Karl Stappert
Flow Solutions Advisor
Flow Control Magazine – July 2014
For the most part, calibration intervals on flowmeters are specified by regulation or determined by historic record and process condition. Intelligent flowmeters, like Coriolis and ultrasonic, have diagnostics that identify when a meter’s performance is outside of normal limits. These capabilities can be used to mitigate fiscal risk between calibration intervals or extend calibration intervals. What factors come into play? Factors that affect calibration intervals are the severity of the service, which includes dirty processes, two-phase, surging applications, high and low temperature, level of fiscal & HSE risk attributable to measurement. These same factors also determine the frequency of calibration.
How do the type of application(s) the flowmeter is being used for affect the frequency/necessity of calibration?
Dirty processes can cause pipe and flow conditioner build-up, inducing abnormal flow velocity profiles for meters like orifice, turbine, v-cone, ultrasonic, wedge, vortex, etc. that are sensitive to this change. Dirt and debris can build up on the internal flow diameter of the flowmeter, reducing flow diameter, increasing flow velocity, and inducing over registration. Flowmeters that utilize density measurement to infer volume from mass are susceptible to density error caused by coating of the meter flow element. Turbine meters are highly sensitive to Reynolds number change, change in fluid density, viscosity and flowrate, which may dictate the need for recalibration. Corrosive or erosive fluids will drive the need for more frequent calibrations. Surging applications (well production, engine and boiler fuel start-up flows) are extremely damaging to flowmeters with rotating elements (turbine and positive displacement meters).
What are some of the problems that can occur when a flowmeter is not calibrated properly or at all?
Over-registration (grandma eats dog food), under-registration (stockholders eat dog food), non-compliance with regulation … product quality and quantity out of tolerance (fiscal and regulatory liability).
Have stricter government mandates increased the need for flowmeter calibration? How?
Tighter regulation on product quality, quantity, health, safety, and environmental protection have created mandates on calibration interval and practice. The potential liability of regulatory non-compliance has driven users to self regulate their calibration practice.
What are some common pitfalls end-users encounter/fall into when it comes to flowmeter calibration?
Blind trust (trust but no verification) of their calibration references; calibration of instruments outside of the reproducible condition limits of the technology being calibrated.
How do you see the issue of flowmeter calibration evolving going forward? Are there any technology or application trends that will influence the flowmeter calibration process in the future?
Master Metering with highly reproducible flowmeters will become more common. The on-line diagnostics of intelligent flowmeters will begin to govern calibration interval. Master metering Coriolis meters will most likely have the biggest impact on flowmeter calibration practice in the future.
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