ASTM D4007 standard test method for water and sediment in crude oil
ASTM D4007 standard test method for water and sediment in crude oil by the centrifuge method (laboratory procedure)
8. Procedure
8.1 Fill each of two centrifuge tubes (5.2) to the 50-mL mark with sample directly from the sample container. Then, with a pipet, add 50 mL of toluene, which has been water saturated at 60°C (140°F) or 49°C (120°F) (see Note 2). Read the top of the meniscus at both the 50 and 100-mL marks. Add 0.2 mL of demulsifier solution (6.2) to each tube, using a 0.2-mL pipet. An automatic pipettor may be used. Stopper the tube tightly and invert the tubes ten times to ensure that the oil and solvent are uniformly mixed.
8.2 In the case where the crude oil is very viscous and mixing of the solvent with the oil would be difficult, the solvent may be added to the centrifuge tube first to facilitate mixing. Care must be taken in order not to fill the centrifuge tube past the 100-mL mark with the sample.
8.3 Loosen the stoppers slightly and immerse the tubes to the 100-mL mark for at least 15 min in the bath maintained at 60 +/- 3°C (140 +/- 5°F) (see Note 2). Secure the stoppers and again invert the tubes ten times to ensure uniform mixing of oil and solvent. The vapor pressure at 60°C (140°F) is approximately double that at 40°C (104°F).
8.4 Place the tubes in the trunnion cups on opposite sides of the centrifuge to establish a balanced condition. Retighten the corks and spin for 10 min at a minimum relative centrifugal force of 600 calculated from the equation given in 5.1.5.
8.5 Immediately after the centrifuge comes to rest following the spin, read and record the combined volume of water and sediment at the bottom of each tube to the nearest 0.05 mL from 0.1 to 1-mL graduations and to the nearest 0.1-mL above 1-mL graduations. Below 0.1 mL, estimate to the nearest 0.025 mL (refer to Fig. 2). Return the tubes without agitation to the centrifuge and spin for another 10 min at the same rate.
8.6 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.
8.7 The temperature of the sample during the entire centrifuging procedure should be maintained at 60 +/- 3°C (140 +/- 5°F) (see Note 2).
8.8 To avoid the danger of tubes breaking in the cups, care must be taken that the tubes are bedded onto the bottom cushion so that no part of the tube is in contact with the rim of the cup.
