Question
From Walt
Location: Canada

I am putting together some work plans for an upgrade to a refinery and some of the work activities reqire recalibration of some flow meters. these flow meters are either vortex of ultrasonic type. My question is can they be recalibrated in place or does it require removal from service? If the system they are in is shutdown, can they be recalibrated in place. If it requires removal, can they be recalibrated on site utilizing a calibration facilty?

Answer
Normally the CV values for valves are determined by the manufacturer. They are a function of the internal design of each valve. Please consult the supplier for details and if possible request a flow calibration to ensure the CV value you have is really that for the individual valve. They may vary slightly.

The Flow Professor

Question
Do you have a list of choke coefficients used to estimate gas flow rates for natural gas wells? Thank you for your attention.

Glen, Texas

Answer
Normally the CV values for valves are determined by the manufacturer. They are a function of the internal design of each valve. Please consult the supplier for details and if possible request a flow calibration to ensure the CV value you have is really that for the individual valve. They may vary slightly.

The Flow Professor

Question
From Bob Goldstein

Dear Professor Flow

What flowmeters can be used for steam applications?

Answer
Hi Bob,

Here is what I came up with. Hope it helps you-

There are many types of steam flowmeters available, those suitable for steam applications include:

• Orifice plate flowmeters.
• Turbine flowmeters (including shunt or bypass types)
• Variable area flowmeters
• Spring loaded variable area flowmeters
• Direct in-line variable area (DIVA) flowmeters
• Pitot tubes.
• Vortex shedding flowmeters
• Target Flowmeters

Each of these flowmeter types has its own advantages and limitations. To ensure accurate and consistent performance from a steam flowmeter, it is essential to match the flowmeter to the application.

It is always best to discuss technical details and installation parameters with knowledgeable manufacturers as some steam applications are tricky.

Question
From Carlos

Dear Professor,

I suspect someone has been tampering with our Flow Computers when we are offloading petroleum products through the night. We are offloading to ships and some nights we do not have enough staff to properly man the offloading. I would like to install a system that can prevent people from tampering with products from our company. Please can you suggest something?

Answer
Dear Carlos,

This is extremely serious . It would not be prudent for me to get too involved in this one. This looks like a people problem and not a flow problem. Sorry I cannot be of more help

The Professor

Question
From Solomon

Dear Professor,

I have a problem measuring flow on a 1 inch Freon line. I can see from the sight glass 12 inches away from the valve that the freon is bubbly sometimes and sometimes it is not. Whatever meter I put in the line goes crazy. Is there anything you can recommend?

Answer
Dear Solomon,

Hmmm. I would like to throw this one out to the audience as this one looks like a toughy! You can always try calulating the pressure drop across the valve to determine the flow (there are programs for this on the net or you can buy books on how to calculate it if you have time to read them) If you can do this, then install a DP transmitter reading pressure before and after the valve

Hope this helps

The Professor

Question
From Faisal
Saudi Arabia

Dear Professor

I have an application for flowmeters on large pipes that are full of raw sewage. We need a low cost solution for 1M diameters pipes. Accuracy is not that critical. 10% will be ok. We need something that is easy to install and that does not require maintenance. Should we use electromagnetic meters?

Answer
Dear Faisal

Mag meters will work well, so will a few other things but what strikes me about your questions is that you are looking for a low cost solution. How "low cost" do you want to go? I guess if you add up material costs and manpower/installation costs and the fact that accuracy is not critical, then you are a candidate for a clamp on doppler flowmeter. If the meter is going to be installed outside, make sure the transmitter and cables/sensors are not flimsy. I have had personal experience with doppler meters that did not have protected sensors and the rain and elements managed to creep in and mess with the readings. To be honest, I would recommend you buy a meter on 45 days credit. Put in online and see what happens. Don't buy something you are not sure of.