AU2002242467B2

AU2002242467B2 - Application of coating

Info

Publication number: AU2002242467B2
Application number: AU2002242467A
Authority: AU
Inventors: Ross Mcneil
Original assignee: WELDTRONICS Ltd
Current assignee: WELDTRONICS Ltd
Priority date: 2001-03-21
Filing date: 2002-03-21
Publication date: 2004-02-12
Anticipated expiration: 2022-03-21

Description

WO 02/075012 PCT/AU02/00323 "Application of Coating" Field of the Invention This invention relates to the application of a titanium-based alloy to a ferrous substrate for the purposes of providing a protective coating.

Background In many instances it is necessary to apply a protective coating to the surface of a ferrous substrate in order to provide protection to that surface. This is particularly the case in the case of process vessels and lines which are used in mineral processing. Furthermore, instances occur when it becomes necessary to connect a titanium-coated surface to another titanium-coated surface (such as in the interconnection of flow lines) whereby such connection requires the excising of the titanium coating from the surface adjacent to the edges to be welded prior to welding the surfaces together. Subsequent to the welding of the edges the excised zone surrounding the weld must be recoated with the titanium coating.

Unfortunately titanium does not readily bond to surfaces which are formed predominantly of a steel alloy, as a result the application of the titanium coating requires the utilisation of specialised techniques which include roll bonding or explosive bonding processes. Conventional welding techniques are generally not appropriate in the application of a titanium coating to a ferrous substrate.

In the past when it has become necessary to weld two surfaces together in a manner described above, the coating of the zone in the region of the weld by a titanium coating is effected by the overlying the zone with a copper billet which substantially fills the space above the weld and then the application of a titanium coating between the opposed edges of the current coating and the overlying copper billet. Unfortunately this form of coating can often prove to be unsatisfactory and will readily break down.

The preceding discussion of the background to the invention is intended only to facilitate an understanding of the present invention. It should be appreciated that WO 02/075012 PCT/AU02/00323 -2the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia as at the priority date of the application.

Disclosure of the Invention Accordingly the invention resides in a method of applying a coating formed predominantly of titanium to the surface of a ferrous substrate comprising the thermal application of a layer of copper and/or a copper alloy to the surface and subsequently thermally applying a layer of the coating to the surface of the layer of copper, wherein the application of the layer comprises applying molten copper to the surface whereby the degree of diffusion of iron into the layer is no greater than 3% prior to the application of the coating.

According to a preferred feature of the invention the application of the coating is effected by a sequential application of a plurality of layers of coating over the layer of copper.

According to a preferred feature of the invention the copper comprises oxygen free copper.

According to a preferred feature of the invention the application of molten copper to the surface comprises application of molten copper droplets onto the surface.

According to a preferred feature of the invention the application of molten copper to the surface comprises a brazing/welding process.

According to a preferred feature of the invention the depth of the fusion interface between the surface and the layer is between 1 to 3mm.

According to a preferred feature of the invention only one layer is applied to the surface.

WO 02/075012 PCT/AU02/00323 -3- Accordingly the invention also resides in an article formed of a ferrous material having a surface coated with a coating formed predominantly of titanium where the coating has been applied to the surface by the method described above.

The invention will be more fully understood in the light of the following description of several specific embodiments.

Brief Description of the Drawings The description is made with reference to the accompanying drawing of which: Figure 1 is a schematic sectional illustration of a surface which has been coated according to the first embodiment; and Figure 2 is a schematic sectional illustration of a surface which has been coated according to the third embodiment.

Detailed Description of Specific Embodiments The first embodiment has application to a process for application of a protective coating to a welded zone interconnecting two components where each of the components are provided with a wall 11 and 13 formed of a suitable steel alloy to effect containment. The walls of each of the components are interconnected by a weld 15. Each of the walls provide a containment surface 17 and 19 respectively, which is provided with a protective coating 21 and 23 respectively, formed of titanium or a suitable titanium-based alloy. In order to effect the weld 15 between each of the components 11 and 13, the titanium coating 21 and 23 on each component must be excised from the area adjacent to the weld. Subsequent to the completion of the weld 15, the area between the coatings 21 and 23 above the weld 15 must be recoated.

