Improving Tank Temperature Measurement to Optimize Inventory Control and Custody Transfer Systems

The measurement of temperature is critical in the determination of the true volume of product in a hydrocarbon storage tank and how that may be improved with the use of true averaging sensors or multiple-spot temperature sensors. Simple temperature measurement has been performed for many years, in ways as simple as glass thermometers hung in a tank or as sophisticated as a tank gauging system mounted on the tank roof. Temperature has the most significant effect on the accurate determination of liquid quantities when correcting to standard conditions for custody transfer and inventory control purposes. "An error in the determination of temperature may result in either over-or understatement of the quantity, regardless of the accuracy obtained in gauging the liquid's level". The accurate measurement of temperature is a critical factor in determining the volume of the contents of a tank and the transfer of the material out of the tank. "A change of 1 deg. F in the product temperature can allow an error of 120 barrels, in a tank of approximately 300,000 barrels". At the current price of petroleum, an error of that magnitude could be significant. In the past, a single thermometer inserted into the tanks was sufficient for monitoring the temperature of the tank. Now, that method is decidedly not sufficient according to new standards from the American Petroleum Institute.