CA2409880A1

CA2409880A1 - Erosion-resistant coatings for steel tubes

Info

Publication number: CA2409880A1
Application number: CA002409880A
Authority: CA
Inventors: Chinnia Gounder Subramanian; Konstantin K. Tzatzov; David Aaron Easton
Original assignee: Bodycote Metallurgical Coatings Ltd
Current assignee: Bodycote Metallurgical Coatings Ltd
Priority date: 2002-10-25
Filing date: 2002-10-25
Publication date: 2004-04-25

Abstract

A method of providing a protective, erosion-resistant coating of a WC-MX
composite on a carbon or low-alloy steel pipe or tube where M is one of nickel, cobalt, chromium or iron or combination thereof and X is one of silicon, boron or combination thereof, and heat treating the coating to metallurgically bond the coating onto a steel substrate of the pipe or tube. The coating may be deposited in one or more layers by plasma transferred arc deposition or may be deposited as a slurry coating or thermal spray coating with sintering of the coating. The steel substrate is prepared for coating by at least one of boring, honing, bright finishing, grit blasting, grinding, chemical pickling or electro-polishing of the substrate.

Description

EROSION-RESISTANT COATINGS FOR STEEL TUBES
BACKGROUND OF THE INVENTION
(i) Field of the Invention The present invention relates to a method of coating a steel pipe or tube and, more particularly, relates to a method of providing a protective, erosion-resistant coating of a metal composite on a carbon or low alloy steel pipe or tube.
(ii) Description of the Related Art Tubular goods used in oil and gas production or slurry transportation are subjected to severe erosion due to abrasive particles present in the fluid streams. To protect these structures many materials solutions are sought. A viable solution is based on surface coatings. Providing erosion resistant coatings inside such tubular structures pose practical difficulties. The techniques of coating large diameter tubes with erosion resistant coatings are well known in the art. However, depositing erosion resistant coating on the inner surfaces of smaller diameter long tubes encounters many practical difficulties.
Various weld overlay methods can be used to deposit erosion resistant coatings on conducting substrates. 'l~he selection depends on the iocanon anu orientation of the surface to be covered, substrate and coating material types, thickness, dilution, speed and economics. Most commonly used welding methods to deposit erosion-resistant coatings on the inner surfaces of tubular goods include gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding and gas metal arc welding (GMAW), also known as metal inert gas (MIG) welding. The feed material can be in the powder or wire form with an inert gas providing the shield against oxidation. In the GTAW process, the arc is formed between a tungsten electrode and the substrate that melts the wire or powder fed in between them whereas a consumable wire is used as the electrode in the GMAW.

- 2 -The main limitation of existing techniques is their inability to deposit coatings on inner surfaces of small diameter tube or pipe with longer lengths.
Plasma transferred arc (PTA), as disclosed for example in U.S. Patents 4,878,953 and 5,624,717, is a technique used to apply coatings of different compositions and thickness onto conducting substrates. The material is fed in powder or wire form to a torch that generates an arc between a cathode torch and the substrate work-piece. The arc generates plasma in a plasma plume that heats up both the powder or wire and the surface of the substrate, melting them and creating a liquid puddle, which on solidification creates a welded coating. By varying the feed rate of material, the speed of the torch, its distance to the substrate and the current that flows through the arc, it is possible to control thickness, microstructure, density and other properties of the coating (P. Harris and B.L. Smith, Metal Construction 15 (1983) 661-666). The technique has been used in several fields to prevent high temperature corrosion, including surfacing MCrAIYs on top of nickel based superalloys (G.A.
Saltzman, P. Sahoo, Proc. IV National Thermal Spray Conference, 1991, pp 541-548), as well as surfacing high-chromium nickel based coatings on exhaust valves and other parts of internal combustion engines cylinders (Danish Patent 165,125, U.S.
Patent 5,958,332).
This technique has been proposed for coating internal surfaces of tubular goods used in oil and gas production or abrasive slurry transportation.
Key limitations of known PTA process are the inability to deposit thin layers due to large waviness of the deposits, necessitating larger machining allowance and hence thick deposits to obtain smooth surfaces. Excess dilution from the substrate on one hand or lack of bonding on the other hand often results in poor coating.
It is accordingly a principal object of the present invention to provide a method for coating long lengths of steel pipe and tubing, particularly carbon and low alloy steels, with an inexpensive, dense, continuous and smooth protective coating substantially free of defects.

