Determination of density with a hydrometer. State System for Ensuring the Uniformity of Measurements Density of oil. Requirements for methods for performing measurements with a hydrometer during accounting operations Determination of the density of oil products with a hydrometer
Determination of the density of oil, oil products is performed by hydrometers according to GOST 3900-85 in a sample taken from a tank, tank or tank. In the work, hydrometers of the AN, ANT1 type are used with a division value of 0.5 kg / m 3 according to GOST 18481-81E.
The essence of the method is to immerse the hydrometer in the product under test and take readings on the hydrometer scale at the test temperature. The readings are counted along the upper meniscus, since the hydrometers AN and ANT1 are calibrated to the upper meniscus (see Fig. 4.1)
Rice. 4.1 - Determination of the density of oil products with a hydrometer
The cylinders can be glass or metal, and their dimensions allow the hydrometer to float. Cylinders are established on a plain flat surface.
Thermometers must comply with GOST 28498 type A liquid or type TIN5 in accordance with GOST 400-80 with a division value of 0.1 ° C.
It is allowed to measure the temperature of the test sample before and after measuring the density using a hydrometer thermometer, for accurate measurements - with an additional thermometer. In this case, it is allowed to measure the temperature on the tank, and measure the density in the brought sample in the laboratory, bringing the test temperature in the laboratory to the temperature of the tank.
The reading on the hydrometer scale corresponds to the density of the product at the test temperature.
To measure the amount of oil or oil products from a known volume, the density is determined at the temperature at which the volume is measured.
GOST 3900-85 has Appendix 1, according to which density values are converted from the measured temperature to density values at 20 to fill out passports or convert volume and density to standard conditions (20 ° C, Rg = 0).
GOST 3900-85 defines density measurement at atmospheric pressure. In order to take into account the pressure in the pipeline, if necessary, in addition to GOST 3900-85, guidelines MI 2153-2001, which determine the procedure for converting hydrometer readings at atmospheric pressure and any temperature to temperature and pressure at which the volume is known, and has an application for converting density from temperature t ° C to 15 ° C at atmospheric pressure, since at present, 15 ° C, Rg \u003d 0, are considered standard conditions.
The recalculation of density, taking into account temperature and pressure, is carried out according to formula 4.5:
, (4.5)
ρ ar is the density measured with a hydrometer;
β – coefficient of volumetric expansion, gr -1;
t ar - temperature when measuring density with a hydrometer, ° С;
t is the temperature at which the volume was measured;
γ – oil compressibility factor, MPa -1, given in MI;
P is the excess pressure at which the volume is determined.
Density is determined in a sample taken from tanks, containers, pipelines, railway and road tanks.
For the quantitative assessment of oil, oil products by the volume-mass static method, the sampling operation is as important as the determination of density.
Sampling is regulated by GOST 2517-85.
Since, as a rule, oil is subject to transportation through pipelines, gasolines with a saturated vapor pressure below 750 mm Hg. Art. (below 100 kPa), then from this GOST we will be interested in the information that relates to these oils and oil products.
Sampling of the product with P h.p.<750 мм рт. ст. из резервуаров типа РВС производится:
Stationary samplers with a perforated sampling tube located inside the tank from the measuring hatch to the bottom of the tank. To ensure that the mixing of all parts of the product along the height of the tube meets the required ratio between the top, middle and bottom, perforations (holes) are made at a distance in accordance with fig. 4.2;
Stationary samplers providing product selection from three levels;
Portable samplers, which may be metal, metal-braided bottles, temperature-controlled.
For horizontal tanks and cisterns, manual samplers are generally used.
For sampling from pipelines, automatic and manual samplers are used.
Schemes of sampling devices are shown in fig. 4.2 - 4.5.
Rice. 4.2 - Sampling device with perforated tube
1 - the maximum level of the product;
2 – reservoir body;
3 - perforated rack;
Rice. 4.3 - Sampling device with sampling from three levels
1 - float;
2 - bearing articulated arm;
3, 4, 5 – sampling tubes open at the upper end;
6 - hinge;
7 - sampling valves
Rice. 4.4 - Portable sampler
1 - body with inlet and tube, product included
under the influence of gravity;
2 - cover;
3 - fitting for the outlet of the displaced air
Fig.4.5 - Temperature controlled sampler
1 - bottle;
2 - a frame made of metal strips of bars with a weighted bottom;
3 - plug;
4 - rope cables for lowering the sampler and opening the plug
Temperature controlled samplers consist of a cylinder surrounded by an outer insulating cover. The top of the cylinder is closed with a stopper. Dimensions: height - 250 mm, diameter - 80 mm.
The sampler is used to transfer the sample from the tank to the laboratory if the ambient and product temperatures differ significantly from each other.
All portable samplers must have a mass that ensures their immersion in the liquid layer in the tank with further installation on the bottom of the tank.
For sampling from a pipeline with a diameter greater than 400 mm, five-layer samplers are most often used (Fig. 4.6.). Five tubes located at different distances from the center make it possible to take a sample from 5 points along the diameter of the pipe.
Rice. 4.6 - Five layer samplers
1 - tubes;
2 - cover;
3 – external sampling tube;
4 - valve
Tube diameters:
d 1 - in the center of the pipeline (1 tube);
d 2 - 0.4 diameter from the center (2 tubes);
d 3 - 0.8 diameter from the center (2 tubes).
