1) Wrong side: This is a common problem in pre-welding, and the wrong side is out of tolerance, which directly leads to the degradation or scrapping of lsaw steel pipes. Therefore, it is required to strictly control the amount of misalignment during pre-welding.
2) Welding on the back and burn-through: If the welding on the back is removed, it will take time and affect the normal production process; Burn-through will affect the quality of internal and external welding and needs to be filled.
3) Porosity: Porosity in pre-welded welds leads to internal defects in internal and external welding.
4) Poor weld formation: Poor weld formation affects the subsequent internal and external welding tracking, affects the stability of the welding process, and thus affects the welding quality. The welding seam forming is closely related to the line energy. The welding current and arc voltage are constant, the welding speed increases, and the welding seam penetration and width decrease, resulting in poor welding seam forming. When pores are generated in the weld, poor weld formation often occurs.
5) Splash: The splash in pre-welding is easy to burn the surface or groove of the lsaw steel pipe, and it is not easy to remove, thus affecting the welding quality and the quality of the outer surface of the lsaw steel pipe. The reason for the splash is mainly due to the wrong composition of the shielding gas or the wrong process parameters, and the proportion of argon in the shielding gas should be adjusted.
When the whole or most half of the lsaw steel pipe billet is 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 asymmetric, or the radial elongation of the opposite pressure roller is inconsistent), there is no pressure round ;
3) The pre-bending edge is not pre-bent in place, which is caused by the phenomenon that the plate edge is abundant in the straight edge.
When the head or tail of the tube blank is out of tolerance, it is generally due to:
1) The position of the import and export roller table is wrong;
2) The center of the ring frame is wrong;
3) The seam pressure roller is not well rounded, and the position of individual pressure rollers is deviated;
4) The forming is not good (the height difference between the two sides of the formed tube blank is large);
5) The width of the opening seam is more than 150mm;
6) Caused by the pressure fluctuation of the hydraulic system.
The reasons for backside welding and burn-through are generally:
1) The seam is not tight, or the pressure of the hydraulic system may be too low;
2) The molding is not good, and the roundness deviation is large;
3) Improper selection of pre-welding process parameters. A certain 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 flashes and burn through.
Porosity in pre-welded welds is generally due to:
1) The quality of the protective gas is not good, such as containing moisture, insufficient pressure flow, etc.;
2) The gas cover formed by partial blockage of the shielding gas in the welding torch is uneven, and the harmful gas is disturbing;
3) There is rust and oil stains on the groove.