Ultrasonic Evaluation Of Fl Aws; Flaw Boundary Method; Echo Display Comparison Method - GE SpotChecker Operating Manual

Important information on ultrasonic testing
Ultrasonic evaluation of fl aws
In present-day test practice, there are basically two
different methods of fl aw evaluation:
If the diameter of the sound beam is smaller than the
extent of the fl aw, then the beam can be used to ex-
plore the boundaries of the fl aw and thus determine its
area.
If, however, the diameter of the sound beam is larger
than the size of the fl aw, the maximum echo response
from the fl aw must be compared with the maximum
echo response from an artifi cial fl aw provided for com-
parison purposes.

Flaw boundary method

The smaller the diameter of the probe's sound beam,
the more accurately the boundaries (and therefore
the fl aw area) can be determined by the fl aw bound-
ary method. If, however, the sound beam is relatively
broad, the fl aw area determined can substantially dif-
fer from the actual fl aw area. Care should therefore
be taken to select a probe which will give a suffi ciently
narrow beam at the position of the fl aw.
SpotChecker

Echo display comparison method

The echo from a small, natural fl aw is usually smaller
than the echo from an artifi cial comparison fl aw, e.g.
circular disc fl aw of the same size. This is due, for in-
stance, to the roughness of the surface of a natural
fl aw, or to the fact that the beam does not impinge on
it at right angles.
If this fact is not taken into account when evaluating
natural fl aws, there is a danger of underestimating
their magnitude.
In the case of very jagged or fi ssured fl aws, e.g. shrink
holes in castings, it may be that the sound scatter-
ing occurring at the boundary surface of the fl aw is so
strong that no echo at all is produced. In such cases,
a different evaluation method should be chosen, e.g.
by using the backwall echo attenuation in the evalua-
tion.
The distance sensitivity of the fl aw echo plays an im-
portant part when testing large components. Attention
should be paid here to choosing artifi cial comparison
fl aws which are as far as possible governed by the
same "distance laws" as the natural fl aws to be evalu-
ated.
Issue 02, 03/2009
Introduction
13