GB/T 18273-2000 Petroleum and liquid petroleum products — Direct static measurement of oil quantity in vertical tanks (HTG mass measurement method)

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1. Method number / full title / English title / supersession relationship

• Standard number: GB/T 18273—2000
• Chinese title: Petroleum and liquid petroleum products — Direct static measurement of oil quantity in vertical tanks (HTG mass measurement method)
• English title: Petroleum and liquid petroleum products—Direct static measurements—Contents of vertical storage tanks—Mass measurement by hydrostatic tank gauging
• Adoption relationship: eqv ISO 11223-1:1995 (equivalent adoption)
• Supersession relationship: not provided in the available source
• Issuance / implementation: approved by the State Bureau of Quality and Technical Supervision 2000-12-18, implemented on 2001-07-01
• Main differences from ISO 11223-1:1995 (foreword):
  1. Delete referenced standard ISO 7078, and at the same time add "Annex C HTG Height measurement from the reference point to the tank calibration datum point", replacing the relevant content of the deleted referenced standard;
  2. In A3, add "Note 7:" regarding the floating roof being affected by uneven friction from the tank wall;
  3. Annex C becomes Annex D, Annex D becomes Annex E.
• Annex status: Annex A and Annex B are normative annexes of the standard; Annex C, Annex D and Annex E are informative annexes.
• Secretariat: Sinopec Research Institute of Petroleum Processing
• Drafting organizations: Sinopec Research Institute of Petroleum Processing, China Aviation Industry First Group Corporation 634 Research Institute
• Main drafters: Wei Jinxiang, Jin Dexi, Dong Haifeng, Wang Beian

2. Scope of application and non-applicability

• Scope of application: provides guidelines for the installation, commissioning, maintenance, verification and calibration of hydrostatic tank gauging (HTG) systems for directly measuring the mass of static oil in vertical cylindrical tanks.
• Applies to hydrostatic tank gauging systems in which one end of the pressure sensor is open to the atmosphere.
• Applies to hydrostatic tank gauging systems used on atmospheric vertical cylindrical fixed-roof or floating-roof tanks.
• Does not apply to hydrostatic tank gauging systems used on pressurized tanks.
• Note 1: When the output signal of the sensor in this standard is a standard signal, it is also called a pressure transmitter.

3. Method principle

• Hydrostatic tank gauging (HTG) is a method for determining the total static mass of liquid petroleum and petroleum products in vertical cylindrical storage tanks.
• HTG uses high-precision and highly stable pressure sensors installed at specified positions on the tank shell.
• The total static mass is derived from the measured pressure and the tank capacity table. Other variables (liquid level, observed volume, standard volume, observed density, standard density) may be calculated from the product type and temperature using established industry standards for inventory calculation.
• The term "mass (mass)" means mass in vacuum (true mass); in the petroleum industry, apparent mass (in air) is usually used for custody transfer.
• Calculation principle (A3 pressure balance): the pressure increment between two points is independent of the path taken, that is:
  • P1 − P3 = total pressure head of the liquid product between sensors P1 and P3 + vapor pressure head in the tank − ambient air pressure head between sensors P1 and P3;
  • P1 − P2 = liquid product pressure head between sensors P1 and P2 − ambient air pressure head between sensors P1 and P2.
• In fixed-roof tanks, the tank vapor is a mixture of product vapor and air; in floating-roof tanks, the tank vapor is ambient air that may be contaminated by product vapor.
• The floating roof load includes two parts, fixed (floating roof mass) and variable (floating roof load mass), both of which are input as constants by the user in this standard; it is also suitable for floating pans used in fixed-roof tanks.
• Note 7: When metering oil, the floating roof is treated as a free-floating body and the floating roof weight is directly deducted; however, during oil transfer the floating roof is subject to uneven friction from the tank wall (sometimes even sticking), the immersed depth changes, and directly deducting the floating roof weight may cause metering error; for high-precision metering, measures are recommended to eliminate this effect as much as possible.

4. Reagents and materials (purity / preparation)

not provided in the available source.