It is another object to provide a erosion-resistant coating within long lengths of steel pipe and tubing suitable for use in the erosive environments of oil-and-gas fields.
A further object of the present invention is the provision of a thin erosion resistant coating metallurgically bonded to the interior of pipes and tubes by plasma transferred arc deposition, or by slurry coating or thermal spraying and sintering.
Summary of the Invention In its broad aspect, the method of the invention of providing a protecting coating on a steel substrate comprises metallurgically bonding one or more continuous coatings of a WC.'-MX composite where M = one of nickel, cobalt, chromium, iron or combination thereof and X == one of silicon, boron or combination thereof, having about 50 to 95% WC, 5 to 50 wt°ro M and 0 to about 20 wt% X, by plasma transferred arc deposition of the coating onto the steel substrate, by slurry coating or thermal spraying and sintering, or weld overlays such as by gas tungsten arc welding or gas metal arc welding. The steel substrate preferably is a plain carbon or low alloy steel and comprises the inner surface of a pipe or tube. The composite coating has a thickness of 0.1 to 10 mm, preferably 1.0 to 7.0 mm, and most preferably 3 to 6 mm.
A preferred WC-MX composite comprises 50 to 95 wt% WC, 5 to 30 wt% Ni or Co, and 5 to 20 wt% Cr and incidental impurities.
The preferred method comprises preparing the steel substrate by boring, honing, bright finishing, grit blasting, grinding, chemical pickling or electro-polishing the steel substrate prior to deposition of the coating. The preparation of the tube surface prior to deposition determines coating microstructure with acceptable level of porosity. Pre-heating the steel pipe or tube at a temperature in the range of 100 to 800°C, preferably 250 to 600°C, is effective to avoid cracking and to enhance wetting and bonding of the coating to the substrate. The coated pipe or tube preferably is heat treated at a temperature in the range of 800 to 1 l00°C for a time effective to restore pre-coating strength, ductility and toughness of the substrate and is smoothed by boring, honing, extruding, drawing, roll-forming, grit blasting, grinding or electro-polishing. A second thin coating of the WC-MX composite having a thickness of about 0.1 to 1.0 mm deposited by plasma transferred arc onto a first continuous thin layer of the WC-MX composite previously deposited by plasma transferred arc provides a smoother coating.
In accordance with another aspect of the invention, the method comprises providing a protective coating on an inner steel substrate of a carbon or low-alloy steel pipe or tube comprising roughening the steel substrate by wet or dry grit blasting, knurling or abrasive cleaning and depositing by slurry coating or thermal spraying a WC-MX composite coating powder on the substrate, where M = one of nickel, cobalt, iron, chromium or combination thereof and X = one of silicon, boron, or combination thereof, having about SO to 93 wt% WC, about 5 to 50 wt% M, about 0.8 to about 20 wt% Si, preferably 0.8 to 5 wt% Si, 0 to about 8 wt% B, preferably 0.8 to about 5 wt°io B, and heat treating the coating at a temperature in the range of 600 to 1200°C, preferably in the range of about 950 to 1150°C, for sintering and metallurgically bonding the coating to the substrate.
A preferred WC-MX composite in which M = one of nickel, cobalt or combination thereof comprises 50 to 93.4 wt% WC, 5 to 50 wt% M, 0.8 to 8 wt%
Si, 0.8 to 5 wt% B, and incidental impurities.
Pipe or tube coating produced according to the method of the invention preferably has a length of 5 to 50 feet, more preferably 7 to 20 feet. The coating has a thickness of 0.1 to 10 mm, preferably 1.0 to 7.() mm, has a sound metallurgically bond with the steel substrate, and has a dense microstructure particularly suitable for pipe or tubing used in slurry transportation such as tar sand mixtures.

