Customized Acoustical-Analysis Programs Speed Delivery of Critical Information

By Mark Ferdinand President On-line Digital Technologies, Inc.
Carmichael, California

Acoustic emission is used to detect defects in structures such as pipes and containment vessels. Cluster analysis, which summarizes acoustic signal characteristics such as amplitudes and waveform shape factors, indicates whether or not there is a likely defect source at a particular location. Arriving at a cluster analysis by means of spreadsheet calculations required the user to manually search for the appropriate data segments within sets of data containing 35,000 to 50,000 or more points. With a new custom acoustic-emission analysis program based on Origin, it is simply a matter of pushing buttons on the screen. The software automates the majority of the analysis process, walking the user through the sequence and delivering the necessary plots at each step of the way.

Figure 1- Event histogram and Peak Amplitude both plotted vs Location, with waveguide positions indicated. Shows entire pipe section under test. Plotted first to identify locations of high AE activity for further cluster analysis.

AE monitoring is a non-invasive testing technique that uses sound waves emitted by defects growing in a structure under stress. AE sensors "listen" to the structure at very high frequencies (300 to 400 kHz) and can sense the sounds of microstructural failures such as cracking and inclusion decohesion. Combined with the ability to perform "source location" using arrival time difference techniques, AE is the only method that can yield a real-time assessment of structural health under operational conditions. AE has proven to be the most sensitive technique for global inspection of seam-welded piping systems, such as the high-energy piping systems in fossil power plants.