ISO 4266-5:2002 pdf download

ISO 4266-5:2002 pdf download.Petroleum and liquid petroleum products —Measurement of level and temperature instorage tanks by automatic methods —Part 5: Measurement of temperature in marinevessels.
NOTE 1 This protection may require mounting the ATT sensor(s) in a thermowell.
NOTE 2 AU sensors can be an integral part of the ALG level sensor assembly (e.g. float and tape, pole). Some design (e.g. float and tape) may need the level/temperature sensor assembly to be raised to a “store” position when it is not being used. Note that such ATTs cannot be used during tank washing.
4.3.6 The design and installation of ATTs may be subject to the approval of the national measurement organization, who will normally have issued a type or pattern approval (“Type Approval”) for the design of the ATT for the particular service for which it is to be employed. Type approval is normally issued after an ATT has been subjected to a specific series of tests and is subject to the AU being installed in an approved manner. Type approval tests may include the following: visual inspection, performance, vibration, humidity, dry heat, inclination, fluctuations in power supplies, insulation, resistance, electromagnetic compatibility and high voltage.
5 Accuracy
5.1 General
The accuracy of petroleum temperatures taken by the ATTs should be consistent with the accuracy of the levels taken by the automatic level gauging system so that the overall accuracy of the standard volume measurement is not seriously degraded.
5.2 Intrinsic error of ATTs
The intrinsic error of the ATT, i.e. the accuracy of the ATTs when tested under controlled conditions as specified by the manufacturers, can be a major component of the uncertainty of the temperature measurement of the ATT as installed. The calibration reference device used to calibrate the ATT should be traceable to appropriate national standards.
NOTE The temperature elements and onboard transmitters used for fixed, automatic tank temperature measurement are calibrated prior to installation. The transmitters normally do not provide on-board calibration adjustments.
5.3 Calibration prior to installation
5.3.1 General
The AU can be calibrated/verified either as a system (see 3.1) or by components.
5.3.2 AlT calibrated as a system
If verified as a system, the temperature reading of the ATT readout should agree with that of the thermostatically controlled reference bath or oven temperature within 0,25 °C at a minimum of three test temperatures spanning the anticipated working range of the ATT.
5.3.3 AlT calibrated by components
If the AU is verified by components:
a) the temperature equivalent of the measured resistance should agree with the bath temperature within 0,20 °C at each temperature;
b) the temperature transmitter/converter and the ATT readout should be checked using precision resistors or a recently calibrated thermal calibrator. The ATT readout should agree with the temperature equivalent of the resistors or calibrator within 0,15°C at each temperature.
5.3.4 Multiple-point ATTs
The required accuracy for each spot temperature sensor should be as given in 5.3.2 or 5.3.3, depending on the
method used.
5.3.5 Uncertainty of the reference
The uncertainty of the reference should not exceed ± 0,05 °C.
5.4 Error caused by installation and operating conditions
The total error of the ATT for custody transfer service can be affected by the installation and by variations in the operating conditions.
NOTE 1 The accuracy of an ATT depends on the following:
— the number of temperature-sensing elements;
— the location of the temperature-sensing elements.
NOTE 2 The tank content’s temperature may be subject to stratification which varies with
— cargo-heating method and/or location of heating coils;
— multiple sources of supply;
— viscosity of the liquid in the tanks;
— tank insulation;
— adjacent tank temperatures, and
— sea water temperature for tanks in contact with the ship’s hull and bottom.
NOTE 3 Temperatures in large tanks (i.e. 750 m3 or larger) are often vertically stratified unless the contents are thoroughly mixed. Larger stratification may be expected in high-viscosity petroleum liquids. Temperatures in wing tanks can also be horizontally stratified due to the effect of the sea temperature.
5.5 Overall accuracy
5.5.1 General
The overall accuracy of temperature measurement by the ATT, as installed, is limited by the intrinsic error of the ATT equipment (temperature-sensing element, transmitter and readout), the effect of installation methods, and the effect of the operating conditions.
In tanks with vertical temperature stratification, the temperature gradient is rarely linear. An average temperature should be used for fiscal/custody transfer services. The mid-level temperature of the tank contents may not give an accurate average temperature.
5.5.2 Use of Afl for fiscal/custody transfer purposes
An Afl system should be considered suitable for fiscal/custody transfer services, if the ATT system meets the following on-board verification tolerances.
The ATT should meet the calibration tolerances prior to installation (see 5.3).
Including the effects of installation methods and changes in operating conditions, the ATT should meet the on-board verification tolerance (see 9.2.2 and 9.3.2).
The remote readout, if used, should meet the recommendations of this part of ISO 4266 (see clause 10).