JP5217277B2 - Manufacturing method of high alloy pipe - Google Patents

Description

  The present invention relates to a method for producing a high alloy tube that exhibits excellent corrosion resistance even in a carbon dioxide gas corrosion environment and a stress corrosion environment and has high strength. The high alloy pipe produced according to the present invention can be used, for example, in oil wells and gas wells (hereinafter collectively referred to as “oil wells”).

As a high alloy tube used in deep wells and oil wells used in severe corrosive environments containing corrosive substances such as wet carbon dioxide (CO ₂ ), hydrogen sulfide (H ₂ S), and chlorine ions (Cl ⁻ ) Conventionally, a high alloy tube made of a high Cr-high Ni alloy has been used. However, in recent years, oil wells have a tendency to become deep wells, and have a high strength of 110 to 140 ksi grade (minimum yield strength of 757.3 to 963.8 MPa), particularly for use in harsher environments. There is a need for high strength alloy tubes having corrosion resistance.

  Patent Documents 1 to 4 disclose a method of obtaining a high-strength, high-alloy oil well pipe by cold working a high Cr-high Ni alloy at a thickness reduction rate of 10 to 60% after hot working and solution treatment. Has been.

  Further, in Patent Document 5, in order to obtain an austenitic alloy having excellent corrosion resistance in a hydrogen sulfide environment, each of La, Al, Ca, S, and O is contained in a specific relationship to control the shape of inclusions. And cold working is disclosed. The cold working here is performed for strength addition, but thickness reduction processing of 30% or less is performed from the viewpoint of corrosion resistance.

  Furthermore, Patent Document 6 discloses a high Cr-high Ni alloy in which the SCC resistance in a hydrogen sulfide environment is improved by adjusting the contents of Cu and Mo, and the degree of work is further increased by 30% after hot working. It is described that the strength is preferably adjusted by the following cold working.

JP 58-6927 A Japanese Patent Laid-Open No. 58-9922 JP 58-11735 A U.S. Pat. No. 4,421,571 JP-A 63-274743 Japanese Patent Laid-Open No. 11-302801

  However, although the above-mentioned document discloses that high strength can be achieved by cold working, specific studies have been made on increasing strength by cold working considering the composition of high alloy pipes. There is no suggestion of any suitable component design or cold working conditions for obtaining the target strength, particularly yield strength.

  In view of such circumstances, the present invention provides a method for producing a high alloy pipe having not only the corrosion resistance required for oil well pipes used in deep wells and severe corrosive environments, but also the target strength. For the purpose.

  In order to solve the above-mentioned problems, the present inventors manufactured high alloy pipes for various types of high alloy materials having various chemical compositions by varying the final cold drawing degree, and the tensile strength thereof was changed. As a result of the experiment to confirm, the knowledge shown in the following (a) to (g) was obtained.

  (a) Corrosion resistance is required for high alloy pipes used in deep wells and oil wells used in harsh corrosive environments. If the basic chemical composition of the high alloy tube is (20-30%) Cr- (25-40%) Ni, it is necessary to lower the C content from the viewpoint of corrosion resistance.

  (b) If the C content is lowered, the strength will be insufficient as it is, but the high alloy base tube formed by hot working or further solution heat treatment will have its strength reduced by subsequent cold drawing. Can be improved. However, if the degree of work at that time exceeds 40% in terms of the cross-sectional reduction rate, it has high strength, but because work hardening occurs, ductility and toughness are reduced. Further, if the degree of processing at that time is less than 10% in terms of the cross-sectional reduction rate, a desired high strength cannot be obtained. Therefore, the degree of processing in the cold drawing process needs to be 10 to 40% in terms of the cross-sectional reduction rate.

  (c) And in the range of 10 to 40% of the cross-section reduction rate when the cold drawing is performed, (20 to 30%) Cr— (25 to 40%) Ni is the basic chemistry. It was found that, in the high alloy pipe having the composition, as the workability Rd in the final cold drawing process increases, a higher yield strength YS can be obtained, and the workability Rd and the yield strength YS are expressed in a linear relationship.

