Corrosion Under Insulation (CUI) is an extremely common occurrence and makes up a huge chunk of pipeline maintenance costs. Even though we know about CUI and understand what causes it, the struggle remains to prevent corrosion and mitigate its’ effects.
What Is CUI?
Corrosion Under Insulation is just what it sounds like: corrosion of the surface of insulated piping or equipment. The corrosion occurs as a result of moisture build-up under the insulation. Without a way to evaporate, the moisture eats away at the metal parts of a piece of equipment. This could be the actual pipe, the hardware, or even the jacketing.
Trouble arises when the corrosion becomes so severe that equipment is damaged or even fails. Undetected corrosion can lead to pipeline leaks, which cause a shut down in business until they can be repaired, to more severe complications like an explosion that endangers employees and the surrounding community.
One primary cause of CUI is moisture build-up. Anytime water gets trapped and cannot evaporate, metals are at risk of corrosion. Equipment design is constantly improving to prevent water from entering a system, and allowing it to leave the system if it gets in, but to date the problem still exists.
For corrosion to occur the following must be present: oxygen, high temperatures, and a concentration of dissolved chemicals, elements, or minerals. One of the biggest causes of CUI are the drying/wetting cycles that many pipelines are put through. These cycles accelerate CUI problems due to the chemical reactions of the materials in the pipe, the pipe itself, heat, and water.
This means CUI can attack a pipeline both inside and out.
Inspection Techniques For Corrosion Under Insulation
To head off these problems before they start, companies rely on regular CUI inspections. Regular inspections provide measurable data that can be tracked over time to gauge changes in the equipment and identify problem areas. Then repairs or replacement can be scheduled before the problem becomes too severe.
There are different types of corrosion under insulation. This adds to the complexity of mitigation efforts, but it also means there are several different NDT technologies that can be used to test for and measure CUI, including:
- Visual Inspections
- Ultrasonic Testing
- Remote TV Monitoring
- Electromagnetic Testing
- Computed and Digital Radiography
- Positive Material Identification (PMI)
The truth of the matter is, there aren’t any 100% effective ways to prevent corrosion under insulation. Some techniques have been tried with spotty success. So much of CUI depends on the material used and the conditions under which they are placed. Most of the environmental elements that contribute to CUI are impossible to control. That means, prevention can only be achieved by making changes to factors we can control such as design and specification, installation, and maintenance.
Some common preventative measures used to combat CUI are:
- Inhibitors or Protective Coatings can be used to prevent corrosion but wet/dry cycles make them ineffective over time.
- Keeping water out is key to preventing corrosion, but waterproofing can also lock in moisture that does manage to get in and increase corrosion.
- Insulation materials. The insulating materials themselves often contain corrosive elements. Eliminating them from the insulating material may help eliminate or decrease the rate of corrosion.
Although disheartening, this gives us plenty of areas of opportunity to improve our designs and processes to prevent or decrease CUI occurrences.
Identify CUI Before It Becomes A Problem
Until engineers develop a solution for CUI, regular inspections are the best way to ensure it does not gain a foothold and cause problems in your facility. Amerapex uses a variety of methods to identify areas of corrosion, adapting our methods to meet the specific characteristics of the material being inspected.
Contact the experts at Amerapex today at 1-713-263-0900 to design a custom solution for your corrosion problems.