In the processing of thick-walled seamless steel pipes, many steps are required to obtain such high-quality pipes. By eliminating the work hardening of the seamless pipe, a satisfactory metallographic structure can be obtained. The process equipment is bright annealing furnace, which is mainly used for. The finished stainless steel is heat treated in a protective atmosphere. When the application performance requirements of the thick-walled seamless steel pipe are different, the requirements for the metallographic structure after bright annealing are also different, so the bright heat treatment process will also be different.

The residual stress of the thick-walled seamless steel pipe material remains after cold working, and the residual stress is very unfavorable to the stress corrosion cracking of the pipeline. Any degree of cold working can significantly improve a material’s resistance to stress corrosion cracking. The degree of cold working can also adversely affect the high temperature resistance of austenitic stainless steels. Generally speaking, the higher the working temperature or the higher the fracture life requirement, the lower the degree of cold working.

It can be seen from the above introduction that the heat treatment process of thick-walled seamless steel pipes is quite troublesome. In order to obtain a qualified metallographic structure, the adjustment part of the cooling section equipment of the bright annealing furnace needs to be very large. Therefore, the current advanced bright annealing furnace usually adopts strong convection cooling in its cooling section, and has three cooling sections, and the air volume can be adjusted independently. It is divided into three sections along the width of the strip.

According to the production method, thick-walled seamless steel pipes can be divided into three categories: hot rolling (extrusion), welding and cold working. Hot-rolled seamless steel pipe is a steel pipe in which a solid billet or ingot is pierced and rolled into a hollow section. The basic process is piercing and rolling. Cold-worked seamless steel pipe is the secondary processing of steel pipe (also includes the secondary processing of thick-walled seamless steel pipe and thin-walled seamless steel pipe). Cold working is an important method to obtain high-precision, high-performance pipes, including cold rolling, cold drawing, cold drawing and cold spinning, etc. Extruded non-ferrous metal seamless pipes for high alloy steel grades are mainly extruded.

thick wall seamless alloy steel pipe — Thick wall seamless alloy steel pipe

Characteristics of thick-walled seamless carbon steel pipe

1. High wear resistance: The thickness of the wear-resistant layer of the thick-walled seamless carbon steel pipe is 312mm, and the hardness of the wear-resistant layer can reach HRC5862. The wear resistance is more than 1520 times that of ordinary steel plates, 510 times that of low-alloy steel plates, and 25 times that of high-chromium cast iron. Wear resistance is much higher than spray welding and thermal spraying.

2. Good impact resistance: The thick-walled seamless steel pipe is a double-layer metal structure, and the wear-resistant layer is metallurgically combined with the base metal. High bonding strength, can absorb energy when impacted, and the wear-resistant layer will not fall off. It is suitable for strong vibration and shock conditions, which is unmatched by cast wear-resistant materials and ceramic materials.

3. Good temperature resistance: the alloy carbide of the thick-walled seamless pipe has strong high temperature stability, and the wear-resistant steel plate can be used at 500 ℃. Other special requirements can be customized production, within 1200 can be used. Wear-resistant materials, such as ceramics, polyurethane, polymer materials, etc., cannot meet such high temperature requirements.

4. Good connection performance: The base material of the thick-walled seamless pipe is ordinary Q235 steel plate, which not only ensures the toughness and plasticity of the wear-resistant steel plate, but also provides the strength to resist external force. It can be connected with other structures by welding, plug welding, bolt connection, etc., the connection is firm, not easy to fall off, and there are more connection methods than other materials;

5. Selective performance: Thick-walled seamless pipes can be made into steel plates of different thicknesses and uses by selecting base materials of different thicknesses and surfacing alloy wear-resistant layers of different layers and thicknesses, and the maximum thickness can reach more than 30mm. ;

6. Simple processing: thick-walled seamless pipes can be processed into different sizes according to requirements, which can be processed, cold-formed, welded, bent, etc., and easy to use; they can be welded and formed on site, saving time, facilitating maintenance and replacement, and greatly reducing work intensity.

7. Cost-effective: The price of thick-walled seamless pipes is higher than that of ordinary materials, but considering the service life of the product, maintenance costs, spare parts costs, downtime losses and other factors, its cost-effectiveness is much higher than that of ordinary materials. Ordinary steel plate and other materials.

Of course, the above seven points are important features of thick-walled seamless pipes, and they also perform well in other aspects. For example, the zero heat treatment process for thick-walled seamless pipe cutting

The correct furnace installation and fabric during zero-cut heat treatment should ensure smooth airflow in the furnace, so that the thick-walled seamless pipe can be cut evenly, heated, and obtained uniform organization and performance. Generally, there is no limit to the furnace temperature when the furnace is installed, and it can be a cold furnace or a hot furnace.

