Sea Water Flow Measurement – Magnetic vs Ultrasonic Flowmeters

Importance of Sea Water Flow Measurement

Seawater stores 96.54% of the earth’s fresh water, which contains a huge amount of minerals, energy and other resources. The current forms of seawater resources development and utilization mainly include: seawater desalination, direct utilization of seawater and utilization of seawater chemical resources.

In seawater desalination

In coastal cities and islands where water resources are seriously short. Mainly large-scale industrial seawater desalination projects. Mainly concentrated in high water consumption industries such as electric power and steel. Seawater desalination projects for islands used in offshore cities.

In terms of direct use of seawater

Mainly for seawater cooling applications. Among them, seawater DC cooling technology is mature and is mainly used in coastal thermal power, nuclear power, petrochemical, steel and other industries. Seawater circulating cooling technology has been gradually applied in the coastal power industry.

In the utilization of seawater chemical resources

It mainly includes salt production from seawater, potassium extraction from seawater, bromine extraction from seawater, magnesium extraction from seawater, etc. In addition to seawater salt production, the main products include bromine, potassium chloride, magnesium chloride, magnesium sulfate, and potassium sulfate.

Therefore, the utilization rate of seawater is getting higher and higher. Even in the future, people will find more favorable treatment and utilization of seawater. Among them, flow measurement before and after seawater treatment, or flow measurement before and after seawater use will become more and more important.

Difficulties in sea water measurement

Seawater is a highly corrosive fluid. Seawater is a very complex multi-component aqueous solution, which contains various ions such as sodium, potassium, calcium, magnesium, copper, zinc, manganese, etc. Its salt content is very high and it is highly corrosive.

Simultaneously, waves and tides create low-frequency mutual stress and impact metal parts. Marine microorganisms, attached organisms and their metabolites also produce direct or indirect accelerated corrosion processes.

Marine corrosion is mainly localized corrosion, which starts at the surface of the component and occurs in a small area. Examples include galvanic corrosion, pitting and crevice corrosion.

Therefore, it is very necessary to consider corrosion issues when selecting seawater flowmeter sensors.

Magnetic flowmeter to measure sea water

Electromagnetic flow is the preferred flowmeter for measuring the volume flow of liquids with a certain conductivity.
Electromagnetic flowmeter is a flow measuring instrument that works based on the principle of electromagnetic induction. It consists of sensors and transmitters.

Advantages

1. There are no moving parts and bluff bodies in the measuring conduit. Therefore, the pressure loss is very small, and there is no mechanical inertia, so the response is sensitive;
2. Wide measurable range: the turndown ratio is generally 10:1, up to 100:1. The flow velocity range is generally 1-6m/s, and can be extended to 0.5-10m/s. The flow range can be from 90mL/h to hundreds of thousands of m3/h. Pipe diameters can range from 2mm to 2400mm or 3000mm.
3. It can measure the volume flow of liquids containing solid particles, suspended matter, or acids, alkalis, and salt solutions with certain conductivity. It can also measure pulsating flow, and can carry out two-way measurement.
4. There is a linear relationship between the flow signal and the fluid volume flow, so the meter has a uniform scale. And the volume flow rate of the fluid has nothing to do with the physical properties and flow state of the medium. Therefore, the electromagnetic flowmeter only needs to be calibrated with water, and it can be used to measure the volume flow of other conductive liquids without correction.
5. Compared with most other flow meters, the requirements for the front straight pipe section are lower.

Disadvantages

1. The temperature and pressure should not be too high;
2. The scope of application is limited. It cannot be used to measure the flow of non-conductive fluids such as gas, steam and petroleum products, and fluids containing more and larger bubbles;
3. When the flow rate and velocity distribution do not meet the set conditions, large measurement errors will occur;
4. When the flow rate is too low, it is difficult to amplify and measure the induced potential of the order of magnitude opposite to the interference signal. And the instrument is also prone to zero drift;
5. The signal of the electromagnetic flowmeter is relatively weak. A little interference from the outside world can affect the accuracy of the measurement.

Extended Reading: Special Magnetic Flowmeter Installation situation

Featured Magnetic flow meters for sale

ultrasonic flowmeter to measure sea water

Ultrasonic flowmeters are instruments that measure volume flow by detecting the action of ultrasonic beams (or ultrasonic pulses) when fluid flows.

The sound wave propagates in the fluid, and the sound wave propagation speed will increase in the downstream direction. , the countercurrent direction decreases, and the same propagation distance has different propagation times. The propagation time method is to calculate the flow velocity by using the relationship between the difference of the propagation velocity and the flow velocity of the measured liquid. Combined with the pipe diameter to obtain the flow rate.

