Company A is producing a gaseous form of product and is selling it to 2 companies. This product is transfer from company A’s site to company’s B and company C’s site by a pipeline of more than 10km long.

At company A’s site, there is a flow-meter (FA1), which will monitor the total flow rate of the product produced by company A. At the other end of company B and C’s sites, there also flow-meters (FA2 and FA3), which belong to company A, to monitor the flow rate of the product flowing into company B’s and C’s site.

However, the problem is the total flow rate in FA1 is not equal to the sum of FA2 and FA3. The discrepancy is about 4%.

The pressure does drop over the pipeline and the temperature in pipeline is also depends on the ambient temperature. And these two parameters do affect the flow rate parameter in one way or the other. But these 2 parameters are normally within the specification.

Hence, besides calibrating the 3 flow meters for about once every 6 months, what other possible solutions are available?

 

The list of questions to ask regarding this issues is long:
1) 4% out of how many SCF, gallons or what ever total? (4% of 10M SCF or 4% of 1K SCF?)
2) IS there a loss in the system that accounts for what % of the error?
3)What is the acuracy of the flow meters?
4) Is each flow meter within spec?
5) Is the error a additive error between flow meters?
6) What is the specified allowed error between the primary custody flow meter and the other two units?
7) Can the pressure drop and temperature changes
account for what % of the error?
8) Since these are primary and secondary custody transfer flow meters is it unacceptable to calibrate every 6 mos.
9) is the error due to flow meter totalization cut off below a certain flwo rate?
10) are the flow meters correctly configured?
11) what type of flow meters are used?
12) when were the flow meters last verified to be within specification? Who verified them?
(Ideally a thrid party should be used to verify the meters and their standard should be a order of magnitude - ideally - better than the flow meters used by the three companies.)

When you have these answers drop a note here.

MJH

 

If volumetric flow technology is used, in order to have accurate compensation signals from pressure and temperature transmitters and flow computer is a must.
Furthmore accuracy of flowmeters is one of the mojor items, for instance with having normal orifice plate and differential pressyre transmitter for your application, 4% difference is normal.

Generally for two flowmeters in the same line, if accuracy of each meter is +/- 1%, maximum difference of 2% could be acceptable (in the worst condition).

 

First, you don't mention what kind of flowmeters... I am assuming differential pressure flow transmitters. You don't mention the flow ranges or accuracy statements. In fact, an agreement within 4% between two "daughter" flowmeters and a "parent" that is some distance away is probably statistically insignificant.

If you want more answers, I would be willing to run this question, which is a good one, as the Problem of the Month in Control. You'll have to email me privately if you want this done, because I need your contact information.

Best,

Walt Boyes
Editor
Control magazine
[email protected]
www.controlmag.com

 

What kind of flow meters are you using? Have you accounted for pumping losses if any? How old is the pipeline? What kind of construction materials? Are leaks a possibility?

 

Here is my thoughts:
1. Ever device has a certain accuracy. For example plus or minus 0.0002 % or something.
Is the difference between the two flow meters above your potential error percentage.
The longer and more flow that you are measuring means that this percentage of error can add up pretty quickly and it just might appear that the two meters are off when they are actually doing as great a job as they can.
2. You mention that you are measuring a gaseous flow but you don't mention the type of flow meter you are using.
Is the stream mixed phase like liquid and gas? Could the differences in temperature across the pipline be causing condensation? And if so does your flow meter accomodate that?

That is just thoughts off the top of my head.
Good luck.

 

Guotai,

Given the lenght of the line, the value of the gas is likely significant (say, well over US$100,000 per month). The pragmatic solution is to hire a flowmeter expert to come onsite and physically examine all of the installations. While this may seem expensive, it will be cheap when compared to the discrepancies and the problems they cause.

Contact me directly if you need help finding a flowmeter expert in your area.

David W Spitzer
845.623.1830
[email protected]
www.spitzerandboyes.com

 

Is flowmeter parameter menu protected with password?

 

Hi Mr Mattew Hyatt,

Thanks for your offering of questions. And below are some of my answer for your questions.

On March 2, 2004, Matthew Hyatt wrote:
> The list of questions to ask regarding this issues is long:
> 1) 4% out of how many SCF, gallons or what ever total? (4% of 10M SCF or 4% of 1K SCF?). <
ANS: 4% of 35MT/hr

> 2) IS there a loss in the system that accounts for what % of the error? <
Ans: Not very sure, but I presumed no.

> 3)What is the acuracy of the flow meters? <
ANS: I will get back to you again on this question.

> 4) Is each flow meter within spec? <
ANS: Yes

> 5) Is the error a additive error between flow meters? <
ANS: No

> 6) What is the specified allowed error between the primary custody flow meter and the other two units? <
ANS: Will get back to you again.

> 7) Can the pressure drop and temperature changes
> account for what % of the error? <
ANS: Will get back to you again.

> 8) Since these are primary and secondary custody transfer flow meters is it unacceptable to calibrate every 6 mos. <
ANS: It is quite unacceptable. However, my company lacks of manpower to perform the task for every three months.

> 9) is the error due to flow meter totalization cut off below a certain flwo rate? <
ANS: NO.

> 10) are the flow meters correctly configured? <
ANS: Yes, of course

> 11) what type of flow meters are used? <
ANS: (ORIFICE) Differential pressure flow transmitters.

> 12) when were the flow meters last verified to be within specification? Who verified them? <
ANS: We verfied it and it was last done in 7 months ago. I do agree to you statement which you wrote below.

> (Ideally a thrid party should be used to verify the meters and their standard should be a order of magnitude - ideally - better than the flow meters used by the three companies.)
>
> When you have these answers drop a note here. <

Please do feedback to me again if you want any more info. Hopefully, you are able to list down of the causes of the problem which I am facing.

A Million Thanks.
Guotai

 

Differential pressure flow transmitter. There is no pumoping loss. The pipeline is about 4 to 5 years old. And there should be no possible of leaks.

As for the construction material, I afraid that I do not have any answer for that.

Thks
Guotai

 

Guotai,

Assume you are having pressure and temperature compensation for the orifice flow meters? Also try matching them on volumetric flow at STP (standard temp and pressure) than mass flow because, orfice meters are volumetric flow meters. You get a mass (MT/hr) reading only by multiplying with a sp.gravity figure which is assumed constant and which never is. SO you will find it very diffcult to improve your accuracies on a mass flow figure.

Thanks
Boby

 

Hi!

This is a typical problem with the industry & its good that you have taken a step forward to understand whats going wrong... as everyone suggested there could be lots of problem. As orifice is being into use, first of all for how many years, are this orifice calibrated recently & was well within the expected accuracy. What kind of pipe orientation is there at all the three flow meter site... how the tappings have been taken... whether proper straight run available etc. etc.

Temperature & pressure compensation is must for gas flow measurement & I would advice either you do that or install Thermal Mass Flow Meter which have proved to be better instrument on dry gas applications.

The other option could be turbine flow meter with temperature & pressure compentation... it would be our great help to know the location so that we can suggest on site calibration agencies who can really help you out.

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