Distributor / authorized representative that deals with supply & delivery of seamless pipe plants to industrial enterprises of Russia
Engineering company ‘Intech GmbH’ LLC (ООО «Интех ГмбХ»), Russia, has been successfully working with a number of Russian industrial enterprises at the local market for more than 20 years. Since the company’s founding, it has acquired immense engineering experience, market reputation, and has realized more than a hundred large-scale projects at the industrial plants in Russia. Our company is continuously in search of new business partners, who consider Russian market investment-attractive and want to boost their sales in the region, as well as expand their field of activities and enter a new international level.Contents:
We are interested in cooperation with the manufacturers of complete seamless pipe mill plants and seamless pipe single equipment such as straighteners, hydro-testers, upsetting, beveling, threading, cold pilgers, who are looking for an official and reliable distributor that deals with supply & delivery of their equipment to the industrial plants in Russia.
The company’s top management and sales team are well acquainted with the Russian market, its mentality and laws; they also understand industrial specifics of the financial and economic activities of the Russian customers. All our sales managers have a large customer database, extensive experience of successful sales and well-established connections with the potential buyers of your seamless pipe mills. This allows our managers to promptly set out the most promising directions for promotion and to ensure a rapid entry of the products into the promising Russian market. Our employees, who are fluent in English and German, are focused on working at the international market with the supplies of foreign equipment.
Our team of experienced engineers, who can handle the most serious technical problems, constantly keeps in touch with the Russian customers, holds meetings and delivers presentations regarding the latest achievements of our manufacturing partners. They point out the engineering challenges and actively communicate with all the departments at Russian plants. That is why the specifics of doing a business in the Russian Federation are well-known to us, and we also know the equipment of the local industrial plants and their up-to-date modernization needs.
Once we become your authorized representative in Russia, our marketing staff will carry out a market research in order to check the demand for seamless pipe mills, will submit a market overview for seamless pipe mills that you offer and evaluate the needs for this type of equipment at local plants. Our specialists will also estimate the potential and capacity of this market at local industrial plants. Our IT-team will start developing a website for your products in Russian. Our experts will assess the conformity between your seamless pipe mills and customer needs as well as analyze the common reaction to the new goods in general. We will look into the categories of potential customers, and pick out the largest and the most promising plants.
Upon becoming your authorized agent on the territory of Russia, ‘Intech GmbH’ LLC (ООО «Интех ГмбХ»), will obtain certificates, if required, for a batch of the goods, for various types of complete seamless pipe mill plants and seamless pipe single equipment in compliance with Russian standards. We can also arrange the inspection in order to obtain TR TS 010 and TR TS 012 Certificates. These certificates provides permission to operate your equipment at all industrial plants of the EAEU countries (Russia, Kazakhstan, Belarus, Armenia, Kyrgyzstan), including the hazardous industrial facilities. Our company is eager to assist in issuing Technical Passports for complete seamless pipe mill plants and seamless pipe single equipment as per Russian and other EAEU countries’ requirements.
Our engineering company ‘Intech GmbH’ LLC (ООО «Интех ГмбХ»), collaborates with several Russian design institutes in various industrial segments, which allows us to conduct preliminary design as well as subsequent design works according to the standards, construction rules and regulations that are applicable in Russia and other CIS countries. It also enables us to include your seamless pipe mills into the future projects.
The Company has its own logistics department that can provide packing service, handling as well as the most efficient and cost effective mode of transportation of the goods (incl. over dimensional and overweight goods). The goods can be delivered on DAP or DDP-customer’s warehouse basis in full compliance with all the relevant regulations and requirements that are applicable on the Russian market.
Our company has its own certified specialists who will carry out installation supervision and commissioning of the delivered equipment, as well as further guarantee and post-guarantee maintenance of seamless pipe mills. They will also provide necessary training and guidance for the customer’s personnel.
Grade and size schedule and its peculiarities. Types of units and their components
The lines containing automatic-controlled mills are most commonly used in seamless pipe production. These mills have high maneuverability, versatility and capacity. In the modern industry pipes are produced of carbon steel grades, medium- and high-alloy steels as well as of heat- and corrosion-resistant steels. These products are manufactured in a pipe-rolling plant (PRP) equipped with a plug mill. The following products are large-scale produced on these plants:
- pipes for oil industry (casing, drill, compression pipes and tubings);
- pipes for E&P and oil-processing industry sectors (cracking);
- semi-finished products for machine-building parts, etc.
A common layout includes the following production stages:
1) heating of billets in the annular furnace,
2) rotary piercing,
3) elongation of hollow billet walls,
4) pipe reeling in reeling mills, and
5) pipe sizing or reducing. Depending on the product mix the units have three standard sizes: small size for pipes max. 159 mm in diameter (with reducing mill up to 30 mm); medium size to produce pipes from 102 to 205 mm in diameter (with reducing mill up to 60 mm), and large size to produce pipes from 159 to 426 mm in diameter.
Pipe production in PRP with plug mill
A common layout of a line with plug mills includes production of hollow billets in a piercing unit and rolling of these billets into pipes (to be processed on plug mills). After that the pipe is rolled in reeling mills and sized on sizing lines. Reducing is often applied to obtain a pipe with smaller diameter and thinner walls.
Technological process includes the following sequence of operations. A semi finished billet heated to a set temperature comes out from the furnace and rolls down the inclined skid to the roller table. There is a centering machine at the exit of the roller table that makes guide holes in the billet end prior to piercing. If the billet is poorly heated or there are piercing mill delays and the billet is on the roller table for a long time, the billet is conveyed off-line by the reverse roller table and kicked off into the pocket. The kickoff device delivers the centered billet from the roller table to the inclined skid and next the billet moves to the piercing mill inlet trough covered with the hood. The pneumatic pusher injects the billet into piercing mill rolls along guides located between the spindles at the work stand front side. During the billet moving by the pusher it goes into the roll bite at pass entrance; the pass is restricted by guides.
A piercing mandrel located along the pass line is fixed on a long piercing point bar. This point bar mounted in the way that allows rotation in the fixed thrust head. Roll steadiers are located one by one at equal distances at the mill exit to provide billet centering during piercing and prevent billet bending under piercing force.
While progressively rotating in the roll pass the billet approaches the mandrel and is rolled into a hollow billet (a shell). The dimensions of the shell are determined by piercing mandrel diameter and distance between the mandrel and the rolls. The shell head end face moves through the roll pass and next along mill exit side relatively to the piercing point bar. When the shell end face approaches the steadier rollers that grip the piercing point bar, the rollers open and the shell moves uninterrupted. In this position the steadiers operate as a shell guide.
There are driven exit rollers between the steadiers that unload the shell from the stand after piercing, when the shell tail end leaves the roll pass. Then the shell is transferred off-line by rollers along the mill axis or away from the axis by the ejector and transported to the entry side of the second piercing mill where the shell is elongated. The second mill operates as the first piercing mill.
The shell rolls over the inclined grid to the plug mill inlet trough. This plug mill is suitable for elongation of the shell into the pipe (with specified wall thickness). The main plug mill component parts are a work stand and tables: an inlet and an outlet tables. The inlet table is a frame travelling track-mounted on wheels along grooved work rolls. The table is aligned with the pass through which rolling is performed. The table has a receiving trough, shell retainer, shell ejector, and inclined feeding and delivery grates. If occur any plug mill delays that prevent feeding of the next shell to the rolling process occur, the shell is retained on the grate by the shell retainer.
The middle section of the trough often designed as a turntable what allows feeding the shell (pipe) into the work stand with its other end first in case of a failed shell grip or buckling of a mandrel bar. The inlet table end has a tilting device for turning 90° of the pipe before the second pass. In small-size mills this tilting device is designed as closing rollers and in medium- and large-size mills it is designed as rack tilters. The shell arrives to the inlet trough and the pusher delivers it between the work rolls that grip the shell. Then the shell moving perpendicularly to the rolls axis approaches a short mandrel located in the center of the pass. The shell wall is rolled in the roll pass between the mandrel and the rollers to the thinner specified dimensions. However some metal gets into the gap between the rolls during rolling and cannot be rolled by them. It causes formation of two ridges on the side face of the shell after the first pass, i.e. wall thickenings along the outer pipe generating line.
