Testing of Magnetic Flow Meters in Nonideal Conditions

Magnetic flow meters have become common meters for closed pipeline flow measurement due to their accuracy and non-invasive measurement. In the past, magnetic flow meters have been difficult to install (particularly in existing sites) due to straight pipe requirements upstream and downstream of the meter. The testing in this project was performed to quantify the effect various conditions have on the accuracy of several magnetic flow meters. Six models from six manufacturers in 4” and 10” sizes (12 meters total) were tested. Testing found about half of the meters had a baseline error (no obstructions upstream or downstream) of less than ±2%. Conditions found to have a significant effect for a majority or all the meters: double elbows directly (2D) upstream of a meter reduced accuracy; throttling a butterfly valve upstream of a meter by more than 50% reduced accuracy. Conditions found to have minimal or no obvious effect for most or all meters: obstructing the flow upstream in two planes, rather than one plane; electrical grounding of the meter. The results presented in this report are preliminary and subject to revision.