Electric welded steel pipes for low and medium pressure boilers
Electric-welded steel pipes for low- and medium-pressure boilers are specifically used to manufacture components such as heating surface tubes, economizer tubes, and superheater tubes in low- and medium-pressure boilers. Operating pressures typically do not exceed 5.9 MPa, and operating temperatures are below 450°C. They play a vital role in industrial boilers and power plant boilers. These pipes are made from high-quality carbon structural steel or low-alloy structural steel, such as No. 20 steel and 16Mn steel, using high-frequency welding or submerged arc welding. They exhibit high strength, excellent ductility, and weldability, and can withstand the pressure and temperature fluctuations associated with boiler operation, ensuring safe and stable operation.
In terms of production technology, the manufacture of electric-welded steel pipes for low- and medium-pressure boilers requires strict process control to ensure product quality. First, qualified steel strips are selected as raw material. The chemical composition, mechanical properties, and surface quality of the steel strips are rigorously inspected to ensure they meet standard requirements. Subsequently, the steel strips undergo slitting and forming processes before being processed into tubular shapes. During the forming process, the roundness and straightness of the tube blanks must be ensured to prepare for subsequent welding. Welding is a key step, and currently the two main methods used are high-frequency induction welding and submerged arc welding. High-frequency induction welding uses the resistance heat generated by high-frequency current to melt the edges of the tube blanks. The tubes are then squeezed together using extrusion rollers and welded together. This method is characterized by high production efficiency and high weld quality. Submerged arc welding, on the other hand, is performed under a layer of flux and is suitable for the production of large-diameter steel pipes, resulting in high weld strength. After welding, the steel pipes undergo deburring, sizing, and straightening processes to ensure dimensional accuracy and straightness. In addition, heat treatment is required to eliminate welding stress and improve weld structure. Normalizing is typically used, heating the steel pipe to 850-920°C, holding it for a period of time, and then air-cooling it to achieve more uniform and stable mechanical properties. Finally, the finished steel pipe undergoes hydrostatic testing and non-destructive testing (such as ultrasonic testing and eddy current testing) to ensure it is leak-free and free of internal defects, meeting service requirements.
Electric-welded steel pipes for low- and medium-pressure boilers possess a range of performance characteristics tailored to the boiler’s operating environment. First, sufficient strength is a core requirement, with a tensile strength of 335-570 MPa and a yield strength of no less than 195 MPa to withstand the pressure within the boiler and prevent plastic deformation or cracking. Second, good plasticity and toughness ensure a certain degree of deformation during installation and use, with an elongation of greater than 20% to avoid cracking caused by temperature fluctuations or vibration. Third, excellent welding performance ensures the quality of the steel pipe splicing during boiler installation, with weld strength no less than 80% of the parent material strength. Fourth, a certain degree of corrosion resistance enables long-term use in the water vapor environment within the boiler, reducing damage caused by oxidative corrosion. Fifth, precise dimensional accuracy, with an outer diameter tolerance within ±0.5 mm and a wall thickness tolerance within ±10%, ensures accurate assembly with other boiler components.
Electric-welded steel pipes for low- and medium-pressure boilers have a wide range of applications. In industrial boilers, they are often used to manufacture heating surface tubes such as water-wall tubes and convection tube bundles. These tubes come into direct contact with the flame, absorbing heat and transferring it to the water within, turning it into steam. In power plant boilers, they are used in economizer tubes and low-temperature superheater tubes. Economizer tubes utilize flue gas heat from the boiler’s exhaust to heat the feedwater, improving boiler efficiency, while low-temperature superheater tubes heat saturated steam to a desired temperature. In waste heat boilers, they serve as heating surface tubes to recover waste heat from industrial production, generating steam for power generation or heating. Furthermore, electric-welded steel pipes for low- and medium-pressure boilers can also be used in other heat exchange equipment with similar operating conditions, such as heat exchanger tubes. With industrial development and increasing energy demand, the application range of low- and medium-pressure boilers continues to expand, and the demand for electric-welded steel pipes is also growing.
Industry trends indicate that the production of electric-welded steel pipes for low- and medium-pressure boilers is moving toward high quality, high specifications, and environmentally friendly production. To improve boiler efficiency and safety, the quality requirements for steel pipes are becoming increasingly stringent. By optimizing welding processes and improving heat treatment technologies, weld quality and the stability of the pipe’s mechanical properties are being enhanced, reducing defects. In terms of specifications, demand for large-diameter, thick-walled electric-welded steel pipes for low- and medium-pressure boilers is increasing to accommodate the development of larger boilers. Currently, pipes with an outer diameter of 325 mm or greater and a wall thickness of 20 mm or greater are being produced. Furthermore, the use of low-alloy, high-strength steels, such as 12Cr1MoV, is increasing. These alloys offer superior high-temperature strength and corrosion resistance, making them suitable for operating in higher-temperature environments. Green production is also a key development direction, minimizing the environmental impact of the production process through the use of energy-saving equipment, recycling scrap steel and water resources, and reducing pollutant emissions. In the future, with the advancement of energy-saving and emission reduction policies and the upgrading of boiler technology, even higher performance and quality requirements for electric-welded steel pipes for low- and medium-pressure boilers will be placed, driving the industry to achieve greater progress in material research and development, process innovation, and other areas.
