High-pressure boiler tubes are a type of boiler tubes and belong to the category of seamless pipes. The manufacturing method is the same as that of the seamless pipe, but there are strict requirements on the steel type used in the manufacture of the steel pipe. High-pressure boiler tubes are often under high temperature and high pressure conditions when used, and the tubes will be oxidized and corroded under the action of high-temperature flue gas and water vapor. Steel pipes are required to have high durable strength, high resistance to oxidation and corrosion, and good structural stability. High-pressure boiler tubes are mainly used to manufacture superheater tubes, reheater tubes, gas guide tubes, main steam tubes, etc. of high-pressure and ultra-high pressure boilers.
Classification of the use of high pressure boiler tubes
1. Heating surface tubes for low and medium pressure boilers (working pressure generally not greater than 5.88Mpa, working temperature below 450°C);
2. Used for heating surface pipes, economizers, superheaters, reheaters, petrochemical industry pipes, etc. of high-pressure boilers (working pressure is generally above 9.8Mpa and working temperature is between 450°C and 650°C).
Manufacture and use
1. Manufacturing method:
①Generally, the operating temperature of boiler tubes is below 450°C, and they are mainly made of carbon-structured steel hot-rolled tubes or cold-drawn tubes.
②High-pressure boiler tubes are often exposed to high-temperature and high-pressure conditions during use, and the tubes will be oxidized and corroded under the action of high-temperature flue gas and water vapor. Steel pipes are required to have high durable strength, high resistance to oxidation and corrosion, and good structural stability.
2. Purpose:
①General boiler tubes are mainly used to manufacture water wall tubes, boiling water tubes, superheated steam tubes, superheated steam tubes for locomotive boilers, large and small smoke tubes and arch brick tubes, etc.
②High-pressure boiler tubes are mainly used to manufacture superheater tubes, reheater tubes, gas guide tubes, main steam tubes, etc. of high-pressure and ultra-high pressure boilers.
3.The production process of high-pressure boiler tubes varies with different steel types. Taking pearlitic chromium molybdenum vanadium steel as an example, the production process characteristics of boiler tubes are:
①The tube blank should be peeled, and the peeling amount is usually 5mm;
②Due to the hard steel, the tube blank is often cut or sawed with oxygen;
③ Since the thermal conductivity of chrome-molybdenum-vanadium steel is lower than that of carbon steel, the heating rate should be slightly slower, the heating temperature is 1120-1180°C, and the piercing temperature is 1100-1160°C;
④This type of steel has good plasticity and low deformation resistance in the range of 1000-1100 ° C, so the perforation performance is better, and the deformation parameters can be selected according to medium carbon steel or alloy steel (such as 30CrMnSiA);
⑤ After rolling, the steel pipe should be normalized and tempered. The normalizing temperature is 950-980°C, the tempering temperature is 730-750°C, and the holding time is 2-3 hours;
⑥The dimensional tolerance of the steel pipe is relatively strict to ensure the butt joint welding; the length of the pipe is as long as possible to reduce the number of welding joints.
Thermal Processing Technology of High Pressure Boiler Tube
Heat treatment is a method that uses heating and cooling to change the physical properties of high-pressure boiler tubes. Heat treatment can improve the microstructure of high pressure boiler tubes to meet the required physical requirements. Toughness, hardness and wear resistance are some of the properties obtained by heat treatment. To obtain these properties, heat treatment operations such as quenching, tempering, annealing and case hardening are used.
1. Quenching: Heating the high-pressure boiler tube evenly to an appropriate temperature, and then quickly immersing it in water or oil to quench it, or cooling it in the air or in a freezing zone, so that the high-pressure boiler tube can obtain the required hardness.
2. Tempering - the high-pressure boiler tube will become brittle after hardening, and the stress caused by quenching and rapid cooling can cause the high-pressure boiler tube to break due to a light blow. To eliminate brittleness, tempering treatment can be used. Tempering is to reheat the high pressure boiler tube to the appropriate temperature or color and then quench it. Although the hardness of the high-pressure boiler tube is slightly reduced by tempering, it can increase the toughness of the high-pressure boiler tube and reduce its brittleness.
