GB/T 13894-2023 Petroleum and liquid petroleum products — Liquid level measurement — Manual method

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

• Standard number: GB/T 13894—2023
• Chinese full title: Petroleum and liquid petroleum products — Liquid level measurement — Manual method
• English title: Petroleum and liquid petroleum products—Level measurement—Manual methods
• Replacement relationship: replaces GB/T 13894—1992 "Petroleum and liquid petroleum products — Liquid level measurement method (manual method)"
• Publication/implementation: published by 2023-11-27, implemented by 2024-03-01
• Custodian: National Technical Committee for Standardization of Petroleum Products and Lubricants (SAC/TC280)
• Drafting organizations: Sinopec Research Institute of Petroleum Processing Co., Ltd.; Science and Technology Department of China Petroleum & Chemical Corporation; China Certification & Inspection Group Shandong Co., Ltd.; Tianjin Petrochemical Branch of China Petroleum & Chemical Corporation; Sinopec Fuel Oil Sales Co., Ltd.; Beijing Yanshan Branch of China Petroleum & Chemical Corporation; Beijing Petroleum Branch of Sinopec Sales Co., Ltd.; Northern Pipeline Co., Ltd. of National Pipeline Network Group; Zhejiang Petroleum Branch of Sinopec Sales Co., Ltd.; Qingdao Aobang Measuring Instrument Co., Ltd.
• Main drafters: Wei Jinxiang, Bi Haipeng, Liu Chongwei, Cui Guangwei, Sun Yan, Xu Min, Jin Tao, Zeng Fanming, Wang Zhixue, Li Genchen, Cao Lei, Zhang Shanyou
• First publication: first published in 1992, this is the first revision

2. Scope of application and non-applicability

• Describes a method for measuring the liquid level and bottom free water height of petroleum and liquid petroleum products (hereinafter referred to as "oil products") in non-pressure tanks (compartments) using manual liquid level measurement equipment.
• Applicable to liquid level measurement of oil products with a Reid vapor pressure less than 103 kPa; other liquid products with similar characteristics may be used as a reference.
• Applicable to liquid level measurement of atmospheric tanks (compartments) that can be open-gauged and low positive pressure gas-tight tanks (compartments) equipped with vapor lock valves that can be closed or restricted gauged.
• Note: When used for liquid level measurement of oil tanker compartments, "tank" in this document is equivalent to "compartment".
• Not applicable: no explicit "not applicable" clause is provided in the available source.

3. Method principle

• Liquid level measurement is divided into innage gauging and ullage gauging (see Figure 1 and Figure 2). The gauge reading of the liquid surface relative to the reference datum is obtained by vertically suspended gauging equipment (gauge tape). The reference datum should remain stable and horizontal under all operating conditions. The gauge reading should be read accurately to the smallest graduation of the gauge tape (usually 1 mm) according to the liquid trace tangent, the gauging reference point, or the reading pointer. (6.1)
• Innage gauging usually uses the dipping datum specified in the tank capacity table as the reference datum to measure innage; ullage gauging usually uses the gauging reference point specified in the tank capacity table as the reference datum to measure ullage, and the equivalent innage can be calculated from the difference between the reference height and the gauged ullage. (6.3, 6.4)
• Liquid level measurement data involve some or all of oil height, water height, and reference height, which can be obtained directly by innage gauging or indirectly by ullage gauging. (6.5)
• Closed and restricted gauging require the use of PEGD to measure oil height and water height under closed or restricted conditions; by placing the sensing probe of PEGD successively at the oil surface, the oil-water interface, and the dipping datum plate (tank bottom), all measurements of oil ullage, water ullage, and tank reference height can be completed in one operation. (8.1)

4. Reagents and materials (purity / preparation)

• Water-indicating paste: should be a paste-like substance that changes color upon contact with water but does not readily react with petroleum and its emulsions. When measuring the water height at the bottom of a container, it is applied to the water gauge, dipping weight, or gauge tape; the immersed portion undergoes a color change, thereby clearly indicating the position of the oil-water interface. (4.3.2)
• Oil-indicating paste: should be a paste-like substance that changes color or dissolves upon contact with oil products. Applied to the gauge tape or weight, it can effectively solve the problem that the liquid trace tangent of light oil products is not easily retained, but it should not cause the indicated liquid level to have an upward creeping tendency. (4.3.3)
• Selection and use of water-indicating paste are given in Annex B (informative). (Annex B)
• Purity, preparation concentration, etc.: not provided in the available source.

