JP5262949B2 - Manufacturing method and equipment for seamless steel pipe - Google Patents

Abstract

In the production of a seamless steel tube by piercing-rolling a heated billet with a piercing machine to form the billet into a hollow blank, and without reheating the hollow blank, by successively subjecting the hollow blank to elongation-rolling with an elongation-rolling mill and diameter-adjusting rolling by a diameter-adjusting rolling mill, it is made possible to prevent non-uniform longitudinal temperature distribution from occurring in a steel tube after diameter-adjusting rolling and enable energy saving to be accomplished by including a step 1 of measuring a temperature of the hollow blank along a longitudinal direction at the exit of the elongation-rolling mill; and a step 2 of spraying water onto the hollow blank to cool the hollow blank at the entrance of the diameter-adjusting rolling mill according to a measured longitudinal temperature distribution of the hollow blank, whereby the longitudinal temperature distribution of the hollow blank becomes uniform.

Description

  The present invention relates to a method for manufacturing a seamless steel pipe by the Mannesmann pipe manufacturing method, and a seamless steel pipe manufacturing facility suitable for carrying out the manufacturing method.

Seamless steel pipes are used for oil well pipes that require high strength and excellent toughness, and can be manufactured by the Mannesmann pipe manufacturing method. This pipe making process consists of the following steps:
(1) A billet heated to a predetermined temperature is pierced and rolled by a piercing machine (piercer) and formed into a hollow shell (hollow shell);
(2) The hollow shell is stretch-rolled by a stretching mill (eg, mandrel mill);
(3) Using a constant diameter rolling mill (eg, sizer, stretch reducer), the stretched hollow shell is constant-rolled to a predetermined outer diameter and thickness;
(4) The seamless steel pipe obtained by constant diameter rolling is air-cooled in a cooling bed, or the seamless steel pipe is quenched and tempered.

  Conventionally, a production facility that employs the Mannesmann tube method performs constant diameter rolling by heating a stretched hollow shell in a reheating furnace. Moreover, when quenching a steel pipe that has been rolled with a constant diameter, the steel pipe is heated and quenched in a quenching furnace.

  In recent years, in order to save energy and improve production efficiency, we have eliminated reheating furnaces during constant diameter rolling and quenching furnaces during quenching, from piercing to constant diameter rolling, and sometimes even quenching. A series of on-line manufacturing facilities may be employed. In a production facility that excludes a reheating furnace and a quenching furnace, after the material to be rolled is heated during piercing and rolling, no reheating is performed until constant diameter rolling or quenching. When this production facility is used, the steel pipe after constant diameter rolling has a non-uniform temperature distribution in the longitudinal direction, and the temperature is low on the top (tip) side and the temperature on the bottom (rear end) side. Get higher. Such a phenomenon occurs for the following reason.

  At the time of piercing and rolling, the heated billet is pierced from the top part side to the bottom part side by the plug, so that heat is radiated significantly on the top part side that is first pierced and becomes tubular. For this reason, the hollow shell after piercing and rolling has a low temperature on the top side and a high temperature on the bottom side. This non-uniform longitudinal temperature distribution does not reheat the material to be rolled, and therefore occurs in the same tendency even in a hollow shell after drawing and rolling, and also in a steel pipe after constant diameter rolling. Thereby, nonuniform temperature distribution appears in the longitudinal direction in the steel pipe after constant diameter rolling.

  If the temperature distribution in the longitudinal direction is non-uniform in the steel pipe after constant diameter rolling, the amount of thermal shrinkage accompanying cooling differs in the longitudinal direction, so that the outer diameter of the steel pipe becomes non-uniform in the longitudinal direction after cooling. Also, when quenching a steel pipe after constant diameter rolling, if the temperature distribution in the longitudinal direction is non-uniform, the degree of quenching differs in the longitudinal direction, so the mechanical properties of the steel pipe become non-uniform in the longitudinal direction after quenching. .

  Conventional techniques relating to temperature control of a material to be rolled when manufacturing a steel pipe include the following.

