JP2002155341A - Corrosion resistant steel having excellent carbon dioxide gas corrosion resistance and weld zone toughness, and corrosion resistant line pipe using the steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a corrosion resistant steel which has excellent carbon dioxide gas corrosion resistance and weld zone toughness and suitable as oil well pipes and line pipes for the production and transportation of gas, petroleum or the like used in an energy field or steel for plants, and to provide a corrosion resistant line pipe. SOLUTION: The corrosion resistant steel having carbon dioxide gas corrosion resistance and weld zone toughness has a composition containing, by mass, <=0.30% C, 2.0 to <13.0% Cr and 0.0001 to 0.01% Mg, and, if required, containing <=0.5% Si, 0.2 to 2.0% Mn, 0.001 to 0.20% Al and <=0.015% N, and, if required, further containing Ti, Nb, Cu, Ni and Mo, and balance iron with inevitable impurities. The corrosion resistant line pipe uses the steel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to oil well pipes and line pipes for producing and transporting gas and petroleum used in the field of energy, and steels for plants, and more particularly to gas and petroleum containing carbon dioxide gas. The present invention relates to a corrosion-resistant steel and a corrosion-resistant line pipe capable of obtaining good carbon dioxide gas corrosion resistance and welded toughness when used in an environment of the type described above.

[0002]

2. Description of the Related Art Oil well pipes, line pipes, and the like for producing and transporting oil, gas, and the like generally use materials of carbon steel and low alloy steel. However, in the case of petroleum and gas containing a large amount of carbon dioxide, the corrosion rate is much higher than that of ordinary corrosion under a neutral humid environment or atmospheric corrosion. For oil well pipes and line pipes for the production and transportation of oil, 13% C, which is a material that has excellent corrosion resistance to carbon dioxide as a material by adding a corrosion inhibitor or the like to the oil.
Stainless steel materials such as r steel have been used. However, the use of corrosion inhibitors is not preferable from the viewpoint of environmental protection, and the application of stainless steel to line pipes and the like is expensive in terms of material costs and is cost-effective to apply to oil wells with limited remaining life. It is over spec in the point of.

[0003] On the other hand, Japanese Patent Application Laid-Open No. 56-93856 discloses that the content of Cr is 3 to 12% in order to improve the local corrosion of the welded portion as well as the overall corrosion by carbon dioxide gas,
Is regulated to 0.1% or less. However, in the invention described in this publication, the toughness of the welded portion is low, and in the example, the toughness of the welded portion when using the inventive steel in which C is reduced to 0.01% or less is V notch charpy at 0 ° C. The absorption energy is limited to 16 kg / mm2 or less (about 160 J or less).

Accordingly, as a material used in a carbon dioxide corrosive environment such as petroleum or gas containing a large amount of carbon dioxide, a corrosion resistant steel excellent in low temperature toughness of a welded portion together with carbon dioxide corrosion resistance and a corrosion resistant line using the same are provided. The development of a pipe was desired.

[0005]

The present invention is used in the field of energy, particularly when applied as an oil well pipe or line pipe for producing or transporting gas or petroleum containing carbon dioxide, or as a material for a plant. It is an object of the present invention to provide a corrosion-resistant steel having excellent carbon dioxide corrosion resistance and good toughness of a welded portion, and a corrosion-resistant line pipe using the same.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a proper amount of Cr is contained in order to improve carbon dioxide corrosion resistance.
A corrosion-resistant steel and a corrosion-resistant linepipe using the same, characterized by containing an appropriate amount of Mg in order to improve the toughness of the welded portion, are as follows. (1) As a chemical component, in mass%, C: 0.3% or less,
Cr: less than 2 to 13%, Mg: 0.0001 to 0.01
% Corrosion resistant steel with excellent carbon dioxide gas corrosion resistance and weld toughness, characterized in that the steel contains iron and inevitable impurities. (2) As chemical components, in mass%, C: 0.02% or less, Cr: 2 to less than 13%, Mg: 0.0001 to 0.
Corrosion-resistant steel with excellent carbon dioxide corrosion resistance and weld toughness, characterized in that it contains 0.1% and the balance consists of iron and unavoidable impurities. (3) As chemical components, in mass%, C: 0.02% or less, Cr: 2 to 5%, Mg: 0.0001 to 0.01%
Corrosion-resistant steel excellent in carbon dioxide corrosion resistance and weld toughness, characterized by containing iron and the balance of iron and unavoidable impurities. (4) Further, in mass%, Si: 0.5% or less, Mn:
0.2-2%, Al: 0.001-0.2% or less, N:
The corrosion-resistant steel having excellent carbon dioxide corrosion resistance and welded toughness according to any one of the above (1) to (3), containing 0.015% or less. (5) Further, in mass%, Ti: 0.001 to 0.2%
And Nb: one or two of 0.01 to 0.5%
The corrosion-resistant steel having excellent carbon dioxide corrosion resistance and weld toughness according to any one of the above (1) to (4), characterized by containing a seed. (6) Any one of the above (1) to (5), wherein one or more of Cu, Ni and Mo are contained in a total amount of 0.1 to 1%. Corrosion-resistant steel excellent in carbon dioxide gas corrosion resistance and weld toughness described in the item. (7) Carbon dioxide gas corrosion resistance characterized by being manufactured using the corrosion resistant steel having excellent carbon dioxide gas corrosion resistance and weld toughness described in any one of the above (1) to (6). Corrosion-resistant line pipe with excellent weld toughness.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the components of the steel of the present invention will be described below. In addition,% shown below shall mean the mass% unless there is particular description. C: C is an element effective for improving the strength of steel, but in the present invention, as the C content increases, the low-temperature toughness and carbon dioxide gas corrosion resistance of the welded portion decrease. In particular, when the C content exceeds 0.3%, a large amount of carbides precipitate at the grain boundaries during the tempering process of the steel material, and the low-temperature toughness of the welded portion is deteriorated, and the carbon dioxide gas corrosion resistance is also reduced. Therefore, in the present invention, the C content is set to 0.3% or less. Further, in the present invention, when used in an environment in which good low-temperature toughness and carbon dioxide gas corrosion resistance of a welded portion are required, the C content is set to 0.02% or less.

