JP2008057007A - Low alloy steel material and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-strength low alloy steel material superior in SSC resistance. <P>SOLUTION: The low alloy steel material comprises, by mass%, 0.15 to 0.60% C, 0.05 to 0.5% Si, 0.05 to 3.0% Mn, 0.025% or less P, 0.010% or less S, 0.005 to 0.10% Al, and 0.01% or less O (oxygen), and the balance Fe with unavoidable impurities; and has former austenite grains of which the aspect ratios (major axis/minor axis) are 1.5 or more, when the cross section is observed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a low alloy steel material and a method for producing the same, and in particular, a seamless steel pipe and other low alloy steel materials excellent in sulfide stress cracking resistance and suitable for use as casings and tubing for oil wells and gas wells, and the like. It relates to a manufacturing method.

  Conventionally, 80 ksi class or 95 ksi class oil well pipes have been used. However, as deep wells are made, higher strength is required, and recently, 110 ksi-class oil well pipes are often used.

  The 80 ksi class is an oil well pipe having a yield stress (YS) of 80 to 95 ksi (551 to 654 MPa), the 95 ksi class is YS of 95 to 110 ksi (654 to 758 MPa), and the 110 ksi class is 110 of YS. -125 ksi (758-861 MPa) respectively.

  On the other hand, recently developed deep wells, gas wells and the like often contain corrosive hydrogen sulfide. In such an environment, the high-strength steel material causes hydrogen embrittlement called sulfide stress cracking (SSC) and leads to fracture. As a method for improving the SSC resistance of YS95-110 ksi (654-758 MPa) grade oil well pipes, a method of highly cleaning steel, a method of refining the structure, and the like have been widely used.

  For example, Patent Document 1 discloses an invention relating to a method for producing a low alloy high-strength oil well steel having improved SSC resistance by reducing impurity elements such as Mn and P. Patent Document 2 discloses an invention relating to a method for producing a high-strength steel in which crystal grains are refined by twice-quenching heat treatment to improve SSC resistance.

  In recent years, oil well pipes having a higher strength such as 125 ksi class, that is, YS of 125 to 140 ksi (862 to 965 MPa) have begun to be studied. Since SSC is more likely to occur as the strength of steel increases, 125 ksi-class oil well pipes are required to further improve material quality than conventional 95-110 ksi-class (654-758 MPa class) oil well pipes.

  Patent Document 3 discloses an invention of a method for producing a 125 ksi class (about 862 MPa) high-strength steel material having excellent SSC resistance by refining the structure by induction heating heat treatment.

  Patent Document 4 discloses a method for producing a 110 to 140 ksi class (758 to 965 MPa class) high-strength seamless steel pipe excellent in SSC resistance by increasing the hardenability and tempering temperature using a direct quenching method. The invention is disclosed.

  In the patent document 5, the applicant disclosed an invention of a method for producing a high-strength steel material having excellent SSC resistance of 110 to 140 ksi class (758 to 965 MPa class) by optimizing alloy components. In addition, in the patent document 6, the patent document 7, and the patent document 8, the applicant controlled 110 to 140 ksi class (758 to 965 MPa class) low alloy oil well steel with improved SSC resistance by controlling the form of carbide. An invention relating to a manufacturing method has been disclosed.

  Patent Document 9 discloses an invention relating to a high-strength steel material of 110 to 125 ksi class (758 to 862 MPa class) in which the generation time of SSC is delayed by precipitating a large amount of fine V-based carbides.

JP-A-62-253720 JP 59-232220 A JP-A-6-322478 Japanese Patent Laid-Open No. 8-311551 JP-A-11-335731 JP 2000-178682 A JP 2000-256783 A JP 2000-297344 A JP 2000-119798 A

  In the prior art, it may not be possible to stably give excellent SSC resistance to an oil well pipe having a high strength, particularly 125 ksi class or higher. Therefore, further improvement of SSC resistance and its stabilization are required.

  The steel material for oil country tubular goods mentioned above is normally manufactured by quenching and tempering treatment. However, given these heat treatments, there is a limit to improving performance by optimizing component systems.

  The present inventors thought that if a structure elongated in the rolling direction can be created by thermomechanical treatment, resistance to the occurrence and progress of SCC may increase.

