1 Misalignment. This is the most common problem in pre-welding. Misalignment beyond tolerance directly leads to the downgrading or scrapping of steel pipes. Therefore, the amount of misalignment must be strictly controlled during pre-welding.
When the whole or half of a steel pipe billet has misalignment beyond tolerance, it is generally due to:
(1) The opening seam is not adjusted properly
(2) The joint roller is not adjusted properly (the circumferential angle of the roller is incorrect, or the left and right rollers are asymmetrical with the center line of the pipe billet as the axis, or the radial extension of the relative rollers is inconsistent), and there is no rounding;
(3) The pre-bent edge is not pre-bent in place, and the plate edge is straight.
When the head or tail of the tube billet is misaligned, it is generally due to;
(1) The position of the inlet and outlet rollers is incorrect;
(2) The center of the ring frame is incorrect;
(3) The rounding rollers are not rounded well, and the position of individual rollers is deviated;
(4) The forming is not good (the height difference between the two sides of the tube billet after forming is large;
(5) The width of the opening seam is more than 150mm);
(6) It is caused by the pressure fluctuation of the hydraulic system.
2 Back weld nodules and burn-through.
If the back weld nodules are removed, it will take time and affect the normal production process; if they are not removed, it will affect the internal welding forming and the tracking of the internal welding seam. Burn-through affects the quality of internal and external welding and needs to be filled.
The reasons for the back weld nodules and burn-through are generally
(1) The seam is not tight, and it may also be that the pressure of the hydraulic system is too low;
(2) The forming 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. Excessive wire energy or too low welding speed will easily produce back weld nodules and burn-through.
3 Porosity.
Porosity in pre-weld welds leads to internal defects in internal and external welds.
Porosity in pre-weld welds is generally caused by
(1) poor quality of shielding gas, such as water content, insufficient pressure and flow, etc.;
(2) partial blockage of the welding gun, uneven gas hood formed by shielding gas, and harmful gas stirring
(3) rust and oil stains on the groove.
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. Weld formation is closely related to wire energy. When the welding current and arc voltage are constant, the welding speed increases, the weld penetration depth and weld width decrease, resulting in poor weld formation. When pores are generated in the weld, poor weld formation often occurs.
5 Spatter. Spatter in pre-welding can easily burn the surface or groove of the steel pipe and is difficult to remove, thus affecting the welding quality and the quality of the outer surface of the steel pipe. The main reason for spatter is the incorrect composition of the shielding gas or the incorrect process parameters. The proportion of argon in the shielding gas should be adjusted.
