Slip-On Reducing flange pass through welding

[MattNCSU03]

I have a settling tank with 18" Class 150 flange on one end. I've been asked to design a 6" bell-mouth exit for the settling tank through the flange. I couldn't get it to insert inline, but I've attached a sketch of the pipe spool concept I've mocked up. The site requires that it be designed to B31.3 or B31.1 NBEP, design pressure/temp is 100psi/100F.

My concept is using a 18x6 reducing slip on flange to pass 6" SCH 40 pipe through the flange into the settling tank. The bell-mouth would be buttwelded to the pipe and on the other end a 6" SO or WN flange would be used. My question is how would the pipe need to be welded to the flange? I would assume a fillet on both sides but the B16.5/B31.3 does not appear to cover this scenario. I am also open to other approaches if someone has a suggestion.

Thanks,

Matt

 

[XL83NL]

We've done similar situations, though with smaller sizes (say 1x3" or 1.1/2x4"). The 6" flange then was put under scope vessel, and we had our vessel vendor include the weld design of those 2 fillet welds of the SO flange under VIII-1.

Huub

 

[MattNCSU03]

In my head I was stuck in piping mode and I didn't think of the 18" being the boundary between B31 and BPVC. I'll look through VIII-1 discussion on welding nozzles, perhaps UG-39 holds the key...

 

[marty007]

I've done this in the past and used ASME VIII-1 Figure UW-(21) - sketch (2).

On the flange hub I would have just a fillet weld (size = x-min).

On the inside weld, I would have a groove per sketch (2) - except that the pipe extends past the gasket surface. I would then cover this with an additional fillet weld to avoid stress risers.

 

[LittleInch]

Why bother with the bell mouth?

Or just weld both sides of the reducing flange.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MattNCSU03]

I ended up switching to specifying a weld neck reducing 18x6 flange and a lap joint flange with the bellmouth welded to the interior side of the flange. Cuts the number of welds from 5 to 2 and eliminates the question of how to properly weld the SO flange.

To answer Littleinch, its a hydraulic test loop and we're going the extra mile to ensure the flow entering the study area is as uniform as possible.