JPH05301075A - Method for base treatment of powdery polyethylene lining - Google Patents

Abstract

PURPOSE:To enable formation of excellent polyethylene lining even in a high- temp. environment by degreasing the surface of a material to be lined, washing with water, pickling with hydrochloric acid, washing with water, dipping in a specified boiled soln. to form a specified film, neutralizing with an acid soln., washing with water, and then drying. CONSTITUTION:The lining method of powdery polyethylene includes the following process. A material to be lined consisting of carbon steel is preheated at temp. higher than the melting point of the powdery polyethylene, to which the polyethylene powder is supplied. The powder is molten by the heat of the material to be lined to form a continuous polyethylene film on the surface of the material. As for the base treatment of the material to be lined, the surface of the material is degreased, washed with water, pickled with hydrochloric acid, washed with water, dipped in a boiled soln. comprising caustic soda, sodium orthophosphate and sodium nitrite to form a film essentially comprising Fe3O4, washed with water, neutralized with an acid soln. of pH 4.5 to 6.0, washed with water, and then dried.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, in polyethylene powder lining, the surface of a material to be lined made of carbon steel is degreased and washed, blasted or acid-washed, and a chemical conversion treatment film with a phosphate is formed, and then 200 to 300 ° C. The polyethylene lining is continuously melted by preheating the lining material and then supplying the polyethylene powder and heat-melting the polyethylene powder by the heat retained by the lining material or the heat supplied from the opposite side of the lining surface. Methods for forming coatings are in place.

[0003]

Polyethylene powder linings have hitherto been frequently used in environments where they come into contact with liquids having a relatively low temperature (30 ° C. or less) such as water pipes and seawater intake pipes, and have a certain durability. Has a track record. However, the polyethylene powder lining material constructed by the conventional method has a liquid temperature of 50 to 6 in chemical plants and power plants.
When used in an environment of 0 ° C, the polyethylene coating often peels off in a short time, and blisters often occur.
When the lining surface of the peeling and blister part is examined, the lining surface is always corroded.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 the base surface is easily corroded when used.

The base treatment such as the blast treatment or the chemical conversion treatment with a phosphate in the conventional polyethylene powder lining method is a method widely applied in the industry as a base treatment such as coating and resin or rubber lining. It is hard to say that the polyethylene powder lining method in which the material to be lined is heated at 200 to 300 ° C. to heat-melt the polyethylene powder is not always appropriate for the following reasons.

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 purpose is to suppress corrosion due to local battery formation due to adhesion. However, the blasted surface has an active metal surface exposed, and when exposed to a corrosive environment, general corrosion proceeds,
The effect of suppressing corrosion cannot be expected.

Therefore, in general coating, resin lining, rubber lining, and the like, a method of applying a primer containing powder of Zn, Sn, Al, etc. to prevent corrosion of the blast surface is adopted. However, in the case of polyethylene powder lining, since it is heated to 200 to 300 ° C., the primer that is expected to have the above-mentioned anticorrosion effect undergoes thermal decomposition of the resin and Zn, Sn, and Al are oxidized to produce ZnO ₂ , Sn.
It cannot be used because it changes to O ₂ , Al ₂ O _3, etc. and the electrochemical anticorrosive action disappears, and polyethylene powder for lining is directly supplied for lining. In addition, the pre-heating process of the lining material and the melting of the polyethylene powder are performed in air, during which the blasted surface of the lining material is locally oxidized and, if exposed to a corrosive environment, local battery formation A Fe ₂ O ₃ -based oxide film that is easily corroded due to is easily formed partially.

