API MPMS 16.2:1994(R2017) pdf download.Manual of Petroleum Measurement Standards Chapter 16—Measurement of Hydrocarbon Fluids By Weight or Mass
1 Scope
This standard provides guidance on the installation, commissioning, maintenance, validation, and calibration of hydrostatic tank gauging systems for the direct measurement of static mass in petroleum storage tanks. This standard is applicable to hydrostatic tank gauging systems that use pressure sensors with one port open to the atmosphere. This standard is applicable to the use of hydrostatic tank gauging on vertical cylindrical atmospheric storage tanks with either fixed or floating roofs. This standard is not applicable to the use of hydrostatic tank gauging on pressurized tanks. Safety and material compatibility precautions should be taken when using HTG equipment. ManufacturerÕs recom- mendations on the use and installation of the equipment should be followed. Users should comply with all applicable codes and regulations, API standards, and the National Elec- tric Code.
6.1.3 Pressure Sensor Position Determination
Sensor positions should be measured to the pressure sensor effective centers. Since the diaphragms are not normally accessible, external reference markings on the sensor body should be provided. An estimate of the uncertainty in the external reference marking also should be provided. The accuracies of the sensor positions and the distances between sensors are important in achieving high HTG measurement accuracy. Guidelines for distance measurement accuracy are as follows: a. P1 elevation Hb above the HTG reference point is used to calculate the tank bottom mass. The error in P1 elevation measurement should not exceed ± 1 Ú 32 inch or 1 mm. b. P1-P2 vertical distance H is used to calculate the observed density, which in turn is used to calculate the heel mass. The error in the vertical distance P1-P2 should not exceed ± 1 Ú 32 inch or 1 mm. c. P1-P3 vertical distance Ht is used to calculate the magnitude of vapor mass and the effects of ambient air. Both the vapor mass and the ambient air are secondary correction factors that are subject to a number of approximations. The error in the vertical height Ht should not exceed ± 2 inches or 50 mm.
6.1.4 Pressure Sensor Movement Limitation
Tank walls undergo hydrostatic deformations during tank filling and discharge. This results in movements of the sensors such that the elevation of P1 above the HTG refer- ence point and the vertical distance of P2 above P1 may not be constant. Changes in P1 elevation will have a direct effect on measured mass and should therefore be minimized. P1 is normally mounted on the lower part of the tank where the movements of the tank shell are small (tank datum plates fixed to the tank shell may incur similar movements). P1 elevation above the HTG reference point should be measured with the tank full and again with the tank empty. If the elevation changes by more than 1 Ú 32 inch or 1 mm, a tie- bar should be considered to maintain a constant vertical distance between P1 and P2.
API MPMS 16.2:1994(R2017) pdf download
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