CN106011666A - Low alloy steel, steel pipe and manufacturing method of steel pipe - Google Patents

Abstract

The invention provides low alloy steel with favorable carbon dioxide gas corrosion resistance and welded-part toughness. The low alloy steel comprises the following chemical component in percentage by mass: 0.0,035-0.02% of C, 3.0%-5.0% Cr, 0-0.1% of Si, 0.6-2.0% of Mn, Fe and inevitable impurities, wherein the relation between the Mn content [T.Mn] and the C content [T.C] conforms to the formula that [T.Mn] multiplied by [T.C] ranges from 0.007 to 0.03. The invention further provides a low alloy steel pipe made of the low alloy steel and a manufacturing method of the low alloy steel pipe, and the low alloy steel pipe has favorable carbon dioxide gas corrosion resistance and welded-part toughness.

Description

A kind of low alloy steel, steel pipe and manufacturing method thereof

technical field

The invention relates to petroleum and natural gas transportation pipelines used in the energy field, in particular to low alloy steels used in petroleum and natural gas environments containing carbonic acid gas, having good corrosion resistance to carbonic acid gas and toughness of welded parts, and low alloy steels using the alloys Alloy steel pipe and its manufacturing method.

Background technique

Oil well pipes and pipelines used in the production and transportation of oil and gas are usually made of carbon steel and low alloy steel. However, compared with the corrosion or atmospheric corrosion in the usual neutral and humid environment, the corrosion rate of oil and gas containing more carbon dioxide is very fast. For piping and piping, a corrosion inhibitor is usually added to the oil, and 13% Cr steel, which is excellent in carbonic acid corrosion resistance, is used as the material of the piping steel. But on the one hand, the corrosion inhibitors used in oil are not good for environmental protection. On the other hand, the cost of using stainless steel pipelines is high, and the service time is limited. If it is used in an environment where the corrosion conditions are not too severe, the cost-effectiveness ratio will be lower. exceed the limit.

In view of this problem, in order to improve the general corrosion of carbonic acid gas and the localized corrosion of welding parts, it has been clearly stipulated in JP-A-56-93856 that the steel used for pipelines should contain 3-12% Cr and below 0.1% C. However, the welded part of the invention described in this gazette has low toughness. For the steel of the invention, when the C content is reduced below 0.01%, the absorbed energy is lower than 16kg/mm2 (below about 160J) in the V-notch impact test at 0°C, and the toughness of the welded part of this steel is low.

Therefore, it is hoped to develop a low-alloy steel and a steel pipe using this low-alloy steel that can be used in the carbonic acid corrosive environment of high-carbonic acid oil and gas, have good carbonic acid corrosion resistance and low-temperature toughness of the welded part, and are inexpensive.

Contents of the invention

In the present invention, while adding an appropriate amount of Cr in order to improve the corrosion resistance of carbonic acid gas, the content of C and Si is suppressed in order to improve the toughness of the welded part, and the content of C-Mn or C-Mn-Mo is balanced according to a specific relationship. The composition includes various low-alloy steels according to the specified content, steel pipes using such low-alloy steel pipes and the manufacturing method of such steel pipes. The main components are as follows:

(1) Chemical composition, by mass percentage, contains C: 0.0035-0.02%, Cr: 3.0%-5.0%, Si: 0.1% or less, Mn: 0.6-2.0% and the amount of Mn [T.Mn] and the amount of C The relation of [T.C] accords with [T.Mn]×[T.C] at 0.007～0.03, and other parts are iron and unavoidable impurities. According to this composition, it is a low-alloy with good carbon dioxide gas corrosion resistance and toughness of welding parts. steel.

(2) In addition, in terms of mass percentage, it also contains Al: 0.001-0.20% or less, N: 0.015% or less, Ti: 0.001-0.2%, Nb: 0.01-0.5%, and other low-alloy steels described in (1) above , has good resistance to carbon dioxide gas corrosion and toughness of welded parts.

(3) In addition, in terms of mass percentage, it also contains one or more of Cu and Ni, each component is 0.01% to 1%, and other components are the same as those described in (1) and (2) above. Low alloy steel with good carbon dioxide corrosion resistance and toughness of welded parts.

(4) In addition, according to mass percentage, it also contains Mo: 0.01%-1%, and [T.Mo], [T.Mn], [T.C] represent Mo, Mn, C content respectively, ([T.Mo] +[T.Mn])×[T.C] ranges from 0.007 to 0.03, and the other ingredients are the same as any one of the above (1) to (3), and the technical solution characterized by this content has good resistance to carbon dioxide gas Low alloy steel for corrosion resistance and weld toughness.

