JP2917097B2 - Protective paint and protection method for welded pipe of plant - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention paints a pipe welded portion of a plant such as a nuclear power plant or a thermal power plant for rust prevention and corrosion prevention temporarily from the completion of production and assembly to the start of operation. The present invention relates to a protective paint and a protective method.

[0002]

2. Description of the Related Art Plants such as a nuclear power plant and a thermal power plant require less than a variety of circumstances from the time of completion of manufacture and assembly to the time when they are installed in an actually operated facility and started to operate. It may be left for half a year or about two years if it is long. During this time, rust may be generated in the welded part of the pipe, and rust is carefully removed from the welded part of the pipe of the plant immediately before full-scale installation, and then rust prevention painting and other surface treatment are performed.

[0003] However, the welded portions of pipes reach tens of thousands per plant, and many rusts are generated due to a long standing period. Takes very much. In addition, the welded portions of these plants are extremely severely welded due to their properties, and are often triple or quadruple welded.
Therefore, it is necessary to completely remove the rust from the welded part,
Work is extremely difficult.

[0004] For this reason, there is an idea that rust-proof coating is applied to the entire pipe including the welded part of the pipe at the time of manufacturing the plant. However, various types of plants need to be temporarily left after being manufactured and then installed in a predetermined place, and subjected to a pressure resistance test before starting full-scale operation. If there is a welding defect at the welded part during the pressure test, it must be repaired, but if rust prevention coating is applied over the entire pipe, it will be difficult to identify the defective welded part, or In order to repair defective parts, the paint film must be peeled off.However, this work is difficult. Is not currently done.

[0005]

Accordingly, the problem to be solved by the invention is to have a rust-preventing ability to prevent the generation of rust in a welded portion of a pipe for at least several years, and at the same time, to fully install a plant and pressurize the plant. Prior to the test, the aim is to develop a protective coating and a protective method for the welded pipes of the plant, which makes it possible to remove the adhered coating very easily.

[0006]

[Means for Solving the Problems] To solve the above problems,
As a result of diligent studies, the present inventors have developed a styrene-butadiene rubber-based room temperature dry-type protective coating which can be applied as a thick film, and a protective method by applying to a pipe welding portion of a plant. The summary is as follows.

It contains 1.5 to 3.0% by weight of finely divided silica and 25 to 35% by weight of styrene-butadiene rubber, and is composed of another organic solvent. Protective paint for pipe welds in plants. And a method for protecting a pipe weld of a plant, wherein the protective paint is applied to a pipe weld of the plant at a dry film thickness of 100 μ or more and dried.

As the finely divided silica, anhydrous finely divided silica and hydrated finely divided silica can be used. The blending amount is indispensable from 1.5 to 3.0% by weight. If the compounding amount is less than 1.5% by weight, sufficient thixotropic properties cannot be imparted to the coating material, so that the coating tends to sag at the time of application such as brush application or roller application, so that a required dry film thickness cannot be secured. When the content exceeds 3.0% by weight, the viscosity of the paint is remarkably increased, and the level of the paint is not sufficient at the time of the paint application. There are disadvantages such as a hindrance, an increase in viscosity during storage of the paint, and a decrease in storage stability such as gelling of the paint itself.

[0009] The styrene-butadiene rubber can be used in the form of a solvent solution. A blending amount of 25 to 35% by weight is essential. When the content is less than 25% by weight, the solid content ratio in the coating material is small, and the intended film thickness is not adhered when a dried coating film is formed. If the content exceeds 35% by weight, the viscosity increases and the coating workability decreases. As the organic solvent, aromatic solvents such as toluene and xylene, alcohol solvents such as ethanol and butanol, various aliphatic solvents and the like can be used, and aromatic solvents are particularly preferable.

