Sound performance

Acoustics emissions monitoring is the only tried and tested way of evaluating the condition of critical, slow-moving high-capital plant and machinery, according to engineers at

(CNES). Though rather overlooked, they claim its time may now have arrived.

CNES has been using this non-intrusive monitoring technique at its steelmaking plants for the past 20 years but only made it commercially available to other industries recently.

Acoustic emissions are the high-frequency stress waves generated by the rapid release of strain energy that occurs within a material during crack growth, plastic deformation or phase transformation. Monitoring systems use surface-mounted transducers to detect the waves, which lie within the 25kHz to 1MHz frequency range.

Ian Taylor, business development engineer, plant condition monitoring at CNES, said this type of monitoring is beneficial when there are fluctuating load conditions and where a breakdown would impact production. Still, many companies use vibration monitoring systems to check critical plant machinery. 'Vibration monitoring is fine for high-speed motors, fans and pumps,' said Taylor. 'Anything less than 80rpm, that's our cut-off point for vibration against acoustic — it becomes difficult to interpret with vibration monitoring.'