Ratio d 1:d 2:d 3 = 6:10:13. The calculation of the diameter of the tubes is determined from the condition: the fluid velocity at the inlet to the sampling device must be at least 1/2 and not more than 2 times the flow velocity in the pipeline.
For automatic sampling, it is necessary to assemble an additional circuit, which looks like shown in Fig. 4.7
The sample is pumped by pump 5 and with the help of regulators 6, 7 at certain intervals enters the receiver 8. The locking device 7 is actuated by an electric, pneumatic or electromagnetic actuator, which is activated according to a given program. Crane 4 and receiver 3 are provided for manual sampling when automatic sampling is not working.
Rice. 4.7 - Scheme for automatic sampling
1 - pipeline;
2 – sampling device;
3, 8 – sample receivers;
5 - pump;
6 - regulator;
7 - locking device;
9 - check valve;
The basic rules for sampling from tanks are as follows:
Before sampling, the product is allowed to stand for at least 2 hours, then the sediment of water and contaminants is removed;
Point samples of the product from the VST can be taken by stationary or portable samplers from three levels:
upper - 250 mm from the surface of oil or oil product;
medium - the middle of the height of the column of oil or oil product;
lower - the lower generatrix of the receiving and distributing branch pipe for oil and 250 mm from the bottom of the tank for oil products.
The combined sample for the tank is made up of point samples in a ratio of 1:3:1.
At a level height in the tank of 2000 mm or less, two samples are taken: from the upper and lower layers. The combined sample is obtained by mixing the selected samples in a ratio of 1:1.
If the overflow in the tank is less than 1000 mm, take one sample from the lower level.
Sampling from tanks.
One point sample is taken from the tanks from a level located at a distance of 0.33 of the tank diameter from the bottom generatrix.
For the route, the combined sample is made up of incremental samples taken from every fourth tank car and mixed in equal proportions.
Sampling from pipelines.
A sample of oil or oil product is taken from the pipeline with a stationary five-layer sampler only during the pumping process in the presence of a homogeneous liquid flow. The sampler should preferably be placed on horizontal sections and the sampling device outlet assembly should be placed on top of the pipeline.
Point samples are taken either hourly or through certain volumes of pumped liquid. Consolidated samples per day, per batch (according to production needs) are made up of point samples mixed in equal volumes. Automatic sampling from the pipeline is carried out using the above scheme. The frequency of taking point samples that fall into the general sampler also depends on the production need.
Bottom sampling from tanks, tanks are produced by portable samplers such as the metal portable sampler shown above, the readings of the liquid in which occur due to gravity or, in other words, the pressure force of the liquid column.
Sample storage is also important..
In the operations of acceptance and delivery of petroleum products to the PSP, the combined sample is divided into two parts. One part is analyzed, the other is kept sealed in case of disagreement with the Consumer or Customer in assessing quality or quantity.
When transported on river vessels (tankers), the combined sample is divided into parts according to the number of recipients. One part - for analysis, the other - in case of possible disagreements, the rest are given to the recipients.
For export deliveries by rail or pipeline, the combined sample is divided into three parts: one part for analysis, two parts for disagreement.
Samples must be labeled with:
Sample number according to the journal;
Type of product, TU or GOST for this product;
Name of the supplier enterprise;
Tank number, filling level;
Batch, tank, route number;
Date, time of sampling;
Shelf life;
Position, full name persons who took and sealed the sample.
The neck of the corked bottle is wrapped with polyethylene, tied with a cord, both ends of the cord are threaded into a hole on a plate of hard cardboard or wood, tied, and the ends are either sealed or filled with sealing wax and sealed. Stored in a specially equipped room. Shelf life:
45 days from the date of shipment or delivery;
In the case of export deliveries for oil - 3 months, for oil products - 4 months;
When delivered to the DPRK, China - 6 months.
Determination of the density of oil and oil products
The objective of the workshop is to develop a clear and consistent understanding of the various methods for determining the density of oil and oil products, processing the results obtained and comparing them with the density that meets the requirements of GOST and technical specifications of oil products and passports of the studied oils.
Lab #1 (6 hours)
Determination of relative density with a hydrometer (GOST R 51069-97) and calculation of density in API degrees
Objective: experimental determination of the relative density of oil and liquid petroleum products with a hydrometer, calculation of density in API degrees and comparison of the obtained density data with the requirements of technical specifications for an oil product or with a quality certificate for a specific batch of oil.
Work tasks:
1. master the methodology for determining the relative density of oil and liquid petroleum products with a hydrometer;
3. compare the obtained and processed results with the requirements of technical specifications for an oil product or with a quality certificate for a specific batch of oil.
Density, relative density (specific gravity) or gravity in degrees API is a factor that determines the quality of crude oil and oil products, necessary to convert measured volumes into volumes at standard temperature, in settlement operations for export deliveries of oils and oil products. International crude oil prices are often listed next to API gravity values.
This method for determining density, relative density (specific gravity) or API gravity using a glass hydrometer applies to crude oil, petroleum products, mixtures of oils and liquid petroleum products with a Reid vapor pressure (GOST 1756) of 179 kPa or less.