  Furthermore, it was also found that the N content has a great influence on the strength of the high alloy tube, and that a high alloy tube with higher strength can be obtained with a higher N material. This is considered to be because when more N is contained, more solid solution strengthening due to N is expressed and the strength is improved.

  FIG. 1 plots the workability Rd (%) at the cross-section reduction rate and the yield strength YS (MPa) obtained in the tensile test for the high alloy tubes having various chemical compositions used in the examples described later. Is. Both the high N material (N content: 0.1960% by mass) and the low N material (N content: 0.0738 to 0.0916% by mass) have a workability Rd and a yield strength at the cross-section reduction rate, respectively. YS is shown to be in a linear relationship. And it is shown that the yield strength YS obtained from the high N material is higher than that from the low N material, and it is understood that a higher strength high alloy tube can be obtained by increasing the N content.

  (d) Next, if the yield strength of a high alloy pipe is dependent on the workability Rd at the time of cold drawing and the chemical composition of the high alloy pipe, In order to obtain the target yield strength, it was considered possible to establish an appropriate component design method related to the pipe processing conditions. That is, in order to obtain the target yield strength of the high alloy pipe, it is possible to make fine adjustment by the working degree Rd when performing the cold drawing process instead of fine adjustment by the chemical composition of the high alloy pipe. It is not necessary to change the alloy composition for each level to melt many kinds of high alloys, and therefore, the stock of material billets can be suppressed.

  Thus, if an appropriate component design method related to pipe processing conditions can be established, the alloy composition of the material can be obtained without changing the alloy composition of the material each time in order to obtain a high alloy tube having the target strength. It is only necessary to perform cold drawing with a target cold drawing process condition determined in consideration of the above, that is, with a target degree of processing Rd or higher.

(e) Under such an idea, repeated investigations and experiments were conducted on the correlation between the yield strength of a high alloy pipe and the degree of processing Rd during cold drawing and the chemical composition of the high alloy pipe. As a result, in the high alloy tube having a basic chemical composition of (20-30%) Cr- (25-40%) Ni, the degree of work Rd at the time of cold drawing is 10-40 in terms of the cross-sectional reduction rate. In the range of%, the yield strength YS (MPa) is based on the workability Rd when performing cold drawing and the contents of Cr, Mo, and N in the chemical composition of the high alloy tube. It was found that the calculation can be made based on the following equation (2).
YS = 11 × (Rd + 1.3 × Cr + 2 × Mo + 90 × N) +83 (2)
However, YS and Rd in the formulas mean the yield strength (MPa) and the degree of work (%) at the cross-section reduction rate, respectively, and Cr, Mo and N mean the content (% by mass) of each element. To do.

  FIG. 2 shows values obtained by substituting the degree of processing Rd (%) at the chemical composition and the reduction rate of the cross section for the various high alloy pipes used in the examples described later into the right side of the above equation (2). The Y-axis is a plot of the yield strength YS (MPa) actually taken in the tensile test on the X-axis. If it is a high alloy pipe having a basic chemical composition of (20-30%) Cr- (25-40%) Ni, the chemical composition and the degree of workability Rd (the cross-sectional reduction rate) according to the equation (2) %) Shows that the yield strength can be obtained accurately.

(f) Therefore, in order to obtain a high-alloy tube having a target strength, cold drawing is performed on the material excluding the yield strength expressed by the alloy components, that is, the contents of Cr, Mo and N. It should be expressed by. In order to obtain the target yield strength MYS (110 to 140 ksi grade (minimum yield strength is 757.3 to 963.8 MPa)), after selecting the chemical composition of the high alloy tube, the workability obtained from the above equation (2) Since the final cold drawing process may be performed with a working degree of Rd (%) or higher, the working degree Rd at the cross-section reduction rate in the final cold drawing process is within the range of 10 to 40%. In the meantime, it is only necessary to perform cold drawing under conditions satisfying the following expression (1).
Rd (%) ≧ (MYS−83) / 11− (1.3 × Cr + 2 × Mo + 90 × N) (1)
However, Rd and MYS in the formula mean the workability (%) and the target yield strength (MPa) at the cross-section reduction rate, respectively, and Cr, Mo and N are the contents (mass%) of the respective elements. means.

