Material and quality of the tubes
For other types of materials of tubes, it is necessary to use different tubes and wiper dies from suitable materials. if you make a poor choice this will result in local damage to the material and result in damaged mandrels, wiper dies and tubes and lead to poor bends.
It is the case that lower quality of tubes will result in lower quality bends, which can lead to cracks in the surface of the tubes. The causes are often related to poorer tensile properties of the tubes (see Material properties of tubes)..