5. Instruments and equipment

• Gauging equipment and auxiliary tools (items) should meet the requirements of GB/T 13236, especially should be suitable for the hazardous environment in which they are used and be easily grounded; they should be verified or calibrated as required and used effectively. (4.1)
• Oil gauge tape: consists of a gauge tape combined with a dipping weight or an ullage weight through a connector in a fixed or non-fixed manner to measure liquid level. The dipping weight can be used for innage or ullage measurement of the oil surface and oil-water interface, but the ullage weight is only used to measure the ullage of the oil surface. (4.2.1)
• Portable electronic metering device (PEGD): consists of a gauge tape and an electronic weight used in combination to directly measure the ullage of the oil surface or oil-water interface. Some can measure the reference height by electronic or manual sensing when the electronic weight touches the bottom. PEGD is usually designed for open gauging, restricted gauging, or closed gauging to adapt to tank pressure or environmental requirements, but the electronic weight used in the latter two cases should enter the tank through a vapor lock valve. The electronic weight can generally also sense temperature, and some can also sense density. (4.2.2)
• Metering rod: includes two types, the dipping rod and the ullage rod, which can replace the oil gauge tape for gauging small oil tanks and can be graduated by length or volume, wherein the ullage rod is also called a "T-square". When graduated in length units, the zero point of the dipping rod is at its bottom position, and the zero point of the ullage rod is at the bottom surface of its upper transverse bar; the position error of all graduation lines should not exceed ±1 mm. (4.2.3)
• Water gauge: can replace the weight, used in combination with the gauge tape of the oil gauge tape in a fixed or non-fixed connection or directly tied with a rope. Through the color change of the water-indicating paste applied on its surface, it is specifically used to measure water height. (4.3.1)
• Bottom liquid core sampler: a cylindrical sampler with a diameter of about 60 mm, a height that can cover the general bottom water height, an open top, and a manually or touch-controlled valve at the bottom. The cylinder should preferably be transparent tempered glass and can be reinforced with spark-free metal; the bottom surface of the sampler should be taken as the zero point, and the cylinder should be linearly graduated in millimeters. (4.3.4)
• Vapor lock valve: a special valve installed on the gauging port on the tank top or tanker deck, or on the stilling well passing through them, and combined with PEGD through a quick connector for restricted or closed metering applications. (4.3.5)

6. Recommended operating conditions

• Liquid surface stabilization time: generally not less than 15 min for light oils, and generally not less than 30 min for heavy oils. (Note to 5.2.3.3)
• Static electricity prevention: the oil tank or the oil products therein should satisfy at least one of the following conditions: correctly installed stilling well; floating roof or floating pan connected to the tank body by a conductor; an anti-static additive added to the oil products to ensure its conductivity is greater than 50 pS/m, and no mist or fine particles are formed in the space above the liquid surface. (5.1.4 a))
• When the above conditions cannot be met, during the oil loading period and for a period after loading (for tanks greater than 5000 m³, 30 min; otherwise 10 min, but for railway tank cars and road tank cars 2 min), metal equipment used for gauging should not be placed in or left in the tank. (5.1.4 b))
• The change in the measured reference height relative to the table-listed reference height should preferably not exceed 2 mm. (5.2.1.2)
• When the difference between the measured reference height and the calibrated value exceeds 5 mm, the cause and solution may only be found in the design and construction of the oil tank. (Note to 5.2.1.2)
• Stilling well perforation: it is generally more appropriate to drill a vertical row of holes with a diameter of 25 mm and a center spacing of 300 mm in the stilling well. (Note 5.2.1.5 2)
• Gauge readings should be read accurately to the smallest graduation of the gauge tape (usually 1 mm). (6.1)
• Continuous gauging determination: when the difference between two consecutive gauge readings exceeds 1 mm (for water height gauging, 2 mm), gauging should continue until the difference between two consecutive gauge readings does not exceed 1 mm (for water height gauging, 2 mm), or the difference among three consecutive gauge readings does not exceed 3 mm, but at least three gauge readings should be taken for tanker compartments, and the gauging result should be rounded to 1 mm. (6.6)
• Gauging of tanker compartments under severe weather conditions: at least five consecutive gauge readings should be taken within a short time, the maximum and minimum values should be discarded, and the gauging result should be the average of the remaining three gauge readings. (6.6)
• Reference gauging (Chapter 9): measurement data should be read accurately to 0.5 mm; repeat the measurement until 3 consecutive readings are within 1 mm or take 10 readings, and take the average as the reference gauging result; reference gauging should be carried out under mild weather conditions. (9.4)
• The resolution of the thermometer should be better than 0.1 ℃. (9.3)