The heating temperature should be determined according to the steel grade and heat treatment type, as well as the conditions of the heat treatment furnace and the charging distribution. After preliminary screening, it is recommended to pass the test verification. Various heat treatment methods. In addition to martensitic steels, other types of thick-walled seamless pipes generally heat up as quickly as possible. This not only shortens the heat treatment cycle and increases the productivity of the furnace, but also reduces the oxidation of thick-walled seamless tubes.

What are the processing characteristics of thick-walled seamless carbon steel pipes?

Dimensional stability. For high-precision seamless carbon steel pipes, high precision is required, so dimensional stability needs to be maintained. Due to straightening in air, the cooling rate is slow, so it has a stabilizing effect on austenite. It will increase the amount of retained austenite in the structure, so cold treatment is required.
Reduce quenching deformation. Due to the slenderness of the ms seamless tube, it is easy to deform during the quenching process, so its deformation should be strictly controlled. Heat treatment is a very critical process. In the process of quenching and cooling, timely straightening by using the plasticity of supercooled austenite is a key step to ensure the improvement of its pass rate. For this purpose, hot bath quenching or cooling in oil for a certain period of time should be carried out to bring out thermal calibration.
High hardness. The seamless steel pipe mainly bears the contact fatigue load, so it has high hardness, so it should be quenched or surface quenched or chemical heat treatment, etc., and then be tempered at low temperature.

In order to safely cut thick-walled seamless steel pipes, the following operations are recommended.

Mechanical cutting adopts two methods: exterior and interior. It uses the turning tool principle to cut and bevel the nozzle. The single machine has a large span and can process large thicknesses with less waste. The processing process does not generate high temperature, does not affect the pipe, and is conducive to welding. Water cutting processes the pipeline through the combined action of a high-pressure pump and emery. The incision is clean and the processing span is large, but the efficiency is low, and the processing thickness is severely limited.
Oxygen C2H2 flame cutting, by adjusting the oxygen valve [gate and C2H2 valve, changing the mixing ratio of oxygen and C2H2, three different flames are obtained: neutral flame, oxidation flame and carbonization flame.
Ion cutting and plasma cutting can use different working gases to cut various metals that are difficult to cut by oxygen cutting, especially non-ferrous metals (stainless steel, aluminum, copper, titanium, nickel), and the cutting effect is better: the main advantage is the cutting thickness When the metal is not large, the plasma cutting speed is fast, especially when cutting ordinary carbon steel sheets, the speed can reach 5~6 times that of the oxygen cutting method, the cutting surface is smooth, the thermal deformation is small, and the heat affected zone is small.

Application and characteristics of thick-walled seamless steel pipe

Thick-walled seamless steel pipes are widely used in vehicles, airlines, crude oil, chemical plants, engineering construction, heating furnaces, military and other units, and have a significant impact on the social economy. With the development trend of my country’s economy, the application field of thick-walled seamless steel pipes has continued to develop, the production scale and specifications have been greatly improved, and the requirements for product quality have become higher and higher. Therefore, thick-walled seamless steel pipes need to pass strict inspections before they leave the factory to meet the requirements of use.

The manufacturing level of thick-walled seamless steel pipes should consider the sales market and support the corresponding mechanical equipment. In the whole process of forging and cold rolling of seamless welded thick-walled seamless steel pipe of stainless steel plate, one of the main performance indicators considering the quality of seamless welded thick-walled seamless steel pipe is parallelism. Most thick-walled seamless steel pipes need to be straightened, and the high efficiency of skew roll straightening is the primary influence. However, for the top deformation of thick-walled seamless steel pipes and large-diameter thick-walled seamless steel pipes, the working pressure straightening method is often used.

The working pressure straightener has a simple and flexible structure. Due to the lack of theoretical research on work stress correction technology, old workers and teachers have always carried out experiments and corrections based on their own work experience. The work pressure correction accuracy is poor, the efficiency is low, and the labor efficiency is high. Therefore, analyzing the deformation behavior of the thick-walled seamless steel pipe in the whole straightening process and accurately calculating the straightening stroke arrangement are the prerequisites to ensure the straightening quality of the thick-walled seamless steel pipe, improve the straightening efficiency and design the scheme of the automatic straightening machine. condition.

In order to improve the corrosion resistance of the thick-walled seamless steel pipe and prolong the service life of the product, it is necessary to pickle and passivate the thick-walled seamless steel pipe to form a protective film on the surface.

1. Grinding and polishing of thick-walled seamless steel pipe branch pipe: After laser cutting, the plastic layer of the branch pipe should be polished with a polishing machine, which is to prevent the plastic layer from melting or even burning during flange welding, thereby damaging the pipe. Sand and polish the plastic layer of the branch with a polisher.

