Permeation of organic compounds through ductile iron pipe gaskets

Abstract

Ductile iron (DI) pipes have been used for the conveyance of drinking water in drinking water distribution systems over the past several decades. It has been estimated that almost half of all new water mains installed in North America are DI pipes. Although DI pipe itself is resistant to chemical permeation, the polymeric gaskets that join and seal the pipe segments are reported to be susceptible to permeation by organic contaminants. Pipe-drum, diffusion cell experiments, and numerical simulations were conducted in this research to obtain a faster mean to evaluate possible permeations through DI gaskets. Of the five types of gasket materials tested using the gravimetric sorption test, ethylenepropylene-diene monomer (EPDM) had the highest sorption of gasoline, while fluoroelastomer rubber (FKM) exhibited very low sorption of gasoline. The sorption test results suggested that the least to most resistance to permeation of premium gasoline for the five gasket materials were EPDM, styrene-butadiene rubber (SBR), chloroprene rubber (CR; neoprene), acrylonitrile butadiene rubber (NBR), and FKM. A typical gasket was found to be made of two portions, the heel and the bulb, of the same polymer but different formulation. Gravimetric sorption tests suggested that the heel portion of all gaskets may be more resistant to permeation than the bulb making it the limiting step for permeation of organic compounds in gasoline. Pipe-drum experiments showed that SBR gasket had the highest permeation rates of benzene, toluene, ethylbenzene, and xylenes (BTEX), followed by CR, EPDM, and NBR. With regards to threats to drinking water under water stagnation conditions in the pipe, the 5 μg/L maximum contaminant level (MCL) for benzene will likely be exceeded during an 8-