The appearance defects of ERW welded pipes include long knife bends, wavy bends, gnawed edges, scars, scratches, embossing, uneven head and tail, tower-shaped rolls, loose rolls, surface oxide scale, etc.
1. Long knife curve
This is caused by the uneven deformation of the hot-rolled strip in the width direction on both sides during the cold rolling process. It bends to one side along the length of the hot-rolled strip on the horizontal plane, or is called a crescent bend. Hot rolled steel strip. Long knife-bent welded pipes can easily cause lap welding during production and processing, and the direction may shift or even rotate during forming.
2. Wavy bend
This is the continuous vertical bending of the edge part of the hot-rolled strip; it is caused by the uneven deformation of the center and edge along the width direction of the hot-rolled strip during cold rolling. The corrugated elbow will cause severe overlap welding during forming welding and cannot be processed, so it is not allowed to appear.
3. Bite the edge
This is the phenomenon of jagged unevenness on the edge of hot-rolled strip, which usually occurs on slit hot-rolled strip. The reason is that the disc scissors of the slitting machine are broken, dull or chipped. Hot-rolled strips with severe undercuts will have some cracks and gaps during electric welding, endangering the welding quality and reliability.
4. Scabs, indentations, scratches, uneven head and tail
Strain and embossing are caused by dirt sticking to the rolls during cold rolling. Scratches are caused by the hot-rolled strip being scratched by dirt on the roller table or floor during travel, especially when the cold-rolled strip is not oiled. The uneven head and tail are caused by the hot-rolled strip not being uncoiled and cut directly after cold rolling. This defect causes the appearance quality of the welded pipe to be unqualified and must be rejected or judged to be scrapped, which reduces the yield and qualification rate of the welded pipe.
5. Tower Roll
Pylon-shaped coils arrange ten hot-rolled steel strips from the inner ring to the outside to obtain hot-rolled steel strip coils, which are generally not allowed to exceed 50mm.
6. Loose rolls
Slightly loose coils can be used after sorting. Severely loose coils cannot be used because they cannot be sorted and must be cut into loose parts, which increases the consumption of metal materials and reduces the yield.
Cause: The packaging is not firm and does not meet the packaging requirements; poor operation during loading and unloading.
7. Surface oxide scale
Casting defects can result from scale entering the weld zone between the edges of hot rolled strip. In addition, the compound flakes on the surface of the hot-rolled strip enter the forming machine and accelerate the damage of the forming roll. Hot-rolled strips with severe scale must be descaled.
Read more: ERW Pipe Production Line and Machine Unit
