3.2.3 Types of Gauges A tank gauge is a measure of the vertical distance of the liquid in the tank. There are two basic procedures for obtaining a tank gauge. The Innage Method: the vertical distance from the top of the liquid to the bottom of the tank. Note: the bottom of the tank may be the tank itself or a datum plate, which is a level metal plate directly under the reference gauge point and close to the tank floor. This plate provides a fixed surface from which liquid level measurements can be made. The innage method is also called a "dip". This is a European term. The Outage Method: This is the vertical distance from the surface of the liquid to the top of the tank, measured at the reference gauge point. The outage method is also called the "Ullage" method. This is a nautical term and is used extensively, especially on ships and barges.
Volumes that are adjusted for temperature are called Standard Volumes, as they are reported at a standard temperature, usually 60 ° F. Factors, known as "volume correction factors (VCF)", are used to convert volumes at observed temperature to volumes at standard temperature. Volume correction factors will be discussed in greater detail in the "calculation" section. Total Observed Volume (TOV), this is the total measured volume of all liquids/ material in the tank; oil, free water and sediment and water at the observed temperature. Gross Observed Volume (GOV). This is the total volume of the oil, and sediment and water; but not the free water. GOV = TOV – FW. Gross Standard Volume (GSV), this is the total volume of the oil and sediment and water; but not the free water, corrected by a "volume correction factor (VCF)", to a standard temperature of 60 ° F. GSV = GOV x VCF. Net Standard Volume (NSV) , this is the total volume of the oil, without free water or sediment and water, adjusted to a standard temperature. NSV = GSV less the S&W. Total Calculated Volume (TCV), this is the Gross Standard Volume plus the Free Water, GSV + FW. This volume is used in loss control to compare transferred volumes.
Relationship of volumes at observed and standard temperature
Total Observed Volume at observed temperature (TOV)
S&W
OIL
FW
Free Water volume at observed temperature (FW)
FW
Gross Observed Volume at observed temperature (GOV)
OIL
S&W
x VCF
Gross Standard Volume at standard temperature (GSV)
S&W
OIL
Net standard volume at standard temperature (NSV)
OIL
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