ISO 3734 Petroleum products - Determination of water and sediment in residual fuel oils - Centrifuge method
7 Procedure
7.1 Fill each of two centrifuge tubes (5.2) to the 50 ml mark with toluene which has been water saturated at 50°C; then immediately pour the laboratory sample directly from the sample container into the centrifuge tubes until the total volume in each tube is 100 ml. Read the top of the meniscus at both the 50 ml and 100 ml marks. Add 0.2 ml of demulsifier solution (4.2) to each tube, using a 0.2 ml pipette or an automatic pipettor. Stopper the tubes tightly and shake vigorously until the contents are thoroughly mixed. Immerse the tubes to the 100 ml mark for 10 min in the bath maintained at 50°C +/- 1°C.
7.2 If wax contributes to the volume of water and sediment observed (see 7.5) preheat the oil-solvent mixture to 60°C before each spinning; the final temperature of the mixture shall not drop below 47°C.
7.3 Invert the tubes to assure that the oil and solvent are uniformly mixed and shake cautiously.
7.4 Place the tubes in the trunnion cups on opposite sides of the centrifuge (5.1) to establish a balanced condition, and spin for 10 min at a relative centrifugal force of between 500 and 850 at the tip of the spinning tubes, as calculated using the equation given in 5.1 (see table 2 for the relationship between diameter of swing, relative centrifugal force and revolutions per minute).
7.5 Immediately after the centrifuge comes to rest following the spin, read and record the combined volume of water and sediment (see 7.2) at the bottom of each tube to the nearest 0.05 ml from 0.l to 1 ml graduations. Below 0.l ml, estimate the reading to the nearest 0.025 ml (see figure 2). Return the tubes without agitation to the centrifuge and spin for another 10 min at the same rate.
7.6 Repeat this operation until the combined volume of water and sediment remains constant for two consecutive readings. In general, not more than two spinnings are required.
