In simplest terms, CUI (corrosion under insulation) is any type of corrosion that occurs due to a moisture buildup on the external surface of insulated equipment. It can be caused by multiple factors and can occur in equipment operating at ambient, low, and high temperatures, depending upon conditions. Moreover, CUI can occur in equipment that is in service, out of service, or in cyclic service.

Damaged insulation (as well as many other factors) provide a very easy route for water ingress into insulation. Once inside it can cause very serious damage to pipework and other susceptible steel elements.

Below are a couple of examples of damaged insulation that we recently identified during routine CUI Risk inspections for one of our clients. 


Example 1: Insulation damage, visible water/moisture intrusion. 

Visible insulation damage and moisture spread.


Example 2: Insulation damage caught early.

Damaged insulation caught early.


Example 3: Not so obvious, no visible sign of insulation damage.

Not so obvious, no visible signs of damage to insulation.


Inspection programs should ensure comprehensive coverage of all plant (vessels and pipework) including ‘running’ plant (pumps, valves etc) which may be subject to CUI. It is essential to consider items exposed to localized cooling/heating effects, as well as the effects of outage periods for components operating at high temperature. This promotes CUI in plant or pipework which would otherwise be excluded from the survey.

To discover more out more about this inspection service click here.

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