JP2013147726A - Corrosion resistant steel material for oil tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a corrosion resistant steel material for an oil tank, in an oil tank filled with crude oil, heavy oil, light oil or the like, capable of suppressing pitting corrosion generated at the inside face of the bottom plate of the coated steel material thereof and effectively preventing the hole opening of the bottom plate.SOLUTION: The componential composition of a steel material is controlled to include, by mass, 0.03 to 0.25% C, 0.01 to 0.50% Si, 0.1 to 2.0% Mn, ≤0.035% P, ≤0.015% S, 0.005 to 0.10% Al, 0.001 to 0.01% N, 0.001 to 0.20% Sn and 0.001 to 0.050% Nb, and further including one or two selected from 0.005 to 0.5% W and 0.01 to 1.0% Mo, and the balance Fe with inevitable impurities, and further, solid solution Nb is included in the range of 0.0005 to 0.050% into the steel material.

Description

The present invention relates to a corrosion resistant steel material for oil tanks that can suitably suppress the corrosion of above-ground oil tanks filled with oil such as crude oil, heavy oil, and light oil, and in particular, the bottom plate of an above-mentioned cylindrical oil tank.
In addition, the corrosion-resistant steel material for oil tanks referred to in the present invention mainly refers to thick steel plates and thin steel plates.

  Ground oil tanks are filled with crude oil, heavy oil, light oil, etc., but due to pitting corrosion on the inner surface of the bottom plate, there are frequent accidents in which holes are opened in the bottom plate and the contents flow out. As the cause of this, it is reported that the corrosiveness of petroleum itself is small, and a small amount of water containing NaCl stays on the bottom plate surface when it is filled with petroleum.

  On the other hand, as an anticorrosion specification, vinyl ester resin containing glass flakes is mainly coated on the inner surface of the bottom plate, which itself has a very high anticorrosion property. However, a defect occurs in the coating film due to poor coating work or scratches after coating, and pitting corrosion occurs and grows in the defective portion of the coating film, and the bottom plate steel plate is perforated. Accordingly, there is a demand for corrosion resistant steel that suppresses pitting corrosion on the inner surface of the bottom plate of the oil tank and prevents perforation of the bottom plate.

The following are proposed as steel materials for suppressing pitting corrosion in the petroleum environment.
That is, in Patent Document 1, C: 0.001 to 0.2 mass% of steel, Mo, W, and Cu are added together, and the content of P and S as impurities is limited, so that the entire surface generated in a crude oil tank. Steels that suppress corrosion and local corrosion are disclosed.
Patent Document 2 discloses that the corrosion resistance and pitting corrosion resistance of a cargo oil tank, which is a crude oil tank in a tanker, can be obtained by adding Ni: 0.01-3 mass% in steel of C: 0.01-0.3 mass%. Enhanced steel is disclosed.
Further, in Patent Document 3, Cu: 0.05-2 mass% and W: 0.01-1 mass% are added to steel of C: 0.01 to 0.2 mass%, and a crude oil tank, particularly a cargo oil tank which is a crude oil tank in a tanker, is added. Steels having improved overall corrosion resistance and pitting corrosion resistance are disclosed.

However, Patent Document 1 also deals with an object in which one or more coating films having a thickness of 10 μm or more are formed, but pitting corrosion resistance in a coated steel material is unknown.
Patent Document 2 also deals with steel materials that have been subjected to anticorrosion treatment, and Patent Document 3 deals with steel materials that have an anticorrosion coating, but the pitting corrosion resistance of painted steel materials is unknown.

JP 2004-204344 A Japanese Patent Laid-Open No. 2003-082435 JP 2005-325439 A

  The present invention was developed in view of the above situation, and in a petroleum tank filled with crude oil, heavy oil, light oil, etc., the pitting corrosion that occurs on the inner surface of the bottom plate of the coated steel material is suppressed, and the perforation of the bottom plate is effective. An object of the present invention is to provide a corrosion-resistant steel material for oil tanks that can be prevented.

Now, in order to meet the above-mentioned demands, the inventors have intensively studied and examined the improvement of pitting corrosion resistance of coated steel materials.
As a result, it was found that by appropriately defining the steel material component, it is possible to effectively suppress the pitting corrosion progress from the coating film defect portion such as a paint scratch and to significantly improve the pitting corrosion resistance of the oil tank.
The present invention has been completed based on the above findings and further studies.

