A seamless steel pipe production process and production line

Abstract

The present invention relates to the field of seamless steel pipe processing and discloses a seamless steel pipe production process and production line. A resizing process is added between the traditional heating and piercing processes to resize square or large-diameter round billets (first billets) into smaller-diameter round billets (second billets). The resizing process can be achieved through rolling, push rolling, and cross-rolling, either individually or in combination. For example, push rolling is used to convert square billets into round billets, while a two-roll or three-roll cross-rolling round billet mill is used for diameter reduction. The first billets are arranged in two rows within the heating furnace. The product outline is adjusted based on the unit's capacity, with the resizing process divided into the front section (to achieve double-row distribution), the rear section (to reduce head loss due to finished products up to 12 meters long), and the middle section (to select low-cost billets) for optimized production. The supporting production line incorporates resizing equipment (such as a combination of a section steel rolling mill, a push rolling mill, and a cross-rolling mill) between the heating furnace and the piercing mill, enabling flexible processing of square or round billets. The resizing process balances distribution efficiency, finished product length, and cost, improving the economic efficiency and flexibility of seamless steel pipe production.

Description

Technical Field

[0001] The present invention relates to the field of seamless steel pipe processing, and in particular to a seamless steel pipe production process and production line. Background Art

[0002] The processing of seamless steel pipes is based on heating the billet to a certain temperature in a furnace, punching it into a rough tube through a piercing mill, and then processing it into the finished product through subsequent rolling mills, reducing mills, and finishing mills. Each unit has a clear product outline, covering the types of steel pipe specifications that can be produced, the types of billet specifications that need to be matched, and the annual output. The diameter of the steel pipe specifications has a specific matching relationship with the billet diameter. That is, a billet of a certain diameter can produce a limited number of finished product diameters, and the larger the diameter of the finished product, the larger the billet diameter required. Taking the 250 inclined pipe rolling mill (capacity of 200,000 tons / year) as an example, the billet of φ230mm can produce finished steel pipes with specifications of φ273mm and wall thickness of 7mm to 20mm; the billet of φ210mm can produce steel pipes with specifications of φ245mm and wall thickness of 6mm to 20mm; and steel pipes with specifications of φ219mm and wall thickness of 6mm to 20mm; the billet of φ180mm corresponds to steel pipes with specifications of φ194mm and wall thickness of 6mm to 20mm and finished steel pipes with specifications of φ180mm and wall thickness of 6mm to 20mm. For steel pipe specifications, diameter × wall thickness is generally used to express. For example, steel pipes with specifications of φ273mm and wall thickness of 6mm are generally simplified as φ273×6mm pipes in the industry.

[0003] Appropriate process parameters and equipment capacity must be designed for each process step. For example, a 250mm cross-rolling mill (generally referred to in the industry by the maximum diameter of the steel pipe it can produce, meaning a cross-rolling mill capable of producing pipes up to 250mm in diameter) has a ring-shaped heating furnace with a design diameter of 26m. The furnace chamber allows for billets with a maximum length of 3.8m and diameters of 160-230mm in diameter (with a maximum allowance of 250mm in diameter), resulting in a full furnace chamber load of 180 pieces. When producing thin-walled products, double-row feeding up to 360 pieces is possible for billets less than 1.9m long, while single-row feeding is required for billets exceeding 1.9m. For example, when producing φ273×7mm (over 12m), the material length required is 1.7m, and 360 counts can be made in double rows; when producing φ273×8mm (over 12m), the material length required is 2.1m, and 180 counts can only be made in single rows. Similarly, when producing φ273×20mm, the material length is limited to 3.9m, and the finished product length is only about 7m.

[0004] The billet problems of the unit are mainly reflected in three aspects:

[0005] One is the influence of the laying method. The gas energy consumption of single-row laying is 15%-20% higher than that of double-row laying. According to tests, the heating gas consumption of 2.1m long billets in a single-row layout is 45 cubic meters per ton of steel, and the heating gas consumption of 1.8m long billets in a double-row layout is 37 cubic meters per ton of steel. Compared with the two, the former consumes 9 cubic meters per ton of steel more than the latter.

[0006] In addition, single-row fabric results in a 15%-20% lower production efficiency. The main reason for the low production efficiency of single-row fabric is that when single-row fabric is used, even if the heating furnace works under rapid forced heating conditions, its heating efficiency still cannot meet the processing rhythm of the subsequent punching machine, and production often needs to be suspended for 20-30 minutes to wait for the heating furnace to heat up.

[0007] Second, the thick-walled pipe is short in length due to the maximum length limit of the billet, which cannot meet the market demand for the standard length of 12m.

