Standard of the Ministry of Petroleum Industry of the People’s Republic of China
Petroleum and liquid petroleum products -- Vertical metal tank custody transfer measurement specification
This specification covers the custody transfer measurement of petroleum and liquid petroleum products (PP) under normal pressure in stationary using vertical metal tank gauges.
This specification should be carried out in accordance with related regulations of the Petroleum and liquid petroleum products -- Administration for custody transfer measurement issued by the Ministry of Petroleum Industry of the People’s Republic of China.
1. General
1.1 Measurement Accuracy
Custody transfer measurement error in this specification is +/- 0.35%.
1.2 Container Verification
1.2.1 Capacity of vertical metal tanks is verified in accordance with JJG 168-76 Capacity verification specification of vertical metal tanks.
1.2.2 Period for capacity verification of vertical metal tanks: initial check within three years and recheck within five years.
1.2.3 Vertical metal tanks used for PP measurement are verified by container verification stations approved by the Ministry of Petroleum Industry of the People’s Republic of China.
2. Measurement Tools and Agents
2.1 Gauging Tape
2.1.1 Certified and calibrated tapes used for petroleum measurement are steel tapes with three sizes of length 10m, 15m, 20m (Min Scale: 1mm) which are determined based on the size of tanks.
2.1.2 Plumbs of oil gauging tapes should be made of copper materials. 500g plumbs are used for gauging light petroleum products and 1000g for crude oil and heavy petroleum products.
2.1.3 Water gauging tapes should be made of coppers or aluminum alloy, 300mm long (Min Scale: 1mm) with an error of the full length about +/- 0.5mm.
2.1.4 Gauging tapes are biannually verified in technical accordance with the specifications of JJG 4-80 Verification specification of steel tapes.
2.1.5 Gauging tapes in any of the following conditions should not be used:
a. with folded, bent and chained tape band;
b. with blurred scale or number;
c. with damaged plumb tip;
d. with exceeded allowable scale error;
e. without calibration table.
2.2 Thermometer
2.2.1 Thermometers used for gauging the temperature of petroleum products are generally mechanical total immersion mercury thermometers (min division 0.2℃) with certificate and calibration table.
2.2.2 Mercury thermometers are biannually verified in technical accordance with the specifications of GB 514-65 Technical specification for liquid thermometer for testing petroleum products.
2.2.3 Thermometers in any of the following conditions should not be used:
a. with broken mercury column in capillary tube;
b. with broken bulb;
c. with blurred scale and number;
d. with exceeded allowable scale error;
e. without calibration table.
2.2.4 Thermometers of other types should be:
a. verified and listed in national approved products;
b. periodically verified according to relevant verification specifications or technical specifications;
c. with the same measurement accuracy as mercury thermometer’s (minimum scale 0.2℃);
d. thermo-electrical thermometer (e.g. semiconductor thermometer etc.) which is explosion-proof product provided with explosion proof grade and certificate and explosion-proof and shielded connections between sensor and displayer.
2.3 Hydrometer
2.3.1 Hydrometer used for the density determination of petroleum products is SY-1 petroleum hydrometer.
2.3.2 Measurement range of petroleum hydrometer should be in conformity with GB/T 1884 Petroleum and liquid petroleum products - Density determination (Hydrometer method).
2.3.3 Petroleum hydrometer should be verified once every half year and its technical specification should be in conformity with SY/T 3301 Technical specification of petroleum hydrometer.
2.4 Test Kit
2.4.1 Test kit should be made of copper materials or aluminum alloy materials.
2.4.2 Capacity of test kit should be not less than 200 ml.
2.4.3 Lifting rope of test kit should be made of antistatic materials.
2.5 Sampler
2.5.1 Sampler should be made of copper materials or aluminum alloy materials.
2.5.2 Weight of sampler should be 1.5~2 times of the weight of discharged liquid.
2.5.3 Capacity of sampler should be in conformity with the Petroleum and liquid petroleum products - Sampling method.
2.5.4 Lifting rope of sampler should be made of antistatic materials.
2.6 Oil Indicating Paste
Requirements for oil indicating paste:
No longer than 10 seconds of color change when immerging the oil indicating paste evenly coated on gauge into 120# solvent gasoline under 15~20℃ and no more than 0.5 mm difference between indicating values after 10 seconds and 20 seconds.
2.7 Water Indicating Paste
Requirements for water indicating paste:
No longer than 5 seconds of color change when immerging the water indicating paste evenly coated on water gauge into 120# solvent gasoline under 15~20℃ and no more than 0.5 mm difference between indicating values during 5 seconds.
3. Measurement Methods
3.1 Sequence of Operation
Before transfer: first check the HBT, then measure temperature and take sample.
After transfer: check the HAT and measure temperature.
3.2 Gauge
3.2.1 Glossary
a. Gauge point: position specified for run gauge from the top of tank.
b. Total gauging height: vertical height from gauge point to bottom tank (or gauge platform).
c. HBT: the vertical height from liquid level in tank to bottom tank (or gauge platform) before transfer.
d. HAT: the vertical height from liquid level in tank to bottom tank (or gauge platform) after transfer.
e. Content height: the vertical height from liquid level in tank to bottom tank (or gauge platform).
f. Ullage height: the vertical height from gauge point to liquid level in tank.
g. Oil mark: boundary mark on oil gauge by measured oil.
h. Water mark: boundary mark on water gauge by bottom water.
