JPS62196384A - Electrolytic protection method for metallic structure - Google Patents

Abstract

PURPOSE:To prevent the corrosion of a metallic structure in the atm. by providing a conductive coating material via an electrolytic coating material to the part in the atm. of the metallic structure installed across the atm. and sea water, further covering the surface thereof with a water absorptive and retentive mat and attaching a galvanic anode to the part in the sea water. CONSTITUTION:The part to be exposed above the sea during the high tide of a steel pipe pile or the like 1 which is installed across the sea water and the atm. which is highly corrosive by the sea water, the splashes of the sea water, etc., is cleaned and the mortar electrolytic coating material 2 which is added with an org. resin and has good adhesiveness is injected and struck to said part 2-3mm thickness. The conductive coating material 3 contg. graphite powder, Ni powder, etc., as a conductive filler and consisting of an urethane, epoxy or acrylic resin as a binder is coated thereon to 300-500mum thickness. The water absorptive and retentive mat 6 consisting of a polyurethane resin or the like is then coated on the outside surface in the lower part of the material 3 down to at least about the surface at the low tide level and the galvanic anode 4 consisting of an Al alloy, etc. is welded by a steel core metal 5 onto the part in the sea water of the steel pipe pile 1. The corrosion preventiveness of the steel pipe pile in the atm. on the sea water having high corrosiveness is thus improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is applicable to metal structures that span an atmospheric environment and an electrolyte environment, such as steel pipe piles in port facilities;
Concerning cathodic protection methods for steel sheet piles, etc.

[Conventional technology]

The tidal zone and splash zone of steel pipe piles, steel sheet piles, etc. in the marine environment are subject to repeated drying and wetting, and are subject to the most severe corrosion because they are constantly supplied with abundant oxygen.

Conventionally, as a corrosion prevention method that has been put into practical use in such a corrosive environment, a corrosion prevention device (for example, the 51 -36341 Publication) or a corrosion-proof coating in which a protective cover made of fiber-reinforced plastic is coated with a petrolatum-based corrosion-proofing material and a cushioning material such as plastic foam is attached to the outside (for example,
Utility Model Publication No. 56-9703) etc. have been put into practical use, and cathodic protection devices covered with a water-absorbing and water-retaining mantle and having galvanic anodes attached thereto (for example, Utility Model Publication No. 51-172) have been put into practical use.
No. 10) has been proposed.

(Problems to be Solved by the Invention) However, in the above-mentioned anti-corrosion device, since the anti-corrosive material has the property of being penetrated by seawater, special attention must be paid to the water honey structure at the lower end.

In addition, the anti-corrosion coating can prevent the intrusion of seawater into the anti-corrosion layer in the case of single steel sections and steel pipes, but steel sheet piles and steel pipe sheet piles that are constructed by connecting single steel materials at connecting parts. However, there is a problem in that a gap is created between the anti-corrosion layer and the protective cover, allowing seawater to enter the anti-corrosion layer and deteriorating the performance of the anti-corrosion layer.

Currently, there is no means for continuously confirming the anticorrosion effect of both of these methods, and maintenance problems remain in that the development of anticorrosion monitoring technology is slow.

On the other hand, in the electrolytic protection device, there is a limit to the height at which the water absorption and water retention property 771 wrapped around the splash band can absorb moisture.
Even when cathodic protection is possible, moisture and oxygen are abundantly supplied, so there is a drawback that a higher than necessary corrosion protection electrical density is required.

This invention solves the above-mentioned problems of conventional structures, and provides an economical solution to metal structures that span both atmospheric and electrolytic environments without requiring a watertight structure and with a low corrosion protection current density. Enabling cathodic protection and further simplifying IJv
It is an object of the present invention to provide an extremely effective cathodic protection method that makes it easy to determine the corrosion protection effect by measuring electric potential G.

[Means for solving problems]

This invention succeeded in achieving the above objective by making it possible to apply cathodic protection methods to metal structures in the atmospheric environment, which was theoretically impossible. It is structured as follows.

That is, the corrosion prevention method for metal structures according to the present invention is as follows:
The surface of the structure in the atmospheric environment is coated with an electrolyte coating, the electrolyte coating is coated on top of the electrolyte coating, and the surface of the structure in the electrolyte environment is coated with a water-absorbing and water-retaining mat covering the conductive coating. At the same time, a cathodic protection device is installed on the structure in an electrolyte environment so that a part of the anticorrosive current flowing into the structure passes through the water-absorbing water-retaining mat and the conductive coating.

[For production]

In the cathodic protection method configured in this way, the corrosion protection current i due to cathodic protection flows directly into the surface of the metal structure in the electrolyte environment and maintains the surface in a good corrosion protection state. The current 51 first flows through the water-absorbing and water-retaining mat in the electrolytic environment to the outer surface of the conductive coating in the atmospheric environment, and then flows through the electrolytic coating to the surface of the structure in the atmospheric environment. flows to provide a uniform potential distribution to the surface.

