Thermoplastics such as Polyvinylchloride (PVC), Acrylonitrile-Butadiene-Styrene (ABS) and Polyethylene (PE), are popular choices for potable watermains and sewage forcemains owing to advantages over traditional materials such as Ductile-Iron (DI) and Steel. Unfortunately, the physical properties give thermoplastics their comparative edge over metallic pipes, also make them poor candidates for traditional non and minimally invasive acoustic leak detection and condition assessment techniques. This is because plastics pipes, being soft and flexible, and thus acoustically dispersive, are better at absorbing sound than transmitting it. If these factors are not appropriately accounted for in modeling and analysis, significant error can be introduced.
Another complication is that is that failure modes for plastic pipes differ from those of iron pipes. While wall thickness measurements can be sufficient for remaining service life prediction for iron pipes, research has shown that at the time of failure, plastic pipes are often as thick as they were at installation. Rather, many plastics pipes fail because they have become too brittle to handle pressure transients or changes in surface loading or have become too deformed to properly distribute stresses. Likewise, changes in material properties of the pipe-wall can affect the quality of bonds and the tightness of joints leading to leaks.
ICONAC’s Tonal Pipe AssessmentTM (TPATM), has been used to assess several km of PVC and PE watermains ranging in size from 150 to 250 mm overcomes these challenges through a SODAR type system that takes a different approach than conventional, acoustic time of flight or ∆T systems. Using a sound source that emits a series of pairs of tones of equal amplitude, varying very slightly from one another in frequency, over a wide frequency range, TPATM matches the frequency dependent propagation function of those tones with the frequency dependent effective wall impedance function which is directly related to the stiffness and thickness of the pipe wall. Additional measurements using a Thermodilatohydrometer, which measures the dissolved gas fraction, temperature and density of the liquid in the pipe, allows TPATM to correct for in-pipe attenuation and scattering due to bubbles.
Following inspection, ICONAC uses measured data together with operational history, manufacturer specifications, industry standards and public research literature to score each plastic pipe segment according to a classification matrix:
Within “x” Years
Within “x” Years