As part of custody transfer, technicians routinely calibrate all the pressure and temperature transmitters involved in the flow of oil and gas as well as the pressure in the pipelines and related equipment.
Too often in search of accuracy, attention is focused entirely on the flow meter's performance under ideal conditions. But there are many other controllable factors that affect system accuracy. Here are some actions to consider:
- Properly align the pipes leading to and away from the flow meter.
- A typical custody transfer system has multiple flow meters installed across a single header. Size these headers properly to avoid inaccurate results.
- Place temperature sensors at locations that follow AGA guidelines.
- Choose high-quality flow system components appropriate for the desired accuracy.
- Maintain and calibrate flow system components regularly and properly.
Regular calibration is a vital part of maintaining system accuracy. It can be done in situ or in a laboratory. Calibrations for this application are typically done with three calibrators to measure low pressure, high pressure, and temperature. Alternately, you can use a multifunction calibration tool like the Fluke 721 or 721EX Precision Pressure Calibrator, which have two built-in pressure ranges and the ability to measure temperature.
Most pumps used to supply pressure for calibrations above 600 psi are hydraulic. But since hydraulic pumps use fluids to generate the pressure, liquid contamination of the system being calibrated is a risk. You can use gas instead, with a gas cylinder, but that is a burden to lug into the field and it can also be a safety risk. For field calibration, the best solution is a pneumatic pump designed for pressures up to 3000 psi. An example of this type of pump is the Fluke Calibration 700 HPPK Pneumatic Pressure Pump. It can supply pressures up to 3000 psi in the field without the risk of liquid contamination. It's also lightweight and easy to carry.