JP2650007B2 - High corrosion resistant composite steel plate for tank bottom plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for a bottom plate of an oil storage tank for crude oil, petroleum, etc., and has an effect on the corrosion resistance of Al-
The present invention relates to a highly corrosion-resistant composite steel sheet of Zn and Zn.

[0002]

2. Description of the Related Art Oil storage tanks for crude oil, petroleum, and the like are generally installed on a sand foundation or an asphalt sand foundation and used for a long period of time. However, the tank bottom plate (steel plate) causes considerable corrosion. In extreme cases, it is extremely important to prevent this corrosion, since the corrosion holes may lead to the destruction of the tank. It is considered that the cause of the corrosion of the tank bottom plate is that the tank bottom plate is in direct contact with the base soil, and that moisture is oozing out from the ground or rain invades from around the tank, causing dew condensation on the bottom plate surface. Conventionally, the method mainly employed to prevent this corrosion is cathodic protection. That is, in the external power supply method or the sacrificial anode method, corrosion is prevented by placing the tank bottom plate on the cathode.However, in these methods, uniform current distribution is not obtained, so that complete corrosion protection is not achieved. Since hydrogen is generated on the side of the steel sheet, there is a big problem such as a problem of hydrogen embrittlement of the steel sheet. The use of an anti-corrosion steel sheet (Al coating) is also disclosed in Japanese Patent Application Laid-Open No. 57-171658, but this has not been put to practical use yet.

[0003]

According to the experimental results of the present inventors, according to the technique disclosed in the above-mentioned publication, once local corrosion occurs in Al, the sacrificial anticorrosion effect is extremely reduced due to the oxide film. It is considered to be weak and accelerated.
That is, the prior art has extremely many problems in completely preventing corrosion of the tank bottom plate, and a high corrosion resistant steel plate that completely prevents corrosion of the tank bottom plate has not been developed. An object of the present invention is to solve the above-mentioned drawbacks of the tank bottom plate anticorrosion method and provide a high corrosion-resistant composite sprayed steel plate capable of achieving maintenance-free tank bottom plate.

[0004]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method of forming a thermally sprayed thickness on the surface of a thick steel plate.
A Zn coating of 100 μm or more and 400 μm or less was provided.
Thickness 10 µm or more and 40 µm or less formed by thermal spraying on the surface
A Zn coating containing 5% or more and 55% or less of Al is provided, which is large in size and excellent in local corrosion resistance in soil.
High corrosion resistant composite steel sheet for oil storage tank bottom plate. Especially above
Is the soil of the present invention in the soil having a water content of 50% or more.
An excellent effect of local corrosion resistance in the inside is obtained . Ma
In addition, the present invention relates to a steel plate having a thickness of 100 μm or more 4
A Zn coating of not more than 00 μm is formed by thermal spraying,
Furthermore, when the thickness is 10 μm or more and 40 μm or less, 5% or more and 5% or more.
A Zn coating containing 5% or less of Al is formed by thermal spraying.
Large size with excellent local corrosion resistance in soil characterized by
A method for producing a high corrosion resistant composite steel plate for a bottom plate of a type oil storage tank.
You.

The Al concentration of the Al—Zn film is 5% or more and 55% or more.
% Or less is appropriate. That is, if it is less than 5%, the effect of corrosion resistance is small, and if it exceeds 55%, the natural electrode potential difference from the Zn coating becomes too large. Zn coating thickness is 100μ
m or more and 400 μm or less. If it is less than 100 μm, the minimum service life of the tank is 10 years, which is not enough to be maintenance-free. If it is more than 400 μm, the long service life can be secured, but the film thickness is too thick and the adhesion to the base steel sheet is too large. It is because it becomes impossible to secure. The thickness of the upper Al—Zn coating film is set to 10 μm or more and 40 μm or less. If the thickness is less than 10 μm, corrosion resistance is not secured because pinholes remain, and the thickness of the Al—Zn film is optimally about one tenth of the Zn film thickness, judging from the potential difference between the Al—Zn film and the Zn film. If it exceeds 40 μm, the degree of wear of the underlying Zn film is severe in preventing corrosion when a local corrosion hole is formed.
It was as follows. The coating is formed by thermal spraying as described above, and the thermal spraying may be performed by any method such as ordinary arc spraying (wire material, powder) and plasma spraying. After removing rust and surface adjustment of the black scale of the thick steel plate by blasting, Zn spraying is performed, and after reaching a predetermined film thickness, Al-Zn spraying may be performed immediately.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. FIG. 1 is a cross-sectional view of the present invention, wherein reference numeral 1 denotes a thick steel plate, reference numeral 2 denotes a Zn thermal spray coating, and reference numeral 3 denotes an Al—Zn thermal spray coating. First, the results of measuring the natural electrode potentials of the Al—Zn layer and the Zn layer are shown in Table 1. As is clear from the table, in the present invention 1, although the Al—Zn coating is initially more base than the Zn coating, it reverses over time, and
Corrosion protection with -Zn, and if local corrosion occurs in the Al-Zn coating, Z
The n-coat has the ability to resist this. On the other hand, when the Al concentration used as the comparative material exceeds 55%,
-The Zn coating material is the same as that of the present invention in the initial stage of corrosion, but after the corrosion, the potential difference becomes too large.

