Eddy current testing
Three probes are used in eddy current testing. Internal probes are usually used for testing the performance of the heat exchanger tubes. The inscribed probes are used to test the bars and tubes during fabrication. Surface probes are used to find the place of cracks, materials classification, measurement of the coating thickness, and measurement of the depth of the hardened surface. This method is used for:
- Identifying imperfections in tubing
- Materials classification
- Thin coating measurement
- Measuring the thickness of thin wall only from one side
- Measuring the depth of hardened surface
Some of the benefits are:
- No couplant needed
- Quick response
- No difficult stages during installation
- Quite sensitive to defects
- Highly repeatable
- The high-speed scan can be used
- Very accurate for dimension analysis of defects and coating thickness
Some of the limits are:
- Low penetration depth
- It needs a good knowledge of electrical principles and mathematics
- Very sensitive to surface changes so a good surface is needed
- Only usable for conductive materials
- It can be used for magnetic and non-magnetic materials but in carbon steels is not reliable to diagnose sub-surface defects
- Crack tightness and orientation of eddy current in a crack or linear discontinuity, affects the power of detection.
