What is it?

This defect becomes highlighted on a coated surface, and typically runs throughout the length of the coil. These areas may also be light creases in the steel. This defect is also known as heat ridge or longitudinal crease. It is caused by overheating the sheet before entering a galvanizing pot, or by uneven temper rolling, uneven hot mill profile, or an overheated area of a work roll.

Ridges