Brief Description of the Drawing Figure 1 is a photograph of a microstructure of a coating/alloy interface of an WC-Co coating on a carbon steel tube according to the present invention Description of the Preferred Embodiments A first embodiment of the present invention will be described with reference to Figure 1 of the drawings. A continuous coating of a WC-MX composite is shown deposited onto and metallurgicaly bonded to a substrate of a carbon steel tube. The WC-MX composite of the invention in which M is a metal selected from the group consisting of nickel, cobalt, chromium and iron or mixture thereof and X is an element selected from the group consisting of silicon, boron or combination thereof, has about 50 to 95 w% WC, about 5 to 50 wt% M, and 0 to about 20 wt% X.
Preferred WC-MX composites are nickel base composites such as Eutectic CastolinTM powder 6503 having a general composition of 50 to 95 wt% WC and 5 to SO wt% Ni alloy.
Steel substrates to be coated by the method of the invention, particularly internal surfaces of pipes and tubes used for oil and gas production, slurry/chemical transportation and the like typically are formed of carbon steels and low-alloy steels.
The inner surface to be coated usually is rough as produced and covered with millscale and rust and must be; cleaned in order to receive a thin, level, dense coating free of imperfections and defects such as porosity and pin-holes. The inner bore surface of a pipe or tube can be prepared by processes such as boring, honing, bright finishing, grit blasting, grinding, chemical pickling or electro-polishing prior to deposition. The pipe or tube is then pre-heated to a temperature in the range of 100 to 800°C, preferably 250 to 6()0°C, to avoid cracking and to enhance wetting and bonding of the coating on the substrate.