7. Sampling and sample preparation

• When measuring the liquid level before and after gauging, the same equipment and procedure should be used, and the temperature of the oil products in the tank should be measured in accordance with GB/T 8927; if necessary, sampling should also be carried out in accordance with GB/T 4756. (6.8)
• Determination of free water and emulsion layer height by sampler method: use a bottom liquid core sampler; with the bottom valve and top fully open, slowly lower the sampler along the gauging port to the tank bottom, wait for a sufficient time, and then close the sampler; retrieve the sampler and pour the internal oil products back into the tank from the top opening until water is seen; measure the height of the liquid remaining inside as the total height of free water and oil-water emulsion layer in the tank; slowly open the bottom valve to return the free water to the tank, and measure the height of the remaining liquid as the thickness of the oil-water emulsion layer; subtract the emulsion layer thickness from the total height to approximately obtain the free water height. (7.3.3)
• Other sampling and sample preparation content: not provided in the available source.

8. Analytical procedure

8.1 Open gauging (Chapter 7)

• Oil innage gauging:
  • Dipping oil gauge tape method (7.1.1): look up the table-listed reference height from the tank capacity table and select a suitable oil gauge tape; safely ground the gauge tape, slowly lower the gauge tape and weight into the tank from the gauging port until the bottom of the weight is close to the dipping datum plate; rest the gauge tape against the gauging reference point, slowly lower the tape until the weight just touches the dipping datum plate or tank bottom, and read the measured reference height; note the change in the measured reference height relative to the table-listed reference height; withdraw the gauge tape and read the gauge tape reading at the liquid trace tangent as the innage gauge reading; repeat the operation and determine the innage gauging result in accordance with 6.6.
  • Dipping rod method (7.1.2): look up the reference height from the tank capacity table and select a dipping rod graduated in length units and with a length exceeding the reference height; lower the dipping rod vertically along the gauging reference point, gently touch the bottom, and read the dipping rod reading; note the change in the measured reference height; withdraw the dipping rod and read the liquid trace tangent reading as the innage gauge reading; repeat the operation and determine the innage gauging result in accordance with 6.6.
• Oil ullage gauging:
  • Sounding tape method (7.2.1): Look up the table-referenced reference height from the tank capacity table, and select a sounding tape whose tape length is greater than the expected ullage to be measured; make the tape safely grounded, and lower the tape and bob into the tank until the bob just touches the oil; pause the tape briefly at the reference gauge point, and continue lowering the tape (when the liquid trace tangent line is selected on the tape, at least 250 mm, stabilize for about 30 s–60 s; when the liquid trace tangent line is selected on the bob, continue lowering the tape 20 mm–100 mm), until a convenient scale on the tape (whole centimeter) coincides with the reference gauge point; read the tape reading at the reference gauge point, withdraw the tape and read the tape (or bob) reading at the liquid trace tangent line; subtract the tape (or bob) reading at the liquid trace tangent line from the tape reading at the reference gauge point to obtain the ullage gauge reading; repeat the operation, and determine the ullage gauge result according to 6.6; subtract the ullage gauge result from the table-referenced reference height to convert the gauged ullage into equivalent true height.
  • Ullage tape method (7.2.2): Look up the table-referenced reference height from the tank capacity table, and select an ullage tape whose tape length is greater than the expected ullage to be measured; make the tape safely grounded, and slowly lower the ullage tape from the gauge hatch into the tank until it contacts the oil surface; rest the tape steadily at the reference gauge point until the ullage tape and liquid surface are stable, and continue lowering the tape slowly 20 mm~100 mm, until a convenient scale on the tape (whole centimeter) coincides with the reference gauge point, but only the part below the zero point of the ullage tape enters the oil; read the tape reading at the reference gauge point, withdraw the tape and ullage tape, and read the ullage tape reading at the liquid trace tangent line; add the ullage tape reading at the liquid trace tangent line to the tape reading at the reference gauge point to obtain the oil surface ullage gauge reading; repeat the operation, and determine the oil surface ullage gauge result according to 6.6; subtract the ullage gauge result from the table-referenced reference height to convert the gauged ullage into the oil surface equivalent true height.
