Metal Bellow Mechanical Seals Material Seal Face : Carbon, Ceramic, TC Secondary Seals : VitonPTFEGraphite Metal Parts : SS 316, Welded Metal Bellow Seals Metal Bellow Seals are widely used in high temperature and highly corrosive media and suitable for high start-up toque since the bellows unit is independent of torque transmission. The unique feature of Welded Metal Bellow Mechanical Seals is that, there is no dynamic 'O' rings and therefore it will never hangup or damage the shaft and sleeve.