API 6A Flange
Type 6B Flanges:
Type 6B flanges are not used for face-to-face makeup and are of the ring joint type. The bolt force for connection makeup is applied to the metallic ring gasket. Type 6B flanges adopt through bolted or studded design. Dimensions for 6B flanges blind type shall conform to Table 36, Table 37 & Table 38 with reference to figure no.8 on pg.no.108 of API 6A (19th Edition, July 2004) as applicable.
Type 6BX Flanges:
The 6BX type flanges are the ring connection type, which is designed with a raised surface. Depending on the tolerances, when the gasket has been properly seated, the connection make-up bolting force may react on the raised face of the flange. This support prevents the flange or gasket from the damage by excessive bolt torque. For this reason, one of the flanges in the 6BX connection should have a raised face. Type 6BX flanges adopt through bolted or studded design. It is not necessary for the proper functioning of the 6BX flange to have Face-to-face contact. Dimensions for 6BX flanges blind type shall conform to Table 46 of API 6A (19th Edition, July 2004) as applicable.