Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing, UT

A test program had been first carried out to determine the maximum size of
graphite flakes that could be permitted in the casting and still maintain a
minimum tensile strength of 200 MPa (30 ksi). Then, ultrasonic tests were
made on sample castings to determine to what intensity level the second
back reflection was lowered by the attenuation effects of graphite flakes larger
than permitted. Next, a gate was set on the ultrasonic instrument in the region
of the second back reflection, and an alarm was set to signal whenever the
intensity of this reflection was below the allowable level. The testing
equipment was then integrated into an automatic loading conveyor, where the
castings were 100% inspected and passed or rejected before any machining
operation.