  • Ullage rod method (7.2.3): Look up the table-referenced reference height from the tank capacity table, and select an ullage rod whose measuring length is not less than the liquid surface ullage; suspend the ullage rod vertically and slowly lower it into the oil in the tank, until the bottom surface of the crossbar of the ullage rod rests horizontally on the upper reference plane of the gauge hatch; withdraw the ullage rod, and read the length of the part not wetted by oil, which is the oil surface ullage gauge reading; repeat the operation, and determine the oil surface ullage gauge result according to 6.6; subtract the ullage gauge result from the table-referenced reference height to convert the gauged ullage into the oil surface equivalent true height.
  • PEGD method (7.2.4): The PEGD designed for restricted or closed gauging may also be used for open gauging; the operating method is basically the same as for restricted or closed gauging (see 8.2), but readings can only be taken through the reference gauge point rather than the reading pointer, so additional corrections may be required. The PEGD designed for open gauging uses its support base as the ullage reference plane; during measurement, the ullage reference plane is placed directly on the gauge hatch, and the operating method is basically the same as for the PEGD used for restricted or closed gauging (see 8.2). When the reference gauge point is not consistent with the upper reference plane of the gauge hatch used, additional corrections shall be made. When the PEGD can measure the reference height of the oil tank (see 8.2) or the reference height is known and fixed, this method may also be used to determine the equivalent true height of the liquid surface.
• Water height gauging:
  • Water-indicating paste method (7.3.1): Apply water-indicating paste to the tape of the sounding tape, the bob, or a water-finding ruler used in place of the bob; the water-indicating paste reacts with water and changes color, indicating the water height through the water trace tangent line; the water height should preferably be measured by the true height method. Sounding tape (or water-finding ruler) with water-indicating paste: select a sounding tape or use a water-finding ruler in place of the sounding bob combined with the tape to measure water height; select a suitable water-indicating paste and apply a thin layer; make the tape safely grounded, and carefully lower the sounding bob or water-finding ruler into the tank until it gently touches the sounding datum plate; keep it vertical at the sounding datum point for a sufficient time (in cold climates, about 90 s is required); withdraw the sounding bob or water-finding ruler, and read the water height gauge reading from the water trace tangent line on the water-indicating paste; repeat the operation, and determine the water height gauge result according to 6.6. Sounding rod with water-indicating paste: apply a thin layer of water-indicating paste to the expected water height section on the sounding rod, suspend and lower the sounding rod into the tank until it gently touches the tank bottom or sounding datum plate, keep it for a sufficient time for the water-indicating paste to react and change color, take out the sounding rod and read the water height gauge reading, repeat the measurement, and determine the water height gauge result according to 6.6.
  • PEGD method (7.3.2): The preferred PEGD designed for open gauging, using the same method as for 7.2.4 and 8.2, may continue downward or directly downward to the oil-water interface after the oil surface ullage measurement is completed, to measure the water ullage, and may continue downward to measure the reference height of the oil tank. Subtracting the water ullage from the reference height gives the equivalent true height of free water (water true height).
  • Sampler method (7.3.3): When the above methods cannot measure water height or the accuracy of water height measurement is doubted, or when an oil-water emulsion exists or is suspected to exist, the sampler method may be used to determine the height of free water and the emulsion layer or to obtain a sample of the emulsion layer, but the relevant parties shall reach agreement. Use a bottom liquid-core sampler, and operate according to the steps 7.3.3 a)~g).