5. Instruments and equipment

• Pressure sensors: up to three pressure sensors mounted on the tank wall (P1, P2, P3).
  • P1: installed on the tank wall near the tank bottom, at the lowest position, with an installation height of H₀ to the HTG reference point.
  • P2: intermediate pressure sensor, used for density and liquid level calculation; if installed, it should be installed at a fixed vertical distance above P1; usually installed about 2 m to 3 m above P1.
  • P3: pressure sensor for the tank ullage space, usually installed at the top of the tank; P3 is not required on floating-roof tanks.
• Temperature sensors: used to measure the liquid temperature in the tank (T) and the ambient air temperature (Tₐ); for high-precision measurement, an ambient air pressure sensor (Pₐ) may also be installed.
• HTG data processor: receives data from the sensors and uses the received data, tank and liquid parameters to calculate the inventory mass in the tank; may perform linearization and/or temperature compensation correction on the pressure sensors; may be used for a single tank or shared among several tanks.
• Linkage: used to prevent excessive displacement of the HTG pressure sensor relative to the HTG reference point caused by tank expansion when filled.
• Pressure lead valves, shut-off valves, drain valves, pressure snubbers (for overpressure protection).
• Pressure balance pipe (for protection against wind effects): should be essentially vertical, without airtight seals or water traps, closed at the top and open at the bottom.
• Calibration equipment:
  • Standard pressure source method: a traceable deadweight tester, accurate to 25 Pa, suitable for on-site use.
  • Standard pressure sensor method: a traceable pressure sensor, accurate to ±25 Pa, suitable for on-site use.
• Annex C instruments:
  • C2.1 optical level: accuracy not lower than S3 grade.
  • C2.2 leveling staff: minimum division 1 mm, with level bubble.
  • C2.3 gauging tape: meets the requirements of GB 13236.
  • C2.4 auxiliary devices: gauging tape holder and magnetic base.

6. Recommended operating conditions

• Sensor installation position: all HTG pressure sensors should be installed on the same side of the tank, with additional protection where necessary to avoid wind and sun; pressure lead holes on the tank wall should be made where the product is relatively static.
• P1 should be installed as low as possible on the tank, but above the height of sediment and water.
• The maximum vertical distance from P2 to P1 is not specified; the limiting factor is that when the liquid level falls below P2, the observed density can no longer be measured; the minimum vertical distance from P1 to P2 depends on the accuracy requirements for density measurement and the sensor performance.
• P3 If installed on the tank roof, it should be equipped with a sunshade and windbreak shelter.
• Distance measurement accuracy requirements:
  • a) The measurement error of H₀ (the height of P1 above the HTG reference point) should not exceed ±1 mm;
  • b) The measurement error of H (the vertical height from P1 to P2) should not exceed ±1 mm;
  • c) The measurement error of Hₛ (the vertical height from P1 to P3) should not exceed ±50 mm.
• The height H₀ of sensor P1 above the HTG reference point should be measured both when the tank is full and when it is empty; if this height changes by more than 1 mm, a linkage should be provided.
• Wind effects: when all three pressure sensors are installed on the same side of the tank in a single vertical line, the wind effect is minimal; if exposed to strong wind, the external ports of P1 and P3 should be connected together with a pressure balance pipe; if P3 is not used, the external port of P1 should be connected to a pipe that slopes downward away from the tank and opens at a point where wind-induced ambient pressure changes are minimal, preferably at least 0.5 m away from the tank at ground level.
• Temperature effects: for high-precision measurement, methods such as eliminating temperature gradients on the sensor body and maintaining the sensor at constant temperature may be used to improve HTG performance; users should note and comply with the manufacturer's insulation requirements and type.
• Temperature sensor location: the product temperature sensor may be a single-point temperature measuring element installed between P1 and P2, or an average temperature measurement system; the ambient air temperature sensor should be close to the tank and installed on the same side as the pressure sensors.
• HTG reference point: should be located outside the tank directly below sensor P1, and preferably on the bottom edge of the tank; if the bottom edge of the tank cannot be seen, the reference point may be marked on the tank wall.
• Calibration (manual measurement calibration on the tank) is preferably carried out with the same liquid at liquid levels spaced about 4 m apart.
• Calibration (standard pressure source method / standard pressure sensor method): the pressure sensor remains stationary at the installation position and is isolated from the tank by closing the pressure lead valve.

