Abbreviated by CA on vessel name plates and many calculations. A corrosion allowance is, essentially, the amount of material in a pipe or vessel that is available for corrosion without affecting the pressure containing integrity.
In all piping systems, the expected corrosion rate may be constant or change with time. External corrosion (atmospheric corrosion, dampness in the soil, or chlorides from insulation) may be a factor. Many companies usually specify a 1/16-inch (0.0625") minimum corrosion allowance for carbon steel and low alloy steel piping if the corrosion rate can be predicted accurately and is less than a defined threshold (3 mils per year or less as an example). For stainless steels, a 1/32-inch (0.0 3125") minimum corrosion allowance is usually sufficient.
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