Ultrasonic testing

To correctly interpret ultrasonically test, the thickness of the test parts should not be less than 8 mm. See also code case 2235-3 of ASME BOILER AND PRESSURE VESSEL CODE.

The are a lot of variables to your question-material,defect size and type, sizing accuracy needed,code etc. Ultrasonics are routinely applied to butt welds at less than 4mm with varying results. The poster below mentioned 2235, but in comparision there is B31.3 CC 181 with no minimum thickness. The whole application, code requirements etc need to be reviewed. Often with thinner materials the test may become essentially go-no go type results but not necessarily. There have been a lot of developemnts in ultrasonic equipment, especially in phased array transducers (curved in passive axis etc) that allow for thinner materials to be tested. Sizing ultrastraonically essentailly comes down to beam size, while detection is a bit more varied.

if i'm not wrong the preferred test on butt weld is a radiography. how ever ASME section V will be more helpful for this.