Understanding the Inspection Process for Corrosion under Insulation  

Corrosion under insulation (CUI) is a common concern faced by several industrial sectors around the world, including petroleum, chemical, food processing, power generation, and many others. Most of the factors contributing to corrosion under insulation (CUI) are extremely difficult or even impossible to control.  

In recent years, corrosion under insulation (CUI) has become more critical to the industry because of a number of reasons. Firstly, as a whole, the industry has become more complex these days. Many industries now require highly sophisticated instruments, equipment, and piping arrangements that are more difficult to insulate and demand extremely skilled professionals. Moreover, many businesses are now forced to reduce their staff and budgets, jeopardising their maintenance and inspection activities to some extent. 

As a result of these factors, industries often suffer from premature wet insulation systems that can eventually lead to external corrosion of pipelines or equipment. Naturally, early detection is imperative to preventing failure or serious damage to their process systems. Also, as a result of strict environmental regulations, any system failure or process spill can lead to can lead to serious legal ramifications.  

Inspection Locations 

Ultrasonic methods are commonly used for the inspection of internal erosion in equipment and piping. Certain locations on the pipe and equipment are pinpointed by inspectors to indicate areas where maximum erosion is likely to occur. The same procedure can also be performed to inspect external erosion under fireproofing and insulation. 

Discussed below are some common locations where corrosion can be found because of wet insulation and accumulation of moisture.  

Insulated Piping 

  • On a vertical line at the bottom of the lower elbow 
  • Near tees or at the bottom for branch lines.  
  • Near or at the bottom of where the pipe hangers or instruments protrude through the system. 
  • At the bottom of horizontal lines with visible water or rust stains. 
  • Above flanges or valves on vertical lines. 
  • Any other location where it is difficult to apply insulation on pipe and equipment. 

Insulated Tanks and Vessels 

  • Above the intermediate insulation support rings on vertical tanks and vessels 
  • Around the tank’s base, at the base plate. 
  • Near manholes and tank nozzles, particularly if the insulation jacket shifts from the nozzle. 
  • at the bottom of horizontal tanks 
  • Along the roof’s outer edge. 
  • Under the legs of any platform protruding through the roof or sidewall. 

Vessel Skirts and Fireproofing of Structural Steel Columns 

  • Areas around the base of the steel column. 
  • At the column’s angular cross bracing. 
  • At the opening of the skirt access in skirted vessels.  

Inspection Method 

Commonly used inspection methods for corrosion under insulation (CUI) are non-destructive. Instead of sawing or cutting or sawing a hole in the insulation, use a duct tape to seal it. If the insulation is dry, please ensure that it remains that way. There is a wide range of NDT port assemblies that provide easy access for inspection. However, these port assemblies should be installed as per the manufacturer’s instructions to ensure that they are able to seal out moisture. Always use the largest available inspection port for easier visual inspection. Fill the port with the new or existing insulation before sealing it. In case of re-inspection, high-temperature blanket insulation is recommended.  

If you have more questions about the inspection of corrosion under insulation (CUI) or any other type of industrial coating, please get in touch with us at Coating Management Solutions.