Designation:D1298–99e2
MPMS Chapter8.3Mixing and Handling of Liquid Samples of Petroleum and Petroleum Products(ASTM Practice D5854)
2.3Institute of Petroleum Standards:7
IP389Determination of wax appearance temperature (WAT)of middle distillate fuels by differential ther
mal analysis(DTA)or differential scanning calorimetry(DSC) IP Standard Methods Book,Appendix A,Specifications–IP Standard Thermometers
editorially2.4ISO Standards:8
ISO649-1Laboratory glassware–Density hydrometers for general purpose–Part1:Specification
3.Terminology
3.1Definitions of Terms Specific to This Standard:
3.1.1density,n—the mass of liquid per unit volume at15°C and101.325kPa with the standard unit of measurement being kilograms per cubic metre.
3.1.1.1Discussion—Other reference temperatures,such as 20°C may be used for some products or in some locations.Less preferred units of measurement;for example,kg/L or g/mL are still in use.
3.1.2relative density(specific gravity),n—the ratio of the mass of a given volume of liquid at a specific temperature to the mass of an equal volume of pure water at the same or different temperature.Both reference temperatures shall be explicitly stated.
3.1.2.1Discussion—Common reference temperatures in-clude60/60°F,20/20°C,20/4°C.The historic deprecated term specific gravity may still be found.
3.1.3API gravity,n—a special function of relative density (specific gravity)60/60°F,represented by:
°API5141.5/~sp gr60/60°F!2131.5(1) 3.1.3.1Discussion—No statement of reference temperature is required,as60°F is included in the definition.
3.1.4observed values,n—values observed at temperatures other than the specified reference temperature.These values are only hydrometer readings and not density,relative density (specific gravity),or API gravity at that other temperature. 3.1.5cloud point,n—temperature at which a cloud of wax crystalsfirst appears in a liquid when it is cooled under specific conditions.
3.1.6pour point,n—lowest temperature at which a test portion of crude petroleum or petroleum product will continue toflow when it is cooled under specified conditions.
3.1.7wax appearance temperature(WAT),n—temperature at which waxy solids form when a crude petroleum or petroleum product is cooled under specified conditions.
4.Summary of Test Method
4.1The sample is brought to a specified temperature and a test portion is transferred to a hydrometer cylinder that has been brought to approximately the same temperature.The appropriate hydrometer,also at a similar temperature,is lowered into the test portion and allowed to settle.After temperature equilibrium has been reached,the hydrometer scale is read,and the temperature of the test portion is taken. The observed hydrometer reading is reduced to the reference temperature by means of the Petroleum Measurement Tables.If necessary,the hydrometer cylinder and its contents are placed in a constant temperature bath to avoid excessive temperature variation during the test.
5.Significance and Use
5.1Accurate determination of the density,relative density (specific gravity),or API gravity of petroleum and its products is necessary for the conversion of measured volumes to volumes or masses,or both,at the standard reference tempera-tures during custody transfer.
5.2This test method is most suitable for determining the density,relative density(specific gravity),or API gravity of low viscosity transparent liquids.This test method can also be used for viscous liquids by allowing sufficient time for the hydrometer to reach equilibrium,and for opaque liquids by employing a suitable meniscus correction.
5.3When used in connection with bulk oil measurements, volume correction errors are minimized by observing the hydrometer reading at a temperature close to that of the bulk oil temperature.
5.4Density,relative density(specific gravity),or API grav-ity is a factor governing the quality and pricing of crude petroleum.However,this property of petroleum is an uncertain indication of its quality unless correlated with other properties.
5.5Density is an important quality indicator for automotive, aviation and marine fuels,where it affects storage,handling and combustion.
6.Apparatus
6.1Hydrometers,of glass,graduated in units of density, relative density,or API gravity as required,conforming to Specification E100or ISO649-1,and the requirements given in Table1.
6.1.1The user should ascertain that the instruments used for this test conform to the requirements set out above with respect to materials,dimensions,and scale errors.In cases where the instrument is provided with a calibration certificate issued by a recognized standardizing body,the instrument is classed as certified and the appropriate corrections listed shall be applied
7Available from Institute of Petroleum,61New Cavendish St.,London,W1M 8AR,UK.
8Available from American National Standards Institute,11W42nd St.,13thfloor, New York,NY10036.