The rolled pipe arrives to the plug mill outlet where it is centered by the guide shoes mounted on the frame. The mandrel is removed from the bar by the moving pipe end face and then transported inclined trough into the tank with water. Stripper rolls transport the pipe back to the mill inlet. The rolls are located behind the work rolls; they rotate in the direction opposite to that of the work rolls.
When the pipe is returned to the plant inlet, the top work roll is slightly lifted to form an enlarged idle pass. The bottom returning roller is lifted by the pneumatic actuator to press the pipe against the top roller. The pipe is transferred to the inlet through the enlarged working pass. The top feeding roller is installed slightly above the pipe that protrudes from the rollers to prevent rubbing against the pipe during the passage. The roller is not height-adjustable. The bottom roller is mounted on the movable lever. It is located in the bottom position during the rolling.
After piercing, the bloom leading end is cooled to a higher extent than the trailing end. Its deformation in the automatic mill requires higher forces. Therefore, the wall of the front pipe end is thicker than the rear one (by 0.3 - 0.5 mm).
Prior to rolling, sodium chloride or its mixture with graphite is fed into the pipe to reduce the friction and its coefficient.
After the pipe had been returned to the mill inlet by the feeding rollers (of the reverse feed), it is turned over at an angle of 90°. On small mills, the overturning is performed during the pipe feeding. The front table moves over the guides, and the pipe is placed opposite to the next pass, where it is rolled on the mandrel with the diameter exceeding that of the first-passage mandrel by 1 - 2 mm. Sometimes, rolling is performed on the mandrel with the same diameter that was used in the first passage. Prior to rolling, the mandrel lies in the trough or on a special device and mounted onto the mandrel bar by the leading end of the pipe when the mandrel is feed into the rolls. After rolling, the mandrel is dripped again into the bath with water and is taken from there either manually or by a special device to perform the next rolling.
The ejector feeds the rolled pipe onto the gravity chute, over which the pipe is transferred to the reeling mills and 2- or 3-roll screw rolling mills. The plant comprises two reeling mills operating simultaneously, and the pipes from the automatic mill are fed sequentially into each of the reeling mills.
At the area of transferring of the pipes from the automatic mill to the reeling mills, the possibility of accumulation of the pipes is provided. For this, the grating is provided with dosing units and pockets with circular ejectors.
The pipe is fed from the grating to the inlet of one of the reeling mills, which is a roller table section with height-adjustable driving rollers. At the work stand, there is an inlet guide shoe to be replaced in case of switching to rolling of pipes of other diameter. The roughing pipe transferred over the roller table is caught by the work rolls, being deformed on the mandrel. The mandrel is secured against displacement along the axis of the pass by the rollers and guide bars. To produce the pipes with the diameter equal over the length and with uniformly thick wall, the drafting value is set according to the variation of the load on the main drive so that the load would be constant. The reeling is performed at a feeding angle from 6° to 8°30'.
Prior to rolling, the mandrel lies on the bottom bar and placed at the fixing point in the thrust bar by the roughing pipe being fed into the rolls. After rolling, the pipe is ejected to the outlet similarly to the procedure at the outlet of the piercing line. In case of lateral ejection, the mandrel bar is retracted to the rearmost position and the mandrel remains on the bottom bar.
Nowadays, the design of the 3-roll reeling mill has been developed. The increase in the number of work rolls provides for some reduction of wall variation of the pipes produced.
After reeling, the pipes are transferred to the calibration mill that includes 5-7 2-hi longitudinal-rolling stands (all the rolls are driving). The pipe is fed to the first stand of the mill over the roller table, and then it is caught by the rolls and passes sequentially through all the stands getting the specified drafting over the diameter.
On the calibration mill, it is expedient to use a group drive because slight tension of the pipe occurring here does not affect the variation of the pipe wall thickness. The rolls’ axes of the pair of neighboring stands form an angle of 90°. It provides for deformation of the pipes in two mutually perpendicular directions during rolling.
The roll passes of the calibration unit are usually oval with the axis ratio decreasing gradually down to 1.0 in the last stand. After leaving it, the pipe has a regular round cross section. To guide the pipes to the mill inlet, an inlet funnel at the first stand and the guide shoes at the last case and between the stands are installed. After rolling on the calibration plant, the pipes are transferred over the roller table to the chain- or screw-type cooling table; then they are fed to the straightener and for finishing.
After rolling on the reducing plant, the pipes are dropped onto the bypass grating. They bypass the calibration mill and then are fed to the furnace for preheating. The preheated pipes are fed to the reducing mill designed as a calibration one, but comprising up to 26 stands.
Peculiarities of the size and grade schedule. Types of pipe-rolling plants and their components
The continuous rolling is featured by simultaneous deformation of the pipe material in several stands arranged in a series. The stands are interconnected by the pipe being rolled and mandrel. The advantage of the rolling process lies in the possibility to roll the roughing pipes with the large length (max. 33 m) at a high speed (max. 6.5 m/s). Other advantages of the plants of this type include:
- favorable preconditions for deformation of metal on the continuous-rolling plant,
- small quantity of process waste,
- arrangement of the equipment being convenient for carrying out the process operations.
On these lines, the pipes are produced in round passes on continuous rolling mills. The mandrel used is long. The mandrel floating in a usual way is retained while moving with the specified speed. The development of the traditional continuous rolling method was held back due to the following reasons:
- the length of the pipe being reeled is limited to max. 30 m;
- the mandrel weight increases with the increase of the pipe diameter;
- the mandrel length is limited by the manufacturing procedure to max. 20 m;
- difficulty of removal of the mandrel (thin wall).
Today the method of continuous rolling using a mandrel, which is held while moving in the rolling direction, is developed. The speed is identical to that during the rolling in the first stand, which is held partially by the mandrel. This method provides for production of pipes with even diameter and wall thickness, shortening of the mandrel and its wear as well as creation of normal thermal conditions in its working mode. It is achieved by uniform deformation of the material throughout the length of the product. A good quality of internal surfaces of the pipes and prolongation of the service life of the mandrels are achieved by the speed of their movement, which is always equal to or slightly less than the pipe’s delivery speed after the first stand of the mill. The relative speed of the pipe movement relatively to the mandrel is set at a level of speeds used in continuous rolling plants with the full-floating mandrel.
When rolling the pipes on partially retained mandrel, the mandrel with the roughing pipe moves at a constant speed during the whole rolling stage. The maximum length of the pipes produced on such a mill is 48 m; the rolling cycle time is 22 seconds. However, to produce the pipes of the required schedule on continuous rolling mills, the mandrels moving at a speed of 0.3 - 2.0 m/s are used. The mandrel movement speed is controlled by a special device, which generates the force of 1,600 – 3,500 kN to retain the mandrel. This mechanism ensures a certain mandrel movement speed:
either 1) till the complete unloading of the pipe being rolled from the mandrel (retained mandrel), or
2) till the moment when the mandrel begins to move as a floating, i.e. partially retained one.
Both methods are applicable for production of pipes with the certain diameter:
- for a small diameter, mainly, rolling on a floating mandrel;
- for a medium diameter (max. 200 mm), rolling on a partially retained mandrel;
- for the maximum diameter of 340 mm and more, rolling on a retained mandrel.
Production of seamless pipes on the pipe-rolling plant with a continuous rolling mill
The advantages of this pipe production method are explained by its high productivity and economic performance. The two main factors favored its intensive development:
1. Development of an individual drive of a continuous rolling mill, ensuring adjustment of tension. It has led to creation of such a roll pass system which is featured by the presence of the gap between the mandrel and pipes. This pipe facilitates the removal of a long mandrel. As a result, rolling of long (max. 32 m) roughing pipes has begun;
2. Installation of stretch-reducing mills that made the plant more maneuverable. It allowed producing a wide range of finished pipes from a roughing pipe with single or double diameter as in term of both the diameter and wall thickness.
