2. The ratio of the mass of given volume of a substance to the mass of a like volume of a standard substance, such as water or air. Also referred to by the archaic term, specific gravity. representative sample : a small portion extracted from the total volume of material that contains the same proportions of the various flowing constituents as the total volume of liquid being transferred. The precision of extraction must be equal to or better than the method used to analyze the sample. running sample : a sample obtained by lowering an unstoppered beaker or bottle from the top of the oil to the level of the bottom of the outlet connection or swing line and returning it to the top of the oil at a uniform rate of speed so that the beaker or bottle is about three-quarters full when withdrawn from the oil. S&W abbr: sediment and water. API Committee on Petroleum Measurement prefers this abbreviation to the older “BS&W”. sediment : the matter that settles to the bottom of a liquid; also called tank bottoms .
sediment and water (S&W) : a material coexisting with, yet foreign to, petroleum liquid and requiring a separate measurement for reasons that include sales accounting. This foreign material includes emulsified or suspended water and sediment. The quantity of suspended material present is determined by laboratory testing of a sample of the petroleum liquid. semi-liquid : a substance that is intermediate between a liquid and a solid. solubility : the capacity of a substance to be dissolved in another. solvents : a substance, usually liquid, in which another substance, the solute dissolves. specific gravity : archaic term, see relative density . spirit level : a device consisting of a bubble tube designed to determine a horizontal line or plane. spot sample : a sample obtained at some specific location in the tank by means of a thief, a bottle, or a beaker. static pressure : the pressure exerted by a fluid on a surface that is at rest in relation to the fluid.
reference height : the distance from the reference point to the datum plate or the bottom of the tank. It should be stamped on the fixed benchmark plate or stenciled on the tank roof near the gauging hatch. Also called gauge height. reference point : 1. The point at which a tape is lowered and read on a tank, usually at the rim of the 3.The point from which the reference height is determined and from which ullages or innages are taken. Also called gauge point. Reid vapor pressure : the vapor pressure of a liquid at 100º Fahrenheit (37.78º Celsius, 311º Kelvin) as determined by ASTM D 323-58, Standard Method of Test for Vapor Pressure of Petroleum Products (Reid Method). relative density : 1. The ratio of the weight of a given volume of a substance at a given temperature to the weight of an equal volume of a standard substance at the same temperature, usually water. Example, if one cubic inch of water at 39 ° F weighs one unit and, if hatch, manway, or expansion dome. 2.A point to which all subsequent measurements are related. 1 cubic inch of another solid or liquid at 39 ° F weighs 0.95 unit, then the relative density of the substance is 0.95. In determining the relative density of gases, the comparison is made with the standard of air or hydrogen.
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