JP2014201758A - Steel material for crude oil tank with excellent corrosion resistance, and crude oil tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel material for a crude oil tank which has excellent whole surface corrosion resistance on a top plate of a crude oil tank such as a tanker oil tank part and excellent local corrosion resistance on a bottom plate of the crude oil tank.SOLUTION: A steel material for a crude oil tank has a chemical composition comprising, in mass%, C: 0.03-0.18%, Si: 0.03-1.50%, Mn: 0.1-2.0%, P: 0.025% or less, S: 0.010% or less, Al: 0.005-0.10%, N: 0.008% or less, Co: 0.001-0.5%, Cu: 0.05-0.4%, Ni: 0.01-0.4%, Mg: 0.0002-0.01% and Cr: more than 0.1% and 0.5% or less, and one or two selected from W: 0.01-1.0% and Mo: 0.01-0.5%, with the balance being Fe and inevitable impurities.

Description

The present invention relates to an oil tank of a crude oil tanker formed by welding steel materials or a tank for transporting or storing crude oil (hereinafter collectively referred to as “crude oil tank”). The present invention relates to a steel material for a crude oil tank that reduces the overall corrosion that occurs at the ceiling and side walls and the local corrosion that occurs at the bottom of the crude oil tank, and a crude oil tank that is composed of the steel material.
In addition, the steel material for crude oil tanks of the present invention includes thick steel plates, thin steel plates, and shaped steels.

It is known that the steel used on the inner surface of a tanker's crude oil tank, particularly on the back of the upper deck and the upper part of the side wall, is totally corroded. As a cause of this total corrosion,
(1) Repeated condensation and drying (wet and dry) on the steel sheet surface due to temperature difference between day and night,
(2) Inert gas enclosed in crude oil tanks for explosion protection (O ₂ approx. 4 vol%, CO ₂ approx. 13 vol%, SO ₂ approx. 0.01 vol%, remaining N ₂ as representative composition boiler or engine exhaust gas, etc.) Of O ₂ , CO ₂ , SO ₂ into condensed water,
(3) Dissolution of corrosive gas such as H ₂ S volatilized from crude oil into condensed water,
(Four) For example, residual seawater used to clean crude oil tanks.
These can be recognized from the fact that sulfate ions and chloride ions are detected in strongly acidic condensed water during dock inspections of actual ships that are usually conducted every 2.5 years.

In addition, when H ₂ S is oxidized using iron rust generated by corrosion as a catalyst, solid S is formed in layers in the iron rust, but these corrosion products easily peel off and fall off, and the crude oil tank Deposit at the bottom of the. For this reason, in the dock inspection, the current situation is that repair of the upper part of the tank and collection of deposits at the bottom of the tank are performed with great expense.

On the other hand, steel materials used as bottom plates for tankers' crude oil tanks, etc., have been affected by the corrosion of the crude oil itself and the protective action of oil-derived protective coat (oil coat) formed on the inner surface of the crude oil tank. It was thought not to occur. However, recent research has revealed that bowl-shaped local corrosion (pitting corrosion) occurs in the steel of the tank bottom plate. As a cause of such local corrosion,
(1) Presence of condensed water in which salts represented by sodium chloride are dissolved at a high concentration,
(2) Oil coat detachment due to excessive cleaning,
(3) Increase the concentration of sulfides contained in crude oil,
(4) High concentration of O ₂ , CO ₂ , SO _2, etc. in the explosion-proof inert gas dissolved in the condensed water
Etc.
Actually, when the water stayed in the crude oil tank was analyzed during the dock inspection of the actual ship, high concentrations of chloride ions and sulfate ions were detected.

  By the way, the most effective method of preventing the above-mentioned general corrosion and local corrosion is to apply heavy coating on the surface of the steel material to shield the steel material from the corrosive environment. However, the painting operation of the crude oil tank not only has an enormous application area, but also requires repainting once every 10 years due to the deterioration of the coating film, resulting in an enormous cost for inspection and painting. Furthermore, it has been pointed out that corrosion is promoted in the damaged part of the heavy-painted coating film in the corrosive environment of the crude oil tank.