That is, the gist configuration of the present invention is as follows.
1. In mass%, C: 0.03-0.25%, Si: 0.01-0.50%, Mn: 0.1-2.0%, P: 0.035% or less, S: 0.015% or less, Al: 0.005-0.10%, N: 0.001-0.01% Sn: 0.001 to 0.20% and Nb: 0.001 to 0.050%, W: 0.005 to 0.5%, and Mo: 0.01 to 1.0%, one or two selected, the balance being Fe and A corrosion-resistant steel material for petroleum tanks, characterized in that it is a steel material consisting of inevitable impurities, and 0.0005 to 0.050% of solid solution Nb is contained in the steel material.

2. 2. The corrosion resistant steel material for a petroleum tank as described in 1 above, which contains, in addition to the above component composition, Sb: 0.001 to 0.20% by mass.

3. 3. Petroleum according to 1 or 2 above, wherein, in addition to the above component composition, one or two selected from Cr: 0.01 to 0.5% and Co: 0.01 to 0.5% are contained by mass%. Corrosion resistant steel for tanks.

4). 4. The corrosion resistant steel material for a petroleum tank according to any one of 1 to 3, further comprising at least one element selected from the following groups A to C in addition to the above component composition.
Group A: By mass%, Ti: 0.001 to 0.05%, Zr: 0.002 to 0.1%, and V: 0.002 to 0.1% or more selected from Group B: Mass%, B: 0.0001 to 0.003%
Group C:% by mass, Ca: 0.0002 to 0.01%, REM: 0.0002 to 0.015%, and Y: 0.0001 to 0.1%

  According to the present invention, in oil tanks filled with crude oil, heavy oil, light oil, etc., pitting corrosion occurring on the inner surface of the bottom plate of the coated steel material can be effectively suppressed, and as a result, the occurrence of perforations in the bottom plate can be prevented. can do.

Hereinafter, the present invention will be specifically described.
First, the reason why the component composition of the steel sheet is limited to the above range in the present invention will be described. In addition,% showing the following component composition shall mean the mass% unless there is particular notice.
C: 0.03-0.25%
C is an element effective for increasing the strength of the steel material. In the present invention, it is necessary to contain 0.03% or more in order to obtain a desired strength (preferably a tensile strength (TS) of 400 MPa or more). On the other hand, the content exceeding 0.25% lowers the toughness of the heat affected zone. Therefore, the C content is in the range of 0.03 to 0.25%. In addition, Preferably it is 0.05 to 0.20% of range.

Si: 0.01-0.50%
Si is an element added as a deoxidizer and for the purpose of increasing the strength of the steel material. In the present invention, Si is contained in an amount of 0.01% or more. However, addition exceeding 0.50% deteriorates the toughness of the steel, so the upper limit of Si is 0.50%. In addition, Preferably it is 0.05 to 0.40% of range.

Mn: 0.1-2.0%
Mn has the effect of preventing hot brittleness and increasing the strength of the steel material, so 0.1% or more is added. However, addition of Mn exceeding 2.0% decreases the toughness and weldability of the steel, so it is made 2.0% or less. In addition, Preferably it is 0.3 to 1.6% of range.

P: 0.035% or less P is a harmful element that deteriorates the base metal toughness of steel, as well as the weldability and weld zone toughness, and is preferably reduced as much as possible. In particular, when the P content exceeds 0.035%, the deterioration of the base metal toughness and weld zone toughness increases. Therefore, P is set to 0.035% or less.

S: 0.015% or less Since S is a harmful element that deteriorates the toughness and weldability of steel, it is desirable to reduce it as much as possible. In particular, when the S content exceeds 0.015%, the deterioration of the base metal toughness and weld zone toughness increases. Therefore, S is set to 0.015% or less. In addition, Preferably it is 0.008% or less.

Al: 0.005-0.10%
Al is contained as 0.005% or more because it is useful as a deoxidizer. However, the content exceeding 0.10% adversely affects the weld zone toughness, so it is limited to 0.10% or less. In addition, Preferably it is 0.07% or less.

N: 0.001 to 0.01%
N is an element that adversely affects the toughness of the steel material, so the upper limit of its content is 0.01%. On the other hand, since reduction to less than 0.001% is difficult in terms of degassing ability, the lower limit of the content is set to 0.001%. In addition, Preferably, it is 0.007% or less.

