Corrosion allowance is the extra thickness of metal added to a component to account for material loss from corrosion over its service life, ensuring it can withstand pressure and structural loads until the end of its designed life. It is calculated based on the predicted corrosion rate, operating conditions, and the equipment’s anticipated life, using data from laboratory experiments or field experience.
According to ASME B31.3 and ASME Section VIII, the minimum corrosion allowance for carbon steel in typical process applications is 1.6 mm (1/16 inch).