[0008] Third, when cutting fixed-length pipes, it is difficult to completely match the length of the order due to the fixed length of the blank and the limited procurement cycle. Even if the cutting adjustment is used, waste of material heads is often generated.

[0009] The billet problem at the market level is also worthy of attention:

[0010] First, the larger the purchase volume of billets of the same specification, the more beneficial it is for billet manufacturers to reduce switching costs. Therefore, steel pipe manufacturers hope to merge billet specifications to increase the purchase volume of a single specification and improve bargaining power.

[0011] Secondly, billets below φ130mm are rolled billets, while billets above φ130mm are continuously cast billets. The latter costs 100-150 yuan / ton of steel lower than the former, but based on existing processes, manufacturers using billets below φ130 cannot use lower-cost continuous cast billets.

[0012] Third, the cost of continuously casting square billets is 100-150 yuan / ton lower than that of continuously casting round billets. However, based on the existing production process, steel pipe mills can only use round billets to process steel pipes and cannot take advantage of the cost advantage of square billets.

[0013] In summary, the above-mentioned billet-related problems are common in existing steel pipe production units. Researching, solving or improving these problems is of practical significance for improving production efficiency and reducing production costs. Summary of the Invention

[0014] The technical problem to be solved by the present invention is how to solve the problem of high processing cost caused by multi-specification blanks.

[0015] The specific technical solution of the present invention to solve the above technical problems is:

[0016] A seamless steel pipe production process includes a tube blank heating process and a piercing process. A sizing process is provided between the tube blank heating and piercing processes. The sizing process is used to sizing a first blank into a second blank. The first blank is a square blank or a first-diameter round blank. The second blank is a second-diameter round blank. The diameter of the first-diameter round blank is larger than the diameter of the second-diameter round blank.

[0017] Compared with the prior art, the present invention has the following beneficial effects: adding a sizing process between the tube billet heating process and the piercing process greatly expands the selection of tube billets. Therefore, by selecting thicker and shorter tube billets, two rows of tube billets can be placed side by side in the heating furnace, thereby improving the utilization rate of the heating furnace, or using cheaper square billets to process seamless steel pipes, thereby reducing production costs.

[0018] Furthermore, the sizing process is achieved through one or more combinations of rolling, push rolling, and cross rolling processes. The rolling is achieved by using a steel section rolling mill; the push rolling is achieved by pushing the billet by a hydraulic cylinder and achieving rolling deformation through multiple pass frames; the cross rolling is achieved by using a two-roll cross rolling round billet mill or a three-roll cross rolling round billet mill to achieve rolling diameter reduction.

[0019] The beneficial effect of adopting the above further solution is that square billets can be converted into round billets, and large-diameter round billets can be converted into small-diameter round billets, which greatly expands the selection range of tube billets.

[0020] Furthermore, when a square blank is changed into a round blank, the sizing process uses a push-rolling process to deform the square blank into the round blank, and the three-roller oblique rolling round blank mill is used to achieve rolling diameter reduction.

[0021] The beneficial effects of adopting the above further solution are: using a three-roller cross-rolling round billet mill for diameter reduction, the metal is subjected to compressive stress in three directions during the rolling process, and the center of the cross-rolled round billet will not have defects such as looseness and tearing;

[0022] Furthermore, the tube blank heating process is carried out in a heating furnace, and the first blanks are arranged in double rows in the heating furnace. The double-row arrangement of the tube blanks improves furnace utilization and reduces processing costs.

[0023] Furthermore, according to the capacity of the unit, the corresponding product outline is adjusted to form a resized product outline, which refers to the steel pipe specifications and varieties that the unit can produce and the billet specifications and varieties that need to be matched. The resized product outline includes the resized front part, the resized rear part and the resized middle part. The resized front part corresponds to the steel pipe specifications that can realize double-row arrangement of billets in the heating furnace. The resized rear part refers to the specifications of the finished steel pipes produced when the billets are provided according to the maximum length of the heating furnace, which are less than 12 meters in length. The steel pipe specifications not covered in the resized front part and the resized rear part are included in the resized middle part; the purpose of adjusting the resized front part is to realize double-row arrangement of billets in the heating furnace; the purpose of adjusting the resized rear part is to make the final product length reach 12 meters and reduce the cutting loss; the purpose of adjusting the resized middle part is to select cheaper billets based on market conditions.

