Plastic: Permeation of chemicals
Polyethylene Pipes for Transporting Process Water Containing Benzene
PE 100 pipes are used in both drinking water and gas supply (and also for the discharge of municipal wastewater). For these applications, there is very positive operational experience, particularly because of the insensitivity of polyethylene to corrosion. The pipes are standardised in European standards and certified for gas and water supply in Germany by the DVGW (German Technical and Scientific Association for Gas and Water).
Pipes made of PE 100 are also used for industrial applications. Whether the material polyethylene is resistant to the medium to be transported is tabulated (e.g. in Supplement 1 to DIN 8075). According to this standard, PE-HD (as a generic term, PE 100 is a PE-HD) is only conditionally resistant to technically pure (i.e. almost 100%) benzene. Over time, the benzene can penetrate the polyethylene and cause swelling, which in turn weakens the mechanical properties. A pipe made of PE 100 can therefore only be operated with a reduced internal pressure. The reduction factor must be determined on a case-by-case basis for the concentration in question.
SLA® Barrier Pipe (Drinking Water Pipe with Permeation Barrier)
In addition to the resistance of the material, the permeation tightness of the pipe material must also be observed. It has been known since the beginning of the use of polyethylene pipes that they are not permanently diffusion-tight against benzene. The point in time at which the first molecules permeate through the pipe wall and the permeation quantities depend in each individual case on the concentrations and the operating temperature.
Against this background, egeplast developed the SLA® Barrier Pipe back in the 1980s. This polyethylene pipe contains an aluminum barrier layer and is therefore similar in construction to a Tetra Pak. This permeation-resistant PE pipe is approved in the Dutch KIWA regulations for the Installation of drinking water pipes in contaminated soils with a concentration of up to 1780 mg/l benzene in the vicinity of the pipe.