  In a normal quenching and tempering process, since the austenite single phase region is heated during quenching, the austenite grain size varies depending on the quenching temperature and time. Further, since recrystallization of the austenite phase occurs during this quenching, the structure anisotropy usually disappears at the time of quenching. In the subsequent tempering process, a reduction in dislocation density and precipitation of carbides occur.

  In order to make the structure elongated in the rolling direction, it is effective to add processing in a temperature range where recrystallization does not occur sufficiently during heating for quenching and quenching while leaving the effect of processing. Study was carried out. As a result, it has been found that a stretched structure can be formed by processing in an optimum temperature range, and that the SSC resistance can be greatly improved as compared with the conventional quenching and tempering treatment.

  The gist of the present invention is a low alloy steel material shown in the following (1) and a manufacturing method of the low alloy steel material shown in (2).

(1) In mass%,
C: 0.15-0.60%,
Si: 0.05 to 0.5%,
Mn: 0.05 to 3.0%
P: 0.025% or less,
S: 0.010% or less,
Al: 0.005 to 0.10% and O (oxygen): 0.01% or less, the balance is Fe and impurities, and the aspect ratio (major axis / minor axis) of prior austenite grains is 1 in cross-sectional observation. Low alloy steel material characterized by being 5 or more.

The above-mentioned low alloy steel material, instead of a part of Fe, is mass%,
Cr: 0.1 to 1.5%
Mo: 0.1 to 3%,
V: 0.05-0.3%
B: 0.0003 to 0.003%,
Nb: 0.002 to 0.1%,
Ti: 0.002 to 0.1%,
Zr: 0.002 to 0.1%,
N: 0.003-0.03% and Ca: 0.0003-0.01%
You may contain 1 or more types selected from. Moreover, said steel material is a seamless steel pipe, for example.

(2) In mass%,
C: 0.15-0.60%,
Si: 0.05 to 0.5%,
Mn: 0.05 to 3.0%
P: 0.025% or less,
S: 0.010% or less,
A steel material containing Al: 0.005 to 0.10% and O (oxygen): 0.01% or less, with the balance being Fe and impurities, is finally rolled, then water-cooled and quenched, and further tempered. A method for producing a low alloy steel material, characterized in that the final rolling start temperature is 780 to 920 ° C., and the cross-section reduction rate R obtained from the following formula (1) is 40% or more. Manufacturing method.
R = (A−B) / A × 100 (1)
Here, R means the cross-section reduction rate (%), A means the cross-sectional area of the steel material before the final rolling, and B means the cross-sectional area of the steel material after the final rolling.

In the above steel material, instead of a part of Fe, in mass%,
Cr: 0.1 to 1.5%
Mo: 0.1 to 3%,
V: 0.05-0.3%
B: 0.0003 to 0.003%,
Nb: 0.002 to 0.1%,
Ti: 0.002 to 0.1%,
Zr: 0.002 to 0.1%,
N: 0.003-0.03% and Ca: 0.0003-0.01%
It may contain one or more selected from. Moreover, said steel material is a seamless steel pipe, for example.

  According to the present invention, it is possible to obtain a steel material having good SSC resistance while having a high strength of yield stress (YS) of 125 ksi (862 MPa) or more.

(A) About the chemical composition of steel materials About the chemical composition of steel, what is necessary is just to use the component system generally used for a low alloy corrosion-resistant oil well pipe, for example, the following chemical compositions are mentioned.

C: 0.15-0.60%
C is an element effective for improving the hardenability and improving the strength. In order to acquire this effect, it is necessary to make it contain 0.15% or more. On the other hand, the effect is saturated even if it exceeds 0.60%. Therefore, the content of C is set to 0.15 to 0.60%.

Si: 0.05-0.5%
Si is an element effective for deoxidation of steel, and has an effect of increasing temper softening resistance. For the purpose of deoxidation, it is necessary to contain 0.05% or more. On the other hand, when the content exceeds 0.5%, precipitation of the ferrite phase of the softened phase is promoted and the SSC resistance is deteriorated. Therefore, the Si content is in the range of 0.05 to 0.5%.

Mn: 0.05 to 3.0%
Mn is an effective element for ensuring the hardenability of steel. In order to achieve this object, it is necessary to contain 0.05% or more. On the other hand, if the content exceeds 3.0%, it segregates at the grain boundaries together with impurity elements such as P and S and deteriorates the SSC resistance. Therefore, the Mn content is set to 0.05 to 3.0%.

