Significance and Use
5.1 Accurate determination of the density, relative density, or API gravity of petroleum and its products is necessary for the conversion of measured volumes to volumes or masses, or both, at the standard reference temperatures of 15 °C or (60 °F) during custody transfer.
5.2 This procedure is most suitable for determining the density, relative density, or API gravity of low viscosity transparent liquids. This procedure can also be used for viscous liquids by allowing sufficient time for the hydrometer and temperature measuring device to reach temperature equilibrium, and for opaque liquids by employing a suitable meniscus correction. Additionally for both transparent and opaque fluids the readings shall be corrected for the thermal glass expansion effect on the hydrometer body and alternative calibration temperature effects before correcting to the reference temperature.
5.3 When used in connection with bulk oil measurements, volume correction errors are minimized by observing the hydrometer reading at a temperature close to that of the bulk oil average temperature.
5.4 Density, relative density, or API gravity is a factor governing the quality and pricing of crude petroleum. However, this property of petroleum product is an uncertain indication of its quality unless correlated with other properties. Crude petroleum prices are frequently posted against values in kg/m3 (or in degrees API). This correlation may be used to give approximate hydrocarbon composition and heat of combustion.
5.5 Density is an important quality indicator for automotive, aviation and marine fuels, where it affects storage, handling and combustion.
5.6 Typical Field of Application—The procedure is convenient for gathering or main trunk pipelines and other field applications where limited laboratory facilities are available. The thermohydrometer method may have limitations in some petroleum density determinations. When this is the case, other methods such as Test Method D1298 (API MPMS Chapter 9.1) should be used.
Scope
1.1 This test method covers the determination, using a glass thermohydrometer and/or a separate (alternative) temperature measuring device in conjunction with a series of calculations, of the density, relative density, or API gravity of crude petroleum, petroleum products, or mixtures of petroleum and nonpetroleum products normally handled as liquids and having Reid vapor pressures (Test Method D323) of 101.325 kPa (14.696 psia) or less. Values are determined at existing temperatures and corrected to 15 °C (or 60 °F) by means of a series of calculations and international standard tables. Alternative temperature measuring devices shall be either the appropriate liquid-in-glass ASTM thermometers meeting either Specifications E1 or E2251 or digital contact thermometers (Guides E2877 and D8164).
1.2 The initial thermohydrometer readings obtained are uncorrected hydrometer readings and not density measurements. Readings are measured on a thermohydrometer at either the reference temperature or at another convenient temperature, and readings are corrected for the meniscus effect, the thermal glass expansion effect, alternate calibration temperature effects and to the reference temperature by means of calculations and Adjunct to D1250 Guide for Use of the Petroleum Measurement Tables (API MPMS Chapter 11.1). Values measured (determined) at other than the reference temperature being hydrometer/thermohydrometer readings and not density measurements
1.3 Readings determined as density, relative density, or API gravity can be converted to equivalent values in the other units or alternate reference temperatures by means of Interconversion Procedures (API MPMS Chapter 11.5) or Adjunct to D1250 Guide for Use of the Petroleum Measurement Tables (API MPMS Chapter 11.1), or both, or tables as applicable.
1.4 The initial thermohydrometer reading (including temperature) shall be recorded before performing any calculations. The calculations required in 9.1.5 and Section 10 shall be applied to the initial thermohydrometer reading with observations and results reported as required by Section 11 prior to use in a subsequent calculation procedure (measurement ticket calculation, meter factor calculation, or base prover volume determination).
1.5 Annex A1 – Annex A3 contain procedures for determining fit-for-service, verifying, or certifying the equipment for this test method.
1.6 The values stated in SI units are to be regarded as standard.
1.6.1 Exception—The values given in parentheses (inch-pound) are for information only.
1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
