ABB Rotameter (Variable Area Flow Meter) Application Notes

The Variable Area Flowmeter is an instrument for measuring the flow of liquids and gases in pipelines. It includes a vertical tube through which the fluid flows whose diameter increases from the bottom to the top and a float which can move vertically in the tube.

As the flow increases this float moves to a higher position until its resistance to the fluid flow is balanced by the float’s buoyed weight in the fluid, a value which is constant and independent of the flowrate. The position of the float is a measure of the flowrate. The flowrate values can be read on a scale.

Here is a listing of applications where rotameters (variable area flow meters) are commonly used and links to where their PDF documents can be downloaded.

Important Flowmeter Performance Metrics

Animation of differential flow
Animation of differential flow
Common to most flowmeters are rated levels of performance; some of the more universal
performance metrics include accuracy, precision/repeatability, turndown ratio, resolution, ease of installation, straight pipe run requirements, on-going operations and maintenance, and costs.

Accuracy
Accuracy is the difference between a measured value and the actual value. No flowmeter is 100% accurate and most manufacturers provide a range of accuracies in their product line - tighter accuracy requirements are typically more expensive and may also be more restrictive to specific applications.

Precision/Repeatability
The precision or repeatability of a measurement entails the ability to reproduce the same value (e.g., flow rate) with multiple measurements of the same parameter, under the same conditions.

Turndown Ratio
Rotameter
Rotameter
(ABB)
The turndown ratio refers to the flow rates over which a meter will maintain a certain accuracy and repeatability. For example, a steam flow meter that can measure accurately from 1,000 pounds per hour (pph) to 25,000 pph has a turndown ratio of 25:1. The larger the turndown ratio, the greater the range over which the meter can measure the parameter within the accuracy stated.

Resolution
The resolution is the smallest increment of flow that can be incrementally registered by the meter. For example, a water meter designed for a small diameter pipe may be able to provide a resolution of 100 pulses per gallon (or more) as a signal output, but a meter designed for a larger pipe or higher maximum flow may only be able to provide 1 pulse per 100 gallons. Further, a very large flow meter may only be able to provide 1 pulse per 1000 gallons. The metering system may have limitations with regard to peak signal frequency or minimum time between pulses to properly register the data signal.

Ease of Installation
Select make-and-model decisions considering size and weight constraints, specific electrical and communications needs, and the overall environment the flowmeter will operate in.

Magmeter
Magnetic flowmeter
(TECO)
Straight-pipe Run Requirements
Applicable to some types of fluid (gas, liquid and steam) flowmeters, straight-pipe run requirements relate to the length of unobstructed straight pipe required leading up to and immediately following the flow meter’s location. Obstructions in the fluid flow (such as elbows, tees, filters, valves, and sensor fittings) cause changes in the flow pattern (flow regime and velocity profile). Straight-pipe runs allow the flow pattern to normalize/stabilize making measurements by velocity-type and differential-pressure-type flow meters less prone to measurement error. Straight-pipe run requirements are usually expressed in terms of the number of pipe diameters.

The straight pipe requirement is in addition to the length of the flowmeter itself. The straight-pipe run requirements can be reduced with the addition of flow straightening or flow conditioning devices installed upstream.

Ongoing Operations and Maintenance
Vortex flowmeter
Vortex flowmeter
(ABB)
The lowest cost flow metering technology may not be the best choice if it has high associated maintenance costs (e.g., frequent service, calibration and recalibration, sensor replacement). As with most capital purchases, a life-cycle cost approach (including all capital and recurring costs) is recommended for decision making.

Installation Versus Capital Cost
In some situations, the cost to install a flowmeter can be greater than the capital cost; this can be true where system shutdowns are necessary for flowmeter installations, or where significant redesign efforts are needed to accommodate a flowmeter’s physical size, weight, or required connection. In these cases, decision makers should consider alternative technologies that may have a higher capital cost but a much lower installed cost. A good example of this is the use of non-intrusive flow metering technologies (e.g., ultrasonic flowmeters) that typically have a high capital cost but often a significantly reduced installed cost. It is recommended that meters be installed with isolation valves or switches making it easier to remove, replace, or service the meter in the future.

Reprinted and abstracted from US Department of Energy paper titled "Metering Best Practices: A Guide to Achieving Utility Resource Efficiency, "

Severe Service Magmeters for Fracing Operations

Proven in the heat of a West Texas summer, and the cold of an Alberta winter, this TECO magmeter is designed from the ground up to withstand corrosive slurries, acids, bases and solvents.



Severe Application Meter
Severe Application Meter (TECO)
Magnetic flow meters (magmeters) installed on blender trucks are of particular concern. The application involves accurately measuring the flow of an extremely erosive slurry comprised of sand and “frac water” (a mixture of water and harsh chemicals). Replacing failed magmeters can take up to 4 hours, and requires the shutting down of the entire frac spread.

Calling upon sixty-plus years experience in magmeter application, failure analysis, repair, and design, TECO developed several innovative magmeter features intended to improve longevity in fracing operations.

FRAC Trucks
FRAC Trucks
First, TECO developed a ceramic sleeved liner made of “magnesia partially stabilized zirconia”, a very tough ceramic used in severe-service applications that provides corrosion resistance and durability.

Second, TECO developed electrodes built from a solid tungsten carbide billet, which afford unparalleled wear resistance. Given the sand density in the frac fluid, noise reduction is critically important; so, the tungsten carbide is polished leaving a hard, smooth finish that significantly reduces noise in the electrode circuit.

FRAC Sand
Erosive sand tears up
other magmeters. 
Finally, TECO designed the magmeter as a drop-in replacement. It operates with a variety of secondaries and matches the “lay length” of the meter being replaced. There is no need for a new transmitter and no need for repiping, allowing for simple retrofit in existing installations.

Internal view of TECO SAM after 500,000,000 pounds of sand
Internal view of SAM after 500,000,000
pounds of sand flowed though the core.
Upon inspection, the customer found the
flow tube to be looking “brand new”.
In 2017 TECO introduced the SAM (Severe Application Meter) magmeter as a flow meter designed specifically for hydraulic fracturing operations. By specifying SAM, operators save money through increased uptime; decreased health, safety and environmental risk; and reduced costs related to magmeter purchase and repair.

Download the PDF version of this article here.

Contact TECO by visiting https://teco-inc.com of call 800-528-8997 for more information.