Sediment and Water (S&W), these are very fine particles of water and sediment that remain suspended in the liquid and do not separate out. Sediment and water is always deducted from crude oil quantities but only very rarely deducted from refined product quantities. Do not deduct S&W from refined product quantities unless instructed to do so by your supervisor. The oil and free water levels can be measured by gauging. "Sediment and Water" can only be determined by laboratory analysis of a sample of the tank's contents. 3.2.2 Volume Terminology Before we discuss tank gauging specifics, we need to review the various types of volumes and what they are called. This terminology is standard throughout our industry, and you must become familiar with it if you want to be understood by others and understand them. Most volumes fall into two categories. Volumes that are not adjusted for temperature are called Observed Volumes, because they are reported at the observed temperature.
In this case, each tank involved in the transfer is measured and the amount transferred into or out of each tank is added, to determine the total amount transferred. This training book will limit itself to the measurement of crude oil and refined petroleum products such as gasoline, diesel, kerosene, jet fuel, intermediate and heavy fuel oils, etc., although these procedures are also applicable to many petrochemicals. 3.2 Shore Tank Gauging The basic premise of shore tank gauging is to determine the depth of liquid in the tank, its temperature; and use this and other information to calculate the volume of material in the tank. 3.2.1 Tank Contents There are essentially, three types of liquid / material in a shore tank, to be measured: The oil, is the commercial product that we are wanting to measure. Free Water (FW) is water that lies at the bottom of the tank and is distinct from the oil that is sitting on top of it. The boundary between the oil and the free water is referred to as the oil/water interface or free water interface.
3.1 Introduction Static measurement refers to the measurement of a liquid when it is not in motion. Static measurement of petroleum is usually performed on shore tanks, ship tanks or barge tanks. There are, however, some points that need to be addressed before we go into detail on the specifics of static tank gauging. All liquids expand if their temperature increases and contract if their temperature decreases. This is fundamental to all aspects of petroleum measurement. Liquids can be measured in either volume or weight (mass). Petroleum quantities are frequently sold in units of volume; either the barrel or the liter. Because volume varies with temperature, it is necessary to calculate these volumes at a standard temperature in order to maintain consistency. The most common standard temperatures used are 15 ° C and 60 ° F. Most tank measurement is undertaken as part of a product transfer. To determine how much material has moved into or out of a tank, the tank is measured, and the quantities calculated, before and after the product is transferred. The quantity in the tank before product transfer is deducted from the quantity in the tank after transfer. The difference is the amount transferred. The total amount of product to be shipped may be in more than one tank.
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