The stages of technology for pipe making on the pipe rolling line equipped with the continuous rolling mill are following:
1) stage of preparation of billets for rolling;
2) process of heating of billets;
3) process of piercing of billets into blooms;
4) rolling of blooms into pipes;
5) release of rolled pipes from mandrels;
6) heating of pipes prior to the reduction or calibration processes;
7) rolling of pipes on stretch-reducing or calibration mills;
8) cutting of pipes;
9) process of cooling of pipe products and finishing of them.
The main advantage of the line with the continuous rolling mill lies in their high productivity. The equipment of modern plants with reducing mills, which operate with tension, expands the schedule of the rolled products as in terms of both the diameter and wall thickness. In old pipe rolling plants that didn’t have stretch-reducing mills, the schedule is narrower and its expansion is limited by considerable enlargement of the replaceable equipment stock: rolls and mandrels.
In modern plants equipped with continuous rolling mills, pipes of a single diameter are rolled, and the reduction decreases the diameter to the required value.
The modern plants are also provided with the calibration mill, which is a reducing one. It differs from the reducing mill in the lesser number of stands and operation without tension. It can operate with tension as well, but this tension should provide for the wall thickness not to change during reduction. The pipe diameter diminishes considerably on the reducing mill. The pipe wall thickness can also diminish if applying high tension.
The starting material is a round rolled billet; however, round ingots (of killed or semikilled steel) are sometimes used.
The production of pipes on the first plant, manufactured in Russia, involves heating of starting material in the form of rod with a length of 4 - 12 m in sectional through-type furnaces. The rods are heated simultaneously in three grooves of each of the two furnaces. The heated rods are fed sequentially to the hot-cutting dividing shears, where the rods are cut into billets with the certain length. The shears are of cantilever type and perform bottom cutting. When cutting the billet, it is retained by a clamp. Every knife has three grooves with round passes corresponding to the billet diameter. To reduce the collapse of the billet ends during cutting, the passes of the knives are provided with the tooth with the height of 5 - 7 mm. The knives are fixed in two supports, which move over the columns by an eccentric shaft and connecting rod. The shears are driven from an electric motor by universal spindles. The shears for cutting the billets of different length are provided with the screw swinging stop. The maximum cutting force of the shears is 1 MN and the maximum productivity is 660 cuts per hour.
According to another scheme, the starting metal, in the form of rods with the maximum length of 12 m, is cut into billets by shear presses or using presses for cold breaking. Then, the billets are loaded into the circular furnaces, where they are heated to the temperature required for rolling.
The heated billets are transferred to the 2-hi piercing mill, where they are pierced into blooms with the specified dimensions. Prior to piercing, the hot billets are centered by a centering machine with the air gun. The piercing mills with 2-hi guide bars are usually used. At present, guide disks are used instead of bars; this allows accelerating the piercing process considerably, improving the wear resistance of the guide tool and quality of the blooms. One of plants, which is operated in England, is equipped with the 3-hi piercing mill. This is also expedient because this plant uses continuously cast billets with poor quality in the axial zone.
In piercing mills manufactured in Russia, the bloom delivery is axial that ensures efficiency of operation. As seen from the practice of operation of foreign plants, their bottleneck is the piercing mill. Therefore, in Japan, they install two piercing mills on one of the plants. In Germany, the axial bloom delivery is also used on piercing mills, but along with a bar. And the bar is removed outside the mill. This increases the throughput capacity of the piercing mill but requires additional line for circulation of bars.
The work stand of the mill has barrel- or cup-shaped rolls with the toe angle of 7° and diameter of 900 - 950 mm in the gorge. The rolls run on the rolling bearings. The maximum peripheral velocity of the rolls is 8 m/s, and the torque on each roll is 120 kN*m. The work rolls are driven by a gear stand and universal spindles. The motor is supplied with direct current; its power is 3,650 kW. The roll is changed through the top access holes in the bed while turning the drums at an angle of 90°.
The billets with the diameter of 140, 150 mm are pierced at feed angles of 13 - 15°; the length of the billets is up to 3 m and that of the blooms is up to 6 m.
The design of the piercing mill outlet ensures reliable centering of the bloom and bar due to four 3-hi three-lever centering machines. The first centering machine is movable (the stroke is 800 mm), which is required for drawing the bar with the mandrel from the roll zone to replace the mandrel in case it has worn out. Each centering machine has also two driving ejecting rollers for accelerated ejection of the bloom from the centering machine. To eject the bloom, the rollers are brought together until they contact the bloom’s surface (using an air drive).
A thrust adjusting mechanism with a thrust head is installed downstream the centering machines. It perceives the forces from the metal to the mandrel, and the bar during the rolling. After finishing the piercing, the thrust head turns up relatively to the rolling axis until the bloom is ejected.
During piercing, the thrust head is fixed in the working position by the lever provided with a pneumatic drive. To set the mandrel position, the thrust head is moved by adjusting screws in the forming zone along the rolling axis within 150 mm in order to set up the mill. After piercing, the bloom is transported by rollers at the outlet at a speed of 1.0 - 1.5 m/s (along the rolling axis). After catching the bar by the tong catcher mounted on the outlet trough and opening the thrust head, the movement speed is increased up to 6 m/s. After ejecting the bloom onto the roller table located downstream the piercing mill, the thrust head is directed to the starting position.
The cycle of rolling the blooms with a length of 6 m is 9.0 seconds, 4.5 seconds of which are the piercing time and the remaining 4.5 seconds are the time of auxiliary operations.
During piercing, the tools of the piercing mill are cooled intensively with water: the work rolls, bars and mandrel are cooled from the outside at the coolant pressure of 0.2 - 0.3 MPa. The mandrel is also cooled from the inside under the maximum coolant pressure of 2.5 MPa.
The bloom is transported without delays to the mill’s inlet, where a long mandrel is drawn into the bloom. The mill’s inlet is designed as receiving troughs and equipped with special feeding cars for the mandrel and bloom. They are arranged according to the rolling axis (on the same line). The cars are moved by cable drives; the car movement speed is 2.5 - 4.0 m/s.
To insert the mandrel, the bloom is pressed against the rollers by the lever; in so doing the force of about 20 kN is created. The mandrel is inserted into the bloom by a feeding car with the force of up to 10 kN with the initial speed of 0.9 m/s. As the mandrel moves in the bloom, the speed is increased up to 2.5 m/s.
When the leading end of the mandrel comes out from the bloom to approximately 4.5 m, the bloom clamping is disabled, the mandrel pusher movement speed is reduced and the bloom pusher is activated. The bloom together with the mandrel enters into the rolls. As the rolling begins, the pushing cars are directed to the starting position (at the maximum speed of 4 m/s).
The continuous rolling mill is equipped with nine 2-hi stands installed on a common pedestal with a spacing of 1,150 mm. The stands are installed at the right angle to one another and at an angle of 45° to the horizon. The diameter of the rolls is the same for all the stands and equals to 550 mm; the body width is 230 mm. The guide shoes are installed at the inlet and outlet (at the first and last stands). The stand beds have the closed-type design and are made of cast steel. The work rolls are provided with rolling bearings as well as adjusting screws. The screws are intended for performing the height movement during the set-up and provided with spring balancing devices.
The stands are driven individually at the controllable speed from the motors each having the power of 1,400 kW and supplied with direct current. The eighth and ninth (finishing) stands have reduced-power drives each having the power of 400 kW.
The maximum pipe rolling speed is 6 m/s with the elongation factor of about 5.5.
The continuous rolling mill mandrels are 19.5 (20) m long that allows rolling the pipes with the maximum length of 27 (30) m. In the rolling process, the pipe “crawls” from the mandrel.
