A Grade: Steel surface is completely covered with adhering mill scale & little if any rust.
B Grade: Steel surface starting to rust & from which the mill scale has begun to flake.
C Grade: Surface where mill scale is rusted or can be scraped off, little pitting is visible to naked eye.
D Grade: Steel surface with rusted mill scale, significant pitting corrosion visible to the naked eye.
Steel Grade A – It is almost entirely covered with mill scale, has little rust or oxidation & is free of pitting corrosion.
Steel Grade B – Steel exposed to the elements shows signs of surface rust, but high levels of mill scale remain.
Steel Grade C – Weather-beaten steel, it is rusting, Little or no mill scale remains & has been scraped off the surface. The pitting is clearly starting.
Steel Grade D – Steel that has been weathered for a long time. You can see pitting and rust inclusions. Extended surface oxidation leaves no mill scale.