Piping Details
Pipe shoes, guides, anchors, low points, branch connections, steam tracing, vertical penetrations and insulation terminations.
Inspect · Assess · Redesign · Reinstate
Corrosion Under Insulation (CUI) Inspection and Prevention
ERATHERM combines risk-based CUI surveys, targeted insulation removal, qualified NDT coordination and corrosion-prevention insulation design to identify hidden damage and reduce recurring moisture-related corrosion in piping, tanks and process equipment.
01Risk Assessment & Inspection Planning
02Screening, Opening & NDT Coordination
03CUI-Prevention Insulation Design
04Reinstatement, QA/QC & Close-Out
Hidden asset-integrity risk
What Is Corrosion Under Insulation and Why Is It Difficult to Detect?
CUI develops when water, oxygen and contaminants reach the metal surface beneath an insulation system. Jacketing may appear serviceable while localised corrosion, pitting or cracking progresses out of sight.
- External corrosion and local metal loss on carbon and low-alloy steels
- External chloride stress corrosion cracking in susceptible stainless steels
- Wet/dry cycling beneath damaged or poorly detailed weather barriers
- Hidden deterioration around supports, penetrations and terminations
The external appearance of insulation is evidence to assess—not proof of the metal condition beneath it.
Where risk concentrates
CUI-Critical Locations in Piping, Tanks and Process Equipment
CUI risk is rarely uniform. Inspection locations should be selected from operating conditions, geometry, exposure, history and consequence—not by random insulation removal alone.
Equipment Interfaces
Nozzles, manways, skirts, support legs, vessel heads, removable covers and transitions between insulation and fireproofing.
Environmental Exposure
Washdown zones, firewater exposure, coastal environments, damaged seams, thermal cycling and locations with recurring leakage.
Closed engineering loop
Risk-Based Corrosion Under Insulation Inspection
The programme converts asset data and field observations into focused inspection, verified findings and practical mitigation workpacks.
Asset Data Review
Materials, temperatures, age, coating history, insulation system, previous findings and maintenance records.
CUI Risk Ranking
Probability drivers, consequence, environmental exposure, accessibility and operating scenarios.
External Walkdown
Jacketing condition, open seams, penetrations, leakage, cold spots, supports and moisture-entry paths.
Screening & Openings
Appropriate screening followed by targeted stripping at selected high-value inspection locations.
Direct Examination
Surface assessment and defined NDT with data captured against the asset and inspection location.
Mitigate & Reinstate
Owner disposition, repairs, coating release, prevention detailing, re-insulation and final QA/QC.
Screening to verification
From Screening to Direct Examination
No single inspection technique is universally suitable. Selection depends on component geometry, insulation thickness, access, expected damage, required resolution and plant constraints.
- Screening methods are selected to find areas requiring investigation.
- Targeted insulation removal provides access for direct visual examination and UT.
- NDT scope and acceptance are coordinated with the owner’s integrity requirements.
- Removed systems are controlled, documented and reinstated to approved details.
Screening identifies where to investigate. It does not automatically establish the remaining integrity of the asset.
Inspection-method selection
CUI Inspection Methods and Technical Boundaries
| Method | Primary purpose | Important technical boundary |
|---|---|---|
| External visual survey | Locate damaged jacketing, open joints, staining, leakage and high-risk details. | Does not directly reveal the metal condition beneath insulation. |
| Infrared thermography | Screen for thermal anomalies and possible wet-insulation zones. | An anomaly is not direct proof of corrosion or remaining wall thickness. |
| Pulsed eddy current (PEC) | Estimate and screen for metal loss through suitable insulation systems. | Results are affected by geometry, supports, lift-off and insulation configuration. |
| Profile radiography | Assess selected piping profiles and potential wall loss. | Limited by component size, access and radiation-safety requirements. |
| Guided-wave UT | Screen longer piping lengths and prioritise indications. | It is a screening technique, not a substitute for precise local thickness measurement. |
| Targeted stripping + visual/UT | Directly examine the exposed substrate and verify thickness at selected points. | Requires controlled removal, surface access and compliant reinstatement. |
Inspection-location planning
CUI Risk Mapping and Inspection-Location Selection
Risk information can be mapped to isometrics, P&IDs, equipment drawings or site layouts, creating a controlled bridge between assessment, field access and work execution.
Typical CUI Risk Map
High riskTargeted opening and direct examination required.
Medium riskDefined screening, surveillance and escalation criteria.
Lower riskRoutine external surveillance and scheduled review.
Known or repairedPrevious findings, wet zones and completed repairs retained in the register.
Online access, shutdown-only work, scaffolding and special-access requirements can be layered onto the same inspection plan.
Beyond inspection
Insulation System Design for CUI Prevention
CUI cannot be controlled by selecting one insulation material alone. Coating, insulation, jacketing, joints, penetrations, drainage, maintenance access and workmanship must operate as one engineered system.
Substrate and Coating InterfaceSurface preparation, coating selection, inspection release and compatibility with the full insulation system.
Insulation System SelectionTemperature range, water behaviour, chemistry, thermal performance and multi-layer joint arrangement.