P: 0.025% or less P is an element that segregates at grain boundaries and degrades SSC resistance. When the content exceeds 0.025%, the influence becomes remarkable. Therefore, the upper limit was made 0.025%.

S: 0.010% or less S, like P, segregates at the grain boundaries and degrades the SSC resistance. When the content exceeds 0.010%, the influence becomes remarkable. Therefore, the upper limit was made 0.010%.

Al: 0.005 to 0.10%
Al is an element effective for deoxidation of steel, and when the content is less than 0.005%, the effect cannot be obtained. On the other hand, the effect is saturated even if it contains over 0.10%. Therefore, the Al content is set to 0.005 to 0.10%. In addition, Al content points out acid-soluble Al (sol.Al).

O (oxygen): 0.01% or less O (oxygen) is present in the steel as an impurity, and if its content exceeds 0.01%, a coarse oxide is formed to lower toughness and SSC resistance. Let Therefore, the upper limit was made 0.01%.
The chemical composition of the low alloy steel according to the present invention may contain the above-mentioned elements, and the balance may be composed of Fe and impurities. For the purpose of improving SSC resistance, Cr, Mo, V, A suitable amount of one or more of B, Nb, Ti, Zr, N and Ca may be added. Hereinafter, effects when these elements are contained will be described.

Cr: 0.1 to 1.5%
Since Cr is an effective element for enhancing the hardenability of steel, it may be contained in the low alloy steel of the present invention. The above effect becomes significant when the content is 0.1% or more. On the other hand, if it is contained excessively, the production of M ₂₃ C ₆ (M is Fe, Cr or Mo) which is a coarse carbide is promoted, and the SSC resistance may be deteriorated. Therefore, when Cr is contained, its content is preferably 0.1 to 1.5%.

Mo: 0.1 to 3%
Mo is also an effective element for enhancing the hardenability of steel. This element also has the effect of forming fine carbides, increasing temper softening resistance by precipitation strengthening, and improving SSC resistance. Therefore, you may make it contain in the low alloy steel material of this invention. The above-mentioned effect becomes remarkable when the content is 0.1% or more. On the other hand, if it is contained excessively, the production of M ₂₃ C ₆ (M is Fe, Cr or Mo) which is a coarse carbide is promoted, and the SSC resistance may be deteriorated. Therefore, when it contains Mo, it is desirable to make the content into 0.1 to 3%.

V: 0.05-0.3%
V is an element that has the effect of forming fine carbides, generating fine carbides MC (M is V or Mo), and increasing the tempering temperature. Therefore, you may make it contain in the low alloy steel material of this invention. Said effect becomes remarkable when it contains 0.05% or more. On the other hand, even if the content exceeds 0.3%, V that dissolves during quenching is saturated and the effect of increasing the tempering temperature is saturated. Therefore, when V is contained, the content is preferably 0.05 to 0.3%.

B: 0.0003% to 0.003%
B is an element effective for improving the hardenability of steel. Therefore, you may make it contain in the low alloy steel material of this invention. Said effect becomes remarkable when the content is 0.0003% or more. On the other hand, when excessively contained, the generation of coarse grain carbide M ₂₃ C ₆ (M is Fe, Cr or Mo) is promoted, and the SSC resistance is deteriorated. Therefore, when B is contained, the content is desirably 0.0003 to 0.003%.

Nb: 0.002 to 0.1%,
Ti: 0.002 to 0.1%,
Zr: 0.002 to 0.1%
Nb, Ti, and Zr are elements that combine with C or N, form carbonitrides, and are refined by the pinning effect, and improve mechanical properties such as toughness. Therefore, you may make it contain in the low alloy steel material of this invention. The above effect becomes remarkable when the content is 0.002% or more. On the other hand, the effect is saturated even if the content exceeds 0.1%. Therefore, when one or more of Nb, Ti, and Zr are contained, the content is preferably 0.002 to 0.1%.

