Flow measurement in buried pipes

S

Thread Starter

Santhosh Kumar

Dear Sirs,

I want to measure the flow in the buried pipe. The fluid is water. We have suggested Averaging pitot tube for this measurement. Is it right? moreover my client is not interested in Averaging pitot tube and asked for some other flow measuring sensor.

CAN ANYBODY HELP ME OUT WITH THIS ISSUE????

Regards,
Santhosh
 
Dear sir,

i think the Averaging pitot tube is one of the methods to measure the buried pipes. if they do not like it, i will advice the another methods:

1: insert vortex flow meter or magnetic flow meter. they will mounted in the well for flow meter.

2: ultrasonic flow meter also will be used.

please select and confirm.
 
Magnetic flow meter. Great accuracy, good turndown, very low installed pressure drop, easy to install. Cost probably only slightly higher than a good DP type measurement.
 
W
IF, and only if you are talking about a spool piece magnetic flowmeter. Insertion magnetic flowmeters, while sharing the same principle of operation, do NOT share the accuracy and performance characteristics of the spool piece magmeter. There is only one that comes even close to the accuracy of the insertion Annubar type meter, and that is the Marsh-McBirney unit which essentially replaced the pitot ports with small magnetic velocity sensors. The problem with insertion sensors is that almost all of them measure the velocity at a single point, and attempt (often really quite badly) to correlate that measured velocity with the average velocity in the pipe. Any single point insertion flow meter will have approximately the same installed accuracy and repeatability as any other, regardless of technology.

I'd like to know why your customer won't take the averaging pitot tube. It is the least expensive alternative that gives the best results.

Walt Boyes
editor in chief
CONTROL magazine
www.controlglobal.com

blogging Sound Off! at www.livejournal.com/users/waltboyes
 
Santhosh-
For retrofit into existing below-grade pipe, a Pitot is good choice because of low installation cost but only if the application turndown (max flow/min flow) is 4:1 or less. For larger turndowns, I agree that ultrasonics are something to consider. Use a transit-time if you can. We have found them to be more reliable than Doppler when the entrained solids concentration is low.

For new below-grade installation, a mag meter rated for IP 67 is the best choice by such a large margin that I won't bother with the alternatives. Many vendors: Yokogawa, Endress and Hauser, ABB, Foxboro among them.

Hope this helps.
 
It depends how big your pipe is. If it is a small pipe, you can consider using orifice plate. If your pipe is around 10" or more, try using annubar or ultrasonic but its a bit expensive.

Bong
 
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