8.2 Closed and restricted gauging (Chapter 8)

• Traditional sounding tapes or water-finding rulers cannot be used for gauging under closed conditions, although they may possibly be used under restricted conditions through a vapor lock valve, the vapor/gas above the liquid surface may fade the oil/water-indicating paste on the tape, affecting the liquid trace tangent line on the tape; therefore, PEGD is required to measure oil height and water height under closed or restricted conditions. (8.1)
• Measurement of oil height, water height, and reference height (8.2):
  • Look up the table-referenced reference height from the tank capacity table; the tape length of the selected PEGD shall be greater than the expected ullage to be measured, and should preferably be greater than the reference height of the oil tank. (8.2.1)
  • Determine the vapor lock valve specified in the tank capacity table, confirm that the valve is fully closed, and check the reference plane of the valve and the reference plane of the matching PEGD. (8.2.2)
  • Install the PEGD onto the vapor lock valve, ensuring correct seating and locking in place; when there is a separate grounding connection wire, it shall be connected to a suitable part of the tank body. (8.2.3)
  • Open the vapor lock valve to the fully open state, turn on the PEGD to the ullage indication mode, and carefully lower the electronic bob into the tank to the oil surface position. (8.2.4)
  • According to the signal change emitted by PEGD, slowly raise the electronic bob, then slowly lower it, determine the response position of the sensing probe to the oil surface, and read the tape reading as the oil ullage gauge reading. (8.2.5)
  • Repeat 8.2.5, and determine the oil ullage gauge result according to 6.6. (8.2.6)
  • When water height needs to be measured, after the oil ullage measurement is completed, continue lowering the tape so that the electronic bob passes through the oil layer to the oil-water interface, determine the response position of the sensing probe to the oil-water interface, read the water ullage gauge reading, repeat multiple times, and determine the water ullage gauge result according to 6.6. (8.2.7)
  • When the reference height needs to be measured and the electronic bob of PEGD has a bottom-touch sensing function, measure according to the steps 8.2.8 a)~c); when the electronic bob does not have a bottom-touch sensing function, PEGD may be used to simulate a traditional sounding tape to measure the reference height of the oil tank, but a weight may need to be added to the electronic bob. To compensate for the height difference between the ullage/interface response point and the bottom surface of the electronic bob or the bottom-touch sensing point, the reading of PEGD shall be added to this height difference (PEGD measured reference height deviation value) to obtain the reference height. (8.2.8)
  • When the tank capacity table is compiled for the PEGD matched with the vapor lock valve, or when PEGD has already integrated the offset correction of the reading pointer, the reading of PEGD is the ullage; otherwise, the gauge reading shall be corrected according to the several cases 8.2.9 a)~c). (8.2.9)
  • Subtracting the oil ullage or water ullage from the reference height gives the equivalent true height of the oil surface or free water. (8.2.10)

8.3 Setting and verification of automatic level gauges (reference gauge for ALG) (Chapter 9)

• In the setting and verification of ALG, the oil height and reference height obtained by manual gauging are usually used as reference data; the gauging method should be more precise and comply with the provisions of GB/T 21451.1 and GB/T 21451.2. (9.1)
• Reference gauge data may be obtained by true height gauging or ullage gauging. Most ALG actually measure ullage, but directly display the liquid level as true height; therefore, when obtaining reference data for the setting and verification of ALG, the reference height of the oil tank should also be verified. It is preferable to compare the measurement data of ALG with the reference gauge data at at least two liquid levels (at intervals of at least 5 m, or near the usual operating height of the oil tank and the lower storage limit liquid level). (9.2)
• Reference gauge data shall be obtained using a sounding tape or PEGD that complies with GB/T 13236, and these devices should preferably have been calibrated recently. Temperature shall be measured using a portable electronic thermometer (PET) or PEGD (with temperature measurement function)) that complies with GB/T 8927. The resolution of the thermometer should be better than 0.1 ℃, and it should preferably have been calibrated recently. Observation data obtained using reference measurement equipment shall be corrected according to the correction values on their calibration certificates. (9.3)
• The measurement method for reference gauge data shall comply with 7.1.1, 7.2.1, and 7.2.4, except for the following aspects: measurement data shall be read accurately to 0.5 mm; repeat the measurement until 3 consecutive readings are within 1 mm or take 10 readings, and take the average as the reference gauge result; reference gauging shall be carried out under mild climate conditions, and if necessary, the setting and verification of ALG shall be postponed. (9.4)
• Correction for thermal expansion effects: Measure the average temperature of the liquid and vapor space in the tank according to GB/T 8927. When the temperature of the reference gauging equipment differs from its calibrated standard temperature and/or the tank wall temperature by more than 10 ℃, in order to eliminate the effect of thermal expansion, supplementary correction shall be made to the observed reading of the tape (see Appendix A). (9.5)

