How Hydrophobic Aerogel Felt Helps Reduce Corrosion Under Insulation
Oct 19, 2026
Corrosion under insulation, commonly known as CUI, is a hidden problem in industrial pipelines, storage tanks and process equipment. Moisture can enter an insulation system through damaged cladding, poorly sealed joints, condensation or maintenance openings. Once trapped, the water may remain in contact with the metal surface and create conditions for corrosion.
Because the insulation covers the pipe or equipment, early corrosion is often difficult to detect. By the time staining, leaks or damaged cladding become visible, the metal surface may already have suffered significant deterioration.
Hydrophobic aerogel felt can help reduce water retention within an insulation system. Its moisture resistance, low thermal conductivity and thin flexible structure make it a useful option for industrial projects where CUI is a major concern.
However, aerogel felt cannot prevent corrosion by itself. Effective CUI control requires the correct combination of insulation, protective coating, cladding, joint sealing and regular inspection.
What Is Corrosion Under Insulation?
Corrosion under insulation is the deterioration of a metal surface beneath an insulation layer.
It is commonly found on:
Carbon steel pipelines
Stainless steel process pipes
Storage tanks
Pressure vessels
Heat exchangers
Valves and flanges
Steam and condensate systems
Offshore and marine equipment
CUI may occur when water enters the insulation system and reaches the metal surface. Temperature cycling, dissolved salts, oxygen and chemical contaminants can further increase the corrosion risk.
The insulation may hide the affected area, making CUI difficult to identify through ordinary visual inspection.
How Moisture Enters an Insulation System
Even when external cladding is installed, moisture may enter through small openings or damaged areas.
Common entry points include:
Open or poorly sealed cladding joints
Damaged metal jacketing
Pipe supports and penetrations
Valves, flanges and instrument connections
Missing or damaged sealant
Improperly installed flashing
Areas opened during maintenance
Condensation inside cold-insulation systems
Water from rain, washdown or fire-protection systems
Once water enters, some conventional fibrous insulation materials can absorb and retain it. The trapped moisture may spread beyond the original entry point and remain against the pipe surface.
What Is Hydrophobic Aerogel Felt?
Hydrophobic aerogel felt is a flexible insulation material made by combining silica aerogel with a reinforcing fiber matrix.
Its internal nanoscale structure restricts heat transfer, while hydrophobic surface treatment helps repel liquid water. The reinforcing layer gives the material sufficient flexibility for installation around pipes, elbows, tanks and other curved surfaces.
Hydrophobic aerogel felt is commonly used for:
High-temperature pipelines
Oil and gas processing equipment
Petrochemical facilities
Power plants
LNG systems
Marine and offshore installations
Storage tanks and vessels
Removable insulation jackets
Different grades are available with varying thicknesses, temperature limits, densities and hydrophobic performance.
How Hydrophobic Aerogel Felt Can Reduce CUI Risk
Reduced Water Absorption
Hydrophobic aerogel felt is designed to resist liquid-water penetration. When water reaches the insulation surface, the material is less likely to absorb and retain it than many untreated fibrous insulation products.
Lower water retention can reduce the amount of time moisture remains in contact with the metal surface.
However, hydrophobic performance should be verified through technical data rather than assumed from the product name.
Faster Drying of the Insulation System
If a limited amount of moisture enters the system, a hydrophobic material may allow it to drain or evaporate more easily instead of being absorbed throughout the insulation layer.
Faster drying can shorten the wet exposure period that contributes to corrosion.
Drying performance also depends on:
Insulation thickness
Cladding design
Drainage
Operating temperature
Ambient humidity
Ventilation
Location of the water-entry point
Less Moisture Migration
Water absorbed by conventional fibrous materials may travel through the insulation and affect a larger area than the original leak point.
Hydrophobic aerogel felt limits liquid-water absorption and can help reduce this type of moisture migration. This may make localized cladding damage less likely to wet a long section of the pipeline.
Thinner Insulation System
Aerogel felt has lower thermal conductivity than many conventional insulation materials. It can often achieve the required thermal performance with a thinner insulation layer.
A thinner system may provide several CUI-related benefits:
Less insulation volume in which moisture can accumulate
Smaller external cladding diameter
Fewer complicated transitions around supports
Easier access during inspection
Simpler removal and reinstatement
Reduced drying time after limited moisture exposure
The exact thickness must still be determined through thermal calculations.
