COATING METHOD AND COATED SUBSTRATE

Abstract

A metal substrate (71) is coated with an enamel or other coating material (72) by irradiating the coating material (72) and substrate (71) with electromagnetic radiation to melt an underlying surface of the metal substrate (71) before melting the coating material (72) to create, after cooling, a fusion bond between the solidified substrate and coating material, whereby the fusion bonded interface (73) has an intermeshing irregular tongue and groove like microstructure profile shown in FIG. 7. The electromagnetic radiation may be unfocussed, circulinear or focussed at a point located within the metal substrate (71) to first melt the substrate (71).

Claims

1. A method for coating a metal substrate, the method comprising the steps of: depositing a coating material on an underlying surface of the metal substrate, the coating material having a coating melting temperature which exceeds the substrate melting temperature; irradiating the metal substrate and coating material with electromagnetic radiation to melt the coating material and the underlying surface of the metal substrate; and cooling the metal substrate and coating material to create a solidified coated metal substrate; characterized in that the underlying surface of the metal substrate is molten before melting the coating material to generate a fusion bond between the solidified metal substrate and coating material.

2. The method of claim 1, the step of irradiating the coating material comprising focussing the electromagnetic radiation to a point of focus located below the underlying surface of and within the metal substrate thereby melting the underlying surface of the metal substrate before melting the coating material.

3. The method of claim 1 or 2, wherein the coating material comprising enamel, the step of irradiating the substrate and coating material providing a fusion bonded enamelled metal substrate.

4. The method of claim 3, wherein the coating material comprises weight fractions comprising one or more of: SiO.sub.2 1 to 50 weight %, B.sub.2O.sub.3 0 to 20%, Na.sub.2O 4 to 20%, Al.sub.2O.sub.3 0.5 to 15%, K.sub.2O, 0.2 to 8%, CaO 0.1 to 3%, CaF.sub.2 0 to 15%, ZrO.sub.2 0-16%, MnQO.sub.2 0 to 4%, NiO 0 to 2%, CoO 0 to 2%, Cu.sub.2O.sub.3 0 to 8%, Zn-.sub.2O.sub.3 0 to 4%, Cr.sub.2O.sub.3 0 to 4%, Fe.sub.2O.sub.3 1 to 40%.

5. The method of claim 3, wherein the enamel comprises a mixture of silica and alumina.

6. The method of claim 1, wherein the electromagnetic radiation is visible laser light.

7. The method of claim 1, wherein the step of irradiating the coating material comprises substantially completely defocusing the electromagnetic radiation.

8. The method of claim 1, wherein the metal substrate forms part of at least one of the group consisting of a downhole well casing, a liner, a production tubing, a surface tubular, and a surface vessel; used in the hydrocarbon production and/or conversion industry.

9. The method of claim 8, the surface being at least one of the group consisting of an inner surface of the casing, a liner, another other tubular, and another vessel.

10. The method of claim 9, the step of irradiating the coating material comprising the steps of: providing optical projection means for transforming a linear laser beam into a circulinear laser beam; and moving the optical projection means in axial direction through the pipe section to irradiate the coating material on the inner surface of the pipe section with the circulinear laser beam.

11. The method of claim 1, the step of depositing the coating material comprising depositing the coating material using thermal spraying, electroplating, brushing, and dipping.

12. A coated substrate made in accordance with the method of claim 1, comprising: a metal substrate having a surface; a layer of molten coating material provided on said surface; and an interface layer interposed between the surface and the layer of molten coating material, the interface layer comprising coating material and molten metal entangled in a fusion bond.

13. The coated substrate of claim 12, the metal substrate forming part of at least one of the group consisting of a downhole well casing, a liner, a production tubing, a surface tubular, and a surface vessel; used in the hydrocarbon production and/or conversion industry.

14. The coated substrate of claim 13, wherein the coating material comprises weight fractions comprising one or more of: SiO.sub.2 1 to 50 weight %, B.sub.2O.sub.3 0 to 20 weight %, Na.sub.2O 4 to 20 weight %, Al.sub.2O.sub.3 0.5 to 15 weight %, K.sub.2O 0.2 to 8 weight %, CaO 0.1 to 3 weight %, CaF.sub.2 0 to 15 weight %, ZrO.sub.2 0-16 weight %, MnO.sub.2 0 to 4 weight %, NiO 0 to 2 weight %, CoO 0 to 2 weight %, Cu.sub.2O.sub.3 0 to 8 weight %, Zn-.sub.2O.sub.3 0 to 4 weight %, Cr.sub.2O.sub.3 0 to 4 weight %, Fe.sub.2O.sub.3 1 to 40 weight %.

