WO2017206321A1

WO2017206321A1 - Low alloy steel, steel pipe and manufacturing method therefor

Info

Publication number: WO2017206321A1
Application number: PCT/CN2016/093512
Authority: WO
Inventors: 张丛
Original assignee: 深圳市樊溪电子有限公司
Priority date: 2016-06-03
Filing date: 2016-08-05
Publication date: 2017-12-07
Also published as: CN106011666A

Abstract

Low alloy steel having good corrosion resistance to a carbon dioxide gas and good toughness of a weld zone, comprising the following components in percentage by weight: C: 0.0035-0.02%, Cr: 3.0%-5.0%, Si: 0.1% or less, and Mn: 0.6-2.0%. The relation between the Mn content [T.Mn] and the C content [T.C] meets a condition that [T.Mn]×[T.C] ranges from 0.007 to 0.03. The remaining components are iron and unavoidable impurities. Also provided are a low alloy steel pipe made of low alloy steel and having good corrosion resistance to a carbon dioxide gas and good toughness of a weld zone, a steel pipe made of low-alloy steel having good corrosion resistance to a carbon dioxide gas and good toughness of a weld zone, and a manufacturing method therefor.

Description

Low alloy steel, steel pipe and manufacturing method thereof

Technical field

The present invention relates to an oil and gas pipeline for use in the energy field, and more particularly to a low-alloy steel for use in a petroleum-natural gas environment containing carbonic acid gas, having good resistance to carbonation gas corrosion and weld site toughness, and low use of the alloy. Alloy steel pipe and its manufacturing method.

Background technique

Oil well pipes and pipes used in the production and transportation of oil and natural gas usually use carbon steel and low alloy steel materials. However, compared with the corrosion or atmospheric corrosion in the normal neutral humid environment, the oil and gas containing more carbonic acid gas corrodes very quickly, and therefore, the oil well pipe for the production and transportation of such highly corrosive carbonated gas and natural gas is transported. And piping, usually adding corrosion inhibitor to oil, and using 13% Cr steel excellent in carbonation resistance in the material of piping steel. On the one hand, the corrosive inhibitors used in oil are not good for environmental protection. On the other hand, the use of stainless steel pipes is costly, the use time is limited, and the use of corrosive conditions is not too harsh, cost-effectiveness will exceed the limit.

In order to improve the overall corrosion of the carbon dioxide gas and the local corrosion of the welded portion, it is stipulated in the Japanese Patent Publication No. Sho 56-93856 that the steel for piping contains 3 to 12% of Cr and 0.1% or less of C. However, the welded portion of the invention described in this publication has a low toughness. In the steel of the invention, when the C content was reduced to 0.01% or less, the absorbed energy in the V-notch impact test at 0 ° C was less than 16 kg/mm 2 (about 160 J or less), and the toughness of the welded portion of the steel was low.

Therefore, it is hoped to develop a low-alloy steel which can be used in a carbonic acid gas corrosive environment for high carbonic acid oil and natural gas, has good carbonation corrosion resistance and low temperature toughness at a welded portion, and is inexpensive. Low alloy steel pipe.

Summary of the invention

In order to improve the corrosion resistance of carbonation gas, the present invention adds an appropriate amount of Cr, and suppresses the content of C and Si in order to improve the toughness of the welded portion, and balances the C-Mn content or the C-Mn-Mo content according to a specific relationship. The composition includes various low-alloy steels according to the specified content, the low-alloy steel pipes and the manufacturing method of the steel pipes, and the main components are as follows:

(1) Chemical composition, containing C: 0.0035 to 0.02%, Cr: 3.0% to 5.0%, Si: 0.1% or less, Mn: 0.6 to 2.0%, and the amount of Mn [T.Mn] and C in terms of mass percentage The relationship of [TC] is in accordance with [T.Mn]×[TC] in the range of 0.007 to 0.03, and the other parts are iron and unavoidable impurities. According to this component, the alloy has good resistance to carbonation corrosion and weld site toughness. steel.

