Measures to ensure the necessary accuracy of accounting petroleum products in the tanks

Abstract

This paper considers the measures to ensure the necessary accuracy of accounting petroleum products in the vertical and horizontal cylindrical tanks at tank farms, gas stations and other facilities, which are subject to the sphere of legislatively regulated metrology. The maximum permissible error of the set of calibrated tank, level gauge and density meter during the measurement of difference of the masses of petroleum products at the start and at the end of the accounting operation in the vertical tanks, as well as the maximum permissible error of the set of calibrated tank, level gauge and density meter during the measurement of difference of the masses in the horizontal tanks at a level approximately equal to half of the height of the tank, have been analyzed. It is shown that the same calibration table is used both for the level of petroleum products at the beginning of the accounting operation and at the end of such operation. The component of the error caused only by the maximum permissible error of the used level gauge is analyzed. On a number of examples with the most common capacity of vertical tanks for tank farms, the relative maximum permissible error of the set of calibrated tank, level gauge and density meter during the measuring the mass of dispensed petroleum products due to the error of level gauges ranges from ±2% to ±9% with the level gauge error from ±1 mm to ±4 mm. This error is significantly larger than ±0.75% given in DSTU 7094. It is concluded that, in accordance with OIML R 85, it is not feasible to consider the maximum permissible error of the level gauge installed on the tank equal to ±4 mm. When installing the level gauge on a rigid crossbar, fixed at the ends of the tank walls, the maximum permissible error of the level gauge during the measuring the level of petroleum products under operating conditions of ±2 mm can be achieved, as specified in the Instruction for accounting of petroleum products.To improve the measurement accuracy, it is necessary to reduce the effect of deformation of the bottom of vertical tanks, which can be achieved by keeping the level of petroleum products in the tank at least two meters.