JPH10323617A - Corrosion protection method for steel tanks, steel towers and inner surfaces of steel structures - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a method for preventing corrosion of the inner surface of a box girder of a steel tank, a steel tower and a steel bridge. SOLUTION: (1) The ratio of the resin to the solid content is 0.2.
A method for preventing corrosion of a steel tank, in which a paint containing trivalent chromium ions of up to 12.0 wt% is applied to the steel tank. (2) Chromium (III) compound content of 0.1 to 65 w on the inner surface
A method for preventing steel towers from being assembled using a steel pipe having a resin film having a thickness of 5% to 150 μm and a normal steel pipe. (3) The steel tower of the above (2) or the steel tower of a steel tower constructed using ordinary steel pipes or shaped steels has a content of 0.1 to 65 on the steel surface.
An anticorrosion method for a steel tower, in which an organic resin paint containing chromium (III) compound by weight is applied to a thickness of 5 to 150 μm. (4) The inner surface of the steel structure having the inner surface has a content of 0.
An anticorrosion method for an inner surface of a steel structure, in which an organic resin paint containing 1 to 65% by weight of a chromium (III) compound is applied so as to have a thickness of 5 to 150 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inner surface of a steel tank such as a tanker (especially a steel ballast tank), a steel tower (especially a power transmission tower) and a steel structure having an inner surface portion (especially a box girder of a steel bridge). About the anticorrosion method of the part.

[0002]

[Prior art]

1. Steel tank tankers and ore carriers have ballast tanks, cargo oil tanks and cargo tanks. When tankers etc. are empty, seawater is stored in the ballast tank, and on the ceiling, water evaporated from seawater is cooled on the deck surface during the daytime, and water drops or thin film water condenses on the surface. . In this description, the “ceiling” of the steel tank may be referred to as the “gas phase”.

[0003] The ballast tank is roughly divided into three parts from the viewpoint of corrosion. In addition to the above-mentioned ceiling part, there are a basin part which undergoes dry and wet repetition due to the increase and decrease of seawater, and a bottom plate part which is always in contact with seawater. Corrosion is severe in the dry and wet parts of the ceiling and the ebb and flow area.
m coating method was usually used. This method is expensive and the period during which the anticorrosion effect is maintained is about 10 years, and it has been required to extend the life of the anticorrosion effect and reduce the cost. In the following description, a ballast tank in which seawater is stored when empty ore such as an ore carrier is not limited to a crude oil tanker is referred to as a “seawater storage ballast tank”.

On the other hand, in a tanker loaded with crude oil, the crude oil is stored in a cargo tank or the like, but is filled with an inert gas (hereinafter referred to as "inert gas") to prevent explosion. As the inert gas, the exhaust gas of the engine is usually used for cost reduction, so that CO ₂ , H ₂ O
Together with SO ₂ . Therefore, corrosion caused by water in which SO ₂ is dissolved occurs in a cargo tank or the like in which crude oil is stored, which is a problem. In the following description, a tank or the like in which crude oil is stored and filled with exhaust gas to prevent explosion will be referred to as a “cargo tank”.

[0005] In the cargo tank, the severely corroded portion is mainly the ceiling like the seawater storage ballast tank. As a countermeasure against this corrosion, there is a method of painting a few tens of μm of a primer on the ceiling of the tank, but the effect is not perfect. There is a limit to using thicker coatings in order to increase the effect, which increases the cost, and there is a limit. At present, it is no exaggeration to say that there is no appropriate anticorrosion method.

[0006] 2. Steel towers Power transmission towers and lighting towers used in atmospheric corrosion environments have been painted or galvanized for corrosion protection. Painting requires repainting work every predetermined life period. However, in a high-rise building such as a steel tower, it is difficult and extremely expensive to install scaffolds for repainting. In addition, when a galvanized steel material is used, the luster of the galvanized steel impairs the surrounding natural scenery, so that a treatment for reducing the surface luster by a chemical conversion treatment or the like is required, which increases the cost. further,
In galvanization, there is a risk of brittle cracking of a steel material due to hot-dip zinc. In addition to these disadvantages, the inner surface of the steel pipe for towers is apt to be unplated, but it is difficult to detect unplated steel by inspection in small-diameter steel pipes used for horizontal connection. When a steel pipe having an unplated inner surface is used, corrosion may progress remarkably from the inside of the steel pipe due to the retained water at locations where water remains inside the steel pipe.

On the other hand, as a method that does not rely on painting or galvanizing, it is conceivable to use weather-resistant steel containing a trace amount of corrosion-resistant elements such as Cr and Cu. Unable to generate stable rust, poor corrosion resistance,
Also, in the inland area, it takes ten years or more for stable rust to occur, and during that time, there is a problem that rust occurs and pollutes the natural landscape and the surrounding environment.

