CN102264937A - Corrosion-resistant steel for crude oil tankers - Google Patents

Abstract

Disclosed is a corrosion-resistant steel material for a tanker, which has excellent corrosion resistance in a corrosive environment produced in an oil tank in the tanker and also has excellent post-coating corrosion resistance in a corrosive environment produced in a ballast tank in the tanker. Specifically disclosed is a corrosion-resistant steel material for a crude oil tanker, which comprises (by mass%) 0.03 to 0.16% of C, 0.05 to 1.50% of Si, 0.1 to 2.0% of Mn, 0.025% or less of P, 0.01% or less of S, 0.005 to 0.10% of Al, 0.008% or less of N, more than 0.1% and not more than 0.5% of Cr, and 0.03 to 0.5% of Cu, and may additionally comprise, as an optional additive element, at least one element selected from W in an amount of 0.01 to 0.5%, Mo in an amount of 0.01 to 0.5%, Sn in an amount of 0.001 to 0.2%, Sb in an amount of 0.001 to 0.5%, Ni in an amount of 0.005 to 0.3% and Co in an amount of 0.005 to 0.3%, wherein Cu, W, Mo, Sn, Sb, Cr, Ni, Co, S and P are so contained as to meet a specific relationship.

Description

Corrosion-resistant steel for crude oil tankers

technical field

The present invention relates to corrosion-resistant steel materials for crude oil tankers used in different parts of the corrosion environment (corrosion environment) such as the oil tank and the ballast tank of the crude oil tanker. steel product), specifically, the ability to reduce local corrosion at the bottom plate and general corrosion at the top and side plates of crude oil tankers Corrosion) and corrosion-resistant steel for crude oil tankers that corrode the ballast tank coating surface on the back of the tank bottom plate.

Background technique

It is known that the inert gas (inert gas) filled in the oil tank ( _O2 : 5 volume%, _CO2 : 13 volume%, _SO2 : 0.01 volume%, balance _N2 Corrosive gases such as O ₂ , CO ₂ , SO ₂ or H ₂ S volatilized from crude oil contained in the boiler (boiler) or engine (engine) exhaust gas (exhaust gas) of the representative composition, in The inner surface of the upper part of the tank portion of the crude oil tanker (back side of upper deck) causes general corrosion.

Furthermore, the above-mentioned H ₂ S is oxidized by catalyst action of iron rust generated by corrosion to form solid S (elemental sulfur), which exists in layers in the iron rust. Also, the above-mentioned corroded products are easily peeled off to deposit on the bottom of the crude oil tank. Therefore, in the dock inspection of the tanker every 2.5 years, maintenance and repair of the upper part of the oil tank and removal of deposits are performed at huge expense.

On the other hand, in the past, it was considered that the bottom plate of the crude oil tank of the tanker was damaged due to the corrosion inhibition function of the crude oil itself and the corrosion inhibition function of the protective film derived from the crude oil formed on the inner surface of the crude oil tank. The steel used does not corrode. However, it has recently been found that bowl-shaped localized corrosion also occurs in the steel used for tank floors.

As the causes of the above-mentioned bowl-shaped localized corrosion, the following can be cited:

(1) There is condensed water (brine) in which high concentrations of salts represented by sodium chloride are dissolved;

(2) Detachment of crude oil protective film caused by excessive cleaning;

(3) High concentration of sulfide contained in crude oil;

(4) High concentration of O ₂ , CO ₂ , and SO ₂ contained in the inert gas for explosion protection;

(5) Participation of microorganisms, etc.,

However, these are only conjectures, and a definite cause cannot be determined yet.

The most effective method of suppressing the corrosion as described above is a method of applying heavy coating on the surface of the steel material so as to isolate the steel material from the corrosive environment. However, some people pointed out that due to the large coating area of crude oil tanks, it takes a lot of construction and inspection costs to paint crude oil tanks. In addition, in the corrosive environment of crude oil tanks, repainting promotes the deterioration of the coating film. Corrosion of damaged parts.

Therefore, steels having corrosion resistance even in environments such as crude oil tanks have been proposed. For example, Patent Document 1 discloses a corrosion-resistant steel for cargo oil tanks having excellent general corrosion resistance and localized corrosion resistance, in which an appropriate amount of Si is added to steel with C: 0.01 to 0.3% by mass. , Mn, P, S, Ni: 0.05-3% by mass, and Mo, Cu, Cr, W, Ca, Ti, Nb, V, B were added selectively. Moreover, it is disclosed that in a repeated dry-wet environment containing H ₂ S, if the content of Cr exceeds 0.05% by mass, the overall corrosion resistance and pitting corrosion resistance (pitting corrosion resistance) will be significantly reduced, so the content of Cr is set to 0.05% by mass. Mass% or less.

In addition, Patent Document 2 discloses a corrosion-resistant steel for crude oil tanks that has excellent general corrosion resistance and localized corrosion resistance and can suppress the formation of corrosion products containing solid S. In the steel, an appropriate amount of Si, Mn, P, S and Cu: 0.01 to 1.5% by mass, Al: 0.001 to 0.3% by mass, N: 0.001 to 0.01% by mass, and Mo: 0.01 to 0.2% by mass are added Or W: at least one of 0.01 to 0.5% by mass.

On the other hand, when cargo is not loaded, the ballast tank of the crude oil tanker plays the role of enabling the ship to sail stably (safety navigation). Due to the injection of seawater, the ballast tank is exposed to a very severe corrosion environment. Therefore, in order to achieve corrosion protection of steel materials used in ballast tanks, formation of a protective coating using epoxy type paint and electrolytic protection are generally used together.

However, even with the above-mentioned anti-corrosion measures, the corrosion environment of the ballast tank is still in a severe state. That is, when seawater is injected into the ballast tank, since the electrolytic protection works, the occurrence of corrosion of the portion completely immersed in seawater can be suppressed. However, when the ballast tank is not filled with seawater, the electrolytic protection does not work at all, so it is severely corroded due to the action of residual attached saline metter.