Advantages

1. Ultrasonic flowmeter can be used for non-contact measurement. The clip-on transducer ultrasonic flowmeter can be installed without stopping the flow-carrying tube. Just install the transducer outside the pipeline to be tested. That is, the flow can be measured with an ultrasonic flowmeter on existing pipelines that cannot be cut off or drilled;
2. Ultrasonic flowmeters measure without flow obstruction. No additional pressure loss;
3. The instrument factor of the measuring meter can be calculated from the geometric dimensions of the actual measurement pipe and sound channel. The dry method can be used for calibration. Except for the type with measuring pipe section, it generally does not need to do real flow calibration;
4. Ultrasonic flow meters are suitable for large round and rectangular pipes. And it is not limited by pipe diameter in principle. Its cost basically has nothing to do with the pipe diameter;
5. Doppler ultrasonic flowmeters can measure liquids with high solid content or bubbles.

More about: Insertion Type Ultrasonic Flow Meter Applications

Disadvantages

1. The ultrasonic flowmeter in the propagation time method can only be used for clean liquids and gases, and cannot measure liquids with suspended particles and air bubbles exceeding a certain range. On the contrary, the Doppler method LSF can only be used to measure liquids containing certain heterogeneous phases;
2. Ultrasonic flowmeters with external transducers cannot be used in lined or heavily scaled pipes. And it cannot be used for stripping the lining (or rust layer) from the inner pipe. If there is gas in the interlayer, the ultrasonic signal will be seriously attenuated. Or pipes with severe corrosion (changing the ultrasonic path);
3. In most cases, the Doppler method ultrasonic flowmeter has a low measurement rate;
4. It cannot be used for pipes with a diameter smaller than DN15mm.

Read more about: Flow Meter Selection Guide

Featured ultrasonic flow meters for sale

conclusion

So, which flow meter should you choose for Sea Water Flow Measurement or salt water flow?
We believe that:

1. If the seawater concentration is low and the salinity is small.

Then ultrasonic flowmeter is a better choice. Such flow meters do not require contact with seawater and avoid corrosion.
At the same time, its flow sensor is not a metal part and is not afraid of corrosive materials.

For this type of seawater, if you choose an electromagnetic flowmeter. Then a 316L stainless steel electrode and rubber lining material should work well.

2. If the seawater has high concentration and high salinity.

Then the external clamp ultrasonic flowmeter is a better solution.

If you want to choose an online electromagnetic flowmeter for better performance. The best choice is Hastelloy C electrode and PTFE lining material. Hastelloy C electrodes are suitable for oxidation of salts such as Fe++, Cu++ and seawater.

3. For seawater desalination projects, plastic pipes are mainly used as water delivery equipment.

Many pipes are in the air. If an in-line electromagnetic flowmeter is used, the electromagnetic flowmeter is heavy. And the plastic tube doesn’t hold it in place very well. As a result, support brackets have to be installed, which adds a lot of cost and inconvenience.

Therefore, we recommend using a transit-time ultrasonic water flow meter. No pipe cutting required, light weight, easy installation, no maintenance etc.

4. If it is to measure the pipeline above DN3000.

Then the external clamp ultrasonic flowmeter is a better choice. For large diameter pipes, clamp-on ultrasonic flowmeters are less costly.

Read more about: Hydrostatic Submersible Level Transmitter-Straight Rod Insertion

More water measurement solutions

Sino-Inst is a manufacturer of electromagnetic flowmeters and ultrasonic flowmeters. It has been used for sea water-salt water flow measurement for a long time.

Sino-Inst supplies more than 30 types of seawater flow meters for sea water flow measurement. 55% are electromagnetic flowmeters and 45% are ultrasonic flowmeters.

Electromagnetic flowmeters and ultrasonic flowmeters have their own advantages in Sea Water Flow Measurement. You can choose the appropriate model based on your measurement needs and cost budget.

Sino-Inst’s Sea Water Flow Measurement – Magnetic vs Ultrasonic Flowmeters are the most commonly used sensors in industrial applications. Widely used in water conservancy and hydropower, railway transportation, intelligent building, production control, aerospace, military chemicall, military industry, electric power, ship, machine tool, pipeline and other industries.

Sino-Inst’s entire team is well trained, so we can ensure that each customer’s needs are met. If you need any help with your product requirements, whether it is a Sea Water Flow Meter, level sensors, or other equipment, please give us a call.

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