Steel for crude oil tank, method for producing the same, crude oil tank and corrosion prevention method therefor

• US 20050230012A1
• Filed: 06/18/2003
• Published: 10/20/2005
• Est. Priority Date: 06/19/2002
• Status: Active Grant

• Current Assignee: Nippon Steel Corporation
• Original Assignee: Nippon Steel Corporation
• Inventors: Hasegawa, Toshiei, Shishibori, Akira, Usami, Akira, Katoh, Kenji
• Granted Patent: US 7,922,838 B2
• Time in Patent Office: Days
• US Class Current: 148/648
• CPC Class Codes: C21D 8/0205 of ferrous alloys
• CPC Class Codes: C21D 8/0257 with diffusion of elements, e.g. decarburising, nitriding
• CPC Class Codes: C21D 9/50 for welded joints
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/06 containing aluminium
• CPC Class Codes: C22C 38/08 containing nickel C22C38/105 takes precedence
• CPC Class Codes: C22C 38/12 containing tungsten, tantalum, molybdenum, vanadium, or niobium
• CPC Class Codes: C22C 38/14 containing titanium or zirconium
• CPC Class Codes: C22C 38/16 containing copper

Abstract

The present invention provides: a steel for a welded structure to be used for a crude oil tank that exhibits excellent general and local corrosion resistance in crude oil corrosion caused in a steel oil tank and is capable of suppressing the formation of corrosion products (sludge) containing solid sulfur; a method for producing said steel; a crude oil tank; and a method for preventing a crude oil tank against corrosion. The present invention makes it possible to obtain general and local corrosion resistance in a crude oil tank environment and suppress the formation of corrosion products (sludge) containing solid sulfur by using a steel: containing, in mass, 0.001 to 0.2% C, 0.01 to 2.5% Si, 0.1 to 2% Mn, 0.03% or less P, 0.007% or less S, 0.01 to 1.5% Cu, 0.001 to 0.3% Al, 0.001 to 0.01% N as basic components and, further, 0.01 to 0.2% Mo and/or 0.01 to 0.5% W; and preferably satisfying the following expression;
Solute Mo+Solute W≧0.005%.

Claims

1. A steel for a crude oil tank characterized by containing, in mass, 0.001 to 0.2% C, 0.01 to 2.5% Si, 0.1 to 2% Mn, 0.03% or less P, 0.007% or less S, 0.01 to 1.5% Cu, 0.001 to 0.3% Al, 0.001 to 0.01% N and one or both of 0.01 to 0.2% Mo and 0.01 to 0.5% W, with the balance consisting of Fe and unavoidable impurities.

2. A steel for a crude oil tank according to claim 1, characterized by satisfying the following expression, in mass %;

Solute MO+Solute W≧

0.005%.

3. A steel for a crude oil tank according to claim 1, characterized in that the carbon equivalent (Ceq.), in mass %, defined by the equation (1) is 0.4% or less;

Ceq.=C+Mn/6+(Cu+Ni)/15+(Cr+Mo+W+V)/5 

 

(1).

4. A steel for a crude oil tank according to claim 1, characterized in that the Cr content is less than 0.1 mass %.

5. A steel for a crude oil tank according to claim 1, characterized by further containing, in mass, 0.1 to 3% Ni and/or 0.1 to 3% Co.

6. A steel for a crude oil tank according to claim 1, characterized by further containing, in mass, one or more of 0.01 to 0.3% Sb, 0.01 to 0.3% Sn, 0.01 to 0.3% Pb, 0.01 to 0.3% As and 0.01 to 0.3% Bi.

7. A steel for a crude oil tank according to claim 1, characterized by further containing, in mass, one or more of 0.002 to 0.2% Nb, 0.005 to 0.5% V, 0.002 to 0.2% Ti, 0.005 to 0.5% Ta, 0.005 to 0.5% Zr and 0.0002 to 0.005% B.

8. A steel for a crude oil tank according to claim 1, characterized by further containing, in mass, one or more of 0.0001 to 0.01% Mg, 0.0005 to 0.01% Ca, 0.0001 to 0.1% Y, 0.005 to 0.1% La and 0.005 to 0.1% Ce.

9. A steel for a crude oil tank according to claim 1, characterized in that the area percentage of microscopic segregation portions where the Mn concentration is 1.2 times or more the average Mn concentration in the steel is 10% or less.

10. A method for producing a steel for a crude oil tank, characterized in that, in the event of applying accelerated cooling after hot rolling a slab containing components according to claim 1, the average cooling rate of said accelerated cooling is in the range from 5 to 100°

C./sec., the accelerated cooling end temperature is in the range from 600°

C. to 300°

C., and the cooling rate in the temperature range from said accelerated cooling end temperature to 100°

C. is in the range from 0.1 to 4°

C./sec.

11. A method for producing a steel for a crude oil tank characterized by applying tempering or annealing at 500°

C. or lower to a steel produced by the method according to claim 10.

12. A method for producing a steel for a crude oil tank, characterized in that, in the event of applying normalizing after hot rolling a slab containing components according to claim 1, the heating temperature of said normalizing is in the range from the Ac₃ transformation temperature to 1,000°

C. and the average cooling rate in the temperature range from 700°

C. to 300°

C. is in the range from 0.5 to 4°

C./sec.

13. A method for producing a steel for a crude oil tank characterized by applying tempering or annealing at 500°

C. or lower to a steel normalized according to claim 12.

14. A method for producing a steel for a crude oil tank according to claim 10, characterized by, before hot rolling a slab applying diffusion heat treatment to said slab at a heating temperature of 1,200 to 1,350′

C. and for a retention time of 2 to 100 hr.

15. A crude oil tank characterized in that the floor plate, deck plate, side walls and structural members thereof are made wholly or partially of a steel for a crude oil tank according to claim 1.

16. A method for protecting a crude oil tank to against corrosion characterized by removing, either mechanically or chemically, hot-rolling scale on the surface of a crude oil tank according to claim 15 and exposing the base steel substrate.

17. A method for protecting a crude oil tank against corrosion according to claim 16, characterized by forming one or more layers of a coating film 10 μ

m or more in thickness on the surface after hot-rolling scale is removed mechanically or chemically.