Treatment measures for common problems in pre-welding of straight seam steel pipes

1. Wrong side.

This is a common problem in pre-welding of straight seam steel pipe, and the wrong side is out of tolerance, which directly leads to the degradation or scrapping of the steel pipe. Therefore, it is required to strictly control the misalignment amount during pre-welding. When the whole or more than half of the steel pipe slabs have misalignment and out-of-tolerance, it is generally due to:

1) The adjustment of the opening seam is not in place;

2) The adjustment of the seam pressure roller is not in place (the circumferential angle of the pressure roller is wrong, or the center line of the tube blank is the axis, the left, and right pressure rollers are asymmetrical, or the radial elongation of the relative pressure rollers is inconsistent), there is no pressure circle ;

3) The pre-bending edge is not pre-bent in place, and the edge of the board is caused by the phenomenon of a straight edge. When the head or tail of the tube blank has a wrong edge and is out of tolerance, it is generally due to;

a) The position of the entrance and exit roller table is wrong;

b) The center of the ring frame is wrong;

c) The pressure circle of the joint pressure roller is not good, and the position of individual pressure rollers has deviated;

d) The forming is not good (the height difference between the two sides of the formed tube blank is large;

e) The opening seam width is more than 150mm);

f) Due to pressure fluctuations in the hydraulic system;

2. Welding bumps and burn-through on the back.

The back welding bump takes a long time and affects the normal production process; it does not affect the internal welding forming and the tracking of the internal welding seam. Burn-through affects internal and external welding and needs to be filled. The causes of back weld bumps and burn-through are generally ① not tight joints, or the pressure of the hydraulic system may be too low; ② poor forming and large deviation of roundness; ③ improper selection of pre-welding process parameters. The welding current and arc voltage should be matched with an appropriate welding speed. If the line energy is too large or the welding speed is too low, it is easy to produce back welding bumps and burn through.

3. Stomata.

Porosity in pre-welded welds causes internal defects in internal and external welds. Pores in pre-welded welds are generally caused by ① poor shielding gas, such as moisture content, insufficient pressure flow, etc.; ② partial blockage of the welding torch, resulting in uneven gas shields and harmful gases; ③ rust on the groove, Oil pollution, etc.

4. Poor weld formation.

Poor weld formation affects subsequent internal and external welding tracking, affects the stability of the welding process, and thus affects welding. Welding seam formation is closely related to line energy, welding current, arc voltage, welding speed increase, weld penetration depth, and fusion width decrease, resulting in poor weld formation. Poor weld formation often occurs when porosity occurs in the weld.

5. Splash.

Splash during pre-welding is easy to burn the surface or groove of the steel pipe, and it is not easy, thus affecting the welding and the outer surface of the steel pipe. The main reason for splashing is that the protective gas composition is incorrect or the process parameters are incorrect, and the proportion of argon in the protective gas should be adjusted.