  (g) As described above, with respect to a high alloy pipe having a basic chemical composition of (20-30%) Cr- (25-40%) Ni, cold working conditions are not added excessively. Since the desired yield strength can be obtained by selecting, the material cost can be reduced. Furthermore, by selecting cold working conditions according to the alloy composition of the material, a high alloy tube having the target strength can be obtained. There is no need to melt, and therefore the stock of material billets can be reduced.

  The present invention has been completed based on such new knowledge, and the gist thereof is as follows.

In mass%, C: 0.03% or less, Si: 0.5% or less, Mn: 0.3-1.0%, Ni: 25-40%, Cr: 20-30%, Mo: 0-4 %, Cu: 0 to 3%, N: 0.15 to 0.30%, the balance is Fe and impurities, and P, S, and O in the impurities are each P: 0.03% or less , S: 0.03% or less and O: 0.010% or less of a high alloy element tube having a chemical composition is produced by hot working or by further solution heat treatment, and then cold drawn to obtain a high alloy. A method of manufacturing a tube, in which the cold drawing is performed under the condition that the working degree Rd at the cross-section reduction rate in the final cold drawing process is within a range of 10 to 40% and the following expression (1) is satisfied. How to make high alloy tubes with minimum yield strength of 757.3 ~ 963.8MPa, characterized by processing Law.
Rd (%) ≧ (MYS−83) / 11− (1.3 × Cr + 2 × Mo + 90 × N) (1)
However, Rd and MYS in the formula mean the workability (%) and the target yield strength (MPa) at the cross-section reduction rate, respectively, and Cr, Mo and N are the contents (mass%) of the respective elements. means. The target yield strength is a value at which the minimum yield strength of the high alloy pipe is set within a range of 757.3 to 963.8 MPa.

    According to the present invention, not only the corrosion resistance required for oil well pipes used in deep wells and harsh corrosive environments, but also high alloy pipes that have the target strength can be excessively added with alloy components. And can be manufactured by selecting cold working conditions.

  Next, the reason for limiting the chemical composition of the high alloy steel used in the method for producing a high alloy pipe according to the present invention will be described. In addition, “%” of the content of each element represents “mass%”.

C: 0.03% or less When the content of C exceeds 0.03%, Cr carbide is formed at the crystal grain boundary, and the stress corrosion cracking susceptibility at the grain boundary increases. For this reason, the upper limit was made 0.03%. A preferable upper limit is 0.02%.

Si: 0.5% or less Si is an element effective as a deoxidizer for the alloy, and can be contained as necessary. The effect as a deoxidizer is obtained at a content of 0.05% or more. However, when the content exceeds 0.5%, the hot workability decreases, so the Si content is set to 0.5% or less. A preferable range is 0.4% or less.

Mn: 0.3 to 1.0%
Mn is an element that is effective as a deoxidizing agent for the alloy, and is an element that is effective for stabilizing the austenite phase. The effect is obtained with a content of 0.3% or more. However, when the content exceeds 1.0%, hot workability is lowered. For this reason, Mn content was made into 0.3 to 1.0%. A preferable range is 0.4 to 0.8%.

Ni: 25-40%
Ni is an important element for stabilizing the austenite phase and maintaining the corrosion resistance. However, if the content is less than 25%, the Ni sulfide film is not sufficiently formed on the outer surface of the alloy, so that the effect of containing Ni cannot be obtained. On the other hand, even if the content exceeds 40%, the effect is saturated, resulting in an increase in the price of the alloy and impairing the economy. Therefore, the Ni content is set to 25 to 40%. A preferred range is 29-37%.

