FR2579717A1 - ANTI-CORROSION COATING ON STEEL PIPES - Google Patents

Abstract

ANTI-CORROSION COATING ON STEEL PIPES. A CONSULTING ACCORDING TO THE INVENTION IS OBTAINED FROM STEEL 1 COATED WITH A COPPER 2 COATING PREFERABLY DEPOSITED ELECTROLYTICALLY. ON THE COPPER IS FORMED A LAYER OF NICKEL OR IRON 4 PREFERREDLY CHEMICALLY DEPOSITED, AND WHICH SUPPORTS A LAYER OF ZINC 3 PREFERABLY DEPOSITED ELECTROLYTICALLY. THE ASSEMBLY IS COVERED WITH A PROTECTIVE LAYER 5, FOR EXAMPLE IN EPOXY OR ACRYLIC RESIN, HARDENED BY BAKING. A CHROMATE LAYER MAY BE INTERPOSED ON THE ZINC LAYER.

Description

The present invention, concerning channeling

  tions, more specifically relates to anti-corrosion coatings on steel, in particular

steel pipes.

  Steel pipes, especially steel pipes with double windings, seamless steel pipes and electrically welded steel pipes with a gauge of 25 mm or less, are often plated with copper in the case of welded pipes. maintain a clean appearance. Such hoses or lines are used in automobiles and other vehicles for brake lines, fuel lines and other oil or air supply lines. FIG. 3 shows an example of a conventional anti-corrosion coating including a layer of copper 12 formed by electrolytic deposition on the surface of a steel tube 11, a layer of zinc 13 formed by electrolytic deposition and directly applied to the layer of plated copper and an outer coating layer 14, formed on the surface of the electrolytically deposited zinc layer

  to provide resistance to corrosion and shocks.

  Usually the outer coating layer comprises a curable material such as a synthetic resin, depending on the type of material to be applied, the curing being produced by firing at a temperature above C. This may cause local blistering, cracking or peeling and drying. other defects in the resulting layer. These defects often cause flaking of the outer layer during subsequent bending or flexing operations, which not only damages the end products but adversely affects their performance.

  resistance to corrosion and shock.

  One of the objects of the present invention consists

  to avoid the disadvantages associated with conventional coatings

  Anti-corrosion, especially for steel pipes and to provide a coating which has a sufficiently high resistance to corrosion and preferably also to shocks. It is believed that the blistering, cracking and peeling of the outer coating layer 14 results from the formation of a brittle diffusion layer between the electrodeposited zinc layer and the

  layer of copper also applied by

  as a result of the heat treatment, which leads to changes in the hardness, the

internal and constraints.

  It is therefore proposed in the invention to form a layer of nickel or iron, preferably by chemical plating or by electrolytic deposition 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 to eliminate the possibility of

  blowholes, cracks and flakes.

  In accordance with the present invention, a steel pipe with anti-corrosion coating comprises a layer of copper, preferably formed by electroplating, on the surface of the steel, a zinc layer preferably formed by electrolytic deposition, which is bonded to the copper layer via a nickel or iron plated layer, and an outer layer, cured by baking, which may be on the

  surface of the zinc layer. According to another possibility

  In this case, a chromate layer is provided between the electrolytically deposited zinc layer and the outer layer. Also, in accordance with the invention, a method for producing a steel pipe with anti-corrosion coating comprises forming a copper layer on the surface of the steel, usually

  after degreasing, rust removal or other

  a nickel or iron layer, a layer of zinc on this surface of nickel or iron, optionally depositing a layer of a chromate on the surface of the zinc layer, and the formation of a layer -3 -

hardened by cooking.

  The baked hardened outer layer which provides resistance to corrosion and impact, can be made of the same material as that used in conventional coatings and preferably it is a curable synthetic resin, for example an epoxy powder applied by electrostatic deposition or coating

  spray applied acrylic.

  Embodiments of the invention will now be described, by way of example, with reference to

drawing appended hereto, in which:

  - Figure 1 is a plan view of a steel pipe with an anti-corrosion coating according to the present invention; FIG. 2 is a cross-section taken along the line A-A of FIG. 1; - Figure 3 is a similar cross-section, but for a conventional steel pipe,

similar type.

  As can be seen in FIGS. 1 and 2, the anticorrosion coating is formed on a steel pipe 1 having a structure with double winding (in

  the cross direction), made of rolled steel,

  on its outer surface is an electroplated copper layer having a thickness of 1 to 4 μm and preferably about 3 μm. This electrolytically plated copper layer serves as a flux for welding the pipe. An electrolytically plated zinc layer 3 is bonded via a layer 4 of nickel or iron, deposited on the surface of the electrolytically plated copper layer 2, and a coating, or topcoat, hardened by firing, is formed on the surface of the electrolytically plated zinc layer 3. A layer of a chromate can be established between the layer of

  electrolytically plated zinc and the coating cooked.

  The thickness of the nickel or iron clad layer may vary depending on the type of fired coating to be applied, the firing conditions (temperature and duration of firing), the thickness of the coating layer and other factors. A suitable thickness

  is 2p. or more, preferably in the range 4 to 6 μm.

