Accurate volume measurements are essential for the transport and trade of oil and oil products. High demands are put on flowmeter performance, especially when it concerns custody transfer or fiscal metering applications. Inaccuracies in volume measurements when buying or selling can cost much money and customer credit. A multibeam ultrasonic flowmeter forms an interesting new flowmeter technology for custody transfer applications where highly accurate measurements are required. It is the first liquid ultrasonic flowmeter to meet the stringent requirements stated in the guidelines of OIML and NPD for custody transfer. The uncertainty range lies within ±0.15% of rate over a wide flow range and the flowmeter has a repeatability of ±0.02%. In addition the multiple beam ultrasonic flowmeter has several benefits:
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operates independent of viscosity,
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is negligible effected by distorted flow profiles and swirl,
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can perform bi-directional measurements;
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gives much information on the flow profile over the cross section of a pipe.
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has no moving parts and therefore no wear and
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is nearly maintenance-free as e.g. frequent and costly periodic calibrations or re-calibrations after product-change are not necessary.
The Forties Pipeline System (FPS) installed a 12" 5 path KROHNE ultrasonic flowmeter at the Dalmeny Export Terminal for an extended trial period of nearly 15 months. Approximately 800,000 barrels of stabilised crude oil are transferred to Dalmeny Terminal each day for transfer to tankers. The customer decided not to make it a research project but the duration of the trial the ultrasonic flowmeter replaced one of the 12 -helical bladed-turbine meters. It was used as an integral part of a fiscal metering system, accounting for the custody transfer measurement of oil to tankers. The Forties Pipeline System is a shared pipeline system with some 50 customers each entitled to their share of the export quantities. The primary purpose of the trial was to establish whether the meter, in particular the transducer ports, would be liable to suffer from wax or particulate deposition. Secondly, the aim of the project was to verify the accuracy, repeatability and long term stability of the multiple beam flowmeter. Accuracy and repeatability were tested using the bi-directional pipe prover and reliability was closely monitored to ensure there was no adverse impact on measurements. The trial was a success. The KROHNE 5 path liquid ultrasonic meter performed to a perfectly acceptable standard for the fiscal standard measurement of Forties Blend stabilised crude oil. Strong points:
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No significant long term drift.
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The meter was reliable and repeatable. Virtually all prove results within +/- 0.10% of the mean. The meter always met the criteria that five consecutive runs were run within +/- 0.05% repeatability.
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The meter showed no signs of deposition of wax or particles. After 15 months in the line the meter did not have even a thin film of oil its on surface.
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The meter did not require any intervention for maintenance or calibration during the 15-month trial period.
