JPS61178891A - Corrosionproof method of tank bottom plate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for preventing corrosion of a tank bottom plate in a tank for storing crude oil or the like.

[Prior art and problems]

The tank bottom plate is installed on top of the tank foundation, such as an oil sand layer or a concrete layer, but the outer surface of the tank bottom plate is particularly susceptible to corrosion as it comes into contact with moisture and oxygen contained in the tank foundation. be.

For this reason, various anticorrosion methods have heretofore been implemented to protect tank bottom plates from corrosion, examples of which include cathodic protection methods such as the external power source method and the galvanic anode method. The external power supply method here refers to a method in which the tank bottom plate is connected to the negative pole of a DC power supply, and at the same time, an auxiliary electrode installed underground is connected to the positive pole of the power supply, thereby applying a corrosion protection current to the tank bottom plate. The galvanic anode method is a method in which the tank bottom plate is electrically connected to a metal at a low potential underground (for example, zinc for iron), and a corrosion protection current is passed through the tank bottom plate by battery action.

However, the above-mentioned cathodic protection method has the following drawbacks, and therefore has the problem of lacking reliability as a long-term corrosion protection method.

(1) It is difficult to uniformly apply anti-corrosion current to the tank bottom plate, which causes localized corrosion and thinning areas.

(2) Hydrogen generated at the cathode causes hydrogen embrittlement of the tank bottom plate.

(3) Aside from the outer surface of the tank bottom plate, separate anti-corrosion measures are required for the inner surface.

In addition to the cathodic protection method described above, a surface treatment anticorrosion method is also known in which a coating layer is formed on the outer surface of the tank material, but this requires additional anticorrosion measures for the inner surface of the tank material.

Furthermore, if there is a welded part on the tank bottom plate, the nature of the material of the tank bottom plate will not interfere with the welding work.
At present, there is no well-balanced corrosion prevention method that has a sufficient corrosion prevention function.

[Purpose of the invention]

An object of the present invention is to provide a corrosion prevention method for a tank bottom plate that eliminates all of the above problems.

[Structure of the invention]

The present invention is a method for preventing corrosion of a tank bottom plate, characterized in that a steel material coated on both sides with an anti-corrosion coating material is used as the tank bottom plate, and a steel material not coated with the anti-corrosion coating material is used for the welded part of the tank bottom plate, This is a corrosion prevention method in which the entire surface of the weld is coated with an anti-corrosion material after welding is completed, and when the weld is butt welded, a backing steel material is placed on the back of the weld. This is a corrosion prevention method in which the entire surface of the welded part is coated with an anticorrosion coating material after the welding is completed and welded, and if necessary, thermoplastic resin, thermosetting resin, rubber, or bitumen is applied to the back surface of the welded part. This is a corrosion prevention method in which a water-impermeable material made of one or more substances selected from among substances is filled prior to welding, and this water-impermeable material is hardened by welding heat.

[Embodiments of the invention]

Next, the present invention will be described with reference to embodiments shown in the drawings.

FIG. 1 is a vertical cross-sectional view of a steel material used in the corrosion prevention method of the present invention, where 1 is a steel material and 2 is an anticorrosion coating material coated on both sides of the steel material. Examples include plastic resins (polyethylene resin, polyvinyl chloride, etc.), thermosetting resins (polyurethane resin, acrylic resin, etc.), inorganic filled resins, fiber-reinforced resins, rubber, and the like.

The material for this anti-corrosion coating 2 is determined based on the tank foundation side (
The optimum one must be selected depending on the humidity, properties of the base sand, components of infiltrated water from the outside, etc.), and the internal fluid conditions of the tank (eg, properties, temperature, etc.).

Furthermore, as a method for coating steel material l with anti-corrosion coating material, first, the rust etc. on the surface of the steel material is removed and the entire surface is cleaned, and then coating, thermal spraying, crimping, or a combination of these methods is used. It is done.