  Patent Document 1 discloses a technique for preventing an excessive decrease in the temperature of a material to be rolled in the process of passing through a continuous rolling mill in a multistage continuous rolling mill used in the manufacture of seamless steel pipes. The technique disclosed in this document is to arrange a reheating furnace at the entry side and intermediate part of the continuous rolling mill, and at the entry side and exit side of the intermediate reheating furnace arranged at the intermediate part of the continuous rolling mill, and continuous rolling. A thermometer is arranged on the exit side of the machine, and the temperature of the intermediate reheating furnace is controlled based on the steel pipe temperature measured by each thermometer.

  Patent Document 2 discloses a technique for preventing a thickness deviation from occurring due to a temperature decrease in the circumferential direction of a steel pipe in a stretch reducer used in the manufacture of an electric resistance steel pipe. The technique disclosed in this document is that a plurality of induction heating coils are arranged in series on the entrance side of the stretch reducer, and a thermometer is arranged on the exit side of the induction heating coil and the exit side of the stretch reducer. The power supply amount to the induction heating coil is adjusted based on the temperature measurement value in the circumferential direction of the steel pipe.

  Patent Document 3 discloses a technique for suppressing the occurrence of bending when a hot-formed square steel pipe or a round steel pipe is cooled. In the technique disclosed in this document, a reheating furnace is disposed in front of the forming means for hot forming the steel pipe into a predetermined shape and a water discharge means is disposed in the subsequent stage of the forming means. The steel pipe is uniformly cooled by discharging water from all directions on the outer periphery by the water discharge means.

  The techniques disclosed in Patent Documents 1 to 3 above reheat the steel pipe before constant diameter rolling to make the temperature uniform, so that the longitudinal temperature distribution is not uniform in the steel pipe after constant diameter rolling. The situation will not occur. However, any of the techniques disclosed in Patent Documents 1 to 3 requires a reheating furnace and an induction heating coil in front of the constant diameter rolling mill, which consumes enormous amount of fuel and power and saves energy. It cannot be a countermeasure.

JP 2004-58128 A Japanese Patent Laid-Open No. 2005-7452 JP 2007-301574 A

An object of the present invention is to provide a method and apparatus for producing a seamless steel pipe having the following characteristics:
(1) In the steel pipe after constant diameter rolling, the longitudinal temperature distribution does not become uneven;
(2) Achieving energy saving.

  The gist of the present invention is as follows.

(I) A seamless billet is formed by piercing and rolling a heated billet into a hollow shell, and then stretching and rolling the hollow shell with a drawing mill without constant reheating and rolling with a constant diameter rolling mill. A method of manufacturing a steel pipe,
The manufacturing method is
(Step 1) measuring the temperature of the hollow shell along the longitudinal direction on the exit side of the drawing mill,
(Step 2) Depending on the measured longitudinal temperature distribution of the hollow shell, water is blown to the hollow shell at the entrance of the constant diameter rolling mill to cool the hollow shell, and the longitudinal temperature distribution of the hollow shell is determined. Uniform,
A method for producing a seamless steel pipe, comprising a series of steps.

  The manufacturing method of said (I) can be set as the structure which quenches without reheating following the said constant diameter rolling.

  These manufacturing methods are preferably configured to adjust the amount of water sprayed to the hollow shell in each of a plurality of regions obtained by dividing the hollow shell in the longitudinal direction in Step 2.

(II) A piercing machine for piercing and rolling a heated billet to form a hollow shell, a stretching mill for stretching and rolling the hollow shell without reheating, and a constant diameter rolling mill for constant diameter rolling. A production facility for seamless steel pipes,
The manufacturing equipment is
A thermometer arranged on the exit side of the drawing mill and measuring the temperature of the hollow shell along the longitudinal direction;
According to the longitudinal temperature distribution of the hollow shell, which is arranged on the entrance side of the constant diameter rolling mill and measured by the thermometer, the hollow shell is cooled by spraying water on the hollow shell, and the longitudinal direction of the hollow shell A water cooling device for uniform temperature distribution;
A seamless steel pipe manufacturing facility characterized by comprising:

The method for producing a seamless steel pipe of the present invention has the following remarkable effects:
(1) In the steel pipe after constant diameter rolling, the longitudinal temperature distribution does not become uneven;
(2) Achieving energy saving.