Several proposals have been made regarding steel materials used in parts such as ballast tanks that are exposed to severe corrosive environments. For example, Patent Document 3 discloses a corrosion-resistant low-alloy steel for ballast tanks in which Cu: 0.05 to 0.50 mass % and W: 0.01 to less than 0.05 mass % are added as steel to C: 0.20 mass % or less. A corrosion resistance improving element, or one or more of Ni, Ti, Zr, V, Nb, Ge, Sn, Pb, As, Sb, Bi, Te, and Be is further added. In addition, Patent Document 4 discloses a corrosion-resistant low-alloy steel for ballast tanks in which Cu: 0.05 to 0.50 mass % and W: 0.05 to 0.5 mass % are added as corrosion-resistant steel materials to steel materials having C: 0.20 mass % or less. As a property-improving element, one or more of Ge, Sn, Pb, As, Sb, Bi, Te, and Be is added. In addition, Patent Document 5 discloses a corrosion-resistant low-alloy steel for ballast tanks in which Cu: 0.05 to less than 0.15% by mass and W: 0.05 to 0.5% by mass are added to steel having C: 0.15% by mass or less. .

In addition, Patent Document 6 discloses a ballast tank in which low-alloy corrosion-resistant steel is coated with tar epoxy paint, pure epoxy paint, or solvent-free epoxy paint. (solventless epoxy paint), polyurethane paint (urethane paint) and other anti-corrosion coatings, the low-alloy corrosion-resistant steel material is obtained by adding P: 0.03 to 0.10 mass %, Cu: 0.1 to 1.0 mass % to steel of C: 0.15 mass % or less , Ni: 0.1 to 1.0% by mass is obtained as a corrosion resistance improving element. The above-mentioned technology prolongs the service life of the anti-corrosion coating by improving the corrosion resistance of the steel itself, and realizes maintenance-free (maintenance-free) during the service period of the ship for 20 to 30 years.

In addition, Patent Document 7 proposes a steel material for ballast tanks, which improves corrosion resistance by adding Cr: 0.2 to 5% by mass as a corrosion resistance improving element to steel having C: 0.15% by mass or less, thereby realizing shipbuilding. maintenance-free. In addition, Patent Document 8 proposes a method for preventing corrosion of ballast tanks, which is characterized by using a steel material in which Cr: 0.2 to 5 mass % is added as a corrosion resistance improving element to steel having C: 0.15 mass % or less. Steel, and make the oxygen concentration (oxygen gas concentration) inside the ballast tank relative to the value in the atmosphere less than 0.5.

In addition, Patent Document 9 proposes to improve corrosion resistance by adding Cr: 0.5 to 3.5% by mass to steel having C: 0.1% by mass or less, thereby achieving maintenance-free corrosion prevention of ships. In addition, Patent Document 10 discloses steel materials for ships, which improve coating film damage resistance by adding Ni: 0.1 to 4.0 mass % to steel with C: 0.001 to 0.025 mass %, thereby reducing maintenance costs such as repair coating. .

In addition, Patent Document 11 discloses a steel for ships in which Cu: 0.01 to 2.00 mass % and Mg: 0.0002 to 0.0150 mass % are added to steel of C: 0.01 to 0.25 mass %, whereby the outer plates and compression Corrosion-resistant in use environments such as load tanks, cargo oil tanks, ore and coal cargo holds (cargo hold for ore and coal).

In addition, Patent Documents 12 and 13 disclose steel materials for cargo oil tanks, which suppress the addition of Cr and Al to steel with C: 0.01 to 0.2%, add Cu: 0.05 to 2%, and add P, Ni, W and Sn, etc., improve the resistance to general corrosion and local corrosion in crude oil corrosion environment (crude oil corrosion environment) and seawater corrosion environment (seawater corrosion environment).

Patent Document 1: Japanese Patent Laid-Open No. 2003-082435

Patent Document 2: Japanese Patent Laid-Open No. 2004-204344

Patent Document 3: Japanese Patent Application Laid-Open No. 48-050921

Patent Document 4: Japanese Patent Application Laid-Open No. 48-050922

Patent Document 5: Japanese Patent Application Laid-Open No. 48-050924

Patent Document 6: Japanese Patent Application Laid-Open No. 07-034197

Patent Document 7: Japanese Patent Application Laid-Open No. 07-034196

Patent Document 8: Japanese Patent Application Laid-Open No. 07-034270

Patent Document 9: Japanese Patent Application Laid-Open No. 07-310141

Patent Document 10: Japanese Patent Laid-Open No. 2002-266052

Patent Document 11: Japanese Patent Laid-Open No. 2000-017381

Patent Document 12: Japanese Patent Laid-Open No. 2005-325439

Patent Document 13: Japanese Patent Laid-Open No. 2007-270196

Contents of the invention

As mentioned above, conventionally, the steel materials used for the tank part of a crude oil tanker, and the steel materials used for the ballast tank part were developed separately in many cases. However, the back of the bottom plate of the tank part of the tanker used in the bare state is usually also the ballast tank part painted and used, so the corrosion resistance in the corrosive environment inside the tank part and the ballast tank part cannot be considered separately. The corrosion resistance in the corrosive environment is used as the characteristic that the steel used in the tanker should have.

On the other hand, the techniques described in Patent Documents 12 and 13 focus on loading seawater in ballast tanks located outside cargo oil tanks when crude oil is not loaded, and aim at taking into account both the corrosive environment of crude oil and the corrosive environment of seawater. In addition, in seawater corrosive environments, the corrosion resistance of the coating film as the anti-corrosion coating on the outer surface of the cargo oil tank has been deteriorated, focusing on the corrosion resistance of the steel itself. However, in the above techniques, no consideration is given to the improvement of the corrosion resistance in the state where the coating film exists.