Before the mandrel is inserted into the bloom, its surface is lubricated with process lubricant (water solution of trisodium phosphate (17 – 18 %)). Water solution of sulfite alcohol spent liquor (up to 40 %) with addition of flaked graphite (3 – 5 %) is also acceptable to be used as lubricant. In addition, lubricant consisting of water solution of superphosphate (up to 25 %), sodium chloride (10 – 15 %) and lime (about 5 %) was used for long time. The lubricant would favor reduction of the friction coefficient when metal contacts the mandrel and protection of the mandrel against thermal shock.
After rolling, the pipe with the mandrel is ejected from the mill into the gravity chute; that allows removing the pipe from the rolling axis by chain-linked conveyor and transferring it to one of the chain-type mandrel stripper that are arranged in parallel to the continuous rolling mill line. The mandrel shank passes through the mandrel stripper lunette and is caught by one of the forks. The extracted mandrel is transferred to a separate drum-type cooling bath and the pipe is transported to the subsequent processing (on the reducing or calibration mill) by a roller table.
The cooling bath volume allows cooling 12 - 13 mandrels simultaneously. The roller table carries the cooled mandrels after the lubricating device to the inlet of the continuous-rolling mill for reuse during rolling.
Then the rear disheveled pipe end is cut off by a disk saw, and the pipe is sent to the through induction furnace. During heating, the temperature over the pipe length is equalized. The pipe is preheated prior to subsequent reducing and calibration. The induction furnace is equipped with 16 inductors with the total length of 21 m. It is supplied with electric power from 9 generators, each having the power of 1,500 kW. The current frequency is 1,000 Hz. The speed of the pipe moving through the induction heater is 2 m/s. The heaters are provided with the automatic system for controlling the pipe heating temperature. After rolling, one can see four dark longitudinal strips of cooled metal on the pipe, caused by a contact with the mandrel. The front part of the pipe, which crawls from the mandrel during rolling, has the temperature 100 - 150°C higher than the rare part of the pipe, which contacts the mandrel both during rolling and after the pipe leaves the mill.
Characteristic defects of pipes and preventive measures
Many kinds of pipe defects are typical for many kinds of industry:
- pipe wall variation (the heating or piercing procedure is violated);
- internal blisters appearing due to insufficient plasticity of the material in the forming zone;
- external defects due to poor quality of the starting material or heating procedure violation.
Only pipe defects arising due to the continuous pipe rolling method are described below.
The rejection related to the pipe wall thickness and its variation takes place when a bloom with the dimensions that significantly differ from the design ones, or when a bloom with increased wall thickness variation is fed into the continuous rolling mill. However, the main cause of defects related to wall thickness (exceeding of the allowable parameter as to the wall thickness) is increased wear of the passes and mandrels of the continuous-rolling mill. It is necessary to monitor the wear (dimensions) of the passes and dimensions of the mandrels. The maximum allowable distance between the diameters of the mandrels of the same set is 0.3 mm. The pipe dimensions are monitored by regular sampling and measurement of the samples.
On the external surface of the pipes, the cracks arise due to incorrect settings of the continuous-rolling mill. Increased drafting in the first stands and increased bloom diameter create non-uniform deformation. It causes longitudinal cracks; this is additional stress (overstress) of metal. The drafting node shall be monitored.
The roll wear causes scratch formation on the external surface; it causes mechanical damages of the pipes when they leave the mill. The condition of the rolls and discharge trough shall be monitored.
The causes of scratch formation on the internal surface of the pipes are insufficiency or unevenness of lubrication of the mandrels; contamination of the lubricant with foreign particles; excessive wear of the mandrels, incorrect set-up of the mill (too close adjoining of the pipe to the mandrel). It makes the mandrel extraction difficult.
If reducing is performed with tensioning, butted pipe ends appear. The butted pipe ends with the maximum length of 2.5 m after the reducing mills are usually cut off and then removed from the process flow. One should observe the norms for pipe end crop as well as modes of drafting in the reducing mill.
New schemes of pipe making on the PRP with the continuous rolling mill. Promising directions of improvement of the process and equipment
To the above processes, units being slightly different in the manufacturing technology and equipment components are applicable. Thus, a cheaper square billet with the side of 140 mm is used to produce the pipes with a diameter of 80 - 102 mm on the continuous pipe rolling mills. The incoming square billets are divided by breaking in the cold state on a press, and then heated to 1,260 - 1280°C in a circular furnace, and the ribs are calibrated on a 2-hi descaling mill. Then, the billet is pierced on a vertical press (under the force of 2.5 MN) to form a bloom with the base and pushed on the push bench through eight roller cages, then the billet is heated in a furnace and rolled off in the elongating mill. The total elongation factor on the push bench and elongation mill is 4 - 5.2.
The blooms produced in such a way are rolled on the continuous rolling mill with 9 stands on the mandrel with a length of 15 m. The mill stands are of 2-hi design (five horizontal and four vertical stands). The work rolls have diameters of 275 - 320 mm and are installed in the rolling bearings. The rolling of the mill is performed with tension; the maximum elongation factor is 6. The pipe length after the mill is 16-18 m at the maximum rolling speed of 4 m/s. The mandrel is extracted from the pipe by a chain stripper. Prior to inserting the mandrel into the bloom, the mandrel temperature is maintained at a level of 150 - 200°C. In case of long-term downtime, the cool mandrels are heated by gas torches. The pipe ends are cut off by two stationary saws. Then the pipes are preheated in a walking-beam batch furnace to 900 – 1,000°C and reduced in the reducing mill with 22 stands (stress reducing). The mill stands are of 2-hi type with the cantilever-type roll fixation at an angle of 45° to the horizon.
After reducing, the products are divided into specified length by four lever-type disk saws and cooled on the chain-type cooling table.
A continuous pipe rolling plant intended for manufacturing the pipes with the diameter of 16 - 100 mm and wall thickness of 2.35 - 4 mm is also interesting. This plants uses round continuously cast ingots with the diameters of 100 and 130 mm with the maximum weight of 200 kg as incoming billets.
Heating in the circular-type furnace and centering by pneumatic centering machines are followed by piercing of ingots in the 2-hi mills with the guide disks with a diameter of 950 mm. The piercing mill is driven by the electric motor. This is a DC motor; its power is 1,250 kW, the rotational speed of the disks is set within the range of 93 - 186 rpm.
The bloom is rolled off on a continuous rolling mill comprising 9 stands with 5-6-fold elongation to form a pipe with a length of 20 m. The mill’s productivity is up to 240 pieces/hour and it is provided with the chain stripper. Then the pipe is preheated to 950°C in the furnace (with end charge and discharge) and reduced on the 20-stand reducing mill (reduction with tensioning). The maximum speed of rolling the pipes with the diameter of 16 mm on the reducing mill is 7 m/s. At the outlet, the pipe is divided by flying shears and transferred by the roll table onto the cooling table. Another continuous-type pipe rolling mill at the metallurgical complex is intended for manufacturing of the pipes with a diameter of 27 - 133 mm and wall thickness of 2.6 to 12 - 16 mm of carbon or alloy steel of various sorts, billets to be used when performing the cold process as well as of hot-rolled boiler pipes. Round rolled billets with the diameters of 140 and 175 mm are used as starting materials.
The scale is removed by water descaling (the water pressure is 15 MPa) and centered. The centered billets are pierced on two piercing mills arranged in parallel (with lateral ejection of the blooms) with the total productivity of up to 360 pieces/hour. The feed angle in the piercing mills is constant and equals to 10°, the diameter of rolls is 930 – 1,065 mm. Prior to feeding to the continuous rolling mill, the blooms are descaled by water under pressure and rolled off into the pipes with a length of 22 m.
The continuous rolling mill is equipped with 8 2-hi stands with individual drive. Each roll is driven by the electric motor with the power of 750 kW. Only the last stand is provided with the motor being common for two rolls.