Equipment, materials and reagents:
· glass hydrometers, graduated in units of density, relative density (specific gravity) or density in degrees API, hydrometers for oil according to GOST 18481;
- glass thermometers for testing oil products of the TIN-5 type according to GOST 400 (when using AN hydrometers) or mercury glass laboratory thermometers of the TL-4 type No. 2 and 3. Thermometers must be calibrated for full immersion;
- hydrometer cylinder made of transparent glass, plastic or metal. To facilitate pouring, the cylinder may have a spout on the rim. The height of the cylinder must be such that the distance from the bottom of the cylinder to the hydrometer is not less than 25 mm. Plastics used to make cylinders for hydrometers should be resistant to discoloration and exposure to oil samples and should not become hazy after prolonged exposure to sunlight or exposure to oil samples;
- thermostat or water bath to maintain the temperature with an error of not more than 0.2 ° C.
Preparing for the test. Sampling is carried out in accordance with GOST R 51069-97. Depending on the properties of the product to be tested, the sample is brought to the test temperature indicated in Table 3. In cases not covered by the table, the sample of the product to be tested is kept at ambient temperature until this temperature is reached.
Table 3 - Test conditions and temperatures
State Scientific Metrological Center
Federal State Unitary Enterprise "All-Russian Research Institute of Metrology
them. DI. Mendeleev"
(GNMTs FSUE "VNIIM named after D.I. Mendeleev")
Gosstandart of Russia
State system ensuring the uniformity of measurements
OIL DENSITY
Requirements for methods for performing measurements with a hydrometer
in accounting transactions
MI 2153-2004
ST. PETERSBURG 2003
DEVELOPED |
State Scientific Metrological Center Federal State Unitary Enterprise All-Russian Research Institute of Metrology named after V.I. DI. Mendeleev |
PERFORMERS |
Domostroeva N.G. - candidate of technical sciences, Gershun M.A. - candidate of technical sciences, Snegov V.S. - candidate of technical sciences |
DEVELOPED |
ZAO IMS Engineering |
PERFORMERS |
Kozhurov V.Yu., Ablina L.V., Dvoryashin A.A. - Candidate of Physical and Mathematical Sciences, Sagdeev R.S. |
APPROVED |
|
REGISTERED |
|
Instead MI 2153-2001 |
2.8 Tanks for taking and transferring oil samples.
2.9 Gasoline solvent according to TU 38.401-67-108.
2.11 Distilled water of single distillation according to GOST 6709.
It is allowed to use other measuring instruments and materials that provide density measurements in accordance with this recommendation.
3 Measurement method
3.1 The methodology outlined in this recommendation is used when determining the mass of oil by the indirect method of dynamic and static measurements in the absence or failure of the in-line density transducer (in-line DP) and to control in-line PP.
3.2 The essence of the method consists in immersing the hydrometer in the tested oil sample, taking readings on the hydrometer scale at the test temperature and converting the hydrometer readings to the temperature and pressure at which the volume of oil is determined. When monitoring in-line PP, the hydrometer readings are recalculated to the temperature and pressure of oil in the density meter at the time of sampling for control.
4 Safety, environmental and operator qualification requirements
When measuring the density of oil, the following safety requirements are observed:
4.1 The room for measuring the density of oil in terms of fire danger is classified as category A. It meets the requirements of the "Fire Safety Rules for Industrial Enterprises" approved by the Main Directorate of Fire Protection of the Ministry of Internal Affairs of Russia.
4.2 The room is equipped with supply and exhaust ventilation devices and fume hoods. Persons performing measurements are provided with personal protective equipment.
4.3 Flammable testing and flushing liquids are placed in metal canisters for storing petroleum products. Canisters are placed in rooms specially designed for storing petroleum products or metal cabinets.
4.4 Persons at least 18 years of age who have been instructed in safety precautions and have studied the operational documentation for the measuring instruments used and this recommendation are allowed to perform measurements.
5 Measurement conditions and preparation for measurement
5.1 All used measuring instruments are verified, have valid verification certificates or impressions of verification marks.
5.2 Measurements are carried out in the block for measuring oil quality parameters (BIK) or in the premises of the testing (analytical) laboratory.
5.3 When performing measurements, the following conditions are observed:
5.4 If the temperature of the oil sample before filling the measuring cylinder differs from the ambient air temperature by more than 3 °C, use a heat-insulated, temperature-controlled or built-in cylinder.
5.6 Filling the measuring cylinder or other container during sampling, packaging and testing is carried out in a closed way using a tube lowered to the bottom.
5.7 Before measurements, the oil sample in the sample receiver or other vessel is mixed without leaking (the capacity of the container and the volume of the sample taken allow for uniform mixing).
5.8 Hydrometers, cylinders, sample receiver and other equipment used are washed with nefras or hot water and dried in air.
6 Taking measurements
7.6 The result of oil density measurements is taken as the value calculated in accordance with paragraph . Numbers are recorded and rounded to four significant digits.
