Corrosion under insulation for austenitic and duplex stainless steels takes the form of chloride stress corrosion cracking or chloride pitting. Chloride stress cracking occurs at metal wall temperatures above 50°C (120°F), pitting may occur at lower temperature.
For detailed description of these degradation mechanisms see CEN.16.10641 - Chloride Pitting and CEN.16.10642 - Chloride Stress Corrosion Cracking. This degradation module describes management and inspection of CUI for stainless steel equipment and piping.
The most (cost) effective management of CUI is fabric maintenance on the coating system, the main barrier. Maintenance of secondary barrier (insulation) prevents premature failure of the coating system.