Mg: Mg is an element effective for precipitating fine Mg-based oxides in the heat affected zone of the steel material and suppressing the growth of austenite grains, thereby significantly improving the toughness. Particularly, in Cr-containing steel, tempering embrittlement due to coarsening of the austenitic grain size in the weld heat-affected zone causes remarkable deterioration in toughness. Therefore, Mg is added in an amount of 0.0001% to improve the toughness of the welded portion of Cr-containing steel. It is necessary to add above. On the other hand, the Mg content is 0.01%
If the Mg content exceeds the upper limit, the Mg-based oxide becomes coarse and it becomes difficult to improve the toughness of the welded portion.
1%.

Cr: Cr is an element effective for suppressing carbon dioxide gas corrosion. In particular, it has a sufficient resistance to corrosion under the conditions of a temperature of 80 ° C. and a pressure of 0.1 MPa or more, which are the corrosive environments targeted by the present invention. In order to obtain carbon dioxide gas corrosiveness, the Cr content needs to be 2% or more. On the other hand, when the Cr content is 13% or more, the effect of improving the carbon dioxide gas corrosion resistance that is commensurate with the added amount cannot be obtained. Therefore, in the present invention, Cr
The content is less than 2 to 13%. Further, in order to obtain better corrosion resistance to carbon dioxide, the lower limit of the content is set to 3%.
%.

[0010] In addition, particularly when used in an environment where a large amount of oxygen is mixed in oil or gas, for example, in a dissolved oxygen amount of 100 ppm or more, the addition of a large amount of Cr causes the steel material to be used. Since pitting corrosion, which is local corrosion of carbon dioxide, occurs, the upper limit of the Cr content is set to 5 in order to suppress local corrosion as well as overall corrosion of carbon dioxide in such an environment.
%, And the range of the Cr content is set to 2 to 5%. Also in this case, the lower limit of the content is preferably set to more than 3% in order to obtain more excellent carbon dioxide gas corrosion resistance.

The above are the basic components of the present invention. In order to improve the strength, toughness and corrosion resistance to carbon dioxide gas, the following components can be added. Si: Si is an element having the same deoxidizing action as Al and Ti, and may be added. However, the Si content is 0.5%
If it exceeds, the low-temperature toughness of the welded portion deteriorates, so the upper limit of the content is set to 0.5%.

Mn: Mn is an element having an effect of improving low-temperature toughness and may be added. In order to obtain the effect sufficiently, the Mn content needs to be 0.2% or more. On the other hand, if the content exceeds 2%, the toughness is rather reduced. Therefore, when Mn is added, the content is 0.1.
2 to 2%. Al: Al is an element having the same deoxidizing action as Si and Ti, and may be added. To get the full effect,
The Al content needs to be 0.001% or more. On the other hand, if the Al content exceeds 0.2%, the cleanliness of the steel is reduced and low-temperature toughness is deteriorated. Therefore, the content when Al is added is set to 0.001% to 0.2.