[0024] The beneficial effect of adopting the above further solution is that different optimization strategies are provided for steel pipes of different specifications. By optimizing the correspondence between steel pipe specifications and tube billet specifications, the utilization rate of the heating furnace can be improved, the procurement cost of tube billets can be reduced, or the length of the final product can be increased to improve market competitiveness, thereby greatly improving the competitiveness of the product.

[0025] The present invention also discloses a seamless steel pipe production line, including a heating furnace and a piercing machine. A sizing device is also provided between the heating furnace and the piercing machine. The sizing device is used to sizing a first blank into a second blank. The first blank is a square blank or a first-diameter round blank, and the second blank is a second-diameter round blank. The diameter of the first-diameter round blank is larger than the diameter of the second-diameter round blank.

[0026] This production line can select tube billets in a wider range. It can produce seamless steel pipes using round billets that are thicker than those of conventional production lines, or square billets that are cheaper than round billets and cannot be used in conventional production lines.

[0027] Furthermore, the length-changing equipment is one or more combinations of a section steel rolling mill, a push rolling mill, and a cross-rolling mill.

[0028] Furthermore, the length-changing equipment is a pusher mill, a two-roller cross-rolling mill, or a three-roller cross-rolling mill. If the first billet is a square billet, it is deformed from square to round by the pusher mill, and then reduced to a second billet by the two-roller cross-rolling mill. If the first billet is a round tube of the first diameter, it is directly reduced to the second billet by the two-roller or three-roller cross-rolling mill. When the tube deformation is less than 10%, a two-roller cross-rolling mill can be selected. This is because the metal is subjected to radial biaxial compressive stress and biaxial tensile stress during rolling with a two-roller cross-rolling mill. When the reduction is large, such as greater than or equal to 10%, the center of the cross-rolled round billet will exhibit defects such as looseness and tearing, i.e., the Mannheim effect. However, when the deformation is less than 10%, a two-roller cross-rolling mill can also meet the requirements.

[0029] Furthermore, the heating furnace is a ring furnace or a walking beam furnace. DETAILED DESCRIPTION

[0030] The principles and features of the present invention are described below in the form of embodiments. The examples are only used to explain the present invention and are not used to limit the scope of the present invention.

[0031] A seamless steel pipe production process includes a tube blank heating process and a piercing process. A sizing process is provided between the tube blank heating and piercing processes. The sizing process is used to sizing a first blank into a second blank. The first blank is a square blank or a first-diameter round blank. The second blank is a second-diameter round blank. The diameter of the first-diameter round blank is larger than the diameter of the second-diameter round blank.

[0032] Assume that the first blank is the heated blank P1 and the second blank is the perforated blank P2. Here, if the heated blank is a circular blank (hereinafter referred to as a round blank), P1 and P2 both represent diameters. The sizing process is to reduce the diameter of the large-diameter circular heated blank P1 to the small-diameter circular perforated blank P2.

[0033] The first blank may also be a square blank (hereinafter referred to as the square blank). In this case, P1 represents the side length of the square blank. The resizing step is to deform the square heated blank P1 into a round perforated blank P2.

[0034] The specific steps of changing the size, if the square billet is changed into a round billet, can be completed by combined rolling:

[0035] First, the square billet P1 is heated and rolled to transform it into an intermediate round billet P11 (P11 represents the diameter). Then, through further rolling, the round billet P11 is processed into a round perforated billet P2 of the required size and directly fed into the piercing machine.

[0036] The transformation of square billets into round billets can also be achieved based on a single rolling step: the heated square billet P1 is directly processed into the pierced billet P2 of the required size by rolling and directly fed into the piercing mill;

[0037] The transformation of a large round billet into a small round billet is generally achieved through a single rolling process: that is, the heated large-diameter round heated billet P1 is processed into a small-diameter round perforated billet P2 through one or more rolling processes; the rolling mentioned here includes longitudinal rolling or oblique rolling processes.

[0038] The rolling mentioned in the above-mentioned length-changing process specifically refers to one or more combinations of profile rolling, push rolling and cross-rolling processes;

[0039] The section rolling process utilizes a section steel mill to achieve rolling deformation. This process can be performed using a single section steel mill, comprising two active rolls with multiple pass profiles, and conveying and transverse movement equipment on the front and rear tables. During rolling, the billet is rolled at one pass and then moved to the next pass for rolling until the required dimensions are achieved. Alternatively, multiple mills can be used in tandem, where multiple pass profiles are installed on a single rolling line, allowing the billet to be rolled and shaped simultaneously through multiple passes.

[0040] The push rolling is a process in which the billet is pushed by a hydraulic cylinder and the rolling deformation is achieved through multiple hole profiles. Especially after the size is changed, compared with the traditional process, a billet with a larger diameter is generally selected. Under the condition of a certain volume, the length of the billet is generally shorter. The push rolling process is selected, the process is simple, and the work efficiency is higher.

