Maximum uncertainty When the Recommended Straight Run for an Orifice Plate Flow Measurement Is Not Observed?


Thread Starter



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.

Once you are under 40D/10D straight runs it all depends on your piping layout, the Reynolds number, the function of the measurement, etc.

Any flow metering handbook, will answer your question and there is certainly a lot of published work dealing with the topic.
Thanks d,

Is there a simple (rule of thumb sort of thing) to address this case?

I understand proper assessment is required for a more precise answer since the dynamic of the fluid is involved but we do not want to go through a thorough study. A table would be best.

The ASME flow meter handbook (1971, 6th ed) has such charts, they haven't changed much. You'll need specifics regarding the piping layout.

The more pressing issue is that for common non-custodial measurements, the cost of a proper piping installation cannot be justified, and you take what you can get. That said there are installation tricks that mitical some of these errors, but you'll have to work closely with you piping designer.

Good sailing!

<b>Moderator's note:</b> Not sure but I think mitical is a typo. Could be mitigate or critical.