15. The coated substrate of claim 1, wherein the coated substrate comprises a fusion bonded interface with an irregular tongue and groove like microstructure between the solidified coating material and metal substrate.

16. The method of claim 2 and creating and metal a fusion bonded interface with an irregular tongue and groove like microstructure between the solidified coating material and metal substrate.

Description

[0042] The invention will be described in more detail and by way of example with reference to the accompanying schematic drawings in which:

[0043] FIG. 1 shows a cross-section of an embodiment of a method to apply a coating material to an inner surface of a pipe;

[0044] FIG. 2 shows a cross-section of a metal substrate provided with the coating material, irradiated and heated according to a method of the invention;

[0045] FIG. 3 shows a cross-section of the metal substrate provided with the coating material, while being irradiated according to a method of the invention;

[0046] FIG. 4 shows a diagram indicating hardness of the metal substrate on the y-axis after irradiation according to the invention versus distance from the surface of the metal substrate on the x-axis;

[0047] FIG. 5 shows a detail of a cross-section of an embodiment of a metal substrate provided with a coating according to the invention;

[0048] FIG. 6 is diagram that shows a material distribution(k) at a fusion bonded interface between a metal substrate and enamel coating made with the sequential heating method according to the invention; and

[0049] FIG. 7 is a longitudinal sectional view of a fusion bonded interface between an enamel coating and a metal substrate made with the sequential heating method according to the invention.

[0050] In the figures and the description, like reference signs relate to like components.

[0051] FIG. 1 shows a longitudinal cross-section of a tubular pipe 1. A central longitudinal axis of the pipe is indicated by line 2. The pipe has inner surface 4 and outer surface 6. The pipe may be a tubular section selected from typical Oil Country Tubular Goods (OCTG), including casing or liner for a wellbore. Opposite ends 8, 10 of the pipe section 1 may be provided with threaded connectors to connect the pipe section to another pipe section. The connectors (not shown) typically comprise a pin member and a box member interconnectable with the pin member.

[0052] Initially, a selected surface, for instance inner surface 4, may be cleaned. Subsequently, a layer of coating material is applied to the selected surface. For example, the coating material may be applied by thermal spraying, electroplating, or brushing.

[0053] A coating device 20, for instance a torch 22, may be axially moveable with respect to the pipe 1. The coating device can deposite a layer 24 of coating material 26 on a selected surface of the pipe, such as the inner surface 4. The coating material may comprise enamel.

[0054] The enamel coating material may comprise one or more of weight fractions: SiO2 (e.g. 1 to 50%), B2O3 (e.g. 0 to 20%), Na2O (e.g. 4 to 20%), Al2O3 (e.g. 0.5 to 15%), K.sub.2O (e.g. 0.2 to 8%), CaO (e.g. 0.1 to 3%), CaF2 (e.g. 0 to 15%), ZrO2 (e.g. 0-16%), Mno2 (e.g. 0 to 4%), NiO (e.g. 0 to 2%), CoO (e.g. 0 to 2%), Cu2O3 (e.g. 0 to 8%), Zn2O3 (e.g. 0 to 4%), Cr2O3 (e.g. 0 to 4%), Fe.sub.2O.sub.3 (e.g. 1 to 40%).

[0055] The enamel coating material may be a mixture of silica (silicium oxide) and alumina (aluminium oxide).

[0056] Conventional vitreous enamel is glass bonded by fusion to a metal surface. The most common glass is a fusion of silica, soda, lime, and a small amount of borax. Though normally transparent, various amounts of opacity can be produced by adding or growing crystals within the glass structure. A wide range of colors are produced by incorporating certain elements, mostly transition metals. The physical properties of the glass can be controlled to permit bonding to most metals, including steel, aluminum and titanium. The word Enamel refers to the glass material, as well as to the finished product.

[0057] The enamel (glass) coating material is crushed to a powder. The powder may be somewhat finer than granulated sugar and somewhat coarser than flour. The powder is applied, by one of several methods, to the selected metal surface.

[0058] As shown in FIG. 1, an embodiment to deposited the powdered enamel coating material on the inner surface 4 of the pipe 1 may be an axially moveable torch 22. An example of a suitable torch system for depositing the powdered enamel coating 26 is, for instance, provided in U.S. Pat. No. 5,426,278 or EP-1247878.

[0059] Conventionally, the metal article provided with the powder coating is heated to 1000 to 1600 F. (530 to 870 C.), either in a preheated furnace or with a torch. After 1.5 to 10 minutes, the article is removed and allowed to cool to room temperature. Subsequent coats can be applied. For instance, 10 to 20 layers of coating can be applied consecutively to bring about the desired results.