  The excellent effect of the production method of the present invention can be sufficiently exhibited by the seamless steel pipe production facility of the present invention.

It is a schematic diagram which shows the structural example of the manufacturing equipment of the seamless steel pipe of this invention. It is a figure which shows the structural example of the water cooling apparatus in the manufacturing equipment of the seamless steel pipe of this invention, The figure (a) is a sectional side view along the conveyance direction of a hollow shell, The figure (b) is a front view, respectively. Show. It is a figure which shows the correlation with the amount of water sprayed per meter of a hollow shell, and the amount of temperature drops.

  In order to achieve the above object, the present inventor presupposes that after rolling the material to be rolled at the time of piercing rolling, reheating is not performed until constant diameter rolling or quenching treatment, In this study, we made extensive studies on the method that does not cause uneven temperature distribution in the longitudinal direction. As a result, the following findings (a) and (b) were obtained.

(A) By making the longitudinal temperature distribution uniform in the hollow shell before constant diameter rolling, nonuniformity of the longitudinal temperature distribution of the steel pipe does not occur after constant diameter rolling.
(B) In order to make the temperature distribution in the longitudinal direction uniform in the hollow shell before constant diameter rolling, water is sprayed on the hollow shell according to the longitudinal temperature distribution of the hollow shell and the hollow shell is cooled. Is effective.

  The present invention has been completed based on the above findings (a) and (b). Below, the manufacturing method of the seamless steel pipe of this invention and the preferable aspect of the manufacturing equipment are demonstrated.

1. Seamless Steel Pipe Manufacturing Equipment FIG. 1 is a schematic diagram showing a configuration example of a seamless steel pipe manufacturing equipment of the present invention. As shown in the figure, the production facility 1 includes a heating device 2, a piercing machine 3 (piercer), a drawing mill 4 (eg, mandrel mill), and a constant diameter rolling mill 5 (eg, sizer, stretch reducer). And a cooling bed 6 as a series of on-line facilities. Further, the manufacturing facility 1 is connected to a thermometer 7 disposed on the exit side of the drawing mill 4, a water cooling device 8 disposed on the entry side of the subsequent constant diameter rolling mill 5, and the thermometer 7 and the water cooling device 8. The control device 9 is provided.

  The heating device 2 heats a billet as a material to be rolled to a predetermined temperature suitable for piercing and rolling. The piercing machine 3 pierces and rolls the heated billet to form a hollow shell. The drawing mill 4 performs drawing rolling without reheating the hollow shell. The constant diameter rolling mill 5 performs constant diameter rolling without reheating the stretched hollow shell, and finishes the steel pipe with a predetermined outer diameter and wall thickness. The steel pipe subjected to constant diameter rolling is air-cooled in the cooling bed 6.

  In this production facility 1, when performing constant diameter rolling with the constant diameter rolling mill 5, the temperature of the hollow shell stretched and rolled with the stretching mill 4 is measured along the longitudinal direction by the thermometer 7. The control device 9 sequentially receives the measurement temperature signal from the thermometer 7, calculates the temperature distribution in the longitudinal direction of the hollow shell, and sends a drive signal corresponding to the temperature distribution to the water cooling device 8. The water cooling device 8 sprays water with an appropriate amount of water on the hollow shell based on the drive signal from the control device 9 and cools the hollow shell so that the longitudinal temperature distribution of the hollow shell is uniform. The cooled hollow shell is subjected to constant diameter rolling with a constant diameter rolling mill 5.

  In this production facility 1, the hollow shell is conveyed in the longitudinal direction by a roller conveyor from the punching machine 3 to the drawing mill 4, and from the drawing mill 4 through the water cooling device 8 to the constant diameter rolling mill 5. Is done.