TABLE1Recommended Hydrometers
Units Range Scale A Meniscus
Total
Each
Unit
Interval A Error A Correction
Density,kg/m3at15°C600-1100
600-1100
600-1100
20
50
50
0.2
0.5
1.0
60.2
60.3
60.6
+0.3
+0.7
+1.4 Relative density(specific
gravity)60/60°F
0.600-1.100
0.600-1.100
0.600-1.100
0.020
0.050
0.050
0.0002
0.0005
0.001
60.0002
60.0003
60.0006
+0.0003
+0.0007
+0.0014 Relative density(specific
gravity),60/60°F0.650-1.1000.0500.000560.0005
API−1-+101120.160.1
A Interval and Error relate to
Scale.
to the observed readings.Instruments that satisfy the require-ments of this test method,but are not provided with a recognized calibration certificate,are classed as uncertified.6.2Thermometers ,having range,graduation intervals and maximum permitted scale error shown in Table 2and conform-ing to Specification E 1or IP Appendix A.
6.2.1Alternate measuring devices or systems may be used,provided that the total uncertainty of the calibrated system is no greater than when using liquid-in-glass thermometers.
6.3Hydrometer Cylinder ,clear glass,plastic (see 6.3.1),or metal.The inside diameter of the cylinder shall be at least 25mm greater than the outside diameter of the hydrometer and the height shall be such that the appropriate hydrometer floats in the test portion with at least 25mm clearance between the bottom of the hydrometer and the bottom of the cylinder.6.3.1Hydrometer cylinders constructed of plastic materials shall be resistant to discoloration or attack by oil samples and shall not affect the material being tested.They shall not become opaque under prolonged exposure to sunlight.
6.4Constant-Temperature Bath ,if required,of dimensions such that it can accommodate the hydrometer cylinder with the test portion fully immersed below the test portion liquid surface,and a tem
perature control system capable of maintain-ing the bath temperature within 0.25°C of the test temperature throughout the duration of the test.
6.5Stirring Rod ,optional,of glass or plastic,approximately 400mm in length.
7.Sampling
7.1Unless otherwise specified,samples of non-volatile petroleum and petroleum products shall be taken by the procedures described in Practices D 4057(API MPMS Chapter 8.1)and D 4177(API MPMS Chapter 8.2).
7.2Samples of volatile crude petroleum or petroleum prod-ucts are preferably taken by Practice D 4177(API MPMS Chapter 8.2),using a variable volume (floating piston)sample receiver to minimize any loss of light components which may affect the accuracy of the density measurement.In the absence of this facility,extreme care shall be taken to minimize these losses,including the transfer of the sample to a chilled container immediately after sampling.
7.3Sample Mixing —may be necessary to obtain a test portion representative of the bulk sample to be tested,but precautions shall be taken to maintain the integrity of the sample during this operation.Mixin
g of volatile crude petro-leum or petroleum products containing water or sediments,or both,or the heating of waxy volatile crude petroleum or petroleum products may result in the loss of light components.The following sections (7.3.1to 7.3.4)will give some guidance on sample integrity maintenance.
7.3.1Volatile Crude Petroleum and Petroleum Products Having an RVP Greater than 50kPa —Mix the sample in its original closed container in order to minimize the loss of light components.
N OTE 1—Mixing volatile samples in open containers will lead to loss of light components and consequently affect the value of the density obtained.
7.3.2Waxy Crude Petroleum —If the petroleum has a pour point above 10°C,or a cloud point or WAT above 15°C,warm the sample to 9°C above the pour point,or 3°C above the cloud point or WAT,prior to mixing.Whenever possible,mix the sample in its original closed container in order to minimize the loss of light components.
7.3.3Waxy Distillate —Warm the sample to 3°C above its cloud point or WAT prior to mixing.
7.3.4Residual Fuel Oils —Heat the sample to the test temperature prior to mixing (see 8.1.1and Note 4).
7.4Additional information on the mixing and handling of liquid samples will be found in Practice D 5854(API MPMS Chapter 8.3).
8.Procedure
8.1Temperature of Test :
8.1.1Bring the sample to the test temperature which shall be such that the sample is sufficiently fluid but not so high as to cause the loss of light components,nor so low as to result in the appearance of wax in the test portion.
