Threadolet Wall Thickness for Sect VIII Apps 1

[BigTank]

Can anyone advise me on the subject? It seems to me that the wall thickness of this type of branch connection would depend on the run to which it is being welded.

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[rneill]

O-lets are manufactured to MSS SP-97. This standard says ...

"Fittings manufactured to this standard practice are designed to make a fully reinforced branch connection in accordance with applicable piping code requirements, when attached, at an opening in a run pipe by means of a full penetration weld."

Table 1 of this standard provides information on which class of O-Let fitting is to be specified based on the schedule of pipe wall in use. It also notes that the use of run or branch pipe thinner or thicker than listed constitutes a deviation from the practice and then the fittings would essentially need to be custom designed and made to special dimensions agreed to by the Manufacturer and the Purchaser.

Note: in effect the standard is written under the general assumption that the branch pipe and the run pipe will have the same schedule (which was probably true long ago but with changes in code formula's doesn't hold today). However, if you specify the O-Let based on the heavier of the run and branch you should be conservative.

Here is a quick summary:

For buttwelding branches
Sch Std = Standard O-Let
Sch XS = Extra Strong O-Let
Sch 160 = Schedule 160 O-Let

For threaded or socket welding branches
Sch XS = Class 3000 O-Let
Sch 160 - Class 6000 O-Let

 

[BigTank]

rneill: Thank you. That is all very helpful information.

I suppose describing my particular proposed use might be in order. I have some guys that want to use up blind flanges we have in stock. These flanges need and instrument tap, and will then be attached to the end of a pipe header. Rather than use a full coupling, drilling and filleting both sides per Section VIII, they asked if the use of a threadolet might be possible. It seems as if it is. This would allow for a smaller hole, and welding from only one side. Understanding that the threadolet is designed to provide reinforcement as a piping branch, I would still like to calculate the available reinforcement in my application. Thus the need to know the wall thickness.

Actually, if I knew the full dimensional description of the threadolet, I wouldn't be asking the question. I could instruct the welders on a particular welding procedure and/or size if need be different from standard threadolet practice. Does this information also appear in B16.9? Unfortunately, I cannot find our company's copy.

In the future we will be using reducing flanges in this application. Frankly, I'm not sure why the shop doesn't want to use them now and save the blinds for another fabrication.

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[vesselfab]

I always use a threaded reducing flange for this.

WHY? you ask?

Because I am lazy and don't want to go through the calcs to say it's ok through blind.

 

[rneill]

The O-let is designed so that it has enough reinforcement to replace the metal cut away from the pipe. The problem you have is that the blind is going to be much much thicker than the pipe so an O-let is unlikely to have sufficient reinforcement to replace the metal that is removed but you could try to do the calcs.

Myself, I'd look at the actual thickness of the blind XX inches and then see if this corresponded to some schedule of pipe (Say 24" Sch XXS). If you could find a piece of pipe that was thicker than the blind and then buy an O-let rated for that pipe, it should provide sufficient reinforcement for the blind as well - I think ?

 

[vesselfab]

EXCEPT THE CONTOUR OF BOTTOM

 

[rneill]

Good point, the better solution might be to call Bonney Forge or one of the other suppliers and ask them if they have something suitable for a flat plate.

 

[BigTank]

All branch connections can be ordered for a FLAT run. Thus no contour.

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[BigTank]

rneill...not a bad idea you have there. I've got the shop to concede and tap the blind. I am curious to know the answer to this question, though. I might have to run it by our AI.

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[rneill]

You may find some guidance in the Engineering section of the Bonney Forge "Branch Connection" Catalogue. Alternatively, there may be something of use to you in Pipe Fabrication Institute (PFI) ES49 "Guidelines for installation of Integrally Reinforced Branch Connection Outlet Fittings" but I haven't actually seen it so I don't know.