Corrosion Under Insulation (CUI) remains one of the most persistent and costly challenges facing refineries, petrochemical plants, power generation facilities and other industrial operations.
Hidden beneath insulation systems, corrosion often progresses undetected until it results in wall loss, leaks, unplanned outages or safety incidents. As facilities continue to extend asset life while managing tighter maintenance budgets, preventing CUI has become just as important as detecting it.
Moisture is the primary driver of CUI. Water entering through damaged cladding or poorly sealed joints becomes trapped within insulation, where thermal cycling concentrates chlorides and other contaminants against metal surfaces. Insulation characteristics, including moisture absorption, drying rate and conformity to piping, can significantly influence corrosion risk. Because deterioration occurs beneath the insulation system, damage often remains hidden until costly repairs are required.
Left: Corrosion only in enforced hole. Center: Corrosion due to lack of hydrophobicity. Right: Corrosion due to water migration through channels.
Over the past two decades, the industry has shifted from reactive inspections to predictive, risk-based asset management. API 581 provides a framework for risk-based inspection by evaluating factors such as operating temperature, insulation type, coating condition and environmental exposure to prioritize maintenance activities. At the same time, ASTM G189 introduced a more realistic method for evaluating CUI by simulating cyclic temperatures and wetdry conditions that lead to water channeling. Additional standards, including ASTM C1617, ASTM C795 and ASTM C1728, help quantify corrosion performance, leachable ions and insulation characteristics, enabling engineers to make more informed material selections.
Advances in insulation technology are also changing how owner-operators approach CUI mitigation. Rather than relying solely on coatings or increased inspection frequency, new generations of flexible, hydrophobic aerogel insulation are designed to minimize moisture ingress and migration, addressing one of the root causes of corrosion.
AlkeGel Ember is one example of this evolution. Its combination of hydrophobic chemistry and exceptional flexibility allows it to conform tightly around piping, minimizing gaps where moisture can accumulate that can retain and trap moisture. Modified ASTM G189 testing demonstrated that AlkeGel Ember limited corrosion to directly wetted areas while preventing the lateral moisture migration commonly associated with conventional insulation systems. Combined with ASTM C795 compliance and performance characteristics that align with API 581 methodologies, it demonstrates how insulation can become an active component of an overall asset integrity strategy rather than simply a thermal barrier.
As CUI management continues to evolve, the industry's focus is shifting beyond finding corrosion sooner to preventing the conditions that allow it to develop. Advances in testing standards and insulation technology are giving owner-operators new tools to improve reliability, reduce maintenance costs and better protect critical assets over the long term.
For more information, visit alkegel.com.
