Corrosion Under Insulation (CUI)
Definition
External corrosion of a pipe or vessel surface that occurs beneath thermal insulation, hidden from visual inspection, driven by moisture infiltrating the insulation system.
- Location
- Beneath thermal insulation on pipes or vessels
- Visibility
- Hidden from visual inspection
- Driver
- Moisture infiltrating the insulation system
Common questions
Why is CUI a common finding in explosion and pressure-vessel failure investigations?+
Because it develops unseen under insulation for years, wall thickness can be reduced well below the safe operating margin before any external sign appears, so a vessel can fail catastrophically despite passing a purely visual inspection.
What inspection methods can detect CUI without removing all the insulation?+
Techniques such as pulsed eddy current testing and certain radiographic profiling methods can screen for wall-thickness loss through insulation, though point removal for direct visual and ultrasonic checks is still used to confirm findings.
Related terms
- API 579
- The American Petroleum Institute's Fitness-For-Service standard, which provides assessment methods for determining whether a damaged or corroded pressure vessel or piping component...
- BLEVE
- Boiling liquid expanding vapour explosion. Catastrophic failure of a vessel containing a superheated liquid, producing an expanding pressure wave and, if the...
- Deflagration
- A subsonic combustion front propagating through an explosive by thermal conduction. Characteristic of low explosives such as black powder and smokeless powder;...
- Detonation
- A supersonic shock wave coupled to a chemical reaction front, propagating through a high explosive at velocities between approximately 4,500 and 9,100...
- Overpressure
- Pressure above ambient atmospheric pressure produced by an explosion. The peak overpressure and its duration (impulse) together determine structural damage and injury...