9. Qualitative and quantitative and calculation formulas

• True height gauging: Measure the true height using the sounding datum point specified in the tank capacity table as the reference datum. When measuring the true height using another sounding datum point as the reference datum, the gauge reading shall be corrected to the height relative to the sounding datum point specified in the tank capacity table. (6.3)
• Ullage gauging: Measure the ullage using the reference gauge point specified in the tank capacity table as the reference datum, and the equivalent true height may be calculated from the difference between the reference height and the gauged ullage. When measuring the ullage using another reference gauge point or reading pointer as the reference datum, the gauge reading shall be corrected to the height relative to the reference gauge point specified in the tank capacity table. (6.4)
• Conversion of ullage gauging to equivalent true height: Subtracting the ullage gauge result from the table-referenced reference height converts the gauged ullage into equivalent true height. (7.2.1.7, 7.2.2.7, 7.2.3.5)
• Water true height: Subtracting the water ullage from the reference height gives the equivalent true height of free water (water true height). (7.3.2, 8.2.10)
• Temperature correction formula (Appendix A):
  • Temperature correction when measuring true height:
    • Correction of the measured actual height using the linear expansion coefficient according to formula (A.1): hc = h[1 + αdt(tl - 20)], where hc is the corrected actual height, h is the measured actual height, αdt is the linear expansion coefficient of the tape, and tl is the temperature of the liquid being measured. (A.3.3.2 a))
    • Use the corrected actual height to look up the tank capacity table, read the corresponding table-listed volume, and correct it using the area expansion coefficient according to formula (A.2): VC = V[1 + 2αtk(tS - 20)], where VC is the corrected volume, V is the table-listed volume, αtk is the linear expansion coefficient of the tank wall metal, and tS is the tank wall temperature. (A.3.3.2 b))
    • The tank wall temperature of an uninsulated tank is assumed to be calculated according to formula (A.3): tS = 7tl/8 + ta/8, where ta is the ambient air temperature. (A.3.3.2)
    • Simplified calculation: use the measured actual height to look up the tank capacity table to obtain the table-listed volume; multiply the table-listed volume by [1 + 3α(t - 20)] to obtain the volume of the liquid in the tank at its current temperature, where α is the linear expansion coefficient of the tank wall and tape metal, and t is the common temperature of the tank wall and the liquid. (A.3.3.2)
  • Temperature correction when measuring ullage (A.3.3.3):
    • Subtract the measured ullage from the tank reference height (at the reference temperature) to obtain the equivalent actual height;
    • Multiply the equivalent actual height by (1 + αΔT) to obtain the corrected equivalent actual height, where α is the linear expansion coefficient of the tank wall metal, and ΔT is the tank wall temperature of the liquid-filled zone minus the reference temperature;
    • Use the corrected equivalent actual height to look up the tank capacity table to obtain the corresponding table-listed volume;
    • Multiply the table-listed volume by the coefficient (1 + 2αΔT) to obtain the volume of the liquid in the tank at its current temperature.
• Meniscus effect: the difference between the liquid trace tangent and the true oil surface depends on the surface tension of the oil and may reach approximately 2 mm. Direct reading from the liquid trace tangent will result in a slightly larger actual height and a slightly smaller ullage. (A.2.6)
• Other calculation formulas: not provided in the available source.

