Permeability of PVC pipes
Permeability is the ability of chemical substances to enter the pipe system through the pipe walls or joints.
The occurrence of this kind of event has been reviewed by various water distribution companies and no major problem has occurred with PVC piping systems.
As an example the intrinsic permeability of PVC is in the order of 10 times lower than for polyolefins.
There have been several studies concerning the permeability of plastic pipes and pipes of other materials(1 – 3). The most recent study of plastics pipes was carried out by the Awwra Research Foundation on the ‘Impact of Hydrocarbons on PE/PVC pipes and Pipe Gaskets [Project #2946]’(4).
This concluded that either PVC or ductile iron (DI) water mains can be safely used in any level of gasoline contamination, even free product, as long as there is a minimal average water flow in the mains. Although benzene, toluene, ethylbenzene, and xylenes (BTEX) will permeate the gaskets, US EPA MCLs will not be exceeded. Similarly, PVC and DI pipes can be used with periods of stagnation (i.e., service connections) for any level of groundwater contamination by gasoline. PVC itself is impervious to gasoline, BTEX, and trichloroethylene (TCE) in groundwater at commonly encountered levels of contamination.
Berens(3) concluded that rigid PVC is an effective barrier against permeation of environmental pollutants.
In PVC pipe systems, the joint zone may be a weak point, but the exposed area of the elastomeric seal compared to the total area of the pipe surface is very small. Several of the studies mentioned below have also looked at the effect of hydrocarbons on the sealing rings; two of them concluded that NBR seals are more resistant than SBR seals.
References
1.Vonk, ‘Permeation of Organic Compounds Through Pipe Materials’, Pub. # 85, KIWA, Neuwegein, Netherlands, 1985.
2. Cassaday, Cole, Bishop & Pfau, ‘Evaluation of the Permeation of Organic Solvents Through Gasketed Jointed Unjointed Poly (Vinyl Chloride), Asbestos Cement and Ductile Iron Water Pipes - Phase 1 Report’; Battelle Columbus Laboratories, Columbus, OH, for the Vinyl Institute, Div. of Soc. of Plastics Indus, Inc. 1983.
3. Berens, ‘Prediction of Organic Chemical Permeation through PVC Pipe’, JAWWA 77 (11), 57-64 (1985).
4. Ong, Gaunt, Mao, Cheng, Esteve-Agelet, Hurburgh, ‘ Impact of Hydrocarbons on PE/PVC Pipes and Pipes Gaskets [Project #2946] , Awwra Research Foundation, 2007.
