JP2999059B2 - Surface treatment method for polyethylene powder lining - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating a surface of a polyethylene lining used for piping and equipment of various devices made of carbon steel.

[0002]

2. Description of the Related Art Conventionally, a polyethylene powder lining is prepared by subjecting the surface of a lining material made of carbon steel to degreasing and washing, blasting or acid washing, and then forming a chemical conversion treatment coating with phosphate, followed by 200 to 300 ° C. The lining material is preheated to supply polyethylene powder, and the polyethylene powder is heated and melted by the retained heat of the lining material or the heat supplied from the opposite side of the lining surface to continuously polyethylene lining A method of forming a coating has been performed.

[0003]

Hitherto, polyethylene powder lining has been frequently used in an environment where it is in contact with a liquid having a relatively low temperature (30 ° C. or less) such as a water supply pipe or a seawater intake pipe, and has a reasonable durability. Has a track record. However, when the polyethylene powder lining material constructed by the conventional method is used in a chemical plant, a power plant, or the like, the liquid temperature is 50-6.
When used in an environment of 0 ° C., there are many accidents in which a polyethylene coating peels off in a short time or blisters occur.
When inspecting the lining surface of the peeling and blister parts, corrosion of the lining surface is always observed.Therefore, the conventional polyethylene lining material has a high liquid temperature and is exposed to a temperature gradient environment where the permeation of water vapor and oxygen is accelerated. It can be seen that when used, the underlying surface is easily corroded.

Undercoating treatments such as blast treatment or chemical conversion treatment with phosphate in the conventional polyethylene powder lining method are widely applied in the industry as undercoating treatments such as coating and resin or rubber lining. It is not always appropriate for the ground treatment method in the polyethylene powder lining method in which the lining material is heated at 200 to 300 ° C. and the polyethylene powder is thermally melted for the following reasons.

[0005] First, the blasting treatment removes rust or foreign matter on the surface to be lined and improves the adhesion of the coating film or lining by the anchor effect of the unevenness of the surface caused by the blasting. The aim is to suppress corrosion due to local cell formation due to adhesion. However, the active metal surface is exposed on the blasted surface, and when exposed to a corrosive environment, overall corrosion progresses,
The effect of suppressing corrosion cannot be expected.

Therefore, in general coating, resin lining, rubber lining and the like, a method is adopted in which a primer containing a powder of Zn, Sn, Al or the like is applied to prevent corrosion of the blast surface. However, in the case of polyethylene powder lining, since the primer is heated to 200 to 300 ° C., the primer expected to have the anticorrosion effect is thermally decomposed of the resin and the Zn, Sn, and Al are oxidized, and ZnO ₂ , Sn
It changes to O ₂ , Al ₂ O _3, etc. and cannot be used because the electrochemical anticorrosion action is also lost, and lining is directly supplied by supplying polyethylene powder for lining. In addition, the pre-heating step of the lining material and the melting of the polyethylene powder are performed in the air. During this time, the blast surface of the lining material is locally oxidized, and when exposed to a corrosive environment, a local battery is formed. An Fe ₂ O ₃ -based oxide film, which is easily corroded by the above, is likely to be partially formed.

On the other hand, a base treatment for forming a chemical conversion coating with phosphate is generally used as a coating base treatment for the purpose of suppressing the diffusion of corrosive substances and the electrochemical rust-preventing effect of metal salts contained in the coating. This is the method applied. However, the chemical conversion coating with phosphate is Mn.
_{3 (PO 4) 2 · 2MnHPO} 4 · 4H 2 O and FeHP
O ₄ · 4H ₂ O mixed crystal or Zn ₃ (PO ₄ ) ₂
· 4H ₂ O and FeHPO ₄ · 2~4H ₂ O mixed crystal or gamma · Fe ₂ of _{O 3 · FePO 4 · 2H 2} O or F
eHPO ₄ · 4~8H ₂ O is made from such. These crystals release water of crystallization at 100 to 240 ° C., and oxidative decomposition starts at about 250 ° C. for a manganese phosphate coating and at 130 ° C. for a zinc phosphate coating. Therefore, 20
In the polyethylene powder lining heated and melted at 0 to 300 ° C., not only the formation of a porous material by dehydration, cracking of the phosphoric acid film during dehydration and a decrease in the adhesion of the chemical conversion film, but also Mn and Zn in the phosphoric acid film. If the oxidation of these salts progresses, the corrosion potential will be reversed, leading to accelerated corrosion. The effect cannot be expected, and peeling and blistering are likely to occur in a short time due to a decrease in adhesive force due to formation of a porous material and cracking.

Accordingly, in order to expand the application to a high-temperature environment in which blister resistance is more problematic than in the environment near normal temperature where polyethylene linings excellent in corrosion resistance, adhesion, abrasion resistance, etc. have conventionally been used. There is a demand for the development of a base treatment method which is excellent in adhesion and corrosion resistance, and is a technical problem.

The present invention has been made in consideration of the above-mentioned technical level, and has as its object to provide a base treatment method capable of applying an excellent polyethylene lining even in a high-temperature environment in accordance with the above technical problems.

