API RP 85:2003 pdf download
API RP 85:2003 pdf download.Use of Subsea Wet-gas Flowmeters in Allocation Measurement Systems.
3.1.26 specified imbalance limit: A limit on System Balance which is established for the purpose of satisfying contractual obligations andlor regulatory requirements.
3.1.27 standard deviation: The square root of the vanance of a random variable.
3.1.28 system imbalance (I): The difference between the measured Master Quantity (Q-) and the sum of the mdividual Theoretical Quantities (XQ). sometimes referred to as the System Balance.
3.1.29 systematic error: The difference between the mean value of a measurement and its true value, generally a constant or near-constant value.
3.1.30 true value: The underlying characteristic of the measurand which would be recorded if the measurement were perfect, (i.e., there were no random or systematic measurement errors).
3.1.31 uncertainty (of measurement): A parameter associated with the result of a measurement that characterizes the dispersion of the values that could be reasonably be attributed to the measurand, often expressed in terms of its variance or standard deviation.
3.1.32 uncertainty-based allocation: A method of hydrocarbon allocation in which the relative uncertainties of the measurements are taken into consideration, including measurements made by each of the allocation meters, by the reference meters. and by any other instrumentation, the readings from which affect hydrocarbon flow measurement.
3.1.33 uncertainty of allocation meter: The uncertainty of an Individual Theoretical Quantity relative to the flowing conditions experienced by the meter, which includes the uncertainty of the meter. any uncertainty in EOS application, and the uncertainties due to errors of ancillary devices such as pressure and temperature.
3.1.34 uncertainty of reference meter: The uncertainty of the Master Quantity relative to the flowing conditions experienced by the meter.
3.1.35 variance: The expected value of the square of the difference between the measurement and its mean value.
3.1.36 watercut (water-liquid ratio): The volumetric fraction of water in a liquid stream composed of water, liquid hydrocarbons, and perhaps other liquids.
3.1.37 water volume fraction: The volumetric percentage of water in a total fluid stream composed of water, liquid hydrocarbons, other liquids, and gas.
3.1.38 wet gas: A particular thrm of multipha.se flow in which the dominant fluid is gas and in which there is a presence of free-flowing liquid.
4 Subsea Meter Calibration and Testing
4.1 GENERAL
This section addresses testing and calibration of meters that is performed for the purpose of qualification, prior to installation for actual field operation.
The status of multiphase measurement for wet gas service is immature. Accepted calibration practice uses test and production separation techniques, which rely on separation and metering of each individual phase to known standards by traditional methods and metering equipment.
Further complicating the situation is the subsea location of these meters when in service. This means that not only are they unavailable for removal and verification of their performance, hut that even routine test and inspection of sensors and other components is extremely difficult.
The following describes what reference ioop testing is required prior to a meter’s being declared qualified for subsea wet-gas service, what these reference facilities must possess in order to be certified as fit for the task, and what a successful calibration test should entail.
4.2 TESTING REQUIREMENTS
The nature of multiphase flows is complex. It is much more difficult to assure the reproducibility of fluid flow behavior at flow measurement sections — at different installation locations and through service life—than is the case for single phase flow. This results in a significantly higher degree of uncertaint)’ in meter calibration for multipha.se applications.
4.2.1 Meter Calibration Testing
Each flow meter design used for a specific wet gas application shall be qualified prior to use. A meter in an application may be exempted if it has already been qualified for the same application. Qualification testing should subject the actual meter design to the full range of conditions expected. This includes phase flow rates, pressures, temperatures, and fluid properties, using test fluids exhibiting similar properties and phase mass transfer behavior to the in-situ application process fluids. The meter under test shall be installed in a piping configuration similar to that of the intended service installation configuration, to demonstrate that it meets the uncertainty requirements over the range of flow conditions specified for the application. Reference meters used in this testing should meet the requirements of 4.3. 1.
Some of the parameters which should be considered are the following.
