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Fabricated 4way cross section

Fabricated 4way cross section

RE: Fabricated 4way cross section

I guess it depends on your design code, so lets start with that. Is this a part for a piping system, e.g. falling under B31.3?

RE: Fabricated 4way cross section

(OP)
Yes it is falling under B31.3

RE: Fabricated 4way cross section

Then you probably have to resort to para 304.7.2.

RE: Fabricated 4way cross section

(OP)
There is no detail at para 304.7.2

RE: Fabricated 4way cross section

Thats absolutely correct. B31.3, as I recall it, is not a cook-book when it comes to such customs fittings. Youve made an unlisted component. Which as an example might require FEA by means of 304.7.2(d).

RE: Fabricated 4way cross section

hi,
for special design, better to perform finite element analysis (FEA) to ensure stress integrity of the equipment/Component.
And to ensure the integrity of product that you have fabricated just follow normal inspection/testing, UT and hydrotest for welding strength.

RE: Fabricated 4way cross section

If you really it that way, go for it, but why not try a forged 6" cross / standard pipe fitting? Im sure you should be able to get them somewhere.

RE: Fabricated 4way cross section

I can't see why you can't analyse this as two branch connections. I suspect you will need some compensation plates for any appreciable reviewable pressure.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: Fabricated 4way cross section

(OP)
Little Inch.u mean reinforcement pad??

RE: Fabricated 4way cross section

Yes - see section 304.3.3 and appendix H.

What you're doing is a bit odd, but I can't see why this should be any different than welding two branches side by side, though there are rules somewhere in that section about minimum distance between them.

A forged component would solve all your problems....

At a design pressure of 1440 psig you can't afford to make mistakes.

You also need to talk to whoever is approving / authorising / inspecting this thing to make sure they are happy.

At the very least it's some sort of start point for your analysis.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: Fabricated 4way cross section

That would be an interesting POV LI. Never thought of it that way before, I wonder if B31.3 allows to apply 2 branches at one point (180 degree located from each other).

RE: Fabricated 4way cross section

I've had a reasonable look and currently can't see why not, but then neither does it say that it does.... The welds from the branches look far enough away to me and I've never seen anything saying you can't have a staggered set of branches, so why not directly opposite? I will stand to be corrected and maybe someone has asked the question before either to the 31.3 committee or here.

You can't write a code covering everything so need to apply some judgement from time to time.

The reinforcement pad is almost definitely needed on both branches, but that you can work out quite easily.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: Fabricated 4way cross section

Just because you can fabricate it, and the code doesn't say no, that doesn't mean that it's a good idea.


RE: Fabricated 4way cross section

No, I agree, but why is it a bad idea? You can buy a forged cross much the same way you can but an integrally reinforced branch fitting or a tee, but if you can replace the O-let type fittings with your own branch and some reinforcement, why not a forged cross?

I'm happy to be pulled up on this, but I think it needs some explanation as to why it is not a valid approach?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

RE: Fabricated 4way cross section

I didn't say you can't do it.

Interference in the HAZ?
Warping during fabrication?
Axial stress?
Bending Stress?
Torsion?
Stress concentration factors?

There's just very little metal left that can handle any kind of a load.
I'd tend to leave it only for someplace I would know will always be in a very low stress condition.


RE: Fabricated 4way cross section

These people make forged sch80 fittings that you may desire

http://www.notokfittings.com/equal%20tee%20buttwel....

Unreinforced (stub-in) type intersections in this pressure and diameter range will fail ASME B31.1.

If pad reinforced intersections are used, it may become to expensive/difficult to fabricate.

Have weld-o-lets been considered ? They have slightly more cost but the pressure reinforcement is assured and fabrication is easy.

http://www.bonneyforge.com/resources/BC.pdf

I also have a lot of trouble with this " I just welded something up, now you engineers tell me why I can't use it" approach.

If your piping fabricator does not understand simple piping/pressure vessel concepts like pressure reinforcement, there is real trouble here.....

MJCronin
Sr. Process Engineer

RE: Fabricated 4way cross section

A 6" WOL on a 6" 80 run pipe?? How much heat input will that require - what weld metal thicknesses will you get? I bet theyre HUGE!
Let alone the fact IF you can get a full WOL (i.e. 6" to 6").

RE: Fabricated 4way cross section

PS: Im pretty sure your answer lies with these Indian guys that can provide e.g. tantalum unequal crosses (!) if they meet Code requirements ....

RE: Fabricated 4way cross section

"Not OK" Fittings. LOL.

Piping Design Central

RE: Fabricated 4way cross section

Haha, thats a good one (its actually Potok, but who cares :))

RE: Fabricated 4way cross section

I've worked for several companies that prohibited fabrications with outlet diameters > D/2


RE: Fabricated 4way cross section

This raises something I've always wondered about: could you split 2 tees down the centerline of the run, then bevel the two pieces and make a cross by welding together the 2 pieces with the branches? Same question with 2 - 45's to make a symmetrical Y?

RE: Fabricated 4way cross section

A forged cross is preferred. If you have to use the fabricated cross, you have to make sure the material does not get too brittle for your service. Check HAZ and make sure proper stress release was employed during fabrication.

RE: Fabricated 4way cross section

Then there may be implications due to flow within. Crosses are not good for equalizing flow to the outlets, as far too much of the flow wants to continue in a straight trajectory. There may be erosion issues. There may even be cavitation. On the other hand, impinging flow problems would seem to be eliminated.


RE: Fabricated 4way cross section

Biggun, thats an interesting Idea. In terms of Code requirements, thats probably not allowed without detailed calcs per 304.7.2, since youd have unlisted components.

RE: Fabricated 4way cross section

CFR Title 49 Part 192 § .153 Components fabricated by welding.
(a) Except for branch connections and assemblies of standard pipe and fittings joined by circumferential welds, the design pressure of each component fabricated by welding, whose strength cannot be determined, must be established in accordance with paragraph UG-101 of the ASME Boiler and Pressure Vessel Code (BPVC) (Section VIII, Division 1) (incorporated by reference, see§ 192.7).
(b) Each prefabricated unit that uses plate and longitudinal seams must be designed, constructed, and tested in accordance with section 1 of the ASME BPVC (Section VIII, Division 1 or Section VIII, Division 2) (incorporated by reference, see§ 192.7), except for the following:
* * * * *
(d) Except for flat closures designed in accordance with the ASME BPVC (Section VIII, Division 1 or 2), flat closures and fish tails may not be used on pipe that either operates at 100 p.s.i. (689 kPa) gage or more, or is more than 3 inches in (76 millimeters) nominal diameter.


RE: Fabricated 4way cross section

But thus thing is two branch connections which just happento be opposite each other. A cross is also a standard fitting.

The thing pictured needs some reinforcement but is simply a branch connection x 2.

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

RE: Fabricated 4way cross section

Yes and it also looks a lot like a component fabricated by welding. smile


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