JPH0593243A - Steel for line pipe excellent in corrosion resistance to carbon dioxide gas and hydrogen sulfide gas - Google Patents

Abstract

PURPOSE:To provide superior corrosion resistance under the environment where carbon dioxide gas and hydrogen sulfide gas exist in the form of a mixture by adding Cr, Cu, Ni, Ca, etc., while regulating the balance among them and also specifying the ACR value and the value of Pcm%, respectively. CONSTITUTION:A steel for line pipe has a composition containing, by weight, 0.04-0.10% C, 0.15-0.50% Sr, 0.80-1.50% Mn, <=0.015% P, <=0.005% S, 0.30-1.50% Cr, 0.05-0.20% Ni, 0.05-0.25% Cu, 0.005-0.050% Al, and 0.0020-0.0060% Ca. Further, Cu/Ni is regulated to 0.8-3.0, and also, the value of ACR represented by equation I and the value of Pcm represented by equation II are regulated to 1.0-3.0 and <=0.19%, respectively. If necessary, one or more kinds among 0.010-0.030% Ti, 0.010-0.050% Nb, 0.010-0.050% V, and 0.05-0.15% Mo are incorporated into the steel having the above composition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel for line pipes having excellent corrosion resistance against carbon dioxide gas and hydrogen sulfide gas, and at the same time excellent circumferential weldability.

[0002]

2. Description of the Related Art Corrosion of steel pipes used for transporting natural gas containing carbon dioxide or hydrogen sulfide gas or petroleum causes problems of general corrosion and local corrosion at welds in the former case and hydrogen sulfide in the latter case. Hydrogen Induced Cracking (HIC)
There is a problem called cracking. As a countermeasure against these problems, Japanese Patent Publication No. 59-
19179, JP-B-61-16418, JP-A-57-5848 and JP-A-58-1333.
As disclosed in Japanese Patent Laid-Open No. 48-48, Cr is 1.0 to 3.0%, 0.5 to 5.0%, and 1.0 to 3.0, respectively.
A method of containing 5.0% or a method with high running cost such as injection of an inhibitor and control of a dew point is adopted. There is also a method of adding a small amount of Cu or Ni.

On the other hand, as a measure against HIC by hydrogen sulfide gas, Japanese Patent Publication No. 60-35982 and Japanese Patent Publication No. 61-55.
No. 570, Japanese Patent Publication No. 1-21849, and Japanese Patent Laid-Open No. Sho 6
JP-A-2-21326 and JP-A-63-13714.
As disclosed in Japanese Patent Laid-Open No. 0, it is shown that Cu is contained as a basic additive element, and Ni and Cr are further contained if necessary.

However, in the actual use environment of the pipeline, carbon dioxide gas and hydrogen sulfide gas are often mixed. In addition, both may be contained in large amounts, and in some places the composition of the environmental gas may change little by little over time, and hydrogen sulfide gas will gradually be mixed in even after the carbon dioxide environment was initially in operation. There are also many. When used in such an environment, conventional steel for carbon dioxide gas is resistant to HI.
The C property was insufficient, and the steel for hydrogen sulfide gas had problems in general corrosion and local corrosion resistance in the weld. As described above, steels targeted for hydrogen sulfide gas corrosion or steels targeted for carbon dioxide gas corrosion have been conventionally used, but they have satisfactory corrosion resistance against both hydrogen sulfide gas and carbon dioxide gas. However, steel having good weldability has not yet been developed.

[0005]

DISCLOSURE OF THE INVENTION The present invention provides a line pipe steel having good corrosion resistance even in an environment in which carbon dioxide gas and hydrogen sulfide gas are mixed without impairing the weldability which should be provided as a basic characteristic of the line pipe. It was made to provide.