N: N is an element that remains in steel as an unavoidable impurity. In order to improve the low-temperature toughness, the lower one is preferable. In particular, when the N content exceeds 0.015%, the low-temperature toughness is significantly deteriorated.
15%. Ti, Nb: Ti and Nb are effective for improving the strength of the base material, and by setting the lower limit of the fine Ti content to 0.001% in the weld heat affected zone and forming Nb carbide, It is an element effective for suppressing the growth of austenite grains and increasing the weld toughness. In order to sufficiently obtain these effects, the lower limit of the Ti content is set to 0.1.
001% and the lower limit of the Nb content needs to be 0.01%, while the Ti content exceeds 0.2%
Excessive addition such that the b content exceeds 0.5% degrades toughness. Therefore, when one or two of Ti and Nb are added, the Ti content is set to 0.001 to 0.2.
%, And the Nb content is in the range of 0.01 to 0.5%.

Cu, Ni, Mo: Cu, Ni and Mo
Are all in Cr-containing steel in a total amount of 0.1 in order to improve the stability of a corrosion-resistant film such as Cr.
When the total content exceeds 1%, the effect is saturated, and conversely, the carbon dioxide gas corrosion resistance is deteriorated. Therefore, in the present invention, when one or more of Cu, Ni and Mo are added, the total amount thereof is in the range of 0.1 to 1%.

The above-mentioned steel of the present invention can obtain a necessary balance between strength and low-temperature toughness by adjusting the metal structure by heat treatment such as controlled rolling or quenching and tempering. The method for producing a steel pipe using the steel of the present invention is not particularly limited, and any method such as a pipe forming method by seamless rolling, a method of forming a steel sheet, and a method of forming a pipe by welding may be used. Can be. The steel pipes manufactured by these methods have an effect of being excellent in carbon dioxide gas corrosion resistance and also having excellent weld toughness in a steel pipe having a seam weld.

The seam welding at this time may be applied to submerged arc welding with relatively large heat input in addition to electric resistance welding and laser beam welding. The steel of the present invention, which is excellent in carbon dioxide gas corrosion resistance and strength and low-temperature toughness, can be used for various devices that require carbon dioxide gas corrosion resistance. It is used as a line pipe or a flow line which requires low temperature toughness, and has a remarkable effect that the life can be improved as compared with the conventional one.

[0017]

EXAMPLES Table 1 shows the results of a corrosion resistance test and a test of low-temperature toughness of a weld, together with the chemical composition of steel. The corrosion resistance test is a general test 1 of a carbon dioxide gas corrosive environment without oxygen contamination.
And Test 2 in the case where oxygen was mixed. As a condition of Test 1 without oxygen contamination, a 2-week immersion test was performed in a formation water simulation solution having a chlorine concentration of 5% at a temperature of 80 ° C. and a carbon dioxide pressure of 0.3 MPa. As the condition of Test 2 with oxygen contamination, oxygen was blown for 3 hours a day until the dissolved oxygen concentration reached 2 ppm, and pure carbon dioxide gas was blown for the other times, and the carbon dioxide gas partial pressure was 0.1 MPa and the temperature was 80.
A 4-week immersion test was performed in a formation water simulating solution having a chlorine concentration of 10% and a temperature of 10 ° C.

The results of the evaluation of carbon dioxide gas corrosion resistance shown in Table 1 are as follows. The corrosion amount of carbon steel having a Cr content of 0.01% or less is 1, and the corrosion amount of carbon steel having a corrosion amount of 0.05 or less is ◎. 0.
A sample having a rating of 5 or less was evaluated as ○. In the case where local corrosion occurred, even when the amount of overall corrosion was small, it was indicated by x. In addition, the evaluation test for the low-temperature toughness of the weld was performed at a heat input of 2.7 kJ / mm.
After performing the IG welding, a 2 mm V notch Charpy test piece taken so that the center of the notch was a melting line was subjected to a Charpy impact test. Table 1 shows the results of the evaluation of the low-temperature toughness of the welded portion. As a result of measuring the absorbed energy in a Charpy impact test at −20 ° C., the absorbed energy value was 200 J.
The above-mentioned ones were regarded as having excellent low-temperature toughness and indicated by ◎, those having an absorbed energy of less than 30 J were regarded as having poor low-temperature toughness, indicated by ×, and the middle was indicated by ○.

The strength of the steel was adjusted to a grade of X65 to X80 in the API standard by quenching and tempering heat treatment. In Table 1, Nos. 8 to 11 and 21 are X70 grades, Nos. 17 and 22 are X80 grades, and all the others are those whose strength is adjusted to X65 grade. The steels of Nos. 1 to 18 are steels of the present invention whose chemical components are within the range specified by the present invention, and the steels of Nos. 19 to 20 are comparative steels whose chemical components are out of the range specified by the present invention.

