Straight seam welded steel pipes are steel pipes where the weld seam is parallel to the longitudinal direction of the pipe. They are generally classified into metric electric welded steel pipes, electric welded thin-walled pipes, transformer cooling oil pipes, etc. The production process of straight seam welded steel pipes is simple, with 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.
1. Misalignment in straight seam welded steel pipes: 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. (1) When the entire or most of a steel pipe billet exhibits excessive misalignment, it is usually due to:
① Inadequate adjustment of the opening seam;
② Inadequate adjustment of the closing seam pressure roller (incorrect circumferential angle of the pressure roller, or asymmetry between the left and right pressure rollers with the center line of the steel pipe billet 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.
(2) When the head or tail of the steel pipe billet exhibits excessive 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 roller, with positional error of a single pressure roller;
④ Poor forming (significant difference in concavity and convexity at both ends of the formed steel pipe billet;
⑤ Opening seam width exceeding 150mm);
⑥ Pressure fluctuations in the hydraulic system.
2. Backside weld beads and burn-through in straight seam steel pipes: Removing backside weld beads is time-consuming and disrupts the normal production process; leaving them on affects the internal weld formation and monitoring. Burn-through affects both the inner and outer welds, requiring rework. The causes of backside weld beads and burn-through are usually: ① Loose joint, possibly due to insufficient hydraulic system pressure; ② Poor forming, large roundness error; ③ Inappropriate selection of pre-welding parameters. The welding current and arc voltage must be matched with an appropriate welding speed. Excessive linear energy or insufficient welding speed easily leads to backside weld beads and burn-through.
3. Porosity in straight seam steel pipes: Porosity in the pre-weld leads to internal defects in both the inner and outer welds. Porosity in the pre-weld is usually caused by: ① Inadequate shielding gas, such as high moisture content, insufficient pressure, or flow; 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 in straight seam steel pipes: Poor weld formation affects subsequent internal and external welding tracking, impacts the stability of the welding process, and ultimately affects the weld itself. Weld formation is closely related to heat input; increasing welding current, arc voltage, and welding speed reduces weld penetration and width, resulting in poor weld formation. Poor weld formation also frequently occurs when porosity forms in the weld.
5. Spatter in straight seam steel pipes: 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.
Post time: Feb-28-2026