N: 0.003 to 0.03%
N is an element present in steel as an impurity. When positively contained, it is an element that forms carbonitrides with Al, Nb, Ti, or Zr and refines them by the pinning effect, and improves mechanical properties such as toughness. This effect becomes remarkable when the content is 0.003% or more. On the other hand, this effect is saturated even if the content exceeds 0.03%. Therefore, the N content is desirably 0.003 to 0.03%.

Ca: 0.0003 to 0.01%
Ca combines with S in the steel to form a sulfide, improves the shape of inclusions and improves the SSC resistance, and therefore may be included in the low alloy steel of the present invention. The above effect becomes remarkable when the content is 0.0003% or more. On the other hand, the effect is saturated even if it contains exceeding 0.01%. Therefore, when Ca is contained, the content is preferably 0.0003 to 0.01%.

(B) Aspect ratio of prior austenite grains of steel material The aspect ratio (major axis / minor axis) of the prior austenite grains in the cross section is 1.5 or more. This is because when the aspect ratio (major axis / minor axis) of the prior austenite grains is less than 1.5, the resistance to the generation and progress of SSC is low.

(C) Steel production method In order to increase the aspect ratio of the prior austenite grains and increase the anisotropy to improve the SSC resistance, it is necessary to perform final rolling at a low temperature and then directly quench the steel. .

Final rolling start temperature: 780-920 ° C
When the starting temperature of the final rolling is less than 780 ° C., the anisotropy of the prior austenite grains becomes large, but this temperature range is a two-phase region of an austenite phase and a ferrite phase, and is heated at such a temperature for a long time. As a result, a softened ferrite phase is generated, and the SSC resistance is lowered. On the other hand, when the starting temperature of the final rolling exceeds 920 ° C., recrystallization proceeds, the anisotropy of the prior austenite grains decreases, and the resistance to the generation and progress of SSC decreases. Therefore, the starting temperature of the final rolling was set to 780 to 920 ° C.

Final rolling workability: 40% or more in cross-sectional reduction rate The larger the cross-sectional reduction rate of final rolling, the larger the aspect ratio of the prior austenite crystal grains, but the remarkable improvement in resistance to the occurrence and progress of SSC This is the case when the cross-sectional reduction rate is 40% or more. Therefore, the cross-sectional reduction rate in the final rolling is set to 40% or more.

  In the method for producing a low alloy steel according to the present invention, direct quenching is performed after the final rolling. After the final rolling, it is allowed to cool, reheat, and subjected to quenching from a high temperature such as 920 ° C., recrystallization of the austenite structure occurs at the time of quenching, the aspect ratio of the prior austenite grains becomes small, SSC generation and Resistance to progress deteriorates. Therefore, in this invention, it decided to carry out direct hardening after final rolling.

  In addition, since the aspect ratio of the prior austenite crystal grains strongly depends on the starting temperature of the final rolling and the workability at the time of final rolling, the heat treatment history of the steel material before that is not particularly limited.

  Examples in which the effects of the present invention are verified will be described below.

  150 kg of steel having the chemical composition shown in Table 1 was melted and subjected to evaluation. This component system is a component used for a low-alloy well pipe that requires normal SSC resistance. From the melted billet, a block having a thickness of 60 mm was collected by hot forging. After these blocks were heated to 1100 to 1250 ° C., they were hot-rolled to a thickness of 12 mm, and immediately after that were quenched by water cooling.

FIG. 1 is a schematic diagram of the above process. The starting temperature of the final rolling was changed between 750 and 1100 ° C. by adjusting the waiting time between the hot rolling passes. Similarly, by adjusting the waiting time between the hot rolling passes, the workability of the final rolling was changed between 20% and 70% by the cross-section reduction rate defined by the following formula (1).
R = (A−B) / A × 100 (1)

However, the meaning of each symbol in the formula (1) is as follows.
R: Cross-sectional reduction rate (%)
A: Cross-sectional area of the plate material before the start of rolling B: Cross-sectional area of the plate material after the end of rolling.

  In the examples of the present invention, tempering was performed by holding the plate directly quenched after the final rolling at 600 to 700 ° C. for 30 minutes and then allowing to cool. As a result, YS was adjusted to around 140 ksi (965 MPa), which is the upper limit of the 125 ksi class (862 MPa class). Further, in the comparative example, the conventional quenching and tempering, that is, after final rolling, allowing to cool, reheating, quenching by holding at 920 ° C. for 15 minutes and then water cooling, and holding at 600 to 700 ° C. for 30 minutes and then allowing to cool. Tempered.

