Difference Between Flange Adaptor and Dismantling Joint

We are in water carbon steel pipe line projet with this spec

pipe according to Api 5L Gr 52

80 in dia

9.53 mm thikness

working pressure 9 bar

in the valve champer which beter to install flange adaptor or dismantling joint.

and is there a specific direction for the flange adaptor while installation (in the diriction of the flow or the opposite direction).