R 50.2.075-2010
State system for ensuring the uniformity of measurements
OIL AND PETROLEUM PRODUCTS
Laboratory Methods for Density, Relative Density, and API Gravity
State system for ensuring the uniformity of measurements. Crude petroleum and petroleum products. Laboratory methods for determination of density, relative density and API gravity
OKS 17.020
75.080
OKSTU 0008
Introduction date 2011-07-01
Foreword
The goals and principles of standardization in the Russian Federation are established by the Federal Law of December 27, 2002 N 184-FZ "On Technical Regulation", and the rules for the application of national standards of the Russian Federation - GOST R 1.0-2004 "Standardization in the Russian Federation. Basic provisions"
Information about recommendations
1 DEVELOPED by the Federal State Unitary Enterprise "All-Russian Research Institute of Metrology named after D.I. Mendeleev"
2 INTRODUCED by the Department of Metrology of the Federal Agency for Technical Regulation and Metrology
3 APPROVED AND PUT INTO EFFECT by Order of the Federal Agency for Technical Regulation and Metrology dated December 28, 2010 N 1135-st
4 INTRODUCED FOR THE FIRST TIME
Information about changes to these recommendations and the text of changes and amendments are published in the monthly published information indexes "National Standards". In case of revision (replacement) or cancellation of these recommendations, a corresponding notice will be published in the monthly published information index "National Standards". Relevant information, notification and texts are also posted in the public information system - on the official website of the Federal Agency for Technical Regulation and Metrology on the Internet
Introduction
Introduction
These recommendations have been developed taking into account the provisions of GOST R 51069-97 "State system for ensuring the uniformity of measurements. Oil and oil products. Method for determining density, relative density and density in API degrees with a hydrometer", GOST 3900-85 "Oil and oil products. Methods for determining density", MI 2153-2004* "GSI Recommendation. Oil Density. Methodology for Performing Measurements with a Hydrometer during Accounting Operations", MI 2823-2004* "GSI Recommendation. Density of Oil Products during Accounting and Calculation Operations. Methodology for Performing Measurements with a Hydrometer and the Program (Tables) for Bringing the Density of Oil Products to the set temperature.
________________
* Documents are the author's development. See the link for more information. - Database manufacturer's note.
1 area of use
These recommendations establish laboratory methods for measuring the density, relative density and density in degrees API of oil, oil products or mixtures of oil and liquid non-petroleum products (hereinafter referred to as oil and oil products) having a saturation vapor pressure (VVP) of not more than 101.325 kPa.
Oil density is measured by hydrometric, pycnometric or vibrational method at standard temperature (20 °C or 15 °C). It is allowed to measure the density of oil at a temperature set on the basis of the physicochemical properties of the test liquid, or close to the temperature of measuring the volume of the liquid, after which the indicators are reduced to a standard temperature, using the tables in the appendix to the manual or recommendations.
These recommendations may be used in accounting transactions.
2 Normative references
These guidelines use normative references to the following standards:
GOST R 8.563-2009 State system for ensuring the uniformity of measurements. Techniques (methods) of measurements
GOST R ISO 5725-2-2002 Accuracy (correctness and precision) of measurement methods and results. Part 2: Basic method for determining the repeatability and reproducibility of a standard measurement method
GOST R ISO 5725-6-2002 Accuracy (correctness and precision) of measurement methods and results. Part 6. Using precision values in practice
GOST R 51330.11-99 (IEC 60079-12-78) Explosion-proof electrical equipment. Part 12: Classification of mixtures of gases and vapors with air according to safe experimental maximum clearances and minimum ignition currents
GOST R 52659-2006 Oil and oil products. Manual sampling methods
GOST R 53228-2008 Scales of non-automatic action. Part 1. Metrological and technical requirements. Tests
GOST 8.207-76 State system for ensuring the uniformity of measurements. Direct measurements with multiple observations. Methods for processing the results of observations. Basic provisions
GOST 12.0.004-90 Occupational safety standards system. Organization of labor safety training. General provisions
GOST 12.1.005-88 System of labor safety standards. General sanitary and hygienic requirements for the air of the working area
GOST 12.1.007-76 Occupational safety standards system. Harmful substances. Classification and general safety requirements
GOST 400-80 Glass thermometers for testing petroleum products. Specifications
GOST 1756-2000 (ISO 3007-99) Oil products. Determination of saturation vapor pressure
GOST 2517-85 Oil and oil products. Sampling methods
GOST 2603-79 Reagents. Acetone. Specifications
GOST 2652-78 Potassium bichromate. Specifications
GOST 3900-85 Oil and oil products. Methods for determining density
GOST 4204-77 Reagents. Sulfuric acid. Specifications
GOST 6709-72 Distilled water. Specifications
GOST 8505-80 Nefras-S 50/170. Specifications
GOST 18481-81 Hydrometers and glass cylinders. General specifications
GOST 22524-77 Glass pycnometers. Specifications
GOST 25828-83 Normal standard heptane. Specifications
GOST 29230-91 (ISO 835-4-81) Laboratory glassware. Pipettes graduated. Part 4. Blow pipettes
Note - When using these recommendations, it is advisable to check the validity of reference standards in the public information system - on the official website of the Federal Agency for Technical Regulation and Metrology on the Internet or according to the annually published information index "National Standards", which was published as of January 1 of the current year , and according to the corresponding monthly published information signs published in the current year. If the reference document has been replaced (modified), then when using these recommendations, one should be guided by the replacing (modified) document. If the referenced document is canceled without replacement, the provision in which the link to it is given applies to the extent that this link is not affected.
3 Terms and definitions
3.1.1 density(density): The ratio of the mass of a substance to the volume it occupies.
NOTE The SI unit for expressing density is kg/m. Less preferred units are: kg/l or g/ml.