[0006]

The present invention provides C: 0.04.
~ 0.10%, Si: 0.15-0.50%, Mn:
0.80 to 1.50%, P ≦ 0.015%, S ≦ 0.0
05%, Cr: 0.30 to 1.50%, Ni: 0.05
~ 0.20%, Cu: 0.05-0.25%, Al:
0.005-0.050%, Ca: 0.0020-0.
And Cu / Ni = 0.8 to 3.0, the ACR value represented by the following equation is 1.0 to 3.0, and the Pcm (%) represented by the following equation is 0. A steel for line pipes having excellent corrosion resistance to carbon dioxide gas and hydrogen sulfide gas, which is less than 19%. ACR = (%) Ca ^{* /} 1.25 (%) S, where (%) Ca ^* = (%) Ca- [130 (%) Ca + 0.18] × (%) O, Pcm (%) = (%) C + (%) Si / 30 + (%) Mn / 20 + (%) Cu / 20 + (%) Ni / 60 + (%) Cr / 20, and

C: 0.04 to 0.10%, Si: 0.1
5 to 0.50%, Mn: 0.80 to 1.50%, P ≦
0.015%, S ≦ 0.005%, Cr: 0.30
1.50%, Ni: 0.05 to 0.20%, Cu: 0.
05-0.25%, Al: 0.005-0.050%,
Ca: 0.0020 to 0.0060% and Cu / Ni
= 0.8 to 3.0, the ACR value represented by the following formula is 1.0
To 3.0, and further Ti: 0.010 to 0.030
%, Nb: 0.010 to 0.050%, V: 0.010
To 0.050%, and Mo: 0.05 to 0.15%, and one or more of them is contained, and Pcm (%) represented by the following formula is 0.19% or less. A steel for line pipes having excellent corrosion resistance to carbon dioxide gas and hydrogen sulfide gas. ACR = (%) Ca ^{* /} 1.25 (%) S However, (%) Ca ^* = (%) Ca- [130 (%) Ca + 0.18] × (%) OPcm (%) = (%) C + (%) Si / 30 + (%) Mn / 20 + (%) Cu / 20 + (%) Ni / 60 + (%) Cr / 20 + (%) V / 10 + (%) Mo / 1 5 Here, all% are weights. % Shall be indicated.

[0008]

According to the present invention, Cr, Cu, Ni and Ca as well as Ti, Nb, V and Mo are added in a well-balanced amount and Pcm (%) that reflects the maximum hardness during welding is appropriate. It is a steel for line pipes with a good balance.
The reasons for limiting the chemical composition and each characteristic value will be described below.

C: If it is less than 0.04%, it is necessary to add other elements in the range where Pcm (%) exceeds 0.19% in order to obtain the required strength, and good weldability cannot be secured. Further, when C exceeds 0.10%, the present invention is characterized by the addition of Cr and Cu, so that it becomes difficult to adjust Pcm (%). Therefore, C is 0.04 to 0.10.
Limit to the range of%. Si: Si is necessary as a deoxidizer during steel making,
If it is less than 0.15%, it is necessary to add a large amount of Al, which may further deteriorate the toughness. On the other hand, if it exceeds 0.50%, the toughness is similarly deteriorated. Therefore, Si is limited to the range of 0.15 to 0.50%. Mn: Mn is an effective element that gives strength to steel,
If it is less than 0.80%, the amount of other elements added becomes too large,
Weldability deteriorates. On the other hand, if it exceeds 1.5%, the amount of low-temperature transformation products increases and the HIC susceptibility remarkably increases. Therefore, Mn is limited to the range of 0.80 to 1.50%.

