Sun Wee is correct. Also be aware that the various codes treat corrosion differently depending on the load case. B31.3 for example, considers corrosion in the SUS and OCC load cases, but not the EXP load case. If you want the EXP case corroded, you have to change the configuration and set the "ALL_STRESS_CASES_CORRODED" flag (on the "SIF & Stress" tab).