JPS63143275A - Method for preventing corrosion of steel structure - Google Patents

Abstract

PURPOSE:To form a steel structure capable of being coated even in the water by applying electrolytic protection treatment to the structure in a wet state after the surface of the submerged steel structure is cleaned and before the anticorrosive coating is applied. CONSTITUTION:The surface of the submerged steel structure is cleaned, and then applied with the anticorrosive coat with the use of water-curing paint or water-curing putty. In this case, electrolytic protection treatment is applied to the surface while keeping the surface wet after the surface is cleaned and before the anticorrosive coat is applied. An external energizing system or a galvanic anode system can be used for the electrolytic protection treatment, and the anticorrosive current density is controlled to about 50-500mA/m<2>. By this method, a steel structure capable of being easily coated even in the water by the same operation as that on the ground is obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for preventing corrosion of underwater steel structures using underwater paint or underwater curing putty. This relates to pretreatment performed when anticorrosive construction is performed using underwater paint or putty.

[Conventional technology]

In recent years, steel structures such as oil drilling rigs or oil stockpile purging associated with offshore development, offshore plants, ships, etc., steel structures such as steel sheet piles used for seawall construction, etc., bridge piers of large tanks constructed offshore, Although the construction of underwater structures for marine ports is increasing, these steel structures almost never have to be moved from the installation area for maintenance.

Therefore, problems such as anticorrosive coating, cleaning, and maintenance occur in the underwater part of these marine steel structures or in the splash zone, and the need for maintenance at sea has become a major issue.

Therefore, it would be of great benefit if there was a coating method that could be applied as efficiently underwater as on land, and that would provide a coating film with excellent corrosion resistance.

Conventionally, the method of painting the submerged parts and sbrushes zones of ships and underwater structures is to use a type 2 coating method, which involves simply scraping away floating rust, etc. as a surface treatment, and then spraying a high-speed water jet to further clean the surface. In order to remove rust and scale even better, there are methods such as mixing sand in a high-speed stream of water and blowing it onto the steel surface.After these surface treatments, underwater curing is Generally, a hardening paint or putty is applied using a brush or a spatula, but after the above-mentioned surface treatment is applied and the steel surface is adjusted, an underwater hardening paint or putty is applied using a brush or a spatula. When painting, it is virtually impossible to paint the submerged parts of underwater structures, especially the splash zone, because they are in a severe corrosive environment.Also, even if it can be painted, the efficiency of the painting will be extremely low, making it difficult to paint. There are almost no

[Problem that the invention seeks to solve]

The problem to be solved by the present invention is to solve the above-mentioned difficulties of the conventional underwater painting method.More specifically, it is possible to easily perform painting underwater by the same operation as on land, and to apply it in submerged or splash areas. The objective is to develop a coating method that can be applied with considerable coating efficiency.

[Means for solving problems]

The above-mentioned problems arise when painting objects such as ships and underwater structures with underwater curing paints. This is achieved by applying cathodic protection treatment while keeping the surface of the object to be coated in a substantially wet state for the period from the time of treatment until the time when the underwater-curing paint or putty is applied to the object. .

[Structure and operation of the invention]

In the present invention, prior to painting an object with an underwater curing paint or an underwater curing putty, the object is cleaned, or the surface of the object is substantially moistened, and then electrolytic protection treatment is performed. After cleaning, cathodic protection is performed under wet conditions until further application of underwater curable paint or underwater curable putty.

The "wet state" used in the present invention includes not only a state in which the object to be coated is in water, but also a state in which water is substantially present on the surface of the object to be coated, such as spraying water. Water can be applied to water-retaining cloth, paper, etc. by passing water through a pipe with countless holes, and by applying countless streams of water to the surface of the object to be coated. This includes a state that can be achieved by attaching it to the object to be coated or by combining the above methods, and whether the surface of the object to be coated is substantially the same? B It means to be in a state of ecstasy. Furthermore, an important point in the present invention is to uniformly moisten the entire coating area on the surface of the object to be coated, and to maintain a continuous wet film of water on the water surface when the object itself is not submerged in water. It is to let If this wet water film is not connected to the surface of the water, the effect of the cathodic protection treatment, which is important in the present invention, may be sufficiently exhibited, and the effects of the present invention may not be fully expected.

As is clear from the above, the "underwater steel structure" of the present invention
This refers not only to things that exist underwater, but also to steel structures that exist in splash zones, on water, and on land.

The cathodic protection treatment of the present invention refers to applying a cathodic protection method to a steel structure to apply a corrosion protection current. The cathodic protection method can be applied to either an external ffi source method or a galvanic anode method.

The external power supply method refers to a method in which the counter electrode, in which current flows through the positive electrode of an external DC power supply, is connected to a steel structure to the negative electrode, and the anticorrosion current flows from the counter electrode toward the steel structure. A lead-tin alloy electrode, a magnetic iron oxide electrode, a silicon iron electrode, a platinum electrode, a carbon electrode, etc. are used.

The galvanic anode method is a method in which an anode made of aluminum, magnesium, zinc, aluminum alloy, magnesium alloy, zinc alloy, etc. is connected to a steel structure, and the current generated by the potential difference between the two walls is used as a corrosion protection current.

The anticorrosion current density is generally about +00 mA/m2 as a standard, and is used in the range of about 50 to 500 mA/m2.

