GB2173424A

GB2173424A - Anticorrosive coated steel pipe

Info

Publication number: GB2173424A
Application number: GB08607480A
Authority: GB
Inventors: Toshio Kanasashi; Masashi Kajiyama
Original assignee: Usui Kokusai Sangyo Kaisha Ltd
Current assignee: Usui Kokusai Sangyo Kaisha Ltd
Priority date: 1985-03-28
Filing date: 1986-03-26
Publication date: 1986-10-15
Also published as: JPH0517319B2; DE3610701A1; GB2173424B; JPS61222736A; DE3610701C2; FR2579717B1; FR2579717A1; GB8607480D0

Abstract

An anticorrosive coated steel pipe comprises an electroplated copper layer (2) formed on the external surface of the steel pipe (1); and electroplated zinc layer (3) bonded, via a plated nickel or iron layer (4), to the surface of the electroplated copper layer (2); and a baked outer layer or finish (5) formed on the surface of the electroplated zinc layer (3). A chromate layer is optionally provided between the electroplated zinc layer (3) and the baked coating (5). The plated nickel or iron layer (4) interposed between the electroplated copper layer (2) and the electroplated zinc layer (3) completely suppresses mutual diffusion between the two electroplated layers, thereby preventing local blistering, cracking and peeling in the outer layer during baking, and eliminating the possibility of the outer layer peeling off during subsequent bending operations. The value of final products, as well as resistance to corrosion and impact, can thus be greatly enhanced. <IMAGE>

Description

SPECIFICATION Anticorrosive coatings on steel pipes The invention relates to anticorrosive coatings on steel, especially steel pipes.

Steel pipes, more particularly, double-wound steel pipes, seamless steel pipes and electroseamed steel pipes with a pipe size of 25 mm or smaller, are often plated with copper for case of pipe welding and to maintain a clean appearance. Such pipes are used in motorcars and other vehicles as brake pipes, fuel pipes, and other oil- or air-supply pipes. One example of a conventional anticorrosive coating shown in Fig. 3, includes an electroplated copper layer 12 formed on the surface of a steel pipe 11, an electroplated zinc layer 13 applied directly on the electroplated copper layer, and an outer coating layer 14 formed on the surface of the electroplated zinc layer to afford resistance to corrosion and impact loads.Usually the outer coating layer comprises a curable material such as synthetic resin and depending on the type of materials to be applied, curing involves baking at a temperature higher than 200 C. This can cause local blistering, cracking, peeling and other defects in the resulting layer. These defects often result in peeling of the outer layer during subsquent bending operations, thus not only degrading the final products but adversely affecting their resistance to corrosion and impact loads.

One object of this invention is to avoid the disadvantages associated with conventional anticorrosive coatings particularly for steel pipes and to provide a coating that exhibits sufficietnly high resistance to corrosion, and preferably also to impact loads. Blistering, cracking, and peeling in the outer coating layer 14 are thought to arise due to the formation of a brittle diffusion layer between the electroplated zinc layer and the electroplated copper layer as a result of heat treatment, which causes changes in hardness, internal structure and stresses.

We now propose forming a nickel or iron layer, preferably by chemical plating or electroplating, between the copper layer and the zinc layer, so as to prevent the formation of a diffusion layer between the copper and zinc layers and eleminate the possibility of blistering, cracking and peeling.

According to this invention, an anticorrosive coated steel pipe, comprises a layer of copper, preferably an electroplated layer, on the surface of the steel; a layer of zinc also preferably electroplated, bonded to the copper layer via a plated nickel or iron layer, and a baked outer layer which may be on the surface of the zinc layer. Alternatively, a chromate layer is provided between the electroplated zinc layer and the outer layer.

Also, according to the invention a method for producing an anticorrosive coated steel pipe, comprising forming on a copper layer on the surface of the steel, usually following degreasing, derusting, or other surface pretreatment a layer of nickel or iron, a zinc layer on the surface of the nickel or iron layer, optionally providing a chromate layer on the surface of the zinc layer, and forming a baked outer layer.

The baked outer layer which affords corrosive and impact resistance may be of the same material as used in conventional coatings and is preferably a curable synthetic resin, for example, an epoxy powder applied by electrostatic deposition or an acrylic coating applied by spraying.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a plan view of a steel pipe having an anticorrosive coating according to this invention; Figure 2 is a cross-section taken on line A-A in Fig. 1; Figure 3 is a similar cross-sectional but of a conventional steel pipe of similar type.

As can be seen from Figs. 1 and 2, the anticorrosive coating is formed on a steel pipe 1 of a double-winding structure (in a crosswise direction) made from strip steel, having on the external surface thereof, an electroplated copper layer with a thickness of 1 to 4,u, preferably about 3 It.

This electroplated copper layer serves as a flux for pipe welding. An electroplated zinc layer 3 is bonded, via a plated nickel or iron layer 4, to the surface of the electroplated copper layer 2 and a baked coating or finish 5 is formed on the surface of the electroplated zinc layer 3. A chromate layer is optionally provided between the electroplated zinc layer and the baked coating.

