Surface Morphology and Cavitation Analysis of Selected Oilfield Elastomers Under Simulated Underground Hydrogen Storage Conditions

Abstract

Abstract. This study continues earlier work on the mechanical degradation of general-purpose elastomers exposed to hydrogen-rich environments relevant to underground hydrogen storage. While the previous phase examined changes in hardness and compressive strain, this follow-up focuses on microstructural integrity and early signs of material failure under similar aging conditions. Three common oilfield elastomers, ethylene propylene diene monomer (EPDM), fluoroelastomer (FKM/Viton), and nitrile butadiene rubber (NBR), were aged in autoclave systems using controlled environments of 100% H2 and 50% H2–50% methane (CH4) at 25 °C and 70 °C for up to 7 days. Postaging surface analyses were conducted using scanning electron microscopy (SEM), along with statistical evaluations of surface cavity formation to assess degradation onset. SEM imaging revealed increased surface roughness and randomly distributed microcavities on EPDM and NBR aged in pure H2 at 70 °C for 7 days, suggesting cross-link formation. Surface precipitates, likely residual additives, were also observed. Statistical analysis confirmed cavity formation for most samples except NBR aged in 100% H2 at 70 °C for 3 days. Degradation mechanisms were attributed to gas plasticization, chain scission, and cross-linking from chemical aging. Carbon dioxide (CO2) exposure was more damaging due to low diffusivity and strong plasticization despite lower reactivity. By integrating microstructural and statistical analyses, this study builds on prior mechanical findings, offering a more complete understanding of elastomer degradation in subsurface hydrogen environments. The results underscore the importance of both macrolevel and microlevel assessments for material selection in long-term hydrogen storage systems.