Hierarchical Channel Morphology in O-rings after Two Cycling Exposures to 70 MPa Hydrogen Gas: A Case Study of Sealing Failure

Abstract

Abstract This study investigates the impact of high-pressure hydrogen gas exposure on the structural and morphological characteristics of O-ring materials. O-ring specimens undergo two cycles of sealing under 70 MPa hydrogen gas, and their resulting variations are examined using advanced characterization techniques, including powder X-ray diffraction (PXRD), small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Our findings reveal that at the microscopic level, the lattice spacing of the O-ring material shows no significant changes when exposed to 70 MPa hydrogen gas. However, at a larger scale in the micrometre range, the formation of a hierarchical channel morphology becomes evident. This morphology is accompanied by the separation of carbon black filler from the rubber matrix, contributing to mechanical weakening of the O-ring. These observations can be attributed to the pressure gradient that develops between the inner and outer radii of the O-ring, resulting from compression forces acting perpendicularly to the radial direction due to clamp locking.