For the corrosion problem as described above, several techniques for improving the corrosion resistance of the steel material itself in the corrosive environment of the crude oil tank have been proposed.
For example, in Patent Document 1, in mass%, C: 0.001 to 0.2%, Si: 0.01 to 2.5%, Mn: 0.1 to 2%, P: 0.03% or less, S: 0.02% or less, Cu: 0.01 to 1.5% , Al: 0.001 to 0.3%, N: 0.001 to 0.01%, Mo: 0.01 to 0.5%, and W: 0.01 to 1%, or the balance of Fe and unavoidable impurities A technique for forming a welded joint so that the contents of Cu, Mo, and W in the weld metal satisfy the following three expressions when welding the steel materials to form a welded joint is disclosed.
3 ≧ Cu content of weld metal (mass%) / Cu content of steel (mass%) ≧ 0.15
3 ≧ (Mo content of weld metal + W content (mass%)) / (Mo content of steel + W content (mass%)) ≧ 0.15
−0.3 ≦ Cu content of weld metal (mass%) − Cu content of steel (mass%) ≦ 0.5

Further, in Patent Document 2, in mass%, C: 0.001 to 0.2%, Si: 0.01 to 2.5%, Mn: 0.1 to 2%, P: 0.03% or less, S: 0.02% or less, Cu: 0.01 to 1.5 %, Al: 0.001 to 0.3%, N: 0.001 to 0.01%, Mo: 0.01 to 0.5%, and W: 0.01 to 1%, or the remainder, Fe and inevitable impurities A technique for forming a welded joint so that the contents of Cu, Mo, and W in the weld metal satisfy the following two equations when welding a steel material made of the above to form a crude oil tank is disclosed.
3 ≧ Cu content of weld metal (mass%) / Cu content of steel (mass%) ≧ 0.15
3 ≧ (Mo content of weld metal + W content (mass%)) / (Mo content of steel material + W content (mass%)) ≧ 0.15

JP 2005-21981 JP 2005-23421 A

  In order to protect the marine environment and operate the crude oil tanker safely, it is important to manage the crude oil tank so that it does not leak, and it is necessary to prevent the occurrence of through holes due to corrosion in the crude oil tank. . Therefore, when the docking is done every 2.5 years, the corrosion status of the bottom plate of the crude oil tank is investigated, and pitting corrosion over 4 mm deep is repaired, in order to reduce the maintenance cost of the crude oil tanker. Thus, the application of corrosion resistant steel to tankers has been proposed as one of the means for suppressing the occurrence of pitting corrosion with a depth of more than 4 mm.

  However, with the techniques described in Patent Documents 1 and 2, it is difficult to suppress local corrosion (pitting corrosion) generated on the tanker bottom plate to 4 mm or less in 2.5 years. This is because, in recent years, corrosion surveys of actual ships have revealed that the pH of the solution inside the pitting corrosion generated on the tanker bottom plate is 1.0 or less. In general, steel material corrosion in an acidic solution is rate-determined by a hydrogen reduction reaction, and it is well known that the corrosion rate dramatically increases as the pH decreases. Therefore, the immersion test at pH 2.0 as described in the examples of Patent Documents 1 and 2 cannot be said to sufficiently reflect the corrosive environment in an actual ship.

  On the other hand, regarding the suppression of the overall corrosion that occurs on the upper plate of the tanker, among the invention examples described in Patent Documents 1 and 2, the actual corrosion rate is about 0.11 mm / y even at the lowest corrosion rate. Since the service life of the tanker is 25 years and the design corrosion allowance of the tanker upper plate is about 2 mm on one side, the corrosion rate of the corrosion-resistant steel applied to the upper plate is required to be 0.08 mm / y or less. In particular, longages welded to the tanker upper plate are exposed to the corrosive environment inside the tanker, so repair is required when applying corrosion-resistant steel with a corrosion rate exceeding 0.1 mm / y. Therefore, the techniques described in Patent Documents 1 and 2 cannot be expected to omit painting.

