Orifice meter - wrong installation

[Trond]

We have an gas orifice meter that was wrongly installed, with the conical opening facing the wrong way. Unfortunately there are was external indication of flow direction, and assurances had been given that it was correctly installed - something that could probably justify a separate thread on QA, but I'll pass on that subject for now.

Anyway, when the orifice plate was repositioned, measured flowrates increased by about 10-15 percent (flow is unfortunately not constant, so a direct comparison is not possible), and I was wondering if there is any way to recalculate the old (erroneous) readings that we have?

 

[danw2]

Check out the statements and links on this thread that covers reverse installed orifice plates:

http://www.eng-tips.com/viewthread.cfm?qid=250966

 

[hacksaw]

the quick answer is yes but you have to use the reverse flow coefficients for the plate (if you can find them. some of the metering companies can run a calc for you

 

[JLSeagull]

Consider advising whether this is a custody transfer, related high-accuracy flow meter, or internal operating unit flow meter that can handle less precision.

 

[zdas04]

I'm surprised that the error was only 10-15%, numbers I usually see are above 25%. I've never found a reliable way correct a meter for a backwards plate, and I've looked for years. I took a test trailer to CEESI (a big meter test station in Colorado) quite a few years ago. We finished our testing a bit early and tacked on some backwards plate tests. I got the data and found that the error is very much Reynolds Number and beta ratio dependent. I spent several weeks manipulating that data over the next couple of years and if there is a decent correlation I never found it.

When I was operating a gathering system we had a couple of big wells get backwards plates. I applied a 26% factor to the data and my system material balance went from +5% to +2% (there were other problems in the system at that time as well). The problem with that technique is that it is rare to have the ability to do a material balance because someone else usually operates the aggregation meter.

David

 

[Trond]

Thanks all!

It is (unfortunately) a fiscal meter, although the measurement is only for injection gas, for which the company is obliged (and previously seemed to fail) to provide a minimum amount of throughput per day.

Indications are that measurement has been off by about 15-20%, but it appears that making an accurate calcualtion of what amount has been underreported is rather difficult.

Appreciate the leads given above, though - at least it gives me something to work with.