Acoustic Emission Testing of Aboveground Storage Tanks

Acoustic emissions are stress waves produced by sudden movement in stressed materials.  The classic sources of acoustic emission are defect-related deformation process such as crack growth and plastic deformation.  Sudden movement at the source produces a stress wave which radiates out into the structure and excites a sensitive piezoelectric transducer.  Leaking gases and liquids also cause acoustic emission.

Acoustic emission differs from most other nondestructive testing methods in two key respects.  First, the signal has its origin in the material itself, not in an external source.  Second, acoustic emission detects movement while most other methods detect existing geometrical discontinuities.

A major benefit of acoustic emission inspection is that it allows the whole volume of the structure to be inspected non-intrusively in a single loading operation.  It is not necessary to scan the structure looking for local defects; it is only necessary to connect a suitable number of fixed sensors.  This leads to major savings in testing large structures for which other methods require removal of insulation, decontamination for entry to vessel interiors, or scanning of very large areas.  Typically, the global AE inspection is used to identify areas with structural problems and other NDT methods are then used o identify more precisely the nature of the emitting defects.

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