What is Mill Scale in Welding?

Mill scale is a thin, flaky layer of iron oxide that forms on the surface of hot-rolled steel. It is used as a protective coating during storage and transport to prevent corrosion of the underlying steel. When welding, the mill scale must be removed from the surface of the metal to ensure a strong bond between the two pieces.

There are several methods of removing mill scale, including:

sanding,
grinding,
and using a descaling solution.

Welders must be aware of the presence of mill scale on the surface of the metal before beginning a welding project. Failure to remove the mill scale from the weld area can result in a weak or porous weld. In some cases, the mill scale can also cause welding defects such as porosity, slag inclusions, and weld metal contamination.

How do you correct the mill scale?

The best way to avoid problems associated with mill scale is to remove it from the surface of the metal before welding.

Can you weld through mill scale?

The short answer is, yes you can weld through mill scale. If the mill scale is heavy, it’s best to remove as much as possible by grinding, sanding, or using a descaling solution.

What is mill welding?

The term “mill welding” likely refers to the process of removing the mill scale from the surface of the metal before welding.

Painting over mill scale

If the mill scale is not removed from the surface of the metal, it can prevent paint and other coatings from adhering properly. This can lead to peeling, chipping, and other problems with the finish.