Sn: 0.001 to 0.20%
Sn is the most important element for improving corrosion resistance in the steel material of the present invention. Sn is present in the rust layer as the steel material corrodes, and has the effect of refining the rust particles. As the rust particles become finer, the anode reaction of Fe is suppressed. Further, along with the suppression of the anode reaction, the generation of OH ⁻ generated from H ₂ O and O _2, which is a cathode reaction, is suppressed, and alkalinization at the tip of the coating film bulge is suppressed. By suppressing this alkalinization, the subsequent swelling of the coating film is suppressed. By suppressing the swelling of the coating film, the progress of corrosion in the depth direction of the steel material is also suppressed. Such an effect is manifested with a Sn content of 0.001% or more, but when the Sn content exceeds 0.20%, the base metal toughness and HAZ part toughness are deteriorated. For this reason, Sn shall be contained in the range of 0.001 to 0.20%. In addition, Preferably it is 0.01 to 0.15% of range.

Nb: 0.001 to 0.050%
Nb is an important element for improving corrosion resistance after Sn in the steel material of the present invention. Nb is present in the rust layer as the steel material corrodes, and has the effect of refining the rust particles. As the rust particles become finer, the anode reaction of Fe is suppressed. Further, along with the suppression of the anode reaction, the generation of OH ⁻ generated from H ₂ O and O _2, which is a cathode reaction, is suppressed, and alkalinization at the tip of the coating film bulge is suppressed. By suppressing this alkalinization, the subsequent swelling of the coating film is suppressed. By suppressing the swelling of the coating film, the progress of corrosion in the depth direction of the steel material is also suppressed. Such an effect is manifested when the Nb content is 0.001% or more, but when the Nb content exceeds 0.050%, the weld joint HAZ toughness is deteriorated. For this reason, Nb shall be contained in the range of 0.001 to 0.050%. In addition, Preferably it is 0.004 to 0.020% of range.

Solid solution Nb: 0.0005 to 0.050%
Nb has the effect of improving corrosion resistance as described above, but Nb exists as solid solution Nb or precipitated Nb in the steel. Of these, solid solution Nb improves the corrosion resistance. That is, corrosion resistance is manifested when the solid solution Nb content is 0.0005% or more, and the effect is saturated when it exceeds 0.050%. For this reason, the amount of solid solution Nb shall be contained in 0.0005 to 0.050% of range.

One or two selected from W: 0.005-0.5% and Mo: 0.01-1.0% W is one of the important elements for improving corrosion resistance. This effect of improving corrosion resistance is manifested when the content of W is 0.005% or more. However, if it exceeds 0.5%, the effect is saturated. Therefore, the W content is in the range of 0.005 to 0.5%.
The reason why W has an effect of improving the corrosion resistance is as follows. That is, as the steel sheet corrodes, WO ₄ ^2- is generated in the generated rust, and the presence of this WO ₄ ^2- suppresses chloride ions from entering the steel sheet surface. When the pH of the surface, such as the anode part, decreases, poorly soluble FeWO ₄ is produced, and the presence of this FeWO ₄ also suppresses the entry of chloride ions to the steel sheet surface, and chloride ions enter the steel sheet surface. By inhibiting the intrusion of steel, corrosion of the steel sheet is effectively suppressed. Moreover, corrosion of steel is also suppressed by the inhibitor action by adsorption of WO ₄ ^{2- on} the steel material surface.

Mo, like W, is one of the important elements for improving corrosion resistance in the steel material of the present invention. This effect of improving corrosion resistance is manifested when Mo: 0.01% or more is contained. However, if it exceeds 1.0%, the effect is saturated. Therefore, the Mo content is in the range of 0.01 to 1.0%.
The reason why Mo has an effect of improving corrosion resistance is that MoO ₄ ^2- is generated in the generated rust as the steel sheet corrodes, and the presence of MoO ₄ ^2- makes chloride ions on the surface of the steel sheet. This is because the penetration of the steel sheet is suppressed and the corrosion of the steel sheet is effectively suppressed by suppressing the penetration of chloride ions into the steel sheet surface.
Since W and Mo coincide with each other in forming an oxygen acid, both elements can be contained selectively or in combination. Compared to Mo, W is superior in that it produces poorly soluble FeWO ₄ in a low pH environment and has a high inhibitor effect due to adsorption to the steel surface. Therefore, W has a higher content than Mo. At least, good corrosion resistance can be exhibited.