Since the conductive coating acts as a wide current distribution electrode, the anodic current density is low and the degree of consumption of the conductive coating is extremely low.

〔Example〕

Hereinafter, an example of the present invention will be explained based on the drawings.

FIG. 1 is a schematic cross-sectional view of a pier steel pipe pile. In Fig. 1, the part of the steel pipe pile 1 to be coated, that is, the surface treatment is applied to the level of Type 3 polishing with a wire brush from the upper end to about the high tide level to remove floating rust, marine organisms, algae, etc. is removed, and an electrolytic coating 2, such as a mortar-based coating with good adhesion to which an organic resin or the like is added, is applied to the surface.
Spray and weld 0x slurry (product name) manufactured by Showa Sekiyu θ-sun) to a film thickness of 2 to 3 coats. The electrolytic coating 2 should preferably be porous and have excellent water retention properties, and it is optimal if it has high alkalinity since it can reduce the anti-corrosion current.

The electrolytic coating 2 may be a mortar-based coating or a water-absorbing polymer, a compound of bentonite and gypsum, Ohergrau, or the like.

Furthermore, a conductive coating 3, such as a conductive paint, is applied to the surface of the electrolyte layer. This conductive paint is a highly weather-resistant paint made of urethane, Evokin, and acrylic resin binder mixed with conductive fillers such as grapha (Grapha®), carbon powder, nickel powder, lead peroxide powder, or zinc dust. use.

The film thickness of these paints may be approximately 300 to 500μ, and when applying this paint, leave holes for potential measurement at appropriate sizes and intervals, and place a reference electrode on the exposed mortar surface. The corrosion protection effect of steel pipe piles in atmospheric environment is determined by pressing against them and measuring the potential.

The conductive coating 3 is made of a conductive paint, a seal-shaped conductive resin, or a corrosion-resistant gold E (Ti, Ta, Nb, Cu).
In addition, conductive composite coatings with different natural potentials can be used, such as those coated with conductive paint on corrosion-resistant fully-flexible sheet I, or those made by gluing a conductive resin sheet and a corrosion-resistant fully-flexible sheet. You can also.

This conductive composite coating is a conductive coating having a base potential (
The electromotive force can be reduced by attaching the conductive paint or conductive resin sheet 1-) on the electrolyte coating side and the conductive coating with a noble potential (corrosion-resistant fully flexible sheet) on the electrolyte environment side. is ideal for use in high resistance environments.

Further, it is effective to further strengthen the outer surface of the conductive coating by covering it with a fiber-reinforced plastic cover or the like.

Next, a water-absorbing and water-retaining material 1.6 is applied to the surface of the steel pipe pile 1 from the lower outer surface of the conductive covering 3 to at least about 1,000 to 1,000 yen.

This Man 1-6 is made of water-absorbing polymers such as Polyurekne resin and synthetic fiber paper.

On the other hand, a galvanic anode 4 made of 81 alloy, Zn alloy, Mg alloy, etc. is attached to the surface of a steel pipe pile in the sea by welding its steel core 5. It goes without saying that in addition to this galvanic anode type cathodic protection, an external power source type cathodic protection has the same effect.

In the above example, the pier steel pipe pile was explained as an example, but
The present invention is not limited thereto, and can be used for structures made of gold IFS that span an atmospheric environment and an electrolyte environment, such as the inner surface of a tank containing a corrosive liquid or the outer wall and bottom plate of a land tank.

〔Effect of the invention〕

As explained above, according to the method of the present invention, the conductive coating acts as a distributed electrode for cathodic protection and as a shield from the atmosphere, so that the steel surface in the atmospheric environment can be uniformly protected from corrosion over a wide range.

Therefore, cathodic protection can be applied as a through-hole for structures that span both atmospheric and electrolytic environments, so there is no need for a watertight structure, and the corrosion-protected state can be maintained simply by measuring the potential after construction. You can easily check if it is.

Furthermore, since oxygen and the like are blocked, the corrosion protection current density of steel materials in an atmospheric environment can be reduced, and can be further reduced if a mortar-based ml material is used as the electrolyte coating.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing an embodiment of the present invention.

Claims (1)

[Claims] A method for preventing corrosion of a metal structure that spans an atmospheric environment and an electrolyte environment, the method comprising: coating the surface of the structure in the atmospheric environment with a conductive coating via an electrolyte coating; The surface of the structure in an electrolyte environment is covered with a water-absorbing and water-retaining mat, and a cathodic protection device is installed on the structure in the electrolyte environment so that some of the corrosion protection current flowing into the structure absorbs water. A method for cathodic protection of metal structures, characterized by passing through a water-retaining mat and a conductive coating.