Internal Eddy Current Tube Testing
Eddy current internal tube testing is an internal testing method for pipes where coils are moved inside to detect corrosion, cracks, or wall loss. It is commonly used on heat exchangers.
Physical-Chemical Mechanism of Action
Eddy current tube inspection uses electromagnetic induction to detect metal defects in tubes. A coil pair generates a magnetic field and detects changes in that field with a sensitive coil. Corrosion or cracks affect the magnetic field and are thus revealed.
Metallurgical Relevance & Welding Risks
When welding tubes, corrosion spots can develop that aren't visible. Eddy current tube inspection detects these defects and prevents corrosion from worsening or spreading. Without such inspection, cracks or corrosion can continue to grow and cause damage to the tube, leading to heat exchanger failures.
Shop Practice & Instructions
For eddy current tube inspection, a special testing device with coils is used. The device is moved inside the tube while continuously monitoring for metal defects. The coil sensitivity and movement speed must be adjusted for optimal results. Some key parameters are:
• Sensitivity: Adjust the sensitivity so it only reacts to real defects.
• Movement speed: Move the device at a speed of 100 to 200 mm/s for a detailed inspection.
• Temperature: The test should be done at normal ambient temperature to avoid false results due to temperature variations.