The main advantage of non-intrusive acoustic detection is that it does not require magnets installed in the pigs. It basically detects a sound profile in one of two ways:
-Either active, where it transmits a signal through a pipeline and analysing the reflected signal as it returns. In this case you do require a partially or completely liquid-filled pipeline to transmit the signal.
-Or passive, where it ‘listens’ for a certain acoustic signature. Although more difficult in their initial setup they will offer reliable detection so long as the acoustic environment does not change significantly. The other advantage is that these can be used for mixed phase and gas-filled pipelines as well.