The inner straight pipe in the production of stainless steel seamless pipe is a common defect of the automatic pipe rolling mill and a difficult problem to solve. In most cases, the straight path is small and will not turn the stainless steel seamless pipe into waste; but sometimes, when rolling aviation pipes and alloy stainless steel seamless pipes, this defect will cause great damage, so it should be paid attention to.

The reason for the inner straight line defect in the production of stainless steel seamless pipes is that there are concave and convex defects on the surface of the rolling pipe plug, such as the burning of the oxide scale welded on the plug, the wear of the plug, the deformation of the plug shape, etc., which scratches the inner and outer surfaces of the stainless steel seamless pipe. Due to the characteristics of longitudinal rolling, the scratches are linear, so they are called inner straight paths.

The inner cut of stainless steel seamless pipes is caused by unreasonable plug design, sharp protrusions on the edge of the connecting rod connecting the plug, or metal spot welding scratching the inner and outer surfaces of the capillary. The design of the plug is unreasonable. If the fillet of the inverted cone is too small and the edge is sharp, the inner and outer surfaces of the capillary will be scratched. If the cone angle of the expansion section of the used plug is inconsistent with the cone angle of the roller outlet, the plug is of poor quality or there are defects on the plug surface, the inner and outer surfaces will also be scratched.