At the end of the day, Corrosion Under Insulation (CUI) is preventable if insulation is installed and maintained properly. In industrial facilities where piping, vessels, and equipment are exposed to harsh environments, corrosion is an ever-present threat. Metal components can be attacked from both sides of the wall. Internal processes can vary between aggressive and inert, but the external environment will always have oxygen and the potential for moisture and when moisture becomes trapped beneath insulation materials it leads to accelerated corrosion of metal surfaces in the form of cracking and general thinning.
CUI is such a common issue that the American Petroleum Institute have created a recommended practice, API RP 583, just for guidance on how to manage it. In this blog, we will explore the intricacies of CUI, common issues associated with it, and opportunities to prevent it in industrial settings.
CUI is particularly challenging because it often remains undetected until significant damage has occurred and is a threat to the mechanical integrity of a facility’s assets.
Common Issues Seen with CUI at Industrial Facilities:
A chemical facility in south Texas capable of producing over 11 million pounds of ethylene per day embarked on conducting a Retro Positive Material Identification (RPMI) project in a strategic partnership with Pinnacle. The initial field work evaluation scope was limited to piping operating below 750 degrees Fahrenheit for safety and PMI test instrumentation exposure purposes. While stripping and testing a piping system susceptible to High Temperature Hydrogen Attack (HTHA) damage, the RPMI team encountered CUI damage in addition to significant insulation damage. The facility is operating on a Time-Based Approach (TBA) and during previous damage mechanism assignments, these line numbers had not been identified as susceptible to the CUI damage mechanism based on the assigned temperature and environment.
The damage to the piping was so significant that the RPMI inspection could not be completed without additional preparation, and the findings were reported back to the facility. Through an investigation completed by the site’s reliability team, it was determined that the system was considered a cyclical service and operated at different temperatures for significant periods of time. When damage mechanisms were originally assigned, they were done so based on the operating conditions associated with a potential HTHA failure due to the associated Consequence of Failure (COF). But the site is situated in a coastal region that is highly susceptible to CUI and by only focusing on one set of operating conditions, the site ignored the potential additional damage mechanisms, putting it at unknown risk. This example highlights the importance and risks associated with proper data collection and reliability modeling. If the pipe had failed and released the HTHA service to the atmosphere, there is a high chance that it would have auto ignited and the consequences would have been catastrophic, leading to tens of millions of dollars in damage. This unit also provides feed to another local facility and would have impacted their operations as well.
Preventing and Managing CUI
Preventing CUI requires a proactive approach that involves multiple strategies aimed at mitigating moisture ingress and creating a protective barrier for the underlying metal surfaces. Here are some effective measures to prevent CUI from occurring:
At the end of the day, CUI only occurs when insulation and inhibitors have not been installed or maintained properly. CUI programs can be time-consuming and expensive, and by adopting a comprehensive approach that includes proper insulation selection, installation, maintenance, and proactive monitoring, industrial facilities can significantly reduce the occurrence of CUI and safeguard their equipment and infrastructure from the detrimental effects of corrosion.