Method High Frequency sound is reflected from defects and received by one or more transducers. Sensitivity Excellent to I.D. and O.D. defects.   Size Range Normally 2” (50mm) diameter, 0.1” (3mm) wall and up.   disadvantages Slow, Wet, Complex. Can be fast, but complexity increases.   Advantages Very sensitive. Can test end zones. Can be quantitative.   Cost Highest. Low consumables cost.   Operator Skill Level Highest