[0008] 3. Steel bridge box girder Steel structures with an inner surface, especially when the inner surface of the bridge box girder is condensed due to changes in the outside air temperature, and its moisture is difficult to evaporate, which significantly accelerates corrosion. There is. Even if weathering steel is used for such a steel structure, the weathering steel produces stable rust in the atmosphere to improve corrosion resistance,
Stable rust cannot be generated on the inner surface of a steel structure in a dew condensation environment.

For this reason, steel structures have conventionally been assembled and coated with an organic resin such as tar epoxy paint for the purpose of preventing corrosion of the inner surface. These coatings are generally
If the coating is not more than m, corrosion resistance is poor, and corrosion progresses after a relatively short period of time. Further, the tar epoxy resin coating requires a blast treatment as a base treatment, so that there is a problem that the cost is high.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a steel tank, (b) a steel tower, especially a power transmission tower, by applying a coating and forming a stable rust layer on the surface of the steel material at an early stage.
And (c) to provide a maintenance-free and economical anticorrosion method for a steel structure having an inner surface, particularly an inner surface of a box girder of a steel bridge.

[0011]

SUMMARY OF THE INVENTION The present invention has been completed through various tests on a simulated environment such as a ballast tank for storing seawater, a simulated steel tower and a prototype box girder based on the matters described below. The gist of the invention lies in the following method for preventing corrosion of the inner surfaces of steel tanks, steel towers and steel structures.

(1) An anticorrosion method for a steel tank in which a paint containing an organic resin and a chromium ion having a content of 0.2 to 12.0% by weight of the solid content is applied to the steel tank (Invention 1 ]).

(2) A steel tower having a chromium (III) compound content of 0.1 to 65% by weight on its inner surface and having an organic resin film having a thickness of 5 to 150 μm and an ordinary steel pipe are assembled into a steel tower. Corrosion prevention method for steel towers (referred to as [Invention 2]).

(3) a steel tower to which the method of (2) is applied;
Alternatively, an organic resin paint containing a chromium (III) compound having a content of 0.1 to 65% by weight of the solid content is coated on a steel surface of a steel tower constructed using a normal steel pipe or a section steel with a film thickness of 5%.
An anticorrosion method for a steel tower to be coated so as to have a thickness of 150 μm (referred to as [Invention 3]).

(4) Chromium (I) having a content of 0.1 to 65% by weight of the solid content on the inner surface of the steel structure having the inner surface.
II) An organic resin paint containing a compound is coated with a film having a thickness of 5 to 15
An anticorrosion method for an inner surface of a steel structure to be coated to have a thickness of 0 μm (referred to as [Invention 4]).

In [Invention 1], the "steel tank"
These include (a) ballast tanks and cargo tanks for tankers and ore ships, (b) crude oil storage tanks (marine storage tankers), and (c) onshore crude oil tanks.

In [Invention 1] to [Invention 4], "steel materials" such as tanks, steel towers, box girders, etc., to be coated are carbon steel and low alloy steels including weathering steel as long as they generate rust. And so on regardless of steel type. The “solid content” or “film” refers to a material that is dried and solidified after the “paint” is applied. Solid content or film is trivalent chromium ion (hereinafter, referred to as
Chromium ion) or a chromium (III) compound and an organic resin, and may contain sodium molybdate, barium sulfate, ferrous sulfate, red iron oxide, etc. depending on the application as described later. . A solvent or water is added to the solid content in order to form a paint at the time of painting.

[0018] Again, the "% by weight of chromium ion" or "chromium (III) compound" is the solid content excluding volatile components such as water and solvent, that is, the weight in the coating formed by drying and solidifying. Means%. The “organic resin film” may be abbreviated to “organic” and simply referred to as “resin film”.

In the above [Invention 2], the "steel pipe having the above-mentioned organic resin film on the inner surface" is incorporated in a steel tower and used mainly at locations where water retention occurs. The organic resin film may be provided on the entire “inner surface” or may be provided on a part of the inner surface. The “assembling of the steel tower” may be performed by welding or fastening the flanges with bolts and nuts.

In the above [Invention 3], the steel tower may be a steel tower whose main component is a steel pipe, or may be assembled mainly from a shaped steel. The method of the present invention includes not only a newly constructed tower but also a method of applying the above organic resin paint after several years of use as a tower.

The "organic resin paint" is one which is adjusted to a viscosity suitable for the coating operation with an appropriate amount of a solvent or water before coating, and the solvent or moisture evaporates by natural drying after the coating to form a film. To form

In the above [Invention 4], the "inner surface portion"
A part whose periphery is surrounded to some extent by a steel material is referred to, but the four circumferences do not necessarily have to be sealed. For example, the inside of the box-shaped structure, the base of the rib of the H-section steel, etc. correspond.
"Assembly" is performed mainly by welding,
It may be assembled with bolts and nuts.

Next, the technical background of the above invention will be described.