2. The solution to the plastic plating of thick-walled seamless steel pipe: After grinding, heat the pipe outside the pipe with O2 and C2H2 until a part of the plastic layer inside melts. Then the skilled worker wipes the branch pipe evenly with the prepared powder, pay attention to wipe it in time, and wipe the plastic coating of the flange sheet on the waterproof line. During the whole process, the heating temperature should be strictly controlled. If the temperature is too high, small air bubbles will appear during the plastic plating process. If the temperature is too low, the electrostatic powder will not melt completely during the plastic plating process. The above situation will definitely cause the plastic layer to fall off after the pipeline is put into use, and eventually part of the thick-walled seamless steel pipe of the pipeline will be corroded and damaged.

3. Laser cutting of thick-walled seamless steel pipe: According to the specific length of the pipe, the alloy saw and hand-held cutting machine are used for laser cutting of the pipe. When applying water welding in the laser cutting process, ensure the raw material. During laser cutting, flame-retardant and high-temperature resistant raw materials should be used as partitions on both sides of the fracture to maintain the original plastic layer of the raw materials.

4. Connection of thick-walled seamless steel pipe: After filling with plastic, connect the pipe to the pipe. During the whole connection process, add a rubber plate in the middle of the flange and fix the nut until it is closed.

Oxidation treatment method of thick-walled seamless steel pipe

The air oxide film on the surface of the thick-walled seamless steel pipe is thin and high in density, which is not easy to remove. Under normal circumstances, the thick-walled steel pipe will cause 0.2-0.3mm of oxide scale in the heat treatment equipment, and the casting defects in this range can be With the removal of galvanized iron by air oxidation, if the defects are not within this range, the surface defects on the billet will inevitably be brought into the final product if they are not treated in all aspects. Thick-walled seamless steel pipes generally cannot use flame to eliminate the surface defects of the billet. Flame elimination will cause changes in the composition and crystal phase composition of the area where the billet is eliminated, which will affect the corrosion resistance of the stainless steel sheet. Therefore, industrial equipment elimination is a widely effective method for the metal surface solution of stainless steel sheets. The general methods include air oxidation galvanized iron cleaning mechanical treatment, water explosion, shot blasting machine elimination.

1. Air oxidation galvanized iron cleaning mechanical treatment

The air oxidation galvanized iron cleaning machine is mainly composed of steel brush roller, controller equipment, high pressure water system, refrigeration system and clamping equipment. Two rollers with stainless steel wires (called steel brush rollers) are installed on the roller seat, and the steel brush rollers run at high speed in the opposite direction of the slab running. Surface air oxidation galvanized iron.

The air oxidation galvanized iron cleaning machine can use more steel grades, but the elimination of air oxidation galvanized iron is not thorough enough.

2. Water burst pool

The water blast pool uses the refrigerating and cooling circulating water at room temperature as the cooling chemical substance, puts the high-temperature billet into the water storage tank, and uses “water blast” to remove the air-oxidized galvanized iron on the surface of the billet. The basic concept is that when the water encounters the high-temperature billet, it vaporizes in an instant, resulting in a “water explosion”, resulting in a lot of high-pressure steam. The impact force of the steam acts on the surface of the billet to cause the air-oxidized galvanized iron to fall. In addition, the air-oxidized galvanized iron on the billet and its surface is greatly cooled by water under high temperature conditions, resulting in a shrinkage stress field. The specifications of the stress field are different between the billet and the air-oxidized galvanized iron on its surface.
Air-oxidized galvanized iron will crack and fall off.

The water explosion pool has low investment projects, less maintenance and low cost of production, processing and operation. However, fewer steel grades can be used, and only a part of austenitic stainless steel sheets, such as 301, 304 and other steel grades, can be used.

3. Elimination of shot blasting machine

Shot blasting machines are mostly used to eliminate air oxidation of galvanized iron on the surface of the billet. The shot blasting machine is mainly composed of a sandblasting and derusting room, a grinding rod, a sandblasting and derusting conveying system, a shot removal machine and equipment, a shot compensation device, a dust collector, an air inlet and an automatic control system for electrical equipment. The basic principle is to use the spring steel shot thrown by the shot blasting machine to destructively oxidize the surface of the galvanized iron to the surface of the billet to make it fall.

How to control the defects of the inner surface of the thick-walled seamless steel pipe?

1. In addition to metal oxides

Metal oxides are specified in a molten state when the mandrel is pre-threaded. Its range, etc. are strictly managed.