However, in the techniques of Patent Documents 12 and 13, the improvement of the corrosion resistance after coating, that is, the corrosion resistance after coating, which is not considered at all in the state of the coating film on the surface of the steel material, is important for realizing the long life of the corrosion-resistant steel material for crude oil tankers. It is extremely effective on the basis of the above, and although the development of this technology is expected, the current actual situation is that there is no technology to achieve the above-mentioned long life.

Therefore, an object of the present invention is to provide a corrosion-resistant steel material for crude oil tankers, which has excellent corrosion resistance in a corrosive environment caused by corrosive gases such as H ₂ S in the oil tank of the tanker, and which has excellent corrosion resistance in the ballast tank. It also has excellent corrosion resistance after painting in the corrosive environment.

The inventors of the present invention have conducted intensive studies in order to develop a corrosion-resistant steel material for an oil tanker that has excellent corrosion resistance in any of the corrosive environments of the oil tank portion and the ballast tank portion of the oil tanker. As a result, it was found that by containing Cr: more than 0.1% by mass and not more than 0.5% by mass, Cu: 0.03 to 0.5% by mass, and containing W: 0.01 to 0.5% by mass, Mo: 0.01 to 0.5% by mass, Sn: 0.001 ～0.2 mass%, Sb: 0.001～0.5 mass%, Ni: 0.005～0.3 mass%, and Co: 0.005～0.3 mass%, one or more kinds are optional additive elements, and the above-mentioned components satisfy a certain Corrosion-resistant steel materials for tankers exhibiting excellent corrosion resistance in any corrosive environment in the oil tank part of the tanker and the ballast tank part can be obtained thereby, and the present invention has been completed.

That is, the present invention is a corrosion-resistant steel material for crude oil tankers characterized by containing: C: 0.03 to 0.16% by mass, Si: 0.05 to 1.50% by mass, Mn: 0.1 to 2.0% by mass, and P: 0.025% by mass or less , S: 0.01 mass % or less, Al: 0.005 to 0.10 mass %, N: 0.008 mass % or less, Cr: more than 0.1 mass % and 0.5 mass % or less, Cu: 0.03 to 0.5 mass %, and containing 1 of W: 0.01 to 0.5% by mass, Mo: 0.01 to 0.5% by mass, Sn: 0.001 to 0.2% by mass, Sb: 0.001 to 0.5% by mass, Ni: 0.005 to 0.3% by mass, and Co: 0.005 to 0.3% by mass One or more kinds are optional addition elements, and the above-mentioned components are contained in such a way that the X value defined by the following (1) formula is 0.5 or less, and the Y value defined by the following (2) formula is 0.5 or less. The amount is composed of Fe and unavoidable impurities,

X value = (1-0.8×Cu ^0.5 )×{1-(0.8×W+0.4×Mo) ^0.3 }×{1-(0.8×Sn+0.8×Sb) ^0.5 }×{1-(0.05×Cr+ 0.03×Ni+0.03×Co) ^0.3 }×(1+S/0.01+P/0.05)…(1)

Y value = (1-0.3×Cr ^0.3 )×{1-(0.8×W+0.5×Mo) ^0.3 }×{1-(Sn+0.4×Sb) ^0.3 }×{1-(0.1×Ni+0.1× Co+0.05×Cu) ^0.3 }×{1+(S/0.01+P/0.08) ^0.3 }…(2)

Here, the element symbols in the above formulas indicate the content (% by mass) of each element.

The corrosion-resistant steel material for crude oil tankers of the present invention is characterized in that it contains W: 0.01-0.5% by mass, Mo: 0.01-0.5% by mass, Sn: 0.001-0.2% by mass, and Sb: 0.001-0.5% by mass. 1 or more than 2 kinds can be used as the optional additional elements mentioned above.

In addition, the corrosion-resistant steel material for crude oil tankers of the present invention is characterized in that, in addition to the above-mentioned optional additive elements, one or more selected from Ni: 0.005-0.3 mass % and Co: 0.005-0.3 mass % 2 kinds.

In addition, the corrosion-resistant steel material for crude oil tankers of the present invention is characterized in that, in addition to the composition of the above components, it further contains: % and V: one or more of 0.002 to 0.2% by mass.

In addition, the corrosion-resistant steel material for crude oil tankers of the present invention is characterized in that, in addition to the composition of the above components, it further contains: 1 or more of %.

Moreover, the corrosion-resistant steel material for crude oil tankers of this invention is characterized by containing B: 0.0002-0.003 mass % in addition to the said component composition.

Moreover, the corrosion-resistant steel material for crude oil tankers of the present invention is characterized in that a primer coating film containing Zn is formed on the surface of the steel material.

Moreover, the corrosion-resistant steel material for crude oil tankers of the present invention is characterized in that an epoxy-based coating film is formed on the surface of the steel material.

Invention effect

According to the present invention, in the corrosive environment of the oil tank part of the tanker, it is possible to provide a product in a bare state, a zinc-rich primer coating (zinc primer coating), or a zinc-rich primer and epoxy-based coating. In any state, it has excellent general corrosion resistance and local corrosion resistance, and even in the corrosive environment of the ballast tank, after the implementation of zinc-rich primer coating or the implementation of zinc-rich primer and epoxy A steel material that has excellent corrosion resistance after painting even in the painted state. Therefore, the steel material of this invention can be used suitably as a structural material of a tanker tank part and a ballast tank part.

Description of drawings

FIG. 1 is a diagram illustrating a test device used in a general corrosion test.

Fig. 2 is a diagram illustrating a test device used in a localized corrosion test.

Detailed ways

The reason for limiting the component composition of the steel material of the present invention to the above range will be described.