(~
In a preferred embodiment, a powder of the metal alloy to be coated on the interior of the carbon or low-alloy steel pipe or tube is fed from a hopper at a predetermined rate via an elongated stainless steel tube to a plasma transferred arc torch head inserted into the tube to be coated which is rotated on its longitudinal axis.
The transferred arc between the inner surface of the tube and the torch head provides the heat energy in a plasma plume needed to melt the powder and a thin layer of the tube substrate, forming a mixture of the molten metal in a molten pool. This mixing of molten metal leads to metallurgical bonding at the interface of the coating and the substrate. As the tube is rotated, the molten pool moves away from the plasma plume and solidifies. The rate of solidification, which can be controlled by post heating and by the dwell time of the plasma plume, is important to maintain the level of dilution of the coating by the substrate to less than 50°/>, preferably less than 10% dilution.
The torch is cooled by circulating water from a cooler. The power input is controlled by controlling the plasma current and voltage, in addition to pre-heating temperature, powder flow rate, rotational speed and step-over distance.
Once the coating process is completed, the tube is cooled down to room temperature in a controlled manner. Then the tube is subjected to a standard heat treatment cycle appropriate to the substrate-coating system, involving austenitizing at a temperature in the range of 800 to I 100°C,, fast cooling by quenching in a suitable medium such as water, oil and polymer mixture, and tempering at a temperature in the range of 200 to 750°C to obtain the required level of coating hardness and,to restore pre-coating strength, ductility and toughness of the steel substrate.
The inner exposed surface of the coating is rough and is finished smooth such as by machining, for example, by grinding or honing to a depth of 0.20 to 1.00 mm to render the inner surface smooth. The surface can be further finished by grit or shot blasting.
The metal composite of the coating preferably is deposited in a continuous layer having a thickness of 0.1 to 10 mm, preferably 1.0 to 7.0 mm, and more preferably a thin layer of 3.0 to 6.0 mm. A deterrent to the use of plasma transferred arc deposition has been the high cost of the coating material. It has been found that a dense, uniform coating less than 3 mm in thickness metallurgically bonded to the substrate providing an inexpensive and erosion-resistant dense coating in long pipes and tubes up to a length of 50 feet, preferably in a range of 7 to 20 feet can be effected by plasma transferred arc deposition. A second thin coating of the WC-MX
composite having a thickness of about 0.5 to 3 mm deposited by plasma transferred arc onto a first continuous thin layer of the WC-MX composite previously deposited by plasma transferred arc provides a uniformly thick coating.
The coating may be deposited onto the steel surface by a variety of methods including but not limited to physical vapour deposition (PVD), plasma arc-based techniques, thermal spray, slurry coating techniques with reactive sintering occurring simultaneously with deposition or following deposition, and weld overlay methods such as provided by TIG and MIG welding. In the case where reactive sintering does not occur during deposition, the overlay coating and substrate are heat-treated subsequently at a soak temperature in the range of about 600 to 1200°C, preferably about 950 to 1150°C for at least about 10 minutes to initiate reactive sintering.
The WC-MX composite coating can be applied to a substrate of carbon steel or low-alloy steel such as tubes and fittings by adding a blended powder of two or more of the WC-MX constituents to an effective amount of an organic binder, if necessary, and mixed with a solvent combined with a viscous transporting agent to form a slurry and coating the substrate with the slurry. The coated substrate is dried and heated in a vacuum furnace or in an oxygen-free atmosphere for evaporation of the organic binder and for reactive sintering of the coating with the substrate for adhesion of the coating to the substrate.
A preferred slurry composition comprises at least two powder constituents of WC and MX of which M is nickel and X is silicon, boron or combination thereof.
The powder is blended and is added to an organic binder. A portion of the nickel has a relatively smaller average size of 2 to 10 Vim, compared to the average size of 50 to 150 ~m for the remaining constituent or constituents. Some or all of the powder preferably has an angular, irregular or spikey shape compared to the rounded or - g _ spherical shape of the remaining constituent or constituents for improved adhesion to the substrate prior to heat-treatment.
The inclusion of silicon in the blended powder produces lower melting point constituents during the reaction sintering process, thereby allowing the molten composite to wet the surface of the substrate and to produce an effective metallurgical bond between the coating and substrate. The coated workpiece is heated to a temperature of at least about 600°C to 1200°C, preferably about 950 to 1150°C, to initiate reaction sintering of the coating on the workpiece substrate and held at the soak temperature for at least 10 minutes, more preferably about 20 minutes to hours, to provide a continuous impermeable coating metallurgically bonded to the substrate.
The coated and heat-treated samples were characterized for uniformity, metallurgical bond, microstructure density, thickness and composition by standard laboratory techniques using optical microscope and scanning electron microscope with energy dispersive spectroscopy.
The method of the invention and the products produced thereby will now be discussed with reference to the following non-limitative example.
Example 1 WC-Co alloy powder (Eutectic Castolin 6503) comprising 60 wt% WC and 40 wt% Ni-Si-B alloy was deposited on the inner surface of a carbon steel tube (ASTM
A 106) using plasma transferred arc deposition. The current used was 93A and voltage was 26V. The powder was fed at a rate of 10 gpm. The rotational speed of the 3.Oinch inside diameter tube was 0.3 rpm and the step over distance was 0.25 inch.
The microstructure shown in the microphotograph of Figure 1 has a tight metallurgical bond between substrate 10 and coating 12. The coating appears to be dense.

It will be understood, of course, that modifications can be made in the embodiments of the invention illustrated and described herein without departing from the scope and purview of the invention as defined by the appended claims.

Claims

Claims:

1. A method of providing a protective coating on an inner steel substrate of a carbon or low-alloy steel pipe or tube comprising preparing the steel substrate by at least one of boring, honing, bright finishing, grit blasting, grinding, chemical pickling or electro-polishing the steel substrate, depositing at least one continuous coating on the substrate of a WC-MX composite where M = one of nickel, cobalt, chromium, iron or combination thereof and X = one of silicon, boron or combination thereof, having about 50 to 95% WC, 5 to 50 wt% M, and 0 to about 20 wt% X.

2. A method as claimed in claim 1 in which pipe or the tube inner diameter is between 1.5 and 11.0 inches.

3. A method as claimed in claim 1 or 2, additionally comprising pre-heating the steel pipe or tube at a temperature in the range of 100 to 800°C for a time effective to avoid cracking and to enhance wetting and bonding of the coating.