N OTE 2—The density,relative density or API gravity determined by the hydrometer is most accurate at or near the reference temperature.
N OTE 3—The volume and density,the relative density,and the API corrections in the Petroleum Measurement Tables are based on the average expansions of a number of typical materials.Since the same coefficients were used in compiling each set of tables,corrections made over the same temperature interval minimize errors arising from possible differences between the coefficient of the material under test and the standard coefficients.This effect becomes more important as temperatures diverge from the reference temperature.
N OTE 4—The hydrometer reading is obtained at a temperature appro-priate to the physico-chemical characteristics of the material under test.This temperature is preferably close to the reference temperature,or when the value is used in conjunction with bulk oil measurements,within 3°C of the bulk temperature (see 5.3).
8.1.2For crude petroleum,bring the sample close to the reference temperature or,if wax is present,to 9°C above its pour point or 3°C above its cloud point or WAT,whichever is higher.
N OTE 5—For crude petroleum an indication of the WAT can be found using IP 389,with the modification of using 50µL 65µL of sample.The precision of WAT for crude petroleum using this technique has not been determined.
9.Apparatus Verification or Certification
9.1Hydrometers and thermometers shall be verified in accordance with the procedures in Annex A1.
10.Procedure
10.1Bring the hydrometer cylinder and thermometer to within approximately 5°C of the test temperature.
10.2Transfer the sample to the clean,temperature-stabilized hydrometer cylinder without splashing,to avoid the
TABLE 2Recommended Thermometers
Scale Range Graduation Interval
Scale Error °C −1-+380.160.1°C −20-+1020.260.15°F
−5-+215
0.5
6
0.25
formation of air bubbles,and minimize evaporation of the lower boiling constituents of more volatile samples. (Warning—Extremelyflammable.Vapors may causeflash fire!)
10.3Transfer highly volatile samples by siphoning or water displacement.(Warning—Siphoning by mouth could result in ingestion of sample!)
10.3.1Samples containing alcohol or other water-soluble materials should be placed into the cylinder by siphoning. 10.4Remove any air bubbles formed after they have col-lected on the surface of the test portion,by touching them with
a piece of cleanfilter paper before inserting the hydrometer.
10.5Place the cylinder containing the test portion in a vertical position in a location free from air currents and where the temperature of the surrounding medium does not change more than2°C during the time taken to complete the test. When the temperature of the test portion differs by more than 2°C from ambient,use a constant temperature bath to maintain an even temperature throughout the test duration.
10.6Insert the appropriate thermometer or temperature measurement device and stir the test portion w
ith a stirring rod, using a combination of vertical and rotational motions to ensure uniform temperature and density throughout the hy-drometer cylinder.Record the temperature of the sample to the nearest0.1°C and remove the thermometer/temperature mea-suring device and stirring rod from the hydrometer cylinder. N OTE6—If a liquid-in-glass thermometer is used,this is commonly used as the stirring rod.
10.7Lower the appropriate hydrometer into the liquid and release when in a position of equilibrium,taking care to avoid wetting the stem above the level at which itfloats freely.For low viscosity transparent or translucent liquids observe the meniscus shape when the hydrometer is pressed below the point of equilibrium about1to2mm and allowed to return to equilibrium.If the meniscus changes,clean the hydrometer stem and repeat until the meniscus shape remains constant.
10.8For opaque viscous liquids,allow the hydrometer to settle slowly into the liquid.
10.9For low viscosity transparent or translucent liquids depress the hydrometer about two scale divisions into the liquid,and then release it,imparting a slight spin to the hydrometer on release to assist in bringing it to restfloating freely from the walls of the hydrometer cylinder.Ensure that the remainder of the hydrometer stem,which is above the liquid level,is not wetted as liquid on the stem affects the reading obtained.
10.10Allow sufficient time for the hydrometer to come to rest,and for all air bubbles to come to the surface.Remove any air bubbles before taking a reading(see10.4).
10.11If the hydrometer cylinder is made of plastic,dissi-pate any static charges by wiping the outside with a damp cloth.(Warning—Static charges often build up on plastic cylinders and may prevent the hydrometer fromfloating freely.)
10.12When the hydrometer has come to restfloating freely away from the walls of the cylinder,read the hydrometer scale reading to the nearest one-fifth of a full scale division in accordance with10.12.1or10.12.2.