The technical solution characterized by the low-alloy steel described in any one of (1)-(4) above is a low-alloy steel pipe with good carbon dioxide corrosion resistance and toughness of welded parts.

The invention is applied in the field of energy, especially oil well pipes and pipelines for the production and transportation of petroleum and natural gas containing carbonic acid gas, or suitable as raw materials for factories. The object of the present invention is to develop a low alloy steel having both good carbon dioxide corrosion resistance and weld toughness, and a steel pipe using the low alloy, and to provide a method for manufacturing the steel pipe.

Regarding the manufacture of the above-mentioned low-alloy steel pipeline, the steel billet needs to be manufactured into a steel pipe according to the following procedures. The technical solution characterized by this is a method of manufacturing a low-alloy steel electric-seam steel pipe with good carbon dioxide corrosion resistance and toughness of the welded part. The steps as follows:

(1) After the steel billet is heated at a temperature of 1050°C to 1300°C, it is hot-rolled, and then hot-rolled at a temperature range below 950°C and above the Ar3 critical point to complete the hot-rolling with a reduction rate of 50% or more, and then at 20°C/ The engineering operation of cooling to below 500°C at a cooling rate above s, and then taking out the hot-rolled coil;

(2) After the above-mentioned hot-rolled coil is cut according to the specified width of the steel strip, it is continuously formed into a cylindrical shape, and the two ends of each steel strip are welded with resistance to produce an engineering operation of electric seam steel pipe.

Those skilled in the art will be more aware of the above and other objects, advantages and features of the present invention according to the following detailed description of specific embodiments of the present invention in conjunction with the accompanying drawings.

Description of drawings

Hereinafter, some specific embodiments of the present invention will be described in detail by way of illustration and not limitation with reference to the accompanying drawings. The same reference numerals in the drawings designate the same or similar parts or parts. Those skilled in the art will appreciate that the drawings are not necessarily drawn to scale. In the attached picture:

Fig. 1 is a schematic diagram showing the relationship between C content and Mn content for 3% Cr steel.

detailed description

The reason why the composition of the steel of the present invention is limited is explained in the following. % represents mass %.

C: Carbon is an element that increases the strength of steel. In the present invention, when the carbon content increases, the low-temperature toughness and carbon dioxide gas corrosion resistance of the welding part will decrease, especially when the carbon content exceeds 0.02%, a large amount of carbides will be precipitated from the metal crystal during the tempering process of the steel, which will lead to the deterioration of the low-temperature toughness of the welding part And carbon dioxide gas corrosion resistance is reduced, so the upper limit of the carbon content is 0.02%. According to the relationship between the amount of manganese and temperature crosslinked manganese [T.Mn], the inventors reduced the carbon content while keeping the corresponding manganese content above a certain value to find out the proportion that makes it have good low-temperature toughness of the welded part. The amount of carbon is determined by the corresponding amount of manganese. In order to prevent the reduction of toughness, the addition amount of manganese itself is also limited. Therefore, the lower limit of the carbon content is 0.0035%.

Cr: Chromium is an element that can effectively inhibit carbon dioxide gas corrosion. Especially in the corrosive environment targeted by the present invention, under the conditions of temperature 80°C and pressure 0.1 MPa or more, in order to obtain sufficient carbon dioxide gas corrosion resistance, the chromium content must be within 3% or more. On the other hand, if the chromium content is more than 5%, especially when oxides are mixed therein, localized corrosion may occur.

Si: Silicon is an element that has the same deoxidation effect as Al and Ti, and can be added in a small amount. For the steel in the present invention that needs to improve the low-temperature toughness of the welded part, if the silicon content exceeds 0.1%, it is unfavorable to improve the low-temperature toughness of the welded part, so the upper limit is 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, it is necessary to improve the low-temperature toughness of the welded steel, in order to obtain sufficient effect, the minimum manganese content must be more than 0.6%. On the other hand, if the content exceeds 2%, it will reduce the toughness. %. In addition, its effect is related to the carbon content. The inventors found that the relationship is that when the carbon content is low, the manganese content needs to be increased, and when the carbon content is high, the manganese content needs to be reduced to obtain good low-temperature toughness of the welded part. Therefore, for the carbon content temperature crosslinking carbon [T.C] and manganese content and temperature crosslinking manganese [T.Mn] (indicated by mass %), the product is limited to more than 0.007 and less than 0.03, using the relational formula 0.007≤[T.Mn ]×[T.C]≤0.03.