7. Sampling and sample preparation

not provided in the available source.

8. Analytical procedure

8.1 Installation

• 5.1.1 Tank preparation: sensor position selection, pressure lead connections, HTG reference point, linkage.
• 5.1.2 Pressure sensor installation: process connection (should be capable of being disconnected from the tank on site and connected on site to calibration and/or verification equipment; install pressure lead valve; install drain valve); overpressure protection (a pressure snubber may be provided, or the drain valve may be opened to relieve pressure when the pressure lead valve is closed).
• 5.1.3 Pressure sensor position determination: measure to the effective center of the pressure sensor; an external reference mark and an estimate of its uncertainty should be provided on the sensor body.
• 5.1.4 Pressure sensor displacement limitation: the height change of sensor P1 should be minimized; if H₀ changes by more than 1 mm, a linkage should be provided; if HTG is used to calculate liquid level, density and mass, a linkage should be considered between P1 and P2.
• 5.1.5 Wind effects (see Section 6).
• 5.1.6 Temperature effects (see Section 6).
• 5.2 Temperature sensor (see Section 6).
• 5.3 HTG reference point and liquid level measurement reference point: the HTG reference point is different from the liquid level measurement reference point; the vertical distance between the HTG reference point and the manual liquid level measurement reference point should be measured by the method described in Annex C; the manual gauging point is usually the tank calibration datum point.

8.2 Commissioning

• 5.4.1 Overview: After installing the HTG system, the commissioning procedure should be performed; after hardware damage or system updates, some or all commissioning procedures may need to be repeated; keep all data records.
• 5.4.2 HTG Parameter Input: Determine all tank, environmental, HTG sensor, and liquid parameters listed in Table 1, and input them into the HTG processor; when parameters change, the new values should be input.
• 5.4.3 Pressure Sensor Zero Adjustment Procedure:
  • a) If the sensor external ports are connected together to avoid wind effects, remove the connecting tube when adjusting the zero point;
  • b) Close the pressure introduction valve to disconnect the sensor from the tank;
  • c) Open the drain valve to remove all liquid from the pressure introduction tube to the sensor;
  • d) Make the pressure introduction tube to the sensor open to the atmosphere;
  • e) Adjust the sensor zero point according to the manufacturer's instructions;
  • f) After adjustment, monitor the sensor zero reading at approximately 1 h, and make further adjustments if necessary.
• 5.4.4 Tank Capacity Table Confirmation: It is recommended to verify the consistency of the tank capacity table with GB/T 13235.1 and GB/T 13235.2, and recalibrate if necessary; the data stored in the HTG data processor should be verified against the data in the tank capacity table.
• 5.4.5 Verification by Manual Measurement Method: The calculated value of HTG should be compared with manual measurement data, and can only be used as reference data for temporary acceptance; if the consistency is within the uncertainty range of the two, the HTG system is considered to be operating normally, otherwise further study should be conducted; when comparing HTG with a floor scale, it is recommended to use the apparent mass in air.
• 5.4.6 Temperature Sensor Verification: The reading should be compared with temperature readings obtained from other temperature measurement devices; if the consistency exceeds the uncertainty range, the HTG parameter should be adjusted or the sensor replaced.

