AU6177694A

AU6177694A - Tube formed from steel strip having metal layer on one side

Info

Publication number: AU6177694A
Application number: AU61776/94A
Authority: AU
Inventors: Trevor Maxwell Height; Paul Raymond Kelly
Original assignee: Onesteel Trading Pty Ltd
Current assignee: Onesteel Trading Pty Ltd
Priority date: 1993-03-24
Filing date: 1994-03-15
Publication date: 1994-10-11
Anticipated expiration: 2014-03-15
Also published as: AU673247B2

Description

TUBE FORMED FROM STEEL STRIP HAVING METAL LAYER ON ONE SIDE

Field of the Invention

The present invention pertains to coatings for steel tube and pipe and more particularly to an internal coating which is applied before the welding operation which forms the tube.

Background of the Invention

Past and current practices for protecting the internal surface of an externally galvanised steel pipe are known to comprise at least three methods. In the first method, pipe or tube is hot dip galvanised. This coats both the internal and external surfaces. In the second, a protective layer of paint or lacquer is applied by means of a spray lance passed through the bore of the pipe after manufacture and cutting to length. In a third method a protective layer of paint or lacquer is applied in the pipe mill immediately after welding into the tubular shape. In this instance, the spray nozzle is held inside the bore of the tube as the tube is being formed and welded. It is noted that zinc rich paints offer good corrosion resistance but flake severely when the tube is deformed or manipulated. Further, prior art paint or lacquer coatings are considered complex and maintenance intensive.

Objects and Summary of the Invention

It is an object of the invention to provide a meaningful alternative to prior art internal coating methods.

Accordingly, a steel strip is provided before formation into a tube. A thin layer of metal is deposited directly onto one side of the steel strip before formation into a tube. In preferred embodiments the metallic layer is approximately 3 to 15 microns in thickness, is applied to what will be the interior of the tube, is applied at mill speed and is applied before the strip enters the first forming section of the tube/pipe mill.

The application of heat prior to, and during, the in-line galvanising step results in the formation of an alloy layer, giving metallurgical bonding between the substrate and the sprayed metal.

In certain preferred embodiments the thin metal layer would be applied by metal arc spray.

Brief Description of the Drawing Figure

Figure 1 is a flow chart illustrating steps in tube or pipe formation.

Best Mode and Other Embodiments of the Invention

A best mode will now be described. One example is disclosed in Figure 1. Reference numerals in this text pertain to Figure 1.

Certain metallic coatings such as zinc, aluminium and mixtures of these are known to offer superior corrosion resistance. Metallic zinc particles will adhere to the steel pipe during subsequent bending or forming operations and are much more resistant to flaking than zinc rich paints. The present invention contemplates the use of metal coating where the deposited metal comprises various mixtures of aluminium and zinc, or zinc, or aluminium. Other metals and mixtures such as nickel-chromium and nickel molybdenum alloys, tungsten, tantallum and chromium alloys may also be used. The current limit of metallic arc sprays is thought to be about 200mm in width. Accordingly, a metal arc spray machine 10 may be used to deposit a zinc layer up to 200mm wide and about 3 to 15 microns in thickness. A preferred thickness is about 8 to 15 microns. The layer is applied directly onto one side of a steel strip before it is formed into a tube 11. In a preferred embodiment, the side forming the interior of the tube is coated. Methods other than metal arc spray techniques may be employed to deposit the metal on to the strip. These include plasma spray and flame spray using wine or powder compounds.

The metal coating may be preceded by shot blasting 9 (e.g. class 2Vι) to promote adhesion of the metal coating to the substrate. It is preferred that the metal arc spray operation or other coating operation be performed just before the strip enters the first forming sections of a pipe mill. Other locations may be desirable in certain instances. For example, the steel could be coated prior to slitting into strips.

The coated steel is then roll formed and welded 12 into pipe or tube sections. After seam welding the tube or pipe may be subject to surface preparation 16 such as acid pickling. A diluted hydrochloric acid (preferably 11-15%) is used to remove scale dust and grit. At a later process stage the pipe or tube is subjected to a heat source 13 preferably prior to sizing and shaping which facilitates the formation of an alloy layer. This alloy layer means that full metallurgical bonding of the metal spray has been achieved and allows deformation without delamination of the metal coating. The heat sources in this case are electrical induction heaters and the molten zinc bath, but may be other forms of heat source. Pre -heating the pipe or tube prior to galvanising 15 requires that it be brought to about 350-450°C. Pre-heating may also improve the quality of the spray coating near the weld area.

As a further protection, an optional layer of paint or lacquer may be applied 14 in accordance with conventional paint and lacquer technology.

The above referenced technique is intended for use with externally galvanised steel tube and pipe, however, it could be used for any steel section, whether hollow or open.

Industrial Applicability

The invention may be applied to industrial methods for producing pipes and tubes, particularly where it is desirable that the interior of the pipe or tube be protected from corrosive or reactive constituents.

While the present invention has been disclosed with reference to particular details the above description is provided by way of an example and not as a limitation to the scope or spirit of the invention.

Claims

CLAIMS:

1. A process for fabricating a steel tube or pipe with a corrosion resistant coating, comprising the steps of: providing a steel strip; depositing a layer of metal on one side of the strip; forming the strip into a tube.

2. The process of claim 1, wherein the layer of metal is deposited by a metal arc spray.

3. The method of either of claim 1 or claim 2, wherein depositing occurs before the strip enters the first forming sections of a pipe mill.

4. The method of any one of claims 1 to 3, wherein the metal is deposited before the strip is slit to a final width.

5. The method of any one one of claims 1 to 4, wherein forming is accomplished by roll forming and seam welding.

6. The method of any one one of claims 1 to 5, wherein paint or lacquer are applied to the interior of the tube after forming.

7. The method of any one of claims 1 to 6, wherein the metal layer is 3 to 15 microns thick.

8. The method of any one of claims 1-7, wherein the metal is a mixture of zinc and aluminium.

9. The method of any one of claims 1-7, wherein the metal is zinc.

10. The method of any one of claims 1-7, wherein the metal is aluminium.

11. The method of any one of claims 1-10 wherein the tube is subjected to a heat source which promotes the formation of an alloy layer and metallurgical bonding.

12. The method of any one of claims 1-11 , wherein the depositing of the layer of metal is preceded by shot blasting.

SUBSTTTUTE SHEET (Rule 26)