3. Annealing - Annealing is a method to eliminate the internal stress of high pressure boiler tubes. The annealing method is to heat the steel pipe above the critical temperature, then put it into dry ash, lime, asbestos or seal it in the furnace, and let it cool slowly.
4. Hardness: It is the ability of a material to resist the penetration of foreign objects. The most common way to test the hardness of high-pressure boiler tubes is to use a file to rub the edge of the workpiece, and the depth of the scratches on the surface can be used to determine the hardness. This method is called the file test method, which is not very scientific. Using a hardness tester to test extremely accurately is a common method for modern hardness testing. The most commonly used test method is the Rockwell hardness test. The Rockwell hardness testing machine uses the depth of diamond penetration into the metal to measure the hardness of the high-pressure boiler tube. The greater the penetration depth, the smaller the hardness. The depth of the diamond into the metal can be pointed out from the pointer to the correct number, which is called the Rockwell hardness number.
5. Forging: It is a method of forming metal into a certain shape by hammering. When the high-pressure boiler tube is heated to the forging temperature, it can be engaged in forging, bending, drawing, forming and other operations. Most high pressure boiler tubes are easily forged when heated to a vivid cherry red color.
6. Brittleness: It means that the high-pressure boiler tube is easy to break. The brittleness of cast iron is high, and it will break even if it falls to the ground. Brittleness is closely related to hardness, and steel pipes with high hardness are usually more brittle.
7. Ductility: It is the property that the metal is permanently deformed by external force without breaking. The ductile high-pressure boiler tube can be drawn into thin lines.
8. Elasticity: It is a property that the high-pressure boiler tube is deformed by external force and returns to its original shape when the external force is removed.
9. Hardness: It is a metal that resists penetration or cutting by foreign objects. A common method that can increase the hardness of high-pressure boiler tubes is quenching.
10. Ductility: Also known as malleability, it is another expression of metal ductility or softness. Ductility is the property of a metal not to crack when deformed by hammering or rolling.
11. Toughness: It is the ability of high-pressure boiler tubes to withstand vibration or impact. Toughness is the exact opposite of brittleness.
Classification of the use of high pressure boiler tubes
1. Heating surface tubes for low and medium pressure boilers (working pressure generally not greater than 5.88Mpa, working temperature below 450°C);
2. Used for heating surface pipes, economizers, superheaters, reheaters, petrochemical industry pipes, etc. of high-pressure boilers (working pressure is generally above 9.8Mpa and working temperature is between 450°C and 650°C).
Manufacture and use
1. Manufacturing method:
①Generally, the operating temperature of boiler tubes is below 450°C, and they are mainly made of carbon-structured steel hot-rolled tubes or cold-drawn tubes.
②High-pressure boiler tubes are often exposed to high-temperature and high-pressure conditions during use, and the tubes will be oxidized and corroded under the action of high-temperature flue gas and water vapor. Steel pipes are required to have high durable strength, high resistance to oxidation and corrosion, and good structural stability.
2. Purpose:
①General boiler tubes are mainly used to manufacture water wall tubes, boiling water tubes, superheated steam tubes, superheated steam tubes for locomotive boilers, large and small smoke tubes and arch brick tubes, etc.
②High-pressure boiler tubes are mainly used to manufacture superheater tubes, reheater tubes, gas guide tubes, main steam tubes, etc. of high-pressure and ultra-high pressure boilers.
