ASTM D1657 Test Method for Density or Relative Density of Light Hydrocarbons by Pressure Hydrometer
6. Apparatus
6.1 Hydrometers, graduated in density with a range from 500 to 650 kg/m3, or in relative density with a range from 0.500 to 0.650, and conforming to the dimensions in Specification E100.
6.1.1 Thermohydrometers, for field applications, thermohydrometers may be more convenient than hydrometers with separate thermometers. They shall conform to Specification E100, Thermohydrometer Nos. 101H or 310H.
6.1.1.1 Thermohydrometers shall be of suitable range and have dimensions to float freely within the pressure hydrometer cylinder with clearances of 5 mm at the wall and 25 mm at the top and bottom.
6.1.1.2 The test report shall state that a thermohydrometer was used.
6.1.1.3 The user should ascertain that the instruments used for this procedure conform to the requirements set out above with respect to materials, dimensions, and scale errors. In cases where the instrument is provided with a calibration certificate issued by a recognized standardizing body, the instrument is classed as certified and the appropriate corrections for the meniscus effect, the thermal glass expansion effect, and alternative calibration temperature effects shall be applied to the observed readings prior to corrections. Instruments that satisfy the requirements of this test method, but are not provided with a recognized calibration certificate, are classed as uncertified and the appropriate corrections for the meniscus effect, the thermal glass expansion effect, and alternative calibration temperature effects shall be applied to the observed readings prior to corrections.
6.2 Hydrometer Cylinder, constructed of transparent plastic; for example, poly(methyl methacrylate) or equivalent material, conforming to the design and recommended dimensions given in Fig. 1. The cylinder shall be of such dimensions that the hydrometer shall float freely within it. The ends shall be tightly sealed with neoprene gaskets and metal end plates as shown in Fig. 1. (Warning - A protective shield shall be placed around the cylinder. Replace any cylinders that show signs of fogging, crazing, cracking, or etching.)
NOTE 1 - Certain compounds attack plastics and cloud the inner surface of the cylinder, making it difficult or impossible to read the hydrometer. Tests showed no attack by ethane, ethene (ethylene), propane, propylene, butane, methylpropane (isobutane), butenes (normal butylenes), methylpropene (isobutylene), pentane, and methylbutane (isopentane), and no attack is expected from butadiene and acetaldehyde. Users are cautioned, however, to clean the cylinder thoroughly after each determination. Ketones and alcohols should not be used for cleaning as they attack and weaken plastics while aromatics also tend to attack the surface of plastics and should similarly not be used. A light aliphatic hydrocarbon is recommended for cleaning. (Warning - Extremely flammable. Harmful if inhaled. Vapors may cause flash fire.)
6.2.1 The liquid inlet valve and the liquid outlet valve shall be tightly connected to a base plate that shall be bored to give both valves a common inlet to the cylinder. The vapor vent valve shall be similarly connected to the top plate, which shall be bored to provide a vapor outlet from the pressure cylinder. All valves shall be 6 mm (1/4 in.) or equivalent needle valves.
6.2.2 The cylinder shall not be operated at a gage pressure greater than 1.4 MPa (200 psi). A hydrostatic test at 2.8 MPa (400 psi) shall be carried out at intervals no greater than 12 months.
NOTE 2 - For Safety - The cylinder should be equipped with appropriate safety devices to prevent over-pressure. Consideration should be given to pressure testing the cylinder at 1.25 to 1.5 times its normal maximum operating pressure on a periodic basis, not to exceed two years.
6.3 Thermometers, conforming to ASTM 12C or 12F in Specification E1. The thermometer shall be held firmly inside the hydrometer cylinder by a clip in such a manner that it does not interfere with the free movement of the hydrometer.
6.4 Constant-Temperature Bath, of dimensions such that it can accommodate the hydrometer cylinder with the test portion fully immersed below the test portion liquid surface, and a temperature control system capable of maintaining the bath temperature within 0.25°C of the test temperature throughout the duration of the test.
7. Reference Liquids
7.1 The following reference liquids are required for standardization of the hydrometer:
7.1.1 Propane, pure grade, having a nominal density of 507.6 kg/m3 at 15°C or a relative density 60/60°F of 0.50699. (Warning - Extremely flammable. Harmful if inhaled. Vapors may cause flash fire.) The density of the reference liquid used shall be known.
7.1.2 Butane, pure grade, having a nominal density of 584.1 kg/m3 at 15°C or a relative density 60/60°F of 0.5840. (Warning - Extremely flammable. Harmful if inhaled. Vapors may cause flash fire.) The density of the reference liquid used shall be known.
