Corrosion allowance is added to which quantity in piping design?

• A. Added to required thickness
• B. Defined by the material's color code
• C. Measured as a percentage of diameter
• D. Not used in design

Answer: (A)

Corrosion allowance is the extra wall thickness added to the minimum required thickness to compensate for material loss from corrosion over the design life. It is combined with the required thickness to determine the design thickness. For example, if the required thickness is 8 units and the corrosion allowance is 2 units, the design thickness becomes 10 units. The allowance is set based on expected corrosion rate, service conditions, material, and design life as specified by the code. It is not defined by a color code, not a percentage of diameter, and it is indeed used in design to ensure the pressure boundary remains adequate throughout service.