Crude oil handover trade commonly uses scraper flowmeters.

With the advancement of economic globalization, crude oil—as a commodity—is increasingly integrated into international trade markets. As a critical component in crude oil transit trade, the measurement and handling of crude oil are receiving growing attention. The accuracy of crude oil trade-handover measurements directly impacts the economic efficiency of supply, sales, and transportation. Among the instruments commonly used for measuring and transferring crude oil, the scraper flowmeter stands out. This type of flowmeter employs mechanical measuring elements to continuously divide the flowing liquid into discrete volume segments, thereby accurately determining the total volume of the fluid—making it widely adopted today in petroleum product measurement across China.

The main features of the scraper flowmeter are: 1. High measurement accuracy, wide flow range, and excellent repeatability; 2. Smooth fluid rotation within the pipeline, with no pressure fluctuations or vibrations; 3. Measurement accuracy is minimally affected by changes in the viscosity of the medium being measured; 4. The single-shell design is simple, compact, lightweight, and easy to handle; the dual-shell structure prevents deformation of the metering chamber under high pressure, ensuring precise measurement while also allowing the inner shell assembly to be easily removed for maintenance, cleaning, purging, or pipeline testing; 5. Various counters and transmitters can be optionally equipped as needed, enabling local indication or remote transmission of electrical signals; 6. Fluid conditions do not impact measurement accuracy, and the flowmeter requires no straight pipe sections upstream or downstream, saving space and reducing costs.

The core structure of the scraper flowmeter includes components such as the top cover, metering chamber body, cam, rollers, inner casing, rotor assembly, scraper blade, bearings, gear set, differential regulator, counter, and meter head. After precision machining, the scraper blade forms a precisely calibrated measuring chamber between the top cover, inner casing, scraper, and rotor. As the rotor—mounted on ball bearings—rotates along with the scraper blade, it displaces a fixed volume of crude oil medium. The gear set then transmits the rotational speed of the scraper blade to the meter head, where the counter converts these rotations into the actual measured volume based on the gear ratio and volumetric conversion factor, thus completing the accurate measurement of the crude oil volume. Additionally, for models featuring remote pulse output, a magnetic-electric induction system transforms the mechanical rotation into electrical pulse signals. By counting these output pulses and applying the corresponding instrument coefficient, the total volume of the fluid being transported can be accurately determined. Scrapers flowmeters are renowned for their high measurement accuracy, independence from fluid properties and Reynolds number, as well as their exceptional wear resistance, corrosion resistance, sand-proof capabilities, and stable performance of both bearings and scraper blades.

Factors affecting the accuracy of scraper flowmeters include medium temperature, medium viscosity, instrument vibration, and wear in the measuring chamber. Higher temperatures lead to lower viscosity and increased leakage, while lower temperatures result in higher viscosity and reduced leakage. Additionally, wear in the metering chamber causes an increase in leakage from the scraper flowmeter, which in turn leads to a negative shift in measurement error. Using a volume tube for online calibration of scraper flowmeters not only enables accurate, real-time verification of these devices but also ensures that crude oil transportation and metering results remain unaffected. Moreover, this method helps reduce costs associated with dismantling and transporting the flowmeters, while minimizing the risk of potential damage—ultimately helping companies achieve greater economic benefits.