8.3 Maintenance

• 6.1 Overview: This operation includes confirmation and calibration of the system; confirmation is different from calibration, in that it does not involve any correction of the HTG data processor parameters.
• 6.2 Confirmation: The purpose is to prove that the HTG system is still operating within the required accuracy; it should usually be carried out periodically in accordance with relevant national regulations; the confirmation process does not require the use of traceable standards, but standard procedures should be used, comparing with stable and repeatable reference values; no adjustments are made during confirmation; if the performance deviation exceeds the predetermined limit, recalibration should be performed.
  • 6.2.1 HTG Sensor Height: It should be compared with the value obtained in Article 5.4.2, and the deviation recorded.
  • 6.2.2 Pressure Sensor Zero Point: It should be verified using the method given in Article 5.4.3, but without any adjustment.
  • 6.2.3 On-Tank Measurement: If compared with the manual method, it should be carried out according to the procedure specified in Article 5.4.5; measurement data obtained by other methods that can replace the manual method can also be used for comparison.
  • 6.2.4 Off-Tank Measurement: Available facilities include a) positive displacement flowmeter with online density meter; b) positive displacement flowmeter with density acquisition from the pipeline; c) mass flowmeter; d) floor scale.
  • 6.2.5 Temperature Sensor: It should be verified using the method given in Article 5.4.6, but without any adjustment.
• 6.3 Calibration:
  • 6.3.1 Overview: The purpose is to check whether the system performance meets the specified accuracy and to make reasonable corrections; calibration should be performed when confirmation indicates degraded performance, or periodically; calibration should be performed using traceable standards and approved current measurement methods; pressure sensors generally cannot be adjusted except for the zero point, and should be replaced if they exceed the specified specifications.
  • 6.3.2 HTG System Parameters: The system parameters determined during commissioning should be re-examined by professional technical personnel, and if necessary, the changed parameters should be input into the HTG data processor.
  • 6.3.3 Pressure Sensor Zero Adjustment: Check the confirmation records; if the zero point deviates beyond the manufacturer's specifications, the pressure sensor should be replaced; if within specifications, the optimal adjustment amount should be determined from the confirmation records, and the zero adjustment should be performed according to Article 5.4.3.
  • 6.3.4 Temperature Sensor Calibration: Check the confirmation records; if necessary, further verify according to Article 5.4.6; if operating outside the limits determined during commissioning, the temperature sensor should be adjusted or replaced.
  • 6.3.5 Pressure Sensor Calibration:
    • 6.3.5.1 Overview: The best method is to directly calibrate the pressure sensor, but the accuracy of the calibration equipment should be better than the HTG system itself; if such equipment is not available, the method described in Article 6.3.6 can be used for calibration, but with slightly lower accuracy; if the pressure sensor position is known, stable, and correct parameters are used in the calculation, the accuracy of the mass measurement obtained from HTG depends on the accuracy of the pressure sensor.
    • 6.3.5.2 Standard Pressure Source Method: The standard device used for calibration is a traceable deadweight tester, accurate to 25 Pa, suitable for on-site use; the pressure sensor remains in its installed position, isolated from the tank by closing the pressure introduction valve, and is sequentially cleaned and connected to the deadweight tester; the deadweight tester is used to generate the pressures of the tank at all liquid levels, to ensure that all static pressures normally experienced by the pressure sensor are checked, i.e., covering the mass range; the pressure measurement values of the HTG system are compared with the pressure values of the deadweight tester; when comparing, the additional static pressure in the connecting tube between the deadweight tester and the pressure sensor should be appropriately considered.
    • 6.3.5.3 Standard Pressure Sensor Method: The standard device used for calibration is a traceable pressure sensor, accurate to ±25 Pa, suitable for on-site use; the pressure sensor remains in its installed position, disconnected from the tank by closing the pressure introduction valve, and is sequentially connected to the standard pressure sensor; the pressure corresponding to each liquid level of the tank is generated by changing the liquid level in the tank or using an external pressure source; the pressure measurement values of the HTG system are compared with the pressure values of the standard pressure sensor; when comparing, the additional static pressure in the connecting tube between the standard pressure sensor and the pressure sensor being calibrated should be appropriately considered.
  • 6.3.6 On-Tank Calibration by Manual Measurement: Compare the mass measured by HTG with the mass indirectly calculated from manually measured liquid level, density, and temperature; because manual density measurement has high uncertainty, this method is used only when direct calibration of the pressure sensor is not possible due to lack of suitable equipment; measure liquid level (GB/T 13894), temperature (GB/T 8927), and density (GB/T 1884) using standard methods, calculate standard volume (GB/T 9109.5) and standard density (GB/T 1885); calculate mass from the product's standard volume and standard density; since manual measurement and HTG measurement use different reference points, the effect of this deviation should be removed from the two mass readings obtained; calibration should preferably be performed with the same liquid, at liquid levels separated by approximately 4 m; if the difference between the transferred mass measured by the HTG system and the manually measured transferred mass is less than 0.2% (expressed as a percentage of the transferred mass calculated from manual measurement values), the HTG system should be considered to be operating normally.
    • Note 6: The limits of 0.2% are based on the following uncertainties: liquid level (initial and final gauge) error ±3 mm; temperature error ±1 ℃; tank capacity table error ±0.1%; other errors ±0.05%. Tank bulging causes the liquid level measurement reference point to shift, and the resulting liquid level measurement error will be added to the manual measurement uncertainty.

