JPH0224914B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a cathodic protection method for metal structures that span an atmospheric environment and an electrolyte environment, such as steel pipe piles and steel sheet piles in port facilities. Regarding.

[Conventional technology]

In the marine environment, steel pipe piles, steel sheet piles, etc., are subject to repeated drying and wetting, and are subject to the most severe corrosion because they are constantly in an abundant supply of oxygen.

Conventionally, corrosion prevention methods that have been put to practical use in such corrosive environments include corrosion prevention devices in which anticorrosive materials such as concrete and mortar are injected between steel pipe piles and fiber-reinforced plastic formwork (for example, -36341 Publication) and anti-corrosion coatings that are coated with a petrolatum-based corrosion-proofing material and covered with a protective cover made of fiber-reinforced plastic with a cushioning material such as plastic foam affixed to the outside (for example,
-9703 Publication) etc. have been put into practical use, and cathodic protection devices (for example, Utility Model Publication No. 51 -
17210) has been proposed.

[Problem that the invention seeks to solve]

However, since the anti-corrosion device has the property of being penetrated by seawater, special attention must be paid to the watertight structure of the lower end.

Furthermore, the above-mentioned anti-corrosion coating can prevent seawater from entering the anti-corrosion layer in the case of single steel sections and steel pipes, but in the case of steel sheet piles and steel pipe sheet piles that are constructed by connecting single steel members at joints. There is a problem in that a gap is created between the anti-corrosion layer and the protective cover, and seawater infiltrates into the anti-corrosion layer, degrading the performance of the anti-corrosion layer.

Currently, there is no means to continuously check the corrosion prevention effect of both of these methods, and maintenance problems remain, such as the delay in the development of corrosion prevention monitoring technology.

On the other hand, in the cathodic protection device, there is a limit to the height of water absorption by the water-absorbing and water-retaining pine wrapped around the splash zone, and even if cathodic protection is possible, moisture and oxygen are supplied in abundance. It has the disadvantage 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. It is an object of the present invention to provide an extremely effective cathodic protection method that makes it possible to perform cathodic protection and to easily judge the corrosion protection effect through simple potential measurement.

[Means for solving problems]

This invention applies to metal structures in the atmospheric environment.
By making it possible to apply the cathodic protection method, which was theoretically impossible, we succeeded in achieving the above object, and it has the following structure.
That is, the method for preventing corrosion of a metal structure according to the present invention includes: coating the surface of the structure in an atmospheric environment with an electrolytic coating, and coating the top with an electroconductive coating;
Further, the surface of the structure in the electrolyte environment is covered with a water-absorbing and water-retaining mat over this conductive coating, and a cathodic protection device is installed on the structure in the electrolyte environment, and the water flowing into the structure is provided with a cathodic protection device. The anti-corrosion current in the area is routed through the conductive coating through the water-absorbing and water-retaining pine.

[Effect]

In the cathodic protection method configured in this way,
The corrosion protection current i caused by 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. It flows through the water-retaining mat to the outer surface of the conductive coating in the atmospheric environment, flows through the electrolyte coating to the surface of the structure in the atmospheric environment, and creates a uniform potential distribution on the surface. give.

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

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a schematic cross-sectional view of a pier steel pipe pile. In FIG. 1, the portion of the steel pipe pile 1 to be covered,
That is, surface treatment is performed using a wire brush to remove floating rust, marine organisms, algae, etc., from the upper end to about the high tide level, and then the electrolyte coating 2, such as organic resin, etc. is applied to the surface. A mortar-based coating with good adhesion (trade name: Melox Slurry, manufactured by Showa Sekiyu Co., Ltd.) containing 2 to 3 mm thick is spray-welded. This electrolyte coating 2 is
A material with excellent porous water retention is preferred, and a material with high alkalinity is optimal because it can reduce the anticorrosion current.

As the electrolytic coating 2, in addition to a mortar-based coating, a water-absorbing polymer, Oher grout, a mixture of bentonite and gypsum, or the like can be used.

Furthermore, a conductive coating 3, such as a conductive paint, is applied to the surface of the electrolyte layer. This conductive paint uses a highly weather-resistant paint made of urethane, epoxy, or acrylic resin binder mixed with graphite powder, carbon powder, nickel powder, lead peroxide powder, or zinc powder as a conductive filler. The film thickness of these paints should be about 300 to 500μ, and when painting with this paint, leave holes for potential measurement at appropriate sizes and intervals.
A reference electrode is pressed against the exposed mortar surface and the potential is measured to determine the corrosion protection effect of steel pipe piles in the atmospheric environment.

The conductive coating 3 is made of a conductive paint, a sheet-like conductive resin, or a corrosion-resistant metal (Ti, Ta, Nb,
Cu), etc. can be used, and conductive composite coatings with different natural potentials, such as a corrosion-resistant metal sheet coated with conductive paint or a conductive resin sheet and a corrosion-resistant metal sheet laminated together, can be used. You can also do it.

This conductive composite coating is a conductive coating (conductive paint or conductive resin sheet) that has a base potential.
By attaching the conductive coating (corrosion-resistant metal sheet) with a noble potential to the electrolytic coating side and the electrolyte environment side, the electromotive force increases, making it ideal for use in high resistance environments. be.

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

Next, the water-absorbing and water-retaining mat 6 is attached to the conductive coating 3.
Cover the surface of the steel pipe pile from the outer surface of the lower part to at least the low tide level.

This mat 6 is made of polyurethane resin, synthetic fiber paper, water-absorbing polymer, or the like.

On the other hand, a galvanic anode 4 made of Al 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.

Although the above embodiments have been explained using pier steel pipe piles as an example, the present invention is not limited to this. Can be used for metal structures that span.

〔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 it is possible to uniformly prevent corrosion over a wide range of steel surfaces in an atmospheric environment. can.

Therefore, cathodic protection can be consistently applied to structures that span both atmospheric and electrolyte environments, so there is no need for a watertight structure, and corrosion protection can be maintained simply by measuring the electrical 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 coating is used as the electrolytic coating.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view showing one embodiment of the present invention. 2... Electrolyte coating, 3... Conductive coating,
4... Galvanic anode, 6... Water-absorbing and water-retaining mat.

Claims (1)

[Claims] 1 A method for preventing corrosion of a metal structure that spans both an atmospheric environment and an electrolyte environment, wherein the surface of the structure in the atmospheric environment is coated with a conductive coating via an electrolyte coating, and the conductive coating is The surface of the structure in an electrolyte environment is covered with a water-absorbing and water-retaining mat across the electrolyte coating, and a cathodic protection device is installed on the structure in the electrolyte environment to prevent corrosion of a portion of the structure flowing into the structure. A method for cathodic protection of metal structures, characterized in that the electric current is passed through a conductive coating through a water-absorbing, water-retaining pine.