3.1.2 relative density(relative density): The ratio of the mass of a given volume of a substance at a certain temperature to the mass of an equal volume of pure water at the same or different temperature. Both temperature values are indicated when recording the results.
Example - (20/20) °C, (60/60) °F, (20/4) °C.
3.1.3 API Gravity (°API): Special function of relative density (specific gravity) (60/60) °F, which is calculated by the formula
When recording the results, the standard temperature is not indicated because 60 °F is included in the definition.
3.1.4 observed readings(observed values): Hydrometer readings observed at a temperature other than the specified standard temperature, but are not density, relative density, or API gravity values at other temperatures.
3.1.5 standard conditions(standard condition): Conditions corresponding to a temperature of 20 °C or 15 °C and an overpressure of zero.
4 Operator qualification requirements
The following persons are allowed to perform measurements:
- who, in accordance with the procedure established in the oil industry, have undergone training and internships in their specialty, qualified as a laboratory assistant, commodity operator, operator of an automatic filling station (gas station) and have access to independent work;
- who have studied these recommendations, operating instructions for the measuring instruments used and auxiliary devices used in the measurement.
5 Safety requirements
5.1 When measuring the density of oil and oil products, the following hazardous and harmful production factors are possible:
- formation of an explosive environment;
- a mixture of vapors of oil and oil products with air, according to the degree of explosiveness, belongs to category II A-T3 according to GOST 51330.11*;
________________
*Probably an original error. Should read: GOST R 51330.11. - Database manufacturer's note.
- gas content in the air of the working area.
According to the degree of impact on the human body (toxicity), oil, depending on the content of hydrogen sulfide in it, belongs to the 3rd hazard class of a harmful substance ("moderately hazardous") or the 2nd hazard class ("highly hazardous"), oil products belong to 4 th hazard class according to GOST 12.1.007.
5.3 Premises for work with oil and oil products must be equipped with general ventilation.
5.4 Persons involved in the performance of measurements must:
- pass a safety briefing in accordance with GOST 12.0.004;
- comply with the safety and fire safety rules established for the object on which measurements are carried out.
5.5 For workers carrying out measurements in accordance with this recommendation, an instruction on labor protection should be developed, which is approved by the head of the structural unit.
Recommendations must be communicated to the performers against signature.
6 Measurement conditions
6.1 When performing measurements of the density of oil and oil products in the laboratory, the following conditions must be met:
Ambient air temperature in the laboratory room |
|
Atmosphere pressure |
(101.3±4.0) kPa; |
Relative humidity of the ambient air in the laboratory room, not more than |
6.2 When measuring the density of oil and oil products at the sampling site (at gas stations, in quality measurement units (BIC) and oil depots), the current values of atmospheric pressure, ambient temperature and humidity are entered into the measurement protocol.
7 Density determination by hydrometric method
The method of determination is based on the action of the hydrostatic law of Archimedes - the depth of immersion of a body in a liquid depends on the density of the liquid.
7.1 The thermometer is immersed in a cylinder filled with the prepared sample of the test product and stirred with a stick to equalize the temperature and density throughout the volume of the cylinder. Record thermometer readings. Then a hydrometer is placed in the cylinder and after the oscillations stop, readings are taken from the hydrometer scale. Hydrometer scale readings refer to standard temperature guidelines and recommendations.
8 Measuring instruments, auxiliary equipment and reagents
8.1 Hydrometers for oil, glass type AN or ANT-1 with a division value of 0.5 kg / m in accordance with GOST 18481 and hydrometers calibrated at 15 ° C according to . Hydrometers calibrated in units of relative density and API gravity in accordance with the specifications according to or according to (see table 1).
Table 1
Unit of measurement |
Measuring range |
Value of division |
Error |
Correction for meniscus |
g/cm at 15°C or 20°C |
||||
kg/m at 15°C or 20°C |
||||
It is allowed to use similar hydrometers that meet the requirements of these recommendations.
8.2 Laboratory glass mercury thermometer type TL-4 with a division value of 0.1 °C according to or a glass thermometer for testing petroleum products of the TIN 5 type with a division value of 0.1 °C according to GOST 400.
Note - If a thermometer according to GOST 400 is used, it must be calibrated for full immersion.
It is allowed to use digital thermometers with a unified output signal that meet the requirements of these recommendations.
8.3 Hydrometers and thermometers must have verification certificates.
8.4 The hydrometer cylinder can be made of transparent glass in accordance with the requirements of GOST 18481 or a double-wall thermostatically controlled hydrometer specially made for density measurements. The inner diameter of the cylinder shall be at least 25 mm greater than the outer diameter of the hydrometer and the height shall be such that when the respective hydrometer is immersed in the test liquid, the gap between the base of the hydrometer and the bottom of the cylinder is at least 25 mm.
8.5 The design of an air or liquid thermostat shall provide the possibility of placing a cylinder for a hydrometer. If a liquid thermostat is used, the surface level of the test liquid in the cylinder shall be lower than the surface level of the liquid in the thermostat. The temperature of the liquid in the thermostat is maintained with an error of no more than 0.2 °C during the entire measurement process.