8.4 Safety

• 7.1 Mechanical Safety: The HTG sensor and its pressure introduction tube form part of the tank surface, and should not only be able to withstand the same mechanical stress or deformation as the tank surface, but also withstand the effects of product corrosion or erosion.
• 7.2 Electrical Safety: All electrical systems should comply with safety regulations; in addition, the requirements of GB 3836.1 should also be considered.

8.5 Appendix C Measurement Procedure (Height Measurement from HTG Reference Point to Tank Calibration Datum Point)

• C3.1 First Case: When the tank contains liquid, fix the optical level with its tripod on the tank roof or another suitable high point at the same height as the tank roof using a magnetic base, and level the level; lower the gauge tape using the gauge tape holder, and when the plumb bob touches the tank calibration datum point, fix the gauge tape, and read the gauge tape reading with the level, thus measuring the horizontal elevation of the tank calibration datum point; similarly, directly above the HTG reference point, lower the gauge tape along the outside of the tank wall to the HTG reference point using the gauge tape holder, and read the gauge tape reading with the level, thus measuring the horizontal elevation of the HTG reference point; when the HTG reference point cannot be measured directly, the same method can be used to measure the horizontal elevation of a point close to the HTG reference point (intermediate point), then move the level to the ground, measure the horizontal elevations of the intermediate point and the HTG reference point, and through the intermediate point convert the horizontal elevations of the HTG reference point and the tank calibration datum point relative to the same horizontal plane; during measurement, tank vibration and wind effects should be avoided as much as possible; horizontal elevation readings should be accurate to 1 mm.
• C3.2 Second Case: When the tank is empty, through the opened manhole, using the above method, directly or indirectly measure the horizontal elevations of the HTG reference point and the tank calibration datum point with as few level setups as possible; in this case, it is best to use a leveling staff instead of the gauge tape.

9. Qualitative and Quantitative and Calculation Formulas

9.1 Symbol Description (A2)

• Unit system: all values substituted into the formulas in this appendix shall be in International System of Units (SI) units. Pressure Pa; liquid level m; area m²; volume m³; mass kg; density kg/m³; gravitational acceleration m/s².
• The calculation procedure is the same for fixed-roof or floating-roof tanks.
• The in-tank vapor density and the ambient air density have only a secondary effect on the calculated variables; they may be treated as constants, or they may be calculated to meet high-accuracy requirements.
• The ambient air density can be calculated from the absolute ambient pressure and the absolute ambient temperature using the gas state equation; changes in ambient air density have only a secondary effect on the observed density.
• The in-tank vapor density can be calculated from the absolute vapor pressure, the absolute vapor temperature, and the vapor relative density using the gas state equation.
• All sensor input data provided to the HTG processor shall be collected at the same time.

9.2 Density Calculation (A4)

Observed density ρ (calculated from pressure):

ρ = [(P1 − P2) / (g·H)] + ρₐ

Where:

• (P1 − P2): the difference between the readings of pressure sensors P1 and P2;
• g: the local gravitational acceleration;
• H: the vertical distance between the force center of the diaphragms of sensors P1 and P2 (see Figure A1 or Figure A2);
• ρₐ: the ambient air density.

Note 8: The observed density may be calculated from the manually entered standard density in accordance with GB/T 1885; the observed density may also be manually entered into the data processor.

