TÜV SÜD National Engineering Laboratory

IntroductionOil worldwide is traded in barrels. In the UK, oil production is reported in tonnes and allocated by mass. Therefore, the accurate measurement of density at the correct conditions of temperature and pressure is critical since oil flow in pipelines is largely measured by volume, and conversions involving density are necessary for accurate financial reporting, fair trade and taxation. Errors in density measurement may be the single biggest measurement issue to affect the oil industry.

All commercial densitometers, for use on gases or liquids, operate on an oscillatory principle and require periodic calibration.

Since launching its calibration service in 2012, TÜV SÜD Nationl Engineering Laboratory has calibrated over 500 units in strict accordance with the UK Oil & Gas Authority (OGA) Guidelines. A key requirement of these Guidelines is that calibration should be carried out at the anticipated operating conditions.

This requirement arose as a result of a Joint Industry Project led by TÜV SÜD Nationl Engineering Laboratory which demonstrated that the previous recalibration procedure of just adjusting the K0 and K2 coefficients based on data obtained at 20ºC and 1 bar was totally inadequate.

The FacilityThe facility is equipped to calibrate densitometers at temperatures from 5 to 100ºC and simultaneously at pressures from 3 to 141 bar (a).

Depending on the temperatures and pressures, the reference fluids’ densities range from 625 to 1005 kgm3,with an uncertainty of 0.02% (k=2).

Densitometer CalibrationFacility

Densitometer Calibration Facility Operating Ranges

Parameter Range Uncertainty (at k = 2)

Tempreture 5 - 100°C 0.0012°C

Pressure 3 - 141 bar(a) 0.02 bar(a)

Refernce Fluid

Iso-octane 625 - 715 kgm-3 0.02%

Iso-butanol 735 - 820 kgm-3 0.02%

Toluene 790 - 890 kgm-3 0.02%

Water 960 - 1005 kgm-3 0.02%

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TÜV SÜD National Engineering Laboratory East Kilbride, Glasgow, G75 0QF, United Kingdom +44 (0)1355 593700 info@tuv-sud.co.uk www.tuv-sud.com/uk

Standard CalibrationFor a standard calibration, two reference fluids are used,normally iso-octane and water, as these cover the densityrange of typical crude oils. Calibration is carried out usingthese two fluids at ± 5°C and ± 5 bar about the anticipatedoperating conditions and new, optimised coefficientsgenerated – typical results are shown below.

Extended RangesFor condensate service densitometers a modified procedure is used, as there are no reference fluids available to cover densities down to ~500 kgm-3. Calibration is carried out using the high and low density fluids at the anticipated operating conditions and new, optimised coefficients generated. Additional measurements are made with an intermediate density fluid, to provide confidence when extrapolating the calibration to low densities, as shown below.

TÜV SÜD National Engineering Laboratory East Kilbride, Glasgow, G75 0QF, United Kingdom +44 (0)1355 593700 info@tuv-sud.co.uk www.tuv-sud.com/uk

Why Choose TÜV SÜD National Engineering Laboratory?TÜV SÜD National Engineering Laboratory is a world class provider of technical consulting, research, measurement, and testing services to clients across many industries including oil & gas, water, power & energy, and government.

TÜV SÜD National Engineering Laboratory is the UK’s National Measurement Institute responsible for the management of the UK National Standard for Flow Measurement.

Related ServicesTÜV SÜD National Engineering Laboratory provide the following related services:

▪ Flow meter selection ▪ Uncertainty analysis ▪ Auditing ▪ Allocation ▪ CFD