WELDING OF WNRF FLANGE DIRECTLY ONTO SHELL / DISHED HEAD

[PEHasan]

Can we weld WNRF (Weld Neck Raised Face) flange
directly on the Shell or Dished Head? In my opinion we
can weld WNRF flange only with set-on connection. It
will be difficult to weld WNRF flange with set-in
connection because of curvature effect. The other
thing is that we can weld WNRF flange directly on the
Shell or Dished Head up to a size of 2.5 inch only.
This is because as per ASME Section VIII Div 1 we do
not have to do nozzle reinforcement check for nozzles
2.5” and below. It will be impossible to provide
reinforcement pad with the direct welding of WNRF
flange to the shell or dished head even with set-on
connection.

 

[prex]

Hope you are speaking about LWN (Long Welding Neck): never seen any WN (short) welded to shell, even for small diameters.
Both sit-on and set-in may be used (set-in being sometimes required by client spec).
And a reinforcement pad is not necessarily required, it depends on reinforcement calculation. As the thickness of the long welding neck is quite generous, the pad should not be required in most common cases. However of course the use of LWN over 2.5" is uncommon: personally I think I used a maximum of 4" LWN.

prex

http://www.xcalcs.com

Online tools for structural design

 

[deanc]

Suggest you look at a "Studding Outlet". Do not have an email address-but try Forged Vessel Connections Inc. out of Houston.

 

[jte]

PEHasan-

I think I agree with you to a point: I've never seen a WN flange (RF or other) studded directly onto or into a vessel. This would be poor practice if only from the perspective of wrench clearance for attaching the mating flange studs and nuts.

However, even in a range where you exceed the 2.5" diameter (where t min is greater than 3/8") limit or if you exceed 3.5" cutout diameter (where tmin - that's excluding CA - is less than or equal to 3/8") - a 4" stub on with a Sch 160 bore would meet this req't, I think you could reinforce such a connection: Either use an insert plate or use an internal repad. As far as I can tell, UG-37 does not restrict the repad to the outside. In fact, Fig. UG-37.1 goes out of its way to provide the disclaimer "This Figure illustrates a common nozzle configuration and is not intended to prohibit other configurations permitted by the code." The reinforcement limits clearly extend into the vessel.

So... it could be done. But don't try to sell me a vessel built like that! As Prex pointed out, that's into the realm of the LWN nozzle, which my local fabricator has indicated is cost effective up to around 6" CL-150 (he saves fitup, welding, and NDT/QC of the WN to nozzle neck weld). I'd avoid studded outlets simply because I've seen issues with the threads being abused by the gorillas (oops, I meant "qualified, experienced contractors") we occasionally use to assemble our piping.

jt

 

[weeeds]

There are certain applications where we have done this type of configuration. A weld neck flange was set onto the center of a dished head and it works well. You have access to clean up the burn-through and for larger nozzles you can actually get in and lay down a backing pass, even from the outside of the vessel.
The Code does not prohibit this construction. If you are using proper materials there is no issue.

 

[PEHasan]

Before allowing any direct welding of WNRF flange to shell or dished head, we have to make sure that we can remove all stud bolts easily. If the connecting member is a pipe flange, we can always remove stud bolts away from vessel flange. However, if we have a valve flange, then it will be difficult to remove stud bolts.