ASME BPVC Section VIII Div.1 nozzle attachment

[TylerM]

Good morning everyone,

I have two questions. The first is about the ASME BPVC Section VIII Div. 1 code, and the second is about general engineering practice.

First question: In the ASME code a nozzle attached with an internal and external (double-sided) fillet weld, as shown in figure UG-40 (i) has a finished diameter (FD) equal to the inside diameter of the nozzle. This seems a little off to me, I know all full penetration-attached nozzles has a FD equal to the inside of the nozzle, and a single-sided fillet welded nozzle has a FD that is the outside of the nozzle. To me it seems a little odd that a double-sided fillet weld has a FD more like a full penetration weld instead of a single-sided fillet weld. Could anyone offer some explanation to this?

Second question: (This question is more to appease my curious mind) If you need to put a weep hold in a reinforcement plate [to let out moisture and air as the vessel heats up and cools down] why don’t you need a weep hole when you are attaching a nozzle with a double-sided fillet weld? Theoretically there’s a small space for air that gets trapped when you finish welding much like the reinforcement place.

Regards,
Tyler

 

[SnTMan]

TylerM, tough to answer your #1 definitively, but partly, the difference is whether the nozzle is inserted thru the vessel wall or not. See UG-40, sketches (a-1), (j) and for double filleted details where the nozzle ID is not FD.

Your #2, yeah it probably should but in my experience is rarely done. I have seen (not often) a drill & tap thru the hub of a slip-on flange. More rarely, the outside fillet is incomplete. The problem with this is you get rust runs from the lapped surfaces. Looks like crap on a new vessel A detail that can be plugged is much preferred.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[Dhurjati Sen]

TylerM

#1 Visualize the assembly from the fit-up stage. You will find the FD is indeed equal to the nozzle ID.

#2 The theoretical air trapped inside is negligible to provide for a weep hole.

 

[SnTMan]

#2 The theoretical air trapped inside is negligible to provide for a weep hole.

Unless you are hydrogen service, in which case you shouldn't be using a double fillet anyway

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[TylerM]

Thank you everyone for all of your help and insight. I'm glad to know that someone (although rare) has addressed the air on the inside of the fillet welds.