Mitigation of CUI is best achieved by _________.

Mitigation of Corrosion Under Insulation (CUI) requires preventing corrosive water contact with the outer surface of metal equipment. Although well-designed jacketing and insulation retard moisture entry, complete water exclusion over time is practically impossible. Therefore, API RP 571 explicitly identifies the application of a high-performance protective coating system as the single most effective primary mitigation method against CUI. Protective coatings (such as immersion-grade epoxy novolacs, liquid-applied coatings, or thermal spray aluminum coatings) create a continuous physical barrier directly on the substrate. This barrier isolates the base metal from trapped moisture, dissolved salts, and atmospheric contaminants, thereby providing long-term corrosion prevention even when water breaches the overlying thermal insulation and jacketing systems.

A. A properly documented inspection program: Inspection helps detect existing damage and monitor equipment condition, but it does not prevent or mitigate the electrochemical corrosion process itself.
B. A properly installed insulation system: Insulation systems inevitably degrade, leak, or trap water over time, making insulation alone an unreliable primary defense against severe CUI.
D. A properly documented NDE program: Non-destructive evaluation programs locate and quantify wall loss, acting as monitoring tools rather than direct mitigation mechanisms for CUI prevention.

1. American Petroleum Institute, API RP 571: Damage Mechanisms Affecting Fixed Equipment in the Refining Industry, 3rd Edition, 2020, Section 3.13.6 (Mitigation of CUI).

2. AMPP (NACE) SP0198-2017, Control of Corrosion Under Thermal Insulation and Fireproofing Materials, Section 4 (Coating Systems).

3. ExxonMobil Engineering Practice (EMEP), Corrosion Control Under Insulation, Guidance Document XI-C.