The steels of the present invention all show good corrosion resistance,
In addition, the low-temperature toughness of the heat affected zone was good. on the other hand,
In all the comparative steels, the low-temperature toughness of the heat affected zone was insufficient, and the superiority of the steel of the present invention is apparent. further,
Using a hot-rolled sheet No. 16 in Table 1, after cold forming, an electric resistance welded steel pipe was formed by high-frequency welding.
A 65 grade line pipe was manufactured. This line pipe was girth welded, Charpy test specimens were taken from the vicinity of the weld line and the low-temperature toughness of the heat affected zone was measured. As a result, at any position from the weld line, the absorbed energy at -20 ° C was 200 J or more. Very high value,
It was possible to manufacture a line pipe with extremely high low temperature toughness in the heat affected zone.

[0021]

[Table 1]

[0022]

According to the present invention, it is possible to obtain a corrosion-resistant steel having excellent carbon dioxide gas corrosion resistance, a good balance of strength and low-temperature toughness, and a good low-temperature toughness of a welded part. This is a great contribution to the device design.

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[Procedure amendment]

[Submission date] January 5, 2001 (2001.1.5)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction contents]

N: N is an element that remains in steel as an unavoidable impurity. In order to improve the low-temperature toughness, the lower one is preferable. In particular, when the N content exceeds 0.015%, the low-temperature toughness is significantly deteriorated.
015%. Ti, Nb: Ti and Nb are effective for improving the strength of the base metal, and also form fine Nb carbide in the weld heat affected zone, thereby suppressing the growth of austenite grains and increasing the weld toughness. It is an effective element. In order to obtain these effects sufficiently, it is necessary to set the lower limit of the Ti content to 0.001% and the lower limit of the Nb content to 0.01%.
Excessive addition of more than 0.2% in content and more than 0.5% in Nb content deteriorates toughness. Therefore, Ti
When one or two of Nb and Nb are added, Ti
The content is set to 0.001 to 0.2%, and the Nb content is set to 0.1 to 0.2%.
The range is from 0.01 to 0.5%.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction contents]

The results of the evaluation of carbon dioxide gas corrosion resistance shown in Table 1 are as follows. The corrosion amount of carbon steel having a Cr content of 0.01% or less is 1, and the corrosion amount of carbon steel having a corrosion amount of 0.05 or less is ◎. 0.
A sample having a rating of 5 or less was evaluated as ○. In addition, those where local corrosion occurred were indicated by black circles even if the overall corrosion amount was small. In addition, the low temperature toughness evaluation test of the welded portion was performed by performing MIG welding at a heat input of 2.7 kJ / mm, and then a 2 mm V notch Charpy test piece was taken so that the center of the notch was a melting line, and a Charpy impact test was performed. Was done. The results of the evaluation of the low-temperature toughness of the welds in Table 1 are as follows. As a result of measuring the absorbed energy in a Charpy impact test at −20 ° C., the absorbed energy value was 200.
Those having J or more were judged as having excellent low-temperature toughness, and were indicated by ◎. Those having an absorbed energy value of less than 30 J were regarded as having poor low-temperature toughness, indicated by ×, and the middle was indicated by ○.

Claims (7)

[Claims] (1) As a chemical component, C: 0.3 by mass%.
% Or less, Cr: less than 2 to 13%, Mg: 0.0001 to
Corrosion-resistant steel with excellent carbon dioxide corrosion resistance and weld toughness, characterized by containing 0.01% and the balance being iron and unavoidable impurities. 2. C: 0.0% by mass as a chemical component.
2% or less, Cr: less than 2 to 13%, Mg: 0.0001
Corrosion resistant steel with excellent carbon dioxide corrosion resistance and welded toughness, characterized in that it contains about 0.01% and the balance is iron and unavoidable impurities. 3. As a chemical component, C: 0.0% by mass.
2% or less, Cr: 2-5%, Mg: 0.0001-0.
Corrosion-resistant steel with excellent carbon dioxide corrosion resistance and weld toughness, characterized in that it contains 0.1% and the balance consists of iron and unavoidable impurities. Further, in mass%, Si: 0.5% or less, Mn: 0.2 to 2%, Al: 0.001 to 0.2%
The corrosion resistant steel having excellent carbon dioxide corrosion resistance and welded toughness according to any one of claims 1 to 3, wherein the steel contains N: 0.015% or less. 5. Further, in mass%, Ti: 0.001 to 0.001.
5. The composition according to claim 1, which contains one or two of 0.2% and Nb: 0.01 to 0.5%.
Corrosion resistant steel excellent in carbon dioxide corrosion resistance and weld toughness according to any one of the above. 6. The method according to claim 1, further comprising one or more of Cu, Ni and Mo in a total amount of 0.1 to 1%. Corrosion-resistant steel excellent in carbon dioxide corrosion resistance and weld toughness described in 1. 7. Carbon dioxide corrosion resistance and carbon dioxide gas corrosion resistance characterized by being manufactured using the corrosion resistant steel excellent in carbon dioxide gas corrosion resistance and weld toughness according to any one of claims 1 to 6. Corrosion-resistant line pipe with excellent weld toughness.