Panametrics MG2, User Manual, Page: 117 / 138

October 2005 910-257B
MG2 Series Page 8-1
8 APPLICATION NOTES
8.1 Factors Affecting Performance
And Accuracy
a.
Surface Condition
Severe pitting on the outside surface of a pipe or tank can be a
problem. On some rough surfaces, the use of a gel or grease rather
than a liquid couplant will help transmit sound energy into the test
piece. In extreme cases it will be necessary to file or grind the surface
sufficiently flat to permit contact with the face of the transducer. In
applications where deep pitting occurs on the outside of a pipe or tank
it is usually necessary to measure remaining metal thickness from the
base of the pits to the inside wall. The conventional technique is to
measure unpitted metal thickness ultrasonically, measure pit depth
mechanically, and subtract the pit depth from the measured wall
thickness. Alternately, one can file or grind the surface down to the
base of the pits and measure normally. As with any difficult
application, experimentation with actual product samples is the best
way to determine the limits of a particular gage/transducer
combination on a given surface.
b.
Transducer Positioning/Alignment
For proper sound coupling the transducer must be pressed firmly
against the test surface. On small diameter cylindrical surfaces such as
pipes, hold the transducer so that the sound barrier material visible on
the probe face is aligned perpendicular to the center axis of the pipe.
See the illustration below.