Abstract
We have developed the world-first 10 channel acoustic emission telemetry system where acoustic emission singals (envelope profile) from incipient crackings are transmitted to signal processing unit by way of FM radio. The system was designed to apply acoustic emission techniqure to the continuous safety surveillance of very large welded structures like oil storage tnaks, line pipes, and chemical reactors where enormous lengths of wiring are required otherwise.
The system was applied to a 17 m diameter spherical tank and a 104 kl cone-roof tank where a pulse simulating acoustic emission was generated at certain point on the surfaces and recieved at the various locations of different distances up to 10 m from the signal source. Both arrival-time triangulation and attenuation calibration method were used to locate acoustic emission events. Sound velocity and attenuation characteristics were obtained by using the leading edge of the FM-radioed acoustic emission envelope and its amplitude respectively. The measured values correspond well with the ones reported in the literatures. Further the system was successfully applied to monitor and locate cracks of hydrogen weld cracking as well as fatigure crack propagation of a 3 m diameter spherical pressure vessel.