(2) In addition, Al: 0.001 to 0.20% or less, N: 0.015% or less, Ti: 0.001 to 0.2%, and Nb: 0.01 to 0.5% by mass percentage, and other low alloy steels as described in the above (1) It has good resistance to carbonation and corrosion of welded parts.

(3) Further, in terms of mass percentage, one or more of Cu and Ni are contained in a mass percentage, and each component is in a range of 0.01% to 1%, and other components are as described in the above (1) and (2). The technical solution characterized by the content is a low-alloy steel with good resistance to carbonation corrosion and toughness of the welded portion.

(4) In addition, Mo: 0.01%-1% by mass percentage, and Mo, Mn, C content, [[T.Mo], respectively, [T.Mo], [T.Mn], [TC] The range of +[T.Mn])×[TC] is in the range of 0.007 to 0.03, and the other components are as described in any one of the above (1) to (3), and the technical solution characterized by the content has good carbonation resistance. Low alloy steel with corrosive and toughness at the weld.

It is characterized by the low alloy steel described in any one of the above (1) to (4), which is characterized by Technical solution, low alloy steel pipe with good resistance to carbonation corrosion and toughness of welded parts.

The invention is applied to the field of energy, especially oil well pipes and pipes for production and transportation of carbonic acid-containing oil and natural gas, or suitable as raw materials for factory use. SUMMARY OF THE INVENTION An object of the present invention is to develop a low alloy steel which has both good carbonation corrosion resistance and weld site toughness and a steel pipe using the same, and provides a method for producing such a steel pipe.

For the above-mentioned low-alloy steel pipe manufacturing, the steel slab needs to be manufactured as a steel pipe according to the following steps, and the technical solution characterized by the low-alloy steel electric seam steel pipe with good resistance to carbonation gas corrosion and weld site toughness, steps as follows:

(1) After the slab is heated at a temperature of 1050 ° C to 1300 ° C, hot rolling is performed, and then hot rolling at a reduction ratio of 50% or more is completed in a temperature range of not more than 950 ° C and above the critical point of Ar 3 , and then at 20 ° C / The cooling rate above s is cooled to below 500 ° C, and then the engineering operation of the hot rolled coil is taken out;

(2) The hot rolled coil is cut into a cylindrical shape by a steel strip having a predetermined width, and is continuously molded into a cylindrical shape, and the electric resistance is welded to both ends of each steel strip to manufacture an electric seam steel pipe.

The above as well as other objects, advantages and features of the present invention will become apparent to those skilled in the <

DRAWINGS

Some specific embodiments of the present invention are described in detail below by way of example, and not limitation. The same reference numbers in the drawings identify the same or similar parts. Those skilled in the art should understand that the drawings are not necessarily drawn to scale. In the figure:

Figure 1 is a graph showing the relationship between C content and Mn content for 3% Cr steel.

detailed description

The following is a description of the reasons why the steel composition of the present invention is limited. % indicates the mass %.

C: Carbon is an element that increases the strength of steel. In the present invention, when the carbon content is increased, the low-temperature toughness and the carbonation-resistant corrosion resistance of the welded portion are lowered, and particularly when the carbon content exceeds 0.02%, a large amount of carbides are precipitated from the metal crystal during the tempering of the steel material, resulting in deterioration of the low-temperature toughness of the welded portion. Moreover, the carbonation resistance is lowered, and therefore, the carbon content is limited to 0.02%. According to the relationship between manganese content and temperature cross-linking manganese [T.Mn], the inventors reduced the carbon content and made the corresponding manganese content above a certain value, finding the ratio of low-temperature toughness of the welded part, the lowest The amount of carbon is determined by the corresponding amount of manganese. To prevent the reduction of toughness, the amount of manganese added is also limited. Therefore, the lower limit of the carbon content is 0.0035%.