4. A method as claimed in claim 1, 2 or 3 in which the coating is deposited by plasma transferred arc deposition.

5. A method as claimed in claim 1, 2, 3 or 4 additionally comprising smoothing the coated substrate by depositing a second thin coating having a thickness of 0.5 to 10.0 mm of said WC-MX composite by plasma transferred arc onto the first continuous thin coating.

6. A method as claimed in any one of claims 1 to 5 in which the WC-MX
composite consists essentially of about 50 to 95 wt% WC, about 5 to 30 wt% Ni or Co, and the balance Cr and incidental impurities.

7. A method as claimed in any one of claims 1 to 6 in which the coated steel pipe or tube is austenitized at a temperature in the range of 800 to 1100°C, water quenched, and then tempered at a temperature in the range of 200 to 750°C for a time effective to restore pre-coating strength, ductility and toughness of the steel substrate.

8. A method as claimed in claim 4 or 5 additionally comprising smoothing the coated substrate by honing, grit blasting, grinding or heat polishing the coated substrate.

9. A method as claimed in claim 8 in which the continuous thin coating has a thickness of 3.0 to 7.0 mm.

10. A method as claimed in claim 4 or 5 in which the pipe or tube has a length of to 50 feet.

11. A method as claimed in claim 4 or 5 in which the pipe or tube has a length of 7 to 20 feet.

12. A method of providing a protective coating on an inner surface substrate of a carbon or low-alloy steel pipe or tube comprising roughening the steel substrate by wet or dry grit blasting, knurling or abrasive cleaning and depositing a WC-MX
coating powder on the substrate, where M = one of nickel, cobalt, chromium, iron or combination thereof and X = one of silicon boron, or combination thereof, having about 50 to 94.5 wt% WC, about 5 to 50 wt% M, about 0.5 to about 20 wt% X and heat treating the coating at a temperature in the range of 600 to 1200°C for sintering and metallurgically bonding the coating to the substrate.

13. A method as claimed in claim 12, wherein M is nickel, depositing said coating powder by blending the coating powder with a liquid organic binder to form a slurry, coating the substrate with the slurry and evaporating the organic binder prior to sintering the coating.

14. A method as claimed in claim 12 or 13, in which the coating is heat treated at a temperature in the range of 950 to 1150°C for sintering and metallurgically bonding the coating to the substrate.

15. A method as claimed in claim 12, 13 or 14, additionally comprising smoothing the coated substrate by honing, grit blasting, grinding, or heat polishing the coated substrate.

16. A method as claimed in any one of claims 12 to 15 in which the continuous thin coating has a thickness of 0.1 to 5 mm.

17. A method as claimed in any one of claims 12 to 15 in which the continuous thin coating has a thickness of 0.5 to 3.0 mm.

18. A method as claimed in any one of claims 12 to 17 in which the pipe or tube has a length of 5 to 50 feet.

19. A method as claimed in any one of claims 12 to 17 in which the pipe or tube has a length of 7 to 20 feet.

20. A method as claimed in claim 1, 2 or 3 in which the coating is deposited by gas tungsten arc welding or gas metal arc welding.

21. A method as claimed in claim 20 additionally comprising smoothing the coated substrate by depositing a second thin coating having a thickness of 0.5 to 10.0 mm of said WC-MX composite by plasma transferred arc onto the first continuous thin coating.

22. A method as claimed in claim 20 or 21 in which the WC-MX composite consists essentially of about 50 to 95 wt% WC, about 5 to 30 wt% Ni or Co, and the balance Cr and incidental impurities.

23. A method as claimed in any one of claim 20, 21 or 22, additionally comprising smoothing the coated substrate by honing, grit blasting, grinding or heat polishing the coated substrate.