  FIG. 2 is a diagram showing a configuration example of a water-cooling device in a seamless steel pipe manufacturing facility according to the present invention, where FIG. 2 (a) is a side sectional view along the conveying direction of the hollow shell, and FIG. Front views are shown respectively. In FIG. 9A, the conveying direction of the hollow shell is indicated by a thick arrow.

  As shown in the figure, the water cooling device 8 includes an annular pipe 11 that is inserted through the conveyance path of the hollow shell P. A water supply pipe 12 is connected to the annular pipe 11, and a water supply pump 13 is connected to the water supply pipe 12. The water supply pump 13 is driven based on the drive signal from the control device 9 shown in FIG. 1 and can adjust the amount of water to be sent out.

  A plurality of nozzles 14 are provided at equal intervals in the circumferential direction on the inner periphery of the annular pipe 11. Each nozzle 14 blows out water supplied to the annular pipe 11 through the water supply pipe 12 as the water supply pump 13 is driven toward the hollow pipe P. Thereby, the hollow shell P conveyed in the longitudinal direction is uniformly cooled in the circumferential direction every time it passes through the annular pipe 11.

  The number of nozzles 14 is not particularly limited, but is preferably about 4 to 24. This is because if the number is less than 4, the uniform cooling in the circumferential direction of the hollow shell P may be insufficient, and if it is more than 24, the degree of the uniform cooling is saturated.

  Each nozzle 14 is preferably provided with a slight inclination toward the direction opposite to the conveying direction of the hollow shell P (the direction toward the bottom portion). This is to prevent water from entering the hollow shell P that has passed through the annular pipe 11 from its rear end.

  The manufacturing equipment 1 shown in FIG. 1 can install a plurality of stages of the water cooling device 8 having such a configuration along the transport path of the hollow shell P. The water cooling device 8 may be installed in one stage. A radiation thermometer can be adopted as the thermometer 7.

  The manufacturing equipment 1 shown in FIG. 1 includes a quenching device without using a quenching furnace in place of the cooling bed 6 or in parallel with the cooling bed 6 in order to quench the steel pipe after constant diameter rolling. be able to. As the quenching device, a water bath immersion type or a laminar water flow down type can be adopted. A tempering furnace can be arranged in the subsequent stage of the quenching device in order to temper the steel pipe after quenching.

2. Manufacturing method of seamless steel pipe The manufacturing method of the seamless steel pipe of this invention is demonstrated referring the said FIG. In the production method of the present invention, a heated billet is pierced and rolled by a piercing machine 3 to form a hollow shell, and then the hollow shell is stretched and rolled by a stretching mill 4 without reheating the constant diameter rolling mill 5. To constant diameter rolling.

  At that time, the hollow shell after piercing and rolling has a non-uniform temperature distribution in the longitudinal direction due to significant heat dissipation on the top portion side during piercing and rolling. For this reason, also in the hollow shell after drawing and rolling, the temperature distribution in the longitudinal direction becomes non-uniform with the same tendency.

  In the production method of the present invention, when performing constant diameter rolling with the constant diameter rolling mill 5, the temperature of the hollow shell is measured along the longitudinal direction by the thermometer 7 on the exit side of the drawing mill 4. Then, according to the measured temperature distribution in the longitudinal direction of the hollow shell, the water cooling device 8 cools the hollow shell by spraying water onto the hollow shell at the entrance side of the constant diameter rolling mill 5, and the length of the hollow shell is reduced. Uniform directional temperature distribution.

  Specifically, the controller 9 connected to the thermometer 7 obtains the temperature for each of a plurality of regions obtained by dividing the hollow shell in the longitudinal direction, selects the minimum temperature among the temperatures of each region, Every time, the temperature difference from the minimum temperature is obtained. Based on the temperature difference, the amount of water sprayed from the water cooling device 8 to the hollow shell is calculated for each region, and a drive signal corresponding to the amount of water is sent to the water cooling device 8. As a result, the conveyed hollow shell is cooled by spraying an appropriate amount of water from the water cooling device 8 for each region, and the temperature distribution in the longitudinal direction becomes uniform.

