Is pressure compensation a necessity while loading tanker trucks with refined petroleum products?
While temperature compensation to API table is a normal requirement on loading trucks, pressure compensation is almost never used except for LPG. The expansion of gasoline at 25 degrees C is 0.012% per bar. Hence, the error due to pressure variations is generally an order of magnitude less than other errors in the system.From the API standards, Chapter 11.2.1M Compressibility Factors for Hydrocarbons, the following errors have been calculated: 1. Density 0.90 kg/l (approximately that of diesel) At 25°C, the error is 0.007% per bar At 40°C, the error is 0.007% per bar2. Density 0.74 kg/l (approximately that of petrol) At 25°C, the error is 0.012% per bar At 40°C, the error is 0.013% per bar These values are calculated using an average pressure of 5 bar in the line. From above, a pressure change of 3 bar in the line at a product temperature of 25°C would result in a measurement error of only 0.039%. Typically, this is well below the accuracy of the flowmeter and, therefore, pressure comp
