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

During inspection, the oscilloscope screen normally shows three indications:
the initial pulse, a small echo from the bond line (due to differences in
acoustical impedance of steel and babbitt), and the back reflection from the
inside surface of the liner. Regions where the bond line indication is minimum
are assumed to have an acceptable bond. Where the bond line signal
increases, the bond is questionable. Where there is no back reflection at all
from the inside surface of the liner (babbitt), there is no bond.
Inspection of other types of bonded joints is often done in a manner similar to
that described above for babbitted bearings. An extensive discussion of the
ultrasonic inspection of various types of adhesive-bonded joints (including
two-component lap joints, three component sandwich structures, and
multiple-component laminated structures) is available in the article "Adhesive-
Bonded Joints" in this Volume.