Reduced section bolting. 1

[Llexlon]

Anyone have experiance/knowledge of the legality of using reduced section bolting to attach a dished head? The vessel is an ASME Section VIII-1 pressure vessel and we want to have the bolting machined to a calculated dimension allowing the head to be the relieving device for the vessel.

 

[jte]

If I understand your description properly, you are proposing to machine down the diameter of the bolts such that they will fail before the vessel splits a long seam. In essence, a concept similar to a frangible roof on a tank. I've seen a similar scheme before where a client wanted to machine the top head to shell circ seam to half the shell thickness so that if a deflagration occurred it would pop the head instead of splitting the long seam. I don't think it got built that way, but I wasn't directly involved in that one. In any case, it was not a scheme to avoid putting a relief device on. I presume in your case that the fluid which would leak is neither harmful nor flammable/explosive.

Simply put, I'd say the answer is no. First, you'd probably not get enough bolt area to seat the gaskets so you'd have a perpetual leaker. The Code legality lies with getting the head/bolts certified as a Code legal device. I'd suspect that you'd have a hard time getting a UD stamp on the head.

This issue sounds to me like an MBA inspired expedition, not one inspired by an ME.

jt

 

[unclesyd]

In addition to the sage advice from jte take a look at the following accident report about a head coming off unexpectedly.

http://www.csb.gov/index.cfm?folder=completed_investigations&page=info&INV_ID=2

 

[MJCronin]

BRAVO..!!!!! JTE

I often wonder how many questions get posted on these forums that are simply put...."expeditions"

-MJC