  The present invention was developed in view of the above situation, and a steel material for a crude oil tank excellent in both general corrosion resistance in a top plate of a crude oil tank such as a tanker oil tank and local corrosion resistance in a bottom plate of a crude oil tank, It aims at providing with the crude oil tank comprised from this steel material.

Now, the inventors have intensively studied to solve the above problems.
As a result, it has been found that the above-described overall corrosion and local corrosion can be remarkably reduced by strictly controlling the component composition of steel.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. % By mass
C: 0.03-0.18%
Si: 0.03-1.50%,
Mn: 0.1-2.0%
P: 0.025% or less,
S: 0.010% or less,
Al: 0.005-0.10%,
N: 0.008% or less,
Co: 0.001-0.5%
Cu: 0.05-0.4%,
Ni: 0.01-0.4%,
Mg: 0.0002-0.01% and
Cr: more than 0.1% and 0.5% or less, and W: 0.01 to 1.0% and
Mo: 0.01-0.5%
A steel material for a crude oil tank having excellent corrosion resistance, comprising one or two selected from among them, the balance being Fe and inevitable impurities.

2. The steel material is further in mass%,
Sb: 0.01 to 0.4%,
Nb: 0.001 to 0.1%,
Ti: 0.001 to 0.1%,
V: 0.002 to 0.2%,
Ca: 0.0002 to 0.01% and
REM: 0.0002 to 0.015%
2. The steel material for a crude oil tank having excellent corrosion resistance as described in 1 above, which comprises one or more selected from among the above.

3. A crude oil tank produced using the steel material for a crude oil tank according to 1 or 2 above.

  ADVANTAGE OF THE INVENTION According to this invention, the general corrosion and local corrosion which generate | occur | produce in the oil tank of a crude oil tanker, the tank which transports or stores a crude oil, etc. can be suppressed, and there exists a remarkable effect on industry.

In the Example of this invention, it is a figure explaining the test apparatus used for the general corrosion test. In the Example of this invention, it is a figure explaining the test apparatus used for the local corrosion test.

Hereinafter, the present invention will be specifically described.
First, the reason why the component composition of the steel material for crude oil tank of the present invention is limited to the above range will be described. Unless otherwise specified, “%” in relation to ingredients means mass%.
C: 0.03-0.18%
C is an element that enhances the strength of steel. In the present invention, C is added in an amount of 0.03% or more in order to ensure a desired strength (490 to 620 MPa). However, addition exceeding 0.18% decreases the weldability and the toughness of the heat affected zone. Therefore, the C content is in the range of 0.03 to 0.18%. Preferably it is 0.06 to 0.16% of range.

Si: 0.03-1.50%
Si is an element added as a deoxidizer, but is also an effective element for increasing the strength of steel. Therefore, in the present invention, 0.03% or more is added to ensure a desired strength. However, additions exceeding 1.50% reduce the toughness of the steel. Therefore, the Si content is in the range of 0.03 to 1.50%. Preferably it is 0.05 to 0.50% of range.

Mn: 0.1-2.0%
Mn is an element that increases the strength of steel, and in the present invention, 0.1% or more is added to obtain a desired strength. However, additions exceeding 2.0% reduce the toughness and weldability of the steel. Therefore, the Mn content is in the range of 0.1 to 2.0%. Preferably it is 0.8 to 1.6% of range.

P: 0.025% or less P is a harmful element that segregates at the grain boundaries and lowers the toughness of the steel, so it is desirable to reduce it as much as possible. In particular, if the content exceeds 0.025%, the toughness is greatly reduced. Moreover, when P is contained exceeding 0.025%, it will also have a bad influence on the corrosion resistance in a tank oil tank. Therefore, the P content is 0.025% or less. Preferably it is 0.015% or less.

