Failure Prevention of Permanent Deformation in HNBR Elastomeric Diaphragms Used in CNG Valve Applications

Hydrogenated nitrile butadiene rubbers (HNBR) and their derivatives have gained significant importance in automotive compressed natural gas (CNG) valve applications. In one of the four-wheelers, CNG valve application, HNBR elastomeric diaphragms are being used for their excellent sealing and pressure regulation properties. The HNBR elastomeric diaphragm was developed to sustain CNG higher pressure However, it was found permanently deformed under lower pressures. In this research work, number of experiments was carried out to find out the primary root cause of diaphragm permanent deformation and to prevent the failure for safe usage of the CNG gas. HNBR diaphragm deformation investigation was carried out using advanced qualitative and quantitative analysis methods such as Soxhlet Extraction Column, Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Optical Microscopy (OM), Scanning Electron Microscopy (SEM), and Thermogravimetric Analysis (TGA). For this purpose, we have carried out experiments on OK (HNBR diaphragm with higher bar pressure) and field-failed diaphragms (HNBR diaphragm deformed after lower bar CNG pressure). We have found that OK and Field failed diaphragms have different filler concentrations and uneven dispersion and distribution. Also, the crosslinking density of the failed Field diaphragms was observed in declining order in comparison with the OK diaphragms. TGA and SEM analysis revealed the filler concentration and morphology of the diaphragms. The chemical nature and thermal properties have been analysed using FTIR and DSC analysis techniques. The Soxhlation extractions study helped to understand the crosslinking density of OK and field failure diaphragms. Preventive measures have been implemented to mitigate the HNBR diaphragm permanent deformation issue.