[0041] The cross-rolling process utilizes a two-roll cross-roll mill or a three-roll cross-roll mill to achieve rolling reduction. A three-roll cross-roll mill is preferred for deformations greater than or equal to 10%, while a two-roll cross-roll mill can be used for deformations less than 10%. Because the metal is subjected to compressive stress in three radial directions during rolling using a three-roll cross-roll mill, the cross-rolled round billet will not exhibit defects such as loosening or tearing at the center. Alternatively, a three-roll planetary mill (PSW) can be used for rolling, where the billet moves in a straight line while the rolls and mill frame rotate.

[0042] The rolling process of the three-roller cross-rolling mill (with the ability to repeatedly roll) is as follows:

[0043] The first process: The round intermediate billet P11 in the foreground is rolled through the pass 1 of the three-roller cross-rolling mill to form the round intermediate billet P12 and move it to the backstage. Then, the pass 1 is quickly opened, and the pusher in the backstage pushes the round intermediate billet P12 from the opened pass 1 back to the foreground. The pass 1 of the three-roller cross-rolling mill is quickly closed and adjusted to the required new pass 2.

[0044] Second process: The round intermediate billet P12 in the foreground enters the second pass for rolling, forming the round intermediate billet P13 and moving it to the backstage. Then the second pass of the three-roller cross-rolling mill is quickly opened, and the pusher in the backstage pushes the round intermediate billet P13 from the opened second pass back to the foreground. After that, the second pass of the three-roller cross-rolling mill is quickly closed to the required new third pass.

[0045] The third process: The action process is the same as the above, so I will not repeat it here;

[0046] Note that, when the billet temperature is appropriate, the above process can be repeated until a round perforated billet P2 that meets the requirements is rolled out.

[0047] It should be pointed out that the above-mentioned oblique round billet rolling machine can also select rollers: multiple passes of rolling are performed by switching the forward and reverse rotation of the rollers: for example, the above-mentioned front-end push rod feeds the circular intermediate billet P11 into the pass 1 for rolling (the rollers rotate forward at this time), forming a circular intermediate billet P12 and moving it to the back stage; then the pass 1 is quickly adjusted to the pass 2, the rollers reverse, and the push rod in the back stage feeds the round billet P12 into the pass 2 for the second pass of rolling, and the formed circular intermediate billet P13 returns to the front stage; then, the pass 2 is quickly adjusted to the pass 3, the rollers are adjusted to rotate forward again, and the push rod on the front stage feeds the circular intermediate billet P13 into the pass 3 for the third pass of rolling, and a circular intermediate billet P14 is obtained in the back stage;

[0048] Repeat the rolling process until the perforated blank P2 that meets the requirements is produced.

[0049] Furthermore, the tube blank heating process is carried out in a heating furnace, and the first blanks are arranged in double rows in the heating furnace. The double-row arrangement of the tube blanks improves furnace utilization and reduces processing costs.

[0050] Furthermore, according to the capacity of the unit, the corresponding product outline is adjusted to form a resized product outline, which is the steel pipe specifications and varieties that the unit can produce and the billet specifications and varieties that need to be matched. The resized product outline includes the resized front part, the resized rear part and the resized middle part. The resized front part corresponds to the steel pipe specifications that can realize double-row arrangement of billets in the heating furnace. The resized rear part is the specification of the finished steel pipe produced when the billets are provided according to the maximum length of the heating furnace, which is less than 12 meters in length. The specifications not covered by the above two parts are included in the resized middle part; the purpose of adjusting the resized front part is to realize double-row arrangement of billets in the heating furnace; the purpose of adjusting the resized rear part is to make the final product length reach 12 meters and reduce the cutting loss; the purpose of adjusting the resized middle part is to select billets with lower cost based on market conditions.

[0051] Specifically, for thin-walled steel pipes, that is, before the length change, the purpose of adjusting the product outline is to achieve double-row feeding in the heating furnace:

[0052] 1) First, determine the specifications Pc and length Lc of the finished steel pipe. Considering the heating oxidation loss of about 1.5%, calculate the required diameter P2 and length L2 of the round perforated blank according to the process without resizing.

[0053] a) If L2 ≤ Lz / 2 (Lz is the maximum blank length allowed by the heating furnace), double-row feeding can be performed directly. In this case, round heated blanks P1 and L1 are directly selected (i.e., P1=P2, L1=L2). Here, "round heated blanks P1 and L1" refer to round blanks with a diameter of P1 and a length of L1.

