Detecting defects in rising mains using the acoustic fluid velocity

It is a serious challenge to detect wall damage in live rising mains that transport wastewater along flat or elevated sections of the sewer pipe network. This work proposes a novel method that uses the acoustic velocity vector in the fluid to detect the onset of wall defects in a ductile iron rising main. Numerical simulations are performed to show that this acoustic velocity vector is more sensitive to the presence of a wall defect than the acoustic pressure or wall acceleration traditionally measured in fluid-filled pipes. The method can detect internal and external wall loss and small (0.020–0.025 m) wall perforations. An adapted triaxial accelerometer is used to demonstrate experimentally the method on an exhumed section of a 0.31 m diameter ductile iron pipe. It is shown that the radial and horizontal components of the acoustic velocity vector are particularly sensitive to the presence of small wall perforations. The proposed acoustic velocity sensor can be easily deployed on a mobile pipe inspection robot with a collocated or remote source of sound.