To identify the mechanism of valve seat deterioration in membrane gas meters, we collected the membrane gas meters used for 10, 20, and 30 years, and disassembled them for the present investigation. It was found that the main factor causing lower airtightness of the valve seat sealing agent was not the change in sealing agent composition (such as decomposition and oxidative deterioration), but the change in configuration. The results of an accelerated heat aging test confirmed that in the gas meter installation environment, valve seat sealing agent configuration change ceases within a few years after installation.

When the environmental stress crack phenomenon of PMMA by ethanol was observed by the chemiluminescence method, it was able to catch that radical had occurred at the moment of destruction.