FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

- 446 -
analysis of the acoustic signals in the time and frequency domains and have
provided a theoretical basis for the flaw localization techniques most used
in industrial applications.
While examples abound in the literature on successful application of acoustic
emission to large structures by use of general purpose large systems which
are computer-controlled to give, in real time, the location and severity of
flows, the operation of such systems depends, to a large extent on the
presence of highly skilled operators which can provide almost immediate
interpretation of the raw data obtained during the tests. Furthermore, these
sophisticated pieces of equipment have only a limited capability to perform
over a long period of time beside the fact that they are costly, bulky and
difficult to transport from one place to another. These drawbacks limit the
use of existing first generation acoustic emission equipment to applications
which have a finite length of time, such as proof tests, where they can be
assembled to perform tha test, proceed with the actual test, analyse the data
and disassemble to move on to another application.
An alternate process to provide continuous monitoring of large structures
with acoustic emission is to use surveillance units which continuously
analyse acoustic emission signals, determine the relevant signals vhlch are
indicative of impending failure and use these signals to trigger a warning
system. These surveillance units would be compact, inexpensive, and a number
of these units can be applied to a very large structure such as a pipeline,
an offshore platform or a nuclear reactor for continuous monitoring of these
structures. The units will each include a micro-processor which is
software-controlled to perform the different functions assigned to each of
these units. This new approach to use of acoustic emission for continuous
monitoring of large structures has been patented by Bassim and Tangri(3).
The description of the system is given by Mitchell and Bassim(4).
An important feature of these surveillance units is that they are
preprogrammed to identify signals corresponding to impending failure. This
requires an intensive research program to identify the sources of acoustic
emission in the structure under consideration and to determine the effect of
attenuation on the waveform of the signal detected by the transducer. In
this paper, this research program is outlined with regard to an industrial
application, involving the use of the acoustic emission system to monitor a
long pipeline.
2. OUTLINE OF MATERIAL TESTING PROGRAM
The material testing program for a continuous monitoring system used in
conjunction with pipelines can be summarized in the following steps:
2.1 Laboratory tests of pipeline materials
The tensile and fracture properties of a pipeline material were determined
using tensile and three-point bending specimens respectively. The effect of