High-Frequency Welded Pipe Production Process
High-Frequency Welded Pipe Production Process
Figure 5-1 shows a schematic of the production process for small high-frequency straight-seam continuous electric welded pipes (without a tension reducer). These units typically use cold-rolled or hot-rolled coils as raw materials. Before forming, the material undergoes processes such as unwinding, straightening, leveling, cutting, and end butt welding. After that, it is molded and welded in the forming machine. If necessary, trimming is applied to ensure consistent width along the length of the strip, resulting in a uniform weld gap and improved weld quality. To maintain continuous forming and welding, not only a butt welding device for coil ends is 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 electric welded pipe units.
Once the steel pipe is formed and welded, internal and external burrs are removed. External burrs are usually scraped off first and then smoothed with rollers, while internal burrs require a specialized device. The weld is then cooled using water. The purpose of this cooling is to ensure the structural properties of the weld and prevent deformation during sizing. Since the steel pipe is subjected to heat during welding, it must be carefully controlled to maintain its integrity.
Figure 5-1: Small high-frequency straight-seam continuous electric welded pipe production process for diameters ranging from φ0.3 to φ168.3 mm
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 accuracy and roundness of the finished pipe help improve weld quality and ensure straightness. The welded steel pipe must go through cold sizing. After sizing, the pipe is cut close to the final length and then straightened on a straightening machine. The pipe ends are processed on a flat-end machine to ensure proper length. Finally, the finished pipe goes through a series of finishing processes such as hydrostatic testing, inspection, coating (or galvanization), and packaging before being stored.
In small and medium-diameter electric welding units, to enhance productivity, reduce roll changes, increase operational efficiency, expand product specifications, and improve quality, a tension reducer can be added. After the sizing and cutting stage, a reheating furnace, a tension reducing machine, and a flying saw are introduced. The pipe is further processed through the previously mentioned finishing steps.
The straight-seam electric welded pipe unit consists of three main sections: blank preparation, forming, welding, and sizing, and the finishing section. The blank preparation section includes an unwinder, a leveler, a shear butt welder, a looper, edge processing equipment, and full-width ultrasonic flaw detection. The forming and welding section includes forming machines, welding equipment, burr removal devices, weld heat treatment systems, sizing machines, and straightening heads. The finishing section focuses on machining, repairing, and inspecting semi-finished products. The selection of key equipment depends on factors such as design scale, product plan, technical conditions, construction budget, and availability of raw materials and energy.
(1) The blank preparation section is largely similar to that of a cold-formed steel preparation system. 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 most being double-cone type. To ensure smooth steel plate feeding, the unwinder should have a centering slide for the coil. It should also be capable of unwinding in two directions to meet the requirements for one-cut and slitting operations.
2. Steel Plate Leveling: The raw material for ERW welded pipes is steel coils. The curvature of the strip is small, and the bending direction is consistent, gradually becoming smoother. Due to the relatively thick material, the leveling machine in ERW units typically has fewer leveling rollers—often five in total—with larger roller spacing and diameter, and no support rollers, simplifying the structure and making it more specialized. Modern models often integrate the pre-leveling delivery roller and the leveling roller into a single frame, allowing the hydraulic cylinder to open and close while maintaining synchronization. The five-roll leveling system may consist of three, two, or a combination of two and three rolls, with the lower amount adjusted manually or electrically. However, it should have the function of mechanical synchronization for the pressing rollers to ensure that the strip remains slack when aligning the head.
3. Shear Butt Welding: This process joins the tail and head of the steel strip and works with the looper to keep the welding process continuous. In advanced ERW units, a slanted seam pattern is used so that the butt weld is at an angle relative to the strip’s centerline. ERW units can use CO2 gas-shielded welding, submerged arc welding, flash welding, or manual arc welding for the head. A hydraulic shearing machine is used to cut the head and tail of the strip. The cutting method can be upper, lower, or both upper and lower. The blade angle is typically around 3 degrees.
4. Strip Edge Processing: To ensure consistent width and meet the requirements of the welded pipe, the edges of the strip must be trimmed or milled. If the material is slit, care must be taken to avoid mechanical damage to the edges during transport to the welding line. If online disc shearing is used, the edges may be rough and usually need to be planed or slightly milled. Otherwise, uneven edges after trimming could lead to poor weld quality. If in-line milling is used, small burrs may form at the corners of the edges, which could cause sparking during welding. Therefore, any small burrs on the edge of the steel strip are cleaned after milling.
