Fittings on pressure vessel

[CRN1990]

Hai all,

Just to clarify an issue. We are currently fabricating a vessel and there is a socket weld that needs to be welded directly on the vessel.

UW 16 f (3) states the below:
(3) See below:
(-a) Fittings not exceeding NPS 3 (DN 80), as shown in Figure UW-16.2, may be attached to vessels that are not subject to rapid fluctuations in pressure by a fillet weld deposited from the outside only without additional reinforcement other than is inherent in the fitting and its attachment to the vessel wall provided all of the following conditions are met (-1) maximum vessel wall thickness of 3/8 in.(10 mm)

And then
UW 16 f (4) mentions:
(4) Fittings not exceeding NPS 3 (DN 80) may be attached by a fillet groove weld from the outside only as shown in Figure UW-16.1 illustration (bb). The groove weld tw shall not be less than the thickness of Schedule 160 pipe (ASME B36.10M) for the nearest quivalent pipe size. [For fittings smaller than NPS ½ (DN 15), use Schedule 160 taken from Table 8 of ASME B16.11.]

Our vessel shell thickness is 12mm. So if i understand correctly, I can weld the fitting on the vessel provided I use the UW 16.1 (bb) welding detail?

Anyone care to explain what the differences are between the this both statements?
Thankful for any helpful answer.

Regards

 

[FormerAIS]

First, consult with your AI in regards to this.

Secondly, the major difference is the thickness required to fulfill UW-16(f)(4), with the small diameter nozzles you are referring to, a SCH 160 is pretty beefy. A good number of manufacturers I have seen would rather not put that thick of a weld on a vessel if they don't have to. The weld having to be calculated based on this SCH 160 thickness results in a 5/16" weld on very small coupling.

Lastly, if you have any other questions, consult with your AI Supervisor.