File:PVE-4711, Last Updated: Jan 11/2011, By: LB

ASME changed the amount of weld required on a standard B16.5 slip on flanges with the 2009 VIII-1 code update. Per section UW-21 of VIII-1 all standard slip on and socket weld flanges need larger welds on the outside. The larger weld size is not required if there is no room for it on the hub.


UW-21(a) ASME B16.5 socket weld flanges shall be welded to a nozzle neck using an external fillet weld. The minimum fillet weld throat dimension shall be the lesser of the nozzle wall thickness or 0.7 times the hub thickness of the socket weld flange. See Fig. UW-21, illustration (4). UW-21(b) ASME B 16.5 slip-on flanges shall be welded to a nozzle neck using an internal and an external weld.See Fig. UW-21, illustrations (1), (2), and (3).


VIII-1 Fig UW-21 – flange attachment weld size 

The weld size change is mandatory, but do you need to update your CRN? That depends – at the present time Manitoba and Saskatchewan say yes, Ontario says no.