JPS6014625B2 - Steel lining method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of lining a steel material with excellent secondary adhesion.

Steel materials that require long-term durability, such as lie pipes and marine structures, are lined with resins such as polyethylene, epoxy, polyester, acrylic, and urethane rubber.

The main purpose of lining is to inhibit corrosion by blocking corrosive substances such as oxygen, moisture, and chlorine ions in the environment from the steel surface. However, the permeation of corrosive substances is not 100% blocked, and there is also intrusion from the end faces and cross sections of the lining, so peeling between the lining layer and the steel surface always progresses as a prelude to corrosion of the steel material. I have to look at it. Conventional methods for preventing this include adding a coin protection pigment to the lining layer, undercoating with a zinc-rich primer, or subjecting the steel surface to a chromate conversion treatment. Chromate chemical conversion treatment is further classified as follows depending on the form in which it is applied to steel materials.

Namely, ■ A method in which electrolytic reduction is performed in an aqueous solution containing chromium oxide (M) using a steel material as a cathode to form a layer mainly composed of an m-valent chromium compound, ■ A method in which chromium oxide (Machi) and a reducing agent (water-soluble resin A method in which a coexisting aqueous solution of (e.g.) is applied to a steel material and heated to chemically reduce the chromium oxide, forming a layer mainly composed of m-valent chromium compounds. The final chromate treatment layer is then formed under the coating film by drying to form a fixed layer, which is further heated, or by abrasion of the coating applied on top of this to decompose the W-valent chromium. The method was representative. Methods (2) and (2) above are called coating-type chromate treatment, and since they do not require washing with water after the treatment process, they are advantageous in terms of waste liquid pollution, and are technically and economically the most effective. It can be said that it is a simple method.

However, in both methods, the W-valent chromium will not decompose into the M-valent chromium unless heating at least 10 mm or higher, preferably 200 mm or higher, is carried out for a considerable period of time at some stage, and therefore the treated layer remains water-soluble and the water is removed. Since the effect is likely to be lost due to the intrusion of the material, conventional methods (1) and (2) above have been applied on the premise that the entire body, including the material, must be heated to 100° C. or 20,000° C. or more. However, in reality, when applying painting or lining, there are often technical or economical circumstances that make it impossible to provide a heating stage in the range of 100 to 20 pm. The method will be limited in scope.

For example, when trying to line a steel pipe with an extruded layer of polyethylene using a hot-melt adhesive, it may be sufficient to have a child heat of 10 P0, but at this temperature, the above chromate treatment has no effect, so
The conventional method (Ma) had no choice but to exclude the application.

As a result of various studies aimed at solving these problems, the inventors of the present invention have developed a lining method that is extremely advantageous in all aspects, from the construction technical aspects and the effect of suppressing corrosion and peeling to the economic aspect.

The gist of the present invention is to apply an aqueous solution containing chromium oxide (Machi) as a main component to the surface of a steel material that has been cleaned by removing scale, and to directly apply a flame or a high-temperature gas flow of 400 qo or more to the applied surface. This method of lining steel materials is characterized by drying the coating agent by applying the coating to the coating agent, thermally decomposing the chromium oxide (W) in the coating agent to lower its water solubility, and then forming a resin layer.

In this case, the aqueous solution containing chromium oxide (N) as a main component is an aqueous solution of chromium oxide (W) alone, or an aqueous solution of chromium oxide (W).
An aqueous solution of chromium oxide (W), chromium oxide (m) composite oxide, such as chromium chromate, which has been partially reduced in advance, or a substance to promote the reduction of these (glycerin, water-dropable acrylic resin, aqueous emulsion type acrylic, etc.) resin, polypynyl alcohol, etc.), or an aqueous solution containing silica sol to improve adhesion with the lining layer. The present invention will be explained in detail below.

Chromium oxide (M) has the property of thermally decomposing at a temperature of around 200℃, and by thermal decomposition, it changes into a low-valent oxide mainly composed of chromium oxide (Machi), and becomes a state with low water solubility. It is believed that the chromium oxide that constitutes the corrosive substance barrier film and remains without being partially decomposed serves to passivate the steel material in the pinhole portion of the barrier film.