P and S: P deteriorates HIC resistance and SSCC resistance through segregation and S through nonmetallic inclusions. Therefore, P ≦ 0.015%, S ≦ 0.0
Limited to 05%. Cr: added to improve carbon dioxide corrosion resistance, but 0.30
If it is less than 1.0%, the effect is substantially absent, and if it exceeds 1.50%, not only the improvement of carbon dioxide corrosion resistance is saturated, but also the weldability is deteriorated. Therefore, Cr is 0.30 to 1.50%
It is limited to the range of. Cu: added to improve HIC resistance, but 0.05
If it is less than%, the effect is substantially absent. Further, Cu hinders the improvement of the carbon dioxide gas corrosion resistance of Cr, so the content was made 0.25% or less. Therefore, Cu is limited to the range of 0.05 to 0.25%. Ni: Ni is less effective than Cr and Cu, but effective in improving carbon dioxide corrosion resistance and HIC resistance, preventing deterioration of hot workability due to addition of Cu, and also effective in improving low temperature toughness. .. If it is less than 0.05%, there is no effect, and if it exceeds 0.20%, the effect is saturated, which causes a cost increase. Therefore, Ni is 0.05 to 0.2
It is limited to the range of 0%. Cu / Ni = 0.8-
Limiting the range to 3.0 is N without increasing the cost.
This is because the effect of i is exerted.

Al: Al is added at 0.005% or more for deoxidation, but if it exceeds 0.050%, cleanliness is impaired.
Therefore, Al is limited to the range of 0.005 to 0.050%. Ca: HI resistance of pipelines used in harsh environments
To improve the C property, addition of Cu alone is not sufficient, and the shape of sulfur (S) -based inclusions is controlled by the addition of Ca, but 0.0020% or more must be added to obtain the effect. On the other hand, addition of 0.0060% or more, on the other hand, is
Sex deteriorates. Therefore, Ca is 0.0020 to 0.0
It is limited to the range of 060%. Even if Ca is in the proper range, there is a proper amount of addition in relation to S, and the proper amount of addition is such that the ACR value shown by the following equation is in the range of 1.0 to 3.0. ACR = (%) Ca ^{* /} 1.25 (%) S However, (%) Ca ^* = (%) Ca- [130 (%) Ca + 0.18] x (%) O. The ACR value used here indicates the ratio at which the added Ca effectively binds to S, and ACR = 1.0 indicates that all S is stoichiometrically fixed. .. A
When the CR value is high, the reliability of the shape control by Ca is improved, but when it exceeds 3.0, the CaO-based inclusions are increased and the HIC resistance and the SSCC resistance are deteriorated. Therefore, the ACR value is limited to the range of 1.0 to 3.0.

[0012] Ti, Nb, V and Mo have the effect of improving the strength and toughness of the steel without promoting segregation which increases the HIC sensitivity, so Ti: 0.010
~ 0.050%, Nb: 0.010-0.050%,
V: 0.010-0.050%, Mo: 0.05-0.
One type or two or more types added in the range of 15 are added as required, but if the content is less than the respective lower limit value, the effect is not remarkable. On the other hand, when the value exceeds the upper limit, the effect becomes saturated, which is not only disadvantageous in terms of cost, but also V and Mo result in unnecessarily increasing the Pcm value. Therefore, Ti, Nb, V and M
o is limited to the above range. Pcm (%) is 0.19%
If it exceeds, the maximum hardness of the heat affected zone (Vickers hardness, load = 10 kg) exceeds 280 when welding with a cellulosic coated arc welding rod with a large amount of diffusible hydrogen in the weld metal. Occasionally, weld hydrogen cracking and HIC susceptibility increase. Therefore, Pcm (%) is limited to 0.19% or less. By making the above-mentioned limitations on the chemical composition, it is possible to obtain an excellent steel for line pipes which simultaneously satisfies the corrosion resistance to carbon dioxide gas and hydrogen sulfide gas.

