What is the effect of the plate material on the measurement?

[Iradah]

Hello all,

What is the effect of replacing an orifice plate with another plate of different material? The vendor said that the material A216 is not avialable and instead he will use stainless steel material.


Thanks in advance.

 

[IRstuff]

You'd need to have some confirmation that cavitation and erosion resistance is no worse.

TTFN
faq731-376

 

[Engdoitbetter]

The material, as far as flow calculation is concerned, is not an issue, provided that the requirements of ISO 5167 1 & 2 are respected. On the contrary, the material is a concern when particular flow conditions, such as erosive fluid, suspended solids, chemical aggression etc. are present, since they may modify the shape of the orifice, leading to unpredictable changes in flow coefficient.

Hope it helps.

Stefano

 

[Iradah]

Thank you IRStuff and Stefano,
so the calculations for the gas orifice plate will not change, I have only to check the plate deflection as the gas is dry, sweet clean gas.

 

[zdas04]

Not so fast. One of the obscure factors in the flow equation includes the coefficient of thermal expansion of the plate. In the program I got from the AGA committee (DOS based) you get (slightly) different answers as you change material within the program. It has been a while since I did the comparison but it seems like the spread of flow rates was around 0.3% (using the max flow as the denominator) at 100[°]F. I don't know if there are any RTU's left in service that do that particular calculation explicitly so it is unlikely that you'll notice it.

If the plate is made to the ISO/AGA/API standards then as long as you don't exceed the max allowable dP you don't need to worry about deflection.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[Engdoitbetter]

Yes, I know that material thermal expansion coefficient will change (I've done many calculations myself!! ).
Anyway, I took for granted that manufacturer has to take care of the flow calculations too (my company operates in this way), so change in material for the end user is only a matter of erosion, corrosion etc.
Regarding deflection, I agree with Dave.

Have a nice day.

Stefano

 

[zdas04]

Another way of saying that is if the RTU has a place to enter plate material then there should be no issue with changing plate material. If it just assumes a material then changing can be a problem.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.