Manway flange hardware used on API 650 Storage Tank

[geesamand]

API 650 section 4.7 calls out the use of a heavy hex bolt and heavy hex nut for flange connections. When I read API 650 both the illustrations and word choice (bolt vs. stud) it's quite clear that a bolt is specified.

Yet I see a studbolt (threaded rod) and two nuts everywhere in North America and Europe. No hex-head bolts (or "screws") that I can find. These appear most similar to API 6A flange hardware, which of course is specific to wellhead equipment.

Please share if there is a uniformity in this practice, what standard is actually being followed, etc.

Bonus points if anyone knows why API 650 12th edition still specifies bolt and nut when so few storage terminals are following it.

Thanks,

David

 

[MJCronin]

"Stud bolts" are the most favored choice by maintenance departments.

The only problem with them, as I recall, is the difficulty in placing identifying markings on them