[0054] b) If L2>Lz / 2, it means that if there is no resizing process, only a single row of materials can be laid in the heating furnace, and the heating furnace utilization rate is low. In this case, according to the principle of constant volume, under the premise of ensuring that the volumes of the heated blanks P1 and L1 are equal to the volumes of the perforated blanks P2 and L2, select a new blank specification within the range of P1>P2 and L1≤Lz / 2;

[0055] b1) Selection of P1 and L1:

[0056] b11) If square heated billet P1 is selected to be rolled into round perforated billet P2:

[0057] The diameter of the round perforated blank is P2 and the length is L2. The theoretical side length of the square heated blank is p1 and the theoretical length is l1. The volumes of the two are the same: , and l1≤Lz / 2, then we can deduce:

[0058]

[0059] From the available range of available square billet specifications, select the side length P1 of the square billet that is greater than P1 and closest to (or equal to) P1, and determine the final L1 based on the selected P1;

[0060] b12) If the selection is: Large round heated billet P1 rolled and small round punched billet P2:

[0061] The perforated blank P2, L2, the theoretical diameter of the heated blank p1, the theoretical length l1, both have the same volume: , and l1≤Lz / 2, then we can deduce:

[0062]

[0063] From the available range of round blank specifications, select the billet diameter P1 that is larger than p1 and closest to (can also be equal to) p1, and determine the final L1 based on the principle of identical volume, and determine the round heated billet P1 and L1.

[0064] For thick-walled steel pipes, which correspond to the rear-end of the resizing process, double-row routing is generally difficult because thick-walled steel pipes require a larger volume of steel. However, by adding a resizing process, production costs can be reduced by selecting cheaper square billets. Alternatively, while maintaining the same billet length, larger billets can be selected to obtain longer finished steel pipes to better meet market demand. Therefore, the purpose of the rear-end resizing process is to select cheaper square billets and / or obtain the longest finished steel pipe possible.

[0065] The conversion calculation process is also based on the principle of volume invariance, the same as the previous part of the scale change, except that the constraint on the billet length is L1≤Lz. The rest of the calculation process is the same and will not be repeated here.

[0066] Calculation shows that if a square billet is selected, the theoretical side length of the square heated billet is p 1 for ;

[0067] If a large round billet is selected, the theoretical diameter of the large round billet is p 1 for .

[0068] If the weight of the selected heated blank is greater than the weight of the largest round heated blank designed for the annular furnace in order to meet the length requirement of the thick-walled tube, the annular furnace must be reinforced and modified.

[0069] For the middle section of the resized steel pipe, that is, steel pipes with specifications other than the aforementioned thin-walled and thick-walled steel pipes, the purpose of the adjustment is to replace round billets with square billets, which are more affordable in the market. This reduces the production cost of steel pipes and improves their market competitiveness. At the same time, the low billet price means low billet processing costs, which also saves energy for the entire industry. Although the energy saved is in the upstream billet production link, it is a saving for society as a whole. Try to choose square billets with a cross-sectional area consistent with the original round billet to avoid additional heating time.

[0070] After making the above preliminary adjustments to the production outline, you can further fine-tune and classify it, that is, according to market conditions, reduce the number of billet specifications as much as possible, because the larger the billet batch, the easier it is to purchase and the lower the price, so as to further reduce production costs through market means and form the final production outline.

[0071] A certain 219 unit (a unit that produces steel pipes with a maximum diameter of φ219mm) is suitable for round billets ranging from φ160 to φ230mm (φ250mm is reserved). The steel pipe specifications that can be produced are: φ159--φ168--φ180--φ219--φ273, a total of five outer diameter specifications. Furthermore, φ160 billets can produce seamless steel pipes with a diameter of φ159mm and a wall thickness of 5--25mm (hereinafter referred to as "φ159×5--25mm pipes"), and can also be processed into φ168×5--25mm pipes; φ180mm to φ200mm billets can produce φ219×6--25mm pipes; φ210mm to φ230mm billets can produce φ273×7--20mm pipes;

[0072] Table 1 below compares the billets and product specifications used in the production of φ159mm steel pipes for the aforementioned Unit 219 before and after process improvements (this table is known as the product outline in the industry):

[0073] Table 1

[0074]

