Permeation Studies of PVC Pipes with near Infrared Spectroscopy

Abstract

Polyvinyl chloride (PVC) pipes are commonly used to transport drinking water. Although PVC is resistant to natural environmental conditions, organic solvents may attack the pipe wall causing swelling, softening, water lines failure and drinking water pollution. Leaks from underground storage tanks and random accidental spills of organic solvents or fuels place the pipes in contact with organic solvents. Near infrared (NIR) spectroscopy was used to track the permeation of PVC pipes by three major organic solvents (toluene, benzene and gasoline) at different concentrations. Partial least squares (PLS) calibrations with NIR spectra and reference data gave accurate models with R² > 0.9, relative performance determinant (RPD) > 3 and low standard errors of prediction (SEP). These models could predict the permeation status measured by mm of solvent moving front, weight gain, or days under permeation. A second study correlated pipe permeation susceptibility to pure toluene in mm h^−1/2 to the pipe spectra. Spectra differences from several pipe brands and sizes were modelled with locally weighted regression (LWR), resulting in models with accuracy (RPD) of around 5. NIR was a suitable tool to evaluate the permeation of PVC pipes and to predict the susceptibility of PVC pipes to permeation.