What Is Corrosion Under Insulation?
Definition: Corrosion under insulation (CUI) is external corrosion that develops on the surface of insulated piping, vessels, tanks, and equipment when water becomes trapped between the insulation and the metal. Because the insulation hides the surface, CUI can progress for years without being seen, leading to wall loss, leaks, and failures. CUI services include inspecting for corrosion, removing insulation, preparing and coating the steel, and reinstalling insulation and weatherproof jacketing.
Insulation is installed to conserve energy, control process temperatures, and protect workers from hot surfaces. But when rain, washdown water, or condensation gets past damaged jacketing or unsealed penetrations, the insulation can hold that moisture against the steel. Carbon steel equipment operating within a range of temperatures that keeps the surface wet — and equipment that cycles between hot and cold — is particularly susceptible, and austenitic stainless steels can suffer chloride stress corrosion cracking under wet insulation.
CUI programs combine risk-based inspection to prioritize susceptible equipment, inspection methods that range from insulation removal and visual examination to radiography and other non-destructive techniques, and repair work to restore and protect the steel. Industry guidance includes API RP 583, Corrosion Under Insulation and Fireproofing, and AMPP (formerly NACE) SP0198. Because most of the work is performed on elevated piping and equipment, CUI projects rely heavily on scaffolding. Through Scaffold Exchange, you can find CUI service contractors across the U.S. and compare their capabilities and availability.
What CUI Services Include
Service offerings vary by contractor, but complete CUI programs typically include the following capabilities.
CUI Inspection
Risk-based selection of susceptible equipment, visual inspection with insulation removal, and non-destructive testing to find and measure wall loss.
Insulation Removal
Removal and disposal of jacketing and insulation to expose the steel, including abatement where older insulation contains asbestos.
Surface Preparation
Abrasive blasting, power tool cleaning, or other methods to remove corrosion and prepare the steel to the required cleanliness and profile.
Protective Coatings
Coating systems selected for the operating temperature and service, applied to protect the steel before reinsulation.
Reinsulation & Jacketing
New insulation and weatherproof jacketing installed with properly sealed seams and penetrations to keep water out.
Common Applications & Facilities
CUI services are performed in refining, chemical, energy, and industrial facilities throughout the United States.
Refinery process piping and pipe racks
Chemical and petrochemical plant vessels
Storage tanks and spheres
Gas processing and LNG facilities
Power plant steam and condensate systems
Pulp and paper and food processing plants
Offshore and coastal facilities
Turnaround and outage inspection programs
How CUI Services Compare to Related Services
CUI programs often overlap with other industrial specialty services. Here is how they compare and which situations each suits best.
Fire protection for industrial structures
- Fire-resistive coatings on steel and vessels
- Protects supports, skirts, and equipment
- Corrosion can also occur under fireproofing
- Best for refinery and plant fire protection
Removal of asbestos materials
- Regulated removal and disposal
- Common in older pipe and vessel insulation
- Requires containment and trained workers
- Best before disturbing suspect materials
Finding and stopping hidden corrosion
- Inspection of insulated equipment
- Insulation removal and surface preparation
- Coatings, reinsulation, and sealed jacketing
- Best for refinery and plant integrity programs
Containment of hazardous work
- Encloses blasting and removal areas
- Controls dust, debris, and spent abrasive
- Protects nearby equipment and workers
- Best for regulated or sensitive sites
Repair and protection of concrete
- Spall repair and crack injection
- Corroded rebar treatment
- Coatings and waterproofing
- Best for deteriorated concrete structures
Find CUI Service Contractors Near You
Use the Scaffold Exchange map to search by location, filter by service type, and connect directly with local contractors that perform CUI inspection, insulation removal, coating, and reinsulation.
OSHA Compliance & Safety Standards
In facilities covered by OSHA's Process Safety Management standard, 29 CFR 1910.119, mechanical integrity requirements call for inspection and testing of process equipment following recognized and generally accepted good engineering practices — and CUI programs are a key part of that effort for insulated piping and vessels. CUI work also involves other hazards: older insulation may contain asbestos regulated under 29 CFR 1926.1101, blasting and coating create dust and chemical exposures, and nearly all work at height requires compliant scaffolding.
- Susceptible equipment identified through a documented CUI program
- Inspection and repair records maintained for mechanical integrity
- Insulation tested for asbestos before removal
- Blasting and coating exposures controlled and contained
- Scaffolds meeting OSHA scaffold requirements
- Facility permits and isolation procedures followed for live units
1910.119
Process Safety Management of Highly Hazardous Chemicals — U.S. General Industry Regulations
OSHA Interpretations & Rulings →