[Table 1]

Next, the composition and thickness of the Al—Zn coating
Table 2 shows the results of investigating the corrosion resistance and adhesiveness of various test materials in which the thickness of the coating was changed. As is clear from the table, in the case of Comparative Materials 1 to 6, those having an Al concentration of less than 5% in the Al-Zn coating film lack corrosion resistance, and those exceeding 55% have sufficient corrosion resistance but adherence. Poor performance, not practical. Further, the thickness of the Al—Zn coating is less than 10 μm, more than 40 μm, and the thickness of the Zn coating is 10 μm.
Those having a thickness of less than 0 μm have poor corrosion resistance and have a Zn coating of 400 μm.
A super-thick one has good corrosion resistance, but has poor adhesion and is not practical. On the other hand, in the case of the present inventions 7 to 9, the corrosion resistance and the adhesion are excellent. In Table 2, * 1 is the amount of film corrosion calculated by multiplying the maximum local corrosion amount that occurs when immersed in a lab at room temperature for one year in masago soil having a water content of 64% by 10 times, and * 2 is * 2. In the results of the right angle bending test, ○ is good and X is bad.

[Table 2]

[0008]

According to the present invention, thermal spraying is performed on the surface of a thick steel plate.
Therefore, a Zn film having a thickness of 100 μm or more and 400 μm or less
And further sprayed on the surface with a thickness of 10 μm or more and 40 μm or more.
A Zn coating containing Al of 5% or more and 55% or less at μm or less
As a result , the obtained high corrosion resistant composite steel sheet for tank bottom plates is excellent even in soil, particularly in soil having a water content of 50% or more.
The anti-corrosion effect has been greatly improved, and the service life of the tank bottom plate can be greatly extended, so that maintenance costs can be significantly reduced as compared with the conventional cathodic protection method, etc. It is also extremely effective in securing the properties.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a high corrosion resistant composite sprayed steel plate for a tank bottom plate according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thick steel plate 2 Zn spray coating 3 Al-Zn spray coating

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Eiichi Endo 20-1 Shintomi, Futtsu City, Chiba Prefecture Nippon Steel Corporation Technology Development Division (56) References JP-A-4-99287 (JP, A) JP-A-62-30867 (JP, A) JP-A-61-295399 (JP, A) JP-A-56-133691 (JP, A) JP-A-54-128015 (JP, A) JP-A-53-127334 (JP, A) JP-A-49-102739 (JP, A) JP-A-46-54771 (JP, A) Proceedings of the 32nd Symposium on Corrosion and Corrosion Prevention, (Showa 60-8), P. 282-285

Claims (3)

(57) [Claims] 1. A thermal spray-formed thickness of 10 on a thick steel plate surface.
A Zn coating of 0 μm or more and 400 μm or less is provided, and
Further, when the thickness of the sprayed film is 10 μm or more and 40 μm or less, 5
Large oil storage having excellent local corrosion resistance in soil , characterized by providing a Zn coating containing Al of at least 55% and not more than 55%.
High corrosion resistant composite steel plate for storage tank bottom plate. 2. The soil has a water content of 50% or more.
A large-sized soil excellent in local corrosion resistance in soil according to claim 1.
High corrosion resistant composite steel plate for oil storage tank bottom plate. 3. A steel sheet having a thickness of 100 μm or more
A Zn coating of not more than 00 μm is formed by thermal spraying,
Furthermore, when the thickness is 10 μm or more and 40 μm or less, 5% or more and 5% or more.
A Zn coating containing 5% or less of Al is formed by thermal spraying.
Large size with excellent local corrosion resistance in soil characterized by
Of high corrosion resistant composite steel sheet for bottom plate of oil storage tank .