Cr: Chromium is an element which can effectively inhibit the corrosion of carbonic acid gas. Especially in the corrosive environment targeted by the present invention, at a temperature of 80 ° C and a pressure of 0.1 MPa or more, in order to obtain sufficient resistance to carbonation gas corrosion, the chromium content must be More than 3%. On the other hand, if the chromium content is 5% or more, particularly in the case where an oxide is mixed, local corrosion may occur.

Si: Silicon is an element having the same deoxidation effect as Al and Ti, and can be added in a small amount. In the steel material of the present invention which is required to improve the low-temperature toughness of the welded portion, a silicon content of more than 0.1% is disadvantageous for improving the low-temperature toughness of the welded portion, and thus is limited to 0.1%.

Mn: Manganese is an element that can effectively improve low temperature toughness and needs to be added in an appropriate amount. In the present invention, in order to obtain a sufficient effect, the manganese content must be at least 0.6% in order to obtain sufficient effect, and on the other hand, the content exceeding 2% may lower the toughness, so the manganese content is set at 0.6-2. %. Further, the effect of the action is related to the carbon content, and the inventors have found that the relationship is that the manganese content needs to be increased in the case of a low carbon content, and the manganese content is required to be in a high carbon content to obtain a good low temperature toughness of the welded portion. Therefore, for carbon content temperature cross-linking carbon [TC] and manganese content and temperature cross-linking manganese [T.Mn] (representing mass %), the product is limited to 0.007 or more, 0.03 or less, and the relationship is 0.007 ≤ [T.Mn ] × [TC] ≤ 0.03.

Figure 1 shows the relationship between the C content and the Mn content under the condition of low temperature toughness of a good welded part based on 3% Cr steel. The evaluation test was carried out. After the MIG welding with an input heat of 2.6 kJ/mm was carried out, a Charpy impact test was performed using a 2 mm V-notch impact test piece at the center weld of the slit. For the Charpy impact test at -20 ° C, the absorbed energy is 30 J or more, and when the low temperature toughness is good, it is represented by ○, and when the absorbed energy is less than 30 J, it is represented by ×. The rectangular area is the basic composition range of the invented steel, and the area sandwiched by the two curves is the correct composition range of the steel of the present invention. The toughness of the portion outside the rectangular shape is poor, and the toughness is still outside the curved portion in the rectangular shape, and the portion having poor toughness in the component region of the present invention is shown in the drawing.

Further, in order to improve the corrosion resistance or the toughness of the welded portion of the present invention, the following components may be contained.

Al: Al is an element having deoxidation action together with Si and Ti, and the Al content is required to be 0.001% or more in order to sufficiently exhibit the effect. On the other hand, when the content exceeds 0.2%, the steel grade is lowered and the low temperature toughness is deteriorated. Therefore, when Al is added, the content thereof is 0.001% to 0.2%.

N: N is an unavoidable impurity remaining in the steel. In order to improve the low temperature toughness, the lower the content, the better, especially when the N content exceeds 0.015%, the low temperature toughness is remarkably deteriorated, so the content is limited to 0.015%. Ti, Nb: Ti and Nb can effectively improve the strength of the base metal, and at the same time, fine (Ti, Nb) carbides are formed in the heat affected zone of the weld to inhibit austenite grain growth, thereby improving the toughness of the welded portion. In order to fully exert the effect, the Ti content needs to be 0.001% or more, and the Nb content needs to be 0.01% or more. On the other hand, excessive addition causes the Ti content to exceed 0.2%, and the Nb content exceeds 0.5%, which causes deterioration in toughness. Therefore, the content of Ti and Nb ranges from 0.001% to 0.2% of Ti and from 0.01 to 0.5% of Nb.