9.3 Liquid Fill Height Calculation (A5)

Liquid fill height L:

L = [(P1 − P3) / (g·Hₚ)] − H₀ − Hₛ + [(ρₙ − ρₐ) / ρ]·Hₚ

(The original formula source-text extraction contains noise; the above is reconstructed from the symbol descriptions and context, requires confirmation against the source standard (source-text extraction))

Where:

• H₀: the vertical distance from the tank calibration datum point to the HTG reference point;
• Hₛ: the vertical distance from the force center of sensor P1 to the HTG reference point (see Figure A1 or Figure A2);
• (P1 − P3): the difference between the readings of pressure sensors P1 and P3;
• g: the local gravitational acceleration;
• Hₚ: the vertical distance between the force center of the diaphragms of sensors P1 and P3 (see Figure A1 or Figure A2);
• ρₙ: the in-tank vapor density;
• ρₐ: the ambient air density;
• ρ: the observed density of the product calculated in accordance with A4.

Note 9: If ρₙ cannot be obtained, it may be assumed that ρₙ = ρₐ.

9.4 Calculation of the Average Cross-Sectional Area of the Tank (A6)

Average cross-sectional area of the tank:

A_E = (V − V₀) / (L + Hₛ + H₀)

(The original formula source-text extraction contains noise; the above is reconstructed from the symbol descriptions and context, requires confirmation against the source standard (source-text extraction))

Where:

• V: the liquid fill volume (at the liquid fill height);
• V₀: the total heel volume;
• L: the liquid fill height calculated in accordance with A5;
• Hₛ: the vertical distance from the force center of sensor P1 to the HTG reference point (see Figure A1 or Figure A2);
• H₀: the vertical distance from the tank calibration datum point (datum plate) to the HTG reference point.

The liquid fill volume and the total heel volume shall be calculated from the liquid fill height and the height of sensor P1 (H₀ + Hₛ) in accordance with GB/T 13235.1.

9.5 Head Mass Calculation (A7)

Product head mass:

Mᵢ = A_E·[(P1 − P3) / g] − ρₙ·A_E·(Hₛ + Hₚ) + ρₐ·A_E·(Hₛ + Hₚ)

(The original formula source-text extraction contains noise; the above is reconstructed from the symbol descriptions and context, requires confirmation against the source standard (source-text extraction))

Where:

• A_E: the average cross-sectional area of the tank calculated in accordance with A6;
• g: the local gravitational acceleration;
• ρₙ: the in-tank vapor density;
• Hₛ: the vertical distance from the force center of sensor P1 to the HTG reference point (see Figure A1 or Figure A2);
• Hₚ: the vertical distance between the force center of the diaphragms of sensors P1 and P3 (see Figure A1 or Figure A2);
• L: the liquid fill height calculated in accordance with A5;
• ρₐ: the ambient air density.

Note 9: If ρₙ cannot be obtained, it may be assumed that ρₙ = ρₐ.

9.6 Heel Mass Calculation (A8)

Product heel volume:

V₀ = Y₀ − V_w

Where:

• Y₀: the total heel volume calculated by looking up the tank capacity table from the height of sensor P1 (H₀ + Hₛ);
• V_w: the free water volume obtained by looking up the tank capacity table from the free water height L_w.

Product heel mass:

M₀ = V₀·ρ

Where:

• V₀: the product heel volume calculated above;
• ρ: the observed density of the product calculated in accordance with A4.

The accuracy of the observed density of the heel product will be affected by liquid stratification (see B4).

9.7 Product Mass Calculation (A9)

Product mass:

M = Mᵢ + M₀ − W_R

Where:

• Mᵢ: the product head mass calculated in accordance with A7;
• M₀: the product heel mass calculated in accordance with A8;
• W_R: the mass of the floating roof (or floating pan).

For a fixed-roof tank without a floating pan, the method for calculating the product mass is the same as for a floating-roof tank, but the floating roof mass shall be zero.

When the floating roof enters the critical zone, the mass of the floating roof and its load is gradually borne by the floating roof legs. For the calculation method within and below the critical zone, see GB/T 13235.1.

9.8 Calculation of the Apparent Mass of the Product in Air (A10)

Apparent mass of the product in air:

Mₐ = M·[1 − (ρₐ / ρ)]

Where:

• M: the product mass calculated in accordance with A9;
• ρₐ: the ambient air density;
• ρ: the observed density of the product calculated in accordance with A4.

