FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

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By design, these A/E monitoring equipments have been targeted toward
inspection type applications. These are typically short term monitoring
tasks that attempt to identify (and in some cases locate) the presence of
active defects in a structure undergoing some form of stress. This
equipment is versatile in that they may be used to monitor several
structure types (pressure vessels, piping, bridges, cranes, etc). However,
with few exceptions, the operation of the equipment and interpretation of
the results requires the constant attention of a skilled operator. These
skills range from an understanding of electronic instrumentation and their
software operating systems, to metallurgical damage mechanism that are
active in the structure being monitored. Hence, the A/E monitor operator
is an incredible individual. Their experience on a given structure is
acquired over a relatively short term test. Also, they are asked to
interpret A/E data without the benefit of learning what affect the service
history of a structure may have had on its acoustic emission behavior.
This is further complicated if the structure is monitored while being
stressed under conditions that do not replicate the service environment
(eg. hydro-static pressure testing of pulp digesters).
Where this equipment has been used for continuous monitoring of large
structures (eg. offshore platforms in the North Sea) the long range
transmission of analog signals appeared as one problem that affects the
overall A/E monitoring reliability. This hardware problem has several
remedies, one of which is to improve the packaging, connectors and to
transmit the A/E signal on a frequency modulated carrier. The overall
system configuration is not changed by this, but it is an improvement in
reliability.
3. Present Concept:
The present concept for the continuous A/E monitoring of large structures
borrows heavily from seismological techniques. As shown in Figure 2 the
concept can be described in terms similar to the operation of several
seismic observatories co-ordinated by a central seismic analysis centre.
In addition, the type of data processing performed by seismologists may
also prove beneficial for the interpretation of A/E signals (ie. assessing
the relavence of A/E signals amongst background noise). Aside from this
concept, the methods of A/E signal analysis presently being investigated
is not possible on conventional A/E monitoring equipment; nor was it
intended to be.