The basic deformation over the wall (more than 60 %) takes place in the first two stands. The finished wall is formed in the two following stands. The wall gets even around the perimeter in the other stands. The pipe is rounded and calibrated to the diameter; in so doing, the required gap is formed between the mandrel and the pipe. The continuous rolling mill is equipped with the electronic system for setting the speed of the rolls in each stand, which provides for even pipe wall thickness throughout the length. The continuous-rolling mill mandrels with a length of up to 18 m are lubricated with high-temperature oils, which are doped with graphite, if alloy steels are to be rolled. The water cooling the mandrel is also doped with special additives reducing the friction factor during the rolling.
The pipes rolled on the continuous rolling mills (with the dimensions of 116 x 3.25 ‑ 12 or 133 x 3.75 ‑ 14 mm) are heated in the walking-beam furnace to 900 – 1,000°С. The furnace productivity is 250 pieces/hour. After furnace, the pipes are descaled by water under pressure and reduced on the stretch-reducing mill comprising 24 stands. The mill is driven individually from the motors with the power of 100 - 150 kW. The stands are of 3-hi type, the stand spacing is 290 - 310 mm. The mill rolls rotate with different speed: from 120 to 620 rpm.
The reducing mill drive is provided with special stabilizing system reducing the length of the butted ends of the reduced pipes by up to 3 %. The maximum rolling speed on this reducing plant is 9 m/s; the length of the reduced pipes is up to 100 m with the elongation factor of up to 6.1.
Pipes from chromium-molybdenum steels are reduced to the diameter of 60 mm only, while the total diameter drafting is up to 48 %. The pipes with the wall thickness of 16 mm are only produced from the pipes with the diameter of at least 60 mm.
After reducing, the pipes are fed to the screw refrigerator. From there, the reciprocating stacker transfers the pipes in turn onto two collecting roller tables equipped with smooth rollers. Here the pipes are divided to lengths by disk saws.
The technology of rolling on a retained mandrel becomes widespread today. The mandrel travels in accordance with the pipe deformation at a specified speed. Such process is the most efficient to produce pipes with high diameter (more than 180 - 200 mm) because the length of the retained mandrels is less than that of the floating ones. It reduces considerably the costs for their production. However, the design of the continuous-rolling mill becomes much more complex, because the inlet side is provided with the rack-type driving mechanism. This mechanism controls the mandrel movement speed. The computer automatically determines the mandrel dimensions and speed of its movement. The actual knowledge of the roll speeds and positions of the bloom and mandrel are taken as a basis.
After rolling, the mandrel is sent to the based position, removed from the rolling line and then transferred for lubrication. Then the next bloom and mandrel are fed to the rolling.
The essence of one of the methods of rolling on a retained mandrel (MRK-S method) lies in the following: first of all, before the finishing the rolling process, the mandrel goes away from the mandrel holder and then arrives to the outlet of the mill together with the roughing pipe and then to the mandrel stripper. The maximum elongation factor μ = 4 and the maximum pipe length is 40 m.
To produce a bloom with high-quality internal surface and prolong the service life of the mandrels, the mandrel speed is selected to be equal to or slightly lower than the speed of the pipe being rolled after the first stand. The movement speed of the pipe relatively to the mandrel is selected at a level accepted for rolling with the floating mandrel (on continuous rolling mills).
Another method of rolling on a retained mandrel is featured by movement of the mandrel with the roughing pipe at a constant speed during the whole rolling period. The maximum length of the pipe rolled on this mill is 48 m and the cycle lasts 22 seconds.
To make the pipes of the required schedule on the continuous rolling mills, the mandrels moving at a speed of 0.3 - 2.0 m/s are used.
The mandrel movement speed is controlled by a special device, which generates the force or 1,600 - 3,500 kN to retain the mandrel. This mechanism ensures a certain mandrel movement speed:
either 1) till the complete unloading of the pipe being rolled from the mandrel (retained mandrel), or
2) till the moment when the mandrel begins to move as a floating, i.e. partially retained one.
The mill with the retained mandrel has been launched. The mill consists of seven stands. The first three stands are equipped with the rolls with the diameter of 780 mm while the other stands are equipped with the rolls with the diameter of 690 mm. The total power of the rolls’ drive is 15,400 kW. The maximum speed of the pipe delivery is 3.7 m/s. The working part of the mandrel has the length of 16 m, and the maximum pipe length is 35 m.
In Japan, a continuous rolling mill comprising 8 stands with the rolls of 790 and 720 mm diameters is used. The total power of the DC motors is 21,800 kW. The continuous rolling is performed on the retained mandrel. The speed of the bloom and mandrel on each stand is constant thus minimizing the longitudinal pipe wall variation in case of larger elongation. The design of the screw-down structures of the mill stands allows variation of the rolls in stands 5 - 7. The mill is provided with a closed mandrel feeding system. The extracting and calibrating mill is installed behind the continuous rolling mill. The mill is controlled by the computer, the functions of which are control of the sequence of the operations being performed; automatic setting of the passes; determination of deviation from the norm; operation in the automatic mode and in the mode of information (advice) of the operator; automatic change of rolls; item-by-item control of each rolled pipe.
For the PRP, the modern mill comprising 7 stands for continuous rolling on a retained mandrel was created.
It has the following main features:
1. Production of pipes with the range of outer diameters (D/5 = 7.2 ‑ 49.5), with a length of up to 32 m at a rolling speed of 3.0 ‑ 4.4 m/s and elongation factor of 2.0 ‑ 6.0, with rolling the roughing pipes of five standard sizes in the passes with the designations 212; 235; 288; 372; 444:D x S, = 212 x 5.4 ‑ 26 mm; 235 х 6.4 ‑ 30 mm; 288 х 7.0 ‑ 40 mm; 372 х 8.0 ‑ 42 mm; 444 х 9.. .30 mm;
2. Rolling of pipes on the mandrel by rolls with deep penetration of passes: the ratio between the roll diameter and the pass diameter is 1.9 ‑ 2.8.
3. Use of the cast-iron rolls in the 4th-7th stands for all the passes and for all the stands for the passes with the designations 212 and 235;
4. Use of the retained mandrels moving at a speed of 0.25 - 1.5 m/s by a special mechanism. The mandrels are replaced after rolling each of the pipes; the same mechanism performs the delivery to the mill inlet;
5. Simultaneous rolling on the mandrel on the continuous rolling mill (comprising 7 stands) and calibration of pipes on the 2-hi extracting and calibrating mill (comprising 10 stands);
6. High automation level, provision with the high-technology monitoring and automatic control.
The components of the process tools required for this mill have no analogues in the Russian practice. They differ from the traditionally used ones in terms of materials, design and manufacturing technology. When rolling in the passes with the designations 212, 235 and 288 - 444, the cast-iron rolls are used instead of the steel ones.
The steel and cast-iron rolls with the maximum diameter have new design concept and are distinguished by high accuracy and cleanness of surfacing.
The mandrels of the continuous-rolling mill having actually extreme dimensions (Ø 160 ‑ 425 mm, length 24 m, maximum weight 20 t) are high-accuracy tools. After chromium plating, their working part has a diameter tolerance of −0.3 - +0.0 mm, surface roughness of 0.4 ‑ 0.8 μm and chromium coating thickness of 45 ‑ 60 μm. The mandrel has three parts: working part, extender and shank (all of them are interconnected). The working part of the mandrel has the diameter of less than 300 mm and length of 15.5 m. It is a solid cylindrical body. The mandrels having larger dimensions are made with the bore diameter of 180 mm over the length of 14 m for cooling with water after rolling.
The mandrels can be moved by a special retaining device. The rolling speed is 0.25 - 1.5 m/s and the idling speed is up to 4.5 m/s. The maximum retaining force is 3.5 MN.
Long mandrels are to be lubricated with graphite containing lubricant. This lubricant is used together with antioxidant powder. The powder is forced into the bloom under head of compressed nitrogen. After insertion of the mandrel, a clean nitrogen jet is used to clean the internal surface of the bloom from products of the reaction between the scale and the antioxidant.
