API 6A Flange
Type 6B Flanges:
Type 6B flanges are ring joint flanges and are not intended for face-to-face assembly. The metallic ring gasket bears the brunt of the connecting bolt force. Type 6B flanges are designed with either through bolts or studs. The dimensions for blind type 6B flanges must conform to Table 36, Table 37, and Table 38, as applicable, with reference to figure number 8 on page 108 of API 6A (19th Edition, July 2004).
Type 6BX Flanges:
Type 6BX flanges are of the ring joint type and come equipped with a raised face. When the gasket has been correctly seated, the connecting bolt force may react on the raised face of the flange, depending on the tolerances. This support prevents excessive bolt torque from damaging the flange or gasket. As a result, at least one flange in a 6BX connection must have a raised face. Type 6BX flanges are designed with either through bolts or studs and do not require face-to-face contact for proper functioning. The dimensions for blind type 6BX flanges must conform to Table 46 of API 6A (19th Edition, July 2004), as applicable.