Be a Hero When Your Straight Run is Zero
One of the questions I get asked all the time is, “What options are available if I don’t have the ideal piping configuration for my mag meters?”
Of course, we always want to encourage people to follow the best practices when it comes to installing their flow meters, and mag meters are no exception. In order to assure the stated accuracy of the meter, the ideal conditions will have five diameters of the same size, straight-run pipe upstream from the electrode and three diameters downstream. However, we realize that these conditions don’t always exist, so rest assured there are other options.
First, let me state that without exception we need the pipe to be full. Mag meters measure velocity and calculate the volumetric flow rate based on the presumption of a full pipe.
There are a couple of basic rules that I like follow when installing a flow meter:
- If you need to mount the meter in a vertical run, always have the flow going up through the meter. Never have the flow going through the meter as vertical down – this happens in situations where the pipe isn’t full.
- If you are mounting the meter in a horizontal pipe, it’s usually best to have the meter mounted in a location where the piping eventually extends above the meter. By having the flow go up after the mag meter, you usually will keep the area where the mag meter is mounted as a full pipe.
We had the MAG 5100W and MAG 8000 independently tested to see what we could offer as an alternate solution to those who don’t have the ideal piping available.
Here is what we did to confirm our meters performance:
A series of tests were conducted by a globally accredited agency, which proved that the MAG 5100W and MAG 8000 are capable of 2% accuracy - even in nonstandard configurations with an insufficient straight run of pipe. A reference test was first conducted by installing the MAG 5100 W and MAG 8000 as recommended by Siemens for the best possible performance with a 5D upstream pipe and a 3D downstream pipe from the sensor. The meters were then tested in various configurations, which do not meet the suggested installation conditions. As the results were consistent, a globally accredited agency accepted the meters with these installation variations to be approved for an accuracy of +/-2.0%, even with zero diameters upstream and downstream of straight run pipe.
How do you ensure that the meter will actually perform in your individual process line/piping arrangement?
As your process environment can impact your meter’s performance, it’s essential to confirm your meters performance. This can be done either by using another flow meter mounted elsewhere in the process or, in my opinion, the best way is to physically check the amount of material coming out of your process against the measurement (usually via the totalizer) indicated by the meter. To do this, I recommend deferring to your QA team as they are probably the best source to go to when determining the best way to make this happen in your process environment.
Remember though, not all mag meters are created equal, and some do not work nearly as well as others, so you must do your due diligence and field testing when prepping your process environment.
What difficulties do you experience when configuring your mag meters?