What are the troubleshooting procedures in the production of straight seam welded steel pipes

Straight seam welded steel pipes are steel pipes where the weld seam is parallel to the longitudinal direction of the pipe. They are typically classified into metric electric welded steel pipes, electric welded thin-walled steel 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 be produced with narrower blanks to produce welded steel pipes with larger diameters, and can also be produced with blanks of the same width to produce welded steel pipes with different diameters. However, compared with straight seam steel pipes of the same length, the weld seam length of straight seam steel pipes increases by 30% to 100%, and the production speed is lower.

Troubleshooting in the production of straight seam welded steel pipes:

1. Misalignment in straight seam welded steel pipes.

This is a common problem in the pre-welding of straight seam welded steel pipes. Excessive misalignment directly leads to the downgrading or scrapping of the straight seam welded steel pipe. Therefore, the amount of misalignment needs to be strictly controlled during the pre-welding of straight seam welded steel pipes. When the entire or most of a straight seam 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's center line as the axis, or inconsistent radial elongation of the opposite 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 positioning of the inlet and outlet roller conveyors;

② Incorrect centering of the ring frame;

③ Poor rounding of the closing seam pressure rollers, or positional error of a single pressure roller;

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 in straight seam steel pipes.

Removing backside weld beads is time-consuming and disrupts the normal production process; leaving them unremoved affects the internal weld formation and the tracking of the straight seam steel pipe weld. 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 formation, large roundness error;

③ Inappropriate selection of pre-welding technical 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-welded straight seam steel pipe welds causes internal defects in both the inner and outer welds. Porosity in the weld of pre-welded straight seam steel pipes is usually caused by:

① Inadequate shielding gas, such as excessive moisture, insufficient pressure, or flow rate;

② Blockage in the welding machine, resulting in uneven shielding gas distribution and the introduction of harmful gases;

③ Rust, oil, or other contaminants on the bevel.

4. Poor weld formation in straight seam steel pipes.

Poor weld formation in straight seam steel pipes affects subsequent internal and external welding tracking, impacts the stability of the welding process, and ultimately affects the weld itself. Weld formation in straight seam steel pipes is closely related to the heat input. Increased welding current, arc voltage, and welding speed reduce the weld penetration and width, leading to poor weld formation. Poor weld formation is also a common phenomenon when porosity occurs 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 process and the outer surface of the steel pipe. The main reason for splashing is that the composition of the protective gas is incorrect or the technical parameters are incorrect. The proportion of argon in the protective gas should be adjusted.