The thickness of the plate nickel or iron layer may vary with the type of baked coating to be applied, its baking conditions (baking temperature and time), the thickness of coating layer and other factors. A suitable thickness is 2 e or greater, more preferable in the range from 4 to 6 It The plated nickel or iron layer which is interposed between the electroplated copper layer and the electroplated zinc layer, completely suppresses mutual diffusion between the copper and zinc layers, thereby preventing local blistering, cracking and peeling in the coating during baking, and eliminating the possibility of the coated layer peeling off during subsequent bending operations.

The value of final products, as well as resistance to corrosion and impact, can thus be greatly enhanced.

Example I A steel pipe (STPG38) having an outside diameter of 10 mm; a wall thickness of 0.7 mm, and a length of 500 mm, and having on its internal and external surfaces an electroplated copper layer 3 It thick was degreased and derusted in the conventional manner prior to formation thereon of a layer of nickel. The layer was produced by electroplating in a bath containing 240 g/l nickel sulfate, 40 g/l nickel chloride, 30 g/l boric acid and having a pH of 4.6. A cathode current density of 3 A/dm2 for 10 minutes at 450C produced a nickel layer 5 um thick.A layer of zinc was then applied on top of the nickel by electroplating in a bath containing 30 g/l zinc oxide, 60 g/l sodium cyanide, 70 g/l sodium hydroxide at a cathode current density 3 A/dm2 for 15 minutes 25 C. The pipe was then washed with water, followed by chromate treatment and further washing. This produced a layer of zinc 8 um thick, An epoxy powder coating (such as V-PET#1340 (trade mark)- Dainippon Toryo) applied by electrostatic deposition, was then baked at 1 800C for 30 minutes; to produce a black coating layer with an average thickness of about 45 It.

Example 2 A copper plated steel pipe as used in Example 1 was dipped in a chemical nickel plating solution (Nimden 5X, Kamimura Industries) at 45 C,.for 12 minutes to produce thereon a 4 u thick nickel layer on top of which a layer of zinc was deposited by electroplating, as in Example 1. An acrylic coating (such as Duraclon CW (trade mark)-Dainippon Toryo) was then applied by spraying and baked at 1 800C for 30 minutes. This produced a black coating layer with an average thickness of about 30 Am.

Example 3 In this Example the pipe was produced as in Example 1 except that in place of the nickel layer a layer of iron was deposited by electroplating in a bath containing 250 g/l ferrous sulfate, 40 g/l ferrous chloride, 20 g/l ammonium chloride. A-cathode current density of 3 A/dm2 for 10 minutes at 400C produced a 5 It thick iron layer.

Comparative Example A coated steel pipe was produced following the procedure set out in Example 1 but omitting the step of forming a nickel (or iron) layer, the zinc layer being deposited directly on the copper plated steel pipe.

Table 1 shows the result of visual inspection of the pipes of this invention (Examples 1, 2 and 3) and a conventional pipe (comparative example) afterbacking and after bending operation.

TABLE 1 After baking After bending Example 1 No abnormality at all No abnormality at all 2 3 11 II Come. Ex. Local blistering Local cracking & peeling

Claims

1. An anticorrosive coated steel pipe comprising a layer of copper on the steel, a layer of zinc bonded thereto by an intervening layer of nickel or iron, and a baked outer layer.

2. A pipe according to claim 1 wherein the copper and zinc layers are electroplated layers.

3. An anticorrosive coated steel pipe comprising an electroplated copper layer formed on the external surface of the steel pipe; an electroplated zinc layer bonded, via a plated nickel or iron layer, to the surface of the electroplated copper layer and a baked outer layer.

4. A pipe according to any one of claims 1 to 3 wherein the baked outer layer is applied on the zinc layer.

5. A pipe according to any one of claims 1 to 3 wherein a chromate layer is provided between the zinc layer and the outer layer.

6: A method for producing an anticorrosive coated on steel pipe comprising forming a layer of nickel or iron on a layer of copper on the steel, forming a zinc layer on the nickel or iron layer, and forming a baked outer layer.

7. A method according to claim 6 wherein the copper and zinc layers are formed by electroplating.

8. A method for producing an anticorrosive coating on a steel pipe, which comprises forming a plated nickel or iron layer on the degreased, derusted and otherwise pretreated surface of an electroplated copper layer on a steel pipe, forming a zinc layer on the surface of the nickel or iron layer by electroplating, and forming a baked outer layer.

9. A method according to claim 7 or claim 8 wherein a chromate layer is further provided on the zinc layer, followed by the baked outer layer.

10. A method according to any one of claims 6 to 10, wherein the thickness of the zinc layer is in the range from 1 to 4 It.

11. A process according to any one of claims 6 to 10 wherein the thickness of the nickel or iron layer is 2 It or larger.

12. A process according to any one of claims 6 to 11, wherein the nickel or iron layer is formed by chemical plating or electroplating.

13. An anticorrosive coated steel pipe constructed and arranged substantially as hereinbefore described with reference to and as illustrated in Figs. 1 and 2 of the accompanying drawings.

14. A method of producing an anticorrosive coated steel pipe substantially as hereinbefore described with reference to any one of Examples 1 to 3.