Methane permeation through advanced high-pressure plastics and composite pipes

There is a clear market wish to use plastic and composite pipes for natural gas pipelines at higher pressures than the traditional limit of 10 bars for PE100 pipes. Candidates are Polyamide 12, plasticized PA6.12, Polyamide 11, other long-chain Polyamide pipes and PE-based composite pipes (Multilayer M pipes).
However, at higher pressures permeation of natural gas through the wall of plastic or composite pipes increases, depending on materials composition and SDR. An international testing programme was started to measure the permeation rate and permeability coefficient of 14 different 110mm plastic and composite pipes. Sponsors are pipe and resin manufacturers and GERG (European Gas Research Group). Included in the investigation were 5 different brands of Polyamide pipe, a pipe produced from a PE100 resin containing 10% of a special anti-permeation additive and a RTP Light pipe. Two PE100 pipes were measured for reference.
Using the permeation curves, the permeability coefficient PC (in ml.mm/m2/bara/day), diffusion coefficient D (in cm2/sec.) and solubility coefficient S (in kbara-1) for methane have been calculated for all measured pipes. The PA pipes show only a few percent of the permeability coefficient of PE100 pipe. The PE100 pipe containing 10 % of a special anti-permeation additive possesses a 5.2 times lower permeability coefficient than regular PE100 pipe. Therefore, this modified PE100 pipe shows a permeation rate in between the values for PE100 and PA pipes.