Which type of coils are typically used for the inspection of tubing?

Encircling coils are specifically designed for the inspection of tubing in Eddy Current Testing. These coils are shaped to completely wrap around the test specimen, allowing for uniform electromagnetic coupling with the surface of the tubing. This configuration is important because it maximizes the interaction between the coil's magnetic field and the material being inspected, facilitating the detection of both surface and near-surface defects effectively.

The benefits of using encircling coils include their ability to inspect the complete circumference of the tube and their efficiency in detecting changes in the material properties across the entire surface area. This makes them particularly suitable for applications involving round and cylindrical components such as tubing.

Other types of coils, like U-shaped and gap coils, may have their specific uses, but they are not optimal for inspecting tubing compared to encircling coils. U-shaped coils tend to be used in applications where the geometry allows for opening to facilitate testing, and gap coils are typically utilized for detecting flaws in thicker materials rather than providing broad coverage around tubing. Therefore, encircling coils stand out as the ideal choice for tubing inspection in Eddy Current Testing.