JP3265869B2 - ERW steel pipe excellent in carbon dioxide gas corrosion resistance and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric resistance welded steel pipe excellent in corrosion resistance to carbon dioxide and a method for producing the same. Here, the carbon dioxide gas corrosion resistance means corrosion resistance to petroleum, natural gas, and the like containing carbon dioxide gas and moisture.

[0002]

2. Description of the Related Art Petroleum and natural gas containing carbon dioxide gas react with water contained in petroleum and natural gas,
Since acidic water is generated, the inner surface of the steel pipe for transporting the same may be completely corroded during use. Therefore, a steel material containing about 0.5% of Cr may be used for the purpose of suppressing this (Japanese Patent Laid-Open No. 4-341540).

[0003] Since this steel material has excellent corrosion resistance in a humid environment containing carbon dioxide gas, it is used as a steel for seamless pipes and arc welded steel pipes such as UOE. However, the electric resistance welded pipe cannot be used in a wet carbon dioxide gas environment because selective corrosion of the electric resistance weld occurs.

[0004]

SUMMARY OF THE INVENTION The present invention relates to an electric resistance welded steel pipe having excellent overall corrosion resistance in the above-mentioned wet carbon dioxide gas environment and not causing selective corrosion of the electric resistance welded part, that is, carbon dioxide gas corrosion resistance. It is intended to provide an excellent ERW steel pipe.

[0005]

[Means for Solving the Problems]

(1) The invention of claim 1 is an electric resistance welded steel pipe having the following component composition (the component composition is wt%) and having excellent carbon dioxide gas corrosion resistance. As a main component, C: 0.01 to 0.2%,
Si: 0.1 to 0.35%, Mn 0.5 to 2%,
P: 0.03% or less, S: 0.002% or less, Cr:
It consists of steel containing 0.3-1%, with the balance being substantially Fe.

(2) The invention of claim 2 is an electric resistance welded steel pipe having the following component composition (the component composition is wt%) and having excellent carbon dioxide gas corrosion resistance. The steel component composition according to claim 1, further comprising: Cu: 0.05 to 0.5%, Ca: 0.0
01 to 0.006%, Ni: 0.5% or less, Mo: 0.
5% or less, Nb: 0.001 to 0.1%, V: 0.00
1-0.01%, Ti: 0.001-0.1%, 1
It consists of steel containing one or more species and the balance being substantially Fe.

(3) In the invention according to claim 3, carbon dioxide corrosion resistance according to claim 1 or 2, wherein S is 0.001% or less of the above component composition (the component composition is wt%). ERW steel pipe with excellent resistance.

(4) A fourth aspect of the present invention is a method for manufacturing an electric resistance welded steel pipe, comprising the following steps. As main components, C: 0.01 to 0.2%, Si: 0.1 to
0.35%, Mn 0.5-2%, P: 0.03%
Hereinafter, a hot-rolled steel sheet containing S: 0.002% or less, Cr: 0.3 to 1%, and the balance being substantially Fe is prepared.
(B) The hot-rolled steel sheet is processed into an electric resistance welded steel pipe, and (c) a heat treatment is performed to heat the electric resistance welded portion of the electric resistance welded steel pipe between Ac3 and 1100 ° C. (5) A fifth aspect of the present invention is a method for manufacturing an electric resistance welded steel pipe, comprising the following steps. (A) The steel component composition according to claim 4, further comprising Cu:
0.05-0.5%, Ca: 0.001-0.006
%, Ni: 0.5% or less, Mo: 0.5% or less, Nb:
0.001-0.1%, V: 0.001-0.01%,
Ti: A hot-rolled steel sheet containing one or two or more of 0.001 to 0.1%, and the balance being substantially Fe is prepared. (B) The hot-rolled steel sheet is used as an electric resistance welded steel pipe. And (c) heat-treating the ERW portion of the ERW steel pipe between Ac3 and 1100 ° C.

[0009]

The reason for limiting the composition of the steel (the composition of the steel is wt%) as described above will be explained. The C content needs to be added in an amount of 0.01% or more to secure the strength of the steel, but the upper limit is set to 0.2% from the viewpoint of weldability and toughness.

