Annubar Mass flowmeter


Thread Starter

J.C bae


We are going to install annubar mass flowmeter at #600 HP steam line(16 inch) for measuring.

My concern is that it can endure in such high pressure.(about 43 kg/cm^2) Are there anyone having experiences in similar condition ? Your reply will greatly helpful to me.

from J.C bae ([email protected])

William T. Dolan Raytheon Engineers & Co

They are designed for high pressure applications and 600 # steam is not a problem. My only reservations in using an annubar flow element is turndown. Design pipe velocities general limit turndown to 5:1 and sometimes less. If turndown is an issue and you may want to consider a reduced pipe size for the metering run so that you can increase the pipe velocity, hence, the turndown. I think most annubar-like device manufacturers will advise you not to attempt
measurement below 1 inwc for steam applications when the transmitter is close coupled. And 2 inwc when your transmitter is remote mounted.
Yes Annubar is a differential producer therefore an immediate mass-flow meter. Like says Williams it will stand your conditions.
Let's explain what the turn down ratio is in flow measurment: ratio of max flow /min flow. A turndown ratio 3/1 is no problem. If it would be for instance 10/1 then the error caused by the square root extraction becomes near the flow itself. No use for that A 5/1 is OK for reading.
but for accuracy in real metering , not very much
reliable. However this depends only upon the XTR having inaccurate response on the lower part of the range.
Steam travels fast in pipe. So, for steam it is recommendable you use the model that seats at the bottom of the pipe to avoid vibration and failure.
Being steam, dictates the XTR installed below piping, the legs will fill with condensate.
There is a point to consider: Annubar are not sized for differential pressure like orifice plate. They produce so much DP for so much flow.
Therefore check for your max flow what DP and calibrate your XTR accordingly.
Detail here my friend. Assume the max DP, calculated is 50 in WC and your XTR is adjustable 0 to 500 in WC (WC= water column)then change the cell or the XTR itself to improve the turn down ratio (for instance a 0 to 100).
Few years ago, the accuracy of Annubar was not referenced and then not tracable. The orifice plate is tracable and normalized by several standards.
A good practice is to calibrate the XTR at 25% DP(50 % flow) and 100% DP (100% flow)