Seams, Flashings and Terminations
Open overlaps, damaged jacketing, unsealed ends and poorly oriented seams can admit rain, washdown water and wind-driven moisture.
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.
Risk AssessmentInspection PlanningNDT CoordinationPrevention DesignReinstatement & QA/QC
Risk-BasedInspection locations selected by service, geometry, exposure and consequence
Targeted AccessScreening followed by controlled insulation opening where justified
Design-Led MitigationFindings converted into coating, insulation, cladding and drainage details
Field ClosureReinstatement, inspection records, punch close-out and QA/QC dossier
Hidden asset-integrity threat
What Is Corrosion Under Insulation and Why Is It Difficult to Detect?
Corrosion under insulation develops when water, oxygen and contaminants reach the metal surface beneath an insulation system. The outer jacketing may still appear serviceable while localised or widespread degradation progresses out of sight.
For carbon and low-alloy steels, the damage can include external corrosion, pitting and local wall loss. For austenitic and duplex stainless steels, moisture and chlorides can contribute to external chloride stress corrosion cracking. Temperature cycling, damaged weatherproofing and moisture-retaining details can intensify both mechanisms.
Core principle: screening identifies where to investigate. It does not, by itself, establish the remaining integrity or fitness for service of the asset.
CUI-critical geometry
Where Corrosion Under Insulation Risk Concentrates
CUI risk is not uniform. Inspection locations should follow operating temperature, geometry, environmental exposure, maintenance history and consequence—not random insulation removal alone.
Pipe Shoes, Guides and Hangers
Metal penetrations, load-bearing inserts and inaccessible crevices can interrupt drainage, coating and weatherproofing continuity.
Nozzles, Branches and Instruments
Geometry changes, small-bore connections, thermowells and tracing penetrations require maintainable, water-shedding closures.
Valves, Flanges and Manways
Repeated access, leakage history and improvised reinstatement can leave gaps, moisture traps and damaged insulation.
Roofs, Shells, Skirts and Legs
Tank-roof edges, vessel skirts, support legs, saddles and fireproofing transitions concentrate difficult sealing and drainage details.
Cycling, Washdown and Coastal Duty
Frequent thermal cycling, steam tracing, firewater, chemical washdown and marine chloride exposure can elevate risk.
Inspection strategy: accessible appearance alone is not evidence that the concealed metal is sound. Risk ranking must combine asset data, walkdown observations and suitable examination methods.
Risk-based inspection programme
From Asset Review to Verified Reinstatement
ERATHERM structures the insulation work around the integrity programme: prioritise, screen, open, examine, redesign, reinstate and document.
STEP 01Data ReviewMaterials, temperatures, age, coating, history, drawings, exposure and consequence.
STEP 02Risk RankingLines and equipment grouped by likelihood, consequence, access and shutdown need.
STEP 03Walkdown & ScreeningJacketing condition, water-entry paths, thermal anomalies and selected NDT screening.
STEP 04Targeted OpeningControlled removal at justified locations for direct visual examination and NDT.
STEP 05Repair & RedesignOwner disposition, coating release and project-specific CUI mitigation details.
STEP 06Reinstatement & QA/QCInsulation, jacketing, sealing, punch close-out, photographs and final dossier.
Screening and direct examination
CUI Inspection Methods and Their Technical Limits
No single technique is universally suitable. Method selection depends on geometry, insulation thickness, operating condition, required sensitivity, access and the owner’s inspection plan.
| Method | Primary Use | What It Can Support | Important Limitation |
|---|---|---|---|
| External Visual Survey | Inspect jacketing, seams, penetrations, leakage evidence and damaged details. | Risk ranking and selection of priority areas. | Does not directly show the condition of concealed metal. |
| Infrared Thermography | Screen for thermal anomalies that may indicate wet insulation or heat-flow differences. | Area prioritisation when operating and environmental conditions are suitable. | Does not independently prove corrosion or quantify remaining wall thickness. |
| Pulsed Eddy Current — PEC | Screen approximate average wall loss through insulation and jacketing. | Comparison and prioritisation across suitable piping or equipment areas. | Results are influenced by geometry, supports, lift-off, insulation thickness and calibration. |
| Profile Radiography | Evaluate selected pipe profiles and potential wall loss without full stripping. | Local screening where size, access and radiation controls permit. | Coverage, component size and radiation-safety requirements can restrict use. |
| Guided-Wave UT | Screen longer pipe lengths from selected test locations. | Identify areas for follow-up examination. | It is not a substitute for local, accurate thickness measurement. |
| Targeted Stripping + Visual/UT | Expose metal for direct examination and defined NDT. | Confirm surface condition and collect local thickness data. | Requires controlled removal, coating disposition and qualified reinstatement. |
NDT procedures, personnel qualification, acceptance criteria and final integrity decisions remain under the responsible owner, inspection authority and applicable equipment or piping code.