On the extracting and calibrating mill, the operations of calibration and extraction of the mandrel are combined. It consists of ten 2-hi stands. Each stand has a drive. The drive motor is supplied with direct current; its power is 450 kW. The maximum diameter of the roll body is 750 and 865 mm, the minimum one is 600 mm, the roll body width is 500 mm. The interaxial distance between the neighboring stands is 1,355 mm. The maximum length of the pipe at the mill outlet is 36 m; the maximum pipe speed at the outlet is 5.5 m/s.
In 2010, the PRP was reconstructed. In the course of reconstruction, the press roll piercing mill was dismantled, the 2-hi elongating mill was reconstructed into a piercing mill and the design of the inlet of the continuous-rolling mill was considerably modified: the mandrel was inserted into the bloom along the continuous-rolling mill axis instead of that performed outside the mill. The billet centering machine was installed, that can perform a centering recess on both the front and rear end of the hot billet. After reconstruction, continuously cast round billets with the diameter of 410 mm are used as incoming billets instead of square billets, which were used earlier for press-roll piercing.
The new billet piercing scheme allows producing more accurate blooms per procedure (process cycle) and increasing the bloom temperature before rolling on the mill that has reduced the loads on the working rolls and main drive of the mill.
The good result for improvement of the quality of the products made on the pipe rolling line with the continuous rolling mill consisting in the expansion of the range of dimensions of the seamless pipes was explained by installation of new continuous rolling lines and plants with 3-hi stands.
The technological advantages of the continuous rolling plants with 3-hi stands and controllably movable mandrel are:
1) reduction of critical stresses and unevenness of deformation in the process of the bloom shape change to form a roughing pipe;
2) improvement of stability of the mandrel position;
3) smooth temperature distribution over the bloom-pipe surface;
4) minimization of the metal slipping in the work rolls.
This improves the pipe quality as regards the accuracy of the geometrical dimensions and condition of the outer surface.
Continuous mandrelless rolling of seamless pipes
The development of rolling mills began at the end of the 19th century. The main task was to create such a rolling line that would allow reducing the diameter of the pipe subjected to continuous hot deformation by the rolls. The first patent for such a plant was issued in 1889. At this stage, it became possible to carry out rolling using a long mandrel, which allowed reducing the pipe wall thickness while the pipe diameter decreases.
The technology of rolling the pipes by continuous method on a long mandrel or without such a mandrel is used today for manufacturing of the pipe products. The spread of the technology of continuous mandrelless rolling (calibrating and reducing) of pipes is conditioned by the necessity to expand the schedule of pipes, by economy of the process and relative simplicity of the technology and equipment. This technology is used on the pipe rolling, electric pipe-welding, pipe welding and pipe-pressing plants.
Reducing mills and calibrating mills are continuous rolling mills where pipes are made without mandrel by rolling in the work stands arranged serially with gradual reduction of the pass diameter. The pipes can be reduced and calibrated in any state:
- hot (the temperature of metal to be deformed is 720 – 1,100°С),
- cold (20 ‑ 40°С) and
- warm (about 100°С). The most widespread method is the “hot” one.
The continuous mandrelless rolling is featured by variation of the pipe walls as the diameter decreases. It is favored by a number of factors:
- ratio between the diameter D and the pipe wall thickness S,
- value of drafting of the pipe in the work stand,
- roll calibration,
- relationship between the roll rotation speed in the mill stands,
- rolling temperature, etc.
On a provisional basis, the following three kinds of mills for mandrelless longitudinal rolling of pipes can be marked out.
Calibrating mills. They are intended for giving the pipes an accurate geometric shape over the outer diameter. Here, the pipe deforms insignificantly, therefore these mills are usually equipped with 3-7 stands. Such units were contained in the plants of obsolete design with automatic push bench, pilger and even 3-roll reeling mills. The total deformation of the pipes over the diameter on the calibrating mills is 15 – 25 % with the partial deformations in the stands of 2.5 - 3.5 %. When calibrating the pipes, the wall thickness increases slightly and can remain invariable, should the tensioning be used.
Reducing or reducing-and-calibrating mills. They are intended for reducing the outer diameter of the pipes and calibrating them. The presence of these mills gives the pipe rolling plant the following advantages:
- improvement of its productivity,
- expansion of the possible schedule, i.e. producing of the pipes with smaller diameter and larger length. Such mills are usually equipped with 12-20 stands. The stands operate either without tension or with low tensioning. The reducing of pipes without tensioning is accompanied by thickening of the wall along the pipe length and formation of transversal wall variation, which is especially noticeable when the deformations are large. Therefore, the total deformation as to diameter in the reducing mills is limited to 40 – 45 % with the partial deformations of 3.5 - 4.5 %.
Stretch-reducing mills. They are intended for producing thin-walled pipes with small diameters. They work with tension, therefore the wall thickness decreases or remains unchanged that is explained by the tensioning degree. The total deformation of the pipes as to diameter can be 75 – 80 %, and the wall thickness reduction can be 30 – 35 %. After reducing with tensioning, the pipes get the higher quality. However, the reducing with tensioning causes formation of pipes with butted ends. During rolling, the tensioning does not affect the leading and trailing ends of the pipe to the full extent. Therefore, it is more expedient to use the stretch-reducing units within the pipe welding and electric pipe welding units, which allow performing stepless reduction or within units, on which pipes with the minimum initial length of 15 - 20 m can be made.
The stretch reducing mills have high productivity. The last stand rolls at a speed of 10 - 13 m/s.
The mandrelless continuous rolling mills can be classified as follows:
- according to the number of rolls in the stands: 2-, 3- and 4-hi units;
- according to the drive type: individual, group and combined.
Pipe plants operate the mills equipped with 2- or 3-hi stands. At present, the reducing mills provided with 3-hi stands are used preferably. The use of 3-hi stands is preferable due to a number of their technological advantages. In the pass with three rolls, the unevenness in the process of change of the pipe walls in the cross section (in comparison with the 2-hi one) as well as lateral spread of metal and sliding of rolls over the pipe are reduced due to less difference of peripheral speeds at the crest and crests of the roll. It allows to preform more drafting in each stand without distorting the pipe profile. Here, the drive power is consumed primarily for lengthening of the metal to be deformed. Moreover, the 3-hi design of the stand reduces the distances between the adjacent stands. That favors the reduction of length of thickenings at the pipe ends in case of the piece-by-piece rolling.
4-hi stands with complex design have not found application.
The design of the mandrelless continuous rolling mill drive performs an important function in the implementation of the process: its type predetermines the possible tensioning mode, both in the stable rolling mode and in the transient period. The drive of the mills can be group, individual or combined.
The group drive is the simplest one: one motor drives all the rolls of the stands. For this aim the special speed reducers (with bevel gears) are used. When using this drive, the rolling is performed in the tensioning mode that is characteristic of such a mill. The group drive was used in the obsolete-design calibrating and reducing mills.
The second drive type is individual. This is a universal drive used for calibrating, reducing and stretch-reducing rolling mills. A DC motor drives the rolls of each stand. Disadvantages of the method:
- difficulty of maintaining of the specified speeds in the rolling process;
- complex and expensive electric equipment.
Striving to exclude the disadvantages of the individual drives has led to the development of combined drives, which have stricter characteristics. In addition to the common electric motor for a group, the work stands are equipped with additional adjustable hydraulic drives. Today, the stretch-reducing mills equipped with variable group drives are built. The variable group drive system consists of two electric motors connected at the outlet to the work stands of the mill by differential trains. Therefore, the rotational speed of the rolls of every stand consists of the sum of speeds transmitted by these motors.
The advantages of the variable group drive system of the stretch-tensioning mills:
1) high rigidity of the drive is especially significant when working with high tensions;
2) simplicity of setting the mills to the specified thickness of walls of the pipes being reduced;
3) possibility of independent adjustment of the tensioning mode and rolling speeds by adjustable DC motors.