3.2.2 Stable duration of liquid level
Liquid level in tank before gauging is kept stable not shorter than 30min.
3.2.3 Gauging position
Gauge is run from the gauging point at the top of tank.
3.2.4 Content height gauge
3.2.4.1Gauge content height when measuring light petroleum products and lubricant oil.
3.2.4.2Gauging requirements: stably run gauge, lightly contact bottom, clearly read; read small scale, then large scale and record.
3.2.4.3Repeat 3.2.4.2; the 1st read prevails when equal to or less than 1mm difference exists between two gauges; repeat gauging when more than 1mm difference.
3.2.4.4Oil indicating paste can be used for unclear oil mark when measuring liquid level of volatile light oil.
3.2.5 Ullage height gauge
3.2.5.1Gauge ullage height when measuring crude oil, heavy oil and fuel oil etc.
3.2.5.2Stop running gauge when tape is immerged in oil and align tape scale with the gauge point; read and record the height when stable and read the immersion height after lifting the gauge.
3.2.5.3Repeat 3.2.5.2; the 1st read prevails when equal to or less than 1mm difference exists between two gauges; repeat gauging when more than 1mm difference.
3.2.5.4For ullage height gauge, oil level height = total gauging height -- ullage height + immersion height.
3.2.6 Water gauge
3.2.6.1Gauge the height of bottom water in tank as gauging the content height.
3.2.6.2Keep the water gauge in tank for 10~30min.
3.2.6.3Coat water indicating paste on water gauge when gauging the water height.
3.3 Temperature Determination
3.3.1 Oil tank temperature determination
Temperature of liquid petroleum products should be measured inside the tank.
3.3.1.1Before temperature determination, put a thermometer of appropriate scale into the middle of the temperature determination kit and lay down the kit to the temperature measuring point from gauge point.
3.3.1.2Take one measurement at the middle height of oil for oil which needs not to be heated in tank.
3.3.1.3Average temperature of oil which needs to be heated in tank is measured step by step and calculated based on each measurement as follows:
a. Take measurements respectively at the 1/6, 1/2 and 5/6 points of the height of liquid level when height of liquid level is higher than 1/2 of total gauging height.
b. Take measurements respectively at the 1/3 and 2/3 points of the height of liquid level when height of liquid level is lower than 1/2 of total gauging height.
3.3.1.4Measurement duration:
Light oil: no less than 5 min;
Lubricant oil: no less than 7 min;
Crude oil, heavy oil, fuel oil and high-temperature lubricant oil etc.: no less than 10 min.
3.3.1.5Pick up the kit after the specified time limit in tank and read the scale (keep the oil in kit); when reading, keep the view line horizontally aligned with the indicating scale; read and record the smaller scale, then larger scale.
3.3.2 Temperature determination of pipes
Temperature of crude oil should be measured in oil conveying pipes.
3.3.2.1Measuring point should be near to the pump outlet.
3.3.2.2Measure as follows and take the average of each measurement as the average temperature of oil.
a. Total oil-conveying time: no longer than 2 hours. Take measurements respectively 10 minutes after the oil flows through the measuring point after conveying, at the intermediate time and 10 minutes before the end of conveying;
b. Total oil-conveying time: 2~24 hours. Take a measurement 10 minutes after the oil flows through the measuring point after conveying, then a measurement every one hour;
c. Total oil-conveying time: more than 24 hours. Take a measurement 10 minutes after the oil flows through the measuring point after conveying, then a measurement every two hours.
3.4 Sampling
3.4.1 Oil tank sampling
Sample of liquid petroleum products should be taken in oil tank according to the SY 2001-77 Petroleum products -- Sampling method.
3.4.1.1Wash the sampler with to-be-sampled oil before sampling.
3.4.1.2Lay down the sampler into the tank to the sampling point; when the sampler is filled with oil, take it out and pour the oil sample into labeled clean bottle.
3.4.2 Pipe sampling
Sample of crude oil should be taken in oil conveying pipe.
3.4.2.1Sampling point should be near to the pump outlet.
3.4.2.2Sampling pipe is installed as follows:
a. Horizontally installed on vertical pipes or installed in flowing area of horizontal pipes with a 90 degree angle (Re>2000)
b. 45 degree slant at the input end of sampling pipe should be in the same direction as the flowing direction and the slant center of input end should be at the 1/3 point of caliper;
c. Exposed part of sampling pipe should be very short.
3.4.2.3Take time scale samples from pipe sampler as follows and mix each sample with the equal volume to be an intermittent sample.
a. Total oil-conveying time: no longer than 2 hours. Take samples respectively 10 minutes after the oil flows through the measuring point after conveying, at the intermediate time and 10 minutes before the end of conveying;
b. Total oil-conveying time: 2~24 hours. Take a sample 10 minutes after the oil flows through the measuring point after conveying, then a sample every one hour;
c. Total oil-conveying time: more than 24 hours. Take a sample10 minutes after the oil flows through the measuring point after conveying, then a sample every two hours.
