Maximum uncertainty if the straight run for an orifice plate flow measurement is not observed

[OzGuy]

Hi,

I am aware that ISO and API have recommendations on straight run requirements of DP flow measurement using orifice plates, but is there a published work about expected maximum uncertainty if such recommendations are not observed, e.g a graph or a table?

I have been asked to specify the expected error (uncertainty) of a flow measurement on an orifice plate DP flow transmitter when the recommended straight run is not observed, say it has only 5D upstream on a DN100 line.

I also understand there might not be a straight forward answer to such a question and it might depend on process condition and the setup of the upstream/downstream pipe arrangements.

Your advice is highly appreciated.

Cheers,
OZI Guy

 

[OzGuy]

PS:

I have found this but I am looking for other resources.

http://www2.emersonprocess.com/site...ty-of-Orifice-Flow-Measurement-techWpaper.pdf

Cheers,OZ Guy

 

[zdas04]

This discussion comes up (too) often on the producer side, but it never comes up on the regulator side--fail to meet the code and you are in violation. It also never comes up on the purchaser or joint interest side--fail to meet the code and you have violated the contract. The reason that it keeps coming up on the producer side is that it takes a lot of room to put in a proper tube, and a proper tube is more expensive than a random number generator--with good reason.

The first reference in your link is really the key. Look at "Natural Gas Fluids Measurement,” API Standard, Chapter
14, Section 3, Part 1, “General Equations and Uncertainty Guidelines,” (you should use the 4th edition from 2013, if you don't have access to it you really have no business designing a measurement station). The driving force behind the uncertainty section was Mark Haefle, who is no longer with us. I spent a fair bit of time with him working out the impact of problems from the API database. He did a good piece of work.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[OzGuy]

David,
Thanks for your reply. It was really helpful.
Cheers,
OZI