What is it?
This defect usually happens on hot-roll pickled, or a cold rolled coil. It looks like red rust patched on a bare steel surface. This defect is also known as rust or stain. It is caused by inadequate oiling or contaminated oil on pickled hot-rolled or cold-rolled coils. This defect can also be caused by condensation that developed from removing paper wrap on the coils too soon after arrival at a customer’s plant.