C: 0.03 to 0.16% by mass

C is an element effective in increasing the strength of steel, and in the present invention, in order to secure the desired strength, it is necessary to add 0.03% by mass or more. On the other hand, if added in excess of 0.16% by mass, the weldability and the toughness of the welded heat-affected zone will decrease. Therefore, C is added in the range of 0.03 to 0.16% by mass. Preferably it is 0.05-0.15 mass %, More preferably, it is 0.10-0.15 mass %.

Si: 0.05 to 1.50% by mass

Si is an element added as a deoxidizing agent and also an element that increases the strength of steel. Therefore, in the present invention, 0.05% by mass or more is added in order to secure the desired strength. However, if added in excess of 1.50% by mass, the toughness of the steel decreases. Therefore, Si is set to be in the range of 0.05 to 1.50% by mass. Preferably it is 0.20-1.50 mass %, More preferably, it is 0.30-1.20 mass %.

Mn: 0.1 to 2.0% by mass

Mn is an element that increases the strength of steel, and in the present invention, 0.1% by mass or more is added in order to obtain the desired strength. On the other hand, if added over 2.0% by mass, the toughness and weldability will be reduced. Therefore, Mn is made into the range of 0.1-2.0 mass %. Preferably it is 0.5-1.6 mass %, More preferably, it is 0.7-1.5 mass %.

P: 0.025% by mass or less

P is a harmful element that segregates at grain boundaries to lower the toughness of steel, and it is desirable to reduce its content as much as possible. In particular, when P is contained in excess of 0.025% by mass, the toughness is greatly reduced. Moreover, when P is contained exceeding 0.025 mass %, it will have a bad influence on corrosion resistance. Therefore, P is set to be 0.025% by mass or less. Preferably it is 0.015 mass % or less. More preferably, it is 0.010 mass % or less, More preferably, it is 0.008 mass % or less.

S: 0.01% by mass or less

S forms non-metal inclusions (non-metal inclusions) MnS and becomes a starting point of localized corrosion, and is a harmful element that reduces localized corrosion resistance, and it is desirable to reduce its content as much as possible. In particular, if it is contained in excess of 0.01% by mass, localized corrosion resistance will be remarkably lowered. Therefore, the upper limit of S is made 0.01% by mass. Preferably it is 0.005 mass % or less, More preferably, it is 0.001 mass % or less.

Al: 0.005 to 0.10% by mass

Al is an element added as a deoxidizer, and in the present invention, it is necessary to add 0.005% by mass or more. However, if added over 0.10% by mass, the toughness of the steel will decrease, so the upper limit of Al is made 0.10% by mass. Preferably it is 0.01-0.06 mass %, More preferably, it is 0.02-0.05 mass %.

N: 0.008% by mass or less

N is a harmful element that lowers toughness, and it is desirable to reduce its content as much as possible. In particular, if it is contained in excess of 0.008% by mass, the decrease in toughness increases, so the upper limit is made 0.008% by mass. Preferably it is 0.005 mass % or less, More preferably, it is 0.004 mass % or less.

Cr: More than 0.1% by mass and not more than 0.5% by mass

Cr moves into the rust layer as the corrosion progresses, and inhibits the enrichment of Cl ^- at the interface between the rust layer and the matrix by blocking the intrusion of Cl ^- into the rust layer. In addition, when a Zn-containing primer is applied, a composite oxide of Cr and Zn centered on Fe is formed, and Zn can persist on the surface of the steel sheet for a long period of time, thereby greatly improving corrosion resistance. In particular, the above-mentioned effects are effective in improving the corrosion resistance of the ballast tanks on the back side of the tanker tank floor, which are in contact with salty seawater. By lacquer treatment, corrosion resistance can be greatly improved compared with steel materials not containing Cr. If the Cr content is 0.1% by mass or less, the effect of Cr cannot be sufficiently obtained. On the other hand, if Cr is added in excess of 0.5% by mass, the toughness of the welded portion will be reduced. Therefore, Cr is set to be in the range of more than 0.1% by mass and not more than 0.5% by mass. In particular, when good weld toughness is required, the amount of Cr is preferably 0.11 to 0.20% by mass, more preferably 0.11 to 0.16% by mass.

Cu: 0.03 to 0.5% by mass

Cu is an element that increases the strength of steel, and is present in rust generated by corrosion of steel, and has an effect of improving corrosion resistance. If the addition is less than 0.03% by mass, the above effects cannot be sufficiently obtained. On the other hand, if the addition exceeds 0.5% by mass, the toughness of the welded heat-affected zone may decrease, surface cracking during production, and the like may occur. Therefore, Cu is added in the range of 0.03 to 0.5% by mass. Preferably it is 0.04-0.20 mass %, More preferably, it is 0.04-0.15 mass %.

The steel material of the present invention needs to contain, in addition to the above-mentioned components, one or two or more selected from W, Mo, Sn, Sb, Ni, and Co as optional additive elements.

W: 0.01 to 0.5% by mass

W has the effect of suppressing the pitting corrosion of the bottom plate of the tank part of the tanker, and also has the effect of improving the corrosion resistance against the general corrosion of the upper deck part of the tanker, and improving the ballast tank part which is repeatedly immersed in salt water and high The effect of corrosion resistance after painting in a wet (high moisture) corrosive environment. The above-mentioned effect is exhibited when adding 0.01% by mass or more. However, if it exceeds 0.5 mass %, the said effect will be saturated. Therefore, W is added in the range of 0.01 to 0.5% by mass. Preferably, it is the range of 0.02-0.3 mass %. More preferably, it is 0.03-0.10 mass %.

The reason why W has the effect of improving the corrosion resistance as described above is that WO ₄ ^2- is generated in the rust accompanying steel sheet corrosion, and the presence of this WO ₄ ^2- suppresses the intrusion of chloride ions. Steel surface. In addition, it is considered that FeWO ₄ is generated at a site where the pH of the steel plate surface is lowered, such as the anode section, and the presence of this FeWO ₄ suppresses the intrusion of chloride ions into the steel plate surface, and as a result, the corrosion of the steel plate is effectively suppressed. . Furthermore, it is considered that the corrosion of steel is suppressed due to the inhibition action (inhibiting action) caused by the adsorption of WO ₄ ^2- to the steel material surface.

