EuroLoop

EuroLoop is one of the largest test- and calibration centres for the oil and gas industry.Several closed loop systems for the oil and gas industry are being built lately on the ‘Europoort’ region near Rotterdam.  Not surprisingly, the name of this NMi operated facility, carries the name ‘EuroLoop’.

The facility comprises of three independent oil-rigs for several oil types and two high pressure gas loops. The purpose of these facilities are to provide in Calibration reference values and to offer a R&D test site. The facility is unique in the sense of the scale (up to 30000 m3/h gas- and up to 5000 m3/h oil flow), high accuracy and operation performance. A test facility of this magnitude offers a great challenge for metrologists while primary standards normally underpin traceability in small to intermediate volume flows and therefore VSL was deeply involved in the designs, front end engineering and the metrological design.

The traceability of the calibration facility for gas and oil meters is guaranteed by means of reference flow meters. These meters are in themselves not traceable to the international standard for length (volume) and time but are in fact only ‘stable information copying devices’ or ‘comparators’. This is because continuous flow meters that generate a traceable reference value for volume do not yet exist. The reading of the fixed, built-in working standards are therefore simply compared with the reading of a comparator meter that is connected in series under the same process conditions (e.g. pressure, temperature, oil-/ gas type). The reading of this ‘traveling’ comparator also known as the transfer standard is on beforehand compared with the primary standard, which is the system of instruments, piping, for ascertaining the fundamental amount of substance for gas or oil per unit time.

The primary standard for HP gas flow is provided by means of the VSL designed ‘Gas Oil Piston Prover’ (2003).  A piston prover is a high precision cylinder in which a piston shuttles from one to another side, generating a well defined amount of volume of liquid or gas product.
The VSL piston prover has a few remarkable features: Any possible gas leakage through the piston seals is measured real time; the average temperature in the cylinder cavity is measured with a taut-string with a chain of temperature sensors moving along with the piston; the piston is hydraulically driven to ensure smooth operation and as little thermal effects as possible. The inner diameter of the cylinder is determined every 30 cm along the 12 meter long run way with digital micro meter gauge-clocks.  These gauges (the length comparators) are calibrated with a fixed precision gauge caliper, which is in turn calibrated to the international defined wavelength of a laser-beam. The defined piston stroke length is determined with a so named Laser Interferometer. The ultimate uncertainty on generated flow rate amounts in the order of 0.06%. However the disadvantage of this gas prover type (although 12 meters long and 585 mm bore) is the restricted flow range of about 230 m3/h. With a specially design ‘traceability multiplier’ the maximum flow rate can be boosted to 2000 m3/h, still not enough for EuroLoop but eventually, the master meters boost the reference value to a higher flow rate by putting more working standards in parallel operation to gain the final 30,000 m3/h.
For the oil loops, the recommendation was followed to build two large piston provers  with the same features as the gas oil piston prover, except that because of the large geometry (max length is about 45 meter, diameter are 590 and 1130 mm respectively) the temperature inside the cylinder is measured by means of speed of sound transmitters.

There is a quite linear relationship between the ‘mixed cup’ or average temperature of oil and its speed of sound.  Beside the fast response time of this temperature measurement principle (some milli seconds) the method is very suitable to cope with temperature profile effects that make conventional temperature metering less reliable. The cylinder diameter will be measured by means of 12 traveling proximity sensors fixed at the outside piston wall comparing the local diameter with a fixed reference value the ‘standard ring gauge caliper’ at one of the two piston terminals.  The data of the inner diameter determination will be stored within the intelligent piston during the traveling stroke. When the piston is close enough to the antenna at the launching or terminal position, the data are transmitted through the oil by means of a high frequent radio signal to the ‘fixed world’.  Because the primary oil piston provers are directly connected to the rigs, the customer can get a primary calibration on request. The calibration and measurement capability of 0.02% is highly valued by the customers of EuroLoop and a nice challenge for engineers and metrologists of VSL. You will be updated at www.vsl/knowledge/euroloop.nl