The difficulty and expense of finding and preventing corrosion of insulation (CUI), a very common but elusive problem, is well known and well documented.
CUIs are difficult to find because they are hidden under insulation, and there are significant costs and logistics involved in removing the covering, inspecting the pipes and then restoring the covering. Even cutting a plug in the covering and testing it is a time-consuming and laborious process, plus it can be further complicated if asbestos is identified and needs to be removed safely. (For an introduction to CUI, read "Corrosion Under Insulation: Challenges and Needs for Insulation.")
Nondestructive Inspection of Corrosion of Insulation (CUI)
Many non-destructive testing methods are used to check for CUIs, which are usually only detected when fairly specialized and when a fluid leak is evident. Naturally, industry would prefer a technology that enables inspection without removing the insulating jacket. (Learn more about the benefits of why non-intrusive inspection (NII) is such an effective corrosion management process.) Often, the various testing methods are not used alone, but rather complement each other to achieve their goals. great result.
Here are four great ways to check for CUI
vision test
Visual inspection is the easiest and most obvious method and involves removing the covering (partial or total), visually inspecting the surface for signs of corrosion or damage, and then replacing the insulation. It works, but the downside is that it's expensive, and engineers can only inspect the outer areas of the pipe for defects, not the interior. Insulation may also need to be replaced, adding to the overall cost. The process needs to be done carefully and correctly, otherwise it can compromise the integrity of the structure and increase the risk of contamination.
Radiography
Radiography is another common method of CUI examination. This X-ray technique is used in several ways, such as real-time radiography (RTR), computed radiography (CR), and digital Detector array (DDA). Each method has pros and cons, and suitability depends on the particular application. For example, CR instruments are only suitable if they have access to both sides of the part being tested, while DDA instruments, while more accurate and with less image distortion, are limited to small structures and their performance degrades as the pipe is lowered. Increased diameter.
Each operates on X-ray principles, viewing the diameter profile of the pipe through the insulation and highlighting areas of change or thickness, which can indicate the development of corrosion. Specialized software and digital imaging capabilities view images in real-time and enhance them to give the operator the best possible view. Other advantages include portability, rapid analysis, traceability and digital archiving.
Ultrasonic Thickness Measurement (UT)
Ultrasonic Thickness Measurement (UT) is an efficient, highly accurate and versatile remote visual inspection technique that is widely used in many industries. It works on the principle of ultrasonic motion and can measure wall thickness through various linings and coatings. Another advantage is that it only requires access to one side of the component under test. But there are disadvantages. Inspections are limited to small areas and require calibration for each different material.
Pulsed Eddy Current (PEC)
Pulsed Eddy Current (PEC) uses electromagnetic waves to determine the wall thickness of any conductive material. Even though the probe does not need to be in contact with the test surface, this method can provide high accuracy, but because the technique only provides average wall thickness, it is usually only used as a screening technique and not for detecting isolated areas of corrosion. PEC can only be used in carbon steel and low alloy steel structures, which limits its application range.
Summary
This is a very comprehensive overview of the various inspection methods for corrosion under insulation, and for very specific applications, any decision on a more appropriate technique (or combination of techniques) deserves a closer examination and understanding. (Related reading: How to choose good value monitoring and testing tools.) There is no doubt that nondestructive testing plays a huge role in detecting and preventing the scourge of CUI, and each method has its own advantages and disadvantages.
