CUI Inspection Should Be Location-Driven, Not Temperature-Driven

Temperature Screening: Useful but Insufficient

Operating temperature is a legitimate CUI susceptibility screening tool. API RP 583 and industry experience identify certain temperature ranges as more conducive to CUI for carbon steel and austenitic stainless steel. Temperature screening efficiently filters out systems that are very unlikely to experience CUI under any realistic scenario. However, within a susceptible temperature range, temperature alone does not tell the inspector where to look.

Where CUI Actually Occurs

Field evidence consistently shows that CUI concentrates at specific engineering features rather than distributing uniformly along a pipe or vessel. These locations include:

• Insulation terminations — especially at flanges, valve bodies, and end caps where water easily enters behind jacketing
• Pipe supports and shoes — where the pipe contacts the support structure, creating crevice geometry, standing water, and temperature variation
• Penetrations through insulation — nozzles, instrument connections, vents, and drains where sealing is difficult
• Low points and horizontal runs — where water collects and drains slowly
• Damaged or poorly sealed jacketing — where physical damage creates direct water entry
• Areas near steam tracing components — where moisture and temperature cycling are elevated
• Dead legs and bypass sections — where temperature may differ from the main circuit
• Areas that experience frequent insulation removal and reinstatement — where reinstatement quality may be inconsistent

Developing a Location-Driven Inspection Scope

A location-driven CUI inspection scope should be based on: mapping of high-probability CUI locations for each system, not just the system as a whole; field walkdown of insulation and jacketing condition; identification of features known to concentrate CUI risk such as supports, terminations, and penetrations; water ingress history and previous findings; consequence of damage at each location; and access, cost, and inspection method constraints.

Combining Location and Consequence

The strongest CUI inspection planning combines location-driven probability assessment with consequence of failure. High-probability locations in high-consequence systems should receive priority. Low-consequence systems with high CUI probability may be managed through monitoring or deferred insulation removal. High-consequence systems with even moderate CUI probability warrant more aggressive inspection planning.

Documentation and Program Improvement

As inspection results accumulate, location-specific findings should feed back into the risk model. Locations where damage is repeatedly found at higher severity should receive increased inspection priority and potentially trigger mitigation actions such as insulation replacement, coating upgrade, or redesign of the insulation termination or support configuration.