Flange Area in Nozzle Reinforcement

[roca]

I am calculating the reinforcement on a 16" 600# LWN Inspection Opening nozzle acc to ASME VIII This is an existing vessel Total nozzle length from o/s shell to flg face = 170mm The flange thickness is 84 mm which leaves 86 mm of nozzle neck The allowable nozzle length 'h' that can be taken in the reinforcement calcs is 106mm The existing calcs which have been approved have taken 106 mm allowable length in the reinforcement calculations which means that part of the flange is taking the flange loads + reinforcement requirements I do not agree with - despite the nozzle being only for an inspection opening and has no other nozzle loads applied

I would normally take a length equal to the length of a WN flange off the available total nozzle length Which in this case would not work as a 16" 600# WN flange is 178 mm long and we only have 170 mm

Alternatively I would allow Square Root (dt), where d = nozzle dia and t = nozzle corroded wall thk, which in this case would be equal to 126 mm This would then leave 170 - 126 = 44 so say 50mm available for reinforcement

Am I being to conservative?

The vessel is obviously ok as it has been in service for a while now.

 

[JoeTank]

ASME VIII does not permit the flange are to be used in the area replacement calc unless its a stud pad type opening.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[jte]

Steve-

I had a similar issue which was resolved using Fig. UG-37 and a couple of blobs (to use the technical term!) of weld buildup. In my research for that problem I did not see where VIII-1 or -2 explicitly exclude the flange area from the allowable reinforcement area. Can you tell me which paragraph this prohibition is in?

jt

 

[roca]

Take a look at UG-40 (e)in ASME VIII Div. 1

 

[jte]

roca-

Thanks for the reference. With the exception of studding outlet type flanges and straight hubs of forged nozzle flanges... bolted flange material within the limits of reinforcement shall not be considered to have reinforcing value.

The way I read it, you can use the barrel - straight hub of a forged nozzle flange - of a long weld neck all the way to where the flange begins. So I wouldn't subtract the entire length of a weld neck flange from the reinforcing area.

In your case I'd use all 86mm of the neck and consider making up the rest with an oversize fillet weld and/or weld buildup on the shell and/or neck. Use the F factor in Fig. UG-37 to minimize the amount of weld buildup req'd. You'll do a lot of buildup on the plane parallel to the longitudinal axis of the shell and probably won't need any on the circ axis of the shell.

jt

 

[roca]

I disagree
Your method means that the flange hub takes not only the flange stresses but also has to take on the role of reinforcement

 

[JohnGP]

Yes, but ASME only provides a cautionary note regarding giving this combined duty special attention "in unusual designs or under conditions of cyclic loading". (I hope latest edition of ASME VIII hasn't changed that, 'cos I haven't got it.)

In your particular case of an inspection opening nozzle loads do not need to be considered anyway, but it's an interesting discussion for nozzles with loads.

Cheers