Relationship Between Design Thickness and Corrosion Allowance

It depends on how you define design thickness. Sounds like you're talking about pressure vessels.

The final thickness is that required to cope with the material stress (calculated from pressure, vessel diameter etc) plus the corrosion allowance (typically 1.5 or 3 mm, usually specified by the end user).

Whether you call the design thickness the one before or after adding the corrosion allowance is up to you.

Cheers.........Codey

BTW aren't you being a bit presumptuous with "Dear Colleagues" on your first post?

From ASME or any other code, the required thickness of straight sections of pipe or vessel, shall be determined in accordance with the equation t_m = t + c

where,

t_m = minimum required thickness, including mechanical, corrosion, and erosion allowances.

t = pressure design thickness, as calculated by the code equation (depends on design pressure, design temp., material and diameter) for internal and/or external pressure.

c = sum of the mechanical allowances (thread or groove depth) plus corrosion and erosion allowances.