In the production of straight seam steel pipes, although each manufacturer conducts multiple inspections at each stage of production, it is inevitable that some pipes of substandard quality will be found during the production process. So, at which step do these defective pipes appear? Identifying the cause allows for prevention in future production, thereby improving efficiency.

First, how does edge chipping occur in straight seam steel pipes?
Edge chipping in straight seam steel pipes usually occurs on the slitting strip coil. It manifests as a jagged, uneven appearance at the edge of the steel strip. This is caused by the dulling or lack of sharpness of the slitting machine’s disc blades. Severely chipped steel strips affect the stability of the weld during welding, as they may experience partial missing sections, leading to cracks and fissures.

Second, how does corrugation occur in straight seam steel pipes?
Corrugation in straight seam steel pipes is a phenomenon where one or both sides of the steel strip edge repeatedly bend longitudinally. Wavy bends are formed when a steel strip (or coil) undergoes uneven deformation along its width direction during rolling, resulting in a smaller elongation at the center and a larger elongation at the edges (one or both sides), creating a wavy warp. The causes may include roll wear, uneven temperature distribution between the center and edges of the strip, or uneven strip thickness. Wavy bends in straight seam steel pipes can lead to severe lap welds during forming and welding, making production impossible.

Third, how do scales, indentations, scratches, and uneven ends occur in straight seam steel pipes?
These defects are all caused by the hot rolling (or cold rolling) of the raw steel strip before straight seam steel pipe production. Scales are an inherent defect of the strip; indentations are formed when foreign objects adhere to the rolls during rolling; and uneven ends are caused by the steel strip or coil not being trimmed before direct coiling after rolling. Scratches are caused by foreign objects on the roller conveyor or floor during the steel strip’s journey. Straight seam steel pipes, especially cold-rolled steel strips, are easily scratched when not coated with oil. Defects such as scabs, indentations, scratches, and uneven ends in straight seam steel pipes ultimately transfer to the surface of the welded steel pipe, resulting in non-conforming products that must be removed or scrapped, reducing the yield and pass rate of welded steel pipes.

Fourth, how does camber occur in straight seam steel pipes?
Camber in straight seam steel pipes is a phenomenon where the strip bends to one side along its length on a horizontal plane, also known as a crescent bend. Camber in straight seam steel pipes is caused by uneven deformation along the width direction of the steel strip during rolling, with one side extending more and the other less, causing the strip to bend towards the side with less extension. The causes may be uneven pressure at both ends of the rolls, uneven temperature on both sides of the strip, or uneven thickness on both sides of the strip. Camber is unacceptable in spiral welded steel pipes, as it leads to instability in the spiral weld and instability in the diameter of the straight seam steel pipe. In straight seam welding of steel pipes, overlapping welds can occur, leading to deviation or even overturning during forming. The camber during straight seam welding must not exceed 3 millimeters per meter.