S: 0.010% or less S is a harmful element that forms MnS, which is a non-metallic inclusion, and serves as a starting point for local corrosion and reduces local corrosion resistance. Therefore, it is desirable to reduce S as much as possible. In particular, when the content exceeds 0.010%, the local corrosion resistance is remarkably lowered. Therefore, the allowable upper limit of the S amount is 0.010%. Preferably it is 0.005% or less.

Al: 0.005-0.10%
Al is an element added as a deoxidizer, and 0.005% or more is added in the present invention. However, if adding over 0.10%, the toughness of the steel decreases, so the upper limit of Al content is 0.10%.

N: 0.008% or less Since N is a harmful element that lowers toughness, it is desirable to reduce it as much as possible. In particular, if the content exceeds 0.008%, the decrease in toughness increases, so the upper limit of the N amount is set to 0.008%.

Co: 0.001 to 0.5%
Co is an element effective in suppressing the overall corrosion of steel because it is taken into the rust layer during corrosion and contributes to the formation of a dense rust layer. This effect is manifested with addition of 0.001% or more, but when added over 0.5%, low temperature toughness is reduced. Therefore, the Co content is in the range of 0.001 to 0.5%. Preferably it is 0.05 to 0.4% of range.

Cu: 0.05-0.4%
Cu is an element that increases the strength of steel, and also exists in rust generated by corrosion of steel and has an effect of increasing corrosion resistance. These effects cannot be sufficiently obtained with addition of less than 0.05%. On the other hand, addition over 0.4% saturates the effect of improving corrosion resistance and causes problems such as surface cracking during hot working. Therefore, from the viewpoint of stably producing the steel material of the present invention, the Cu amount is added in the range of 0.05 to 0.4%. Preferably it is 0.06 to 0.35% of range.

Ni: 0.01-0.4%
Ni has the effect of refining the generated rust particles to improve the corrosion resistance in the bare state and the corrosion resistance in the state where the epoxy primer is applied to the zinc primer. The above effect appears when Ni is added in an amount of 0.01% or more, but even if Ni is added in excess of 0.4%, the effect is saturated. Therefore, the Ni content is in the range of 0.01 to 0.4%. Preferably it is 0.08 to 0.35% of range.

Mg: 0.0002 to 0.01%
Mg is an element that enhances the toughness of the weld heat affected zone, and is present in the rust generated by the corrosion of steel and has the effect of enhancing the corrosion resistance. These effects cannot be sufficiently obtained with addition of less than 0.0002%. On the other hand, addition over 0.01% leads to a decrease in toughness. Therefore, the Mg amount is in the range of 0.0002 to 0.01%. Preferably it is 0.0002 to 0.005% of range.

Cr: More than 0.1% and 0.5% or less
Cr is with the progress of corrosion proceeds in the rust layer Cl ^- in by blocking entry into rust layers, Cl to interface rust layer and base iron ^- suppressing concentration of, whereby corrosion resistance It contributes to the improvement. In addition, when a Zn-containing primer is applied, a complex oxide of Cr and Zn centering on Fe can be formed, allowing Zn to remain on the steel sheet surface for a long period of time, thereby dramatically improving corrosion resistance. be able to. The above-mentioned effect is remarkable especially in a portion that comes into contact with a liquid containing high-concentration salinity separated from crude oil, such as a bottom plate portion of a tanker oil tank, and a Zn-containing primer treatment is applied to the steel material in the above-mentioned portion containing Cr. As a result, the corrosion resistance can be remarkably improved as compared with a steel material not containing Cr. The effect of Cr is not sufficient if it is 0.1% or less, while if it exceeds 0.5%, the toughness of the weld is deteriorated. Therefore, the Cr content is in the range of more than 0.1% and 0.5% or less. Preferably it is 0.11 to 0.3% of range.

