Method High frequency electromagnetic radiation creates an Eddy Current field which is disturbed by defects.   Sensitivity Excellent to O.D. Poor to I.D. defects.   Size Range Any size, but normally 4” (100mm) diameter, 0.25” (6mm) wall and down. Best below 2” (50mm) diameter. disadvantages Poor penetration. Sensitive to geometric and material anomolies. Bad end zone coverage.   Advantages Very Fast.   Cost Lowest. No consumables.   Operator Skill Level Lowest.