CUI - Corrosion Under Insulation
One of the most silent and costly problems in the O&G industry. It starts under the insulation - and by the time it is found, it has already caused structural damage.
What CUI is and why it is so critical
Corrosion Under Insulation (CUI) is the corrosion that develops on piping, pressure vessels and equipment covered with thermal insulation. The combination of operating temperature, thermal cycling and moisture ingress - with chlorides, acids and contaminants - creates a highly corrosive environment that the insulation hides until the damage has already compromised the asset's integrity.
60% of all insulation in service for more than 10 years
contains corrosion-inducing moisture. Industry studies show that conventional coatings in CUI service last 5 to 13 years - far below the asset's expected life cycle.
When and where CUI happens
CUI is especially critical in:
Piping operating between -4°C and 175°C
The temperature range where condensation and thermal cycling are most intense.
Pipelines and pressure vessels
In process plants, refineries and petrochemical facilities.
Support points, flanges and connections
Where the insulation has discontinuities.
Any point of moisture
Wherever moisture can enter the insulation system - gaps, terminations and physically damaged areas.
Why conventional coatings fail
In the service environment
- Water, alkalis, chlorides and elevated temperatures create a highly corrosive environment
- Inadequate film thickness results in insufficient protection or premature cracking
Pre-service
- Handling, transport and construction degrade the coating before the system goes into operation
- Exposure to corrosive environments before start-up compromises performance from day one
The Heat-Flex® solution for CUI
Sherwin-Williams Protective & Marine developed the Heat-Flex® CUI-Mitigation range - a next-generation portfolio of four advanced formulations, all tested and verified to industry standards:
Heat-Flex® 650
MIO-reinforced epoxy for operation up to 150°C. Excellent resistance to erosion and thermal shock.
Learn moreHeat-Flex® 750
MIO-reinforced formulation for temperatures up to 175°C. High resistance to thermal shock and UV.
Learn moreHeat-Flex® 1200 Plus
For operating temperatures up to 260°C. MIO reinforcement with superior mechanical and thermal protection.
Learn moreHeat-Flex® ACE
Functional chemical enhancement. Excellent heat resistance, barrier performance and chemical resistance - without flat pigmentation.
Learn moreInnovation
Heat-Flex® AEB - Advanced Energy Barrier
Next-generation technology that replaces traditional mineral insulation systems with a coating that eliminates CUI rather than merely delaying it.
Eliminates CUI by design
no moisture ingress
Less resource-intensive
than traditional mineral insulation
Superior thermal retention
across a wide operating range
Simplified application
no insulation framework to assemble
CUI standards and verification
ISO 12977
Thermal cycling for coatings at elevated temperature - a requirement for systems in CUI service.
AMPP TM21442
CUI-mitigation-specific test method - developed by AMPP (formerly NACE International).
Atlas Cell Testing
Immersion testing combined with thermal cycling - simulates real service conditions under insulation.
ASTM D5894
Cyclic salt fog and UV exposure - verifies performance in external corrosive environments.
Talk to people who understand your asset, not just paint
Describe your asset's condition and the environment it operates in. Our technical team will come back with a specification aligned to the applicable standard — and the service life you expect from the system.