Prevention-focused detail engineering
Insulation System Design for CUI Prevention
CUI cannot be controlled by choosing one insulation material in isolation. The protective coating, insulation, jacketing, fasteners, sealants, penetrations, drainage, maintenance access and installation quality must operate as one coordinated system.
01
Substrate and CoatingSurface preparation, coating selection, application limits, cure, inspection and release before insulation.
02
Insulation and Joint ArchitectureTemperature and chemistry compatibility, water behaviour, layer arrangement, staggered joints and movement allowance.
03
Weatherproofing and DrainageSeam orientation, overlaps, flashings, terminations, penetrations, water shedding and repairable sealing.
04
Supports and Inspection AccessPipe shoes, load-bearing inserts, removable covers, inspection ports and repeatable reinstatement details.
Technical boundary: no insulation product, coating or cladding component can independently guarantee that CUI will not occur. The defensible objective is CUI risk reduction, control and mitigation.
Material-specific mechanisms
CUI Prevention for Carbon Steel and Stainless-Steel Equipment
The damage mechanism, coating strategy, insulation chemistry and inspection focus change with the substrate material and operating environment.
External Corrosion and Wall Loss
Water and oxygen, coating breakdown, wet/dry cycling and contaminants can produce general corrosion, pitting and local metal loss beneath insulation.
External Chloride SCC
Moisture, chloride concentration, stress and temperature can contribute to external chloride stress corrosion cracking in susceptible stainless steels.
Insulation and Accessory Control
Insulation, mastics, sealants and contaminants are reviewed for compatibility; ASTM C795, C692 and C871 may support specified qualification.
Different Evidence, Different Decisions
Coating condition, corrosion morphology, crack detection and remaining-thickness assessment require methods selected for the expected mechanism.
Test scope: laboratory qualification of insulation materials for stainless-steel contact does not reproduce every field exposure and cannot, by itself, demonstrate that a complete installed system is immune to CUI or chloride stress corrosion cracking.
Remediation and closure
CUI Remediation, Insulation Redesign and Reinstatement
When corrosion is found, the metal condition is recorded and transferred to the owner’s responsible integrity team. Repair or replacement decisions must be completed before the coating and insulation system is reinstated.
- Controlled insulation and cladding removal
- Containment and disposal of removed materials
- Surface cleaning, visual examination and defined NDT
- Owner or integrity-engineer repair disposition
- Approved surface preparation and coating application
- Coating inspection and formal release for insulation
- CUI-mitigation detail implementation
- Weatherproof jacketing, sealing and water-shedding checks
- Photographs, punch close-out and final records
ERATHERM’s role: convert field findings into buildable insulation details and close the loop through controlled reinstatement and QA/QC.
Shutdown and online programmes
CUI Inspection During Turnarounds and Plant Operation
The inspection and insulation scope can be phased around operating access, scaffold strategy, NDT resources, coating cure windows and the shutdown schedule.
Pre-Turnaround Survey
Build the asset register, risk map, access plan, likely stripping quantities, repair scenarios, materials and work packs before the critical outage window.
Integrated Execution
Coordinate controlled opening, inspection access, repair release, coating, re-insulation, jacketing, QA/QC and daily progress control.
Online Screening
Use suitable non-intrusive screening to prioritise areas and define the next shutdown scope without overstating the certainty of the result.
For outage planning and high-volume execution, continue to Planned Shutdown & Turnaround Insulation Services.
Engineering deliverables
Complete CUI Inspection and Prevention Engineering Package
CUI Inspection BasisScope, responsibilities, methods and acceptance workflow
Asset and Line RegisterService, materials, temperature, exposure and history
Risk-Ranking MatrixLikelihood, consequence, priority and access logic
Inspection Location PlanMarked-up isometrics, equipment drawings and area maps
Opening and NDT ScheduleScreening, stripping, direct examination and records
Findings and Photo ReportCondition, damage location, evidence and action register
Prevention Detail DrawingsSupports, penetrations, terminations and inspection covers
Reinstatement SpecificationCoating interfaces, insulation, cladding and workmanship
BOM / MTO and Work PacksTraceable materials and execution quantities
Method Statement and ITPSequence, hold points, inspections and close-out
Repair-Priority RegisterOwner disposition status and coordinated next actions
QA/QC Close-Out DossierInspections, punch list, photographs and final records
Technical framework
Standards and Project References
Applicable editions, owner specifications and contractual precedence must be confirmed for each facility.