9.9 Inventory Accuracy (A11)

Assuming that the installation parameters of the pressure sensors are correct, the accuracy of the calculated mass depends only on the accuracy of the pressure sensors, the tank capacity table, and the local gravitational acceleration. For the HTG system, a typical accuracy calculation is as follows:

Ignoring P3 and considering:

M = P1·A_E / g

Assuming that all errors are statistically independent, then:

E_M² = E_P1² + E_g² + E_AE²

Where:

• E_M: the reading error of the product head mass (absolute mass error/absolute mass);
• E_P1: the reading error of sensor P1;
• E_g: the reading error of the local gravitational acceleration;
• E_AE: the reading error of the average cross-sectional area of the tank.

The reading error of the average cross-sectional area of the tank is the same as that of the tank capacity table, and is usually in the range of ±0.05%～±0.1%.

Table A1 Examples of inventory accuracy:

(In Table A1, the row "0.02 / 0.1 / 0.10 / 0.10" source-text extraction is unclear in the source text, requires confirmation against the source standard (source-text extraction))

9.10 Appendix C Result Calculation (C4)

The height H₀ from the HTG reference point to the tank calibration datum point is calculated as follows:

H₀ = H_a − H_b

(The original formula source-text extraction contains noise; the above is reconstructed from the symbol descriptions and context, requires confirmation against the source standard (source-text extraction))

Where:

• H_a: the horizontal elevation of the tank calibration datum point;
• H_b: the horizontal elevation of the HTG reference point.

10. Precision

• Calibration (manual measurement calibration on the tank): If the difference between the transferred mass measured by the HTG system and the manually measured transferred mass is less than 0.2% (expressed as a percentage of the transferred mass calculated from the manually measured values), the HTG system shall be considered to be operating normally.
• Note 6: The limit of 0.2% is based on the following uncertainties:
  • Liquid level (initial gauge and final gauge) error: ±3 mm
  • Temperature error: ±1 ℃
  • Tank capacity table error: ±0.1%
  • Other errors: ±0.05%
• Tank bulging shifts the liquid level measurement reference point, and the resulting liquid level measurement error will be added to the manual measurement uncertainty.
• Typical inventory accuracy calculation and Table A1 (see Section 9.9).
• The reading error of the average cross-sectional area of the tank is the same as that of the tank capacity table, and is usually in the range of ±0.05%～±0.1%.

11. Report

not provided in the available source.

12. Normative references

• GB/T 1884 Standard test method for density of crude petroleum and liquid petroleum products (hydrometer method)
• GB/T 1885 Petroleum measurement tables
• GB 3836.1 Electrical apparatus for explosive atmospheres—General requirements
• GB/T 8927 Standard test method for temperature of petroleum and liquid petroleum products
• GB/T 9109.5 Dynamic measurement of crude oil—Calculation of oil quantities
• GB/T 13235.1 Petroleum and liquid petroleum products—Calibration of vertical cylindrical metal tanks—Strapping method
• GB/T 13235.2 Petroleum and liquid petroleum products—Calibration of vertical cylindrical metal tanks—Optical reference line method
• GB 13236 Specification for petroleum gauging tapes and steel strapping tapes
• GB/T 13377 Standard test methods for density or relative density of crude petroleum and liquid or solid petroleum products (capillary-stoppered pyknometer and graduated bicapillary pyknometer methods)
• GB/T 13894 Standard test method for liquid level measurement of petroleum and liquid petroleum products (manual method)
• SH/T 0221 Standard test method for density or relative density of liquefied petroleum gas (pressure hydrometer method)
• ISO 11223-1:1995 (equivalent adoption)
• Appendix E Bibliography:
  • [1] ISO 5024:1976 Petroleum liquids and gases—Measurement—Standard reference conditions
  • [2] ISO 8311:1989 Refrigerated light hydrocarbon fluids—Calibration of membrane tanks and independent prismatic tanks in ships—Geometrical measurement method
  • [3] VIM, International vocabulary of basic and general terms in metrology, second edition, 1993 International Organization for Standardization, Geneva

13. Source and verification

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14. Quick-reference questions and answers