Materials and Corrosion Curriculum
Mod 7 - CUI Prevention
Module from the Materials and Corrosion Curriculum curriculum.
CORROSION UNDER INSULATION (CUI) · Learning Objectives · 1. Identify CUI susceptibility by temperature range and environment 2. Select appropriate inspection methods for insulated systems 3. Apply coating specifications and insulation quality standards 4. Prioritize inspections using risk-based methodology (API 581/583) · CUI Risk by Temperature and Environment
| Service Temperature | CUI Risk | Typical Environment | Inspection Priority | Coating Required? | Notes |
|---|---|---|---|---|---|
| <14°F | Low (frozen) | Cold service, LNG, cryogenic | Low | Yes — cold service coating | Moisture frozen, low reaction rate |
| 14-250°F | HIGH | Ambient-condensing zone | HIGHEST | Yes — CUI coating mandatory | Sweating, rain ingress, maximum risk zone |
| 250-350°F | Medium-High | Steam traced, moderate-temp services | High | Yes — high-temp coating | Alternate wet/dry cycling |
| 350-400°F | Medium | Hot service above boiling | Medium | Yes | Water mostly evaporates but still possible |
| 400-600°F | Low | Hot process lines | Low | Optional | Water driven off quickly when present |
| >600°F | Minimal | Very hot service | Low | Usually not feasible | Inspection focused on external damage/erosion |
| Cyclic / Intermittent | HIGH | Batch operations, shutdown/startup | HIGH | Yes — cyclic-rated coating | Repeated wet/dry cycles accelerate CUI |
| CUI Inspection Methods | |||||
| Method | Insulation Removal? | Detection | Cost | Speed | Best For |
| Visual with insulation removal | Yes (total) | All corrosion visible | High | Slow | Confirmed CUI, damage characterization |
| Visual with windowing | Yes (local) | At specific ports | Medium | Medium | Spot checks, RBI priority areas |
| Pulsed Eddy Current (PEC) | No | General wall loss under insulation | Medium | Medium-Fast | Screening long runs without removal |
| Radiography (DR or CR) | No | Wall loss, weld issues | High | Slow | Specific locations, welds, nozzles |
| Profile Radiography | No | Real-time thickness | High | Fast | Pipe supports, complex geometries |
| Thermal Imaging (IR) | No | Wet insulation detection | Low | Fast | Finding wet areas indicating ingress |
| Ultrasonic (after removal) | Yes | Precise thickness measurement | Low (after removal) | Fast | Detail sizing of known damage |
| Source: API 583 (CUI), API 581 (RBI), CUI_Inspection_Guide_v1.xlsx, IPE-EP-11 series (Refractory, Insulation, Fireproofing) |
Source: Materials_and_Corrosion_Curriculum_v1.xlsx · Sheet: Mod 7 - CUI Prevention
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