  Here, there is a correlation between the amount of water sprayed on the hollow shell and the temperature drop. For this reason, the amount of water sprayed on the hollow shell can be calculated based on the temperature difference in each region of the hollow shell, for example, from the correlation with the temperature drop of the hollow shell shown in FIG.

  FIG. 3 is a diagram showing the correlation between the amount of water sprayed per meter of the hollow shell and the amount of temperature drop. The figure shows a test using a hollow shell tube with various changes in outer diameter and wall thickness. The test is performed by spraying water on each hollow shell tube heated to 1100 ° C. by changing the amount of water per meter. It shows the result of investigating the temperature drop in the area.

As shown in the figure, between the water quantity Q [m ³ ] sprayed on the hollow shell and the temperature drop ΔT [° C.], ΔT = 160 regardless of the outer diameter and thickness of the hollow shell. There is a correlation of × Q. From this relational expression, the amount Q of water sprayed onto the hollow shell can be calculated by setting the temperature difference in each region of the hollow shell as ΔT.

  According to the method for producing a seamless steel pipe of the present invention, when performing constant diameter rolling, water can be sprayed to the hollow shell to make the temperature distribution in the longitudinal direction uniform, so that the steel pipe after constant diameter rolling can be longitudinal A situation in which the temperature distribution becomes non-uniform does not occur. For this reason, the steel pipe after constant diameter rolling does not differ in the amount of thermal shrinkage accompanying cooling in the longitudinal direction, and after cooling, the outer diameter of the steel pipe becomes uniform over the entire area in the longitudinal direction. Moreover, even when quenching the steel pipe after constant diameter rolling, the mechanical properties of the steel pipe are uniform throughout the longitudinal direction after quenching without the degree of quenching being different in the longitudinal direction.

  In addition, according to the method of manufacturing a seamless steel pipe of the present invention, after heating the material to be rolled at the time of piercing and rolling, reheating is not performed until constant diameter rolling or quenching treatment. Energy saving can be realized without consumption.

  The method for producing a seamless steel pipe of the present invention can sufficiently exert its effect by the production facility for the seamless steel pipe of the present invention.

Example 1
In order to confirm the effect of the present invention, piercing rolling, stretching rolling and constant diameter rolling were performed using the manufacturing equipment shown in FIG.
・ Dimensions: Outer diameter 406.4mm, Wall thickness: 30.7mm, Length: 12m
・ Material: Low carbon steel (C: 0.6 wt%)

  When performing constant diameter rolling, the temperature of the hollow shell after drawing and rolling was measured, and water was sprayed onto the hollow shell with the amount of water shown in Table 1 below according to the longitudinal temperature distribution. For comparison, the test was performed without spraying water.

  Immediately after the constant diameter rolling, the temperature of the seamless steel pipe was measured, and after cooling the steel pipe, the outer diameter of the steel pipe was measured over the entire lengthwise direction. The results are also shown in Table 1. Table 1 shows a top region in the range of 1 to 3 m from the tip of the steel pipe, a middle region in the range of 2 m in the longitudinal center of the steel pipe, and a bottom region in the range of 1 to 3 m from the rear end of the steel pipe.

  The results shown in Table 1 indicate the following.

  In the present invention example, the temperature of the steel pipe immediately after the constant diameter rolling became uniform in the longitudinal direction by spraying water on the hollow shell before the constant diameter rolling. As a result, the outer diameter of the steel pipe after cooling became uniform in the longitudinal direction.

  In the comparative example, since water was not sprayed on the hollow shell before the constant diameter rolling, the temperature of the steel pipe immediately after the constant diameter rolling varied by about 40 ° C. in the longitudinal direction and became non-uniform. As a result, the steel pipe after cooling became non-uniform with the outer diameter varying about 0.2 mm in the longitudinal direction.

