We talk a lot about flanged and welded connections but not so much about threaded connections. This is mainly based on my limited experience with threaded connections used in HAZMAT processes. But one thing I did learn about threaded connections is a MAJOR prohibition for threaded connections @ vessels when the piping/vessel will contain flammable liquids, gases, or vapors.
Using ASME Section VIII as my RAGAGEP, we can see the limitation that should be caught during the DESIGN phase and any CHANGES to the process via the MOC hazard/RAGAGEP review.
Using UG-43, we see the following: (emphasis and spacing by me)