10. Precision

• Continuous gauging determination: when the difference between two consecutive gauge readings exceeds 1 mm (for water height gauging, 2 mm), gauging should continue until the difference between two consecutive gauge readings does not exceed 1 mm (for water height gauging, 2 mm), or the difference among three consecutive gauge readings does not exceed 3 mm, but at least three gaugings shall be performed on ship tanks, and the gauging results shall be rounded to 1 mm. (6.6)
• Determination of gauging results:
  • When the difference between two consecutive gauge readings does not exceed 1 mm, the gauging result shall be the previous gauge reading;
  • When the difference between two consecutive gauge readings of water height is 2 mm, the gauging result shall be the average of the two gauge readings;
  • When the maximum difference among three consecutive gauge readings is 2 mm or 3 mm, the gauging result shall be the average of the three gauge readings. (6.6)
• Gauging of ship tanks under severe weather conditions: the variation among three consecutive gauge readings may exceed 3 mm. When oil product fluctuation cannot be avoided, at least five consecutive gaugings should be performed within a short time, the maximum and minimum values should be discarded, and the gauging result shall be the average of the remaining three gauge readings. (6.6)
• Reference gauging (Chapter 9): repeat the measurement until 3 consecutive readings are within 1 mm or perform 10 readings, and take the average as the reference gauging result. (9.4 b))
• Other precision indicators: not provided in the available source.

11. Report

• The measurement personnel shall record immediately after measurement, and before leaving the site, all relevant parties shall confirm that the measurement data are consistent. (Chapter 10)
• The recorded actual height, ullage and/or reference height shall be the actual observed values, and shall be read and recorded accurately to the smallest division of the equipment used (usually 1 mm), except for gauging for setting and verifying automatic level gauges (Chapter 9). (Chapter 10)
• When corrections to observed readings are required, for example, considering the height difference between other ullage reference points and the gauging reference point or the height difference between the PEGD reading pointer and the gauging reference point, a full record of the observed readings and correction values shall be made (to avoid possible repeated application of correction values). (Chapter 10)
• The data and related information from temperature measurement and sampling shall be recorded together with the gauging data. (Chapter 10)
• The date, time, tank number, and relevant weather conditions of the measurement shall be recorded together. When the oil tank has more than one gauging port, the actual measurement point shall be indicated in the report. (Chapter 10)
• When gauging ship tanks, corrections for trim and/or list shall also be made, and data such as draft depth shall be observed and recorded. (Chapter 10)
• Where possible, the verification of the closure of the tank inlet and outlet valves and details of the relevant pipelines (such as filling status, pipeline volume and temperature) shall be recorded. (Chapter 10)

12. Normative References

• GB/T 4756 Petroleum liquids — Manual sampling
• GB/T 8927 Petroleum and liquid petroleum products — Temperature measurement — Manual method
• GB/T 13235.1 Petroleum and liquid petroleum products — Calibration of vertical cylindrical tanks — Part 1: Strapping method
• GB/T 13236 Petroleum and liquid petroleum products — Equipment for manual measurement of liquid level in storage tanks
• GB 13348 Electrostatic safety regulations for liquid petroleum products
• GB/T 21451.1 Petroleum and liquid petroleum products — Automatic measurement of liquid level and temperature in storage tanks — Part 1: Liquid level measurement in atmospheric tanks
• GB/T 21451.2 Petroleum and liquid petroleum products — Automatic measurement of liquid level and temperature in storage tanks — Part 2: Liquid level measurement in ship tanks
• References:
  • GB/T 13235 (all parts) Petroleum and liquid petroleum products — Calibration of vertical cylindrical tanks
  • GB/T 19779 Petroleum and liquid petroleum products — Calculation of oil quantities — Static measurement
  • GB/T 40874—2021 Crude petroleum and petroleum products — Bulk transfer — Guidelines for pipeline filling
  • JJG 168 Vertical metal tank capacity
  • ISO/CD 4511 Petroleum and liquid petroleum products—Direct measurement of liquid level in storage tanks—Manual methods
  • API MPMS Chapter 3.1A Standard Practice for the Manual Gauging of Petroleum and Petroleum Products
  • API MPMS Chapter 17—Marine Measurement Section 2—Measurement of Cargoes On Board Tank Vessels
  • API MPMS Chapter 17.11/EI HM52 Measurement and Sampling of Cargoes On Board Tank Vessels Using Closed and Restricted Equipment