Asset Intelligence Report

A Primer on Corrosion Under Insulation (CUI)

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Corrosion under insulation (CUI) and corrosion under fireproofing (CUF) are some of the most well-known phenomena in the process industries, yet they continue to constitute a large percentage of global maintenance expenditures. CUI is a subject that is well researched and understood based on extensive studies to determine its causes, effects, prevention, and mitigation. In simple terms, CUI is any type of corrosion that occurs due to the presence of moisture on the external surface of insulated or fireproofed equipment. It is the presence of improperly specified insulation (i.e., wicking characteristics, chloride content, etc.) that makes this class of corrosion so aggressive and hard to detect and locate. The buildup of moisture can be caused by several factors detailed in the “Causes” section of this primer. The corrosion itself is most commonly galvanic, chloride, acidic, or alkaline corrosion. If undetected, the results of CUI can lead to the shutdown of a process unit or an entire facility. In some cases, it may even lead to a process safety incident.

This Asset Intelligence Report serves as an informative primer to provide an understanding of CUI. This primer contains the following sections:

  • Overview
  • History of CUI
  • Causes
  • Detection
  • Prevention and Mitigation
  • Codes, Standards, and Best Practices
  • References

As with other Asset Intelligence Reports, this document is not intended to serve as a comprehensive guide, but rather an introductory primer on CUI. Since the information is provided in a condensed format, we recommend printing and laminating copies that can be referenced by you and your co-workers at your convenience.

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A Primer on Corrosion Under Insulation (CUI)

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