[0075] The product outline in Table 1 is based on a ring furnace with a maximum length of 3.9 meters. Taking the production of φ159mm steel pipe as an example, it lists the dimensional differences between billets and finished steel pipes before and after the production process change. Specifically, before the production process change (i.e., before the resizing), φ160mm round billets were used, while after the production process change (i.e., after the resizing), φ200mm round billets or 180mm square billets were used. Due to the addition of the resizing step, the following effects were achieved: either the billet blanking length was shortened to enable double-row feeding in the ring furnace, or the final finished steel pipe was longer, reaching the maximum length of 12m specified in the national standard. The specific interpretation is as follows:

[0076] The first column in Table 1 is the wall thickness of the finished steel pipe, the second column is the blank length of the tube in the original product outline (i.e. before resizing), the third column is the length of the finished tube in the original product outline, the fourth column is the blank length of the tube after resizing to φ200mm round billet or 180mm side length square billet, and the fifth column is the length of the finished product after resizing:

[0077] It can be seen that before the re-sizing, only the φ160 billets corresponding to the four specifications of steel pipes with wall thickness of 5.0-6.5mm can realize double-row feeding (single-row length ≤1.95m). These four specifications are classified as the front part of the re-sizing.

[0078] The part with a wall thickness of more than 14mm is classified as the part after the size change. It is limited by the 3.9-meter length limit of the heating furnace. The tube blanks have been cut according to the maximum size allowed by the heating furnace. The steel pipe φ159×14mm produced has a length of only 12.05m after sizing. Because there is a subsequent head cutting process, it is obvious that the length of the finished product after head cutting is less than 12m. Furthermore, the length of the 12 specifications between φ159×14mm and φ159×25mm after sizing is between 12.05 and 7.3m. The length of the finished steel pipe cannot reach 12m, which affects the market competitiveness of the product.

[0079] Note: 12m is the upper limit of the normal length of hot-rolled steel pipes specified in the national standard. Generally, the longer the length, the lower the later processing cost, so end users prefer to purchase steel pipes that are as long as possible.

[0080] The 10 specifications in the middle section, i.e. steel pipes with wall thicknesses of 7.0mm to 13.0mm, can still use φ160mm billets to avoid additional billet heating time.

[0081] The fourth and fifth columns of Table 1 are the outlines of the products after resizing: φ200mm round billets or 180mm square billets are used, which are then heated and resized to φ160mm round billets, and then punched into rough tubes by a piercing machine;

[0082] It can be seen that after switching to φ200mm round billets (or 180mm side length square billets), under the heating furnace constraint condition of single row length ≤1.95m, there are 11 specifications of steel pipes that can achieve double row routing, that is, 11 specifications from φ159×5mm to φ159×10mm, and the blanking lengths of all of them can achieve double row routing;

[0083] For thick-walled pipes, when using resized φ200mm round billets (or 180mm square billets) and blanking at the maximum length of 3.9m allowed by the heating furnace, 10 sizes ranging from φ159×14mm to 23mm are sized to reach a length of 12.46m. After cutting, they basically meet the 12-meter requirement for finished steel pipes. Of the entire φ159mm steel pipe specification, only φ159×24mm and φ159×25mm remain, with sizes smaller than 12m after processing. This significantly improves the competitiveness of the product.

[0084] The middle three specifications: φ159×11 to 13mm steel pipes, because even after the size is changed, double-row feeding cannot be achieved, so they can be left unchanged and the original φ160mm round billets can be used to avoid additional billet heating time or additional processing steps;

[0085] As can be seen, by adding a resizing process, different optimization strategies are provided for different steel pipe specifications. By optimizing the correspondence between steel pipe specifications and tube blank specifications, it is possible to increase heating furnace utilization, reduce tube blank procurement costs, increase final product length, and enhance market competitiveness, significantly improving product competitiveness. Moreover, the addition of the resizing process significantly expands the range of blank selection, so when processing fixed-length pipe, there is a wider range of blank selection options. Combined with the tailoring measures, the generation of blank overhang can be significantly reduced, further improving the yield rate.

[0086] The present invention also discloses a seamless steel pipe production line, comprising a heating furnace and a piercing mill. A resizing device is provided between the heating furnace and the piercing mill. The resizing device is used to resize a first billet into a second billet, wherein the first billet is a square billet or a first-diameter round billet, and the second billet is a second-diameter round billet, wherein the diameter of the first-diameter round billet is larger than the diameter of the second-diameter round billet. The resizing device comprises a pusher mill and a three-roller cross-rolling mill. If the first billet is a square billet, it is deformed from square to round by the pusher mill and then reduced to the second billet by the three-roller cross-rolling mill. If the first billet is a first-diameter round tube billet, it bypasses the pusher mill and is directly reduced to the second billet by the three-roller cross-rolling mill.

