ISO 3675 Crude petroleum and liquid petroleum products - Laboratory determination of density - Hydrometer method
1 Scope
This International Standard specifies a method for the laboratory determination, using a glass hydrometer, of the density at 15 °C of crude petroleum, liquid petroleum products, and mixtures of petroleum and non-petroleum products normally handled as liquids and having a Reid vapour pressure (RVP) of 100 kPa or less.
This International Standard is suitable for determining the density of mobile transparent liquids. It can also be used for viscous liquids by carrying out the determinations at temperatures above ambient using a suitable liquid bath for temperature control. It can also be used for opaque liquids by reading the hydrometer scale where the top of the meniscus meets the stem of the hydrometer and applying a correction from table 1 (see 11.2).
Since hydrometers are calibrated to read correctly at the specified temperature, scale readings made at other temperatures are only hydrometer readings and not values of density at these other temperatures.
NOTES
1 The accuracy of the density, determined by the procedures given in this International Standard, for volatile and/or waxy crude oils containing free and/or suspended water and sediments can be less than inferred from the precision data quoted in clause 13. This is due to the possible loss of light components during sample mixing. However, sample mixing is necessary to ensure that the test portion transferred to the hydrometer cylinder is as representative as possible of the bulk sample. Techniques are given in clause 7 which are designed to minimize such loss of light component.
2 Values of density at 15 °C can be converted using standard measurement tables to equivalent values of API gravity or relative density so that measurements may be made in the units of local convenience.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of IEC and ISO maintain registers of currently valid International Standards.
ISO 91-1:1992, Petroleum measurement tables - Part 1: Tables based on reference temperatures of 15 °C and 60 °F.
ISO 649-1:1981, Laboratory glassware - Density hydrometers for general purposes - Part 1: Specification.
ISO 3170:1988, Petroleum liquids - Manual sampling.
ISO 3171:1988, Petroleum liquids - Automatic pipeline sampling.
3 Definitions
For the purposes of this International Standard, the following definitions apply.
3.1 density
mass per unit volume expressed in either kilograms per cubic metre or grams per millilitre at 15 °C and 101.325 kPa
3.2 cloud point
temperature at which a cloud of wax crystals first appears in a liquid when it is cooled under specified conditions
3.3 wax appearance temperature (WAT)
temperature at which waxy solids form when petroleum or petroleum products are cooled under specified conditions
3.4 pour point
lowest temperature at which a sample of petroleum or petroleum product will continue to flow when it is cooled under specified conditions
4 Principle
The sample is brought to a specified temperature and a test portion transferred to a hydrometer cylinder that has been brought to approximately the same temperature. The appropriate hydrometer, whose temperature has also been regulated, is lowered into the test portion and allowed to settle. After temperature equilibrium has been reached, the hydrometer scale is read, the temperature of the test portion taken and the observed hydrometer reading reduced to 15 °C using standard measurement tables. If necessary, the hydrometer cylinder and its contents are placed in a constant temperature bath to avoid excessive temperature variation during the test.