On the other hand, the base treatment for forming a chemical conversion coating film with a phosphate is generally performed as a coating base treatment for the purpose of suppressing the diffusion of corrosive substances and the electrochemical anticorrosion effect of the metal salt contained in the coating film. It is the method applied. However, the phosphate conversion coating 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
・ Mixed crystal of 4H ₂ O and FeHPO ₄・ 2-4H ₂ O or γ ・ Fe ₂ O ₃・ FePO ₄・ 2H ₂ O or F
It is composed of eHPO ₄ , 4-8H ₂ O, etc. These crystals release water of crystallization at 100 to 240 ° C, and oxidative decomposition starts at around 250 ° C in the manganese phosphate-based coating and at 130 ° C in the zinc phosphate-based coating. Therefore, 20
In the polyethylene powder lining that is heated and melted at 0 to 300 ° C, not only is porosification caused by dehydration, cracking of the phosphoric acid coating during dehydration and reduction of the adhesion of the chemical conversion coating, but also Mn, Zn, etc. in the phosphoric acid coating The anticorrosion effect is reduced due to the oxidation of the salt, and when the oxidation of these salts is progressing, it leads to the acceleration of corrosion due to the reversal of the corrosion potential. No effect can be expected, and peeling and blistering are likely to occur in a short time due to a decrease in adhesion due to porosity and generation of cracks.

[0008] Therefore, in order to expand the application to a high temperature environment, which is a problem in terms of blister resistance, as compared to the environment around room temperature which has conventionally used polyethylene lining excellent in corrosion resistance, adherence, abrasion resistance, etc. Has been desired to develop an undercoating method having excellent adhesion and excellent corrosion resistance, which is a technical problem.

In view of the above technical level and according to the above technical problems, the present invention aims to provide an undercoating method capable of applying excellent polyethylene lining even in a high temperature environment.

[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 a lining method for forming a continuous polyethylene film on the surface of the lining material, the surface of the material to be lined is degreased and washed, washed with water, washed with hydrochloric acid and then washed with water, and then a boiling aqueous solution of caustic soda, sodium orthophosphate, and sodium nitrite. And a film mainly composed of Fe ₃ O ₄ is formed on the surface of the material to be lined, then washed with water, neutralized with an acidic aqueous solution of pH 4.5 to 6.0, washed with water and dried. The method is as follows:

According to the present invention, the surface of the material to be lined is degreased and washed with water, then with hydrochloric acid and then with water to be cleaned, and then concentrated in a boiling aqueous solution prepared by adding sodium orthophosphate and sodium nitrite to a concentrated caustic soda solution for a certain period of time. Immersion is performed to form a uniform and dense black coating mainly composed of Fe ₃ O ₄ on the surface of the material to be lined. Next, the caustic soda aqueous solution adhering to the surface of the material to be lined is washed away with water, and then the pH is adjusted to 4.5 to
This is a method for treating the surface of a polyethylene powder lining that is neutralized with an aqueous solution adjusted to 6.0.

[0012] degreasing of the present invention, pickled, washed with water, to hydrochloric acid pickling and water washing, heat resistance of the next step, excellent corrosion resistance, uniform the lining material surface Fe ₃ O ₄ with excellent adhesion This is because of the formation.

In order to form a uniform and dense Fe ₃ O ₄ coating having excellent heat resistance, corrosion resistance and adhesion on the surface of the material to be lined, caustic soda 40 to 50 wt%, sodium orthophosphate 5 to 15 wt%, sodium nitrite 2-8 wt% boiling water is used, preferably caustic soda 45 wt
%, Sodium orthophosphate 10 wt%, sodium nitrite 5 w
Since it is t% boiling water, a Fe ₃ O ₄ film having a uniform crystal grain size is formed.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The present invention degreasing the surface of the lining material, pickled, washed with water and hydrochloric acid pickling, water washing and then cleaned, heat to this surface, excellent corrosion resistance, Fe ₃ which is excellent in adhesion O ₄
It has a uniform and dense coating and does not have a localized oxide film that was previously generated when polyethylene powder was melted by heat. Even when used in a high temperature environment, a uniform film of Fe ₃ O ₄ provides a base material. Since the corrosion of the polyethylene powder is suppressed, it is possible to provide a polyethylene powder lining material that can withstand long-term use without causing peeling or blistering.

