Orifice meter max differential pressure maximum question 4

[reydR]

I work for a natural gas midstream company and I am working on finding cost conscious ways to improve our design and need some guidance. A little background..

Some of the wells we are putting custody transfer meters on begin flowing at 100-300 MMCFD. Absolutely insane volumes. There are future projections of wells hitting 400 MMCFD at peak. Our operating pressures are around ~800 +/- 50 PSI depending on downstream compression. We currently use 0-1000" DP multivariable sensors, but only calibrate to a range of 0-500" and that was after begging and pleading to increase from 250". Well, I have asked to begin looking at setting my initial calibrations to 0-1000" to reduce construction costs and have been met with some resistance. For example, for a well coming on at 200 MMCFD, this would literally save us hundreds of thousands of dollars on one meter assembly by allowing me to set one 10" meter and set my DP to 0-1000" versus how it is now and installing a 16" header system and two 10" meters calibrated to 0-500".

I have lightly read API 21.1 and AGA Chapter 3 and I cannot find anywhere that says that expanding my DP from 0-500" to 0-1000" would be less accurate. Is there anywhere stating a point in water column at which unacceptable errors begin arise? If someone could point my in the right direction I would be most appreciative!

-Rey

 

[zdas04]

Thank you for sharing. I really have never seen a pronounced liquid dam on the downstream side of a plate, but (actually) that is the only way that the dam height could be so far above the minimum of the orifice hole. Could the piping into and out of the tube be up instead of down or horizontal like AGA 3 recommends?

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

 

[reydR]

I am not sure what you mean by if the piping is up instead of down or horizontal. The inlet piping comes up out of the ground, passes horizontally through the tube, and then back down the outlet. We have our plate carrier roll out horizontally instead of vertically. Is that what you were asking?

 

[zdas04]

No, I've seen a couple of stations where the piping comes down out of a separator into the top of the meter run and then up to a pipe rack. They never work very well.

The piping you described should not be able to support the dams that are clearly visible on the plate. Developing a scenario that matches the evidence will take a bit more pondering.

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

 

[georgeverghese]

There may be some piping reducers in this horizontal metering section with reducers oriented bottom flat, or some other piping fittings which create a low point that encourages condensed liquids to pool up at the meter, maybe a dual disc check valve etc?

 

[reydR]

Sorry for bringing up such an interesting scenario! The piping that comes up out of the ground only has concentric reducers. We have 12" headers for this 8" tube. So it is reducing down from a 12"-8" concentrically.

 

[dcasto]

Hidden in the report 3 is a table with ratio of dP/press. If that ratio is too high, the equations fall apart. The Y factor compensates for density change at high dPs.