Stable Performance in Wet Environments
When water enters absorbent insulation, its thermal conductivity may increase and its insulation performance may deteriorate.
Hydrophobic aerogel felt is designed to maintain more stable performance when exposed to incidental moisture. This is especially useful for outdoor pipelines, coastal facilities and equipment subject to weather changes.
It should not be interpreted as permission to leave damaged cladding unrepaired. Long-term water entry can still affect the complete insulation system and the underlying metal.
Hydrophobic Does Not Mean Waterproof
This distinction is important.
A hydrophobic material repels liquid water, but the complete insulation system may still contain:
Seams
Cut edges
Fasteners
Overlaps
Penetrations
Drainage openings
Metal cladding joints
Water can travel through these areas and reach the pipe surface without being absorbed by the insulation itself.
Hydrophobic aerogel felt therefore reduces one part of the CUI risk-it does not eliminate every route through which moisture can reach the metal.
A reliable system still requires:
Correctly prepared metal surfaces
Suitable corrosion-resistant coating
Properly installed insulation
Sealed external cladding
Correct drainage
Regular inspection
Timely repair of damaged areas
Aerogel Felt vs Conventional Fibrous Insulation
| Comparison Factor | Hydrophobic Aerogel Felt | Conventional Fibrous Insulation |
|---|---|---|
| Liquid-water absorption | Low for properly treated grades | Depends on material and treatment |
| Moisture retention | Generally lower | May retain water when damaged or saturated |
| Required thickness | Relatively thin | Usually thicker for similar thermal resistance |
| Drying potential | Generally better when system design allows drainage | May dry slowly after saturation |
| Installation around complex shapes | Flexible and easy to cut | Flexible, but thicker systems may be difficult |
| CUI prevention | Helps reduce risk but cannot eliminate it | Requires strong moisture protection |
| Initial material cost | Higher | Generally lower |
| Inspection and removal | Thin layers may simplify access | Greater insulation volume may increase removal work |
Actual performance varies by product grade, operating conditions and installation quality.
Importance of Pipe Coating
The insulation material should not be treated as the primary corrosion barrier.
Before installing aerogel felt, the pipe or equipment surface should be inspected and protected with a coating suitable for:
Metal type
Operating temperature
Process environment
Outdoor exposure
Expected service life
Project corrosion specification
The surface should be clean and dry before insulation is applied. Existing rust, damaged coating or contamination should be addressed according to the project procedure.
Hydrophobic insulation and a suitable protective coating perform different functions. Both are important in a complete CUI-control system.
Importance of External Cladding
External cladding protects the insulation from rain, mechanical damage, chemical splashes and maintenance activity.
Common cladding materials include:
Aluminum
Stainless steel
Galvanized steel
Weather-resistant membranes
Flexible coated fabrics for removable covers
Cladding joints should be positioned and sealed to direct water away from the insulation.
Particular attention should be given to:
Vertical terminations
Pipe supports
Low points
Nozzles
Instrument connections
Valves and flanges
Changes in pipe diameter
Areas exposed to foot traffic or maintenance work
Even high-quality aerogel felt cannot compensate for continuously leaking or incorrectly installed cladding.
Installation Practices That Help Control CUI
Inspect the Metal Surface
Before installation, confirm that the surface is clean, dry and properly coated. Do not cover visible corrosion without completing the required surface treatment.
Keep the Insulation Dry
Store aerogel felt in a dry, covered area before installation. Open only the material required for the current work area.
Fit Sections Closely
Avoid large gaps between insulation sections. Poorly fitted joints may create cold spots, condensation and paths for moisture entry.
Stagger Multi-Layer Joints
When installing more than one layer, stagger both longitudinal and circumferential joints.
This improves thermal continuity and prevents several joints from forming one direct path to the pipe surface.
Avoid Excessive Compression
Fasteners should secure the aerogel felt without crushing it. Excessive compression reduces installed thickness and may create uneven thermal performance.
Seal the Cladding Correctly
Cladding should be installed as soon as practical after the insulation is applied. Sealants, overlaps and flashing details must follow the project specification.
Protect Inspection Openings
Any area opened for inspection or maintenance must be properly resealed. Temporary coverings should not become permanent repairs.