[0010] The content of Si must be 0.1% or more as a deoxidizing material for steel, but the upper limit is set to 0.35% because excessive addition makes the steel brittle.

[0011] The Mn content is 0.5 to secure the strength of the steel.
% Or more is necessary, but excessive addition degrades toughness, so the upper limit is set to 2%.

[0012] The P content is 0.03% or less because it is an impurity that deteriorates the toughness of steel.

S is considered to be the cause of the selective corrosion of the ERW part.
The more this is reduced, the more the selective corrosion is reduced. The reason for this is that the steel melted at the time of ERW is quenched, so that part of S does not precipitate as MnS, and the ERW part becomes more base than other parts because it is solid-dissolved in steel. It is because it becomes.

Therefore, when the S content is 0.001% or less, the solid solution S in the ERW portion is so small that it can be ignored. Therefore, selective corrosion of the ERW portion does not occur even without heat treatment. Use in a wet carbon dioxide gas environment is possible. On the other hand,
When the ERW portion is subjected to a heat treatment at a heating temperature of Ac3 or higher, S dissolved in steel precipitates as MnS or the like, so that even when the S content is slightly high, the ERW portion selective corrosion can be suppressed. In this case, the content of S can be set to 0.002% or less.

When the Cr content is 0.3% or more, the carbon dioxide corrosion resistance of the steel is enhanced, but the addition of 1% or more deteriorates the weldability of the steel, so the upper limit is made 1%.

The Cu content of 0.05% or more improves the HIC (hydrogen-induced cracking) resistance, so that it may be added as necessary. Therefore, the upper limit is set to 0.5%.

If the Ca content is 0.001% or more, it may be added as necessary to improve the HIC resistance through the control of inclusion morphology, but excessive addition degrades the toughness of the steel. The upper limit is made 0.006%.

Ni and Mo may be added as necessary to improve the HIC resistance of the steel.
In order to degrade SCC (sulfide stress corrosion cracking) characteristics, the upper limit of each content is set to 0.5%.

The content of Nb, V, and Ti increases the strength by adding 0.001% or more, but the content of Nb, V, and Ti is 0.1% or less because excessive addition deteriorates the toughness.

The above is a desirable steel composition, but other components and unavoidable impurities may be contained as long as the object of the present invention is not impaired.

The heat treatment of the electric resistance welded portion has the effect of eliminating the unevenness of the structure resulting from the electric resistance welded welding and suppressing the selective corrosion of the electric resistance welded portion by precipitating S dissolved in steel as MnS. If the heating temperature is lower than Ac3, the structure is not uniform, and the effect of preventing selective corrosion does not appear. Heating temperature is 1
If the temperature exceeds 100 ° C., the toughness deteriorates, so the upper limit is 1100.
° C. The specific method of the heat treatment is usually performed by so-called post annealing.

Here, various methods such as high-frequency resistance welding, high-frequency induction welding, resistance welding and the like can be used as a method for manufacturing the ERW pipe, and the ERW pipe in the present invention may be any method.

[0023]

EXAMPLE A steel having the chemical composition shown in Table 1 was cast in a laboratory into a 50 kg ingot vacuum-melted. This is 1200 ° C
And rolled to a steel plate having a thickness of 50 mm, and then air-cooled.
A 50 × 150 × 200 mm plate was cut out from this steel plate and rolled to a plate thickness of 6 mm at a heating temperature of 1200 ° C. and a rolling end temperature of 820 ° C. Immediately after the end of rolling, after cooling to 550 ° C at a cooling rate of about 10 ° C / sec by mist spray,
It was inserted into an electric furnace heated to 550 ° C. and cooled.
The above steps were adopted to simulate the conditions of hot rolling in actual production.

6 × 35 × 1 from steel plate cooled to room temperature
A 000 mm test piece was cut out and welded by ERW using an ERW simulator as shown in FIG. As shown in FIG. 1, two steel plates 1 were passed through a squeeze roll 3, and an electric resistance welding operation was performed by a current supplied from a contact tip. ERW welding conditions were as follows: welding speed 15 m / min,
The input power is 240 kW and the upset amount is 2.0 mm.