Mo: 0.01 to 0.5% by mass

Mo not only suppresses the pitting corrosion of the bottom plate of the oil tanker tank, but also improves the corrosion resistance of the general corrosion of the upper deck of the tanker, and improves the corrosion resistance of the ballast tank under repeated salt water immersion and high humidity corrosive environments. effect on corrosion resistance. The above-mentioned effect is exhibited when adding 0.01% by mass or more, but when it exceeds 0.5% by mass, the above-mentioned effect is saturated. Therefore, Mo is added in the range of 0.01 to 0.5% by mass. Preferably, it is the range of 0.03-0.4 mass %. More preferably, it is 0.03-0.10 mass %.

In addition, the reason why Mo has the effect of improving the corrosion resistance as described above is that, like W, MoO ₄ ^2- is formed in the rust that accompanies the corrosion of the steel sheet, and the presence of this MoO ₄ ^2- inhibits the formation of chlorine. The compound ions invade the surface of the steel plate, and as a result, the corrosion of the steel plate is effectively inhibited.

Sn: 0.001 to 0.2% by mass, Sb: 0.001 to 0.5% by mass

Sn and Sb have the effect of suppressing the pitting corrosion of the bottom plate of the oil tank part of the tanker, and in addition, have the effect of improving the corrosion resistance to the general corrosion of the upper deck part of the tanker, and improving the repeated occurrence of salt water immersion and high pressure in the ballast tank part. The effect of corrosion resistance after coating in a wet corrosive environment. The above effects are exhibited when Sn: 0.001% by mass or more and Sb: 0.001% by mass or more are added. On the other hand, when Sn is added exceeding 0.2 mass % and Sb is added exceeding 0.5 mass %, the above effects are saturated. Therefore, Sn is added in the range of 0.001 to 0.2 mass %, and Sb is added in the range of 0.001 to 0.5 mass %. For Sn, it is preferably 0.005 to 0.10% by mass, more preferably 0.01 to 0.06% by mass. Moreover, it is preferable that it is 0.02-0.15 mass % with respect to Sb, and it is more preferable that it is 0.03-0.10 mass %.

Ni: 0.005 to 0.3% by mass, Co: 0.005 to 0.3% by mass

Ni and Co have greatly improved the corrosion resistance in the bare state (no-coating) and the corrosion resistance in the state of epoxy-based coating on the zinc-rich primer coating film by making the generated rust particles finer. sexual effect. Therefore, when it is desired to further improve corrosion resistance, it is preferable to supplementarily contain these elements. The above effects are exhibited when Ni: 0.005% by mass or more and Co: 0.005% by mass or more are added. On the other hand, even when Ni is added in excess of 0.3% by mass and Co in excess of 0.3% by mass, the above effects are saturated. Therefore, it is preferable to add Ni and Co within the above-mentioned ranges, respectively. Ni is preferably 0.01 to 0.2% by mass, more preferably 0.03 to 0.15% by mass. In addition, Co is preferably 0.01 to 0.2% by mass, more preferably 0.03 to 0.15% by mass.

In addition to containing the above-mentioned components in an appropriate range, the steel material of the present invention needs to satisfy the X value defined by the following formula (1) of 0.5 or less and the Y value defined by the following formula (2). 0.5 or less mode contains.

X value = (1-0.8×Cu ^0.5 )×{1-(0.8×W+0.4×Mo) ^0.3 }×{1-(0.8×Sn+0.8×Sb) ^0.5 }×{1-(0.05×Cr+ 0.03×Ni+0.03×Co) ^0.3 }×(1+S/0.01+P/0.05)…(1)

Y value = (1-0.3×Cr ^0.3 )×{1-(0.8×W+0.5×Mo) ^0.3 }×{1-(Sn+0.4×Sb) ^0.3 }×{1-(0.1×Ni+0.1× Co+0.05×Cu) ^0.3 }×{1+(S/0.01+P/0.08) ^0.3 }…(2)

Here, the symbol of each element in the said formula represents content (mass %) of these elements.

Here, the above formula (1) is an formula for evaluating the influence of each component on the corrosion in the tanker tank, and the coefficient of the component that improves the corrosion resistance is expressed as a minus (minus), and the corrosion resistance is expressed as minus. The coefficient of the deteriorating component is expressed as a positive (plus). Therefore, the smaller the value of X, the better the corrosion resistance of the steel material. The inventors of the present invention investigated the relationship between the above-mentioned value of X and the corrosion resistance of steel materials in a corrosive environment in an oil tanker tank, and found that when X is 0.5 or less, the corrosion resistance in a corrosive environment in an oil tanker tank Excellent, but when X exceeds 0.5, the above-mentioned corrosion resistance deteriorates. Therefore, the composition of the steel material of the present invention needs to be designed such that the X value is 0.5 or less. More preferably, the value of X is 0.4 or less.

In addition, the above expression (2) is an expression for evaluating the influence of each component on the corrosion resistance of the ballast tank after painting, and the coefficient of the component that improves the corrosion resistance is set to a negative value as in the above expression (1). In addition, coefficients representing components that degrade corrosion resistance are expressed in positive terms. Therefore, the smaller the value of Y, the better the corrosion resistance of the steel material. The inventors of the present invention investigated the relationship between the value of Y and the corrosion resistance after coating of steel materials in the corrosive environment in the ballast tank, and found that if Y is 0.5 or less, the corrosion resistance in the corrosive environment in the ballast tank After coating, the corrosion resistance is excellent, but when Y exceeds 0.5, the above corrosion resistance deteriorates. Therefore, the composition of the steel material of the present invention needs to be designed so that the Y value is 0.5 or less. More preferably, the Y value is 0.4 or less.