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High-Frequency Welded Pipe Production Process
Figure 5-1 shows a schematic of the production process for small high-frequency straight-seam continuous electric welded pipes (without a tension reducer). These units typically use cold-rolled or hot-rolled coils as raw materials. Before forming, the material undergoes processes such as unwinding, straightening, leveling, cutting, and end butt welding. After that, it is molded and welded in the forming machine. If necessary, trimming is applied to ensure consistent width along the length of the strip, resulting in a uniform weld gap and improved weld quality. To maintain continuous forming and welding, not only a butt welding device for coil ends is 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 electric welded pipe units.
Once the steel pipe is formed and welded, internal and external burrs are removed. External burrs are usually scraped off first and then smoothed with rollers, while internal burrs require a specialized device. The weld is then cooled using water. The purpose of this cooling is to ensure the structural properties of the weld and prevent deformation during sizing. Since the steel pipe is subjected to heat during welding, it must be carefully controlled to maintain its integrity.
Figure 5-1: Small high-frequency straight-seam continuous electric welded pipe production process for diameters ranging from φ0.3 to φ168.3 mm
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 accuracy and roundness of the finished pipe help improve weld quality and ensure straightness. The welded steel pipe must go through cold sizing. After sizing, the pipe is cut close to the final length and then straightened on a straightening machine. The pipe ends are processed on a flat-end machine to ensure proper length. Finally, the finished pipe goes through a series of finishing processes such as hydrostatic testing, inspection, coating (or galvanization), and packaging before being stored.
In small and medium-diameter electric welding units, to enhance productivity, reduce roll changes, increase operational efficiency, expand product specifications, and improve quality, a tension reducer can be added. After the sizing and cutting stage, a reheating furnace, a tension reducing machine, and a flying saw are introduced. The pipe is further processed through the previously mentioned finishing steps.
The straight-seam electric welded pipe unit consists of three main sections: blank preparation, forming, welding, and sizing, and the finishing section. The blank preparation section includes an unwinder, a leveler, a shear butt welder, a looper, edge processing equipment, and full-width ultrasonic flaw detection. The forming and welding section includes forming machines, welding equipment, burr removal devices, weld heat treatment systems, sizing machines, and straightening heads. The finishing section focuses on machining, repairing, and inspecting semi-finished products. The selection of key equipment depends on factors such as design scale, product plan, technical conditions, construction budget, and availability of raw materials and energy.
(1) The blank preparation section is largely similar to that of a cold-formed steel preparation system. 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 most being double-cone type. To ensure smooth steel plate feeding, the unwinder should have a centering slide for the coil. It should also be capable of unwinding in two directions to meet the requirements for one-cut and slitting operations.
2. Steel Plate Leveling: The raw material for ERW welded pipes is steel coils. The curvature of the strip is small, and the bending direction is consistent, gradually becoming smoother. Due to the relatively thick material, the leveling machine in ERW units typically has fewer leveling rollers—often five in total—with larger roller spacing and diameter, and no support rollers, simplifying the structure and making it more specialized. Modern models often integrate the pre-leveling delivery roller and the leveling roller into a single frame, allowing the hydraulic cylinder to open and close while maintaining synchronization. The five-roll leveling system may consist of three, two, or a combination of two and three rolls, with the lower amount adjusted manually or electrically. However, it should have the function of mechanical synchronization for the pressing rollers to ensure that the strip remains slack when aligning the head.
3. Shear Butt Welding: This process joins the tail and head of the steel strip and works with the looper to keep the welding process continuous. In advanced ERW units, a slanted seam pattern is used so that the butt weld is at an angle relative to the strip’s centerline. ERW units can use CO2 gas-shielded welding, submerged arc welding, flash welding, or manual arc welding for the head. A hydraulic shearing machine is used to cut the head and tail of the strip. The cutting method can be upper, lower, or both upper and lower. The blade angle is typically around 3 degrees.
4. Strip Edge Processing: To ensure consistent width and meet the requirements of the welded pipe, the edges of the strip must be trimmed or milled. If the material is slit, care must be taken to avoid mechanical damage to the edges during transport to the welding line. If online disc shearing is used, the edges may be rough and usually need to be planed or slightly milled. Otherwise, uneven edges after trimming could lead to poor weld quality. If in-line milling is used, small burrs may form at the corners of the edges, which could cause sparking during welding. Therefore, any small burrs on the edge of the steel strip are cleaned after milling.
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Hubei Chengze Diamod Products Co., Ltd. , https://www.ryomaltools.com