The disadvantages of such a drive are:
- complexity of the mechanical equipment;
- speeds of the rolls in each stand of the mill can be only varied in accordance with the patterns built in the drive kinematics.
Production process of seamless pipes on the PRP with reeling screw rolling mills
The plants for rolling off the pipes by the screw rolling method produce a small quantity of pipes, 7 – 8 % of the total production volume. However, these plants are valuable, because the pipes produced on them have high accuracy. The limit values for the wall thickness and outer diameter are 2 - 2.5 times higher than for the accepted allowable parameters: for the wall thickness: ± 6 % and for the diameter: ±0,5 %.
The above mentioned plants produce the thick-walled pipes to be used for manufacturing the parts of machines.
High-accuracy characteristics of the pipes allow producing the minimum allowances for subsequent machining and producing the pipes on flowlines with automatic machines. These are the facts that favored the selection of the plants with reeling mills for manufacturing the pipes, which are to be used subsequently for manufacturing the bearing units, by the screw rolling method.
An important advantage of these reeling units with the screw rolling method lies in its high maneuverability, i.e. possibility of quick and simple reconfiguration for rolling the pipes of other schedule. Variation of the outer diameter of the pipes being rolled is achieved by bringing the work rolls together or apart. The wall thickness is varied by selecting the diameter of the reeling mill mandrel. The rolls shall be only replaced in case of considerable wear of them as well as in case of considerable change of the schedule of pipes. In these cases the rolls with other diameter are required.
Thanks to the said facts, the lines with reeling mills are especially valuable when manufacturing the bearing pipes or pipes to be machined subsequently. High accuracy characteristics during the rolling ensure insignificant losses for chip scrap. The simplicity of reconfiguration of the process parameters ensures the rolling of pipes with any diameter within the adopted range that reduces also the metal waste formation during the machining because it allows adopting smaller allowances for turning-off of pipes.
The two schemes of lines for rolling off the bloom on the mill by the screw rolling method:
- The lines with 3-hi mills (Assel mill) are wider spread;
- Abroad (in the USA) the lines with rolling off on the mill with 2-hi stands (with guide disks) are used.
Installation of 3-hi mills in the lines confines somewhat the range of the products produced: on these mills, only thick-walled pipes with the ratio between the diameter and the wall thickness D/S < 10 - 11 can be produced. Still, attempts to produce thin-walled pipes on these plants are unsuccessful. However, during rolling of the pipe end, the transverse strain is developed and a triangle flare is formed at the end part of the pipe. These facts prevent the rolling process from normal implementation. Installation of 2-hi reeling mills with driving disks in the lines has allowed expanding considerably the range of the pipe products being rolled up to D/S = 17. However, these mills are not widespread due to their complex design.
Another limitation is the minimum diameter of the pipes. In the lines equipped with medium- and large-type mills with 3-hi, the lower limit of the pipe diameter is limited to 73 - 76 mm. It is concerned with the possibility of bringing the three rolls together to the minimum diameter. Integration into the reducing mill line ensures the reduction of the final pipe diameter, but worsens considerably its maneuverability, because it will comprise the mill with round passes. Therefore, it will be necessary to change the rolls (stands change) in case of switching to another standard size. Besides, the reducing worsens the pipe size accuracy, therefore, the maximum drafting of the pipes over the diameter is usually 25 %.
Pipe making on the PRP with 3-hi reeling screw-rolling mill
The lines equipped with reeling units with screw rolling serve to produce the pipes with the diameter of 50 - 240 mm and maximum length of 10 m. The process supposes the following main operations:
- works for preparing the billet for the rolling process;
- stage of heating the billet in a circular furnace;
- piercing of the billet;
- rolling-off of the bloom into the pipe on the reeling unit (on a long mandrel);
- extraction of the mandrel;
- preheating of pipes in a special furnace;
- calibrating of pipes in the 2- or 3-hi mill.
To expand the range towards the pipes with small diameters, some units are equipped with multistand reducing mills (provided with 7 - 14 stands). The thick-walled pipes are reduced without tensioning; however, the wall thickness accuracy is noticeable even in case of small degree of deformation. The outer diameter accuracy can be preserved, because the pipes are calibrated in the rolling mill by the transversal screw method after reducing the pipe.
Commissioning of the reducing mill worsens the maneuverability of the plant and expands the stock of rolls, i.e. reduces considerably the main advantages. It seems to be expedient, if the schedule of the mills to be reduced is limited and no strict requirements are placed on the accuracy of these pipes (in particular, if these pipes are to be further deformed).
New production process of seamless pipes by piercing with subsequent rolling-off in a single screw rolling mill
When using the adopted technologies to produce thin-walled pipes, the blooms are rolled off in a specialized 2-hi mill with driving guide disks. The rolling-off is performed on a long floating cylindrical mandrel. Thanks to additional tractive driving forces, the driving disks ensure the production of pipes with the maximum ratio D/S = 30.
The qualitative characteristics of the finished pipes, especially those made of alloy steels, meet the requirements for the oil-schedule. Control of the pipe geometry by varying the process factors is difficult due to the open forming zone. The work stand of the mill is distinguished by increased structural complexity and high energy intensity and weight of the equipment. Besides, it requires more deepening of foundations for the drive and the floor space should exceed that of the stand with guide bars 1.5 - 2 times. Rolling of wide-schedule pipes requires the appropriate quantity of guiding tooling units for each standard size of pipes. Its weight reaches several tens of tons, if the disks are used. The manufacture of the guide disks requires the special expansive mechanical equipment. Use of a long floating mandrel requires heavy costs: for manufacturing the sets of mandrels with different diameters and additional facilities.
New technologies being applied during production of the seamless products include the following process steps:
1. Cutting the incoming rods to specified length by mechanical saws.
2. Making a centering recess on the leading end of the cold billet by drilling.
3. Preheating the billets to the rolling temperature. To preheat the billets, the gas furnace is used.
4. The billets are pierced on the screw rolling mill with the 2-hi stand (cup-shaped scheme). The guiding tools are bars.
5. Rolling off the bloom on the mill of similar design (on a short mandrel: either conical or cylindrical).
6. Calibrating the produced roughing pipe as to diameter on the 3-hi screw rolling mill with simultaneous straightening.
7. Controlled cooling of the pipe.
This technology is implemented on compact automated equipment with low power consumption. The work stand of the screw-rolling piercing/reeling mill is mounted on the welded reduced-weight bed. The bed has increased rigidity and weight of 40 tons. The work rolls Ø 700 mm are operated:
- from the main drive;
- rotation with the speed of 40 - 60 rpm;
- on two AC motors;
- power of motors: 2 х 1,300 kW.
The process equipment together with the transmitting devices forms a unified continuous flow system. This design provides both for single-heating operation and subsequent performance of piercing, heating and rolling-off of the bloom with the following calibration of the pipe. A hot-rolled rod or continuous cast billet is used as an starting billet with the diameter of 80 - 250 mm to produce pipes with the diameter of 73 - 270 mm and wall thickness of 11 - 28 mm for manufacturing of couplings. These couplings are then fitted to casing and pumping-and-compression pipes made of steels of the appropriate strength grade. As a result, the production output of 22,000 tons/year is achieved, which can be increased up to 50,000 tons/year. The maximum hourly productivity of the piercing process is 38.3 tons/hour, that of the rolling-off process is 30.7 tons/hour, the maximum piercing time is 18 s and the time of auxiliary operations is 10 s. The area is serviced by the team consisting of 10 persons per shift.