  The layer of nickel or iron plated, which is

  interposed between the electrolytically plated copper layer

  electrolytically clad zinc layer, completely suppresses mutual diffusion between the copper and zinc layers, which prevents local phenomena from blowing, cracking and peeling in the coating during cooking and eliminates the possibility of that the coating layer does not flake

  during consecutive bending or bending operations.

  Thus, the value of the finished products, as well as the resistance to corrosion and shocks can be

greatly increased.

EXAMPLE 1

  A steel pipe (STPG38) having an outer diameter of 10 mm, a wall thickness of 0.7 mm, and a length of 500 mm, and having on its inner and outer surfaces an electrolytically plated copper layer of 3 μm. thickness, was defatted and derust in a conventional manner, before forming on it a layer of nickel. This layer was produced electrolytically in a bath containing 240 g / l of nickel sulphate, 40 g / l of nickel chloride, 30 g / l of boric acid and having a pH of 4.6. A cathodic current density of 3A / dm2 for 10 minutes at 450C produced a thickness of 5 μm of a nickel layer. A layer of zinc was then applied over the nickel by electrolytic plating in a bath containing 30 g / l of zinc oxide, 60 g / l of sodium cyanide, 70 g / l

  of sodium hydroxide with a cathodic current density

  The duct was then washed with water, then subjected to chromate treatment and rewashing. This produces a

  zinc layer 8 μm thick.

  An epoxy powder coating (such as V-PET # 1340 (trademark) Dainippon Toryo) electrostatically applied was then baked at 180 ° C for 30 minutes to produce a coating layer.

  black having an average thickness of about 45 μm.

EXAMPLE 2

  A copper-clad steel pipe, as used in Example 1, was dipped in a nickel chemical plating solution (Nimden 5X, Kamimura Industries) at 45 ° C for 12 minutes to produce over a layer. 4 m thick nickel on which a layer of zinc was deposited by electrolytic plating as in Example 1. A coating

  acrylic (such as Duraclon CW (Trademark) -

  Dainippon Toryo) was then sprayed and baked at 180 ° C. for 30 minutes. This produced a black coating layer having an average thickness

about 30, jam.

EXAMPLE 5

  In this example, the pipe was manufactured as in Example 1 except that instead of

  a layer of iron was electroplated

  lytic in a bath containing 250 g / l of ferrous sulphate,

  g / l ferrous chloride, 20 g / l ammonium chloride.

  A cathodic density of 3 A / dm2 for 10 minutes at

   It produced an iron layer 5 μm thick.

COMPARATIVE EXAMPLE

  A coated steel conduit was manufactured according to the method set forth for Example 1, but omitting the step of forming a layer of nickel (or iron), the zinc layer being directly deposited on the

copper-plated steel pipe.

  Table 1 shows the result of the examination in view of the ducts of the invention (Examples 1, 2 and 3) and a conventional duct (comparative example) after cooking.

  and after the bending or bending operation.

TABLEAUTJ 1

  After baking After bending Example 1 Absolutely nothing Absolutely nothing abnormal abnormal Example 2 Example 1 Example 3 Comparative Example Blowing Cracks and localized localized spalling

Claims (12)

  1. Steel pipe with anti-scratch coating   corrosion, -characterized in that it comprises a layer of copper (2) on the steel (1), a layer of zinc (3) which is bonded thereto by an intermediate layer (4) of nickel   or iron and a baked outer layer (5).   2. pipe according to claim 1, characterized in that the layers of copper and zinc   are electrolytically plated layers.   3. Steel pipe with anti-wear coating   corrosion, characterized in that it comprises an electrolytically plated copper layer, which is formed on the outer surface of the steel pipe, an electrolytically plated zinc layer which is bonded, via a layer of nickel or iron plated,   on the surface of the electrolytically plated copper layer   only, and a cooked outer layer.   4. Driving according to any of the   Claims 1 to 3, characterized in that the layer   fired exterior is applied to the zinc layer.   5. Driving according to any of the   Claims 1 to 3, characterized in that a layer of   chromate is inserted between the zinc layer and the outer layer. 6. A method for manufacturing a steel pipe with anticorrosive coating, characterized in that it comprises the formation of a layer of nickel or iron on a layer of copper on the steel, the formation of a layer of zinc on the nickel or iron layer and the   formation of a fired outer layer.   7. Method according to claim 6, characterized in that the layers of copper or zinc are formed   by electrolytic plating.   8. Process for forming an anti-corrosion coating   corrosion on a steel pipe, including the formation of   a layer of nickel or iron plated on the surface degreased, derusted and otherwise treated 257971; - 8-   previously, an electrolytically plated copper layer   in a steel pipe, the formation of a zinc layer on the nickel or iron surface by electrolytic plating and the formation of a fired outer layer. 9. The method of claim 7 or 8, characterized in that a chromate layer is further established on the zinc layer, followed by the application of the outer layer is cooked.   10. Process according to any one of   Claims 6 to 9, characterized in that the thickness   the zinc layer is located in the del range at 4m.   11. Process according to any one of   Claims 6 to 10, characterized in that the thickness   the nickel or iron layer is 2 μm or more.   12. Process according to any one of   Claims 6 to 11, characterized in that the layer of   nickel or iron is formed by chemical plating or by a electrolytic plating.