hydrocarbons : organic compounds of hydrogen and carbon whose densities, boiling points, and freezing points increase as their molecular weights increase. All though composed of only two elements, hydrocarbons exist in a variety of compounds, because of the strong affinity of the carbon atom for other atoms and for itself. The smallest molecules of hydrocarbons are gaseous, the largest are solids. Petroleum is a mixture of many different hydrocarbons. hydrometer : an instrument with a graduated stem, used to determine the density of liquids. The liquid to be measured is placed in a cylinder, and the hydrometer placed in the liquid. The hydrometer floats at a certain level in the liquid, depending on the density of the liquid. in-line system : a type of automatic sampling system where the probe and extractor are located directly on the pipeline and the sample is withdrawn from the liquid stream. innage bob : a pointed, cylindrical weight attached to the end of a gauge tape. The tape and bob are used to measure liquid height in a tank. The bob keeps the tape vertical so that an accurate reading can be obtained form the tape. innage measurement : a measure of the liquid height in a tank from the bottom of the tank or datum plate to the top of the liquid.
innage tap-and-bob procedure : a method of measuring the height of the liquid in a tank using a pointed gauger’s bob and a graduated tape. In this method, the liquid height is measured from the bottom of the liquid to the top. Compare outage tape- and-bob procedure. kerosene : a light, flammable hydrocarbon fuel or solvent. light ends : the lighter hydrocarbon molecules that comprise gasoline, light kerosene, heptane, natural gas, and so forth. light fuels : fuels, such as gasoline, that have relatively high volatility. light products : petroleum fractions, such as ethylene, that are relatively light in molecular weight. liquid calibration procedure : a method of determining a tanks capacity by filling and withdrawing from the tank accurately determined volumes of liquid. liquid cut : the mark on the gauge tape indicating the height of the liquid. master tape : a measuring tape that has been certified accurate at a specified temperature and tension by the National Institute of Standards and Technology. liquid head stress : the hydrostatic pressure of the liquid in tanks of 500 barrels or more, which causes the shell to expand and contract.
gauge tape : a graduated, metal, non- sparking, noncorrosive measuring tape used with a gauge bob to measure the height of the liquid in a storage tank. gauging height : the distance from the gauge, or reference, point from the bottom of a tank to a gauge, or reference, point at the top of the tank, usually on the hatch. gear pump : a rotary pump that moves fluid by means of two contra-rotating, meshing gear wheels. The teeth of one wheel mesh with the spaces between the teeth of the other wheel. The fluid enters one side of the pump and is forced through by the moving gears, and is discharged on the other side. gravity : see density . gross volume : the total amount of liquid in a storage tank excluding any adjustments for S&W, temperature, or density. Compare net volume. hatch : 1. An opening in the roof of tank through which a gauging line may be lowered to measure its contents. 2. The opening from the deck into the cargo space of ships.
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