24. A method as claimed in claim 23 in which the continuous thin coating has a thickness of 3.0 to 7.0 mm.

25. A method as claimed in any one of claim 20, 21 or 22, in which the pipe or tube has a length of 5 to 50 feet.

26. A method as claimed in any one of claim 20, 21 or 22, in which the pipe or tube has a length of 7 to 20 feet.

27. A protective coating on an inner steel substrate of a carbon or low-alloy steel pipe or tube comprising a continuous thin coating having a thickness of 0.5 to 10 mm deposited on the substrate of a WC-MX composite where M = one of nickel, cobalt, chromium, iron or combination thereof and X = one of silicon, boron or combination thereof, having about 50 to 95 wt% WC, about 5 to 50 wt% M and 0 to about 20 wt%
X, the coating heat-treated to metallurgically bond the coating onto the steel substrate.

28. A protective coating as claimed in claim 27 in which the thin coating is deposited by plasma transferred arc deposition and in which the coated substrate is smoothed by honing, grit blasting, grinding or heat polishing the coated substrate.

29. A protective coating as claimed in claim 27 or 28, additionally comprising a second thin coating having a thickness of 0.1 to 1.0 mm of said WC-MX
composite deposited by plasma transferred arc onto the first continuous thin coating.

30. A pipe or tube for use in oil and gas production having the coating of claim 27, 28 or 29 in which the pipe or tube has a length of 7 to 50 feet.

31. A protective coating as claimed in claim 27, 28, 29 or 30 in which the continuous thin coating consists essentially of 50 to 95 wt% WC, 5 to 50 wt%
Ni or Co, and incidental impurities.

32. A protective coating on an inner steel substrate of a carbon or low-alloy steel pipe or tube comprising a coating powder deposited on the substrate of a WC-MX
composite where M = one of nickel, cobalt, chromium, iron or combination thereof and X = one of silicon, boron or combination thereof, having about 50 to 94.5 wt%
WC, about 5 to 50 wt% M and about 0.5 to about 20 wt% X, the coating heat-treated at a temperature in the range of 600 to 1200°C. for sintering and metallurgically bonding the coating to the substrate.

33. A protective coating as claimed in claim 32, wherein M is nickel and has a angular, irregular shape, said coating powder deposited by blending the coating powder with a liquid organic binder to form a slurry, the substrate coated with the slurry and the organic binder evaporated prior to sintering the coating.

34. A protective coating as claimed in claim 32 or 33 in which the coating is heat treated at a temperature in the range of 950 to 1150°C for sintering and metallurgically bonding the coating to the substrate.

35. A protective coating as claimed in claim 32, 33 or 34 in which the coated substrate is smoothed by honing, grit blasting, grinding or heat polishing of the coated substrate.

36. A protective coating as claimed in claim 32, 33 or 34 in which the continuous coating has a thickness of 0.1 to 5 mm.

37. A pipe or tube having the coating of any one of claims 32 to 36 for use in oil or gas production or abrasive slurry transportation in which the pipe or tube has a length of 5 to 50 feet.

38. A method as claimed in claim 12, wherein at least some of the powder has an angular, irregular or spikey shape.

39. A method as claimed in claim 1 in which the thin coating is WC-MX
deposited by thermal spraying on an inner steel substrate of a carbon or low-alloy steel pipe or tube having a length of 5 to 50 feet wherein M = one of nickel, cobalt, chromium, iron or combination thereof and X = one of silicon, boron or combination thereof, having about 50 to 94.5 wt% WC, about 5 to 50 wt% M, about 0.5 to about 20 wt% X and heat treating the coating at a temperature in the range of 600 to 1200°C
for sintering and metallurgically bonding the coating to the substrate.

40. A method as claimed in claim 38 in which the pipe or tube has a length of 5 to 50 feet.

41. A method as claimed in claim 39 or 40, in which M = one of nickel, cobalt or combination thereof and the WC-MX composite consists essentially of about 50 to 93.4 wt% WC, about 5 to 50 wt% Ni or Co, about 0.8 to 5 wt% Si, about 0.8 to 5 wt%
B, and the balance incidental impurities.

42. A protective coating on an inner surface of a carbon or low-alloy steel pipe produced by the method of claim 40.

43. A pipe or tube 5 to 50 feet in length having a 0.1 to 5.0 mm thick protective coating as claimed in claim 42 for use in oil and gas production or abrasive slurry transportation.