In addition, the steel material of the present invention is effective in suppressing pitting corrosion of the bottom plate of the oil tanker tank portion and general corrosion of the upper deck portion of the oil tanker with a small number of added elements, and improving the ballast tank portion where repeated salt water immersion and high For the effect of corrosion resistance after painting in a wet corrosive environment, it is preferable to contain elements selected from the above optional additives, especially W: 0.01-1.0% by mass, Mo: 0.01-0.5% by mass, Sn: 0.001- 0.2% by mass and Sb: 0.001 to 0.5% by mass, one or more, and next, preferably one or two selected from Ni and Co.

In addition, the steel material of the present invention may contain one or two or more selected from Nb, Ti, Zr, and V within the following range in addition to the above-mentioned components in order to increase the strength of the steel.

Nb: 0.001 to 0.1% by mass, Ti: 0.001 to 0.1% by mass, Zr: 0.001 to 0.1% by mass, and V: 0.002 to 0.2% by mass

Nb, Ti, Zr, and V are all elements that have the effect of increasing the strength of the steel material, and can be selectively added according to the required strength. In order to obtain the above effects, it is preferable to add 0.001 mass % or more of Nb, Ti, Zr, and 0.002 mass % or more of V, respectively. However, adding more than 0.1 mass % of Nb, Ti, and Zr and adding more than 0.2 mass % of V will lower the toughness, so it is preferable to add Nb, Ti, Zr, and V within the above ranges, respectively. In addition, for Nb, it is preferably 0.004 to 0.05% by mass, more preferably 0.005 to 0.02% by mass. For Ti, it is preferably 0.002 to 0.03% by mass, more preferably 0.002 to 0.01% by mass. Zr is preferably 0.001 to 0.05% by mass, more preferably 0.002 to 0.01% by mass. V is preferably 0.003 to 0.15% by mass, more preferably 0.004 to 0.1% by mass.

In addition, the steel material of the present invention may contain, in addition to the above components, one or two or more selected from Ca, REM, and Y within the following ranges in order to increase strength or improve toughness.

Ca: 0.0002 to 0.01% by mass, REM: 0.0002 to 0.015% by mass, and Y: 0.0001 to 0.1% by mass

Ca, REM, and Y all have the effect of improving the toughness of the welded heat-affected zone, and may be added as needed. By adding Ca: 0.0002% by mass or more, REM: 0.0002% by mass or more, and Y: 0.0001% by mass or more, the above-mentioned effects can be obtained, but if Ca exceeds 0.01% by mass, REM exceeds 0.015% by mass, and Y exceeds 0.1% by mass, On the contrary, it leads to a reduction in toughness, so it is preferable to add Ca, REM, and Y within the above-mentioned ranges. In addition, Ca is preferably 0.001 to 0.005% by mass, more preferably 0.001 to 0.003% by mass. It is preferable that it is 0.0005-0.015 mass % with respect to REM, and it is more preferable that it is 0.001-0.010 mass %. Y is preferably 0.0001 to 0.05% by mass, more preferably 0.0002 to 0.01% by mass.

Furthermore, the steel material of the present invention may contain B within the following range in addition to the above components.

B: 0.0002 to 0.003% by mass

B is an element that increases the strength of steel and can be added as needed. In order to obtain the above effects, it is preferable to add 0.0002% by mass or more. However, if added in excess of 0.003% by mass, the toughness will decrease. Therefore, it is preferable to add B in the range of 0.0002 to 0.003% by mass. Preferably it is 0.0002-0.002 mass %, More preferably, it is 0.0002-0.0015 mass %.

The steel material for tankers of the present invention produced by the above-mentioned method using a steel material having the above-mentioned composition is characterized in that it is not only excellent in corrosion resistance (general corrosion resistance, localized corrosion resistance) in an uncoated state, Moreover, the corrosion resistance after coating is also excellent. In particular, in the crude oil tanker steel material of the present invention, the coating amount of a primer such as a primer containing metal Zn or a Zn compound (hereinafter, collectively referred to as "zinc-rich primer") is 1.0 g/ ^m2 in terms of Zn content. As described above, by forming a zinc-rich primer coating film, localized corrosion resistance and general corrosion resistance can be greatly improved. It is preferably 10 g/m ² or more in terms of the average Zn content. More preferably, it is 15 g/m ² or more. The relationship between the thickness of the zinc-rich primer coating film and the Zn content on the steel surface depends on the Zn content in the zinc-rich primer. Generally, if the average coating thickness is 10 μm or more, it can cover the entire steel surface, regardless of the zinc-rich primer. Regardless of the type of primer, it is possible to ensure a coating amount of at least 1.0 g/m ² or more. In addition, from the viewpoint of improving corrosion resistance, the upper limit of the film thickness of the zinc-rich primer is not particularly set, but if the film becomes thicker, the cuttability and weldability will be reduced. Therefore, after coating the zinc-rich primer In the case of cutting and welding operations, the film thickness of the zinc-rich primer is preferably 100 μm or less, more preferably 50 μm or less. For example, the zinc-rich primer coating described above may be performed after shot blasting the surface of the steel sheet.

In addition, the crude oil tanker steel material of the present invention can form an epoxy-based coating film by coating an epoxy-based paint or the like on the surface of the uncoated steel material or the surface of the steel material coated with the above-mentioned zinc-rich primer. Accordingly, compared with the case of conventional steel materials for ships, local corrosion resistance and general corrosion resistance can be further improved, and especially when used in ballast tanks and the like under severe corrosion environments caused by seawater , can obtain more suitable corrosion resistance after painting, such as the effect of improving the swelling resistance of the coating film.