The present inventors have presumed that the stable rust layer formed on the steel material during the progress of corrosion in the atmosphere mainly consists of a dense aggregate of fine crystals composed of chromium goethite (chemical formula α- (Fe, Cr) OOH). They have found that they form a component, and have developed surface coating technology to grow this chrome goethite at an early stage. These surface coating methods were developed with the aim of improving the weather resistance of steel structures exposed to the atmosphere, and a great effect was recognized in achieving this purpose. Then, when the corrosion of the ballast tank and the like, the steel tower, the box girder, and the like were tested using these surface coating methods, the following items could be confirmed, and the inventions 1 to 4 were completed. Reached.

(A) Since the ballast tanks and the like are substantially closed and the ceiling thereof has a higher frequency of repetition of wet and dry compared to outdoor structures, corrosion occurs more severely than in the atmosphere.

(B) When the surface of the steel tank is coated with an organic resin paint containing chromium ions, the surface of both the seawater storage ballast tank and the cargo tank is removed from the atmosphere in an environment corresponding to a ceiling or a dry and wet repeated part. It was also found that a stable rust layer was formed early. As a result, corrosion is effectively suppressed in a seawater storage ballast tank or the like.

(C) A stable rust layer is formed even in places where water remains on the inner surface of the steel pipe of the steel tower when an organic resin paint containing a chromium (III) compound is applied.

(D) At a place where the steel tower comes into contact with stagnant water,
In order to form a stable rust layer, the composition and thickness of the film after the above coating must be within a certain range.

(E) A stable rust layer is also formed on the inner surface of a steel structure having an inner surface by applying an organic resin paint containing a chromium (III) compound.

(F) In order to form a stable rust layer continuously on the inner surface of the steel surface without generating any missing portions,
The content of the chromium (III) compound in the solid content of the paint must be within a certain range. Also, the thickness of the film needs to be limited.

(G) As long as the conditions relating to the chromium (III) compound and the like are satisfied, the pigment and the above-mentioned film may contain other components such as an antioxidant.

(H) If a stable rust layer is formed at an early stage in any of the above-mentioned anticorrosion targets, subsequent re-coating is unnecessary, and there is no cost problem as in the above-mentioned primer coating.

[0033]

Next, the reason for limiting the present invention will be described.

First, a substance containing chromium ions, that is, a chromium (III) compound will be described.

1. Chromium ion containing material (Chromium (III)
Compounds) In general, when the rust layer is dense, it is easy to be physically shielded from corrosive environments such as oxygen, carbon dioxide, sulfur dioxide, and water, and the elution of iron ions is reduced. As a result, the corrosion rate is reduced. . However, if there are cracks or pores in the rust layer, the rust layer becomes a supply path for corrosive chemical species, resulting in a decrease in the anticorrosion function of the rust layer. Therefore, it is necessary to form a dense and continuous stable rust layer, that is, a rust layer mainly composed of chromium goethite (α-FeOOH).

When chromium sulfate is used as the chromium (III) compound containing chromium ions, when chromium sulfate permeates the film, chromium ions and sulfate ions SO ₄
^2- and dissociate, and both ions reach the interface between the film and the steel. These ions dissolve the steel and, as a result,
Iron ions Fe ²⁺ are generated. Chromium ions are Fe ²⁺
Has the effect of making chromium goethite the main component of the stable rust layer.

If the rust structure is dense, it is easy to physically block the atmospheric corrosion environment, and the subsequent corrosion reaction is reduced. However, if there are cracks or pores in the rust layer, it becomes a supply path for water or oxygen, and the corrosion protection of the rust decreases. For this reason, it is necessary to form a dense and continuous rust layer. Further, when the rust layer formed by the corrosion reaction is γ-FeOOH, γ-FeOOH acts as an oxidizing agent and γ-FeOOH
Instead of reducing OH itself, it oxidizes Fe to promote corrosion. For this reason, in order to form a rust layer having high anticorrosion properties, it is necessary to form dense α-FeOOH.

Chromium ion is not usually handled alone, but is included in a chemical substance which is a salt containing chromium ion, and is added to the organic resin by the salt.
As the salt containing chromium ions, chromium (III) compounds such as chromium sulfate and chromium nitrate can be used. As the chromium (III) compound, chromium sulfate Cr ₂ (SO ₄ )
_3, chromium nitrate Cr (NO _{3) 3} or the like of an inorganic acid chromium compound and chromium acetate Cr (CH ₃ COO) _3, formate chromium Cr
Organic acid chromium compounds such as (HCOO) ₃ are preferred. Even chromium (III) compounds, such as chromium phosphate, which have very low solubility in water have little effect because they hardly generate chromium ions. In addition, chromium halides such as chromium chloride cause the hydrolyzed halogen ions to promote corrosion excessively and hinder the formation of an anticorrosive rust layer.
It is desirable to avoid its use.

Among chromium compounds, it is most preferable to use chromium sulfate. The reason for this is that sulfate ions promote the corrosion of steel and promote the initial iron ion formation, but refine and refine the crystal grains of the subsequently formed rust layer to promote the formation of stable rust.