3.The production process of high-pressure boiler tubes varies with different steel types. Taking pearlitic chromium molybdenum vanadium steel as an example, the production process characteristics of boiler tubes are:
①The tube blank should be peeled, and the peeling amount is usually 5mm;
②Due to the hard steel, the tube blank is often cut or sawed with oxygen;
③ Since the thermal conductivity of chrome-molybdenum-vanadium steel is lower than that of carbon steel, the heating rate should be slightly slower, the heating temperature is 1120-1180°C, and the piercing temperature is 1100-1160°C;
④This type of steel has good plasticity and low deformation resistance in the range of 1000-1100 ° C, so the perforation performance is better, and the deformation parameters can be selected according to medium carbon steel or alloy steel (such as 30CrMnSiA);
⑤ After rolling, the steel pipe should be normalized and tempered. The normalizing temperature is 950-980°C, the tempering temperature is 730-750°C, and the holding time is 2-3 hours;
⑥The dimensional tolerance of the steel pipe is relatively strict to ensure the butt joint welding; the length of the pipe is as long as possible to reduce the number of welding joints.
Thermal Processing Technology of High Pressure Boiler Tube
Heat treatment is a method that uses heating and cooling to change the physical properties of high-pressure boiler tubes. Heat treatment can improve the microstructure of high pressure boiler tubes to meet the required physical requirements. Toughness, hardness and wear resistance are some of the properties obtained by heat treatment. To obtain these properties, heat treatment operations such as quenching, tempering, annealing and case hardening are used.
1. Quenching: Heating the high-pressure boiler tube evenly to an appropriate temperature, and then quickly immersing it in water or oil to quench it, or cooling it in the air or in a freezing zone, so that the high-pressure boiler tube can obtain the required hardness.
2. Tempering - the high-pressure boiler tube will become brittle after hardening, and the stress caused by quenching and rapid cooling can cause the high-pressure boiler tube to break due to a light blow. To eliminate brittleness, tempering treatment can be used. Tempering is to reheat the high pressure boiler tube to the appropriate temperature or color and then quench it. Although the hardness of the high-pressure boiler tube is slightly reduced by tempering, it can increase the toughness of the high-pressure boiler tube and reduce its brittleness.
3. Annealing - Annealing is a method to eliminate the internal stress of high pressure boiler tubes. The annealing method is to heat the steel pipe above the critical temperature, then put it into dry ash, lime, asbestos or seal it in the furnace, and let it cool slowly.
4. Hardness: It is the ability of a material to resist the penetration of foreign objects. The most common way to test the hardness of high-pressure boiler tubes is to use a file to rub the edge of the workpiece, and the depth of the scratches on the surface can be used to determine the hardness. This method is called the file test method, which is not very scientific. Using a hardness tester to test extremely accurately is a common method for modern hardness testing. The most commonly used test method is the Rockwell hardness test. The Rockwell hardness testing machine uses the depth of diamond penetration into the metal to measure the hardness of the high-pressure boiler tube. The greater the penetration depth, the smaller the hardness. The depth of the diamond into the metal can be pointed out from the pointer to the correct number, which is called the Rockwell hardness number.
5. Forging: It is a method of forming metal into a certain shape by hammering. When the high-pressure boiler tube is heated to the forging temperature, it can be engaged in forging, bending, drawing, forming and other operations. Most high pressure boiler tubes are easily forged when heated to a vivid cherry red color.
6. Brittleness: It means that the high-pressure boiler tube is easy to break. The brittleness of cast iron is high, and it will break even if it falls to the ground. Brittleness is closely related to hardness, and steel pipes with high hardness are usually more brittle.
7. Ductility: It is the property that the metal is permanently deformed by external force without breaking. The ductile high-pressure boiler tube can be drawn into thin lines.
8. Elasticity: It is a property that the high-pressure boiler tube is deformed by external force and returns to its original shape when the external force is removed.
9. Hardness: It is a metal that resists penetration or cutting by foreign objects. A common method that can increase the hardness of high-pressure boiler tubes is quenching.
10. Ductility: Also known as malleability, it is another expression of metal ductility or softness. Ductility is the property of a metal not to crack when deformed by hammering or rolling.
11. Toughness: It is the ability of high-pressure boiler tubes to withstand vibration or impact. Toughness is the exact opposite of brittleness.
