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ASME B 31.3 û Manifold design to resist internal pressure

ASME B 31.3 û Manifold design to resist internal pressure

ASME B 31.3 û Manifold design to resist internal pressure

(OP)
Guys,

I’m designing a very simple hydro test manifold. The current manifold is made up of 3000psi 2”ball valves, A106 Grade B shed 80 screwed pipe, cl3000 tees and so on.

When I apply the formulas given in 304.1.2 of 31.3, the shed 80 pipe is not up to task with the 1.5mm threading allowance taken into account (5.5mm-1.5mm = 4mm resulting in a P of 14,300kPa, I need 22,000kPa)

Now if I do away with screw pipe and use Cl3000 nipples, I go to table 2 of ASME B16.11 and see that a CL3000 threaded fitting is correlated with shed 160 pipe. So applying the shed 160 dimensions (8.74mm wall less the 1.5mm threading allowance – do I still need this?) to the formula in 304.1.2, I get a P of 36,700kPa. If I don’t take away the threading allowance then P comes out to be 45,300kPa.

So is my logic flawed? There seems to be a vast difference in the pressures?
On further inspection, nipples are not included within the scope of b16.11, so do I just treat the nipples as a piece of pipe? Just think I answered my own question, but just want some input from the gurus?

On another note, is there no allowance within 31.3 for the fact that screwed fittings will be into a female fitting, reinforcing it, making the allowance for full thread depth unnecessary? Or does it assume the full thread depth will extend beyond the female fitting?

Thanks for any help
Adam

RE: ASME B 31.3 û Manifold design to resist internal pressure

The easy answer is don't use screwed anything. Too much corrosion, concentrated stress and thread damages, plus you have to buy a lot of steel to compensate for thread allowance. In oil, gas and petrochem, the normal, typical practice is to use welded connections on everything above 2" diameter, remembering that it's just as easy to weld everything above 1/2" diameter. Leave threaded connections for the instrument guys.

I hate Windowz 8!!!!

RE: ASME B 31.3 û Manifold design to resist internal pressure

dams,
Please pay attention to what BigInch has told you.

Now to answer your question about Nipples.
A Nipple started in a Pipe Mill as very long piece of pipe (Seamless or ERW). It is the same pipe (material and method, manner and Design Conditions) as all other pipe of the same ASTM rating.

A different company then took many pieces of this pipe and cut it into 4", 6" and 12" lengths and sold them in bulk (by the thousands) with Plain ends, Bevel ends and Threaded ends (one or both) and made a lot of money while also reducing the cost of field labor.

Yes a Nipple is just a short piece of Pipe.

prognosis: Lead or Lag

RE: ASME B 31.3 û Manifold design to resist internal pressure

(OP)
Thanks Gents,

Unfortunately welding is not a proposition for us - the valves we have are screwed. The cost of the pipe is negligible too.

So there is no consideration made for the reinforcement provided by the female fitting? I have to subtract the thread allowance regardless?

Cheers

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