Corrosion Under Insulation (CUI) is a hidden and highly destructive form of external corrosion that develops beneath thermal insulation on pipelines.

Corrosion Under Insulation (CUI) is a hidden and highly destructive form of external corrosion that develops beneath thermal insulation on pipelines, vessels, and process equipment. Moisture penetrating through damaged cladding, vapor barriers, or insulation gaps creates a persistently corrosive microenvironment — often undetected until significant wall loss or leaks occur.

CUI is most common in temperature ranges of -4°C to 175°C, where condensation and moisture retention are highest. Risk factors include damaged or aging insulation, coastal or high-humidity environments, carbon steel substrates, and insufficient maintenance cycles.

Detecting CUI requires specialized inspection techniques that can assess pipe condition beneath insulation without removal. Methods include thermographic imaging, neutron backscatter, pulsed eddy current, and profile radiography. For buried insulated pipelines, EMPIT’s CMI technology provides aboveground corrosion detection that identifies wall loss and coating degradation — supporting CUI risk management within pipeline integrity programs.