The use of ultrasonic devices for non-destructive testing (NDT) has become more common in recent years as equipment has increased in capability and decreased in price. Ultrasonic NDT devices work by creating a pulse of high-frequency sound, generally in the range of 2.5Mhz to 10Mhz, and then measuring the return, a process that makes it possible to measure and resolve anything from the simple thickness of a material through to corrosion and even weld or flaw inspection. The use of ultrasonic NDT devices is attractive because of their non-invasive nature. They don’t require a plant shutdown to obtain a measurement. However, deploying this kind of device within a hazardous (classified) location has implications for safe use that even NDT inspectors may not be fully aware of.
As briefly outlined above, an ultrasonic device operates by combining the creation of a pulse or series of pulses of sound with measurements of the return of those pulses from target back to device. These pulses and echoes are sent and received by a piezoelectric transducer. Equipment that employs the pulse/echo to operate use transducers to:
- Convert electricity into sound = pulse
- Convert sound into electricity = echo
Simple thickness measurement devices, for example, measure the time of flight of the sound wave between the pulse and the echo. The time between the pulse and the echo equates to two times the material thickness when multiplied by the known material velocity value.
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