What’s the Best Way to Measure Pipeline Flow?

A: One of the most important things to know when you’re operating a pipeline is the flow rate, which is typically measured in cubic meters per hour (m³/h), liters per second (l/s), or gallons per minute (gpm).

Although many methods for measuring flow exist, slurry pump engineers typically rely on three common tools: a magnetic flow meter, a Doppler meter, or a sonar flow meter.

A Doppler meter doesn’t require you to disconnect the pipe to install it. It is like a “stethoscope.” You attach a probe on the outside of the pipe. The meter measures the velocity of the slurry by using ultrasonic pulses that bounce off the solid particles in the slurry.

Do you have specific questions on how to measure your pipeline flow? Contact our Technical Services Team.

However, Doppler meters have a couple of quirks that can make them unreliable. First, they are very sensitive to sound, so sudden noises in the pipe environment can cause erroneous readings. If the meter is installed on the bottom of the pipe and the pipe has a bed deposit at the bottom of the pipe, the meter will often give a false reading because the particles move more slowly along the bottom of the pipe than at the center.

In addition, a Doppler meter must be calibrated for each different type of slurry, which may not be practical for engineers in the field.

A more dependable tool is the magnetic flow meter. This meter is installed in a section of the pipeline. The meter has the same diameter as the pipe, so the meter does not restrict the flow through the pipe. The meter applies a magnetic field to the pipeline to measure the velocity of the liquid and solids in the line. When you know the velocity and the diameter of the pipe, you can easily calculate the flow.

Ideally, a magnetic flow meter should be installed in a pipe that’s flowing upward. But in many plants, finding an upward-flowing pipe is difficult so a horizontal line must be used. KSB GIW, Inc. engineers recommend using magnetic flow meters because of their high reliability.

A sonar flow meter is a third type of meter in common use which “listens” to moving eddies in the flow via a series of acoustic sensors to measure their velocity. These “sonar” meters are almost as accurate as a magnetic flow meter at normal slurry pumping velocities, but can become less accurate at lower velocities, if significant stratification of solids in the pipeline exists. These meters have the advantage of no contact with the fluid and can be easily strapped onto the outside of an existing pipeline.