Here, the epoxy-based coating film is not particularly limited, and various epoxy-based resins can be used. For example, modified epoxy resin, tar epoxy resin, etc. can be used. In addition, the film thickness of the epoxy resin coating film is not particularly limited, but is preferably 500 μm or less, more preferably 350 μm or less from the viewpoint of coating cost and workability, and can be appropriately selected according to required characteristics.

Example

Various steels having the compositions of Nos. 1 to 36 shown in Table 1 were melted in a vacuum melting furnace or a converter to produce steel ingots or steel slabs, and the obtained steel ingots or steel slabs were reheated to 1200° C., and then Hot rolling at a finishing temperature of 800° C. was performed to produce a thick steel plate with a plate thickness of 16 mm. The steel plates of Nos. 1 to 36 obtained above were subjected to the following three kinds of corrosion resistance tests.

(1) Comprehensive corrosion test simulating the environment on the upper deck of an oil tanker

In order to evaluate the corrosion resistance to the general corrosion of the back of the upper deck of the oil tanker, cut rectangular pieces with a width of 25 mm x a length of 48 mm x a thickness of 4 mm from the thick steel plates of No. 1 to 36 above, and perform shot blasting (shot blasting) on the surface. ), so as to make a corrosion test piece in a bare state, and use the corrosion test equipment (corrosion test equipment) shown in Figure 1 to conduct a general corrosion test. The corrosion test device is composed of a corrosion test chamber (corrosion test chamber) 2 and a temperature-controlled plate (temperature-controlled plate) 3. In the corrosion test chamber 2, water 6 maintained at a temperature of 40° C. is injected, and then, the water 6 is injected into the above-mentioned water 6. Introduce a mixed gas (mixed gas) composed of 12 volume % of CO ₂ , 5 volume % of O ₂ , 0.01 volume % of SO ₂ , 0.3 volume % of H ₂ S and the balance of N ₂ (introduced gas) 4) Fill the corrosion test tank 2 with supersaturated vapor, so as to reproduce the corrosion environment on the back of the upper deck of the crude oil tanker. Then, a temperature change of 180 days was repeatedly applied to the corrosion test piece 1 provided on the upper back of the test tank by a temperature control plate 3 having a built-in heater (heater) and a cooling system (cooling system). Dew condensation water is formed on the surface to cause general corrosion, wherein, the above-mentioned temperature change takes 30°C×4 hours+50°C to 4 hours as one cycle. In FIG. 1 , 5 denotes an emission gas from the test tank.

After the above test, for each test piece, the thickness loss due to corrosion was obtained from the mass change before and after the test, and the case where the thickness loss was 60% or less relative to the value of the comparative steel No. 36 was evaluated as The general corrosion resistance was very good (⊚), the case of exceeding 60% and 70% or less was evaluated as good (◯), and the case of exceeding 70% was evaluated as poor general corrosion resistance (×).

(2) Pitting corrosion test simulating the environment of the bottom plate of the oil tanker tank

In order to evaluate the pitting corrosion resistance of the tank bottom plate of the tanker, a square of 50 mm in width x 50 mm in length x 15 mm in thickness was cut out from the same No. 1 to 36 steel plates used in the test of (1). Small pieces were subjected to shot blasting on the surface, and then two levels of coating were applied to make the film thickness of the inorganic system zinc-rich primer 0 μm (no coating) and 15 to 25 μm.

Then, masking is performed on the end faces and back faces of the above-mentioned four kinds of small pieces with anti-corrosion paint, and then the sludge containing crude oil collected from an actual tanker is coated on the surface (right face) which becomes the test face of the corrosion test. (sludge) to prepare corrosion coupons. At this time, a sulfur-mixed sludge in which 50% by mass of sulfur was mixed with the sludge was applied to a portion of 2 mmΦ in the center of the test surface, and only the sludge was uniformly applied to the other portions. In this test piece, the portion coated with the sulfur-mixed sludge acts as a starting point of corrosion and promotes localized corrosion. Therefore, the influence of the steel composition, the primer, and their combination on the inhibition of localized corrosion can be more accurately grasped.

Thereafter, the test piece was subjected to a corrosion test in which it was immersed in the test liquid 12 of the corrosion test apparatus shown in FIG. 2 for one month. The above-mentioned corrosion test device is a two-layer device consisting of a corrosion test tank 8 and a constant temperature tank 9. In the corrosion test tank 8, a test solution 12 capable of causing localized corrosion similar to that of the actual crude oil tank bottom plate is injected, and the test piece 7 is immersed in it. The above-mentioned test solution 12 used artificial seawater specified in ASTM D1141 as the test mother water, and introduced a partial pressure ratio adjusted to 5 vol % O ₂ +10 vol % H ₂ S in this liquid. , and the balance is a liquid obtained from a mixed gas (introducing gas 10) composed of N ₂ gas. In addition, the temperature of the test solution 12 was maintained at 50° C. by adjusting the temperature of water 13 poured into a constant-temperature bath 9 . In addition, since the introduction gas 10 is continuously supplied, the test liquid 12 is constantly stirred. In Fig. 2, 11 denotes exhaust gas from the test tank.

After the above-mentioned corrosion test, the rust generated on the surface of the test piece was removed, and then the corrosion form was visually observed, and the corrosion depth of the localized corrosion occurrence part was measured by a depth meter, and the corrosion depth was compared with that of No. 36 comparative steel. When the value is 40% or less, the localized corrosion resistance is evaluated as very good (⊚), when it exceeds 40% and 50% or less, it is evaluated as good (◯), and when it exceeds 50%, the localized corrosion resistance is evaluated as poor (×).

(3) Corrosion test after painting to simulate ballast tank environment

In order to evaluate the corrosion resistance after painting in the ballast tank environment, test pieces with a width of 50 mm x a length of 150 mm x a thickness of 5 mm were cut out from steel plates of No. 1 to 36, which are the same as those used in the test of (1). , after shot blasting the surface of the test piece, the surface treatment of the following conditions A and B was carried out to prepare an exposure test piece.

