Briefly introduce several common defects and effects of straight seam steel pipes

First, how does the edge gnawing of straight seam steel pipes occur? What is the impact on welded pipes?
The edge gnawing of straight seam steel pipes usually occurs on longitudinally cut strips. The edge gnawing of straight seam steel pipes is the phenomenon that the edge of the steel strip is jagged and uneven. The cause is that the disc blade of the longitudinal shearing machine is blunt or not sharp. The stability of the weld is affected when the steel strip with severe edge gnawing is welded because cracks and cracks occur due to a partial lack of meat from time to time.

Second, how does the wave bend of straight seam steel pipes occur? What is the impact on welded pipes?
The wave bend of straight seam steel pipes is the phenomenon in which someone or both sides of the edge of the steel strip are repeatedly bent in the longitudinal direction. The wave bend is formed by uneven deformation of the center and edge parts along the width direction when the steel strip (or plate coil) is rolled. The center part has a small extension, and the edge part (one side or both sides) has a large extension, forming a wave-like warping of the edge part (one side or both sides). The reasons may be roll wear, uneven temperature in the center and edge of the strip, or uneven thickness of the strip. The wave bend of the straight seam steel pipe will cause severe lap welding during forming welding, and production cannot be carried out, so it is not allowed at all.

Third, how do scarring, indentation, scratches, and uneven head and tail occur, and what impact do they have on the welded pipe? The following is a detailed introduction:
These defects are caused by the hot rolling (or cold rolling) of the steel strip. Scarring is an inherent defect of the strip, and the indentation of the straight seam steel pipe is caused by foreign matter sticking to the roll during rolling. The uneven head and tail are caused by the steel strip or plate coil being rolled without cutting the head and tail directly. Scratches are caused by foreign matter on the roller or floor during the movement of the steel strip. Straight seam steel pipes, especially cold-rolled steel strips, are easily scratched when they are not oiled. The defects of the straight seam steel pipe, such as scarring, indentation, scratches, uneven head, and tail, are eventually transferred to the surface of the welded pipe, resulting in unqualified products, which are cut off or scrapped, reducing the yield and qualified rate of the welded pipe.

Fourth, how does the sickle bend of the straight seam steel pipe occur? What is the impact on the welded pipe?
The sickle bend of the straight seam steel pipe is the phenomenon of bending to one side on the horizontal plane along the length of the steel strip, or the crescent bend of the straight seam steel pipe. The sickle bend of the straight seam steel pipe is caused by uneven deformation of both sides along the width direction during the rolling of the steel strip, with one side extending larger and the other side extending smaller, causing the steel strip to bend to the side with smaller extension. The reason may be uneven pressure at both ends of the roll, uneven temperature on both sides of the strip, or uneven thickness on both sides of the strip. The sickle bend is not allowed in the spiral welded pipe, which will lead to the instability of the spiral weld and the instability of the diameter of the straight seam steel pipe. It will also cause lap welding when the straight seam steel pipe is welded, and deviation or even flipping during forming. The sickle bend during straight seam welding shall not exceed 3 mm per meter.

In addition to the types we mentioned above, the tower-shaped coil of the straight seam steel pipe is the shape of the steel strip coil from the inner ring to the outer ring in a tower shape, which is formed by uneven coiling during coiling. The slight tower shape does not affect the welded pipe. The usual tower shape is no more than 50 mm. The severe tower shape of the straight seam steel pipe makes the strip coil unable to run on the unwinding machine, resulting in metal loss.