Accompanying drawing 1 shows the relationship between the C content and the Mn content under the condition of maintaining good low-temperature toughness of welded parts based on 3% Cr steel. The evaluation test is: after MIG welding with heat input of 2.6kJ/mm, a Charpy impact test is performed on the center weld of the incision using a 2mm V-notch impact test piece. For the Charpy impact test at -20°C, if the absorbed energy is above 30J, it is indicated by ○ if the low-temperature toughness is good, and by × when the absorbed energy is less than 30J. The rectangular area is the basic composition range of the invented steel, and the area enclosed by the two curves is the correct composition range of the inventive steel. Parts outside the rectangle have poor toughness, and outside the curved area inside the rectangle are still poor toughness. The part with poor toughness in the composition area of the present invention is shown in the figure.

In addition, in order to improve the corrosion resistance or weld toughness of the present invention, the following components may be contained.

Al: Al, together with Si and Ti, is an element with deoxidation effect. In order to fully exert its effect, the Al content must be more than 0.001%. Therefore, when Al is added, the content thereof is 0.001% to 0.2%.

N: N is an unavoidable impurity remaining in 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 will deteriorate significantly, so the upper limit of the content is 0.015%. Ti, Nb: Ti and Nb can effectively increase the strength of the base metal, and at the same time form fine (Ti, Nb) carbides in the welding heat-affected zone to inhibit the growth of austenite grains, thereby improving the toughness of the welded part. In order to fully exert its effect, the Ti content must be above 0.001%, and the Nb content must be above 0.01%. On the other hand, excessive addition of Ti content exceeding 0.2%, and Nb content exceeding 0.5% will also lead to deterioration of toughness. Therefore, the contents of Ti and Nb range from 0.001% to 0.2% for Ti and 0.01% to 0.5% for Nb.

In addition, adding less than 1% of one or more elements in Cu, Ni, Mo can increase the stability of the corrosion-resistant layer. There is little difference between single addition and compound addition, and one or more kinds need to be added to obtain corresponding corrosion resistance. However, any method lower than 0.01% content will not show its effect, so the minimum content is 0.01%. For Mo, like Mn, its content is related to C content, and its proportion also has an impact on the low-temperature toughness of the welded heat-affected zone. The relationship between the amount of C added and the amount of Mn is: ([T.Mn]+[ T.Mo])×[T.C] is not less than 0.007 and not more than 0.03.

The steel of the present invention can reach the necessary strength-low temperature toughness balance point through heat treatment such as rolling and quenching and tempering to adjust the metal structure. Furthermore, the steel pipe manufacturing method using the steel of the present invention is not particularly limited, and the seamless rolling pipe manufacturing method, the welding pipe manufacturing method after forming a steel plate, and the like can be used. Steel pipes manufactured by these methods have good corrosion resistance to carbon dioxide gas and toughness of gas welding parts. In addition, the toughness of the seam welding area of seamed steel pipes is also very good. At this time, seam welding can adopt submerged arc welding with large input heat such as electric seam welding and laser welding.

However, the purpose of the steel of the present invention is to obtain an inexpensive material. In particular, rolling control is carried out as described below in various methods, and the effectiveness of the present invention can be brought into full play in the manufacture of electric seam pipes. This rolling control-electric seam pipe manufacturing method is carried out according to the following procedures:

(1) After the steel billet is heated at a temperature of 1050°C to 1300°C, it is hot-rolled, and then hot-rolled at a temperature range below 950°C and above the Ar3 critical point to complete the hot-rolling with a reduction rate of 50% or more, and then at 20°C/ Cool at a cooling rate above s to below 500°C, and then take out the hot-rolled coil;

(2) After cutting the above-mentioned hot-rolled coils into steel strips of specified width, they are continuously formed into cylindrical shapes, and electric resistance is welded at both ends of each steel strip to manufacture electric seam steel pipes. The steel of the present invention having excellent carbon dioxide corrosion resistance, strength and low-temperature toughness can be applied to various occasions requiring carbon dioxide corrosion resistance. In particular, it can be used for pipes that require both carbon dioxide corrosion resistance and low-temperature toughness of welded parts. Compared with conventional materials, it has achieved remarkable effects in terms of price reduction and life improvement.

Table 1 shows the chemical composition of the steel of the present invention and comparative steel, as well as the results of the corrosion resistance test and the low temperature toughness test of welded parts. The corrosion resistance test is a two-week immersion test in a formation water simulation solution with a temperature of 80 °C, a carbon dioxide gas pressure of 0.4 MPa, and a salt concentration of 5%. 1) is a test of degassing to a dissolved oxygen concentration of 10ppb or less, and 2) is a test of a dissolved oxygen concentration of 100ppb.

