Monitoring using sparse arrays of ultrasonic transducers


Condition monitoring using ultrasound is increasingly sought after as a means of obtaining up-to-date data on critical components rather than relying on inspections carried out during periodic outages. One limitation of monitoring relative to inspection is that traditional scan patterns cannot be performed, limiting the inspection volume to that defined by the initial placement of the ultrasonic probes. This can be overcome to some degree by the use of phased array sweeps and increasing the number of probes, but restraints on attached probes and commercial pressures are likely to dictate that the smallest possible number of probes be used.

To this end, Wood has carried out simulation studies investigating the use of a sparse array of conventional ultrasonic probes to provide full coverage of an inspection volume in a reducer pipe and the crotch corner of a nozzle. The specification, position and number of probes required were varied to maximise the detectability of specified defects of concern. This paper presents some details of the models used along with their results and limitations.

As continuous monitoring should allow reductions in overall noise level due to increases in the data obtained from individual probes, analysis of likely reductions is also presented.