Corrosion Under Insulation (CUI)
Corrosion under insulation is external corrosion of carbon and low-alloy steel piping and vessels hidden beneath thermal insulation, caused by water ingress that accelerates corrosion in the 60–175 °C temperature range.
Definition
CUI is one of the most costly in-service degradation mechanisms in refineries, chemical plants, and offshore facilities. It is detected by pulsed eddy current (PEC) scanning through insulation, by profile radiography, by UT under stripped insulation windows, and by insulation removal at high-risk locations per API 583 guidelines.
Related terms
- Pitting Corrosion — Pitting corrosion is a localized form of corrosion that produces small, deep holes (pits) in an otherwise relatively unattacked surface, especially in stainless steels and aluminum alloys exposed to chloride-containing environments.
- Erosion-Corrosion — Erosion-corrosion is accelerated metal loss caused by the combined action of erosive wear (from fluid impingement, particles, or cavitation) and corrosion, typically producing smooth, grooved, or directional wall loss patterns.
- Stress Corrosion Cracking (SCC) — Stress corrosion cracking is the brittle cracking of a normally ductile material under the combined action of tensile stress and a specific corrosive environment, propagating along grain boundaries (intergranular) or through grains (transgranular).
Further reading
corrosion under insulation cui detection guide
More defect terms
Crack · Lack of Fusion · Lack of Penetration · Slag Inclusion · Porosity · Undercut · Overlap · Burn-Through · Weld Spatter · Lamination
Where this comes up in practice
Terms like this one appear in three places that matter commercially: the written practice that governs how your personnel are qualified, the procedures and technique sheets that define how an examination is actually performed, and the evidence an auditor or client asks for when they want to know why an inspection was accepted. Getting the terminology right is the easy part; being able to produce the qualification record, the calibration traceability and the procedure revision that applied on the day of the inspection is the part that decides audits.
Atlantis NDT provides NDT training and certification against ASNT SNT-TC-1A and ISO 9712, ASNT Level III consulting for written practices and procedure approval, inspection management software that holds qualification, calibration and procedure-revision evidence in recoverable form, and an asset integrity platform that binds inspection results to the asset they describe. Browse the full NDT glossary or ask a Level III directly.