The Role of Advanced NDT in CUI Assessment: Digital Radiography, Pulsed Eddy Current, and Complementary Screening Methods

Why Advanced NDT Matters in CUI Assessment

Full insulation removal is often impractical, expensive and disruptive. Spot inspection may miss damage if locations are not selected using risk-based logic. Advanced NDT helps screen larger areas, identify suspect locations, reduce unnecessary insulation removal, and prioritise confirmatory inspection. The role of Advanced NDT is to support decision-making, not to replace engineering assessment, corrosion review, and direct verification where required.

Digital Radiography and Computed Radiography

Digital Radiography (DR) and Computed Radiography (CR) use penetrating radiation to produce an image of the pipe or component profile through insulation. In CUI work, radiography can be particularly useful for detecting external wall loss, corrosion morphology, and geometry-related corrosion locations such as elbows, supports, low points, and small-bore piping.

• Can inspect without removing all insulation
• Provides visual image or profile of wall loss and geometry
• Useful for targeted inspection of high-risk locations
• Particularly valuable for small-bore piping, bends, and supports
• Digital techniques provide faster image review, electronic records, and easier comparison over time

Limitations: Radiation safety controls and exclusion zones are required. Access and line-of-sight geometry matter. Findings should be confirmed with UT, direct visual inspection, or additional NDT where remaining wall thickness or FFS decisions are required.

Pulsed Eddy Current (PEC)

Pulsed Eddy Current is an electromagnetic technique mainly used for screening ferromagnetic materials such as carbon steel through insulation, coatings, or fireproofing. It estimates average wall thickness or detects areas of relative wall loss.

• Can screen through insulation and coatings without full removal
• Useful for carbon steel piping, vessels, and structural components
• Efficient for identifying areas of possible wall loss for follow-up inspection
• Supports RBI/CUI programs by helping prioritise locations for confirmatory inspection

Limitations: Typically provides an averaged response over the sensor footprint, not a precise local minimum thickness. Generally not applicable to non-ferromagnetic materials in the same way as carbon steel. PEC is a screening technique; final engineering decisions often require confirmatory UT, PAUT, radiography, or insulation removal.

Neutron Backscatter / Moisture Detection

Neutron backscatter methods are primarily used to detect moisture in insulation. Moisture detection can help identify areas where CUI risk may be elevated. However, wet insulation does not automatically mean corrosion is present, and dry insulation does not prove corrosion is absent. Moisture detection should trigger engineering review and follow-up inspection, not be treated as proof of remaining wall condition.

Infrared Thermography

Infrared thermography may identify thermal anomalies associated with wet insulation or damaged insulation under suitable operating and environmental conditions. It is highly condition-dependent and should not be used alone to confirm CUI or remaining wall thickness.

Guided Wave Ultrasonic Testing / LRUT

Guided Wave UT can screen long lengths of pipe from a limited access location. It is useful for identifying changes in cross-sectional area and potential corrosion zones. LRUT is a screening method and generally does not provide precise remaining wall thickness. Detection and sizing of localised corrosion can be challenging. Requires follow-up local inspection for confirmation.

Conventional UT, PAUT, and Targeted Insulation Removal

Conventional UT thickness measurement, corrosion mapping, and PAUT are often used for verification and sizing after screening methods identify suspect areas. Targeted insulation removal remains important for direct visual examination, surface condition assessment, coating evaluation, and accurate thickness measurement.

Integrating NDT Results into a Risk-Based CUI Program

The strongest CUI programs use a layered inspection strategy: pre-assessment to identify susceptible systems, screening using DR, PEC, neutron backscatter, thermography, or LRUT, direct examination at selected locations, engineering assessment of remaining wall thickness and corrosion rate, and reassessment to update the RBI/CUI database and future inspection plan.