8.6 A stirrer made of glass shall be at least 400 mm long.
8.7 Filter paper.
8.8 Stands for fixing thermometers in a fixed position in cylinders.
8.9 Tank for taking and transferring samples of oil and oil products in accordance with GOST 2517.
8.10 Gasoline-solvent BR-2 "Galosha" according to.
8.11 Nefras-S 50/170 according to GOST 8505.
8.12 Distilled water according to GOST 6709.
8.13 Rubber or silicone tubing, or other device that allows the sample to be transferred in a closed manner.
It is allowed to use other measuring instruments and technical means similar in purpose and approved for use in the prescribed manner, if their characteristics are similar to the requirements specified in these recommendations.
9 Preparing to take measurements
9.1 Sampling of oil and oil products for analysis in accordance with the requirements of GOST 2517, having a saturated vapor pressure of not more than 40 kPa, is carried out in an open vessel, sampling of oil and oil products with a saturated vapor pressure of more than 40 kPa - in a closed vessel. The volume of the sample must be at least 2 dm. Before filling the measuring cylinder, the sample is divided into two parts.
9.2 When measuring density, in order to avoid errors due to the loss of light fractions, volatile samples of oil and oil products are taken using a sampler with a siphon. In case of its absence, the selected sample is quickly transferred to a container cooled to a temperature of 2 °C and below. Mixing of samples is carried out in a closed container. It is not recommended to mix heavy bituminous mixtures before density measurements.
9.3 A sample taken with an automatic sampler into a sampler container is mixed with a mixer designed to mix the sample in containers of this type. To obtain a representative sample from a test tank, oil and oil products must be mixed in a closed container without leaking.
9.3.1 Oil with a high wax content (greater than 6%)—If the pour point of the oil is about 15 °C, the sample is heated to a temperature 9 °C above the pour point.
9.3.2 If the oil product has a pour point of about 10 °C, or a cloud point, or a crystallization onset temperature of about 15 °C, then the sample is heated to a temperature 9 °C above the pour point or 3 °C above the cloud point or crystallization onset temperature. before mixing.
9.4 Hydrometer, cylinder, sampler and equipment used in measurements are washed with nefras or hot water, rinsed with distilled water and dried in air.
10 Taking measurements
10.1 Test temperature
10.1.1 Bring the sample to the test temperature, which shall be such that the sample is sufficiently liquid (9 °C above the pour point) but not hot (not more than 40 °C) to cause loss of light ends.
Notes
1 Density, relative gravity, or API gravity is determined with a hydrometer to be most accurate at near standard temperature.
2 Volume and density, relative gravity and API gravity are corrected according to guidelines and recommendations based on average expansion coefficients for oil and oil products. Using the coefficients given in the guidelines and recommendations at the sample test temperature results in a reduction in the difference between the coefficient of expansion of the test sample at the test temperature and the coefficient at standard temperature.
10.2 Density measurement
10.2.1 The hydrometer cylinder is placed on a flat, horizontal surface in a place where there are no drafts and the ambient temperature does not change by more than 2 °C during the test. If the temperature of the test sample differs from the ambient temperature by more than 3 °C, use a thermostat to keep the temperature constant during the measurement.
The sample is transferred to a clean, dry hydrometer cylinder in a closed manner with a tube lowered to the bottom to avoid the formation of air bubbles and to ensure minimal evaporation of the low-boiling fractions of the volatile samples.
10.2.2 Before immersing the hydrometer in the cylinder, remove air bubbles from the surface of the sample with clean filter paper.
10.2.3 Immerse the stirrer into the sample to be tested, combining vertical movement with rotation of the stirrer to equalize the temperature throughout the cylinder. Remove the stirrer from the cylinder. Then, a stirring stick, an automatic thermometer sensor or a mercury thermometer are immersed in the cylinder, fixing it so that the section of the scale corresponding to the temperature of the test sample is 5-10 mm above the liquid level. Record the sample temperature to the nearest 0,1 °C and remove the thermometer from the cylinder.
10.2.4 Depending on the physicochemical properties of the product to be tested, the sample is brought to the test temperature given in Table 2 and transferred to the hydrometer cylinder.
table 2
Type of tested product |
Product Feature |
Test temperature |
volatile |
Saturated vapor pressure below 180 kPa |
Cool in a closed vessel to 2 °C and below |
medium volatility |
The initial boiling point is not higher than 120 ° C |
Cool in a closed vessel to 20 ° C and below |
Medium volatility and viscous |
The initial boiling point is not higher than 120 ° C, the viscosity is more than 10000 mm / s at 20 ° C |
Heated to pour point |
non-volatile |
Boiling point above 120 °C |
Tested at any temperature not exceeding 90 ° C |
In cases not listed in Table 2, the sample is kept at ambient temperature until the test temperature is reached.
10.2.5 The hydrometer is taken by the upper end of the rod, free from the scale, and immersed in the test sample until 2-3 divisions remain before the intended mark of the hydrometer scale, then the rod is released with a slight rotational movement. In this case, the hydrometer should not touch the walls of the cylinder and the part of the rod located above the immersion level of the hydrometer remained dry and clean. For clear liquids with low viscosity, check the shape of the meniscus. To do this, the hydrometer is immersed approximately 1-2 mm below the equilibrium position and then returned to its original position. If the shape of the meniscus changes, clean the hydrometer scale with 2-3 drops of nefras and repeat the operation until the shape of the meniscus stops changing.
