The straight line on the surface of the pipe is the trace produced by the contact between the surface of the steel strip and the forming roller during the process of forming the steel strip into a steel pipe.
The straight line on the surface of the pipe is the trace produced by the contact between the surface of the steel strip and the forming roll during the process of forming the steel strip into a steel pipe.
The straight line on the surface of the pipe is the trace produced by the contact between the surface of the steel strip and the forming roller in the process of forming the steel strip into a pipe.