The method according to the embodiment comprises application of a layer 25 of copper over the portions of the surfaces 17 and 19 which are free of the titanium coatings 21 and 23 and above the weld 15. The application of the layer 25 of WO 02/075012 PCT/AU02/00323 -4copper is effected by a welding technique which involves the application of molten copper to the surface which results in the fusion interface of the surface and the layer being relatively thin and of the order of 1 to 3mm. In addition the extent of thermal interaction of the steel layer is limited. As a result the diffusion of iron into the copper is maintained at less than This process is achieved by use of a "spray TIG" welding head whereby the copper is rendered into a molten form at the nozzle of the welding head and the molten metal is applied onto the surface.

The copper which is used to form the copper layer comprises oxygen-free copper.

Only one layer of copper is applied to the surface. Subsequent to the application of a copper layer 25, a first titanium layer 27 which is formed of titanium-based alloy is applied over the copper layer 25. This is effected by conventional welding techniques which are used in the application of titanium alloys. On the completion of the first layer 27 of titanium which completely covers the excised area above the copper layer 25, a second titanium layer 29 is applied by the technique which was used in relation to the first titanium layer 27. On completion of the second titanium layer 29 a third titanium layer 31 is similarly applied over the excised portion. The application of titanium layers is repeated until the excised area between the coatings 21 and 23 on each of the components 11 and 13 above the weld 15 has been filled.

As a result of metallurgical testing it has been found that the coating of a test piece which was coated according to the embodiment as described above provided good fusion between the copper layer and the steel, excellent wetting and bonding of the copper to the steel substrate with minimal (ie 3% or less) of iron content or iron diffusion into the copper layer. In relation to each of the layers of titanium, there was found in the first layer a copper titanium matrix which was metallurgically stable, some diffusion of the copper into second layer of titanium was also evident, the subsequent layers were uncontaminated by the copper, and reflected the purity of the titanium clad material.

According to a second embodiment of the invention the surface to be coated comprises the entire surface of an article which can include the internal surface of a pipe and the process of the second embodiment comprises coating the entire containment surface of the article in accordance with the procedure described in WO 02/075012 PCT/AU02/00323 relation to the first embodiment. This involves the application of a first layer of copper over the surface and then the application subsequent layers of titanium over the surface as described in relation to the first embodiment.

According to a third embodiment of the invention and as shown at Figure 2 (the same reference numerals have been used in Figure 2 for corresponding components in Figure 1 in reaction to the first embodiment) the surface 17 to be coated comprises the repair of a damaged area of a coated surface of an article such as the interior of a containment vessel where the titanium coating 21has been destroyed or has deteriorated and requires repair. The process of the third embodiment comprises coating the damaged area of the surface of the article in accordance with the procedure described in relation to the first embodiment. This involves the application of a first layer 25 of copper over the damaged area of the surface and then the application subsequent layers 27, 29 and 31 of titanium over the surface as described in relation to the first embodiment.

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer-or group of integers.

It should be appreciated that the scope of the invention need not be limited to the particular scope of the embodiment described above.

Claims

1. A method of applying a coating formed predominantly of titanium to the surface of a ferrous substrate comprising the thermal application of a layer of copper and/or a copper alloy to the surface and subsequently thermally applying a layer of the coating to the surface of the layer of copper, wherein the application of the layer comprises applying molten copper to the surface whereby the degree of diffusion of iron into the layer is no greater than 3%.

2. A method of applying a coating as claimed at claim 1 wherein the application of the coating is effected by a sequential application of a plurality of layers of coating over the layer of copper.

3. A method of applying a coating as claimed at claim 1 or 2 wherein the copper comprises oxygen free copper.

4. A method of applying a coating as claimed at claim 1 or 2 or 3 wherein the application of molten copper to the surface comprises application of molten copper droplets onto the surface.

A method of applying a coating as claimed at claim 1 or 2 or 3 wherein the application of molten copper to the surface comprises a brazing/welding process.

6. A method of applying a coating as claimed at any one of the preceding claims wherein the depth of the fusion interface between the surface and the layer is between I to 3mm.

7. A method of applying a coating as claimed at any one of the preceding claims wherein only one layer is applied to the surface. WO 02/075012 PCT/AU02/00323 -7-

8. A method of applying a coating substantially as herein described.

9. An article formed of a ferrous material having a surface coated with a coating formed predominantly of titanium where the coating has been applied to the surface by the method as claimed at any one of claims 1 to 8.