Orifice plate acording to AGA3 and ASME.

[sebastiancito]

Hello Everyone!!.
i'm calculating a orifice plate, not for measure, only for restrict the flow rate.. The customer say me that he need it acording to aga 3 and ASME B16.5.
Ok.. I'm calculating it with aga3 software, the values give it are OK.
Now, i have the beta radio and the others values.
But when i see the B16.5, i can't find any section thats speak about the thickness of the orifice plate. Search in the asme code, see that the B16.36 is refers to orifice plate.
My big problem is the thickness of orifice plate and the material of it.
i think in use a 316SS in 9mm.
The flow conditions are.
Downstream pressure. 65 BARG.
Upstream pressure: 1BARG (YES, 1 bar).
Flow rate: 18000 SM3/h.
Density: about 43 kg/m3.
Pipe: 2 Inch SCH 80.
FLUID: Natural Gas.

Sorry by my bad english... I hope that they can help me.
BEST REGARDS FROM ARGENTINA.

 

[ashaari]

So your downstream pressure is higher than upstream pressure? I don't understand. Or is this a typo?

 

[zdas04]

That is some well trained gas to flow from 1 barg into 65 barg. Let's assume that the OP got his upstream and downstream confused. Even with that, his English is far better than my Spanish.

First off, your client is a fool. A huge portion of the research that underlies AGA-3/ASME 14.3 is designed to minimize the permanent pressure drop. With the plates described in the gas-measurement documents up to 95% of the dP across a plate is recovered downstream.

Picking an inappropriate specification is far worse than not picking a spec at all. I've never seen a code spec that discusses taking a permanent pressure drop across an orifice--I don't mean to say that such a standard doesn't exist, just that I've never seen one.

I've designed several "choke nipples" out of 2-inch diameter billets of solid steel. The trick is getting the length such that the pressure at the exit is close enough to the target downstream pressure that the exit velocity is less than 0.6 Mach. The 0.6 Mach number is pretty consistent across a range of gases as the point that the change in density with velocity is "small enough". Above 0.6 Mach very small changes in velocity make very large changes in density so the "incompressible" assumption in the equations based on Bernoulli's equation is not valid.

So you play with diameter vs. length to dump your pressure in friction instead of in pressure waves. If there is a standard it probably tells you how to do this. I've just iterated in MathCAD till I predicted the results I needed.

David