Although the basic components have been described above, in the present invention, other elements described below can be appropriately contained as necessary.
Sb: 0.001 to 0.20%
Sb has an effect of improving the corrosion resistance, and can be contained auxiliary. The effect of this Sb is that it can suppress corrosion at sites where the pH is lowered, such as the anode portion on the surface of the steel sheet. This effect is exhibited when the Sb content is 0.001% or more. However, if it exceeds 0.20%, the base material toughness and the HAZ part toughness are deteriorated, so the range of 0.001 to 0.20% is preferable.

One or two selected from Cr: 0.01-0.5% and Co: 0.01-0.5%
Both Cr and Co are elements that increase the strength of the steel material, and can be added as necessary. This effect appears when the content is 0.01% or more. However, if the content of any element exceeds 0.5%, the toughness of the heat affected zone is deteriorated. Therefore, these elements are all contained in the range of 0.01 to 0.5%.

Furthermore, in this invention, the element of the at least 1 group selected from the group AC described below can be contained suitably.
Group A: One or more selected from Ti: 0.001-0.05%, Zr: 0.002-0.1% and V: 0.002-0.1%
Ti, Zr, and V all have a strong affinity with N and precipitate as TiN, ZrN, and VN to suppress the austenite grain coarsening in the weld heat affected zone, and to increase the toughness of the weld heat affected zone. Contribute. Such an effect is recognized when the content is 0.001% or more for Ti, 0.002% or more for Zr, and 0.002% or more for V. However, if Ti exceeds 0.05%, Zr exceeds 0.1%, and V exceeds 0.1%, TiN, ZrN, and VN become coarser, leading to deterioration of toughness. Therefore, Ti is contained in the range of 0.001 to 0.05%, Zr in the range of 0.002 to 0.1%, and V in the range of 0.002 to 0.1%.

Group B: B: 0.0001-0.003%
B is an element that increases the strength of the steel material, and can be contained as necessary. In order to acquire said effect, it is preferable to contain 0.0001% or more, but when it contains exceeding 0.003%, toughness will deteriorate. Therefore, it is preferable to contain B in the range of 0.0001 to 0.003%.

Group C: Ca: 0.0002 to 0.01%, REM: 0.0002 to 0.015%, Y: 0.0001 to 0.1% selected from one or more
Ca, REM and Y are all elements effective in improving the toughness of the weld heat affected zone, and can be contained as necessary. This effect is obtained when Ca: 0.0002% or more, REM: 0.0002% or more, Y: 0.0001% or more, Ca: over 0.01%, REM: over 0.015%, Y: over 0.1% If each of them is contained, the toughness is deteriorated. Ca, REM and Y are preferably contained in the above ranges.

  In the steel material of the present invention, components other than those described above are Fe and inevitable impurities. However, as long as the effects of the present invention are not impaired, the inclusion of components other than those described above is not rejected.

Next, the manufacturing method of this invention steel material is demonstrated.
The molten steel having the above-mentioned preferred component composition is melted by a known method such as a converter or an electric furnace, and is made into a casting material such as a slab or billet by a known method such as a continuous casting method or an ingot casting method. In addition, vacuum degassing refining or the like may be performed at the time of melting. The component adjustment method of molten steel should just follow a well-known steel refining method. Next, when the steel material is hot-rolled to a desired size and shape, it is heated to a temperature of 1000 to 1350 ° C. When the heating temperature is less than 1000 ° C., the deformation resistance is large and hot rolling becomes difficult. On the other hand, heating above 1350 ° C causes surface marks, increases scale loss, and increases fuel consumption. Preferably it is the range of 1050-1300 degreeC. In addition, when the temperature of the steel material is originally in the range of 1000 to 1350 ° C., the steel material may be hot-rolled as it is without being heated. After hot rolling, air cooling or accelerated cooling is performed to obtain desired strength and toughness. Further, after cooling, a reheating treatment may be performed.

