Q: What stud and nut material should I use with a ANSI 600# Alloy 800 HT pipe class max temperature 1650°F.
A: Given that you are at a high temperature and pressure I would recommend going with an Inconel 625 stud. This will provide the best combination of high temperature strength. Inconel 625 bolting can be used to temperatures of about 1800°F. These fasteners also offer 144ksi ultimate tensile strength. Inconel 625 fasteners are known for their resistance to corrosive environments as well.