  About the steel materials produced by the methods of the present invention and the comparative examples, the extensibility and SSC resistance of prior austenite crystal grains were determined by the following methods.

<Elongation of old austenite grains>
Test pieces of 12 mm thickness (as plate thickness), 20 mm width and 10 mm length were cut out from the as-quenched plate material. The cross section of the test piece in the rolling direction was mirror-polished and corroded with picric acid. The structure of the central part of the thickness of the test piece was observed with an optical microscope at a magnification of 100 times. The extensibility of the prior austenite crystal grains was evaluated by the aspect ratio (value obtained by dividing the major axis by the minor axis).

<SSC resistance>
The SSC resistance was evaluated by performing a low strain rate tensile test (Slow Strain Rate Testing, SSRT test) under cathodic charge and evaluating the magnitude of the breaking strength.
A round bar tensile test piece having a parallel part diameter of 6.66 mm, a parallel part length of 25.4 mm, and a U-shaped notch with a depth of 1.42 mm at the center of the parallel part (notch bottom radius is 0.1 mm) was taken in the rolling direction. . The shape of the test piece is shown in FIG. Using this test piece, a strain of 3 × 10 ⁻⁶ (s ⁻¹ ) was maintained at −1.2 V with respect to the silver-silver chloride reference electrode in a 3% sodium chloride + 3 g / L ammonium thiocyanate aqueous solution while cathodic polarization. Tensile tests were performed at speed.

  FIG. 3 shows the hydrogen penetration behavior into the material in a double cell type hydrogen permeation test. “0 g / L”, “1 g / L” and “3 g / L” in the figure mean the amount of ammonium thiocyanate. As shown in FIG. 3, as the amount of ammonium thiocyanate increases and the potential difference increases, hydrogen penetration becomes more active. However, ammonium thiocyanate is 3 g / L, the potential difference is −1.2 V, and hydrogen penetration is saturated. . For this reason, the corrosive environment was set as described above.

  In addition, about the double cell type hydrogen permeation test method, the method described in “Koji Yamakawa et al., Materials, Vol. 30, No. 335, 1981, pages 836 to 841” was used. According to the above document, the amount of hydrogen intrusion at a potential of -1.2 V in 3% saline + 3 g / L ammonium thiocyanate aqueous solution corresponds to an environment of pH 3.5 in which 0.1 atm of hydrogen sulfide is saturated.

  The evaluation of SSC resistance is usually performed according to the method specified in TM0177-96 by NACE (National Association of Corrosion Engineers, American Petroleum Institute). In this specification, a simple evaluation is possible, and The above evaluation method was adopted because the influence of the surface structure was excluded and the influence of the material structure could be clearly compared.

  FIG. 4 is a diagram showing the relationship between the aspect ratio of prior austenite crystal grains and the starting temperature of final rolling. In FIG. 4, only the data in which the cross-sectional reduction rate of the final rolling is 50% is plotted. Also, the Off. Q is a comparative example.

  As shown in FIG. 4, in the conventional example, the aspect ratio is approximately 1, and the crystal grains have no anisotropy. This is because recrystallization of the austenite structure occurs during quenching. On the other hand, in the example of direct quenching after the final rolling, the aspect ratio takes a value of 2 to 2.5 when the final rolling temperature is in the range of 750 to 950 ° C. Therefore, it can be seen that if the final rolling temperature is in the range of 750 to 950 ° C., the prior austenite crystal grains have anisotropy and the effect of processing remains. When the final rolling temperature is 1000 ° C. or higher, the aspect ratio is almost 1, and the recrystallization of the austenite structure proceeds even after the rolling finish, and there is no crystal grain anisotropy as in the case of the conventional quenching material.

  FIG. 5 is a graph showing the relationship between the breaking strength and the final rolling start temperature in the SSRT test. As in the case of FIG. 4, FIG. 5 plots only data in which the final rolling cross-section reduction rate is 50%. Also, the Off. Q is a comparative example.

  As shown in FIG. 5, the breaking strength of the example directly quenched after rolling reaches its maximum value when the starting temperature of the final rolling is 850 ° C. In addition, the breaking strength of the example directly quenched after rolling is similar to the comparative example when the final rolling start temperature is 750 ° C., but if the final rolling start temperature is in the range of 780 to 920 ° C., the comparative example Compared to higher.