10.2.6 For opaque viscous (kinematic viscosity greater than 200 mm/s) liquids, the hydrometer is slowly immersed in the liquid until a stable hydrometer reading is obtained.
10.2.7 After the oscillations of the hydrometer stop, take readings of the hydrometer scale with an accuracy of 0.1 kg/m.
10.2.8 For transparent liquids, readings are taken along the liquid dividing line of the hydrometer scale in accordance with Figure 1, while the position of the observer's eyes should be at the level of the meniscus.
Figure 1 - Indication of the hydrometer scale for transparent liquids
1 - liquid, 2 - point of recording readings, 3 4 - meniscus
Figure 1 - Indication of the hydrometer scale for transparent liquids
10.2.9 For opaque liquids (Figure 2), the hydrometer scale reading is read along the upper edge of the meniscus (in this case, the position of the observer's eyes should be at the level of the meniscus). When using hydrometers graduated along the lower edge of the meniscus, a correction for the meniscus is introduced into the hydrometer readings in accordance with Table 3.
Table 3 - Meniscus Corrections
Density measurement range, kg/m |
Scale division value |
Correction for meniscus |
Figure 2 - Hydrometer scale reading for opaque liquids
1 - liquid, 2 - point of recording readings, 3 - horizontal surface 4 - meniscus
Figure 2 - Hydrometer scale reading for opaque liquids
10.2.10 After taking readings, the hydrometer is carefully removed from the liquid, the thermometer or digital thermometer sensor is placed in the cylinder and the test liquid is mixed by moving the stirrer vertically. Record the temperature of the test sample to the nearest 0,1 °C. If this temperature differs from that originally measured in accordance with 10.2.3 by more than 0,5 °C, repeat the hydrometer and thermometer measurements until the temperature stabilizes within 0,5 °C.
If a stable temperature cannot be ensured, place the hydrometer cylinder in a thermostat.
NOTE If the test temperature is higher than 38 °C, hydrometers with lead sinkers covered with wax are left to drain in an upright position after use.
10.2.11 Repeat the steps of 10.2.1-10.2.9 using the second part of the sample.
11 Processing measurement results
11.1 The hydrometer readings are recalculated to standard conditions (at a temperature of 20 ° C or 15 ° C) in accordance with the manual and recommendations.
11.2 The result of measuring the density of the test liquid is taken as the value calculated according to 10.2.9. Record the mean of the two temperatures to the nearest 0.1 °C, record the density value obtained from the hydrometer to the nearest 0.1 kg/m, 0.0001 g/cm or 0.1 °API.
If the discrepancies between the obtained results of density measurements in the two parts of the sample do not exceed , both measurement results are considered acceptable and the arithmetic mean of the two readings is taken as the final observed reading.
If the discrepancies between the obtained sample readings exceed , then the acceptability of the hydrometer readings is checked in accordance with GOST R ISO 5725-6.
If the temperature of measuring the density of the test liquid with a hydrometer differs from the calibration temperature of 20 °C or 15 °C by more than ± 3.0 °C, a correction for the expansion of the hydrometer glass is introduced into the hydrometer readings: .
For hydrometers calibrated at 20 °C, the coefficient is calculated by the formula
* The numbering corresponds to the original. - Database manufacturer's note.
For hydrometers calibrated at 15 °C, the coefficient is calculated by the formula
11.3 Corrected readings of the hydrometer scale for density, relative density or density in API degrees are converted to standard conditions (at a temperature of 20 ° C or 15 ° C) using tables for measuring indicators of oil and oil products in accordance with the manual and recommendations.
11.4 The density value in kg/m is converted to the density value in g/ml or kg/l by dividing by 10.
11.5 Record the final value of density expressed in kg/m at standard temperature to 0.1, expressed in kg/l or in g/ml, record to 0.0001.
The final density value in relative units at two standard temperatures is recorded with an accuracy of 0.0001.
The final density value, expressed in degrees API, is recorded to the nearest 0.1 °API.
11.6 When performing accounting operations, the hydrometer readings are recalculated to the conditions for measuring volume according to the formula
Where - oil density values in the first and second parts of the sample according to hydrometer readings, recalculated to the conditions for measuring the volume or density of oil, kg / m;
- indication of the hydrometer taking into account the correction for the meniscus, kg/m;
- correction for the expansion of the hydrometer glass, calculated in accordance with formulas (3) and (4);
- thermometer reading when measuring density with a hydrometer, °С;
- coefficient of volumetric expansion of oil and oil products, the values of which are given in the recommendations, Appendix D (tables D.1 and D.2);
- temperature of oil and oil products during volume measurements, °С;
- coefficient of compressibility of oil and oil products, the values of which are given in the recommendations, Appendix B (tables B.1 and B.2);
- overpressure of oil when measuring volume (density), MPa.
Recalculation of hydrometer readings according to formula (5) can be carried out at values of temperature difference () not exceeding ±10 °С. If the temperature difference exceeds the specified values, the program is used to recalculate the hydrometer readings in accordance with the recommendations; in this case, the correction for the thermal expansion of the glass from which the hydrometer is made is introduced automatically.
11.7 Evaluation of the excluded systematic error in measuring the density of oil and oil products with a hydrometer, due to the evaporation of light fractions during sampling and analysis, is carried out in accordance with Appendix A.
