Corrosion under insulation (CUI) is a severe form of localized external

corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...

that occurs in

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...

and low alloy steel equipment that has been insulated. This form of corrosion occurs when water is absorbed by or collected in the insulation. The equipment begins to corrode as it is exposed to water and oxygen. CUI is common in

refineries A refinery is a production facility composed of a group of chemical engineering unit processes and unit operations refining certain materials or converting raw material into products of value. Types of refineries Different types of refineries ar ...

and process plants that typically operate equipment at high temperatures. Corrosion is at its worst where thermal cycling occurs. In this instance the moist condenses back on to the core material until it is flashed off when the plant is brought back into operation.

References

External links

99 Diseases of Pressure Equipment: Corrosion Under Insulation (CUI)
— Inspectioneering Journal Corrosion {{corrosion-stub