Acoustic
Emissions are high frequent, transient sound waves emitted when rapid local
stress redistributions occur in a material. The stress redistributions are
normally caused by the generation of structural changes in material under a
general loading condition.
By
analysing the quantity and the properties of the acoustic emission signals,
information can be obtained about the processes that are active in the material
under loading. This technique has major advantages
such as:
·
possibility to perform a continous
investigation of the material
·
processes can be monitored at the
time and place of occurrence
·
a large structure can be monitored
by a limited number of sensors
·
the spatial location of the signal
origin can be calculated by using the signal arrival time times at a number of
sensors
That
is the reason why AE is an ideal integral testing method for big pressure
equipment. The results received, allow that follow up NDT's can be reduced to
definite and evaluated areas.
Moreover,
Pressure equipment or piping systems do not have to be taken out of the
production cycle; the reliability is often higher than conventional methods,
like for example visual examination of the interior.
Acoustic
Emissions may be performed according to the following modalities:
·
AE Monitoring during a shop
pressure test.
·
AE Monitoring during
a repetition test with gaseous stok product or water.
·
AE leak detection during pressure
test.
·
AE leak detection under normal
service conditions.
In
the field of global integrity tests the following is only a short list of items
that can be inspected with Acoustic Emissions:
·
Natural-gas storage spheres and
cylinders
·
Reactors for the chemical and
petrochemical industry
·
Steam drums
within paper mills
·
Reactors, filters and storage
vessels within air splitting systems
·
LPG storage
devices
·
Temper furnaces
·
High pressure operations theaters.
