Scales commonly found in oil & gas production are most often sulfates formed when incompatible waters are combined with pressure changes, heat, volume increases.  These can be mixed with one another and may have other substances that can be formed within the scale like frac sand, formation sands, and frac chemicals that can add signifcantly to the scale abrasiveness.

All scales are brittle to some degree and vary condiderably as to hardness. Shape of the deposite can also add to its milling difficulty. Thickness can vary from just a thin 1/8" coating on the pipe to a worm-hole to solid scale.

We have assigned a simple number grade to scales.

Zero = does not dull carbide mills

One = cuts with PDC mills

Two = too brittle for PDC...cuts with MS Mills

Three = too hard/abrasive/brittle for MS...cuts with MDX

Four = dulls standard-set MDX...MDXX required