In an environment simulating the environment of a seawater storage ballast tank or a cargo tank to be used in [Invention 1], the frequency of repetition of wet and dry is higher than that in the atmosphere. It is formed earlier than it is. In particular, in a cargo tank, the initial corrosion is accelerated because SO ₂ is contained in the inert gas, and chromium goethite is formed early. For this reason, it has been found that a more remarkable effect can be obtained than expected from a comparison of corrosion of the bare material in the air and in a seawater storage ballast tank or the like. These phenomena were verified by periodically observing a test material partially attached to an actual seawater storage ballast tank or cargo tank with an electron microscope or the like.

The rust layer formed in the gas phase portion and the dry / wet repeated portion of the seawater storage ballast tank is dense, and functions as a stable rust layer earlier in the air than in the air. Further, even in a gas phase portion where engine exhaust gas containing SO ₂ is used as an inert gas, as in a cargo tank, chromium ions in the coating layer are effective in forming a stable rust layer early.

In [Invention 1], if the chromium ion content in the film is less than 0.2% by weight, in the above-mentioned ballast tank or the like where salt is present, Fe ²⁺ does not migrate to chromium goethite and a stable rust layer is formed. Hateful. For this reason, the chromium ion in the coating is set to 0.2% by weight or more.

When a solid content containing 0.2% by weight or more of chromium ions is applied as a paint and exposed to the above environment such as a ballast tank, the rust layer composed of chromium goethite formed has chlorine ion Cl. ^- the effect of preventing permeation of corrosive anions such as occur. However, if the chromium ion content exceeds 12.0% by weight, the effect of suppressing anion permeation is rather reduced.
2.0% by weight.

When sodium molybdate (Na ₂ MoO ₄₎ is contained in an amount of 0.1 to 5% by weight in addition to chromium sulfate, the effect of suppressing the anion permeation of the formed stable rust layer becomes more remarkable, and in an environment where the chloride ion concentration is high. The corrosion resistance is improved.

In [Invention 2] to [Invention 4], in order to obtain the above-mentioned effects, 0.1% by weight or more of chromium (I
II) Requires compounds. The upper limit is limited to 65% by weight or less because if the content exceeds 65% by weight, chromium (II
I) Insufficient organic resin that plays a role in binding compounds,
The coating becomes brittle and peeling is likely to occur. In addition, a large number of through-holes reaching the steel surface from the coating surface are formed, and as a result of excessive supply of oxygen and water, rust generated is γ-Fe
OOH easily occurs and the anticorrosion property is reduced.

2. Organic resin The organic resin as a binder contained in the film is not particularly limited, and may be an epoxy resin, a urethane resin, a vinyl resin, a polyester resin, an acrylic resin, an alkyd resin, a phthal resin, a butyral resin, a melamine resin, a phenol resin, or the like. Is exemplified. When these resins are used as paints, there is no particular problem whether they are solvent-based paints or water-based paints. However, those that require heating for curing, such as phenolic resin (excluding those that cure at room temperature), or those that must be heated and melted when bonding, such as polyethylene resin, are workable and economical. This is not preferred.

3. Pigments, etc. In addition to salts and organic resins containing chromium ions, the above-mentioned coatings also contain coloring pigments such as red iron oxide, titanium dioxide, carbon black, and phthalocyanine blue, as well as constitutions such as talc, silica, mica, barium sulfate, and calcium carbonate. It may contain conventional additives such as pigments, anticorrosive pigments such as chromium oxide, zinc chromate, lead chromate, and basic lead sulfate, and other thixotropic agents, dispersants, and antioxidants. At the time of use, it is needless to say that the viscosity is adjusted to an appropriate level for the coating operation with an appropriate amount of a solvent or water to obtain a coating. These solvents or moisture evaporate by natural drying after coating the paint. It is considered that a part of the water contributes to the formation reaction of stable rust.

Further, iron sulfate, copper sulfate, nickel sulfate, phosphoric acid or the like, or an aqueous solution thereof may be added, which is rather preferable. Iron ions, copper ions, nickel ions or phosphoric acid have the effect of promoting the formation of chromium goethite when coexisting with chromium ions.

4. Coating In [Invention 1], after the above coating material has been applied and dried and solidified, if the coating becomes 5-150 μm, the supply balance of chromium ions and iron ions in the stage of forming weather-resistant stable rust is optimal, and the desired thickness is obtained. is there.

