Precise measuring of oil flow is becoming ever more important. Because of the ever increasing oil prices, even small deviations can be quite expensive.
Coriolis flow metering technology is well established for its accuracy and reliability.
Oil metering systems based on Coriolis meters are compact because the meter does not require straight inlet runs, filters or strainers.
The Endress+Hauser 10” (254mm) and 6” (152mm) Promass Coriolis meters have been tested using oil products according to American Petroleum Institute (API) procedures and are certified by the respected Dutch metrology institute NMi. This makes them suitable for application in loading crude oil and refined products.
Crude oil is transported via pipelines or with large ocean-going tankers. Once it reaches its destination, the crude oil is unloaded in the port of arrival and often processed in on-site refineries.
The refined products are usually transported using pipelines, trains, tank trucks or ships. During transport, crude oil and oil products usually change owners as well.
Independent of the mode of transportation, there is always a need for accurate information about how much oil has been moved. Even small improvements in metering precision result in large cost savings.
Modern loading and offloading facilities are largely automated with a metering system monitoring and controlling the hydrocarbon loading.
The metering systems can be used for varying purposes, distinguishing between fiscal metering (where taxes are to be paid on the amount of oil transported), custody transfer metering (where the oil changes owners) and especially with pipelines, allocation metering (where product flowing from different sources are joined in one pipeline, or where multiple consumers are supplied through one line).
Metering systems used in the oil industry may be quite different in design: from a single flow meter to a complete system with multiple metering trains, in-line proving facilities, sampling units, BS&W (basic sediment and water) packages, flow computers and operator stations.
However, at the heart of each metering system, there is a flow meter which registers the oil flow.
Traditionally, turbine flowmeters or positive displacement (PD) meters were used. But recently, ultrasonic and Coriolis mass meters based on modern metering principles have begun to capture this sector.
Coriolis meters in particular are now also available for larger diameters up to 10” (254mm) and, as an example, have been installed in pipelines for the loading and unloading of oil tankers.
Having no moving parts, Coriolis flow meters are not subject to wear and tear and filters or strainers are not necessary making them attractive for the oil industry as well. For this reason, API has included the Coriolis technology in its Manual of Petroleum Measurement Standard of 2002 which also stipulates methods for meter proving and validation of Coriolis meters.
Meter proving is a comparison test of meter performance. During this test, a liquid flows through the Coriolis meter first, and then passes through a meter prover.
Essentially, the meter prover consists of a piece of pipeline with a precisely known volume. Thus it can be used as reference for flow measurement: the comparison of the volume displacement in the meter prover with the measured results from the Coriolis meter determines the Coriolis meter’s accuracy.
Coriolis meters not only measure mass flow but also the density of the oil.
Through digital communication protocols such as Modbus, the data can be sent to an online flow computer which calculates the relevant values such as gross and net volume and reference density at 15°C, in accordance with the API 2540 calculation guidelines.
The Endress + Hauser Coriolis meter Promass F has been tested in various oil products following the proving procedures described in the API standard.
A custody transfer approval is only granted following a successful, supervised proving procedure. For this certification, flow meters must comply with the international OIML (International Organisation of Legal Metrology) recommendation R117 (Measuring systems for liquids other than water), which sets performance standards of accuracy and repeatability for the meter.
Product certification for high level of accuracy requires the Coriolis meter to have a maximum deviation of ±0.2% with a repeatability of no more than 0.12% over the total range of measurements.
Under supervision of NMi, Promass returned good test results, with maximum deviations from the prover between -0.11% and +0.07%.
The repeatability was below 0.05%. These values are well within the thresholds required by OIML R117.
Accordingly Promass received the custody transfer approval for measurement facilities and can thus be used for fiscal and custody transfer measurements of oil flows.