ISO 12185 pdf download.Crude petroleum and petroleum products – Determination of density – Oscillating U-tube method
1 Scope
This International Standard specifies a method for the determination, using an oscillating U-tube density meter, of the density of crude petroleum and related products within the range 600 kg/m3 to 1 100 kg/m3 which can be handled as single-phase liquids at the test temperature and pressure. This International Standard is applicable to liquids of any vapour pressure as long as suitable precautions are taken to ensure that they remain in single phase with no loss of light ends and subsequent changes in composition and density during both the sample handling and the density determination. NOTE 1 If the determined density is to be converted to a density at some reference temperature using petroleum measurement tables, the determination should be carried out at a temperature as close as possible to the reference temperature in order to minimize uncertainties due to the use of generalized tables. This method is not intended for use in calibrating on- line density meters.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publi- cation, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most re- cent editions of the standards indicated below. Members of IEC and I S0 maintain registers of cur- rently valid International Standards. I S0 91-1 :I 992, Petroleum measurement tables – Part 7: Tables based on reference temperatures of 15 C and 60 degrees F, I S0 91-2:1991, Petroleum measurement tables – Part 2: Tables based on a reference temperature of 20 “C. I S0 301 5:1992, Petroleum products – Determination of cloud point. I S0 301 6:1994, Petroleum products – Determination of pour point, I S0 31 70~988, Petroleum liquids – Manual sampling. I S0 31 71 :I 988, Petroleum liquids – Automatic pipe- line sampling. IS0 3696:1987, Water for analytical laboratory use – Specification and test methods. I S0 3838:1983, Crude petroleum and liquid or solid petroleum products – Determination of density or relative density – Capillary-stoppered pyknometer and graduated bicapillary pyknometer methods.
3. Definitions
For the purposes of this International Standard, the following definitions apply. 3.1 density: Mass of the substance, expressed in kilograms, divided by its volume, expressed in cubic metres. 3.2 reference temperature: Temperature at which the sample density is to be reported. NOTE 2 This temperature should be either 15。C or 20 °C.
4 Principle
A small (typically less than 1 ml) portion of the test sample is introduced into a temperature-controlled sample cell. The oscillation frequency is noted, and the density of the test sample calculated using cell constants previously determined by measuring the oscillation frequencies when the cell is flldl with calibration fluids of known density.
5 Apparatus
5.1 Density meter, capable, once calibrated, of de- termining density with a resolution of土0,1 kg/m’ or better. NOTES 3 Meters commonly display two forms of digital result, either a density value or the period of oscillation from which density can be calculated. 4 Research has shown that the density meter may show a bias:of up to 1 kg/m3 due to viscosity effects. Users should ascertain whether a viscosity correction is required by checking the result using a pyknometer method such as that given in Iso 3838. Alternatively, viscosity effects can be minimized by using certified calibration standards of chemical characteristics and viscosity similar to that of the sample under test [3]. 5 Problems have been experienced with certain density meters due to condensation gathering on the cell sensors and electronics when the cell temperature is held below the dew-point of the ambient air. If there is risk of this occurring, the surrounding air should be kept dry. 5.2 Circulating constant-temperature bath, if re- quired (see 9.1.21, capable of maintaining the tem- perature of the circulating liquid to within f 0,05 “C of the required temperature. 5.3 Calibrated temperature sensor, capable of measuring the temperature of the cell to an accuracy of at least f 0,lO OC. The rate of energy transfer across the cell is low and therefore care should be taken to use sensors with very fine leads in order to minimize heat transfer in or out of the cell along the leads. 5.4 Homogenizer, suitable for the sample and sample container, and capable of producing hom- ogeneous subsamples for test (see clause 8); a high speed shear or static mixer, or other type as appro- priate.