Areas That Require Special Attention
Some locations are more vulnerable to water entry and corrosion than straight pipe sections.
Pipe Supports
Supports can interrupt the insulation and cladding. Poor detailing may allow water to collect around the contact area.
Valves and Flanges
These components are frequently opened for maintenance. Removable covers should be designed for reliable refitting and sealing.
Vertical Pipes
Water may travel downward behind the cladding. Correct overlaps and termination details are particularly important.
Low Points
Water can accumulate at the bottom of horizontal pipes, tanks and vessels. Drainage and inspection planning should consider these areas.
Outdoor Equipment
Rain, snow, wind and temperature cycling increase the demand placed on the cladding and sealant system.
Coastal and Offshore Installations
Salt contamination can increase corrosion severity. Moisture entry, chloride exposure and mechanical damage must all be considered.
Inspection and Maintenance
CUI control continues after the insulation system has been installed.
A maintenance program may include:
Visual inspection of cladding
Checking sealant and overlaps
Looking for water staining
Inspecting damaged or dented jacketing
Checking areas near supports and penetrations
Monitoring unexpected surface-temperature changes
Infrared thermography
Moisture detection
Selected insulation removal
Ultrasonic thickness measurement
Inspection frequency should be based on operating temperature, environment, equipment criticality and previous corrosion history.
Hydrophobic aerogel felt may reduce moisture retention, but inspection remains necessary because water can reach the metal through system defects.
Selecting Aerogel Felt for CUI-Sensitive Projects
When requesting a quotation, buyers should ask for more than thickness and price.
Important information includes:
Thermal conductivity at relevant temperatures
Maximum continuous operating temperature
Hydrophobicity or water-repellency data
Water-absorption test results
Thickness and density tolerances
Material composition
Fire-performance classification
Chloride and other leachable-ion information, where required
Recommended installation method
Compatible cladding and fastening system
Technical data sheet and safety data sheet
Quality inspection documentation
For stainless steel equipment, project specifications may place limits on chlorides and other substances that could contribute to stress corrosion. Relevant test information should be confirmed before ordering.
Information to Provide to the Supplier
To receive a suitable recommendation, provide:
Pipeline or equipment type
Metal material
Normal operating temperature
Maximum and minimum temperatures
Pipe diameter or equipment dimensions
Indoor or outdoor installation
Coastal, offshore or chemical exposure
Required insulation thickness
Surface-temperature or heat-loss target
Existing protective coating
External cladding material
Required testing standards
Previous CUI history
Project quantity and delivery schedule
Complete operating information allows the supplier to recommend an appropriate aerogel insulation blanket and installation structure.
FAQ
Can aerogel felt completely prevent corrosion under insulation?
No. Hydrophobic aerogel felt can reduce water absorption and moisture retention, but CUI also depends on pipe coating, cladding integrity, joint sealing, operating temperature and maintenance.
Is hydrophobic aerogel felt waterproof?
It repels liquid water, but the complete system is not automatically waterproof. Water may still enter through joints, penetrations or damaged cladding.
Can aerogel felt be used outdoors?
Yes. It is suitable for many outdoor industrial applications when installed with a properly designed weatherproof cladding system.
Does aerogel felt require a corrosion-resistant pipe coating?
Generally, yes. The coating protects the metal surface, while the insulation controls heat transfer. The coating should be selected according to the metal, temperature and project specification.
Can wet aerogel felt be reused?
The material should be inspected for physical damage, contamination and changes in thickness. Reuse should follow the manufacturer's guidance and the project's inspection requirements.
Where should CUI inspections focus?
Priority areas include pipe supports, low points, damaged cladding, valves, flanges, penetrations, vertical terminations and locations with previous corrosion history.
Conclusion
Hydrophobic aerogel felt can help reduce corrosion-under-insulation risk by limiting water absorption, reducing moisture migration and allowing a thinner insulation system.
These advantages make it suitable for industrial pipelines, storage tanks, petrochemical equipment, power plants and offshore facilities where moisture exposure and limited installation space are important concerns.
However, aerogel felt is only one part of CUI management. The metal surface must be properly prepared and coated, the insulation must be correctly installed, and the external cladding must prevent long-term water entry.
Combining hydrophobic aerogel felt with effective coating, sealing, drainage and inspection practices provides a stronger and more reliable approach to controlling corrosion under insulation.
