Composition and property changes of HNBR and FKM elastomers after sour gas aging

Abstract

Assessments of the suitability of elastomeric sealing materials for sour gas service tend to focus on physical property modifications. The lack of emphasis on understanding the chemical changes occurring during these exposure regimes seems surprising given that 40% of untapped gas reserves hold H2S. Study of fluoroelastomer (FKM) and hydrogenated nitrile butadiene rubber (HNBR) compounds post sour gas aging revealed a number of degradative mechanisms had occurred; including, additional crosslinking, chain scission, filler modification, dehydrofluorination, low-level oxidative aging and extraction of soluble matter. In many instances, these mechanisms had opposing effects on the properties of HNBR and FKM compounds. Testing of further samples at incremental stages during aging will allow chemical changes to be correlated with property modifications as a function of time, and may provide a route to more robust lifetime predictions. Analysis of used or failed service parts would help verify that the aging regimes adopted are accelerating the relevant modes of degradation.