Table 1

Corrosion resistance 1) and corrosion resistance 2): ◎ Excellent ○ Good × Poor Local defects

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

Table 1 shows the evaluation results of carbon dioxide corrosion resistance: if the corrosion amount of carbon steel with a Cr content of 0.01% or less is 1, the corrosion amount is 0.2 or less, and ◎ is used, and the corrosion amount is 0.5 or less. The corrosion resistance Good but localized corrosion is represented by black dots. The low-temperature toughness evaluation test of the welded part is a Charpy impact test conducted on the central welding line of the incision with a 2mm V-shaped notch impact test piece after MIG welding with a heat input of 2.6kJ/mm. Table 1 shows the evaluation results of the low-temperature toughness of the welded part: From the measurement results of the absorbed energy of the Charpy impact test at -20°C, the absorbed energy is more than 200J, which means the low-temperature toughness is excellent. It is indicated by ×, and the middle is indicated by ○.

Steels with numbers 1 to 18 whose chemical composition is within the range specified by the present invention are steels of the present invention, and steels with numbers 19 to 23 whose chemical composition is outside the specified range are comparative steels. The steels of the invention all have good corrosion resistance and low-temperature toughness in the welding heat-affected zone.

On the other hand, the comparative steels No. 19-22 have insufficient low-temperature toughness in the welding heat-affected zone, and No. 23 has good low-temperature toughness in the welding heat-affected zone, but insufficient corrosion resistance. The steel of the present invention has obvious advantages. In addition, the 150mm thick steel billet with the chemical composition No. 7 in Table 1 was heated to 1250°C, and when it reached 1100°C, it was thermally extended to 16mm, and when it continued to cool to 900°C, it was rolled to a thickness of 8mm, and then directly cooled with water at a speed of 30°C/s To 500 ° C, take out the hot rolled coil. After the hot-rolled coil is formed in the cold room, the steel pipe of API specification X65 grade can be produced by high-frequency electric seam welding. After the steel pipe is gas-welded, the results of measuring the low-temperature toughness of the heat-affected zone of the weld using a Charpy test piece near the weld show that at a temperature of -20°C, any position of the weld can absorb more than 200J of energy. Through the above method, a steel pipe with very high low temperature toughness in the welded heat affected zone can be manufactured.

The invention has good carbon dioxide gas corrosion resistance, and achieves a better strength-low-temperature toughness balance point, and the low-alloy steel with good low-temperature toughness at welding parts is of great help to the design of efficient energy industry mechanical devices.

So far, those skilled in the art should appreciate that, although a number of exemplary embodiments of the present invention have been shown and described in detail herein, without departing from the spirit and scope of the present invention, the disclosed embodiments of the present invention can still be used. Many other variations or modifications consistent with the principles of the invention are directly identified or derived from the content. Accordingly, the scope of the present invention should be understood and deemed to cover all such other variations or modifications.

Claims (6)

1. a low-alloy steel, it is characterised in that include following composition: chemical composition, by mass percentage, containing C:0.0035 ～0.02%, Cr:3.0%～5.0%, below Si:0.1%, Mn:0.6～2.0% and this Mn amount [T.Mn] and C amount [T.C] Relation meet [T.Mn] × [T.C] 0.007～0.03, other parts are ferrum and unavoidable impurity.

A kind of low-alloy steel the most according to claim 1, by mass percentage, possibly together with Al:0.001～0.20% with Under, below N:0.015%, Ti:0.001～0.2%, Nb:0.01～0.5%.

The most according to claim 1 and 2 a kind of have good resistance to carbonic acid gas corrosivity and the low-alloy of welding position toughness Steel, by mass percentage, possibly together with Cu, Ni one or more of which, each composition is 0.01%～1%.

4. according to a kind of low-alloy steel described in claim 1-3 any one, by mass percentage, possibly together with Mo:0.01%- 1%, with [T.Mo], [T.Mn], [T.C] represents Mo, Mn, C content, the quantitative range of ([T.Mo]+[T.Mn]) × [T.C] respectively It is 0.007～0.03.

5. more than one state the low-alloy steel described in claim 1-4 any one be material manufacture there is good resistance to carbonic acid gas Corrosivity and the low alloy steel of welding position toughness.

6. the method for low alloy steel a kind of described in a manufacturing claims 5, it is characterised in that step is as follows:

(1) after being heated at temperature 1050 DEG C～1300 DEG C by steel billet, carrying out hot calender, then below 950 DEG C, Ar3 is critical Complete the hot calender of reduction ratio more than 50% in the temperature province that point is above, then be cooled to the rate of cooling of 20 DEG C/more than s Less than 500 DEG C, then take out the Engineering operation of hot rolled coil；

(2) after above-mentioned hot rolled coil is pressed the steel strip cutting of specified width, which width, continuously shaped is cylindric, each steel band two ends welding electricity Hinder and be fabricated to the Engineering operation of electricity seam steel pipe.