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Automatic in-situ verification of accuracy for Coriolis mass flowmeters

Measurement made easy

Users often question whether their measuring devices are working properly and within specified measurement accuracy. The new CoriolisMaster flowmeter models by ABB include technology for integrated online diagnosis and accuracy verification. This technology constantly monitors the oscillating meter tube within the flowmeter for erosion and coating deposits. Self-monitoring technology avoids costly downtime needed for proof testing and provides other significant cost savings. It permits compliance with increasingly strict quality standards and legal requirements for verification of flowmeter accuracy.

Fig. 1: Nedalco Plant in Manchester, UK

Coriolis and VeriMass technologies

Aside from measuring highly accurate mass fluid flowrates, the Coriolis technique offers numerous other advantages. The Coriolis metering principle is independent of the fluid's density, temperature and conductivity, making it very flexible to use. It's also independent of the flow velocity profiles. So it does not require upstream and downstream straight runs of piping. As a bonus, the flowmeter provides a measurement of fluid density within the tubes. It also includes a temperature sensor to compensate for dimensional and elasticity changes of the tubes with fluid temperature. Lastly, these flowmeters can measure nearly zero flow, where other measurement methods don't work or result in significant measurement errors.

Self-monitoring capabilities greatly augment the above capabilities. The special metering tubes within the CoriolisMaster flowmeter are mechanically balanced. Balancing the meter tubes minimizes the energy for their oscillation. The amount of energy required is reflected in the electric current needed to drive the tube oscillations. Each measuring device leaves the factory with extremely well-balanced meter tubes and minimized driver current consumption.

coriolis flow measurement

Oscillating meter tubes inside a Coriolis flowmeter

Learning the baseline driver current

VeriMass uses this basic principle and monitors the driver current to detect possible changes of the meter tubes. The major challenge for the use of this kind of verification is the elimination of any short-term process effects. These effects can be accommodated by a learning technique.

After installation of a CoriolisMaster mass flowmeter, users can document the initial baseline driver current. The user defines an initial calibration period, during which the measuring device “learns” the standard behavior of the flowmeter in the specific application. VeriMass technology monitors the driver current to determine its initial baseline, while eliminating any short term effects. This self-calibration period adapts VeriMass to demanding processes such as high viscosity liquids, temporary gas phases in liquids or liquid drops in gases.

The initial calibration duration can be a few minutes up to several weeks. But for well-behaved processes the self-calibration period rarely requires more than a few days following installation. The noisiness of the driver current signal during the self-calibration period sets the tightness of the alarm threshold. Smoother processes will be monitored with tighter alarm thresholds than noisier processes. This avoids possible false alarms.

The self-calibration period also defines the verification monitoring time. At the end of each monitoring period VeriMass compares the newly found current level to the initial baseline. Verification monitoring repeats automatically with no further interaction by the user. If a new current baseline exceeds user-defined tolerances, VeriMass sets off an alarm.

VeriMass technology works best for diagnosing errors caused by coating and/or erosion of the oscillating tubes. In the case of liquids, it suits processes with changing densities as well as those with only small viscosity changes and temporary gas bubbles. Verimass can handle changes of different fluids with significantly different viscosities if the changes were present during the initial calibration period following installation. Liquids with erratic viscosities including changes of 50 mPas or more are NOT good application candidates. VeriMass technology also works well with gases having occasional liquid drops.

Operating VeriMass

Users can set up VeriMass locally by navigating the menu on the LCD display of the CoriolisMaster flowmeter. More convenient, however, is setup using the CoriolisMaster Device Type Manager (DTM) or ABB’s new Field Information Manager using FDI packages. The DTM and FDI packages include a rich and user-friendly graphical interface to make device configuration, maintenance, diagnostics and troubleshooting fast and easy. Users connect to the CoriolisMaster flowmeter via a host computer, HART commissioning device, or directly to a PC.

The CoriolisMaster flowmeter DTM offers all the interaction capabilities provided by the local display. Additionally, the DTM can generate verification reports. The user can enter date and identification details of the operator who checks the verification, and generate two types of reports. A short report focuses on the erosion and coating monitor, including alarm status, event log, and alarm history. The longer, more complete, report version shows the flowmeter's parametrization. The VeriMass option is available for all FCB100 and FCB400, as well as FCH100 and FCH400 CoriolisMaster models.