Weatherproof JacketingCorrect seam orientation, overlap, flashing, water shedding and durable sealing at transitions.
Supports and PenetrationsProject-specific shoes, guides, nozzles, branches and penetrations without avoidable moisture traps.
Movement and ContinuityThermal expansion, contraction, vapour-retarder continuity and detailing at field joints.
Inspection and Maintenance AccessRepairable details, planned inspection ports and repeatable removal/reinstatement at valves and flanges.
No insulation material, coating or cladding component can independently guarantee that CUI will not occur. The engineering objective is measurable CUI risk reduction and control.
Material-specific mechanisms
CUI Prevention for Carbon Steel and Stainless-Steel Equipment
Field execution
CUI Remediation, Insulation Redesign and Reinstatement
ERATHERM connects the field finding to an executable insulation solution, maintaining traceability from controlled opening through close-out.
01–02Controlled insulation and cladding removal
03–04Surface preparation, examination and NDT
05–06Owner disposition and metal repair where required
07–08Approved coating application, inspection and release
09–12New insulation, prevention details, QA/QC and close-out
Flexible project delivery
CUI Inspection During Shutdowns, Turnarounds and Plant Operation
Pre-Turnaround Survey
Define high-risk locations, access needs, likely quantities, NDT interfaces, materials and execution workpacks before the critical path begins.
Integrated Execution
Coordinate insulation removal, NDT access, repair interfaces, coating release, redesigned insulation details and high-volume reinstatement.
Operational Monitoring
Use suitable online surveys and screening to prioritise interventions, preserve records and prepare the next planned outage.
Documented engineering
Complete CUI Inspection and Prevention Engineering Package
Deliverables are adapted to the facility, inspection strategy, integrity workflow and execution phase.
CUI Inspection Basis
Asset and Line Register
CUI Risk-Ranking Matrix
Inspection-Location Plan
Marked-Up Isometrics and Drawings
External Condition Survey
Screening and Opening Schedule
Insulation Removal Plan
NDT Coordination and Data Register
CUI Findings and Photo Report
Repair-Priority Register
Coating / Insulation Selection Matrix
CUI-Prevention Detail Drawings
Reinstatement Specification
BOM / MTO
Method Statement and ITP
QA/QC Checklists
Punch List and Close-Out Dossier
Technical framework
Standards and Recommended-Practice Alignment
Applicable editions, owner requirements and jurisdictional rules are confirmed for each project. References support engineering judgement; they do not replace an asset-specific inspection plan.
CUI/CUF design, maintenance, inspection and mitigation framework.
System approach to corrosion control beneath thermal insulation and fireproofing.
Qualification testing of protective coating systems under insulation.
Relevant chemistry and ESCC evaluations for insulation associated with stainless steel.
Responsibility boundary: Remaining life, fitness-for-service and continued-operability decisions for piping or pressure equipment must be made by the authorised owner/integrity team using applicable equipment codes, verified NDT results and process conditions.
Connected capabilities
Related ERATHERM Engineering and Field Services
Frequently asked questions
Corrosion Under Insulation FAQ
What is corrosion under insulation?
Corrosion under insulation is hidden deterioration that develops when water, oxygen or contaminants reach a metal surface beneath an insulation system. It can affect carbon steel and, through different mechanisms, susceptible stainless steels.
Why is CUI difficult to detect?
The insulation and outer jacketing conceal the substrate. A system may appear acceptable externally while corrosion, pitting or cracking develops below the insulation.
Which locations have the highest CUI risk?
Risk often concentrates at damaged seams, penetrations, terminations, low points, pipe shoes, supports, nozzles, valves, flanges, manways, washdown areas and locations exposed to thermal cycling or recurring leakage.
Can thermography detect corrosion under insulation?
Thermography can help screen for thermal anomalies or possible wet insulation, but it does not directly prove corrosion or determine remaining wall thickness. Indications require appropriate follow-up.
Does CUI inspection always require insulation removal?
Not at every location. Risk assessment and suitable screening can prioritise areas, but targeted insulation removal is normally required where direct examination and precise verification are necessary.
Can one insulation material prevent CUI?
No. CUI control depends on the complete system: substrate coating, insulation, jacketing, seams, penetrations, drainage, thermal movement, access and installation quality.
How should an insulation system be designed to reduce CUI?
The design should limit water entry and retention, use compatible materials, protect the substrate, shed weather correctly, accommodate movement and provide maintainable details at supports, penetrations, terminations, valves and flanges.
What happens when corrosion is found beneath insulation?
The finding is documented and assessed through the owner’s integrity process. Required NDT and repairs are completed, the approved coating is released, and the insulation is reinstated using reviewed CUI-mitigation details.
Can ERATHERM provide inspection planning, insulation removal, redesign and reinstatement?
Yes. ERATHERM can provide an integrated scope covering CUI risk assessment, inspection planning, controlled insulation access, NDT coordination, prevention engineering, field application, QA/QC and close-out documentation.
From hidden risk to controlled action
Plan a CUI Programme That Ends With a Better Insulation System
Share your asset register, operating temperatures, previous findings or turnaround scope. ERATHERM can define the inspection basis, access strategy, prevention details and reinstatement package.