Reducing Lapped Flanges

[gatossi]

Hi everybody,
Our client wants to install a 18" line at the bottom of a tank which has a 24" nozzle. We have two options:
1) either we use a reducer (very expensive as it is made of zirconium) or,
2) we use a reducing lapped flange (18" stub end on zirconium sized to match the 24" face, flange on duplex sized to match the 24" dimensions, except for the bore which would be 18")
Everybody is happy with the idea of the flange (especially the client as it seems to be cheaper!) but I can't find any option on 16.5 for "reducing Lapped Flanges". Table 6 only refer to threaded, Blind or Slip-on welding.

Can anyone tell me if a reducing lapped flange 24" x 18" would be listed as B16.5 or it will fall under the unlisted components of B31.3 para 304.7.2

Thanks!

 

[pennpiper]

This is just my opinion.
I don't think you will find any of the "Stub-End" suppliers who make a 24" x 18" reducing version. At least I have never seen reducing Stub-ends in any catalogs. Then you say that you want it in "zirconium". That is not going to be an "off-the-shelf" item. No, you will have to go to a special fabrication shop and have it custom made. And that is going to cost!

 

[gatossi]

pennpiper,

Yes! you are right... this things are damn expensive! Our supplier says he can do the stub-end, that is not my concern.
My concern is on the flange itself.
Duplex is a listed material (as opposse to Zirc, which is not)
But the only reducing flange on Table 6 of B16.5 is a slip-on flange. Therefore I wanted to know if a "reducing lapped flange" would be covered by the code on any way or it is an unlisted component as per para 304.7.2

 

[moltenmetal]

How about a 24" carbon- or stainless steel blind flange, loose clad on its face with zirconium, bored to install an 18" zirc lap joint stub end (welded to the cladding), and drilled/tapped to act as a studded outlet for the 18" size? A clad reducing flange in effect. It won't give you a nice conical shape for drainage, but otherwise should work. You'd have to check the effect of the studded outlet holes on the required flange thickness: perhaps you'd need some extra thickness beyond what a blind would offer, but in CS that's not so expensive. 18" should fit as a studded outlet on 24".

Or if temperature/corrosion will permit, how about a nice 24x18" ETFE-lined reducing flange from Crane Resistoflex? Won't be a stock item, but probably far chepaer than doing the same in zirc...

 

[MJCronin]

"molten" is on the right track...

I also recommendd the bored-out-blind-flange approach, (with a clad/weld overlay as required.

A ring-type boss may be required to get enough flange thickness for the studs to grip...

-MJC

 

[11echo]

I'd like to offer an easier option we use in the oil fields all the time. Just get a blind flange and have it machined as a slip-on flange, you could even do an off-set hole so you could match up the B.O.P. elevations. My $0.02, good luck!