The Sealing Performance of New Gasketless Flanges Made by Unplasticized Polyvinyl Chloride

This paper deals with a new seal system between flange joints without using gasket. This gasketless flange includes a groove and an annular lip that is machined in one of the flange being in contact with the other flange to form a seal line when the flanges are assembled. In this study, first, fundamental dimensions are examined for PVC-U to obtain the best sealing performance. Then, the effects of material difference and flange nominal size on the sealing performance of new gasketless flange are investigated for two types of materials, 0.25% carbon steel (S25C JIS) and unplasticized polyvinyl chloride (PVC-U JIS). It is found that the critical internal pressure where leakage appears is mainly controlled by the maximum normal stress at the annular lip for each material even if the flange nominal sizes are different. The gasketless flange made by PVC-U shows the higher critical internal pressure compared with the case of S25C if the same clamping forces are applied. The effect of stress relaxation for PVC-U on the sealing performance is also considered. Then, it may be concluded that this PVC-U gasketless flange also has good sealing performance.