[0010]

According to the present invention, the polyethylene powder is supplied to a lining material made of carbon steel preheated to a melting temperature of the polyethylene powder or higher, and the powder is melted by the heat of the lining material. In the lining method of forming a continuous polyethylene film on the surface of the lining material, after blasting or pickling the surface of the lining material, the lining material surface is heated to 300 to 500 ° C.
To form a film mainly composed of Fe ₃ O ₄ , and then contacted with a chromic acid aqueous solution having a pH of 4.5 to 6.0 and a CrO ₃ concentration of 0.005 to 0.05 wt%. An undercoating method for polyethylene powder lining, characterized by drying afterwards.

[0011]

According to the present invention, after the surface of the material to be lined is cleaned by blasting or pickling, the surface is heat resistant.
A uniform and dense coating mainly composed of Fe ₃ O ₄ having excellent corrosion resistance and excellent adhesion is formed by heating the material to be lined at 300 to 500 ° C., and the pH is further adjusted to 4.5 to 4.5. 6.0 and the CrO ₃ concentration is between 0.005 and
This is a base method for strengthening the corrosion prevention of fine cracks generated in the Fe ₃ O ₄ coating formed by heating by contacting with a 0.05 wt% chromic acid aqueous solution.

PH is lower than 4.5 and CrO ₃ is less than 0.0
If the content is higher than 5 wt%, chromic acid that has penetrated into fine cracks in the Fe ₃ O ₄ coating damages the underlying metal, weakens the bonding force between the Fe ₃ O ₄ and the underlying metal, and resists blistering of the polyethylene lining material. Worse. Also pH
Is higher than 6.0 and the CrO ₃ content is less than 0.005 wt%, the corrosion prevention effect of the chromium of the base metal in the fine crack portion becomes low.

[0013]

EXAMPLE A carbon steel sheet having a thickness of 3 mm and a diameter of 120 mm was immersed in a 3% solution of sodium orthosilicate for 10 minutes, degreased and washed, and immersed in a 5% solution of hydrochloric acid at 50 ° C. for 10 minutes.
A blast plate washed with warm water at 90 ° C. and a shot-blasted blast plate after degreasing and washing were produced.

Then, they are placed in a heating furnace, and 300 to 5
Heat treatment was performed at 00 ° C. for 30 to 50 minutes to form a film mainly composed of Fe ₃ O ₄ on the surface of the lining material. Next, the test material cooled to room temperature was immersed in a chromic acid aqueous solution having a pH of 4.5 to 6.0 and a CrO ₃ concentration of 0.005 to 0.05 wt% at room temperature for 10 seconds, and then dried with hot air. .

The test material subjected to the above-mentioned undercoat treatment is heated at 250 ° C.
After heating on a hot plate at ± 10 ° C., a polyethylene powder having an average particle size of 100 μm was evenly sprayed on the surface subjected to the base treatment at a melt flow rate of 3.0 g / 10 min.
An m-thick polyethylene film was formed.

Table 1 shows that in the above-mentioned undercoating process, Fe ₃ O ₄
Using a test material obtained by lining polyethylene powder on carbon steel pretreated by changing the heating temperature during the film formation and the chromic acid concentration in the chromic acid aqueous solution immersion, put a sulfuric acid aqueous solution with a pH of 0.5 on the polyethylene lining side. And 60
℃, and the time until blisters are generated under the condition of cooling with 20 ° C. cooling water on the unlined steel sheet side, and the result is measured by applying the polyethylene powder to the zinc phosphate chemical conversion treated surface. The ratio is shown as a magnification with respect to a period until blisters are generated in the lined reference material. After the conventional blasting treatment, the reference material lined with polyethylene powder generated blisters in the period of 1/3 of the reference material lined with polyethylene powder on the zinc phosphate chemical conversion treated surface.

[0017]

[Table 1]

[0018]

By applying the undercoating treatment of the present invention, the polyethylene powder lining can be applied to an environment of 50 to 60 ° C., which has conventionally been difficult due to peeling and blister generation. Polyethylene powder lining has a lower production cost than other resin (thermosetting resin) linings and rubber linings used in the above-mentioned environmental conditions, and is also applied to the inside of small-diameter pipes that cannot be installed with resin lining or rubber lining Since the present invention is expected to expand the applicable range of the polyethylene powder lining, the present invention has a great industrial effect and a great effect of improving reliability by ensuring a long life.

Continuation of the front page (51) Int.Cl. ⁷ Identification code FI C23C 22/00 C23C 22/00 Z 22/83 22/83 (56) References JP-A-63-27248 (JP, A) JP-A-3 -234527 (JP, A) JP 46-26843 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) B05D 1/00-7/26 C23C 22/00-22/86

Claims (1)

(57) [Claims] 1. The polyethylene powder is supplied to a lining material made of carbon steel which is preheated to a melting temperature of the polyethylene powder or higher, and the powder is melted by the heat of the lining material, so that the polyethylene is continuous on the surface of the lining material. In the lining method of forming a film of the above, after blasting or pickling the surface of the material to be lined, the surface of the material to be lined is heated to 300 to 500 ° C. to form a film mainly composed of Fe ₃ O ₄ , Is 4.5-6.
0 and the CrO ₃ concentration is 0.005 to 0.05 wt.
% Chromic acid aqueous solution, followed by drying.