Can any one suggest the most suitable instrument for Flow measurement under Gravity flow conditions. The service is Produced Water after Crude Oil Separator.

Gravity flow conditions usually will call for either magnetic, ultrasonic or turbine flow meters.

The area of installation is offshore hence getting long straight lengths is difficult. I checked up and found that Coriolis & PD meters do not have much requirement of Straight lengths. As the service is not very critical Coriolis might not be a wise option. Can PD meters be used in water application as the moving parts/gears will be affected. PD meters are used only used in oil services??

 

Coriolis would be the best option long term. With other types of flow meters you will see long term maintenance with moving parts. Coriolis is no moving parts, thus the higher initial cost but if the long term is looked at there is no maintenance costs.

There are low cost less accuracy Coriolis meters available on the market, Endress + Hauser has a 83 model E meter that is very much low cost, simple technology.

 

Electromagnetic flowmeter would be my choice. Loop powered if the water conductivity is high enough.

 

Hi,

Few choices would be Variable Area Flowmeter, Electromagnetic Flowmeter, Ultrasonic Flowmeter, Averaging Pitot Tube, Coriolis etc. What is more important is to know the accuracy requirement, whether this is monitoring or controlling application, line size of the application, whether power is available as its offshore application....to cut it short I would prefer Inline Battery Powered Ultrasonic Flowmeter as there won't be a pressure loss, accuracy is maintained, no power required. If straight length is a constraint try Accelabar which has no moving part, no need of calibration, need NO straight length and gives good turn down of 65:1.

 

Remember all Magnetic flow meters require 10-20 pipe diameters upstream and downstream to get a good measurement.

 

A mag meter would be my choice. you say the measurement is not critical so the straight runs are not so important. PD meters need more DP and you have moving parts to worry about. Just make sure it's in a horizontal or upward flow. Downward flow can be very problematic.

Regards,
Roy

 

Cost will vary significantly from one type of meter to another.
You say this isn't very critical and you may not want a full bore meter. You might consider an insertion type meter.

To answer your question, PD meters can be purchased in materials suitable for the process fluid. (domestic water meters are often PD meters). They come in all sorts but generally have comparatively low pressure drops and good rangeability.

The question of which one to choose would depend on if there is a chance of any sand or solids carry over. Occasional small amounts can be handled by an integral course screen. More would add filtration and maintenance requirements.

But if there is some risk of particles then a mutating disc type meter might be preferred. These are PD meters but have very good dirt handling compared, say, to Rotary piston.

But does it need to be PD meter? Woltman type water meters are inferential pattern and relatively low cost mechanical totaliser types. These are designed for water and I'd suggest that a trace of oil in the water wouldn't hurt - check with the manufacturer (I assume you will select based on working pressure too)

 

If the water is pretty clean, I would use a Badger turbine meter. They work well and are not very expensive.

 

> If the water is pretty clean, I would use a Badger turbine meter. They work well and are not very expensive.

thanks so much for the Badger suggestion. their oval gear meter IOG series is perfect for our client's high temperature low flow gravity fed application.