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

Hydrogenated nitrile butadiene rubbers (HNBR) and its derivatives have gained the significant importance in automotive compressed natural gas (CNG) valve applications. In one of the four-wheeler 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 pressure more than 10 bars. However, it was found permanently deformed under 4 bar pressures. In the present work, a set of experiments were carried out in order to find out the primary root cause of diaphragm permanent deformation and preventing the failure for safe usage of the CNG gas. HNBR diaphragm deformation investigation was carried out using advanced qualitative and quantitative analysis method 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 10 bar pressure) and field failed diaphragms (HNBR diaphragm deform after 4 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 Field failed diaphragms was observed in declined order in comparison with OK diaphragms. TGA and SEM analysis revealed the filler concertations and morphology of the diaphragms. The chemical nature and thermal properties have been analysed using FTIR and DSC analysis techniques. Soxhlation extractions study helped to understand the crosslinking density of OK and field failure diaphragms. Preventive measures have been implemented to mitigate HNBR diaphragm permanent deformation issue. Keywords: Hydrogenated nitrile butadiene rubber, Compressed natural gas valve, Filler concentrations, Crosslinking density, Failure preventions.