Cr: 20-30%
Cr is an effective component for improving the hydrogen sulfide corrosion resistance represented by stress corrosion cracking resistance in the coexistence with Ni and increasing the strength by solid solution strengthening. However, if the content is less than 20%, the effect cannot be obtained. On the other hand, when the content exceeds 30%, the effect is saturated, which is not preferable from the viewpoint of hot workability. Therefore, the Cr content is 20-30%. A preferred range is 23-27%.

Mo: 0 to 4% (including no additive)
Mo is an effective component for improving the strength by solid solution strengthening and has the effect of improving the stress corrosion cracking resistance in the coexistence with Ni and Cr. it can. When it is desired to obtain this effect, the content is preferably 0.01% or more. On the other hand, when the content is 4% or more, the effect is saturated, and excessive content decreases hot workability. For this reason, it is preferable to make Mo content into 0.01 to 4%. In order to obtain better stress corrosion cracking resistance, the lower limit is preferably 1.5%.

Cu: 0 to 3% (including no additive)
Cu has the effect of remarkably improving the resistance to hydrogen sulfide corrosion under a hydrogen sulfide environment, and can be contained as required. When it is desired to obtain this effect, the content is preferably 0.1% or more. However, if the content exceeds 3%, the effect is saturated, and conversely the hot workability is lowered. For this reason, when Cu is contained, the content is preferably 0.1 to 3%. More preferably, it is 0.5 to 2%.

N: 0.05-0.30%
The high alloy of the present invention needs to lower the C content from the viewpoint of corrosion resistance. Therefore, N is positively contained, and the strength is increased by solid solution strengthening without deteriorating the corrosion resistance. Further, by positively containing N, a high alloy pipe having higher strength can be obtained after the solution heat treatment. Thereby, since the desired strength can be ensured even at a low workability without unnecessarily increasing the workability (cross-sectional reduction rate) at the time of cold working, a decrease in ductility due to the high workability can be suppressed. In order to acquire the effect, 0.05% or more must be contained. On the other hand, when it exceeds 0.30%, hot workability will fall. Therefore, the N content is set to 0.05 to 0.30% or less. A preferable range is 0.06 to 0.22%. In order to obtain higher strength, the N content is preferably 0.15% or more.

  Furthermore, P, S, and O contained as impurities are preferably limited to P: 0.03% or less, S: 0.03% or less, and O: 0.010% or less for the following reasons.

P: 0.03% or less P is contained as an impurity. When the content exceeds 0.03%, the sensitivity to stress corrosion cracking in a hydrogen sulfide environment increases. For this reason, it is preferable to make the upper limit into 0.03% or less. A more preferred upper limit is 0.025%.

S: 0.03% or less S is contained as an impurity in the same manner as P described above, but when its content exceeds 0.03%, hot workability is significantly reduced. For this reason, it is preferable that the upper limit is 0.03%. A more preferred upper limit is 0.005%.

O: 0.010% or less In the present invention, since the N content is contained in a large amount of 0.05% to 0.3% or less, hot workability is likely to deteriorate. When the content of O exceeds 0.010%, hot workability is deteriorated. Therefore, the O content is preferably 0.010% or less.

The high alloy pipe of the present invention contains the above-mentioned essential elements or further any of the above-mentioned optional elements, the balance is made of Fe and impurities, and is manufactured by a manufacturing facility and a manufacturing method that are usually used for commercial production. can do. For example, for melting the alloy, an electric furnace, an Ar—O ₂ mixed gas bottom blowing decarburization furnace (AOD furnace), a vacuum decarburization furnace (VOD furnace), or the like can be used. The molten metal may be cast into an ingot, or may be cast into a rod-shaped billet by a continuous casting method. By using these billets, a high-alloy cold work blank can be manufactured by hot working such as an extrusion pipe making method such as the Eugene Sejurne method or a Mannesmann pipe making method. The base tube after hot working is a product tube having a desired strength by cold working such as cold drawing.