Next, Fig. 2 is a longitudinal cross-sectional view when forming a tank bottom plate by welding steel materials, and Fig. 2A shows the case of butt welding, and Fig. 2B shows the case of lap fillet welding. In the case of , the steel parts corresponding to the welded parts are not coated with anti-corrosion coating material, and as a result, the weld metal 3 built up by welding can directly adhere to the exposed steel material, so the welding effect is perfect, and the anti-corrosion coating Care has been taken to ensure that the material does not interfere with welding work.

In addition, in the case of butt welding where the edges of chamfered steel materials are lined up on the same plane, if necessary, a backing steel material 4 is placed on the back side of the welded part to ensure the finish of the welded part. (See Figure 2A).

Note that in the case of lap fillet welding in which the ends of the steel materials are shifted and overlapped, the backing steel material may be omitted (see FIG. 2B).

Next, whether the backing steel material 4 is superimposed on the back surface of the welded part or not, the backing steel material 4 is placed near the back surface of the welded part (
If a backing steel material 4 is present, an impermeable material 5 having a waterproof function is filled below the backing steel material, and the welding heat during welding is used to harden this impermeable material. This is a suitable corrosion prevention method. This water-impermeable material ensures a seal between the welded portion and the tank foundation 6, and it becomes possible to eliminate the cause of corrosion to the steel material and weld metal transmitted from the tank foundation 6 side.

Here, the water-impermeable material 5 is a thermoplastic resin (polyethylene resin, polyvinyl chloride, etc.), a thermosetting resin (polyurethane resin, acrylic resin, phenolic resin, etc.)
, inorganic filled resin, fiber reinforced resin, rubber (such as liquid rubber), or bituminous material.

Furthermore, it is sufficient for the water-impermeable material 5 to have water-blocking ability, and it is even more convenient if it has adhesive strength for sealing.If it does not have adhesive strength, a liquid adhesive may be used together with the tank bottom plate. If there is a gap between the bonding surface between the tank bottom plate and the backing steel, corrosive fluids such as moisture from outside will enter through the gap due to capillary action, and if left for a long time, the welded metal part will be selectively corroded.

After the welding of the welded area is completed as described above, the exposed surface of the welded area and the deposited metal are completely covered with anti-corrosion coating material 2 to complete the tank bottom plate (see Figure 3 A-B). )
.

〔Effect of the invention〕

Therefore, the present invention has excellent advantages such as improving the anti-corrosion function of the tank bottom plate, extending the life of the tank equipment, and significantly reducing the maintenance cost of the tank equipment compared to the cathodic protection method. have an effect.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of a steel material used in the corrosion prevention method of the present invention;
Figure 2 is a longitudinal cross-sectional view when forming a tank bottom plate by welding steel materials, where A is for butt welding, B is for lap fillet welding, and Figure 3 is for the previous time. It is a longitudinal sectional view of the completed state in , and A and B are the same as the previous one. 1... Steel material 2... Anti-corrosion coating material 3... Welded metal 4...
Backing steel material 5... Impermeable material 6...
・・Tank foundation - Two 71 Figure 2A Figure 2B

Claims (1)

[Scope of Claims] 1. A method for preventing corrosion of a tank bottom plate, characterized in that a steel material coated on both sides with an anti-corrosion coating material is used as the tank bottom plate. 2. The welded portion of the tank bottom plate is made of steel material that is not coated with an anticorrosion coating material, and after the welding of the welded portion is completed, the entire surface of the welded portion is covered with the anticorrosion coating material, as described in claim 1. Corrosion prevention method. 3. When welding a tank bottom plate by butt welding, a backing steel material is superimposed on the back side of the weld and welding is performed, and then the entire surface of the weld is covered with an anti-corrosion coating material. The corrosion prevention method according to item 1 or 2. 4. Fill the vicinity of the back side of the welded part of the tank bottom plate with an impermeable material made of one or more substances selected from thermoplastic resin, thermosetting resin, rubber, or bituminous material prior to welding. The corrosion prevention method according to claim 1, 2 or 3, wherein the water-impermeable material is hardened by welding heat.