In [Invention 2] to [Invention 4], the reason for limiting the thickness of the film to the range of 5 to 150 μm is as follows.
If it is less than 1, a large number of pinholes are formed in the film, corrosion progresses in a rust-like manner from the pinhole portion, and the generated rust tends to be γ-FeOOH.
On the other hand, when the film thickness exceeds 150 μm, there is no problem in performance, but it is economically disadvantageous, which is contrary to the purpose of providing an inexpensive anticorrosion method which is an object of the present invention. That is, in the method of the present invention, the chromium (III) compound contained in the film is hydrolyzed to form chromium (III) ions while the condensed water permeates the film and reaches the steel surface, forming chromium (III) ions, and together with the water, Reach Chromium (III) ions form α-FeOOH, which is stable rust on the steel surface,
Alternatively, the transformation reaction from γ-FeOOH to α-FeOOH can be promoted to form a rust layer having high anticorrosion properties. As a result, even if peeling of the rust layer occurs due to corrosion on the steel surface over time, it is possible to prevent corrosion of the steel material by the stable rust layer formed thereafter. The thickness of the film can be arbitrarily changed within the limited range of the present invention. The above paints can be applied by the usual coating methods, such as air spray,
Since the coating can be performed by a conventional method such as airless spraying or brush coating, the coating can be performed at any place. In addition, since the effect can be obtained by one coating operation, the cost is also excellent. Furthermore, the stable rust layer is formed early after coating by coating after cutting or welding steel at the tank construction site, or by coating over rust while the tank is in use.

Further, since on-site painting is possible, it is possible to cope with the on-site processing such as cutting and welding of steel materials. The thickness of the film can be changed by adjusting the amount of application and the dilution ratio.

After the formation of the stable rust layer, the corrosion rate of the steel material becomes extremely low. Therefore, it is possible to further coat a colored coating on the above-mentioned coating. In this way, the steel further coated with a colored coating on the above film, compared with steel coated with a colored coating on bare specification steel material that has been blasted, etc.
The life of the colored coating can be extended.

Even if some external force acts on the stable rust layer to cause crack formation or peeling, if chromium ions remain in the coating film of the healthy part, the chromium ion from the healthy part at the crack part etc. It is needless to say that the so-called self-healing function, which produces a weather-resistant stable rust layer again, is exhibited.

Further, these films have cation selectivity in the first place, and have a function of suppressing the penetration of chloride ions until the resin is deteriorated. This helps to generate a stable rust layer at the interface.

5. Steel material, etc. The steel material of the tank targeted by [Invention 1] is a thick steel plate such as ordinary steel, low alloy steel, a shaped steel, or the like. Further, high-strength steel to which a thermomechanical treatment method (TMCP) is applied may be used.

The steel materials used for the steel towers of [Invention 2] to [Invention 3] are steel pipes, shaped steel, flanges, bolts, nuts and the like. Steel pipes include seamless steel pipes and welded steel pipes. As the section steel, an L section steel, an I section steel or the like can be used. It is desirable that the flange be welded to a steel pipe or the like in advance. For a steel pipe having a coating on its inner surface, it is preferable that the inner surface be coated by a method described later when the steel pipe is a single piece, or that the inner surface be coated after the flange is attached by welding. Further, the type of steel is not particularly limited, and may be ordinary steel or weather-resistant steel. That is, the chromium (II
I) By the action of the compound, the rust of ordinary steel is finally transformed into chemically stable and dense weatherable rust, and can exert a protective effect.

Further, unlike the conventional anticorrosive coating, it is not necessary to apply a blast treatment to the undercoating, and the coating can be performed even when the undercoat is rusty. This is because even if the base is rust of γ-FeOOH which promotes corrosion, γ-FeOOH is transformed into α-FeOOH by diffusion of chromium ions together with moisture from the chromium compound contained in the coating. It is. That is, even after several years have passed since the steel structure was built, the effect of the present invention can be exerted even if the coating of the method of the present invention is performed. Therefore, applying the coating of the method of the present invention to a steel structure having an inner surface several years after construction as described above also corresponds to the method of the present invention.

The steel tower is assembled almost without exception in the case of shaped steel by welding. On the other hand, in the case of a steel pipe, flanges attached by welding or welding to the steel pipe can be assembled by fastening with bolts and nuts.

As the steel material to be protected from corrosion of [Invention 4], a high-strength steel which is a low-alloy steel is often used, but a mild steel may be used. The assembly of the steel structure having the inner surface portion is mainly performed by welding the above-mentioned steel materials. However, the present invention is not limited to welding and may be assembled using bolts, nuts, or the like. The above-mentioned steel structure may be assembled locally, or a partially assembled structure may be installed while being modified locally. As described below, the members of the steel structure may be painted, then assembled, and finally finished.

[0060]

EXAMPLES Next, the effects of the present invention will be described with reference to examples. First, << Experiment 1 >> which is an embodiment of [Invention 1] will be described.

<Experiment 1> Table 1 shows the chemical components of a thick steel plate (plate thickness 25 mm) used in the test.

[0062]

[Table 1]

This steel plate is made of HT32 for shipbuilding (yield strength 3
2 kgf / mm ² or more).
150mm length x 70m for corrosion test from the above thick steel plate
A test piece of m width × 3 mm thickness was cut out and shot blasted.

Table 2 shows the compositions of the eight kinds of organic resins used in the test. Table 3 shows the composition of the solid content (that is, film) of the paint.