  FIG. 6 is a diagram showing the relationship between the aspect ratio of prior austenite crystal grains and the cross-sectional reduction rate of final rolling. In FIG. 6, only data where the starting temperature of the final rolling is 800 ° C. is plotted.

  As shown in FIG. 6, when the cross-section reduction rate is 20%, the aspect ratio is almost 1, and the anisotropy of the prior austenite crystal grains is insufficient.

  FIG. 7 is a diagram showing the relationship between the breaking strength in the SSRT test and the cross-sectional reduction rate of the final rolling. As in FIG. 6, FIG. 7 plots only data with a final rolling start temperature of 800 ° C.

  As shown in FIG. 7, the greater the cross-section reduction rate, the higher the breaking strength, and the effect increases rapidly when the cross-section reduction rate is 40% or more. This is because the aspect ratio of the prior austenite crystal grains increases as the cross-sectional reduction rate increases, and the resistance to the generation and progress of SSC improves.

  According to the method of the present invention, a steel material and a steel pipe having good SSC resistance can be obtained even when the yield stress (YS) is as high as 125 ksi (862 MPa) or more.

Schematic showing the thermal history in the direct quenching method of the example Schematic diagram showing the shape of the test piece used in the SSRT test Hydrogen penetration behavior into materials in double cell type hydrogen permeation test Diagram showing the relationship between the aspect ratio of prior austenite grains and the starting temperature of final rolling The figure which shows the relationship between the fracture strength in the SSRT test and the starting temperature of the final rolling Diagram showing the relationship between the aspect ratio of prior austenite grains and the cross-sectional reduction rate of final rolling The figure which shows the relationship between the breaking strength in the SSRT test and the cross-section reduction rate of the final rolling

Claims (6)

% By mass
C: 0.15-0.60%,
Si: 0.05 to 0.5%,
Mn: 0.05 to 3.0%
P: 0.025% or less,
S: 0.010% or less,
Al: 0.005 to 0.10% and O (oxygen): 0.01% or less, the balance is Fe and impurities, and the aspect ratio (major axis / minor axis) of prior austenite grains is 1 in cross-sectional observation. Low alloy steel material characterized by being 5 or more. Instead of part of Fe, in mass%,
Cr: 0.1 to 1.5%
Mo: 0.1 to 3%,
V: 0.05-0.3%
B: 0.0003 to 0.003%,
Nb: 0.002 to 0.1%,
Ti: 0.002 to 0.1%,
Zr: 0.002 to 0.1%,
N: 0.003-0.03% and Ca: 0.0003-0.01%
The low alloy steel material according to claim 1, comprising at least one selected from the group consisting of:   The low alloy steel material according to claim 1 or 2, wherein the steel material is a seamless steel pipe. % By mass
C: 0.15-0.60%,
Si: 0.05 to 0.5%,
Mn: 0.05 to 3.0%
P: 0.025% or less,
S: 0.010% or less,
A steel material containing Al: 0.005 to 0.10% and O (oxygen): 0.01% or less, with the balance being Fe and impurities, is finally rolled, then water-cooled and quenched, and further tempered. A method for producing a low alloy steel material, characterized in that the final rolling start temperature is 780 to 920 ° C., and the cross-section reduction rate R obtained from the following formula (1) is 40% or more. Manufacturing method.
R = (A−B) / A × 100 (1)
Here, R means the cross-section reduction rate (%), A means the cross-sectional area of the steel material before the final rolling, and B means the cross-sectional area of the steel material after the final rolling. Steel material, instead of a part of Fe, in mass%,
Cr: 0.1 to 1.5%
Mo: 0.1 to 3%,
V: 0.05-0.3%
B: 0.0003 to 0.003%,
Nb: 0.002 to 0.1%,
Ti: 0.002 to 0.1%,
Zr: 0.002 to 0.1%,
N: 0.003-0.03% and Ca: 0.0003-0.01%
It contains 1 or more types selected from these, The manufacturing method of the low alloy steel materials of Claim 4 characterized by the above-mentioned. The method for producing a low alloy steel material according to claim 4 or 5, wherein the steel material is a seamless steel pipe.

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