12 Accuracy values of the hydrometric method
12.1 Limit of repeatability (convergence)
Two results of determining the density of two parts of the test liquid sample, obtained by one performer using the same equipment under the same conditions, are recognized as reliable with a confidence probability of 0.95, if the discrepancy between them does not exceed the values \u200b\u200bspecified in Table 4.
Table 4 - Convergence
Test temperature range, °С |
Repeatability limit, kg/m |
|
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Vladimir Khomutko
Reading time: 4 minutes
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How to determine the absolute and relative density of oil and oil products?
The density of oil and oil products is one of the most important characteristics of oil and oil products, which is why the accuracy of its determination is so important.
There are two indicators of this parameter - absolute and relative.
The absolute density of oil and oil products is the amount of mass per unit volume. It is measured in grams, kilograms and tons per cubic centimeter or meter (g/cm3, kg/m3). The determination of this indicator is carried out at 20 degrees Celsius.
Relative density is the ratio of the density of light oil products, or the density of oil and dark oil fractions, to the value of this parameter for distilled water at certain temperatures of both liquids. This indicator does not have a unit of measurement. In our country, it is determined at 20 degrees, and distilled water - at 4.
This indicator can be determined by the following methods:
- determination by hydrometer and densimeter;
- pycnometric method;
- calculation method.
Measuring the density of an oil product using a hydrometer and a densimeter
Hydrometers measure both the density of oil and oil products and their temperature, and densimeters measure only the density of oil products. This method is regulated by GOST 3900 - 85 and consists in the fact that a calibrated hydrometer is immersed in the test product, and then the readings are read on the instrument scale under the current research conditions. After that, the result obtained is brought to a normal value at 20 degrees (there is a special table for this).
These measuring instruments have the following limits (g/cm³):
- aviation gasoline - from 0.65 to 0.71;
- motor gasoline - from 0.71 to 0.77;
- kerosene - from 0.77 to 0.83;
- diesel fuel and oils (industrial) - from 0.83 to 0.89;
- dark oils and petroleum products - from 0.89 to 0.95.
The research process is as follows:
№ | Useful information |
---|---|
1 | the glass cylinder is placed on a flat surface |
2 | then a pre-taken sample of the test product is poured into it in such a way that air bubbles do not form and there is no loss of volume due to evaporation |
3 | bubbles that appear on the surface are removed with filter paper |
4 | measure the temperature of the sample before and after measurement, using the same hydrometer, or, in the case of a densimeter, with a separate device (the temperature of the sample must be constant with deviations of no more than 0.2 degrees) |
5 | carefully lower a dry and clean device into the vessel, holding it by the upper end |
6 | when the meter stops oscillating, read the upper or lower meniscus (depending on calibration) |
7 | the result obtained is the density of oil or oil product under current conditions |
8 | the temperature of the test is rounded up to the nearest, which is in the table |
9 | according to the same table, using the results obtained, determine the indicator of this parameter of the oil product at 20 ° Celsius |
The essence of the method is that a sample of the tested product is poured into a pycnometer, which is a graduated vessel, then it is heated (or cooled) to 20 ° and weighed on special scales, the error of which is not more than 0.0002 grams. The result obtained is a relative indicator.
Such a calculation is based on the dependence of this parameter on the temperature of the oil product.
Calculation sequence:
- from the passport of the product under study, an indicator of its density at 20 ° is taken;
- measure the average temperature of the test product;
- calculate the difference between the result and 20°, rounding it to the nearest integer;
- in a special table, a correction for one degree of deviation is found, which corresponds to the passport value of the parameter at plus 20 °;
- the resulting constitutive correction is multiplied by the temperature difference;
- the result obtained is added to the passport if the temperature of the study is below 20 °, or subtracted from it if T> 20.
0,650…0,659 – 0,000962; 0,660…0,669 – 0,000949; 0,670…0,679 – 0,000936;
0,680…0,689 – 0,000925; 0,6900…0,6999 – 0,000910; 0,7000…0,7099 – 0,000897;
0,7100…0,7199 – 0,000884; 0,7200…0,7299 – 0,000870;0,7300…0,7399 – 0,000857;
0,7400…0,7499 – 0,000844; 0,7500…0,7599 – 0,000831; 0,7600…0,7699 – 0,000818;
0,7700…0,7799 – 0,000805; 0,7800…0,7899 – 0,000792; 0,7900…0,7999 – 0,000778;
0,8000…0,8099 – 0,000765; 0,8100…0,8199 – 0,000752; 0,8200…0,8299 – 0,000738;
0,8300…0,8399 – 0,000725; 0,8400…0,8499 – 0,000712; 0,8500…0,8599 – 0,000699;
0,8600…0,8699 – 0,000686; 0,8700…0,8799 – 0,000673; 0,8800…0,8899 – 0,000660;
0,8900…0,8999 – 0,000647; 0,9000…0,9099 – 0,000633; 0,9100…0,9199 – 0,000620;
0,9200…0,9299 – 0,000607; 0,9300…0,9399 – 0,000594; 0,9400…0,9499 – 0,000581;
0,9500…0,9599 – 0,000567; 0,9600…0,9699 – 0,000554; 0,9700…0,9799 – 0,000541;
0,9800…0,9899 – 0,000528; 0,9900…1,000 – 0,000515.
To better understand this technique, consider an example.
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