Corrosion under insulation (CUI)

CUI. Corrosion Under Insulation) is one of the biggest threats in industrial insulation. Corrosion hidden beneath a layer of insulation can develop unnoticed for years, and its effects can be dramatic - from plant breakdowns to multimillion-dollar losses in industrial plants. In this article, we explain what CUI is, how to detect it and - most importantly - how to prevent it effectively.

 What is CUI and why is it dangerous?

• This is a corrosion phenomenon that develops under the insulation layer, in areas exposed to moisture and varying temperatures.
• It is most common on pipelines and tanks operating at temperatures between -4°C and +120°C - that is, where insulation should protect, but becomes a source of the problem.
• The consequences: metal degradation, leaks, failures, safety risks and gigantic repair costs.

 Typical sites of CUI

• Flanges and bolted connections.
• Bends and reductions where the insulation has numerous cuts and overlaps.
• Pipeline penetrations through walls and structures.
• Zones close to valves and boxes.
• Places where insulation has been mechanically damaged or poorly installed.

 How to detect CUI in practice?

1. Visual inspections - regular checks on the condition of the insulation and protective coating.
2. Thermal imaging inspection - detection of areas of altered temperature indicating moisture.
3. NDT (non-destructive testing) - ultrasound, radiography to assess wall thickness.
4. Localised insulation openings - spot check areas exposed to moisture.
5. Continuous monitoring - state-of-the-art moisture and temperature sensor systems under insulation.

Methods to prevent CUI

• Correct installation of insulation - maintaining overlaps, use of sealants, correct overlap of protective coating.
• Drainage holes - placed at suitable locations (the lowest points of the pipework) allow water to drain away.
• Use of anti-corrosion coatings - protecting the metal even before insulation is applied.
• Selection of suitable insulation materials - e.g. hydrophobic or closed-cell materials (Armaflex, PIR, FoamGlass).
• Regular inspector supervision - control of compliance with standards (NORSOK M-004, CINI).

 How do we teach about CUI at Natalux?

On our courses:

• Students will learn the theoretical underpinnings of the CUI phenomenon and its implications in practice.
• On the workshop floor, they learn to make drainage holes, seals and laps according to NORSOK standards.
• We simulate faulty assemblies so that students can assess the risk of CUI themselves.
• We discuss real-life accident cases from industrial projects in Scandinavia and Europe.

CUI is a phenomenon that can destroy years of investment if proper installation and inspection of insulation is neglected. Prevention is the key - from good materials and correct installation to regular inspection supervision. At Natalux, we teach our trainees that the fight against CUI begins at the training stage - because an informed fitter is the best protection against costly failures.

 

 The role of the industrial insulation inspector

• Quality control of the insulation installation.
• Checking that the works comply with the technical documentation.
• Receipt of materials and verification of quality certificates.
• Ensuring safety - the inspector is responsible for compliance with PPE standards and health and safety procedures.
• Preparation of reports and photographic documentation.

Inspector's checklist - what needs to be checked?

1. Insulation materials - whether they comply with the specification and have the required approvals.
2. Measurement and surface preparation - are the values in line with the design and is the surface clean.
3. Assembly - correctness of fixing, overlapping, sealing, maintenance of distances.
4. Drainage holes and sealers - checking their location and quality of workmanship.
5. Protective jackets - control of overlap direction and protection against CUI (corrosion under insulation).
6. Documentation - report, photos, signatures of contractors and inspector

 Norms and standards on which the inspector relies

• NORSOK M-004:2018 - Norwegian standard for industrial insulation.
• PN-B-20105:2024-04 - the current Polish standard for technical insulation.
• CINI - the European standard for technical insulation.
• FROSIO - international guidelines for surface inspection and protection.
• ZSK, ZRP - National Training and Vocational Framework.

 The most common inspector errors (and how to avoid them)

• Too cursory a check of material documentation.
• Lack of control of overlaps of the protective coat.
• Failure to consider drainage openings.
• Insufficient photo documentation.
• Omitting the element of ergonomics and occupational safety.

Inspector supervision is key to the quality and safety of insulation projects. It is through inspectors that employers can be confident that the project has been carried out to standards and will be sustainable.