ISO 12185 Crude petroleum and petroleum products - Determination of density - Oscillating U-tube method
7 Sampling
Unless otherwise specified in a commodity specification, samples shall be taken as described in ISO 3170 or ISO 3171, and/or in accordance with the requirements of national standards or regulations.
Special care should be taken to prevent any loss of volatile components from the sample. Wherever possible samples should be drawn, transported and stored in the same container.
The sampling of volatile liquids using automatic techniques is not recommended unless a variable-volume sample receiver is used to collect and transport the sample to the laboratory. The use of a fixed-volume receiver (whether it is pressurized or not) could result in light-end loss from the material being sampled, thereby affecting the density measurement.
When drawing samples using variable-volume receivers, the sampling pressure and temperature of the sample source should be noted on the receiver label.
It is essential that the portion of the sample to be tested is representative of the bulk sample, and sample mixing is sometimes necessary to ensure homogenization prior to subsampling.
8 Sample preparation
8.1 General
Samples shall be handled in such a manner that:
a) light-end loss is minimized;
b) the temperature of the sample does not drop below:
1) its cloud point, when determined in accordance with ISO 3015;
2) or its wax appearance temperature (WAT), when determined in accordance with IP 389/93;
3) or 20 °C above its pour point, when determined in accordance with ISO 3016.
NOTE 9 It should be recognized that loss of light ends during homogenization or heating, necessary when sediment, water or undissolved wax are present in samples of volatile crude petroleum or petroleum products, can cause errors in the determined density value.
8.2 Petroleum products which are free of water and/or sediments and which are sufficiently mobile
Mix by gentle shaking.
8.3 Crude petroleum and petroleum products containing water and/or sediments
Mix the sample in the original container, taking all precautions to minimize light-end loss.
NOTE 10 Mixing volatile crude petroleum and petroleum products in an open container will lead to loss of light components and is therefore not recommended.
8.4 Waxy crude petroleum
Warm the sample to 3 °C above the WAT or 20 °C above the pour point of the crude petroleum prior to mixing in the original container, taking all precautions to minimize light-end loss.
8.5 Waxy distillates
Warm the sample to 3 °C above the cloud point prior to mixing.
8.6 Fuel oils
Heat the sample until it is fluid prior to mixing.
9 Apparatus preparation
9.1 Test temperature
9.1.1 Sample density shall, wherever possible, be determined at the reference temperature.
If this is not possible, a temperature shall be chosen which is 3 °C above the cloud point or wax appearance temperature or 20 °C above the pour point and below the temperature at which gas appears in the sample.
9.1.2 If the density-meter cell is fitted with an integral thermostat, set the cell temperature according to the manufacturer's instructions. Otherwise, connect it to the constant-temperature bath (5.2). Allow the temperature to stabilize.
The manufacturer's specified working temperature and pressure ranges for the density-meter cell shall not be exceeded.
When temperature-controlled baths are used, ensure that the circulating liquid remains clean.
9.2 Cell cleaning
Clean and dry the cell using the flushing solvent (6.1) and if necessary water (6.4) followed by a water-miscible solvent.(6.1) and blow dry with clean dry air.
After testing crude oils containing dissolved salts, clean the cell with water (6.4) after first washing with the flushing solvent (6.1).
If the cell shows signs of organic deposits, clean the cell by injecting ammonium peroxydisulfate solution (6.2) into the cell. After removal of the ammonium peroxydisulfate solution, flush the cell with water (6.4) followed by a water-miscible solvent (6.1) and blow dry with clean dry air.
10 Apparatus calibration
10.1 Density meters shall be calibrated when first installed, and whenever the test temperature is changed or when maintenance has been carried out or the system disturbed in any other way.
The density-meter calibration shall be verified within a period of not more than seven days prior to use.
10.2 Record the density reading or oscillating period with the clean cell filled with ambient air. If air is one of the calibrating fluids, omit 10.3.
10.3 Introduce the first calibration fluid (6.3) into the cell and allow the cell and its contents to reach temperature equilibrium. Record the oscillation period or the density reading and the temperature of the cell.
Clean the cell in accordance with the procedure given in 9.2.
10.4 Introduce the second calibration fluid into the cell and allow the cell and its contents to reach temperature equilibrium. Record the oscillation period or the density reading and the temperature of the cell.
10.5 Calculate the cell constants in accordance with the manufacturer's instructions.
10.6 After calibration, clean and dry the cell in accordance with the procedure given in 9.2.