[0065]

[Table 2]

[0066]

[Table 3]

A solvent was added to the solid content shown in Table 3 to prepare a coating material having a viscosity of 200 to 1000 cps by a B-type viscometer, and applied by air spray. The test pieces thus produced were subjected to a two-month corrosion test in an environment simulating the gas-phase part of a seawater storage ballast tank and a cargo tank.

FIG. 1 is a schematic sectional view showing a test apparatus for simulating the gas phase environment of a seawater storage ballast tank, and FIG. 2 is a schematic sectional view showing a test apparatus for simulating the gas phase environment of a cargo tank.

Tables 4 and 5 show the test conditions of the corrosion test simulating the gas phase environment of the seawater storage ballast tank and the cargo tank, respectively.

[0070]

[Table 4]

[0071]

[Table 5]

Table 6 shows the results of these corrosion tests.

[0073]

[Table 6]

As shown in Table 3, in Comparative Examples 24 to 29, the chromium ion concentration was lower than the limited range of the present invention because the content of chromium sulfate in the solid content was low. As a result, as shown in Table 6, in the seawater storage ballast tank corrosion test, the average corrosion thickness was 30 to
It was 321 μm. In particular, in Test No. 24 having an organic resin film but having no chromium ion concentration and Test No. 29 having no coating, the average corrosion thickness was 1 for each.
It reached 53 μm and 321 μm.

On the other hand, Test Nos. 1-2 of the present invention examples
In No. 3, the average corrosion thickness in the seawater storage ballast tank corrosion test was 4 to 20 μm, and it was a clear result that the corrosion was suppressed. Such a difference in the average corrosion thickness corresponds to the formation of chromium goethite, and the formation of chromium goethite was clearly recognized as having a tendency to suppress the average corrosion rate.

The large average corrosion thickness in Test Nos. 24 to 29 and the correspondence between the formation of chromium goethite and the average corrosion thickness were the same in the cargo tank corrosion test. In Test No. 25, the formation of chromium goethite was slightly observed, but did not reach the point where corrosion was effectively suppressed.

Next, << Experiment 2 >> and << Experiment 3 >> which are examples of [Invention 2] and [Invention 3] will be described.

Table 7 is a list showing the chemical compositions of the steels used in << Experiment 2 >> and << Experiment 3 >>.

[0079]

[Table 7]

The following description will be divided into << Experiment 2 >> in which a simulated steel tower was actually manufactured and the corrosion resistance was tested, and << Experiment 3 >> in which a test was performed using a small-sized test piece.

<< Experiment 2 >> A steel pipe having the chemical composition of steel shown in Table 7 and having an outer diameter of 89.1 mm and a wall thickness of 4 mm, and an outer diameter of 27.
Using a steel pipe having a thickness of 2 mm and a wall thickness of 2.3 mm, a simulated steel tower having a height of 3 m was manufactured.

FIG. 3 is a schematic view of the simulated steel tower manufactured in << Experiment 2 >>. After removing the rust by blasting the steel pipe used for the production of the simulated steel tower, a coating material whose viscosity was adjusted by adding a solvent to the following compounding agent was applied to a film thickness (dry film thickness) of 15 μm.

Ingredients: 40% by weight of vinyl butyral resin as an organic resin, 15% by weight of chromium sulfate as a chromium (III) compound, 3% by weight of phosphoric acid, 18% by weight of bengara, 20% by weight of silica, 2% by weight of zinc chromate %, And 2% by weight of other additives (Test No. 14 in Table 12 described below).
Formulation). This formulation may be considered to represent the component composition of the film.

As the vertical pipe, three pipes each having a length of 1 m and an outer diameter of 89.1 mm were connected by flange connection. A flange was welded to the end of the steel pipe, and the coating was performed on all of the inner and outer surfaces of the steel pipe, the inner and outer surfaces of the flange, and the end face. The horizontal pipe used had a length of 0.8 m and 0.6 m and an outer diameter of 27.2 mm. The connection between the vertical pipe and the horizontal pipe is performed by welding,
The coating was previously removed from the welded portion with a power tool, and after welding, the coating was repainted with the same paint so as to have the same thickness. Also,
Both the horizontal and vertical pipe ends of the steel pipe are open so that rainwater flows into the inside of the steel pipe. As a comparative example of this simulated steel tower, a steel tower having the same structure as above without coating was manufactured.
Both were installed inland 100 m away from the coastline of Naoetsu City, Niigata Prefecture, and an exposure test was performed. After two years of exposure, the steel pipe was dismantled and the thickness of the inner and outer surfaces of the steel pipe and the flange was measured.

In the measurement of the thickness reduction, the inner surface corresponding to the measurement point on the outer surface and the outer surface corresponding to the measurement point on the inner surface were previously determined in order to distinguish the reduction amount on the inner and outer surfaces of the steel pipe. An anticorrosion seal was applied to the film with a thickness of 400 μm or more using a red epoxy. As for the flange, the anticorrosion seal was not performed.
The total thickness reduction of the upper and lower surfaces is shown.