Entirely researched and developed in Italy

Nunzio Bonavita of ABB's Measurement and Analytics business group shares, "This innovative tool is the result of collaboration with TEA Sistemi, a spin-off of the University of Pisa engaged in research and development of advanced technologies in the Oil and Gas industry, and is designed to meet the most stringent industry requirements.

This is a totally Italian product born from collaboration between two companies that differ in terms of mission and size, but share the same focus on innovation and high technology. ABB has a consolidated relationship with TEA Sistemi, both at the level of R&D thanks to the competencies of the Pisan company in the field of Flow Assurance, and at a business level, where for many years ABB has been providing TEA Sistemi with its advanced technologies, especially in the field of pressure measurement, that are continuously improved at our production unit in Lenno, in the province of Como. Of course, in the past few months this collaboration has been further strengthened by working jointly for the definition and ongoing improvement of the new multi-phase flow meter, and for the commercial and service activities necessary to make this "made in Italy" technological excellence fully accessible at a global level".

Fig. 3: VIS operating diagram

Reliable and real-time measurements

For those involved in upstream oil and gas, the possibility of performing multiphase flow measurements provides obvious benefits. Bonavita continues: "In reality, hydrocarbons are not produced through the extraction of a single-phase flow, but rather a multi-phase flow where there is usually a binary liquid phase (oil and water) present as well as a gaseous phase (gas), as well as any sand or solid particles in suspension. This mixture is usually conveyed to a treatment plant under which there are multiple wells in multiple areas and at whose entrance there is a special unit dedicated to the separation of the three phases, which occurs substantially due to gravity.

Once the three phases are separated, the corresponding flow rates are measured using traditional methods and instruments. Measuring the three phases downstream of the separator, however, involves several limitations, because these measurements are available with considerable delay times and provide an average value that is obviously averaged over all the contributions coming from the various wells. Therefore, this type of measurement cannot be used for the purposes of monitoring and optimization of production of individual production areas.

The situation may be further complicated if the gas (or oil) processing unit receives incoming flows from areas managed by different companies, in which case it is clearly also necessary to resolve the problems of allocation of costs, profits and liabilities.

It is precisely in these situations that multi-phase meters assume a key role; these products are able to provide the same type of information as a conventional test separator, but with the advantages arising from the ability to obtain real-time flow-rate measurements, combined with a much more compact size.

By its nature, VIS provides maximum performance precisely in the most difficult applications for traditional multi-phase flow meters, where the gas volume fraction is extremely high. In technical terms, we refer to the GVF (Gas Volume Fraction); the closer the GVF is to 100 %, the more problematic the accurate measurement of the three phases becomes. The VIS measurement system, on the other hand, is designed precisely to better manage these challenges and has no problems, even when the volumetric percentage of liquid drops below 1 % or even 1 ‰.

The tool can also be applied successfully in gas storage fields. Thanks to its particular design, it can provide bi-directional and very accurate real-time measurements of biphasic fluids during production. This can be very useful, because it enables extractions from the tanks to be optimized, minimizing the water content present in the gas"

Unique and innovative technology

The operating principle of VIS, Isokinetic Sampling, consists of the withdrawal of a sample of the three-phase flow in such a way that the sample taken is perfectly representative of the entire stream. Multi-phase flows are characterized by extremely complex fluid dynamic conditions, where the individual components can thicken in particular areas of the duct and / or flow at different speeds. Obviously, sampling a percentage of flow "at random" is not acceptable unless this can be scientifically associated to the real profile of the stream as a whole. The methodology used by VIS starts with an extremely sophisticated sampling system, implemented by means of specially designed and patented devices that required years of computer-based research, made possible by the expertise of TEA Sistemi in the field of Flow Assurance and the associated specialist codes, as well as years of laboratory testing.

The details of the isokinetic sampling operational are obviously confidential. In principle, we can say, however, that careful management of differences in pressure between the interior of the sample probe inserted into the main duct and the duct itself ensure the conditions of equivelocity that are essential to fully representative sampling. Once a portion of the flow has been sampled, the meter performs the separation (another critical step that required the design of highly efficient components) and the measurement of the individual phases with conventional instruments, essentially pressure and temperature transmitters. Proprietary software is then able to use the information from the instruments and link them to extremely accurate measurements of the flow rates of the individual phases.

