Study on the effect of hydrogen cycle pressure relief time on the hydrogen permeability and mechanical properties of polyamide liner materials for type IV hydrogen storage cylinders of HFCVs

Abstract

Plastic liners for type IV hydrogen storage cylinders of hydrogen fuel cell vehicles (HFCVs) experience varying pressure loads, deteriorating both hydrogen permeability and mechanical properties and impacting cylinder safety. This study performs hydrogen cycle tests on polyamide 6 (PA6) and polyamide 11 (PA11) samples (temperature: 288 K; pressure relief times: 6, 60, 3600 s; upper/lower pressure limits: 70/1 MPa). After 50 hydrogen cycles with 60 and 3600 s relief times, PA6 and PA11 exhibit changes in hydrogen permeability coefficients within 2%. However, with a 6 s relief time, the coefficients significantly decrease (>10%). After 6 s cycles, PA6 exhibits tiny holes, while PA11 exhibits clustered pieces of holes. Cracks appear in both materials' internal structures after 60 s cycles. Despite minimal tensile strength changes (within 5%), the nominal strain at tensile fracture of both materials changes significantly under different times. These findings can help determine optimal pressure relief times for hydrogen cycle tests on plastic liners.