1) The powder particle size distribution of the metal oxide removing agent is generally specified at around 16 meshes.
2) The composition of sodium stearate in the metal oxide removal agent should be more than 12%, so that it can be fully ignited in the inner cavity of the capillary.
3) According to the total area of the inner surface of the capillary, the injection amount of the metal oxide removal agent is clearly defined, which is generally 1.5-2.0g/dm2. The amount of metal oxide removal used by the capillary gas generator with different diameters and lengths is different.

2. Main parameters of processing technology of gas generator

1) The working pressure of the gas generator should be matched with the diameter and length of the capillary tube, so as to ensure strong purging and sufficient ignition, and no metal oxide removal agent that is not completely ignited can be blown away from the capillary tube by the cyclone.

2) The purging time should be adjusted according to the immediate and length of the capillary tube, and it is the norm that no floating hydroxide in the capillary tube is blown out.

3) The relative height of the nozzle should be adjusted according to the diameter of the capillary to ensure good alignment. The nozzle should be cleaned once for each train. The seamless steel pipe manufacturer recommends that the nozzle should be removed for cleaning after long-term shutdown. In order to ensure that the metal oxide removal agent is evenly purged on the inner wall of the capillary, the optional equipment is used in the metal oxide removal agent removal process of the gas generator, and it is equipped with a rotating standard air pressure.

3. Mandrel lubrication

The actual effect of mandrel lubricating is not very good or the temperature of the mandrel lubricating fluid is too low, which will cause internal scab. In order to improve the temperature of the mandrel, the method of cooling the circulating water only once can be adopted. During the production process, the temperature of the mandrel should be strictly controlled to ensure that the surface temperature of the mandrel before painting the lubricant is 80-120 °C, and the temperature of the mandrel should not be higher than 120 °C for a long time, so as to ensure that the lubricating fluid on the surface before pre-piercing is dry and smooth. High density, the operator should check the lubrication of the mandrel from time to time.

The direct reason for the wide application of thick-walled steel pipes

When it comes to thick-walled seamless steel pipes, the first thing that will come to your mind is that the quality of the raw materials of this type of pipeline is excellent, which is also the characteristic of thick-walled steel pipes.

The quality of thick-walled steel pipes is the reason for the marketing promotion and development trend of such pipeline raw materials in the industrial processing industry, which is also determined by the complicated processing process of thick-walled steel pipes.

Thick-walled steel pipes are mainly used in pipeline transportation and can be used to transport some liquids, for example, some electric energy, crude oil, and some surface water transportation, which can all be completed with the help of thick-walled steel pipes. In modern society, thick-walled steel pipes The application industry and scope of the 16Mn thick-walled steel pipe is once again the main use is very common. Thick-walled steel pipes for general main purposes are cold-rolled from ordinary carbon steel, low-alloy tool steel or alloy tool steel, and have a large amount of processing. They are mainly used as pipelines or structural parts for transporting liquids. Thick-walled steel pipes made of this type of steel are widely used. It is used in every field such as metal briquetting machine, high pressure gas cylinder, boiler, organic fertilizer machinery and equipment, petroleum cracking, automobile half-shaft sleeve, diesel engine and so on.

Application and manufacturing process of thick-walled seamless steel pipe

The steel pipe with the ratio of the outer diameter of the steel pipe to the wall thickness is less than 20 is called the thick-walled steel pipe.

Application of thick-walled seamless steel pipe:

Mainly used as petroleum geological drilling pipe, cracking pipe for petrochemical industry, boiler pipe, bearing pipe and high-precision structural pipe for automobile, tractor, aviation, etc.

Manufacturing process of thick-walled seamless steel pipe:

Hot rolling (extruded seamless steel pipe): round tube billet → heating → perforation → three-roll cross-rolling, continuous rolling or extrusion → pipe removal → sizing (or diameter reduction) → cooling → straightening → hydraulic test (or flaw detection)→marking→warehousing

The raw material for rolling seamless tubes is a round tube blank, which is cut by a cutting machine into a billet with a length of about 1 meter, and sent to a furnace for heating through a conveyor belt. The billets are fed into the furnace and heated at about 1200 degrees Celsius. The fuel is hydrogen or acetylene. Furnace temperature control is a critical issue. After the round tube blank is released, it will be perforated by a pressure perforator. Generally, the more common punching machine is the conical roller punching machine. This kind of punching machine has high production efficiency, good product quality, large amount of perforation and expansion, and can wear a variety of steel grades.

After perforation, the round tube blank is successively cross-rolled, continuously rolled or extruded by three rolls. After extrusion, the tube should be removed and sizing. The sizing machine rotates into the steel billet at high speed through the conical drill bit to punch holes to form steel pipes. The inner diameter of the steel pipe is determined by the outer diameter of the drill bit of the sizing machine. After the steel pipe is sizing, it enters the cooling tower and is cooled by water spray. After the steel pipe is cooled, it will be straightened.