In the measurement, after measuring points were cut out to remove the remaining film and the rust layer, a mechanical thickness measurement was performed to calculate a difference from the initial thickness. The measurement was 8
Went in places.

Table 8 is a list showing the average value of the thickness reduction.

[0088]

[Table 8]

In the comparative example, both the inner surface and the outer surface of the steel pipe had a thickness reduction of 50 to 60 μm. The flange showed a large thickness reduction of 130 μm. On the other hand, in the example of the present invention, the formation of stable rust was observed at any part of the interface between the steel and the film, and the result that the amount of corrosion was significantly suppressed was obtained.

<Experiment 3> The chemical composition of the test steel used in Experiment 3 is shown in Table 7.

Table 9 shows the treatment method before coating the steel material. Table 10 shows the composition of the organic resin contained in the paint.

[0092]

[Table 9]

[0093]

[Table 10]

The dimensions of the test piece were 150 × 70 × 3.2 m
m and the surface was subjected to a shot blast treatment before the coating treatment described in Table 9.

Tables 11 and 12 show the manufacturing conditions and test results of the samples.

[0096]

[Table 11]

[0097]

[Table 12]

Coatings were prepared by adding an appropriate amount of a solvent to the blending composition of the organic resin and the chromium compound shown in Tables 11 and 12 to obtain a coating composition of 200 to 1000 CPS in a B-type viscometer measurement, and applied by air spray coating. did. The solvent used was a mixture of toluene, xylene, isopropyl alcohol, methyl ethyl ketone, and the like, with the composition varied depending on the resin and the like. The sample test piece was placed in a thermo-hygrostat, and the following (a), (b) and (c) were defined as one cycle, and a combined cycle test of two cycles a day and 730 cycles a year was performed.

(A) Spray at 35 ° C., 0.5% salt water for 4 hours (b) 60 ° C., Rh (Relative humidity) 60% for 2 hours (c) 60 ° C., Rh 95% for 6 hours To simulate, a hot water immersion test was performed at a temperature of 50 ° C.

The presence or absence of stable rust formation (quenching of the stable rust portion) was confirmed by cross-sectional observation with a polarizing microscope of the sample after the test, and the case where a continuous film of stable rust was formed on the steel surface was evaluated: And

The corrosion rate of bare steel in an atmospheric corrosion environment was 30 μm / year on average, whereas the corrosion rate of bare metal in this test was 300 μm in the combined cycle and 200 μm in the immersion test. It is considered to have 10 times the corrosion promotion property in the combined cycle test and 7 times the corrosion promotion property in the immersion test adopted in the examples.

The above test results are shown in the combined cycle test and the immersion test in Tables 11 and 12.

Test Nos. 22 and 25, which are comparative examples, show that the content of the Cr (III) compound in the film is less than 0.1% by weight and that the film thickness is less than 5 μm. The formation was insufficient, resulting in insufficient corrosion protection. In addition, in the case of the conventional tar epoxy coating, a coating of 200 μm exhibits excellent corrosion protection, but corrosion of the base steel surface is gradually starting to occur. Can't expect. Also, above all, the economy is inferior. In the case of a tar epoxy resin coating as shown in Test Nos. 23 and 24 (organic resin code E), when the film thickness is reduced, as shown in Test No. 24, there is no formation of a stable rust film, so that the corrosion rate is extremely high. It was a big result.

On the other hand, Test No. 1 of the present invention example
In Nos. To 21, no generation of flow rust was observed, and it was recognized that stable rust was formed as a continuous film on the steel surface. Further, the corrosion rate was 40 μm / year or less, which corresponded to 6 μm or less in an actual environment. Such an anticorrosion effect was observed not only in the combined cycle test but also in the immersion test. That is, the anticorrosion effect was exhibited not only in the dry and wet repetitive environment simulated by the combined cycle test but also in the wet environment simulated by the immersion test.

In general, in a steel tower design, the margin for corrosion is estimated at 300 μm / 50 years. Therefore, the above-mentioned value of the amount of corrosion can be used for maintenance free without any special treatment other than the method of the present invention. Means possible. The method of the present invention is also effective when ordinary steel is used instead of weather-resistant steel as a base material. further,
The effect is exhibited even when the paint of the present invention is applied on the base rust layer. Therefore, as described above, the case where the steel tower is used for several years and then the coating of the method of the present invention is applied to meet the conditions of the method of the present invention also falls under the method of the present invention.

<Experiment 4> Table 13 shows the chemical composition of the test steel used in << Experiment 4 >>, and Table 14 shows the pretreatment of the steel material before coating. Table 15 shows the composition of the organic resin contained in the paint used for painting. The size of the test piece is 150 mm x 7
The surface before treatment shown in Table 14 was shot blasted.

[0107]

[Table 13]

[0108]

[Table 14]

[0109]

[Table 15]

Tables 16 and 17 show the manufacturing conditions and test results of the samples. An appropriate amount of a solvent was added to the composition of the organic resin and the additives constituting the films shown in Tables 16 and 17 to adjust the viscosity (measured by a B-type viscometer) to 200 to 100.
A paint with 0 CPS was prepared and air-sprayed. As described above, in Tables 16 and 17,
The “composition in the film” may be determined to be “the composition in the paint excluding water or solvent”.