In the present invention, F is formed on the surface of the lining material.
e ₃ O ₄ is formed as a main film, and after washing with water, p
Neutralization treatment is performed with an acidic aqueous solution of H4.5 to 6.0, and this treatment can greatly improve the adhesion of the polyethylene lining. When neutralized with an aqueous solution having a pH of less than 4.5, the anticorrosion property of the Fe ₃ O ₄ coating is remarkably deteriorated. Also, in an aqueous solution having a pH higher than 6.0, Fe ₃ O
₄ The neutralizing ability of the alkaline components adhering to the coating is reduced, and the adhesion of the polyethylene lining is reduced. The acidic aqueous solution used for the neutralization treatment is an inorganic acid,
Organic acid or the like is applied.

[0016]

[Example] Six carbon steel sheets each having a thickness of 3 mm and a diameter of 120 mm were used.
Immerse in 0% C 3% sodium orthosilicate solution for 10 minutes, degrease and wash, then wash with warm water, then 50 ° C. hydrochloric acid 5%
After being immersed in the solution for 10 minutes, it was washed with warm water at 90 ° C.

Next, caustic soda 45 wt%, sodium orthophosphate 10 wt%, sodium nitrite 5 wt%, water 40
The solution of wt% was immersed in a treatment tank heated to 135 to 145 ° C. for 20 minutes. After the immersed steel plate was washed with warm water, it was immersed in a citric acid aqueous solution whose pH was adjusted to 4.5 to 6.0 at room temperature for 1 minute, then immersed in warm water at 80 ° C. for 10 seconds and then dried with hot air. A uniform black coating film of Fe ₃ O _{4 having} a thickness of 1 to 2 μm is formed on the surface of the carbon steel after the treatment.

The carbon steel sheet on which the Fe ₃ O ₄ coating was formed was heated on a hot plate at 250 ° C. ± 10 ° C., and then the polyethylene powder having an average particle size of 100 μm was melt-floated at 3.0 g / 10 min. The coated surface was evenly sprayed to form a 1 mm thick polyethylene lining film. Table 1 shows the results of measuring the adhesive strength when polyethylene lining was performed by changing the conditions of the neutralization treatment in the base treatment.

Further, using a test material lined with polyethylene of 1 mm thickness on each of the steel plates subjected to the base treatment conditions shown in Table 1 above, a sulfuric acid solution having a pH of 0.5 was placed on the lining side and heated to 60 ° C. The period until the occurrence of blisters was measured under the condition that the steel sheet side without lining was cooled with cooling water at 20 ° C.

The results are shown in Table 2 as a magnification with respect to the period until the occurrence of blisters in the reference material in which polyethylene powder was lined on the conventional zinc phosphate chemical conversion treatment surface.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

By applying the base treatment of the present invention, the polyethylene powder lining can be applied to an environment of 50 to 60 ° C., which has been difficult to practically use due to problems such as 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 environmental conditions, and can be applied to the inner surface of pipes with a small diameter that can not be done with resin linings or rubber linings. Since the present invention is expected to expand the range of application of the polyethylene powder lining, it has a large industrial effect and also has a large reliability improving effect by ensuring a long life.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication B05D 7/24 302 G 8720-4D C23C 22/62 22/83 (72) Inventor Morio Nakata Osaka 4-11-88 Takeshima, Nishiyodogawa-ku, Osaka-shi, Ajikawa Iron Works Construction Co., Ltd.

Claims (1)

[Claims] 1. The polyethylene powder is supplied to a lining material made of carbon steel preheated to a melting temperature of polyethylene powder or higher, and the powder is melted by the heat of the lining material, and is continuously applied to the surface of the lining material. In the lining method for forming a polyethylene film, the surface of the material to be lined is degreased, washed with water, then pickled with hydrochloric acid, washed with water, and then immersed in a boiling aqueous solution of caustic soda, sodium orthophosphate, sodium nitrite, A polyethylene powder lining characterized in that a film mainly composed of Fe ₃ O ₄ is formed on the surface of the lining material, then washed with water, neutralized with an acidic aqueous solution of pH 4.5 to 6.0, washed with water and dried. Substrate treatment method.