[0087] It is relatively easy to modify the existing processing production line and add sizing equipment, because the sizing equipment does not require much space, the required sizing process is a relatively simple and mature technology of longitudinal or oblique rolling of steel sections, the investment is small, only a single main machine is needed, and the front and back ends are small and simple.

[0088] The cost of the resizing process is low:

[0089] The cost of one-step square-to-round rolling is estimated to be approximately RMB 5 per ton of pipe. Using a three-roll round billet cross-rolling mill, a single reduction of 25% to 30% is possible, while a double reduction can reach 50%. The main consumption includes rolls and water and electricity. The estimated cost of a single rolling pass is approximately RMB 10 per ton of pipe, while a double rolling pass costs approximately RMB 15 per ton.

[0090] By strengthening the integration of production, technology and market and optimizing the size and shape combination of billets, production efficiency and yield rate can be significantly improved while reducing product costs.

[0091] For example, when the cross-sectional areas of the heated billet P1 and the perforated billet P2 are equal, resizing to a larger square heated billet P1 and a larger round perforated billet P2 can save 100 yuan per ton of square billet (calculated based on a yield rate of 92%, that is, a steel consumption coefficient of 1.087 per ton of pipe, which is 108.7 yuan / ton of pipe). After deducting the resizing cost of 5 yuan / ton of pipe, the efficiency gain of resizing is 108.7-5=103.7 yuan / ton of pipe.

[0092] For example, regarding the resizing of finished thin-walled tubes (large square heated billets P1), resizing to round perforated billets P2 through one step and two cross-rolling operations, and using double-row cloth instead of single-row cloth, can reduce gas consumption by 21 yuan per ton of tube, and save 100 yuan per ton of square billets (calculated based on the steel consumption per ton of tube being 100×1.087=108.7 yuan). The resizing cost is 20 yuan per ton of tube, and the final profit increase is 108.7+21-20=109.7 yuan per ton of tube, without considering the 15% increase in production efficiency.

[0093] Note: The benefit calculation of a 15% increase in production efficiency requires combining the increase in unit output, the calculation of fixed cost allocation, and the increase in profit from increased sales, which is difficult to calculate accurately here.

[0094] For example, the resizing of finished thin-walled tubes (large round heated billets P1) is carried out by resizing them into round perforated billets P2 through two rounds of oblique rolling. Double-row fabrication is used, which reduces gas consumption by 21 yuan per ton of tube, reduces the resizing cost to 15 yuan per ton of tube, and increases efficiency by 6 yuan per ton of tube, mainly due to a 15% increase in production efficiency.

[0095] For another example, regarding the resizing of thick-walled tube products, the large square heated billet P1 of the maximum length can be resized into the round perforated billet P2 through one step and two cross-rolling. The square billet can save 100 yuan per ton (calculated based on the steel consumption of 100×.087=108.7 yuan per ton of tube), and the resizing cost is 20 yuan / ton of tube (5+15). It is expected that the increase in product length will increase the yield rate by 1% (30 yuan / ton of tube), and the efficiency increase is 108.7-20+30=118.7 yuan / ton of tube; it is expected that the gas consumption will increase by 15% (21 yuan / ton of tube), and the productivity will increase by 15%, which are offset here.

[0096] The large square heated billet P1 of the maximum length is resized into the round perforated billet P2 through two cross-rolling operations. The resizing cost is RMB 15 / ton pipe. It is expected that the increase in product length will increase the yield by 1% (RMB 30 / ton pipe), and the efficiency increase is RMB 30-15=RMB 15 / ton pipe. It is expected that the gas consumption will increase by 15% (RMB 21 / ton pipe) and the productivity will increase by 15%, which are offset here.

[0097] Finally, regarding the resizing of rolled billets with a diameter of ≤φ130mm (converted to continuous casting heated billets P1), for example, regarding the resizing of thin-walled tube products (large square heated billets P1), the resizing is carried out in one step and two cross-rolling to round perforated billets P2 (≤φ130mm). Double-row distribution is used, which reduces gas consumption by 21 yuan / ton of tube, saves 100 yuan per ton of square billets, and continuously cast billets are 100 yuan / ton cheaper than rolled billets (steel consumption per ton of tube is 200×1.087=217.4 yuan). The resizing cost is 20 yuan / ton of tube (5+15), and the final profit increase is 217.4+21-20=218.4 yuan / ton of tube, without considering the 15% increase in production efficiency.