  Further, in the present invention, the degree of work at the time of the final cold working is defined, and the raw tube for cold working obtained by hot working is subjected to solution heat treatment if necessary, and then the scale of the pipe surface is measured. The descaling of removal may be performed to produce a high alloy tube having a desired strength by one cold working, or one or more intermediate cold workings may be performed before the final cold working. And a solution heat treatment may be performed, and the final cold working may be performed after descaling. By performing cold work in the middle, it is easy to adjust the degree of work in the final cold drawing process, and at the same time, it is more effective in the final cold work than in the case of cold work with hot work A tube having a highly accurate tube size can be obtained.

  First, an alloy having a chemical composition shown in Table 1 was melted in an electric furnace, adjusted to a target chemical composition, and then melted by a method of decarburization and desulfurization using an AOD furnace. The obtained molten metal was cast into an ingot having a weight of 1500 kg and a diameter of 500 mm. And it cut | disconnected to length 1000mm and obtained the billet for extrusion pipe making. Next, the billet was formed into a cold-working raw tube by a hot extrusion pipe manufacturing method based on the Eugene Sejurnee method.

  The obtained cold-working raw tube was drawn on the way, and then subjected to a solution heat treatment under the condition that it was kept at 1100 ° C. for 2 minutes or more and then water-cooled. As shown in FIG. 2, various changes were made, and a final cold working was performed by a drawing method using a plug and a die to obtain a high alloy. Prior to cold drawing, the tube was shot blasted to remove the surface scale. Table 2 shows the tube dimensions (outer diameter mm × thickness mm) before and after the final cold working.

  Thereafter, an arc-shaped tensile test piece in the tube axis direction was taken from the obtained high alloy tube, and a tensile test was performed. The measured values of the results are shown in Table 2 with the yield strength (0.2% yield strength) YS (Mpa) and tensile strength TS (MPa) in the tensile test, together with the numerical value on the right side of equation (2).

  As described above, according to the present invention, not only the corrosion resistance required for oil well pipes used in deep wells and harsh corrosive environments, but also high alloy pipes having the target strength, It can be manufactured by selecting cold working conditions without adding alloy components.

For high alloy pipes, the degree of work Rd (%) at the cross-section reduction rate and the yield strength YS (MPa) obtained by the tensile test are plotted. For high alloy pipes, the value obtained by substituting the degree of processing Rd (%) at the chemical composition and the rate of reduction of the cross section for the right side of the above equation (2) is taken on the X axis, and the yield obtained by the tensile test The strength YS (MPa) is plotted on the Y axis.

Claims (1)

In mass%, C: 0.03% or less, Si: 0.5% or less, Mn: 0.3-1.0%, Ni: 25-40%, Cr: 20-30%, Mo: 0-4 %, Cu: 0 to 3%, N: 0.15 to 0.30%, the balance is Fe and impurities, and P, S, and O in the impurities are each P: 0.03% or less , S: 0.03% or less and O: 0.010% or less of a high alloy element tube having a chemical composition is produced by hot working or by further solution heat treatment, and then cold drawn to obtain a high alloy. A method of manufacturing a tube, in which the cold drawing is performed under the condition that the working degree Rd at the cross-section reduction rate in the final cold drawing process is within a range of 10 to 40% and the following expression (1) is satisfied. How to make high alloy tubes with minimum yield strength of 757.3 ~ 963.8MPa, characterized by processing Law.
Rd (%) ≧ (MYS−83) / 11− (1.3 × Cr + 2 × Mo + 90 × N) (1)
However, Rd and MYS in the formula mean the workability (%) and the target yield strength (MPa) at the cross-section reduction rate, respectively, and Cr, Mo and N are the contents (mass%) of the respective elements. means. The target yield strength is a value at which the minimum yield strength of the high alloy pipe is set within a range of 757.3 to 963.8 MPa.

Images