In the present invention, the wet treatment and the cathodic protection treatment are carried out, but both are substantially performed using known pretreatments such as high-speed water jets,
It refers to the time from the time when a high-speed water stream containing sand is sprayed onto the surface of the object to be coated to the time when the underwater curable paint is applied. Of course, the same effects of the present invention can be obtained even if the cathodic protection treatment is continued after the application work, or if the cathodic protection treatment is stopped immediately before the application work and the hypochondriacal corrosion protection treatment is not performed thereafter. .

In the present invention, by performing the above cathodic protection treatment,
It is very easy to apply underwater curing paint or putty.

The reason for this is assumed to be as follows. That is, when a steel material to be coated is treated according to the present invention, the surface of the steel material to be coated, which has been cleaned by a high-speed water stream or a high-speed water stream containing sand, is in a wet state, so that due to the action of cathodic protection, an underwater curing type paint or underwater It is kept clean during the period until the hardening putty is applied, and the steel is kept clean due to seawater, which would form on the surface of the workpiece if cathodic protection treatment was not applied. Since inhibitory substances are suppressed by the cathodic protection treatment, the underwater-curable paint reliably adheres to the surface of the object to be coated. Therefore, it is presumed that the paint will reliably adhere to the surface of the object to be coated even in the highly corrosive splash zone of the water surface, making it possible to easily apply the coating by conventional means.

As the underwater curable paint or underwater curable putty used in the present invention, any of those conventionally used in this type of field can be used. For example, epoxy resin as the main ingredient, polyamide resin, modified aromatic family polyamines,
Underwater-curable paints or putty that use modified aliphatic polyamines, heterocyclic polyamines, alicyclic polyamines, etc. as hardeners, and underwater-curable paints or putty that use unsaturated polyester resin as a base material. This can be illustrated as a representative example. Also, as a means of applying this paint or putty, the usual means of painting on land can be widely adopted.
For example, a typical example is painting with a spatula or a trowel.

The effects of the present invention will be illustrated in more detail with reference to Examples below.

Example 1 and Comparative Examples 1 to 3 Shot blasted 9m+mX 300m*x
Immediately after immersing a 30 (1+m) steel plate in 3% saline solution, lift it out of the water, expose 2/3 of the total surface area above the water surface, and immediately cover the steel surface above the water surface evenly with water-soaked gauze. One end is soaked in 3% saline solution. At the same time, an M1 alloy anode is connected to this steel plate and left for one day. Peel off the gauze from this steel plate and use a commercially available brush to apply underwater curing paint to a dry film thickness of approximately 1+III. So that it becomes?!i
I painted the above water part while it was wet.

The underwater curable paint used here is a commonly used epoxy resin based underwater curable paint, and its composition is shown in Table 1.

In addition, the anticorrosion current during immersion in 3% saline solution in Example 1 was 400
It was mA/m2.

Various physical properties of the obtained coated object were measured.

The results are shown in Table 2 below.

The Examples and Comparative Examples shown in Table 2 were visually observed for coating workability, adhesion after a 6-month immersion test in 3% saline, and the presence or absence of rust.

Paint workability The standards for painting workability are shown below.

O...The paint attached to the brush will adhere to the steel surface just by touching it, and the brush can be applied well.

Δ...It will stick if you rub it a few times, but the brush handling is very poor.

×...Even if you rub it several times, it hardly sticks.

<Adhesion> After being immersed in 3% saline for 6 months, the sample was taken out and the tensile adhesive strength was measured using an adhesion tester (manufactured by Elcometer). In addition, visually observe the coating film cohesive failure rate and the presence or absence of rust in the adhesion measurement area.

The above results are shown in Table 2.

Comparative Example 1 in Table 2 shows the case where the gauze wetted with water and the A1 alloy anode were not used in Example 1 (other than that in Example 1).
).

Comparative Example 2 is the same as Example 1 except that the A1 alloy anode was not used (otherwise the same as Example 1).

Comparative Example 3 is the same as Example 1 except that the gauze soaked in water was not used (the other conditions were the same as Example 1).

Example 2 and Comparative Example 4 9mff1X30011 connected to Al1 alloy anode immersed in 3% saline for 1 day immediately after shot blasting
II×30011IM steel plate (it current density 100mA
/m2), an underwater curable paint was applied in water using a commercially available brush so that the dry film was approximately 1 ms+. The underwater curable paint used here was the same as in Example 1.

Various physical properties of the coated product were measured in the same manner as in Example 1.

The results are shown in Table 3.

Table 3 However, in Comparative Example 4, the A1 alloy anode was not connected and the other treatments were the same as in Example 2.

Example 3 and Comparative Example 5 Painting was carried out in the same manner as in Example 18 and Comparative Example 2 using the compositions shown in Table 4 below. The results are shown in Table 5.

Table 4 Table 5 Example 4 and Comparative Example 6 Using the compositions shown in Table 6 below, the current density was 50 mA/
Coating was carried out in the same manner as in Example 2 and Comparative Example 4, except that n2 and dry film thickness were 3 mm. The results are shown in Table 7.

Table 6 Table 7 (that's all)

Claims (1)

[Claims] (1) When applying an anti-corrosion coating with an underwater curing paint or an underwater curing putty after cleaning the steel surface of an underwater steel structure, apply cathodic protection treatment under humidity during the anti-corrosion coating after cleaning. A method for preventing corrosion of steel structures in water, characterized by: