RU2243837C1 - Method for making hot-deformed seamless large-diameter tubes - Google Patents

Abstract

FIELD: rolled tube production, namely processes for piercing ingots and billets for making seamless hot-deformed large-diameter tubes.

SUBSTANCE: method comprises steps of heating ingots and billets until yielding temperature; piercing them to hollow thick-wall sleeves in first skew rolling mill for further expanding to thin-wall sleeves in second skew rolling mill and rolling to large-diameter tubes in plants provided with automatic or pilger mills; piercing ingots and billets to thick-wall sleeves in first piercing mill with working rolls driven to rotation in one side and expanding billets to thin-wall sleeves in second piercing mill with working rolls driven to rotation in opposite side.

EFFECT: enhanced geometry of tubes, lowered metal consumption, improved efficiency of tube rolling plants.

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Description

The invention relates to pipe rolling production, in particular to a method for piercing ingots and billets, and can be used in the production of seamless hot-deformed pipes with a diameter of 465-550 mm with a ratio D / S≥ 13.5 on pipe rolling plants with pilgrim mills made of carbon and low alloy steels and pipes with a diameter of 273-426 mm or more in tube rolling plants with automatic and pilgrim mills made of hard-to-deform grades of steel and alloys.

Known methods for flashing ingots and billets in oblique rolling mills in the production of pipes with a diameter of 530-550 mm with a D / S ratio of 13.5 on TPA8-16 "with pilgrim mills of ChTPZ OJSC from carbon and low alloy steel grades and pipes with a diameter of 351 mm and more of ESR ingots of hardly deformable grades of steel and alloys, consisting in the fact that heated ingots and billets are stitched (deformed) in the piercing mill into two firmwares (TI158-Tr. TB1-38-97 "Production of seamless hot-rolled pipes for steam boilers and pipelines according to TU 14-3-460-75 and TU14-3-420-75 ", TI158-Tr. T 1-56-97 "Production of seamless hot-rolled pipes from grade 20 steel for the oil refining industry according to TU14-3-587-77", TI 158-Tr. TB 1-51-2002 "Production of seamless hot-rolled pipes from steel 15X5M according to TU14-3R -62-2002 "and TI158-Tr. TB1-53-2002" Production of seamless hot-rolled pipes from corrosion-resistant steel grades with high surface quality according to TU 14-3R-197-2001 ").

The disadvantage of these methods is that the double flashing of ingots and billets leads to double heating, and therefore, to reduce the performance of the pilgrim installation and increase the cost of their redistribution. The insertion of sleeves on mandrels with a diameter of 475 or more with a ratio of D / S≥ 8 leads to uneven cooling in the piercing mill and increased curvature, which in turn leads to increased pipe spacing in the pilgrim mill and, as a result, to increased metal consumption during redistribution (ingot billet) - finished pipe. Rolling pipes with a size of 351 mm or more from hard-deformed grades of steel and alloys for one firmware is generally impossible due to the low power of the piercing mill drive at high loads.

The closest technical solution is a method for producing seamless hot-deformed pipes, which consists in heating ingots and billets to a ductile temperature, flashing them into hollow thick-walled sleeves in one oblique rolling mill, followed by rolling into thin-walled sleeves in a second oblique rolling mill and rolling them into large diameter pipes in installations with an automatic mill (production of seamless pipes from corrosion-resistant steels according to GOST 9940-81 at TPA "350" of the Nikopol South Pipe Plant, Ukraine). In this case, the work rolls of the piercing mills rotate in one direction (clockwise).

However, the known method has the following disadvantages. The practice of operation of oblique rolling mills shows that when piercing ingots and billets with uneven heating, we get thick-walled sleeves with increased curvature, rolling them into thin-walled sleeves in the second mill leads to an increase in the initial curvature and, as a result, to an increased transverse and longitudinal delta of the pipes during rolling them on injection molding machines with automatic mills, to increased lateral difference when rolling them into pipes at plants with pilgrim mills or generally to marriage due to the impossibility of introducing I'm inside the sleeves of a long mandrel (mandrel).

The aim of the proposed method is to improve the geometrical dimensions of hot-rolled pipes of large diameter from carbonaceous and low alloy steel grades and pipes of medium and large diameter from stainless and hard-to-deform steels and alloys, to reduce the expenditure coefficient of metal and increase the productivity of tube-rolling plants with automatic and pilgrim mills due to a significant reduction in curvature thin-walled sleeves.

This goal is achieved by the fact that in the known method for the production of seamless hot-deformed large-diameter pipes, which consists in heating ingots and billets to a plasticity temperature, flashing them into thick-walled hollow sleeves in one oblique rolling mill, followed by rolling into thin-walled sleeves in the second oblique rolling mill and rolling them into large-diameter pipes in installations with automatic and pilgrim mills; the ingots and billets are pierced into thick-walled sleeves in the first piercing mill; whose rolls are rotated in one direction, and rolling into thin-walled sleeves in a second mill, the work rolls of which are rotated in the opposite direction. A comparative analysis of the proposed solution with the prototype shows that the ingots and billets are flashed into thick-walled sleeves in the first piercing mill, the work rolls of which rotate in one direction, rolling into thin-walled sleeves in the second mill, the work rolls of which are rotated in the opposite direction. Thus, the claimed method meets the criterion of "novelty." Comparison of the proposed method not only with the prototype, but also with other technical solutions in the art did not allow them to identify signs that distinguish the claimed method from the prototype, which allows us to conclude that the criterion of "significant differences".

For rolling pipes with a size of 530-550 × 15-20 × L mm on an 8-16 "tube rolling system with Pilgrim Mills of ChTPZ OJSC with wall tolerances of ± 12.5%, sleeves of 650-670 × 50-60 × 3000- are required 3500 mm. Flashing sleeves of this size from workpieces with a diameter of 650 mm for one flashing leads to overloading the piercing mill engine and bending the sleeves, and rolling pipes from sleeves with increased curvature in rolls with caliber 538-558 mm with hoods 3.5-4.0 leads to the formation of a lateral difference of more than ± 12.5%. Therefore, pipes of this assortment on TPA 8-16 "are produced in two sewing, namely 650 × 100 × 1200 → 650 × 365 × 1720 → 670 × 550 × 3400 → 550 × 20 × 9500 mm. Heated to plasticity temperature of the blank size of 650 × 100 × 1200 mm sewn in thick-walled sleeve sized 650 × 365 _ext × 1,720 mm on the mandrel diameter of 350 mm, cooled, repair (if necessary) is heated to plasticity temperature sewn (rolled) in the thin-walled sleeve 670 × 60 × 3400 mm in size on a mandrel with a diameter of 525 mm and rolled on a pilgrim mill in pipes of 550 × 20 × 9500 mm in size with an extractor μ = 3.45. If the sleeves have a curvature of more than 30-40 mm, then it is very difficult or impossible to introduce a mandrel in such sleeves, and when rolling them into pipes with hoods 3.5-5.0 and a low polishing coefficient (with an increase in the caliber of the rolls with an ideal diameter D _j = 950 mm, the working length of the arc of the pilgrim roll decreases, which leads to a decrease in the polishing coefficient) it is not possible to roll such sleeves into quality pipes. Therefore, in order to exclude the difference between large-diameter pipes with a ratio D / S≥ 25, pipes are rolled on pilgrim mills with double piercing. The rolling of pipes of size 351-425 × 20-30 × L mm from ESR ingots of stainless steel grades due to increased loads on the drive of the piercing mill on TPA 8-16 "is also carried out in two firmwares, namely 540 × 100 × 1600 → 540 × 265 × 2050 → 540 × 365 × 2870, i.e. an ESR ingot with a diameter of 500-540 mm is flashed on a cork with a diameter of 250 mm, and then on a cork of a larger diameter depending on the diameter of the pipe and wall thickness, i.e. depending on the diameter of the mandrel. When rolling pipes from stainless steel grades, the curvature of the sleeves is even more important. In the production of pipes of medium diameter from hard of graded steel and alloy grades on TPA 350 with automatic mills, the sleeves are pierced in two sequentially oblique rolling mills. When the blanks are unevenly heated, the sleeves after the first firmware have a curvature that increases even more when rolling into thin-walled sleeves in the second mill, the working shaft and which rotate in the same direction as that of the first piercer, ie the twisting of the sleeves after the first mill increases in the second mill, which leads to an increase in the initial curvature of the sleeves. Rolling such sleeves leads to increased pipe delta. Therefore, in order to reduce the difference in pipes, piercing ingots and billets during rolling of large diameter pipes (530-550 mm) from carbon and low alloy steel grades and pipes of medium and large diameter (351-426 mm) from stainless and difficult to deform steel grades and alloys into thick-walled sleeves it is necessary to produce in the first piercing mill, the work rolls of which rotate in one direction, and rolling into thin-walled sleeves in the second mill, the work rolls of which rotate in the opposite direction.

Due to the absence in Russia of two piercing mills in pipe rolling plants in one line, the proposed method for producing seamless hot-deformed large-diameter pipes was simulated and tested on a pipe rolling machine 140 with an automatic mill of ChTPZ OJSC, which has a three-roll rolling mill, whose work rolls rotate in the opposite direction side relative to the piercing mill. According to this method, for the first time in 2003, high-quality pipes with a size of 159 × 8 mm were made of steel grade 12X18H10T according to GOST 9940. Data on the technological parameters of the process of flashing, rolling, calibration, geometric dimensions and expenditure coefficient of the metal when rolling pipes of 159x8 mm in size on 140 with an automatic mill of JSC "ChTPZ" according to the existing and proposed technologies are shown in the table. The table shows that 20 billets of steel grade 12X18H10T were assigned to production: 10 billets of 150 × 3000 size and 10 billets of 150 × 2100 mm size. Ten billets with a size of 150 × 3000 mm were rolled with double piercing, namely, billets with a size of 150 × 3000 mm were heated to a plasticity temperature, stitched in a piercing mill in sleeves of 160 × 20.5 × 5900 mm in size, which, after cooling, were cut into equal parts, reheated to a temperature of plasticity and stitched (rolled) into thin-walled sleeves measuring 170 × 8 × 6500 mm. After repeated flashing, the pipes were calibrated on a calibration mill to a size of 159 × 8 × 6600 mm. Pipes were measured, presented by quality control department, sorted out and delivered in accordance with GOST 9940. The average lateral difference in the pipes according to primary measurements was 32.7%, while the norm in accordance with GOST is 25.0%, and the expenditure coefficient of the metal is 1.259. According to the proposed technology, 10 billets 150 × 2100 mm in size were heated to ductility temperature, sewn into sleeves of 160 × 13 × 6200 mm in size, then, bypassing the automatic mill, sewn (rolled) into pipes of 170 × 8 × 9140 mm in the rolling mill, the work rolls of which are rotated in the opposite direction of rotation of the work rolls of the piercing mill, and then calibrated in a calibration mill into tubes measuring 159 × 8 × 9300 mm. Pipes were measured, presented by quality control department, rejected and delivered in accordance with GOST 9940. The average lateral difference of the pipes according to primary measurements was 24.5%, and the expenditure coefficient of the metal was 1.168.

Thus, according to the results of the experiment, the theoretical justifications for the method of producing seamless hot-formed large diameter pipes from carbon and low alloy steel grades and medium and large diameter pipes from stainless and hard-deformed steel and alloys by installing two piercing mills in the line, work rolls are confirmed which rotate in different directions. The table shows that the pipes rolled according to the proposed technology (method) have the smallest lateral difference and lower expenditure coefficient of the metal. The main indicator of a decrease in the expenditure coefficient of a metal is the reduction of waste (trimming) along the wall thickness and rolling of pipes with tighter tolerances on the wall.

Using the proposed method for the production of seamless hot-deformed large-diameter pipes from carbon and low-alloy steel grades and medium and large-diameter pipes from stainless and hard-to-deform steel and alloy grades will significantly reduce metal consumption by reducing the difference in width and rolling pipes with tighter wall tolerances, and therefore, reduce the cost of commodity pipes of this assortment.

Data on the technological parameters of the process of flashing, rolling, calibration, geometric dimensions and flow coefficient of the metal when rolling pipes 159 × 8 mm in size on TPA 140 with an automatic mill of ChTPZ OJSC according to the existing and proposed technology Pipe Size (mm) Workpiece Size (mm) steel grade Kolich. pipes (pcs) Existing rolling technology Proposed rolling technology The size of the sleeves after the first firmware (mm) Sleeve size after second firmware (mm) Pipe size after gauges. mill (mm) The average cross. pipe differences (%) Consumption. coefficients metal Sleeve size after flashing (mm) The size of the sleeves after flashing (rolling) in the rolling mill (mm) Pipe size after gauges. mill (mm) The average cross. difference. pipes (%) Consumption. coefficient metal 159 × 8 150 × 3000 12X18H10T 10 160 × 20.5 × 5900 170 × 8 × 6500 159 × 8 × 6600 32,7 1,259 - - - - - 159 × 8 150 × 2100 12X18H10T 10 - - - - - 160 × 13 × 6200 170 × 8 × 9140 159 × 8 × 9300 24.5 1,168

Claims (1)

A method for the production of seamless hot-deformed large-diameter pipes, including heating ingots and billets to a plasticity temperature, flashing them into hollow thick-walled sleeves in one oblique rolling mill, followed by rolling into thin-walled sleeves in a second oblique rolling mill, and rolling into large-diameter pipes in plants with automatic or pilgrim mills, characterized in that the firmware of ingots and billets in thick-walled shells is produced in the first piercing mill, the work rolls of which are rotated by one hundred ron, and rolling into thin-walled shells - in the second mill, the work rolls of which are rotated in the opposite direction.