"Dual Inlet" configuration

The meter can also be provided in a "Dual Inlet" configuration that enables the measurement range of the instrument to be expanded.

One of the problems that multi-phase meters have to deal with is the extreme variability of the flow rates that they may be required to measure. Therefore, one of the parameters of interest to end-users is the so-called turndown, that is, how much the flow rate to be measured (on which the individual meter will guarantee the required accuracy) can vary. Given that VIS operates, via the sampling system, on a fraction of the flow, it is clear that the operating range can be extended to much lower flow rates simply by providing a system for direct insertion into the separator that enables the sampling phase to be bypassed. Therefore, with an appropriate additional input and simply by operating the related valves, VIS can hugely expand its "rangeability".

Fig. 5: "Dual Inlet" configuration diagram

Designed for the requirements of the Oil and Gas sector

Having compact high-performance meters that can be used close to wellheads provides detailed, timely and real-time information on the production process. For exactly this reason, the market demand for meters with these characteristics is expected to grow significantly in the coming years, because they will satisfy the specific needs of end users.

Let us not forget that process optimization plays a vital role in the Oil and Gas sector. The possibility of having a high-performance meter may be a determining factor for the profitability of upstream production sites.

Bonavita concludes: "The creation of VIS is a notable example in which theoretical research, applied research, industrial production of devices and software development have led to the market launch of a truly innovative instrument, both in terms of performance and of design. Research and technology – all made in Italy."

Fig. 6: Measurement trends taken at the platform Allegheny (Gulf of Mexico)

Characteristics of the VIS multiphase meter

Unique and patented technology
Isokinetic sampling enables the extraction of a representative portion of the flow and accurate calculation of the flow rates of the different phases. VIS technology, with more than 40 installations worldwide, is capable of providing high accuracy in even the most challenging flow conditions. The reliability of the instrument also remains unaltered in the detection and measurement of liquid fractions below 10-4%.

Totally free of radioactive components
Unlike many products available on the market, VIS is radioactive-free. This is of crucial importance in handling, shipping, commissioning and decommissioning procedures.

Standard instruments
VIS uses only standard process instruments. This is an advantage in maintenance operations, because operators do not have to deal with complicated devices, but with conventional instruments.

Ideal for Gas Storage Fields
VIS is also perfectly suited for the management of natural gas storage fields where detection of the smallest traces of condensation or water during the extraction phases is necessary. VIS technology has several successful applications in this sector.

Investment protection
VIS is ideal for applications in 'mature' gas and oil fields. In fact, there is a natural tendency for the GVF to increase with the age of the oil field. In this situation the installation of VIS also represents an investment protection, because over the years production conditions will tend to move towards those values on which VIS performance is particularly significant.

Wide range of measurement
The design of VIS can be implemented ad hoc to increase the gas turndown to a ratio of 100:1, the highest available on the market, without having to replace any component. Indeed, a strategy of automation enables the management of two different routes of entry for the fluid depending on its flow rate.

TEA Sistemi, partner in technology transfer

TEA Sistemi was founded in 1997 as spin-off of the Centro TEA (Centro Tecnologie Energetiche e Ambientali — Centre for Energy and Environmental Technologies) with the primary objective of promoting the transfer and commercialization of the results obtained in Research and Development.

Through the experience of its researchers, the group offers highly specialized products and services, with a strong sense of innovation in the energy and environmental sectors.

The design methods, calculation models and software used are, to a considerable extent, developed within the group, the result of technological research and innovation. The group currently boasts intellectual property rights to numerous patents, developed both internally and through co-operation with Italian and / or foreign partners, for the protection of equipment and systems of interest both to the process industry and to environmental protection.

TEA Sistemi operates across a broad spectrum in the field of research, supported by the TEA Laboratory, where experiments can be conducted on an industrial scale. Major investments were made in order to equip the laboratory with the instruments necessary for carrying out R&D, design and testing of equipment and processes for the industry.

Today the three companies of the TEA Group have more than 60 highly qualified employees and contractors, including professors and researchers from universities, the CNR (Consiglio Nazionale delle Ricerche — National Research Council) and other institutes. The headquarters of the Group and of its experimental Laboratory is located in Pisa.

Fig. 7: The TEA Sistemi Research Centre in Pisa