Anomalous Hydrogen Permeation in Polymers

Several incidents associated with hydrogen transportation and distribution are caused by leakages in piping, valves, and fitting. These are originated due to the hydrogen permeation in the material, which can be subjected to damage. The selection of polymers materials for linear applications (such as HDPE and PA11) and elastomers for gaskets and seals (such as NBR, FKM, and EPDM) is a relevant issue to ensure the safety of these operations. Thus, knowing the hydrogen permeation rate across these materials is critical for selecting, designing, and operating hydrogen systems.
Typically, permeation in polymers is described according to the traditional diffusion equation, also known as Fickian diffusion. However, this approach does not hold universally. Here we present cases from published data where the experimental data shows a departure from the traditional diffusion approach. Direct consequences of this anomalous permeation imply that the expected hydrogen leakage rate does not scale proportionally with liner thickness, or the loading and unloading times for dissolved hydrogen in elastomers will require less time than the calculated.
In this research, we introduce an approach for this anomalous permeation that will enable a correct representation of the hydrogen permeation in these cases. It was found that polymers present a departure of the traditional parabolic scaling for diffusion, showing a power law. This implies that estimating hydrogen saturation times or hydrogen permeation rates in these polymers can be underestimated when using a result obtained from a different size geometry than in the measurement experiments (up to 20% of error when using a thickness 50% larger than the studied).