In addition, there is no restriction | limiting in particular about the coating material used when using the steel material of this invention as a coating steel material, However, The following coating materials adapt especially advantageously. That is, as a primer after blasting on the surface of a steel material, 1) a bisphenol vinyl ester resin is applied, and then 2) a vinyl ester resin containing novolac glass flakes is applied.
Moreover, it is preferable that the coating film thickness after apply | coating and drying the coating material of said 1) shall be about 20-80 micrometers. And it is preferable that the coating-film thickness after apply | coating and drying the coating material of said 2) shall be about 600-840 micrometers.

Examples of the present invention will be specifically described below.
The molten steel having the composition shown in Table 1 was made into a slab by continuous casting after melting in a vacuum melting furnace or in a converter. Subsequently, the steel sheet was 12 mm thick by hot rolling.

For each steel sheet obtained was investigated tensile properties of the base material (YS, TS, El) and impact properties (absorbed energy vE _O at 0 ° C.).
In addition, as an evaluation of weld toughness, a heat input area of heat input: 50 kJ / cm, a heat affected zone of the weld: 1 mm (1 mm from the fusion line on the base metal side) was given a reproducible thermal cycle. The absorbed energy vE ₀ at ₀ ° C. was measured.
Further, 10 mmt × 150 mmW × 150 mmL test pieces were collected from the steel plate, and each test piece was attached to an actual crude oil tank bottom plate, heavy oil tank bottom plate, and light oil tank bottom plate by welding. Then, after blasting the surface of the test piece, a 50 μm thick bisphenol vinyl ester resin (primer) was applied. Thereafter, a vinyl ester resin containing novolac glass flakes was applied twice to a thickness of 720 μm. Then, after forming a 2 mmφ coating film defect reaching the ground iron in the center of the test piece, it was subjected to an exposure test. The exposure test period was one year. After one year, the test piece was removed, and then the coating film on the surface of the test piece was removed, and the depth of pitting corrosion occurring on the 2 mmφ coating film defect portion was measured with a depth gauge. Then, the pitting corrosion rate (mm / y) was calculated.
Table 2 shows the survey results on mechanical properties, and Table 3 shows the results of exposure tests.

As shown in Table 2, Invention Examples Nos. 1 to 15 satisfying the steel component composition of the present invention are not limited to the base material toughness as compared to No. 16 being the base steel, but also toughness of the welded portion. It turns out that it is excellent.
Moreover, as shown in Table 3, all of Invention Examples No. 1 to 15 satisfying the steel component composition of the present invention were applied to crude oil tanks, heavy oil tanks and light oil tanks as compared to No. 16 which is a base steel. In either case, the pitting corrosion rate is 60% or less, and it can be seen that the film has good coating corrosion resistance.
In contrast, the pitting corrosion rate of No. 17 to 20 that does not satisfy the steel material composition of the present invention is smaller than that of No. 16, which is the base steel, but the pitting corrosion rate is lower than that of the base steel. Thus, it is over 60%, and it cannot be said that it has a sufficient pitting corrosion suppressing effect as compared with the present invention.

Claims (4)

  In mass%, C: 0.03-0.25%, Si: 0.01-0.50%, Mn: 0.1-2.0%, P: 0.035% or less, S: 0.015% or less, Al: 0.005-0.10%, N: 0.001-0.01% Sn: 0.001 to 0.20% and Nb: 0.001 to 0.050%, W: 0.005 to 0.5%, and Mo: 0.01 to 1.0%, one or two selected, the balance being Fe and A corrosion-resistant steel material for petroleum tanks, characterized in that it is a steel material consisting of inevitable impurities, and 0.0005 to 0.050% of solid solution Nb is contained in the steel material.   The corrosion resistant steel material for a petroleum tank according to claim 1, wherein, in addition to the above component composition, Sb: 0.001 to 0.20% is contained in mass%.   3. In addition to the above component composition, it contains one or two selected from Cr: 0.01 to 0.5% and Co: 0.01 to 0.5% by mass%. Corrosion resistant steel for oil tanks. The corrosion resistant steel material for a petroleum tank according to any one of claims 1 to 3, further comprising at least one element selected from the following groups A to C in addition to the component composition.
Group A: By mass%, Ti: 0.001 to 0.05%, Zr: 0.002 to 0.1%, and V: 0.002 to 0.1% or more selected from Group B: Mass%, B: 0.0001 to 0.003%
Group C:% by mass, Ca: 0.0002 to 0.01%, REM: 0.0002 to 0.015%, and Y: 0.0001 to 0.1%