[0111]

[Table 16]

[0112]

[Table 17]

This sample test piece was put in a thermo-hygrostat,
The following tests (a), (b) and (c) were performed for 1 cycle and 12 hours, and the test of dew condensation and drying over 2 cycles a day and 730 cycles a year was conducted.

(A) 15 ° C., Rh (Relative humidity) 60% for 4 hours (b) 60 ° C., Rh 95% for 6 hours (c) 60 ° C., Rh 60% for 2 hours Corrosion rate in an actual dew condensation environment such as a bridge is approximately. In contrast to 50 μm / year, the amount of corrosion of the plain steel
Since it was 0 μm, it was determined that the accelerating property was about 5 times or more.

The presence or absence of stable rust formation (quenching of the stable rust portion) was confirmed by cross-sectional observation with a polarizing microscope of the sample after the test, and the evaluation was made when a continuous film of stable rust was formed on the steel surface. And

The test results are shown in Tables 16 and 17. In Test Nos. 1 to 21 as examples of the present invention, generation of flow rust was not recognized, and it was recognized that stable rust was formed as a continuous film on the steel surface of the base. Also, the corrosion rate
It is 30 μm / year or less, which is equivalent to 6 μm or less in a real environment.

Generally, in bridge design, the margin of corrosion is estimated to be 300 μm / 50 years, so that the above corrosion results can be used for maintenance free without performing any special treatment other than the method of the present invention. Suggest that.
Further, the method of the present invention, not only weather-resistant steel as a base material,
Use of ordinary steel is also effective. Furthermore, even if a rust layer has already formed on the steel surface, the anticorrosion effect can be exerted by coating on it.

On the other hand, as shown in Test Nos. 22 and 25, which are comparative examples, the content of the chromium (III) compound in the film was 0.1%.
When the content is less than 1 wt% or the film thickness is less than 5 μm, the formation of stable rust becomes insufficient, and the anticorrosion property is reduced. Further, in the case of the conventional tar epoxy coating as in Test Nos. 23 and 24, a 200 μm film exhibits excellent corrosion protection, but the corrosion of the underlying steel surface has already started to occur gradually. Therefore, anticorrosion properties cannot be expected in the future. As described above, the economic efficiency is also poor. In the case of the tar epoxy coating, when the film thickness was reduced, as shown in Test No. 24, there was no formation of a stable rust layer, so that the corrosion rate became a very large value.

[0119]

According to the present invention, the corrosion of various steel tanks can be easily and inexpensively suppressed, which greatly contributes to industries related to transportation and storage of crude oil and the like. In addition, for steel towers, by producing stable rust on the steel material surface at an early stage, it exhibits excellent corrosion protection against water accumulation, air, and the like. A continuous stable rust layer is formed even in the dew condensation environment on the inner surface of the steel structure, and long-term corrosion protection can be imparted by inexpensive coating. The method of the present invention is an inexpensive manufacturing method, and is expected to contribute to enhancement of public facilities such as bridges in order to maintain maintenance-free and anticorrosive properties.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a test apparatus for simulating corrosion in a gas phase portion of a seawater storage ballast tank.

FIG. 2 is a schematic sectional view of a test apparatus for simulating corrosion in a gas phase portion of a cargo tank.

FIG. 3 is a schematic view showing a simulated steel tower used in Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Test piece 2 ... Artificial seawater 3 ... Constant temperature bath 4 ... Air inlet 5 ... Air outlet 6 ... Spray pump 7 ... Inert gas inlet 8 ... Inert gas outlet 11 ... Vertical steel pipe 12 ... Flange 13 ... Horizontal steel pipe

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C23C 22/30 C23C 22/30 C23F 11/00 C23F 11/00 BF

Claims (4)

[Claims] An organic resin and a trivalent chromium ion Cr ³⁺ having a content of 0.2 to 12.0% by weight based on solid content.
A method for preventing corrosion of steel tanks, which comprises applying a paint containing the same to a steel tank. 2. A chromium (III) compound content of 0.
A steel tower having a 1-65% by weight and a steel pipe provided with an organic resin film having a thickness of 5-150 μm and a normal steel pipe. 3. A steel tower to which the method of claim 2 is applied, or a steel tower constructed using ordinary steel pipes or shaped steel, has a chromium (I) content of 0.1 to 65% by weight of the solid content on the steel surface.
II) An organic resin paint containing a compound is coated with a film having a thickness of 5 to 15
An anticorrosion method for a steel tower, which is coated so as to have a thickness of 0 μm. 4. The chromium (III) having a solid content of 0.1 to 65% by weight on the inner surface of a steel structure having an inner surface.
The organic resin paint containing the compound has a thickness of 5 to 150 μm.
m.