[0010] If necessary, the coating composition of the present invention may further contain an antifoaming agent, a dispersant, an antisettling agent, an ultraviolet absorber, an antioxidant, and the like. Further, in order to produce the paint according to the present invention, various dispersing machines using a conventionally known dispersing method can be used. Roll mill, Glen mill, Ball mill, Kneader, Planetary mixer, Paint shaker,
A blade type high-speed stirrer can be exemplified. In order to apply the coating material of the present invention to the welded portion of the pipe, brush coating and roller coating are recommended, but spray coating such as air spray coating and airless spray coating is also possible. However, in the case of the spray coating, it may be necessary to mask the rust-preventive coating parts other than the welded parts of the pipes, and the important parts of the plant so that the mist is not scattered.

When the dry thickness of the protective coating is less than 100 μm, the coating cannot absorb the unevenness existing on the surface of the pipe weld, and a gap is generated between the unevenness and the dried coating.
Water and moisture can enter through this gap and cause rust. Further, if the dry film thickness is less than 100 μm, the strength of the coating film is not sufficient, and the coating film is torn due to the above-mentioned irregularities on the surface, or the coating film is peeled off after the end of the protection period. The film breaks and the coating cannot be peeled off at once.

[0012]

The following examples are provided to provide a more detailed understanding of the present invention. As a matter of course, the present invention is not limited only to the following examples.

Styrene-butadiene rubber (SBR), hydrous finely divided silica, a dispersant for paint, toluene, and the above blends are blended according to the following blending amounts, and a high-speed stirrer is used.
Using this roll mill, the mixture was dispersed after mixing and stirring, and the foam in the paint was defoamed by a vacuum defoaming device, followed by filtration to obtain protective paints 1 to 8.

[0014]

Five pipes made of a corrosion-resistant alloy having a diameter of 60 mm are welded at five locations, and at locations other than the welding locations, anti-corrosion coating is performed using ordinary epoxy resin-based synthetic resin paint. 8 is the standard 5
The paint was applied once with a flat brush having a width of cm, the workability of the brush coating was evaluated, the appearance of the paint film was observed after the paint film was dried, and the average dry film thickness of each applied portion was measured by a film thickness meter. 2 remaining
The parts were left as they were and used as test samples.

[0016] The above-mentioned five-point welded and rust-proofed test samples were placed outdoors, covered with a waterproof sheet, fixed at important points, and left for about one year.

[0017]

[Results] The fixing portion of the waterproof sheet was removed, the waterproof sheet was removed, and the surface condition of the test article was observed. Next, the coating films of the protective paints 1 to 8 were peeled off by hand, and it was tested whether or not the coating films were continuously peeled off in a film form, and the surface condition of the welded spot was observed. No rust was observed at any place other than the welded part of the test sample. Welded parts that were not coated with rust preventive paint were 2
Red rust occurred almost everywhere in all places.

[0018]

According to the method for protecting a welded portion of a pipe according to the present invention, tens of thousands of welded portions of a pipe in a thermal power plant or a nuclear power plant can be protected very easily. At the same time, the rust removal work on the welded parts before the test operation after installation in the plant was unnecessary, and the peeling of the protective coating was very easy because a continuous film-like coating could be peeled off in one step. In addition, not only can the cost of plant installation be reduced, but also the schedule from plant installation to pressurization and operation test can be shortened, so that great effects can be expected for these plant installation operations.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideo Takasu 1-1-1 Uchikanda, Chiyoda-ku, Tokyo Investigator, Hitachi Plant Construction Co., Ltd. Toshiko Nakata (58) Field surveyed (Int.Cl. ⁶ , DB Name) C09D 5/20 C09D 109/06-109/08 B23K 31/00

Claims (2)

(57) [Claims] 1. A composition containing 1.5 to 3.0% by weight of finely divided silica and 25 to 35% by weight of a styrene-butadiene rubber, and other organic solvents, which can be used for brush coating or roller coating.
A paint for protecting a welded portion of a pipe in a plant, wherein a dry film thickness by a multiple coating is 100 μ or more. 2. A method for protecting a pipe weld of a plant, wherein the protective paint according to claim 1 is applied to a pipe weld of the plant at a dry film thickness of at least 100 μm and dried.