A test piece of 3.5 × 30 × 60 mm was cut out from the ERW part, and the surface was wet-polished, and then subjected to a carbon dioxide gas corrosion test using the equipment shown in FIG. As shown in FIG.
The test piece 5 was immersed in a test solution, attached to a rotating disk 6, rotated by a motor 7, and subjected to a corrosion test. The test solution was artificial seawater saturated with carbon dioxide, and the temperature of the solution was 80 ° C.
The rotation speed of the test piece is 3 m / sec and the test time is 300 h
r.

The weight of the test piece before and after the corrosion test was measured,
The corrosion weight loss C (mg / cm ² ) per unit area was determined.
Experience with C ≦ 80mg / for use in wet carbon dioxide gas environment
there needs to be a cm ^2. Further, the specimen after the test was cross-sectionally examined to examine the degree of selective corrosion of the electric resistance welded portion. An index α expressed by the following equation was used for evaluation of the ERW selective corrosion. To prevent troubles caused by selective corrosion of the ERW part, experience shows that α ≦ 1.
It must be 2 or less.

Α = d1 / d2 d1: Corrosion depth of the electric resistance welded part (mm) d2: Corrosion depth of the base material part (mm)

Further, an electric resistance welded tube of 508 mm × 12.7 (thickness) mm was manufactured by an actual machine. Table 2 shows the chemical components and the heat treatment conditions of the electric resistance welded portion. A test piece similar to that described above was cut out from the ERW part after the manufacture, and subjected to a carbon dioxide gas corrosion test. The test results are shown in Tables 1 and 2. It is understood that the steel of the present invention has a small amount of corrosion in a wet carbon dioxide gas environment and does not cause selective corrosion of the electric resistance welded portion.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

The electric resistance welded steel pipe according to the present invention is excellent in corrosion resistance even when used as a steel pipe for transporting petroleum or natural gas containing carbon dioxide gas, even when the electric resistance welded portion and other parts on its inner surface are hardly corroded. ing. Further, by adopting the manufacturing method according to the present invention, it is possible to manufacture a line pipe having a small amount of corrosion in the above-mentioned humid carbon dioxide gas environment and not causing selective corrosion of the electric resistance welded portion.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a simulator for manufacturing an electric resistance welded pipe.

FIG. 2 is a schematic view of a steel carbon dioxide corrosion test apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel plate 2 Contact tip 3 Squeeze roll 5 Test piece 6 Rotating disk 7 Motor 8 Heater 9 Carbon dioxide gas inlet 10 Gas outlet

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-57-131346 (JP, A) JP-A-57-5847 (JP, A) JP-A-5-112844 (JP, A) JP-A-5-112844 93243 (JP, A) JP-A-4-341540 (JP, A) JP-A-6-293915 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 9/08 C22C 38 / 00 301 C22C 38/38 C22C 38/58

Claims (2)

(57) [Claims] 1. A method for manufacturing an electric resistance welded steel pipe, comprising the following steps. (A) As main components (component composition is wt%): C: 0.01 to 0.2%, Si: 0.1 to 0.35%, Mn: 0.5 to 2%, P: 0 0.03% or less, S: 0.0007% or less , Cr: 0.3 to 1%, and a hot-rolled steel sheet whose balance is substantially Fe is prepared. processed into, heat treatment is performed for heating the electric resistance welded portion of (c) the electric resistance welded steel pipe between Ac ₃ C. to 1100 ° C.. 2. A method for producing an electric resistance welded steel pipe, comprising the following steps. (A) As main components (component composition is wt%): C: 0.01 to 0.2%, Si: 0.1 to 0.35%, Mn: 0.5 to 2%, P: 0 0.03% or less, S: 0.0007% or less , Cr: 0.3 to 1%, Cu: 0.05 to 0.5%, Ca: 0.001 to 0.
006%, Ni: 0.5% or less, Mo: 0.5% or less, Nb: 0.001 to 0.1%, V: 0.001 to 0.0
1%, a hot rolled steel sheet containing one or more of Ti: 0.001 to 0.1%, and the balance being substantially Fe is prepared. (C) heat-treating the ERW part of the ERW steel pipe between Ac _{3 and} 1100 ° C.