What is the corrosion allowance?

• 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)

The corrosion allowance is extra material thickness added to the required wall thickness to account for the loss of material from corrosion over the service life. This means you don’t rely on the bare calculated thickness alone; you add a designated amount so that, even after corrosion, the remaining wall still meets the strength and integrity requirements specified by the ASME Code. The value is chosen based on the service environment, the material, and the desired design life, and it is included in the design thickness from the start. It is not determined by color codes, not expressed as a percentage of diameter, and it is certainly used in design to ensure safety over the vessel or piping’s life. For example, if the calculated required thickness is 10 mm and the corrosion allowance is 2 mm, the minimum specified thickness becomes 12 mm to accommodate expected corrosion.