Varec temperature measurement devices range from simple spot measurement bulbs to more complex multi-element sensors and transmitters, capable of measuring the temperature at different heights in the vessel. Using temperature compensated volumes allows tighter control of all tank farm liquid inventories and it allows balancing book vs. physical inventories more accurately.
Varec recommends using a multiple element device, such as the 4532 ATS or 4539 ATS to provide the average product temperature in large bulk liquid storage tanks. Alternatively use a 8500 STS to provide the temperature of liquids at a single localized area, such as at or near the bottom of a storage vessel or in a pipeline.
In order to determine net standard volume in the oil and gas industry, it is necessary to measure the temperature of the product. Once the product temperature is known, it is possible to calculate the volume at an internationally agreed upon 'standard' temperature - typically 15°C or 60°F.
A temperature change of 1°C causes a change in volume of about 0.1%. The American Petroleum Institute (API) and American Society for Testing and Materials (ASTM) recommend a minimum of three temperature measurement devices for inventory control applications and a minimum of six points for custody transfer applications.
The more elements used, the more accurate the measurement. In practice, between one and sixteen temperature elements are used in a tank.