Calibrating flowmeters for accurate measurement: even in the installation
Why should we have our flowmeters calibrated?
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Calibrating flowmeters for accurate measurement: even in the installation
Recently, my colleague and I separately spoke with two large production companies in the (petro)chemical industry. Both of them asked a similar question:
“Why should we have our flowmeters calibrated? They just stay in the installation, and we regularly do a check from the outside.”
A logical question. Especially in environments where shutting down installations is not straightforward, you only want to perform calibration if it really adds value. But precisely in such critical environments, the quality of your measurements is crucial. That is why it is useful to explain the difference between a functional check and a calibration.
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A check is not a calibration
A functional check, such as remote diagnostics and/or visual inspection, gives you a first impression. Is the meter still working? Is there no major defect? But it does not tell you how accurate the meter is or to what extent the measured values have drifted over time.
A calibration goes further. The flowmeter is then compared, under controlled and reproducible conditions, with a reference standard. This gives you:
- Insight into the actual deviation:
At high flow volumes, accurate settlement (custody transfer) leads to fewer discussions and a direct financial impact, because the measured values demonstrably match reality. It also improves safe and efficient process control: you base controllers and alarm limits on what you actually measure, which saves energy and raw materials and reduces risks. - Measurement uncertainty that you can include in quality or process analyses:
For example in mass balances, SPC/CPK and reconciliations. This tells you whether differences in flow are real process changes or fall within the uncertainty of the measurement. - Traceable results to international standards (for example SI units):
Your results are traceable, via an unbroken calibration chain, to SI units. This ensures comparability of measurements, legal defensibility and smoother audits. - Substantiation towards auditors, certification bodies or customers:
With a current and complete calibration certificate you can demonstrate that your measurement process is under control. This prevents non‑conformities, reduces discussions about delivered quantities and supports compliance in safety‑ and settlement‑critical applications.
Why this matters so much for production companies?
In the (petro)chemical industry, flow measurements are used for process control, safety and settlement of product streams. A small deviation in the measurement can have major consequences for yield, quality or compliance. Think of direct financial differences in custody transfer, late or incorrect actions by controllers and interlocks, and higher energy and maintenance costs because assets operate outside their optimal setpoint. In that case, calibration is not a luxury, but a prerequisite for reliable operation.
How often should you calibrate?
A commonly used guideline is once a year, but that is not an absolute rule. The correct frequency depends, among other things, on:
- The type of flowmeter:
Mechanically more sensitive meters should be calibrated regularly, especially if abrasive media are used or if there is significant fouling. Coriolis and electromagnetic flowmeters are generally more stable and can operate with longer intervals, provided the installation and medium are stable and clean. Ultrasonic and thermal mass flowmeters are more sensitive to deviations due to installation effects and contamination. That is why you should set the calibration frequency in a risk‑based way, tailored to the process and to the trend data from the flow measurements. - Service conditions and environment:
The harsher the service conditions (for example in terms of temperature, pressure or contamination), the greater the chance of drift in the measured values. In rough service environments you should shorten the calibration interval and perform interim process checks to safeguard the accuracy of measurements. - The impact of an incorrect measurement:
The impact can range from loss of quality and unnecessary shutdowns to safety risks and financial loss in settlement. The greater the impact, the shorter the calibration interval and the more intensive the required trend monitoring of flow data. - Customer or standard requirements:
Some ISO standards (such as ISO 9001 or ISO/IEC 17025) require demonstrable control and justification of your calibration intervals, not fixed terms. So document your choice and review it periodically based on measurement data and audit findings.
A risk‑based approach can help you assess measurements critically and set up an effective calibration plan.
More than a technical obligation
Calibration is more than a technical obligation. It is an investment in reliability. In sectors where every detail counts, you want to be able to demonstrate that your numbers are correct. Checks are valuable, but only calibration makes it truly measurable.
Would you like to know more? Our experts have in‑depth knowledge of flow measurements and are members of internationally renowned working groups, including the BIPM Working Group on Fluid Flow and EURAMET TC‑Flow.