High-Frequency Welded Pipe Production Process
High-Frequency Welded Pipe Production Process
Figure 5-1 illustrates the production process of a small high-frequency straight seam continuous electric welded pipe, without a tension reducer. The high-frequency electric welded pipe units typically use cold-rolled or hot-rolled coils as raw materials. Before forming, the material undergoes flash butt welding after being unwound, straightened, leveled, and cut. It is then molded and welded in the forming machine. When necessary, trimming is performed to ensure that the strip maintains consistent width along its length, resulting in a uniform weld gap and improved weld quality. To enable continuous forming and welding, not only is a head device for butt welding required, but also a looper device. Common types of strip loopers used in electric welded pipe units include pit-type, overhead, cage-type, tunnel-type, and spiral-type. Among these, the spiral looper is most widely used in modern continuous welded pipe units.
After forming and welding, internal and external burrs are removed from the steel pipe. External burrs are typically scraped off and smoothed with rollers, while internal burrs require a specialized device. The weld is then cooled using water, which helps maintain the structural properties of the weld and prevents deformation during sizing. Since the steel pipe is subjected to heat during welding, proper cooling is essential to ensure stability and quality.
Figure 5-1: Schematic of the production process for φ0.3–168.3 mm small high-frequency straight seam continuous electric welded pipe
1 – Belt coil; 2 – Leveling; 3 – Cut head butt welding; 4 – One looper; 5 – Forming machine; 6 – Welding; 7 – Remove internal and external burrs; 8 – Cooling; 9 – Sizing; 11 – Straightening; 12 – Eddy current testing; 13 – Flat end; 14 – Hydraulic test; 15 – Inspection; 16 – Printing; 17 – Oiling; 18 – Packaging
The outer diameter and roundness of the finished pipe are critical for ensuring good weld quality and straightness. After welding, the steel pipe must undergo cold sizing. Once sized, it is cut close to the desired final length, then straightened on a straightening machine. The pipe ends are processed on a flat-end machine to ensure accurate length. Finally, the pipe goes through finishing processes such as hydrostatic testing, inspection, coating (or galvanization), and packaging before being stored.
In small and medium-diameter electric welding units, a tension reducer can be added to improve productivity, reduce roll changes, increase operational efficiency, expand product specifications, and enhance product quality. After the sizing and cutting process, a reheating furnace, tension reducing machine, and flying saw are installed. The pipe is then further processed as described above.
The straight seam electric welded pipe unit consists of three main sections: blank preparation, forming, welding, and sizing, and finishing. The blank preparation section includes an unwinder, leveler, shear butt welder, looper, edge processing device, and full-width ultrasonic flaw detection. The forming and welding section contains forming machines, welding equipment, burr removal devices, weld heat treatment systems, sizing machines, and straightening heads. The finishing section focuses on machining, repair, and inspection of semi-finished products. Equipment selection depends on design scale, product plan, technical requirements, construction budget, raw material availability, and energy conditions.
(1) The blank preparation section is similar to that of a cold-formed steel unit. For more details, refer to the composition and main equipment of the 3.3 strip preparation section.
1. Unwinder: There are various models of unwinders, with the double-cone type being the most common. To ensure smooth steel plate feeding, the unwinder should have a centering slide. It should also be able to unwind in two directions to meet welding requirements for one-cut slitting.
2. Steel Plate Leveling: The raw material for ERW welded pipe is steel coil. Due to the low curvature and consistent bending direction, the leveling machine usually has fewer rollers—typically five. The roller spacing is increased, the diameter is thickened, and support rollers are removed to simplify the structure and enhance functionality. Modern models often integrate pre-leveling delivery rollers and leveling rollers into a single frame, with hydraulic cylinders for opening and closing, synchronized operation, and adjustable pressing rollers.
3. Shear Butt Welding: This process joins the tail and head of the steel strip, working with the looper to ensure continuous welding. Advanced ERW units may use a slanted seam pattern, where the butt weld is angled relative to the strip’s centerline. Welding methods include CO2 gas shielded welding, submerged arc welding, flash welding, and manual arc welding. A hydraulic shearing machine is used to cut the strip’s ends. Cutting methods can be upper, lower, or both. The blade angle is approximately 3 degrees.
4. Strip Edge Processing: To ensure consistent width and proper edge alignment for welding, the strip edges may need trimming or milling. If the material is slit, care must be taken to avoid mechanical damage during transport. Online disc shearing may leave rough edges, requiring additional planning or light milling. Otherwise, uneven edges could lead to poor weld quality. If in-line milling is used, small burrs at the corners may cause sparking during welding, so they are removed afterward.