[0060] However, the steel of OCTG pipes typically has a particular API grade, indicating a particular steel composition and strength suitable for a particular application. For instance:

[0061] i) P110 grade allow steel, typically for deep water applications. Yield Strength may be between 758 MPa min and 965 MPa max (110,000 psi min and 140,000 psi max);

[0062] ii) L80 is usually used in wells with sour (hydrogen sulfide) environments. Yield Strength may be between 552 MPa min and 655 MPa max (80,000 psi min and 95,000 psi max). Hardness may be between 23 Max HRC and 241 Max HBW;

[0063] iii) T95 is an API controlled yield strength grade, generally for use in sour condensate wells. Yield Strength is between 655 MPa min 758 MPa max (95,000 psi min and 110,000 psi max). Hardness is between 25 Max HRC and 255 Max HBW; and

[0064] iv) Q125 is an API grade for deep well service, not generally for use in sour condensate wells. Yield Strength may be between 862 MPa min and 1,034 MPa max (125,000 psi min and 150,000 psi max).

[0065] Heating the steel of the pipes as referenced above in a furnace or with a torch to apply an enamel coating will negatively affect one or more of the particular qualities of the steel, most notably yield strength and hardness. This would render the pipe unsuitable for application in a wellbore, as this may greatly increase the chance of well control incidents due to failed casing. Also, conventional enamel coating is particularly brittle, meaning that for instance chips of the enamel coating may readily come off, even upon relatively minor impact.

[0066] As indicated in FIG. 2, in a method of the invention, the coating layer 24 is irradiated with electromagnetic radiation 40. The radiation may be focused, using lens system 42 or similar optical focusing means. The focused radiation 44 is focused below the surface 4 of the metal substrate 1. I.e., focus 46 of the focused radiation 44 is located at or below the surface of the metal substrate 1, rather than in or above the coating 24. Herein, the width 48 of the radiation beam when it arrives at the surface of the coating 24 is wider than the width of the focused beam at point of focus 46. The wider beam at the surface means that the energy of the radiation is spread over a larger area leading to slower and more even heating of the coating 24 and the metal 1.

[0067] Defocusing of the radiation 40 herein may in the range starting from slight defocusing, wherein the focus 46 is located at or just below the surface 4, to complete defocusing wherein the width 48 is equal to original width 50 of the radiation 40 as it arrives at the optical system 42. The latter may be achieved by removing the optical system 42 altogether, or by moving the optical system 42 in close proximity to surface 52 of the coating layer 24.

[0068] To create a coating according to the invention, the applied coating layer 24 is irradiated at a selected location as described above with respect to FIG. 2, until heat dissipated in the coating 24 and the metal substrate starts to melt a top section 54 of the metal substrate near the surface 4 thereof, and subsequently also melts the coating layer 24 providing a locally melted coating 56. As indicated in FIG. 3, the surface 52 of the coating layer 24 starts to glow when the coating has locally melted. The glowing section 58 of the coating indicates that the coating has melted sufficiently. The glowing section can, for instance, be monitored by visual inspection.

[0069] Once the glowing section 58 indicates sufficient melting of the coating and the top 54 of the metal substrate, the beam 44 of electromagnetic radiation is moved along the metal substrate in the direction of arrow 59. Moving the beam 44 continues until the coating layer 24 has been melted along a preselected length of the metal substrate 1.

[0070] When the beam 44 has passed, the molten coating material and the molten top section of the substrate 1 are allowed to cool. The cooled coating material creates an interface layer 60 at the surface of the metal substrate and a coating layer 62 on the interface layer. The coating layer comprises cooled and hardened coating material. The interface layer 62 comprises a mixture of the metal of the metal substrate and the coating material, providing good bonding of the coating to the substrate.

[0071] The linear laser beam 36 induces a laser line as opposed to the more general laser point, and has sufficient energy to induce melting of the galling resistant metal on the contact surface 22.

[0072] The coating layer 24 may have a thickness between 10 m and 1 mm, preferably between about 200 and 300 m.

[0073] In a preferred embodiment, the radiation 40 is laser light, for instance in the visible spectrum. The radiation energy of the laser beam is sufficient to cause melting of the coating and the top of the metal substrate. The molten coating material and the molten metal flow, to form a uniform coating layer 62. Since the molten coating can flow, the coating layer 62 has a uniform thickness and a smooth outer surface.

[0074] In a practical embodiment, thickness of the coating layer is in the order of 20 m to 2 mm. Thickness of the coating is preferably in the order of 100 to 300 m.