In the steel material of this invention, it is necessary to contain 1 type or 2 types chosen from W and Mo other than the said component in the following range.
W: 0.01-1.0%
W not only suppresses pitting corrosion on the tanker tank bottom plate, but also has the effect of suppressing overall corrosion of the tanker upper deck. The effect of W is manifested when 0.01% or more is added, but when it exceeds 1.0%, the effect reaches saturation. Therefore, the W amount is in the range of 0.01 to 1.0%. Preferably it is 0.01 to 0.5%, More preferably, it is 0.02 to 0.3% of range.
The reason why W has the effect of improving the corrosion resistance as described above is that WO ₄ ^2- is produced in the rust produced as the steel sheet corrodes, and chloride ions are formed by the presence of this WO ₄ ^2-. Intrusion into the steel sheet surface is suppressed, and further, FeWO ₄ is generated at the site where the pH is lowered, such as the anode part on the steel sheet surface, and the presence of this FeWO ₄ also suppresses the penetration of chloride ions into the steel sheet surface. This is because that. Further, it is considered that corrosion of the steel material is also suppressed by the inhibitor action by adsorption of WO ₄ ^{2- on} the steel material surface.

Mo: 0.01-0.5%
Mo not only suppresses pitting corrosion at the bottom plate of the tanker tank, but also improves the overall corrosion resistance of the tanker upper deck and the corrosion resistance after painting in a corrosive environment where salt water is repeatedly immersed and highly humid like a ballast tank. There is an effect to make. The effect of Mo is manifested with addition of 0.01% or more, but when it exceeds 0.5%, the effect reaches saturation. Therefore, the Mo content is in the range of 0.01 to 0.5%. Preferably it is 0.02 to 0.5%, more preferably 0.03 to 0.4%.
The reason why Mo has the above-mentioned effect of improving corrosion resistance is that, like W, MoO ₄ ^2- is formed in the rust generated by corrosion of the steel sheet, and the presence of MoO ₄ ^2- This is thought to be because the penetration of steel into the steel sheet surface is suppressed.

Although the basic components have been described above, in the present invention, in addition to the components described above, the following elements can be appropriately contained.
Sb: 0.01-0.4%
Sb not only suppresses pitting corrosion in the tanker tank bottom plate, but also suppresses overall corrosion of the tanker upper deck. This effect appears when the Sb content is 0.01% or more. On the other hand, even if added over 0.4%, the effect is saturated. Therefore, Sb is preferably added in the range of 0.01 to 0.4%.

Nb: 0.001 to 0.1%, Ti: 0.001 to 0.1%, V: 0.002 to 0.2%
Nb, Ti and V are all elements that increase the strength of the steel material, and can be appropriately selected and added according to the required strength. In order to obtain the above effects, it is preferable to add Nb and Ti to 0.001% or more and V to 0.002% or more, respectively. However, if Nb and Ti are added in excess of 0.1% and V is added in excess of 0.2%, the toughness is lowered. Therefore, Nb, Ti and V are preferably added in the above ranges.

Ca: 0.0002 to 0.01%, REM: 0.0002 to 0.015%
Both Ca and REM are effective in improving the toughness of the weld heat-affected zone, and can be added as necessary. The above effect can be obtained with addition of Ca: 0.0002% or more, REM: 0.0002% or more, but if Ca exceeds 0.01% and REM exceeds 0.015%, it causes a decrease in toughness. Ca and REM are preferably added within the above ranges.

The steel material for crude oil tank of the present invention is preferably produced by the following method.
That is, the steel material of the present invention is prepared by melting the steel adjusted to the above-mentioned preferred component composition using a known refining process such as a converter, an electric furnace, vacuum degassing, etc. A steel material (slab) is formed by a rolling method, and then the material is reheated and then hot-rolled to form a thick steel plate, a thin steel plate, and a shaped steel.

