Definitely use SS fasteners. Avoid galvanic corrosion.
Use bolts of the same alloy as the piping, and nuts of a dissimilar SS class (e.g., martensitic on austenitic bolts) to reduce galling of threads.
Carpenter Technology
has a small chapter on Galling in their SS book. It lists 'Gall-Tough' SS alloys (austenitic SS with a bit of nitrogen), information on the self-galling of SS alloys and the galling between different combinations of SS alloys.
Of course, you could use plated nuts or lubrication to reduce galling.