[0013]

EXAMPLES Tensile strength characteristics, carbon dioxide corrosion resistance and HIC resistance were investigated for steel types having the chemical compositions shown in Table 1. Here, with the exception of Steel D, hot-rolled steel sheets having a thickness of 12.7 mm were prepared by the usual controlled rolling method, and the obtained steel materials were examined for tensile strength characteristics, carbon dioxide gas corrosion resistance and HIC resistance. In the table, steel types A to P are steel types according to the present invention, and steel types Q to T are steel types of comparative examples. For steel type D, after billet processing, the outer diameter was 168.3 mm and the thickness was 1
A 2.7 mm seamless steel pipe was produced. After pipe making, 920 ℃
A heat treatment of water cooling for 10 minutes at 630 ° C. for 15 minutes at 630 ° C. was performed. As a test method, carbon dioxide corrosion resistance is a test piece having a size of 12 mm thickness-50 mm width-100 mm length, and a flow rate of 1 m / sec is applied in an environment of 50 ° C., 3.5% NaCl aqueous solution and 1 atm saturated carbon dioxide gas. It was immersed for 30 days. The HIC test is 12 mm thick-50 mm width-1.
A test piece having a length of 00 mm was immersed in a 0.5% acetic acid + 5% NaCl aqueous solution saturated with 1 atmosphere of hydrogen sulfide gas for 96 hours, and then HIC cracking was detected by ultrasonic flaw detection.
The result was displayed as a crack area ratio (%). The above test results are summarized in Table 2.

[0014]

[Table 1]

[0015]

[Table 2]

As can be seen from Tables 1 and 2, the steels according to the present invention show good carbon dioxide corrosion resistance, HIC resistance and weldability.

[0017]

INDUSTRIAL APPLICABILITY As described above, the steel according to the present invention exhibits good carbon dioxide corrosion resistance, HIC resistance and weldability and can be sufficiently used even in a harsh environment containing carbon dioxide and hydrogen sulfide gas at the same time. It is a steel that can be manufactured at low cost.

Claims (2)

[Claims] 1. C: 0.04 to 0.10%, Si: 0.
15 to 0.50%, Mn: 0.80 to 1.50%, P ≦
0.015%, S ≦ 0.005%, Cr: 0.30
1.50%, Ni: 0.05 to 0.20%, Cu: 0.
05-0.25%, Al: 0.005-0.050%,
Ca: 0.0020 to 0.0060% and Cu / Ni
= 0.8 to 3.0, the ACR value represented by the following formula is 1.0
To 3.0 and Pcm (%) represented by the following formula is 0.19% or less, steel for line pipes excellent in corrosion resistance to carbon dioxide and hydrogen sulfide gas. ACR = (%) Ca ^{* /} 1.25 (%) S, where (%) Ca ^* = (%) Ca- [130 (%) Ca + 0.18] × (%) O. Pcm (%) = (%) C + (%) Si / 30 + (%) Mn / 20 + (%) Cu / 20 + (%) Ni / 60 + (%) Cr / 20. 2. C: 0.04 to 0.10%, Si: 0.
15 to 0.50%, Mn: 0.80 to 1.50%, P ≦
0.015%, S ≦ 0.005%, Cr: 0.30
1.50%, Ni: 0.05 to 0.20%, Cu: 0.
05-0.25%, Al: 0.005-0.050%,
Ca: 0.0020 to 0.0060% and Cu / Ni
= 0.8 to 3.0, the ACR value represented by the following formula is 1.0
To 3.0, and further Ti: 0.010 to 0.030
%, Nb: 0.010 to 0.050%, V: 0.010
To 0.050%, and Mo: 0.05 to 0.15%, and one or more of them is contained, and Pcm (%) represented by the following formula is 0.19% or less. Steel for line pipes with excellent corrosion resistance to carbon dioxide gas and hydrogen sulfide gas. ACR = (%) Ca ^{* /} 1.25 (%) S However, (%) Ca ^* = (%) Ca- [130 (%) Ca + 0.18] × (%) OPcm (%) = (%) C + (%) Si / 30 + (%) Mn / 20 + (%) Cu / 20 + (%) Ni / 60 + (%) Cr / 20 + (%) V / 10 + (%) Mo / 1 5