  The reheating temperature before hot rolling is preferably 900 to 1200 ° C. If the heating temperature is less than 900 ° C, the deformation resistance is large and it is difficult to perform hot rolling.On the other hand, if the heating temperature exceeds 1200 ° C, the austenite grains become coarse, leading to a decrease in toughness, and scale loss due to oxidation. This is because the above becomes remarkable and the yield decreases. A more preferable heating temperature is in the range of 1000 to 1150 ° C.

  In addition, when rolling into a steel material having a desired shape and size by hot rolling, the finish rolling finish temperature is preferably 750 ° C. or higher. When the finish rolling finish temperature is less than 750 ° C., the deformation resistance of the steel increases, the rolling load increases, rolling becomes difficult, or a waiting time occurs until the rolled material reaches a predetermined rolling temperature. It is because rolling efficiency falls.

  The steel material after hot rolling may be cooled by either air cooling or accelerated cooling. However, when higher strength is desired, accelerated cooling is preferably performed. In addition, when performing accelerated cooling, it is preferable that a cooling rate shall be 2-80 degree-C / s, and cooling stop temperature shall be 650-300 degreeC. When the cooling rate is less than 2 ° C./s and the cooling stop temperature exceeds 650 ° C., the effect of accelerated cooling is small, and sufficient strength cannot be achieved. On the other hand, if the cooling rate exceeds 80 ° C./s and the cooling stop temperature is less than 300 ° C., the toughness of the obtained steel material is reduced, or the shape of the steel material is distorted.

Example 1
Steels having various compositions shown in Tables 1 to 34 in Table 1 are melted in a vacuum melting furnace to form a steel ingot, or melted in a converter and made into a steel slab by continuous casting. After reheating to 1150 ° C., hot rolling with a finish rolling finishing temperature of 800 ° C. was performed to obtain a steel plate having a plate thickness of 25 mm.
The thick steel plates No. 1 to 34 thus obtained were subjected to the following dew condensation test and acid resistance test to evaluate their corrosion resistance.

That is, in the following manner, a general corrosion test simulating the upper deck back environment and a local corrosion resistance test simulating the tanker oil tank bottom plate environment were performed.
(1) Full-surface corrosion test (condensation test) simulating the tanker upper deck environment
In order to evaluate the corrosion resistance against the overall corrosion on the back of the tanker upper deck, a rectangular piece of width 25mm x length 60mm x thickness 5mm was cut out from each of the thick steel plates No. 1 to 34 from the position of the surface 1mm. The surface was polished with 600th emery paper. Next, the back surface and the end surface were sealed with tape so as not to corrode, and a full surface corrosion test was performed using the corrosion test apparatus shown in FIG.

This corrosion test apparatus is composed of a corrosion test tank 2 and a temperature control plate 3, and water 6 having a temperature of 30 ° C. is injected into the corrosion test tank 2, and Introduces a mixed gas consisting of 13 vol% CO ₂ , 4 vol% O ₂ , 0.01 vol% SO ₂ , 0.05 vol% H ₂ S and the balance N ₂ through the introduction gas pipe 4 and enters the inside of the corrosion test tank 2. It is filled with saturated steam and reproduces the corrosive environment behind the upper deck of a crude oil tank. The corrosion test pieces 1 set on the upper and rear surfaces of the test tank are each subjected to a temperature change with one cycle of 25 ° C. × 3 hours + 50 ° C. × 21 hours through a temperature control plate 3 incorporating a heater and a cooling device. It was repeatedly applied for 21, 49, 77, and 98 days, and condensed water was generated on the surface of the corrosion test piece 1 to cause general corrosion. In FIG. 1, 5 indicates an exhaust gas pipe from the test tank.