In addition, the addition of one or more of Cu, Ni, and Mo in less than 1% may increase the stability of the corrosion-resistant layer. There is little difference between the individual addition and the composite addition, and one or more need to be added to obtain the corresponding corrosion resistance. However, any method below 0.01% does not reflect its effect, so the minimum content is 0.01%. For Mo, as with Mn, its content is related to C content, and its ratio is also related to welding heat. The low temperature toughness of the affected zone has an influence, and the relationship between the amount of added C and the amount of Mn is: ([T.Mn]+[T.Mo])×[T.C] is 0.007 or more and 0.03 or less.

The steel of the invention is subjected to heat treatment such as calendering and quenching and tempering to adjust the metal structure, so that the necessary strength-low temperature toughness equilibrium point can be achieved. Further, the method for producing a steel pipe using the steel of the present invention is not particularly limited, and a seamless rolling pipe forming method, a steel pipe forming method, and the like can be used. The steel pipe manufactured by these methods has good carbonation corrosion resistance and toughness of the welded portion of the gas welding portion, and the seam weld region toughness of the jointed steel pipe is also excellent. At this time, the seam welding can be performed by submerged arc welding with large input heat such as electric seam welding or laser welding.

However, the purpose of the steel of the present invention is to obtain a material which is inexpensive, and in various methods, rolling control is particularly carried out as follows, and the manufacture of the electric seam tube can maximize the utility of the present invention. This calendering control—the manufacturing method of the electric seam tube is carried out as follows:

(1) After the slab is heated at a temperature of 1050 ° C to 1300 ° C, hot rolling is performed, and then hot rolling at a reduction ratio of 50% or more is completed in a temperature range of not more than 950 ° C and above the critical point of Ar 3 , and then at 20 ° C / The cooling rate above s is cooled to below 500 ° C, and then the hot rolled coil is taken out;

(2) The hot rolled coil is cut into a cylindrical shape by a steel strip having a predetermined width, and is continuously molded into a cylindrical shape, and the electric resistance is welded to both ends of each steel strip to produce an electric seam steel pipe. The steel of the present invention which is excellent in carbonation corrosion resistance and strength and low temperature toughness can be applied to various occasions requiring carbonation gas corrosion resistance. In particular, it can be used for pipes that are resistant to carbonation gas corrosion resistance and low-temperature toughness of welded parts, and has a remarkable effect in lowering the price and improving the life compared with the past materials.

Table 1 shows the chemical compositions of the steels of the present invention and comparative steels, as well as the results of the corrosion resistance test and the low temperature toughness test of the welded parts. The corrosion resistance test was carried out in a two-week immersion test in a formation water simulation solution at a temperature of 80 ° C, a carbonic acid gas pressure of 0.4 MPa, and a salt concentration of 5%. 1) A test for degassing to a dissolved oxygen concentration of 10 ppb or less, and 2) a test for a dissolved oxygen concentration of 100 ppb.

Table 1

Corrosion resistance 1) and corrosion resistance 2): ◎ excellent ○ good × poor ● local defects

Welded part toughness: energy absorbed by the CHARPY impact test at -20 degrees Celsius ◎200J or more ○30-200J × less than 30J

Table 1 shows the results of evaluation of carbonation resistance: when the Cr content is 0.01% or less, the corrosion amount of carbon steel is 1, the corrosion amount is 0.2 or less, and the corrosion amount is 0.5 or less, which is indicated by ○, and the corrosion resistance is shown. Good, but localized corrosion is indicated by black spots. The evaluation test of the low-temperature toughness of the welded portion was carried out by Charpy impact test using a 2 mm V-notch impact test piece at the center weld line of the slit after the MIG welding of the input heat of 2.6 kJ/mm. Table 1 shows the evaluation results of the low temperature toughness of the welded part: From the results of the Charpy impact test at -20 °C, the absorption energy of 200 J or more is excellent in low temperature toughness, and it is indicated by ◎ that the absorption is less than 30 J is poor in low temperature toughness. It is represented by ×, and the middle is represented by ○.

