Principles of Temperature Measurement for Tank Gauging
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.
Use a multiple element device to provide the average product temperature in large bulk liquid storage tanks. Use a single element device 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.
The increase in accuracy achieved by using spot or average temperature measurement allows tighter control of all tank farm liquid inventories, including finished products, raw materials, crude oils and feed stock, increasing overall efficiency. You are also able to track product more effectively and balance book vs. physical inventories more accurately.
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.