ISO 8222:2020 pdf free.Petroleum measurement systems -Calibration – Volumetric measures,proving tanks and field measures (including formulae for properties of liquids and materials)
All the volumetric measures described have a unique hierarchy in the traceability chain. All are traceable to standards of mass combined with the derived density of pure water. There is a hierarchy for traceability which is followed to provide the uncertainty required by the final application.
A primary measure would be calibrated by weighing the water withdrawn to a tank on a weigh scale or to directly weigh the measure and determine the weight of liquid filled or withdrawn. The weigh scale is calibrated with mass standards of the required class[U and uncertainty. The mass and the density of the water are then combined to give the volume.
A primary measure can be used to determine the volume of a secondary measure. This can require multiple measurements fills. A secondary measure can be used to determine the calibration factor of a flowmeter. This can be a reference flowmeter used to measure volume in a pipe prover or large volume measure or to calibrate other meters.
Figure 1 shows schematically a primary measure being used to determine the volume of a small volume prover, which in turn is used to calibrate a reference flowmeter used to determine the volume of a large pipe prover.
Primary and reference measures are calibrated using pure water or clean drinking water. The water density is determined from the recommended formulae relating density to temperature and corrected where required through a measurement of relative density. The water density can also be experimentally determined by the use of a calibrated densitometer.
Some secondary measures, particularly large fixed measures, may need to be calibrated with impure water, seawater or a hydrocarbon product.
Applicable liquid property formulae are given in Annex A.
The uncertainty for volume determination should be specified according to the application. Indicative values of uncertainty applicable to different volumetric measures are given in Annex E.
Volumetric measures are containers of defined internal volume. The nominal volume is derived by design and manufacture with the calibrated volume subsequently determined by calibration. The volume is defined between a top and bottom datum. The top datum can be a reference line on a scale or an overflow weir. The bottom datum can be an overflow weir, the internal plane of a drain valve (when closed) or a scale reading in a bottom sump or neck.
The volume is expressed as being the volume of liquid in the measure when it is at a defined standard condition. Nominal and calibrated volume(s) may be given for one or different standard conditions.
The volume to deliver is the standard volume of a measure which can be withdrawn from a full measure with a defined drain time. It is also the volume which can be filled into a measure which has been prewetted by filling then draining for the defined drain time.
The volume to contain is the standard volume of a clean dry measure. The volume to contain is always larger than the volume to deliver due to residual liquid remaining on the walls of a wet measure.ISO 8222 pdf download.