- Excessive corrosion – An extent of corrosion that exceeds the allowable corrosion.
- Extensive corrosion – An extent of corrosion consisting of hard and/or loose scale, including pitting, over 70% or more of the area under consideration, accompanied by the evidence of thickness diminution.
- Insignificant corrosion, minor corrosion – An extent of corrosion with minor rusty spots. The assessment of the corrosion pattern indicates wear generally up to 30% of the allowable corrosion limits.
- Substantial corrosion – Such an extent of corrosion that assessment of corrosion pattern indicates wastage in excess of 75% of allowable corrosion, but within limits.