Since some of the remaining chromium oxide (Machi) is combined with a large amount of low-valent chromium oxide, the water solubility of the film decreases as a whole, and chromium at the town price can be gradually supplied.
There is no loss of effectiveness due to moisture intrusion as described above.
As the method of applying the treatment liquid, conventional methods such as brush coating, roll coating, dipping coating, and flow coating are used.

The coating amount is selected depending on the purpose, but a range of 9/9 of 50 to 500 is often appropriate as the amount of chromium oxide (W) before thermal decomposition. Next, in order to thermally decompose the chromium (W) oxide, only the coated surface is heated to 200° C. or higher by direct flame-based flame on the coated surface or by direct spraying of a high-temperature gas flow of 400 q or higher. This was adopted as a means to raise only the temperature of the coating agent to the required temperature without raising the temperature of the steel base material. If the temperature of the gas flow is less than 400° C., it will take time to bring the surface coated with the treatment liquid to 200 qo or more, which will cause the temperature of the material to rise significantly. As the high-temperature gas stream, air heated by heat exchange, combustion exhaust gas, or the like can be arbitrarily used.

Of course, if the speed of the gas flow is slow, the effect will be low, so it is desirable to provide a speed of 5'sec or more. The lining resin material after the above chromate treatment is not subject to any particular restrictions.
Polyethylene, epoxy, polyester, acrylic, urethane rubber, nylon, vinyl chloride, phenol, etc.
The method of the present invention can be applied to general linings.
Also, extrusion lining, powder lining, one-component solvent coating,
It goes without saying that any lining method may be used, such as two-component coating, adhesive sheet attachment, cast lining, and flow coating. As described above, by carrying out the method of the present invention, chromate treatment can be effectively and advantageously introduced even in the lining process where the temperature of the steel material cannot be raised sufficiently. For example, when lining a steel pipe using a hot-melt adhesive as described above, an aqueous solution containing chromium oxide as a main component is applied to the surface of the cleaned steel pipe. Direct application of the gas combustion flame dries the coating agent, and the surface temperature rises sufficiently to over 200°C, so the chromium oxide (machi) thermally decomposes and becomes a chromate film with low water-removal properties. If the temperature is close to 100°C, a polyethylene lining using hot melt adhesive can be applied, and this lining will have extremely high secondary adhesion. Chromate pretreatment, which is applied by heating the steel material to about 150°C, will be used. Even in the case of lining systems, it is better to directly heat the surface coated with the chromate treatment agent using flame or the like using the method of the present invention, since the temperature of the entire body including the steel material can be reduced by 150°C.
Since the temperature of the surface to which the chromate solution is applied becomes higher than that of heating to 0.0°C, it is advantageous for insolubilizing the coating agent.

By adopting the present invention, effects can be obtained in terms of both thermal efficiency and product performance as described above, and the contribution to this field is extremely large.

Examples are given below to describe the effects of the present invention in more detail.

Example 1 A steel pipe for gas piping with a diameter of 30 mm and a length of 11 mm was provided with various linings according to the steps shown in Table 1.

When the products in Table 1 were subjected to a secondary adhesion test, the second
It looked like a table.

Table 2 Example 2 Table 3 shows the method of applying lining to the inner surface of a steel pipe with a diameter of 60 mm and a length of 5.5 mm, and the performance of the application results.

Table 3 The effects of the above examples were all caused by the characteristics of the method of the present invention, in which the surface coated with the chromate solution was directly ignited with a flame or a high-temperature gas stream of 400 pm or more was blown onto the surface, and the method of the present invention was advantageous. gender is obvious.

Claims (1)

[Claims] 1. Apply an aqueous solution containing chromium (VI) oxide as the main component to the surface of steel that has been cleaned by removing scale, and dry the coating by directly exposing the coated surface to flame or a high-temperature gas stream of 400°C or higher. Chromium oxide (V
A method for lining steel materials, characterized in that I) is thermally decomposed to lower its water solubility, and then a resin layer is formed thereon.