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High-Frequency Welded Pipe Production Process
Figure 5-1 illustrates the production process of a small high-frequency straight seam continuous electric welded pipe, without a tension reducer. The high-frequency electric welded pipe units typically use cold-rolled or hot-rolled coils as raw materials. Before forming, the material undergoes flash butt welding after being unwound, straightened, leveled, and cut. It is then molded and welded in the forming machine. When necessary, trimming is performed to ensure that the strip maintains consistent width along its length, resulting in a uniform weld gap and improved weld quality. To enable continuous forming and welding, not only is a head device for butt welding required, but also a looper device. Common types of strip loopers used in electric welded pipe units include pit-type, overhead, cage-type, tunnel-type, and spiral-type. Among these, the spiral looper is most widely used in modern continuous welded pipe units.
After forming and welding, internal and external burrs are removed from the steel pipe. External burrs are typically scraped off and smoothed with rollers, while internal burrs require a specialized device. The weld is then cooled using water, which helps maintain the structural properties of the weld and prevents deformation during sizing. Since the steel pipe is subjected to heat during welding, proper cooling is essential to ensure stability and quality.
Figure 5-1: Schematic of the production process for φ0.3–168.3 mm small high-frequency straight seam continuous electric welded pipe
1 – Belt coil; 2 – Leveling; 3 – Cut head butt welding; 4 – One looper; 5 – Forming machine; 6 – Welding; 7 – Remove internal and external burrs; 8 – Cooling; 9 – Sizing; 11 – Straightening; 12 – Eddy current testing; 13 – Flat end; 14 – Hydraulic test; 15 – Inspection; 16 – Printing; 17 – Oiling; 18 – Packaging
The outer diameter and roundness of the finished pipe are critical for ensuring good weld quality and straightness. After welding, the steel pipe must undergo cold sizing. Once sized, it is cut close to the desired final length, then straightened on a straightening machine. The pipe ends are processed on a flat-end machine to ensure accurate length. Finally, the pipe goes through finishing processes such as hydrostatic testing, inspection, coating (or galvanization), and packaging before being stored.
In small and medium-diameter electric welding units, a tension reducer can be added to improve productivity, reduce roll changes, increase operational efficiency, expand product specifications, and enhance product quality. After the sizing and cutting process, a reheating furnace, tension reducing machine, and flying saw are installed. The pipe is then further processed as described above.
The straight seam electric welded pipe unit consists of three main sections: blank preparation, forming, welding, and sizing, and finishing. The blank preparation section includes an unwinder, leveler, shear butt welder, looper, edge processing device, and full-width ultrasonic flaw detection. The forming and welding section contains forming machines, welding equipment, burr removal devices, weld heat treatment systems, sizing machines, and straightening heads. The finishing section focuses on machining, repair, and inspection of semi-finished products. Equipment selection depends on design scale, product plan, technical requirements, construction budget, raw material availability, and energy conditions.
(1) The blank preparation section is similar to that of a cold-formed steel unit. For more details, refer to the composition and main equipment of the 3.3 strip preparation section.
1. Unwinder: There are various models of unwinders, with the double-cone type being the most common. To ensure smooth steel plate feeding, the unwinder should have a centering slide. It should also be able to unwind in two directions to meet welding requirements for one-cut slitting.
2. Steel Plate Leveling: The raw material for ERW welded pipe is steel coil. Due to the low curvature and consistent bending direction, the leveling machine usually has fewer rollers—typically five. The roller spacing is increased, the diameter is thickened, and support rollers are removed to simplify the structure and enhance functionality. Modern models often integrate pre-leveling delivery rollers and leveling rollers into a single frame, with hydraulic cylinders for opening and closing, synchronized operation, and adjustable pressing rollers.
3. Shear Butt Welding: This process joins the tail and head of the steel strip, working with the looper to ensure continuous welding. Advanced ERW units may use a slanted seam pattern, where the butt weld is angled relative to the strip’s centerline. Welding methods include CO2 gas shielded welding, submerged arc welding, flash welding, and manual arc welding. A hydraulic shearing machine is used to cut the strip’s ends. Cutting methods can be upper, lower, or both. The blade angle is approximately 3 degrees.
4. Strip Edge Processing: To ensure consistent width and proper edge alignment for welding, the strip edges may need trimming or milling. If the material is slit, care must be taken to avoid mechanical damage during transport. Online disc shearing may leave rough edges, requiring additional planning or light milling. Otherwise, uneven edges could lead to poor weld quality. If in-line milling is used, small burrs at the corners may cause sparking during welding, so they are removed afterward.
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