[0098] Focusing on the resizing of the finished thin-walled tube (large continuous casting round heated billet P1), it is resized to round perforated billet P2 (≤φ130mm) through two rounds of oblique rolling. Double-row distribution is adopted, which reduces gas consumption by 21 yuan / ton of tube. Continuous casting billet is 100 yuan / ton cheaper than rolled billet (steel consumption per ton of tube is 100x1.087=108.7 yuan). The resizing cost is 15 yuan / ton of tube, and the final profit is 108.7+21-15=114.7 yuan / ton of tube, without considering the 15% increase in production efficiency.

[0099] The front and rear centering process of the billet end face is omitted, and a two-roller or three-roller oblique rolling round billet mill is used. The two end faces of the billet P2 after rolling are funnel-shaped, which is conducive to the alignment of the piercing head and the front end face of the billet, reducing the generation of ears on the rear end face, thereby reducing the cutting head of the steel pipe and improving the yield rate, and completely omitting the front and rear centering process of the billet end face.

[0100] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A seamless steel pipe production process, comprising a tube blank heating process and a perforation process, characterized in that: A resizing step is provided between the tube blank heating step and the piercing step, wherein the resizing step is used to resize the first blank into a second blank, wherein the first blank is a square blank or a round blank of a first diameter, and the second blank is a round blank of a second diameter, wherein the diameter of the first diameter round blank is larger than the diameter of the second diameter round blank; According to the capacity of the unit, the corresponding product outline is adjusted to form a resized product outline, which refers to the steel pipe specifications and varieties that the unit can produce and the billet specifications and varieties that need to be matched. The resized product outline includes the front part, the back part and the middle part. The front part corresponds to the steel pipe specifications that can realize double-row arrangement of billets in the heating furnace. The back part refers to the specifications of the finished steel pipes produced when the billets are provided according to the maximum length of the heating furnace, which are less than 12 meters in length. The steel pipe specifications not covered in the front part and the back part are included in the middle part. The purpose of adjusting the front part is to realize double-row arrangement of billets in the heating furnace; the purpose of adjusting the back part is to make the final product length reach 12 meters and reduce the cutting loss; the purpose of adjusting the middle part is to select billets with lower cost based on market conditions.

2. The seamless steel pipe production process according to claim 1, characterized in that: The length-changing process is achieved through one or more combinations of rolling, push rolling, and cross-rolling processes. The rolling is achieved by using a steel section rolling mill; the push rolling is achieved by pushing the billet by a hydraulic cylinder and rolling deformation is achieved through multiple pass frames; the cross-rolling is achieved by using a two-roll cross-rolling round billet mill or a three-roll cross-rolling round billet mill to achieve rolling diameter reduction.

3. The seamless steel pipe production process according to claim 2, characterized in that: When a square blank is changed into a round blank, the sizing process adopts a push-rolling process to deform the square blank into the round blank, and the three-roller oblique rolling round blank mill is used to achieve rolling diameter reduction.

4. The process for producing a seamless steel pipe according to any one of claims 1 to 3, characterized in that: The tube blank heating process is implemented in a heating furnace, and the first blanks are arranged in double rows in the heating furnace.

5. A seamless steel pipe production line for implementing the seamless steel pipe production process according to any one of claims 1 to 4, comprising a heating furnace and a piercing machine, characterized in that: A sizing device is also provided between the heating furnace and the punching machine, and the sizing device is used to resize the first blank into the second blank. The first blank is a square blank or a first-diameter circular blank, and the second blank is a second-diameter circular blank. The diameter of the first-diameter circular blank is larger than the diameter of the second-diameter circular blank.

6. The seamless steel pipe production line according to claim 5, characterized in that: The length-changing equipment is a combination of a section steel rolling mill, a push rolling mill, and a cross-rolling mill.

7. The seamless steel pipe production line according to claim 6, characterized in that: The sizing equipment includes a push rolling mill and a three-roller cross-rolling round billet mill. If the first billet is a square billet, it is deformed from square to round by the push rolling mill, and then reduced in diameter to the second billet by the three-roller cross-rolling round billet mill; if the first billet is a first-diameter round tube billet, it is directly reduced in diameter to the second billet by the three-roller cross-rolling round billet mill.

8. The seamless steel pipe production line according to claim 6, characterized in that: The sizing equipment includes a push rolling mill and a two-roller oblique round billet mill. If the first billet is a square billet, it is deformed from square to round by the push rolling mill, and then reduced in diameter to the second billet by the two-roller oblique round billet mill. If the first billet is a first-diameter round tube billet, it is directly reduced in diameter to the second billet by the two-roller oblique round billet mill.

9. The seamless steel pipe production line according to claim 5, characterized in that: The heating furnace is a ring furnace or a walking beam furnace.

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