Straight seam steel pipes are steel pipes where the weld seam is parallel to the longitudinal direction of the pipe. They are typically classified into metric welded steel pipes, welded thin-walled pipes, transformer cooling oil pipes, etc. Straight seam welded steel pipes have a simple production process, high production efficiency, low cost, and rapid development. Spiral welded steel pipes generally have higher strength than straight seam welded steel pipes, and can produce welded steel pipes with larger diameters using narrower blanks, and can also produce welded steel pipes with different diameters using blanks of the same width. However, compared with straight seam steel pipes of the same length, the weld seam length increases by 30-100%, and the production speed is lower.
First, troubleshooting straight seam steel pipes:
1. Misalignment. This is a common problem in pre-welding. Excessive misalignment directly leads to the downgrading or scrapping of the steel pipe. Therefore, the amount of misalignment needs to be strictly controlled during pre-welding. When the entire or most of a steel pipe billet exhibits excessive edge misalignment, it is usually due to:
① Inadequate adjustment of the opening seam;
② Inadequate adjustment of the closing seam pressure rollers (incorrect circumferential angle of the pressure rollers, or asymmetry between the left and right pressure rollers with the billet centerline as the axis, or inconsistent radial elongation of the relative pressure rollers), resulting in incomplete rounding;
③ Inadequate pre-bending of the pre-bent edge, causing the plate edge to appear as a straight edge.
When the beginning or end of the billet exhibits excessive edge misalignment, it is usually due to:
① Incorrect position of the inlet and outlet roller conveyors;
② Incorrect centering of the ring frame;
③ Poor rounding of the closing seam pressure rollers, with positional errors in individual pressure rollers;
④ Poor forming (significant difference in concavity and convexity at both ends of the formed billet;
⑤ Opening seam width exceeding 150mm);
⑥ Pressure fluctuations in the hydraulic system.
2. Backside weld beads and burn-through. Removing backside weld beads is time-consuming and affects the normal production process; not removing them affects the forming of the inner weld and the tracking of the inner weld seam. Burn-through affects the internal and external welds and requires repair.
The causes of back weld beads and burn-through are usually:
① Loose joint, possibly due to insufficient hydraulic system pressure;
② Poor weld formation, with large roundness errors;
③ Inappropriate selection of pre-welding parameters. The welding current and arc voltage must be matched with an appropriate welding speed. Excessive heat input or insufficient welding speed easily leads to back weld beads and burn-through.
3. Porosity. Porosity in the pre-weld leads to internal defects in the internal and external welds.
Porosity in the pre-weld is usually caused by:
① Inadequate shielding gas, such as high moisture content, insufficient pressure, or flow rate;
② Some blockage in the welding machine, resulting in uneven shielding gas distribution and the introduction of harmful gases;
③ Rust, oil, etc., on the bevel.
4. Poor weld formation. Poor weld formation affects subsequent internal and external weld tracking, impacts the stability of the welding process, and ultimately affects the final weld. Weld formation is closely related to heat input. Increased welding current, arc voltage, and welding speed reduce weld penetration and width, resulting in poor weld formation. Porosity in the weld also frequently leads to poor weld formation.
5. Spatter. Spatter during pre-welding easily burns the surface of the steel pipe or the bevel, and is difficult to remove, thus affecting the welding and the outer surface of the steel pipe.
The main cause of spatter is incorrect shielding gas composition or technical parameters. The proportion of argon in the shielding gas should be adjusted.
Second, Straight Seam Steel Pipe Production Technology:
1. The production of straight seam steel pipes can be divided into two periods: the forming period and the post-forming manufacturing period. Foreign large-diameter self-seam submerged arc welded steel pipe production is divided into four types according to the forming method: UOE forming, roll forming, progressive die forming, and progressive bending forming. After the forming period is completed, the subsequent manufacturing period of large-diameter self-seam steel pipes includes a series of fundamentally similar processes.
2. Processing the weld bevel at the plate edge. There are two processing methods: milling and planing. One or more milling or planing heads can be used on both sides of the plate. Depending on the plate thickness, the bevel can be machined into an I-shape, a single V-shape with a blunt edge, or a double V-shape. For exceptionally thick steel pipes, the outer seam can be milled into a U-shape to reduce welding material consumption and improve productivity, while the wider root prevents welding defects. Tack welding, also known as pre-welding, is usually performed using CO2 gas shielded welding. Its purpose is to stabilize the steel pipe, which is particularly useful for subsequent submerged arc welding, preventing burn-through.
3. To quickly identify welding defects, wave and X-ray inspections are performed immediately after welding. Defects are repaired promptly. After welding, the roundness and straightness of the steel pipe often do not meet the relevant specifications and technical requirements. Sizing and straightening are performed at the pipe manufacturing plant using mechanical cold expansion methods. The test pressure can reach over 90% of the steel pipe material’s yield strength.
Post time: Dec-10-2025