Flow metering is a critical component in process measurement, and even minor mistakes can lead to inaccurate results, inefficiencies, or costly downtime. Here are 5 common flow metering mistakes I’ve encountered—and more importantly, how to fix them:
1. Using Gauge Pressure Test Equipment on Absolute Pressure Transmitters
This mismatch renders validation inadequate because the reference equipment and the equipment under test are measuring different pressure types. Additionally, without an atmospheric pressure reference, the transmitter’s zero-check point cannot be validated. Invest in appropriate test equipment for your specific instrumentation.
2. Improper Slope of Impulse Lines on Pressure Transmitters
Incorrect impulse line slopes can trap gas or liquid, leading to pressure reading errors. Follow industry best practices by maintaining consistent slopes to prevent blockages. Impulse lines on gas streams should slope up from meter to transmitter so that any condensed liquid falls away from the PT. The opposite applies to liquid streams.
3. Ignoring Low Flow Cutoff
Many flow meters have a low-flow cutoff below which they become inaccurate or stop measuring altogether. This is often overlooked during operation. Ensure the meter is sized correctly for the expected flow range, including low flow conditions, or select a meter with suitable low-flow sensitivity.
4. Incorrect Flow Direction During Commissioning
Even if the meter is properly oriented, incorrect wiring or setup during commissioning can invert readings, especially in bidirectional systems. Validate flow direction and readings during commissioning with reference measurements or system checks.
5. Spot Sampling Frequency Not Data-Driven
Insufficient or overly frequent spot sampling can skew data or overload resources. Base sampling frequency on historic variability of each sample point, stable processes could be sampled less frequently, highly variable processes should be sampled more frequently. Sampling frequency should be justified by historic data and dynamic to accommodate change.
Avoiding these pitfalls requires attention to detail, proper planning, and adherence to industry standards. What other errors have you observed in flow metering and how were they rectified?