What is ultrasonic testing?

Hearing the inaudible — leaks, arcing and early bearing faults.

Ultrasonic instruments convert high-frequency sound — above human hearing — into audible or visual signals. Compressed-air leaks, electrical arcing, steam-trap failures and early bearing friction all emit ultrasound.

Inspectors sweep with a contact probe or parabolic dish on rounds. It's one of the earliest mechanical-fault detectors and the standard tool for compressed-air and steam-leak surveys.

• How it's used