Method Induce a high frequency magnetic field in the tube under test. Eddy current will follow and uniform field will be modified as defects pass by.   Application In any electrical conductive material weld line testing on (but not DSA) on-line.   Product Normally non-ferrous products (aluminum titanium etc). Can test steel materials when used with a magnetic saturator. Best suited to small diameter and thin wall tubing, under 2” (50mm) diameter and under 3/16” (4mm) wall thickness.   Advantages High speed testing, usually completely non-contact with the product. Can test at elevated temperatures.   Disadvantages Very sensitive to changes in geometry, conductivity and other phenomena not related to defects. Often insensitive to long continuous defects. Sensitivity diminishes rapidly with depth of defect. Difficult to calibrate and to relate defect severity to indications from instrument. Although it is frequently used to test magnetic material with a saturator, it is better suited to non-ferrous material.