API RP 583Framework for CUI/CUF design, maintenance, inspection and mitigation practices.
AMPP SP0198System-based control of corrosion under thermal insulation and fireproofing materials.
ISO 19277Qualification testing of protective coating systems used beneath insulation.
ASTM C795 / C692 / C871Selected insulation-material chemistry and stress-corrosion qualification references for stainless-steel contact.
API 510 / API 570May support the owner’s pressure-vessel or piping integrity programme where contractually applicable.
These references do not replace the owner’s inspection strategy, applicable equipment code, qualified NDT procedures, coating specification or fitness-for-service assessment.
Engineering plus field execution
From CUI Risk Map to Installed Prevention Details
ERATHERM combines insulation engineering, high-volume industrial field execution and QA/QC. This allows inspection findings to become practical drawings, work packs, material schedules and maintainable site details.
20+ YearsIndustrial insulation and site-delivery experience
1,000,000+ m²Completed insulation applications
15,000+ MWExperience across major energy projects
3 ContinentsEngineering and project-execution capability
Related expertise
Continue with the Right Technical Scope
Frequently asked questions
Corrosion Under Insulation Inspection and Prevention FAQ
What is corrosion under insulation?
Corrosion under insulation is concealed deterioration that develops when water, oxygen and contaminants reach a metal surface beneath an insulation system. It can affect carbon and low-alloy steels through corrosion and wall loss, and susceptible stainless steels through mechanisms including external chloride stress corrosion cracking.
Why is CUI difficult to detect?
The insulation and outer jacketing hide the metal surface. A system can appear acceptable externally while moisture has entered through seams, penetrations, damaged areas or maintenance openings. Reliable assessment therefore combines risk ranking, screening and direct examination where justified.
Which locations have the highest CUI risk?
Common priority locations include damaged seams, terminations, low points, penetrations, pipe shoes, supports, nozzles, valves, flanges, manways, tank-roof interfaces, vessel skirts, traced lines and areas exposed to washdown, firewater, marine chlorides or frequent temperature cycling. Actual ranking remains asset-specific.
Can thermography detect corrosion under insulation?
Thermography can identify thermal anomalies that may support wet-insulation screening under suitable operating and environmental conditions. It does not directly prove corrosion, define the damage mechanism or quantify remaining wall thickness.
Does CUI inspection always require insulation removal?
Not every location must be stripped initially. Non-intrusive screening can help prioritise areas, but selected insulation removal and direct visual or NDT examination are normally needed to confirm suspected damage and support integrity decisions.
Can one insulation material prevent CUI?
No. CUI control depends on the complete system: substrate coating, insulation, jacketing, seams, flashings, sealants, supports, penetrations, drainage, damage repair, inspection access and installation quality. No single product can independently guarantee zero CUI.
How should an insulation system be designed to reduce CUI?
The design should coordinate compatible coating and insulation materials, joint and layer arrangement, weatherproof cladding, water-shedding seams, sealed penetrations, drainage, movement, support details, removable inspection access, maintenance procedures and QA/QC hold points.
What happens when corrosion is found beneath insulation?
The affected area is documented and examined using the defined NDT plan. The owner or responsible integrity engineer determines repair, replacement, monitoring and fitness-for-service actions. After release, the coating and improved insulation system can be installed and verified.
Can ERATHERM provide inspection planning, insulation removal, redesign and reinstatement?
Yes. The agreed scope can include asset review, risk mapping, inspection-location planning, controlled insulation removal, NDT coordination, CUI findings records, prevention-focused detail engineering, coating and insulation interfaces, BOM/MTO, work packs, reinstatement, QA/QC and close-out documentation.
Plan a CUI Inspection and Mitigation Programme
Share the line and equipment register, operating temperatures, materials, insulation and coating history, previous findings, drawings, access constraints and shutdown schedule. ERATHERM can structure the survey, opening, prevention design and reinstatement package around the facility’s actual risk profile.
CUI likelihood, inspection methods, opening locations, NDT scope, coating system, insulation materials, jacketing, drainage, support and penetration details, repair decisions, acceptance criteria and applicable standards are project-specific. Remaining life, fitness for service and permission to continue operation must be determined by the responsible owner or integrity authority using verified inspection data, applicable equipment or piping codes and approved process conditions. References on this page provide an engineering framework and do not imply that every standard or method applies to every asset.