The chemical composition of steels Nos. 1 to 18 is within the range specified by the present invention, and is the steel of the present invention, and the chemical composition of steels Nos. 19 to 23 is outside the predetermined range and is comparative steel. The steel of the invention has good corrosion resistance and low temperature toughness in the heat affected zone of the weld.

On the other hand, the low temperature toughness of the welded steel heat affected zone of No. 19 to 22 is insufficient, and the low temperature toughness of No. 23 welding heat affected zone is good, but the corrosion resistance is insufficient, and the steel of the present invention has obvious superiority. In addition, according to the chemical composition of No. 7 in Table 1, the 150mm thick billet is heated to 1250 ° C, to 1100 ° C when the heat extension is 16 mm, continue to cool to 900 ° C when the calender is 8 mm thick, and then directly cooled at 30 ° C / s water At 500 ° C, the hot rolled coil was taken out. After the hot rolled coil is formed in the cold zone, the high-frequency welded electric seam welded pipe can be used to manufacture the steel pipe of the API specification X65 grade. After the gas pipe is welded, the Charpy test piece is used to measure the low temperature toughness of the heat affected zone in the vicinity of the weld. The results show that the weld can absorb more than 200 J at any position at -20 °C. By the above method, a steel pipe having a very low temperature toughness in the heat affected zone can be manufactured.

The invention has good resistance to carbonation gas corrosion, and achieves a good strength-low temperature toughness balance point, and a low alloy toughness with good low temperature toughness at the welded portion is very helpful for efficient energy industry mechanical device design.

In this regard, it will be appreciated by those skilled in the <RTIgt;the</RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; </ RTI> <RTIgt; The content directly determines or derives many other variations or modifications consistent with the principles of the invention. Therefore, the scope of the invention should be understood and construed as covering all such other modifications or modifications.

Claims

A low-alloy steel characterized by comprising the following components: a chemical component containing C: 0.0035 to 0.02%, Cr: 3.0% to 5.0%, Si: 0.1% or less, and Mn: 0.6 to 2.0% by mass percentage. The relationship between the amount of Mn [T.Mn] and the amount of C [TC] is in accordance with [T.Mn] × [TC] of 0.007 to 0.03, and the other portions are iron and unavoidable impurities.
A low-alloy steel according to claim 1, further comprising, by mass%, 0.001 to 0.20% or less, N: 0.015% or less, Ti: 0.001 to 0.2%, and Nb: 0.01 to 0.5%.
A low-alloy steel having good carbonation resistance and weld site toughness according to claim 1 or 2, which further contains one or more of Cu and Ni in a mass percentage, and each component is in a range of 0.01% to 1%. %.
A low-alloy steel according to any one of claims 1 to 3, which further contains Mo: 0.01% to 1% by mass percentage, and is represented by [T.Mo], [T.Mn], [TC], respectively. The Mo, Mn, and C contents, and the number of ([T.Mo]+[T.Mn])*[TC] are in the range of 0.007 to 0.03.
A low-alloy steel pipe which is made of a low-alloy steel according to any one of claims 1 to 4 and which has good resistance to carbonation gas corrosion and weld site toughness.
A method of manufacturing a low-alloy steel pipe according to claim 5, wherein the steps are as follows:

(1) After the slab is heated at a temperature of 1050 ° C to 1300 ° C, hot rolling is performed, and then hot rolling at a reduction ratio of 50% or more is completed in a temperature range of not more than 950 ° C and above the critical point of Ar 3 , and then at 20 ° C / The cooling rate above s is cooled to below 500 ° C, and then the engineering operation of the hot rolled coil is taken out;

(2) The hot rolled coil is cut into a cylindrical shape by a steel strip having a predetermined width, and is continuously molded into a cylindrical shape, and the electric resistance is welded to both ends of each steel strip to manufacture an electric seam steel pipe.