Corrosion under insulation: attack on the outside of insulated equipment when water gets past damaged jacketing and soaks the insulation against the metal. Carbon steel is most at risk at operating temperatures roughly between -12 and 175 C, especially in cyclic service, while austenitic stainless suffers chloride cracking instead. Because the damage is hidden, CUI is found by stripping insulation at likely spots or screening with profile radiography, pulsed eddy current or guided waves.
Pulled the lagging at the pipe support and the CUI is through to a pinhole, flag every support on that rack.
Look first where water collects: low points, supports, insulation terminations, nozzles and damaged jacketing seams on the top of the line.
Also heard as
- corrosion under insulation
Related terms
Pitting
Localized corrosion that drills small, deep cavities into metal while the surface around them stays nearly intact.
SCC
Stress corrosion cracking: brittle cracking caused by tensile stress acting together with a specific corrosive environment.
Corrosion allowance
Extra wall thickness added beyond what pressure design needs, meant to be used up by corrosion over the service life.