3.4.2.4 Take some to-be-sampled oil to clean the sampler before sampling, and then collect the sample in sample container or collector.
3.4.2.5Keep the temperature of sampling pipe when taking high freezing point samples to avoid solidification.
3.5 Density Determination
Density of petroleum products is determined according to the GB 1884-80 Petroleum and petroleum products -- Density determination method (Hydrometer method). Density and temperature of each taken sample should be measured twice and reading of hydrometer should be correct to 0.0001 g/cm3, temperature to 0.2℃.
3.6 Determination of Water Cut in Crude Oil
Water cut in crude oil is determined according to the GB 260-77 Petroleum products -- Determination method of water cut. Water cut of crude oil in percentage is the average value of two results of parallel determination of water cut which is made necessary for samples.
4. Petroleum Volume Calculation
4.1 Calculation of Density
In table I of GB 1885-80 standard -- Petroleum apparent density conversion table, apparent density (ρ’t) of petroleum products measured by hydrometer under t ℃ is converted to be standard density (ρ20).
4.2 Calculation of Standard Volume
4.2.1 If given the gauged oil height, content volume Vc will be got according to the oil tank volume table.
4.2.2 If given the gauged water height, volume of bottom water Vw will be got according to the oil tank volume table.
4.2.3 Volume increment △Vp under the static pressure is:
△Vp = △ Vwater * D204
Wherein:
△Vp -- volume increment of petroleum products in tank under static pressure;
△ Vwater -- volume increment of water under static pressure;
D204 -- ratio of petroleum standard density and pure water density under 4 ℃ (ρ20) .
4.2.4 If the difference between petroleum temperature and standard temperature is no more than +/- 10℃, petroleum volume (Vt) should be:
Vt = Vc + △Vp - Vc-water
4.2.5 If the difference between petroleum temperature and standard temperature is more than +/- 10℃, petroleum volume (Vt) should be:
Vt = (Vc + △Vp - Vc-water) * [1 + 0.000036(t - 20)]
Wherein:
0.000036 -- volumetric expansion coefficient of tank (1/℃)
t -- temperature of steel plate of tank, which can be oil temperature.
4.2.6 Standard volume (V20) of petroleum products under 20℃:
V20 = K * Vt
Wherein:
K -- petroleum volume coefficient in GB 1885-80 standard Table II A -- Petroleum volume coefficient table.
4.2.7 Standard volume (V20) is:
V20= Vt [1 -- f (t - 20)]
Wherein:
f -- petroleum volume-temperature coefficient (1/℃) in CB 1885-80 Table II B Petroleum volume-temperature coefficient table.
4.2.8 K and f should be round up after the fifth decimal point when calculating to reduce value difference. Result calculated with K prevails if differences exist between the results calculated in above two methods.
4.3 Calculation of Mass
Effect of air buoyancy should be considered when gauging the petroleum with weight in air, and then the mass (M) in vacuum is conversed to weight (m) in air.
4.3.1 If given the correct value of air buoyancy, the computing formula should be:
m = ( ρ20 -- 0.0011) * V20 (1)
wherein: 0.0011 -- correct value of air buoyancy of petroleum density (g/cm3).
4.3.2 If given the correct coefficient of air buoyancy, the computing formula should be:
m = ρ20 * V20 *F (2)
wherein: F -- correct coefficient of air buoyancy obtained from GB 1885 -80 Table III B Coefficient table for conversing petroleum mass in vacuum to weight in air according to the standard petroleum density.
4.3.3 Calculation result of formula (2) in 4.3.2 prevails when controversy exists between the calculation result of formula (1) in 4.3.1 and formula (2) in 4.3.2.
4.4 Pure Oil Measurement of Crude Oil
Water content should not be included in crude oil when calculating the oil mass in crude oil transfer measurement. Pure oil in crude oil is calculated as follows:
mc- = m * (1 -- W )
wherein: mc- -- weight of pure oil in crude oil;
m -- weight of mixed crude oil;
W-- water weight percentage in crude oil sample.
5. Notes
5.1 Check that measurement instruments and agents are in good conditions and record while checking.
5.2 Get to well know the tank oil to be gauged before gauging.
5.3 Do not smear chalks on tape of oil gauge when measuring liquid level of strongly volatile light petroleum products.
5.4 Don not use water indicating paper when measuring the height of bottom water in tank.
5.5 Gauge at the uptake of tank.
5.6 Eliminate static when gauging.
5.7 Use explosion-proof lights for illumination.
5.8 Line spark-free metal at the gauging point of tank.
5.9 Do not wear spiked shoes and clothes made of artificial fibers when gauging on tank.
Additional Information:
This specification is proposed and managed by the Transportation & Sales Division of the Ministry of Petroleum Industry of the People’s Republic of China.
This specification is compiled by the compiling team of Petroleum and liquid petroleum products -- Transfer measurement specification.
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