CUI Inspection Guide

Corrosion-under-insulation susceptibility, inspection techniques, and risk ranking for insulated piping and equipment.

Temperature Ranges of Concern

CUI Risk Factors per API 581 / API 583 — Temperature ranges where corrosion under insulation is most likely

Material	CUI Temperature Range
Carbon Steel	25°F to 350°F (most aggressive: 200–300°F at intermittent operation)
Austenitic Stainless Steel (Cl− SCC)	140°F to 350°F (chloride stress corrosion cracking under wet insulation)
Duplex Stainless Steel	Similar to austenitic SS but more resistant
Below Ambient (Cold Service)	Any temperature below ambient where condensation occurs on cold surface

Inspection Methods

CUI inspection techniques — capabilities and typical applications

Method	Description / Application
Visual (remove insulation)	Gold standard — remove insulation, clean surface, visually inspect. Expensive but definitive.
Profile Radiography (RT)	Tangential or projection RT through insulation. Detects wall loss without removal.
Pulsed Eddy Current (PEC)	Electromagnetic method — measures average wall thickness through insulation. Fast screening.
Guided Wave UT (GWUT)	Long-range UT screening for piping. Detects wall loss over 100+ feet from single location.
Real-Time Radiography (RTR)	Portable X-ray system for rapid screening of piping under insulation.
Infrared Thermography (IR)	Detects wet insulation (moisture ingress) — does not directly detect corrosion.
Neutron Backscatter	Detects moisture in insulation. Useful for identifying areas of water ingress.
UT Spot Checks	Remove insulation at high-risk locations and perform conventional UT thickness readings.

Source: CUI_Inspection_Guide_v1.xlsx

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