The proposed technology allows producing high-accuracy pipes with the wall-thickness variation of up to ±6 % and high quality of both the external and internal surfaces. It is achieved, firstly, due to the fact that the rods are cut to specified lengths by a mechanical saw providing for a high quality of the end face of the billet avoiding non-perpendicularity of the end and due to accurate mechanical centering of the leading end. The piercing and rolling-off are performed at a feed angle of 12° and rolling-off angle of 7° according to the cup-shaped scheme with the drafting over the diameter before the mandrel nose of 6 – 8 %. The process provides for uniform distribution of elongation between the stages of the piercing and rolling-off. The calibration of the rolls specifies the distribution of particular drafting throughout the forming zone length. This ensures the reliable secondary catching and smooth movement of metal over the deformation zone. The wall thickness decreases symmetrically. The short tapered mandrel allows improving considerably the process controllability during the rolling-off. It becomes possible to vary the wall thickness and diameter of the bloom to be produced not only due to change of the drafting value (position of the rolls), but also by varying the extension of the mandrel nose beyond the place of gorge of the rolls. As a rule, the latter affects the pipe geometry more efficiently and is easier technologically to implement. It allows expanding considerably the size schedule of the pipes produced with the single calibration of the rolls. The costs for the tooling and reconfiguration of the mill are reduced. In addition to rolling-off on the 2-hi mill with the guide bars, the proposed technology is featured by the invariable setting of the forming zone for piercing and rolling-off, except for calibration of the mandrels and extension of the mandrel nose beyond the gorge.
It allowed to implement both the processes on the same plant in the same heating while returning the pierced bloom to the inlet and replacing simultaneously the piercing mandrel with the rolling-off one together with the bar.
Such technological solution allowed reducing considerably enormous quantity of equipment and expenditures for its acquisition. The roughing pipe is calibrated to the diameter on the 3-hi screw rolling mill at a feed angle of 12° and with the maximum drafting to the diameter of 5 % that allows combining the pipe calibrating with the straightening. In addition to the main scheme of implementation of the manufacturing process, there is a variant providing for rolling-off of pipes on the following route: heating of the billet – piercing of it into the bloom – heating of the bloom in the heating furnace to the temperature of 1,100 – 1,150°С – rolling of the bloom into the pipe – calibration of the pipe to the diameter – controllable cooling. The rolling on this route is performed in batches as to the volume of filling of thermostat with blooms (the batch weight is up to 20 tons) with subsequent shutdown of the piercing process and reconfiguration of the stand for rolling of the bloom into the pipe. For the time of adjustment of the mill to another rolling mode (approximately 10 ‑ 15 min), the blooms from the thermostat are fed into the heating furnace by the roller table. The bloom temperature when charging the furnace is 800°C, the time of heating the bloom to the specified temperature is 20 ‑ 30 min. After finishing the rolling of the batch of blooms into pipes, the mill is reconfigured for piercing the billets again. The finished pipes are straightened and calibrated and then cooled.
The third variant provides for heating the billets, piercing the bloom, cooling the blooms completely and storing them until a certain quantity is accumulated. In any other period of time, the blooms are heated from the cold charging and rolled off with subsequent calibration and controlled cooling to the specified standard size.
It is known that the guide bars are intensively worn during the rolling. It entails:
- variation of ovalization of the bloom billet in the forming zone;
- worsening of the quality of blooms and pipes, and
- violation of the piercing process.
Therefore, special attention is paid to the resistance of the bars because the piercing and rolling-off are performed on the same tool, which carries actually the double load.
On the basis of experimental investigations, the new design of the guide bars of carbon steel with overlaying the nickel-based alloy onto the working surface was successfully developed.
For numerous piercing mills, the bars are cast of superalloy, so called special cast iron. It has the following chemical composition: 1.8 ‑ 2.1 % of С; 0.8 ‑ 1.2 % of Si; 0.3 ‑ 0.6 % of Мn; 30.0 ‑ 34.0 % of Cr; 4.0 ‑ 6.0 % of Ni; up to 0.045 % of S and Р.
Heavy wear of the working surface on the bars entails the failure of the bars. During the operation, a net of flame erosion cracks is formed. The pass setting and quantity of the rolled material determine the dimensions and shape of the wear scar. The maximum wear depth is 7 - 8 mm.
To improve the wear resistance, prevent overheating of the bar body and to exclude overlaid working layer with subsequent formation of flame erosion cracks, the bars are made with slots for internal cooling with water.
After wearing of the overlaid refractory layer, the bar surface is restored by repeated overlying to the initial dimensions and the bar is used again.
Using the steel bars of new design excludes their emergency breakdown that is typical for bars of special cast iron with coarse cast structure.
Pipe making on the PRP with the pilger mill
The lines with pilger mills are widely used in our country and abroad. The share of the products made on pipe rolling plants with pilger mills is approximately 15 % of the total volume of the seamless pipes made.
The main advantages of the pilger method are as follows:
1) rolling the pipes with high (up to 15) elongation factor;
2) making the pipes of cast metal due to intensive workup of its structure;
3) possibility of making the pipes with especially thick walls and pipes of special profile purpose (square, hexagon, conical, stepped, gilled, etc.);
4) low primary cost of pipe products.
The lines with pilger mills make the drill, casing, oilfield, boiler and other pipes.
The dimensions of the pipes being rolled determine the division of the plants into 3 standard size:
- small plants: to make pipes with the diameter of less than 114 mm with the minimum wall thickness of 2.5 - 4.0 mm;
- medium plants: to make pipes with the diameter of 114 - 325 mm with the minimum wall thickness of 5-7.5 mm;
- large plants: to make pipes with the maximum diameter of 550 - 665 mm with the minimum wall thickness of 6 - 10 mm;
The most commonly used plants are medium and large ones. They use continuously cast billet or ingot as a starting material for pipe making. This predetermines the lower primary cost of pipes, although the productivity of these plants is slightly inferior to that of the pipe rolling plants with an automatic mill.
Pipe production on plants with push benches
The technology of pipe making on the lines with push benches implies the following main stages:
- preparing the billets for rolling;
- heating the billet;
- calibrating the billet diagonals;
- piercing the billets by a vertical press;
- heating the pierced blooms;
- rolling off them on the elongating mill;
- pushing the blooms through the roller cages by the mandrel;
- cutting the pipe base by the saw;
- calibrating the outer diameter or reducing with tensioning;
- cold finishing of the end products. Pipes with the diameter of 21 - 219 mm with the wall thickness of 2.5 - 11 mm are made by this method.
Sometimes, heating the sleeves and rolling them off on the elongating mill are excluded. In old plants, the billet diagonals are not calibrated either. On the push bench, the reducing dies are used instead of roller cages for pushing the sleeves.
The modern lines with push bench allow producing the pipes with a length of 12 - 14 m after pushing and with a length of up to 21 and 77 m after calibrating and reducing, respectively.
Equipment for metallurgy
- Broaching machines
- Drawing stands
- Drilling machines
- Equipment for billet roughing (reduction)
- Equipment for machining pipe billets and slabs
- Forging presses
- Grinding machines (grinders)
- Heating furnaces
- Hot dipped galvanizing lines and equipment
- Metal cutting equipment (lines)
- Metalworking machinery
- Milling machines
- Pipe billets
- Pressure metal treatment stands (hot isostatic presses & pressing equipment)
- Roll stands and stand replacement parts
- Rotary-table milling machines
- Seamless Pipe Plants
- Screw-cutting lathes
- Thermal furnaces
- Tube and pipe plants and equipment
- Turning lathes
Upon becoming the official distributer of seamless pipe mills, our company ‘Intech GmbH’ LLC (ООО «Интех ГмбХ»), carries out the following: finds the buyers of your products on the market, conducts technical and commercial negotiations with the customers regarding the supplies of your equipment, concludes contracts. Should a bidding take place, we will collect and prepare all the documents required for the participation, conclude all the necessary contracts for the supply of your equipment, as well as register the goods (seamless pipe mills) and conduct customs clearance procedures. We will also register a certificate of transaction (Passport of Deal) required for all foreign trade contracts in the foreign currency control department of the authorized Russian bank so that currency transaction could be effected. If required, our company will implement an equipment spacing project in order to integrate your equipment into the existing or newly built production plant.
We are convinced that our company ‘Intech GmbH’ LLC (ООО «Интех ГмбХ»), will become your reliable, qualified and efficient partner & distributor in Russia.
We are always open for cooperation, so let’s move forward together!