Can anyone clarify what type of gaskets you should use on a CL.150# Flat Face flange (316L material). Full face or IBC??? (Gaskets are Novus 30 3mm Thk)
As Saxon suggested, you'll need to use FF gaskets on flat face flanges. Use of ring gaskets can result in excessive bending of the flanges (which will break if they're not ductile). Permanent distortion of the flanges will make sealing very difficult. Also, if the flanges distort to the point where the OD of the flanges are contacting, then you'll have limited load remaining on the gasket.
Select you material based on chemical compatibility, and then select the lowest stress to seal material that is compatible. Full face gaskets have ~4X the contact area of ring gaskets, so you'll need a low stress to seal material and high strength bolting (B7 or Grade 8).
A gasket manufacturer, Inertech Inc., makes a low stress to seal expanded PTFE gasket in a reduced area design which is ideal for flat face flanges. This would be your best bet for most chemical services at temperatures <400F.