  After the above test, the rust on the surface of each test piece was removed, the mass loss due to corrosion was determined from the mass change before and after the test, and the plate thickness was reduced (corrosion amount on one side) from this value. For each steel type, extrapolation of the plate thickness reduction when the 21, 49, 77, and 98 day tests were performed was performed, and the predicted plate thickness reduction after 25 years was obtained. As a result, when the estimated thickness reduction after 25 years was 2 mm or less, the overall corrosion resistance was good (◯), and when it was more than 2 mm, the overall corrosion resistance was evaluated as poor (×).

(2) Local corrosion test (acid resistance test) simulating the tanker tank bottom plate environment
In order to evaluate the corrosion resistance against pitting corrosion in the bottom plate of the tanker oil tank part, rectangular pieces each having a width of 25 mm, a length of 60 mm and a thickness of 5 mm were cut out from the position of 1 mm on the surface of each of the No. 1 to 34 thick steel plates. The surface was polished with 600th emery paper.
Next, a 10% NaCl aqueous solution was prepared using concentrated hydrochloric acid to prepare a test solution with a Cl ion concentration of 10% and pH 0.85. The test solution was suspended in a 3mmφ hole opened at the top of the test piece. A corrosion test was conducted by immersing in 2 L of test solution for 168 hours. The test solution was preheated and maintained at 30 ° C. and replaced with a new test solution every 24 hours.
The apparatus used for the corrosion test is shown in FIG. This corrosion test apparatus is a double-type apparatus of a corrosion test tank 8 and a thermostatic tank 9, in which the above test solution 10 is placed, and a corrosion test piece 7 is suspended and immersed in a teg 11 therein. Has been. The temperature of the test solution 10 is maintained by adjusting the temperature of the water 12 placed in the thermostatic chamber 9.

  After the corrosion test, the rust generated on the surface of the test piece was removed, the mass difference before and after the test was calculated, the difference was divided by the total surface area, and the reduction in thickness (corrosion rate on both sides) per year was calculated. . As a result, when the corrosion rate was 1.0 mm / y or less, the local corrosion resistance was evaluated as good (◯), and when the corrosion rate was higher than 1.0 mm / y, the local corrosion resistance was evaluated as poor (×).

As shown in Table 1, the thick steel plates Nos. 1 to 26 satisfying the conditions of the present invention are good in both of the general corrosion test simulating the upper deck back environment and the local corrosion test simulating the tanker oil tank bottom plate environment. Corrosion resistance was shown.
On the other hand, the thick steel plates No. 27 to 34 that do not satisfy the conditions of the present invention could not obtain good results in any of the corrosion resistance tests.

DESCRIPTION OF SYMBOLS 1,7 Corrosion test piece 2,8 Corrosion test tank 3 Temperature control plate 4 Introducing gas pipe 5 Exhaust gas pipe 6,12 Water 9 Constant temperature bath
10 Test solution
11 Teguz

Claims (3)

% By mass
C: 0.03-0.18%
Si: 0.03-1.50%,
Mn: 0.1-2.0%
P: 0.025% or less,
S: 0.010% or less,
Al: 0.005-0.10%,
N: 0.008% or less,
Co: 0.001-0.5%
Cu: 0.05-0.4%,
Ni: 0.01-0.4%,
Mg: 0.0002-0.01% and
Cr: more than 0.1% and 0.5% or less, and W: 0.01 to 1.0% and
Mo: 0.01-0.5%
A steel material for a crude oil tank having excellent corrosion resistance, comprising one or two selected from among them, the balance being Fe and inevitable impurities. The steel material is further in mass%,
Sb: 0.01 to 0.4%,
Nb: 0.001 to 0.1%,
Ti: 0.001 to 0.1%,
V: 0.002 to 0.2%,
Ca: 0.0002 to 0.01% and
REM: 0.0002 to 0.015%
The steel material for a crude oil tank having excellent corrosion resistance according to claim 1, comprising one or more selected from among the above.   A crude oil tank produced using the steel material for a crude oil tank according to claim 1.

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