Magnetic Flow Meter Made 3 Simple – Your Ultimate Oil & Gas Industry Guide

Electromagnetic flow meter also known as magmeters, are a type of flow meter that use electromagnetic induction to measure the flow rate of a fluid. These flow meters are particularly useful for measuring the flow rate of conductive fluids, such as water, acids, and bases.

The basic principle behind electromagnetic flow meters is Faraday’s law of electromagnetic induction. When a conductive fluid flows through a magnetic field, an electromotive force (EMF) is generated across the fluid, which is proportional to the velocity of the fluid. The magnitude of the EMF can be measured by two electrodes, which are placed in contact with the fluid and perpendicular to the direction of flow. The voltage generated between the electrodes is proportional to the flow rate of the fluid.

Where They’re Used in Oil & Gas

Mag meters have become increasingly valuable across oil & gas operations because they provide accurate readings with no moving parts, minimal pressure drop, and the ability to handle harsh or abrasive fluids.

Key Oil & Gas Applications:

• Produced Water Monitoring – Handling corrosive mixtures of water, oil, salts, and sand during extraction.
• High-Pressure Injection – Measuring water or slurry injection in hydraulic fracturing and enhanced oil recovery at pressures up to 420 bar.
• Cementing Operations – Accurately tracking cement slurry volumes to ensure proper well casing and integrity.
• Refinery & Petrochemical Processes – Batching, blending additives, and wastewater flow measurement in downstream plants.

Electromagnetic flow meter typically consist of a flow tube made of non-conductive material, such as plastic or ceramic, with two electrodes mounted in the flow tube. The flow tube is surrounded by a magnetic field generated by a coil, which is powered by an external power supply. The magnetic field can be either a constant magnetic field or a pulsed magnetic field, depending on the design of the flow meter.

Electromagnetic flow meter have several advantages, including high accuracy, reliability, and low maintenance requirements. They are also able to measure the flow rate of both conductive and non-conductive fluids, and are not affected by changes in fluid density, viscosity, or temperature. However, they do have some limitations, including the need for a conductive fluid and the potential for signal interference from other sources of electromagnetic radiation.

Applications

Clean water distribution

• Slurry and mining processes
• Chemical dosing and mixing

Oil & Gas:

• Produced water measurement before re-injection or disposal
• Firewater flow monitoring in refineries
• Corrosion inhibitor and chemical injection systems
• Food & beverage processing
• Wastewater treatment plants

Advantages of Magnetic flowmeter

• No moving parts → minimal maintenance
• No obstruction to flow → low pressure drop
• Can handle clean, sanitary, dirty, corrosive, and abrasive liquids
• Works well in short meter runs

Limitations of Magnetic flowmeter

• Cannot measure non-conductive liquids (e.g., hydrocarbons, deionized water, gases)
• Pipe must be full at all times for accurate readings
• Sensitive to coating on electrodes

Magnetic flowmeters measure the velocity of conductive liquids in pipes, such as water, acids, caustic solutions, and slurries. They operate correctly when the electrical conductivity of the liquid is greater than approximately 5 μS/cm.

Note: Using magnetic flowmeters on low-conductivity fluids — such as deionized water, boiler feed water, or hydrocarbons — can cause the flowmeter to stop working and display zero flow.

Installation Requirements Magnetic flowmeter

• Magnetic flowmeters require relatively short straight runs:
• Upstream: 3–5 pipe diameters (from plane of electrodes)
• Downstream: 0–3 pipe diameters

Best Practices  of Magnetic flowmeter

• Install with electrodes horizontal to avoid bubble interference
• Avoid installation near strong magnetic fields
• Maintain proper grounding for stable signal

Design Calculation Magnetic flowmeter

Flow rate (Q) is determined from velocity (V) and cross-sectional area (A):

Q = V × A

Where:

• Q = Volumetric flow rate (m³/s)
• V = Velocity (m/s) from magmeter
• A = Cross-sectional area (π × D² / 4)

Example Calculation

Given:

• Pipe DN = 100 mm (0.1 m)
• Velocity = 2 m/s

A = π × (0.1)² / 4
A = 0.00785 m²

Q = 2 × 0.00785
Q = 0.0157 m³/s = 15.7 L/s

Result: The flow rate is 15.7 L/s.

Magnetic flow meter

Frequently Asked Questions (FAQ)

1. What is a magnetic flow meters?
It is a device that measures the flow of conductive liquids using electromagnetic principles.

2. Can magnetic flow meters measure oil or gas?
No. They only work with conductive liquids, not non-conductive fluids like oil or gas.

3. What is the minimum conductivity needed?
Around 5 μS/cm for accurate readings.

4. Do magnetic flow meters have moving parts?
No. They are designed with no moving parts, so they last longer and require less maintenance.

5. How much straight pipe length is needed?
Usually 3–5 pipe diameters upstream and 0–3 diameters downstream.

6. Can they measure slurry or wastewater?
Yes, they work well with dirty, abrasive, and corrosive liquids.

7. How is velocity measured?
The meter detects the voltage created as the liquid moves through a magnetic field.

8. What happens if conductivity is too low?
The meter may stop working or show zero flow.

9. How do I size a magnetic flow meter?
Use Q = V × A and choose a bore size to keep velocity between 1–5 m/s.

10. Can they be installed vertically?
Yes, but the pipe must be completely full of liquid.