(Example 2)
Using the production equipment shown in FIG. 1, piercing rolling, stretching rolling, constant diameter rolling, quenching, and tempering treatment were performed, and an actual machine test for producing a seamless steel pipe having the following specifications was conducted. The effect of spraying on the mechanical properties of steel pipes was confirmed.
・ Dimensions: Outer diameter 406mm, Wall thickness: 14mm, Length: 12m
・ Material: Low carbon steel whose composition is shown in Table 2 below ・ Mechanical properties: API standard X65 grade

  When performing constant diameter rolling, the temperature of the hollow shell after drawing and rolling was measured, and water was sprayed onto the hollow shell with the amount of water shown in Table 3 below according to the longitudinal temperature distribution. For comparison, the test was performed without spraying water.

  Measure the temperature of the seamless steel pipe immediately before quenching after constant diameter rolling, and further quench and temper the steel pipe. The thickness (YS) was measured. The test method for measuring the crystal grain size conformed to ASTM, and the test method for measuring the yield strength conformed to ASTM. The results are also shown in Table 3. Table 3 also shows the top portion region, the middle portion region, and the bottom portion region as in the first embodiment.

  The results shown in Table 3 indicate the following.

  In the present invention example, the temperature of the steel pipe immediately before quenching became uniform in the longitudinal direction by spraying water onto the hollow shell before constant diameter rolling. As a result, both the grain size and the yield strength of the steel pipe after quenching and tempering became uniform in the longitudinal direction.

  In the comparative example, since water was not sprayed on the hollow shell before constant diameter rolling, the temperature of the steel pipe immediately before quenching varied about 50 ° C. in the longitudinal direction and became non-uniform. As a result, the crystal grain size of the steel pipe after quenching and tempering became fine particles having a particle size number 11 in the top region and coarse particles having a particle size number 5 in the bottom region, and became nonuniform in the longitudinal direction. The reason why the grain size becomes coarse in the bottom region is that the crystal grows and becomes coarse in the bottom region because the temperature until quenching is higher in the bottom region than in the top region. . Moreover, the yield strength of the steel pipe after quenching and tempering varied about 60 MPa in the longitudinal direction and became non-uniform.

  The present invention can be effectively used for the production of seamless steel pipes by the Mannesmann pipe manufacturing method.

1: Production equipment 2: Heating device 3: Punching machine 4: Stretch rolling machine,
5: Constant diameter rolling mill, 6: Cooling bed, 7: Thermometer, 8: Water cooling device,
9: control device, 11: annular pipe, 12: water supply pipe, 13: water supply pump,
14: nozzle, P: hollow shell

Claims (4)

Production of seamless steel pipes, in which heated billets are pierced and rolled with a piercing machine and formed into hollow shells, and then the hollow shells are stretched and rolled with a stretching mill without constant reheating, and then rolled with a constant diameter mill. A method,
The manufacturing method is
(Step 1) measuring the temperature of the hollow shell along the longitudinal direction on the exit side of the drawing mill,
(Step 2) Depending on the measured longitudinal temperature distribution of the hollow shell, water is blown to the hollow shell at the entrance of the constant diameter rolling mill to cool the hollow shell, and the longitudinal temperature distribution of the hollow shell is determined. Uniform,
A method for producing a seamless steel pipe, comprising a series of steps.   The method for producing a seamless steel pipe according to claim 1, wherein quenching is performed without reheating following the constant diameter rolling.   3. The method for manufacturing a seamless steel pipe according to claim 1, wherein in step 2, the amount of water sprayed on the hollow shell is adjusted for each of a plurality of regions obtained by dividing the hollow shell in the longitudinal direction. A seamless steel pipe comprising: a piercing machine for piercing and rolling a heated billet to form a hollow shell; a stretching mill for stretching and rolling the hollow shell without reheating; and a constant diameter rolling mill for constant diameter rolling. Manufacturing equipment,
The manufacturing equipment is
A thermometer arranged on the exit side of the drawing mill and measuring the temperature of the hollow shell along the longitudinal direction;
According to the longitudinal temperature distribution of the hollow shell, which is arranged on the entrance side of the constant diameter rolling mill and measured by the thermometer, the hollow shell is cooled by spraying water on the hollow shell, and the longitudinal direction of the hollow shell A water cooling device for uniform temperature distribution;
A seamless steel pipe manufacturing facility characterized by comprising:

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