Hi, I've seen this standard quite few times (API 6A type 6B) when I read article about piping. Tried to Google it, but couldn't find exact definition that I need. Anyone familiar with this and wouldn't mind to dumb it dowm for me?
API 6A is a standard for wellhead and (christmas) tree equipment. It covers a broad range of equipment, including type 6B and type 6BX flanges. The type 6B flanges are based on ASME B16.5 RTJ flanges (geometry is essentially identical, just slight variations due to rounding and different tolerances) and use the same type R ring gaskets, but have different pressure ratings and material requirements. See below links for more information:
API 6A is not a listed standard in ASME B31.3. If you want to use type 6B flanges in a piping system, I recommend first verifying that it is a listed/recognized standard within your code of construction.