Condition A: A two-layer film of zinc-rich primer (about 15 μm) and tar epoxy resin coating (about 200 μm) is formed on the surface of the test piece

Condition B: A single-layer film of tar epoxy resin paint (about 200 μm) is formed on the surface of the test piece

In addition, on the test pieces of the above-mentioned conditions A and B having a coating film, scratches (scratches) in a straight line with a length of 80 mm from the coating film to the surface of the substrate were given with a utility knife.

Then, the above-mentioned test piece was provided to the following corrosion test in the order of (keeping in artificial seawater at a temperature of 30°C for 1 day)→(keeping in a humid atmosphere with a temperature of 40°C and a relative humidity of 98 to 99% for 1 day) day) as one cycle, and repeated 60 cycles (120 days), thus serving as a corrosion cycle test (corrosion cycle test) simulating the environment of the ballast tank of an actual ship. The corrosion resistance of each test piece was evaluated as follows: For the test pieces under the conditions A and B with the coating film, the swelling area of the coating film that occurred around the scratch was measured, and the ratio was 50 to the value of the comparative steel No. 36. When the percentage is less than 50%, the corrosion resistance after painting is very good (⊚), when it is more than 50% and less than 70%, it is good (◯), when it is more than 70%, the corrosion resistance after painting is evaluated. Bad (×).

The results of the corrosion resistance tests (1) to (3) above are shown in Table 2 together with the X value and Y value obtained from the composition of each steel sheet. It can be confirmed from Table 2 that the thick steel plates satisfying the composition of the present invention and satisfying the conditions No. 1 to 30 of the X value and the Y value all show a higher than target level in all corrosion tests (1) to (3). Good corrosion resistance. Among them, the above-mentioned target level is represented by the ratio of No. 1 to 30 thick steel plates to the basic steel material (No. 36), while No. 31 to 35 do not satisfy the conditions of the present invention. In any one or more of the corrosion tests, corrosion exceeding the target level was observed, wherein the target level is represented by the ratio of No. 31-35 thick steel plates to No. 36 steel.

The steel material of the present invention is suitable for use in other ships, crude oil tanks on the ground, and the like in addition to crude oil tankers.

Label description

1, 7: Test piece

2, 8: Corrosion test tank

3: Temperature control board

4, 10: Introduce gas

5, 11: Exhaust gas

6, 13: water

9: constant temperature bath

12: Test solution

Table 2

Note: Each corrosion resistance was evaluated based on No.36 steel.

Claims (8)

1. A corrosion-resistant steel material for a crude oil tanker, comprising C: 0.03 to 0.16% by mass, Si: 0.05 to 1.50% by mass, Mn: 0.1 to 2.0% by mass, P: not more than 0.025% by mass, and S: not more than 0.01% by mass , Al: 0.005-0.10% by mass, N: 0.008% by mass or less, Cr: more than 0.1% by mass and 0.5% by mass or less, Cu: 0.03-0.5% by mass, and W: 0.01-0.5% by mass, One or more of Mo: 0.01 to 0.5% by mass, Sn: 0.001 to 0.2% by mass, Sb: 0.001 to 0.5% by mass, Ni: 0.005 to 0.3% by mass, and Co: 0.005 to 0.3% by mass are optional Add elements, and the above-mentioned components are contained in such a way that the X value defined by the following formula (1) is 0.5 or less, and the Y value defined by the following formula (2) is 0.5 or less, and the balance is Fe and unavoidable impurities. constitute, X value = (1-0.8×Cu ^0.5 )×{1-(0.8×W+0.4×Mo) ^0.3 }×{1-(0.8×Sn+0.8×Sb) ^0.5 }×{1-(0.05×Cr+ 0.03×Ni+0.03×Co) ^0.3 }×(1+S/0.01+P/0.05)…(1) Y value = (1-0.3×Cr ^0.3 )×{1-(0.8×W+0.5×Mo) ^0.3 }×{1-(Sn+0.4×Sb) ^0.3 }×{1-(0.1×Ni+0.1× Co+0.05×Cu) ^0.3 }×{1+(S/0.01+P/0.08) ^0.3 }…(2) Here, the element symbols in the above formulas represent the mass % content of each element. 2. The corrosion-resistant steel material for crude oil tankers according to claim 1, which contains W: 0.01-0.5% by mass, Mo: 0.01-0.5% by mass, Sn: 0.001-0.2% by mass, and Sb: 0.001-0.5% by mass One or more of % as the optional additional elements. 3. The corrosion-resistant steel for crude oil tankers according to claim 2, which further contains 1 selected from Ni: 0.005-0.3% by mass and Co: 0.005-0.3% by mass in addition to the optional additive elements. species or 2 species. 4. The corrosion-resistant steel material for crude oil tankers according to any one of claims 1 to 3, which further contains, in addition to the composition of the components, a material selected from the group consisting of Nb: 0.001 to 0.1% by mass, Ti: 0.001 to 0.1% by mass %, Zr: 0.001 to 0.1% by mass, and V: 0.002 to 0.2% by mass, or two or more. 5. The corrosion-resistant steel material for crude oil tankers according to any one of claims 1 to 4, which further contains, in addition to the composition, Ca: 0.0002 to 0.01% by mass, REM: 0.0002 to 0.015% by mass % and Y: 1 or more of 0.0001 to 0.1% by mass. 6. The corrosion-resistant steel material for crude oil tankers according to any one of claims 1 to 5, further comprising B: 0.0002 to 0.003% by mass in addition to the composition. 7. The corrosion-resistant steel material for crude oil tankers according to any one of claims 1 to 6, wherein a primer coating film containing Zn is formed on the surface of the steel material. 8. The corrosion-resistant steel material for crude oil tankers according to any one of claims 1 to 7, wherein an epoxy-based coating film is formed on the surface of the steel material.

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