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Acoustic Methods

The simplest of these techniques is simple sounding of the wall with a hammer. The tone of the sound made can vary with the condition of the wall and whether a void is present outside the wall. Measuring the rebound of the calibrated impact of a metal ball on a wall surface can provide additional quantitative information on the local condition of the wall. Acoustic wave methods send acoustic signals into the pipe wall and record reflected waves arriving back at the instrument. Knowing the speed of travel of the wave in the wall material allows an interpretation of the wall thickness. Such methods are very well developed for some industrial uses but their application underground and in the materials used for underground piping or pipe relining systems can be less reliable.

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