic wax, preferably polyolefin, polyamide or fluoropolymer, particularly preferably polypropylene wax.

18. The screw joint according to claim 1, wherein (a) the percentage of said solid lubricant particles in said varnish layer is 1 to 50% w/w, (b) the percentage of said solid lubricant particles in said varnish layer is 1 to 20% w/w, (c) the percentage of said solid lubricant particles in said varnish layer is 1 to 10% w/w, or (d) the percentage of said solid lubricant particles in said varnish layer is 5% w/w.

19. The screw joint according to claim 1, wherein (a) said thickness of said coating of said first contact surfaces that cooperate with each other is less than 120 m, or (b) said thickness of said coating of said first contact surfaces that cooperate with each other is less than 70 m.

20. The screw joint according to claim 8, wherein (a) said thickness of said coating of said second contact surfaces that cooperate with each other is less than 340 m, in the area of said sealing surfaces, or (b) said thickness of said coating of said second contact surfaces that cooperate with each other is less than 180 m, in the area of said sealing surfaces.

21. The screw joint according to claim 8, wherein (a) said thickness of said coating of said second contact surfaces that cooperate with each other is less than 540 m, in the area of said shoulder surfaces, or (b) said thickness of said coating of said second contact surfaces that cooperate with each other is less than 330 m, in the area of said shoulder surfaces.

22. The screw joint according to claim 1, wherein said first and said second layer comprised of ceramic material are formed together as conversion layer.

23. The screw joint according to claim 1, wherein said lubricant particles consist of non-crystalline fluorinated hydrocarbons and/or non-high polymer, if applicable derivatized, hydrocarbons or silicones.

24. A method for surface treatment of threads of a threaded connection of tubular elements comprising applying a coating onto first contact surfaces that cooperate with each other of a female thread and a male thread of said threaded connection and optionally applying a coating onto second contact surfaces that cooperate with each other of said tubular elements adjacent to said female and/or male thread, wherein applying the coating comprises the application of at least a first layer and the application of a second layer on said first layer, wherein a conversion layer is applied onto said contact surface as a first layer in each case, wherein a layer made of ceramic material with a friction reducing effect is applied as a second layer onto one of said first and, if applicable, second contact surfaces that cooperate with each other and a varnish layer with a binding agent made of an organic polymer, throughout which solid lubricant particles are distributed, is applied as a second layer to the other of the two contact surfaces that cooperate with each other.

25. The method according to claim 24, wherein said layer made of ceramic material is applied to said contact surface of the female thread as second layer and said varnish layer is applied to said contact surface of the male thread as second layer.

26. The method according to claim 24, wherein (a) said ceramic layer is applied with a layer thickness of less than 1 m, (b) said ceramic layer is applied with a layer thickness of less than 200 nm, or (c) said ceramic layer is applied with a layer thickness of between 10 and 100 nm.

27. The method according to claim 24, wherein said ceramic layer is produced by means of wet chemical precipitation of nanoparticles.

28. The method according to claim 27, wherein the method further comprises immersing said tubular element with its thread into a bath of a solution of the nanoparticles with primarily perpendicular pipe axis, wherein, optionally, the level of said bath is increased by means of arranging a displacement body in the inside of said tubular element.

29. The method according to claim 27, wherein said method further comprises immersing said tubular element with a circumferential portion into a bath of a solution of the nanoparticles with primarily horizontal pipe axis and rotating said tubular element about said pipe axis.

30. The method according to claim 24, wherein (a) said varnish layer is applied with a layer thickness of between 5 and 80 m, in the area of the first contact surfaces, or (b) said varnish layer is applied with a layer thickness of between 10 and 40 m, in the area of the first contact surfaces.

31. The method according to claim 24, wherein said varnish layer is applied by means of spraying.

Description

[0035] The invention is discussed in more detail below with reference to an example embodiment schematically shown in the drawing. In this drawing, FIG. 1 shows the individual coatings of the female and of the male thread, FIGS. 2 and 3 show the progression of the torque measured during screwing together and unscrewing of the threaded connection as a function of the rotations and FIG. 4 shows a section of a screw joint in the screwed-together state.

[0036] FIG. 1 shows a pipe portion 1 comprising a male thread 6 and a pipe portion 2 as a socket comprising a female thread 7. The pipe portion 1 comprises a pipe axis 3, wherein the wall is designated with 4. The wall of the pipe portion 2 is designated with 5. The male thread 6 and the female thread 7 are formed with contact surfaces that cooperate with each other such that the pipe portion 1 can be screwed into pipe portion 2 formed as a socket to produce a threaded connection between the two pipe portions.

[0037] Onto each of the contact surfaces of the male thread 6 and the female thread 7, a first layer 8 and 9, respectively, is applied directly, which is a manganese phosphate layer in each case. The manganese phosphate coatings 8 and 9 have a thickness of 5 to 20 m, preferably 10-15 m.

[0038] A varnish layer 10 into which wax particles are dispersed is positioned on the manganese phosphate layer 8 of the pipe portion 1. The varnish layer 10 is preferably realised with a varnish with the trade name SILVATHERM 2312-3009-90. This is a baking varnish on the basis of an alkyd resin modified with epoxy resin. The wax particles are preferably particles made of polypropylene wax, wherein a particle diameter of less than 20 m, particularly between 2-10 m, is preferred. The varnish is applied to the metallic sealing seat, the shoulder surfaces and the male threads 10 and then cured at 130-180 C. for about 7-20 min in a temperature chamber. The varnish layer has a thickness of 5-80 m, particularly 10-40 m. A baking varnish on the basis of an alkyd resin modified with epoxy resin does not show any significant degradation of the tribological characteristics, even at low temperatures of up to 40 C.

[0039] A nano quartz layer 11 with a layer thickness of <1 m is arranged on the manganese phosphate layer 9 of the pipe portion 2.

[0040] Tests with such a combination of materials on the contact surfaces of the threaded connection have revealed that there was a constant friction of about 0.06 over a test duration of 400 cycles.

[0041] FIGS. 2 and 3 depict measurements of the progression of the torque during screwing (FIG. 2) and unscrewing (FIG. 3) of the threaded connection according to FIG. 4 as a function of the rotations. On the x-axis, the rotations are shown, on the y-axis, the torque in nm. The measurements of ten successive processes of screwing and/or unscrewing are mapped, wherein the measured values are numbered as 1 to 10 according to the order of the processes of screwing and/or unscrewing.

[0042] It can be seen that with no additional lubrication, a constant torque progression is given even with 10 successive screwing processes.

[0043] FIG. 4 shows one embodiment of the invention, wherein the two pipe portions 1 and 2 are depicted in a screwed together state. The male thread 6 and the female thread 7 are conical and have first contact surfaces that cooperate with each other. Subsequent to the male and female threads 6,7, the pipe portions 1,2 each have second contact surfaces that cooperate with each other, namely sealing surfaces 12 and 13 that lie flat against each other and cooperate with each other as well as shoulder surfaces 14 and 15 that lie flat against each other and cooperate with each other. Preferably, the sealing surfaces 12,13 are conical. The shoulder surfaces 14,15 are mostly inclined with respect to the axis 3 such that the two pipe portions 1 and 2 are pressed against each other upon tightening of the screw joint at the shoulder surfaces 14,15, but also at the sealing surfaces 12,13.