[0075] The present invention may also provide a method for coating an inner surface of a pipe, in particular an OCTG (Oil Country Tubular Goods) pipe, with a coating. Coating the inner surface of the pipe allows the use of relatively cheap pipe, made from relatively low-cost steel, which is subsequently provided with a suitable coating layer in accordance with the method of the invention, to provide corrosion resistance.

[0076] Laser melting of the applied coating layer may be challenging when the entire inner surface of an OCTG pipe section has to be treated. Herein, one pipe section typically has a length in the order of 10 meters. The entire inside surface of the pipe section may be irradiated by laser, for instance using a method or system as described in WO-2013/117754. Other suitable laser systems are for instance described in WO-2012/156230, WO-2012/95422, WO-2012/32116, and WO-2012/76651. Any combination of these laser systems may also be used.

[0077] Heating the coating on the metal will, as described with reference to FIG. 3, create an interface layer which will be affected by heating. The remainder of the metal substrate however will not be negatively affected.

[0078] As shown in FIG. 4, a heat-affected zone (HAZ) of the metal substrate can extend from the surface 4 of the metal to thickness T1. Herein, properties of the metal are most affected near the surface 4 of the metal, and gradually improve to the standard properties in the remainder of the metal. As an example, shown in FIG. 4, the heat affected zone may extend along up to T1 being about 0.5 to 1.5 mm.

[0079] For OCTG pipe, total wall thickness of the pipe may be significant. Production casing or production tubing, i.e. the innermost pipe strings in a wellbore which have to withstand reservoir pressures and are most exposed to corrosive wellbore fluids, typically have a wall thickness T in the range of 0.5 inch (1.2 cm) to T exceeding 1 inch (2.4 cm). The HAZ then may cover T1/T=1.5/12 is about 12.5% of the total T. A lower limit is provided by 0.5/24 is about 2%. Typically, the wall thickness T is greater than 0.5 inch, indicating that the HAZ generally can be limited to affecting about 10 to 2% of the wall thickness, or less. Thus, the extent of the HAZ can be limited to an acceptable limit with respect to the total wall thickness of the pipe, wherein properties of the pipe remain within acceptable levels.

[0080] The exemplary diagram shown in FIG. 4 indicates hardness expressed in units HK on the y-axis. The example indicates that the hardness reduction in the heat affected zone may be limited to 250/350 is about 0.7 at the surface 4 of the pipe. Hardness reduction a between the surface 4 and T1 is more modest, in the range of about 20% to 5% or less.

[0081] FIG. 6 is a diagram showing a material distribution(k) at a fusion bonded interface between a metal substrate and enamel coating made with the sequential heating method according to the invention, wherein curves I-V show the weight distribution (k) of Chromium(I), Manganese(II), Aluminium(II), Silicon(IV) and Iron(V) at both sides of a fusion bonded interface (73), which is located in the middle of the horizontal axis near the 20 m mark and the distance from the fusion bonded interface is measured in m.

[0082] FIG. 7 is a longitudinal sectional view of a fusion bonded interface 73 between an enamel coating 72 and a metal substrate 71 made with the sequential heating method according to the invention. The fusion bonded interface 73 is an irregularly shaped interface where the surfaces of the enamel coating 72 and metal substrate 71 are entangled and intermesh in an irregular tongue and groove like profile, which enhances the metallurgical fusion bond between the enamel coating 72 and metal substrate 71.

[0083] As indicated above, the method of the present invention allows coating of a metal substrate, including the inner surface of OCTG such as (production) casing and tubing, with a relatively cheap material. The method provides good bonding to the substrate, while the interface layer wherein the metal and the coating material are intimately mixed in a irregular tongue and groove like pattern, which allows ductility and bending of the coating to obviate chipping thereof.

[0084] The cost reduction provided by the coating of the present invention is indicated below, wherein the top row indicates the pipe material or additional coating material on the pipe, and the bottom row indicates a cost estimate in Euros:

TABLE-US-00001 Inconel Carbon 625 Additional Add. Add. steel solid Butting CRA Nano spray Enamel 90 ksi pipe quote coating coating coating 400 10,000 6300-8150 3500-9000 2500-3500 180-250

[0085] Bendability of the coated metal surface may be indicated by the following examples, wherein the left column indicates respective samples and the right column indicates strain to break in percent (%), providing a measure of bendability:

TABLE-US-00002 Sample Strain to break (%) 1 (B2L) 1.49 2 1.50 3 1.45 4 (A10) 1.39 5 (A8) 1.52 6 (A6) 1.42 7 (A1) 1.43 8 (G) 1.38 9 (L) 1.49 10 (K) 1.34

[0086] The present invention is not limited to the embodiments thereof as described above, wherein many modifications are conceivable within the scope of the appended claims. Features of respective embodiments may for instance be combined.