This International Standard specifies a method for the laboratory determination of the sum of water and sediment in residual fuel oils using the centrifuge method. With some oils it is difficult to obtain water or sediment contents using this method. When this situation is encountered, ISO 3733 and ISO 3735 should be used. NOTE — It has been observed that centrifugal methods of determination of water and sediment may, in many cases, give erroneous results. This is especially so when use of a high-speed mixer has been employed to obtain a representative sample. The method is therefore not entirely satisfactory and the amount of water determined is almost always lower than the actual water content. Significant quantities of water and sediment can cause operational problems in handling equipment and in engines and burners, particularly when the water present contains mineral salts. Design of residual fuel oil treatment facilities, such as filters or centrifuges, is based on a maximum quantity of material to be removed before combustion. Residual fuel oils destined for further refinery processing also require low levels of water and sediment to minimize corrosion problems.