10.12.1For transparent liquids,record the hydrometer read-ing as the point on the hydrometer scale at which the principal surface of the liquid cuts the scale by placing the eye slightly below the level of the liquid and slowly raising it until the surface,first seen as a distorted ellipse,appears to become a straight line cutting the hydrometer scale(see Fig.1).
10.12.2For opaque liquids record the hydrometer reading at the point on the hydrometer scale to which the sample rises,by observing with the eye slightly above the plane of the surface of the liquid(see Fig.2).
N OTE7—When testing opaque liquids using a metal hydrometer cylinder,accurate readings of the hydrometer scale can only be ensured if the liquid surface is within5mm of the top of the cylinder.
10.13Immediately after recording the hydrometer scale reading,carefully lift the hydrometer out of the liquid,insert the thermometer or temperature measurement device and stir the test portion vertically with the stirring rod.Record the temperature of the test portion to the nearest0.1°C.If this temperature differs from the previous reading(10.6)by more than0.5°C,repeat the hydrometer observations and thermom-eter observations until the temperature becomes stable within 0.5°C.If a stable temperature cannot be obtained,place the hydrometer cylinder in a constant temperature bath and repeat the procedure from
10.5.
FIG.1Hydrometer Scale Reading for Transparent
Liquids
10.14If the test temperature is higher than 38°C,allow all hydrometers of the lead shot-in-wax type to drain and cool in a vertical position.
11.Calculation
11.1Apply any relevant thermometer corrections to the temperature reading observed in 10.6and 10.13and record the average of those two temperatures to the nearest 0.1°C.
11.2For opaque samples,apply the relevant meniscus correction given in Table 1to the observed hydrometer reading (10.12.2)as hydrometers are calibrated to be read at the principal surface of the liq
uid.
N OTE 8—The meniscus correction for a particular hydrometer in use is determined by observing the maximum height above the principal surface of the liquid to which liquid rises on the hydrometer scale when the hydrometer in question is immersed in a transparent liquid having a surface tension similar to that of the sample under test.For hydrometers specified in this test method,the corrections in Table 1are approximate.
11.3Apply any hydrometer correction to the observed reading and record the corrected hydrometer scale reading to the nearest 0.1kg/m 3in density,0.0001g/mL,kg/L or relative density,or 0.1°API.
11.4If the hydrometer has been calibrated at a temperature other than the reference temperature,use the equation below to correct the hydrometer scale reading:
r r 5
r t
1–@23310–6
~t –r !–2310–8~t –r !2#
(2)
where:
r r =hydrometer reading at the reference temperature,r °C,
and
r t =hydrometer reading on the hydrometer scale whose
reference temperature is t °C.
11.5Convert the corrected hydrometer scale reading to density,relative density or API gravity using the appropriate parts of the Petroleum Measurement Tables referenced in Guide D 1250according to the nature of the materials under test.Table 3gives some examples of relevant table numbers in the Petroleum Measurement Tables.
11.5.1The strictly correct procedure for the conversion is to use the computer implementation procedures contained in the Petroleum Measurement Tables and not the printed tables.If the printed tables are used,ensure that all errata discovered since original publication have been included in the v
ersion used.The tables include corrections for soda-lime glass expan-sion and contraction of the hydrometer over the temperature range,and thus the observed hydrometer reading is added directly after correction (11.2-11.4)as necessary.
11.5.2To convert densities expressed in kg/m 3to densities expressed in g/mL or kg/L,divide by 103.
11.5.3To convert hydrometer readings from one unit to another,Tables 51(density at 15°C),21(relative density at 60/60°F)or 3(API gravity),referenced in Guide D 1250,are appropriate.
12.Report
12.1Report the final value as density,in kilograms per cubic metre,at the reference temperature,to the nearest 0.1kg/m 3.12.2Report the final value as density,in kilograms per litre or grams per millilitre at the reference temperature,to the nearest 0.0001.
12.3Report the final value as relative density,with no dimensions,at the two reference temperatures,to the nearest 0.0001.
12.4Report the final value as API gravity to the nearest 0.1°API.
13.Precision and Bias
13.1Precision —The precision of the method as determined by statistical examination of interlaboratory results is as follows:
13.1.1Repeatability —The difference between two test re-sults,obtained by the same operator with the same apparatus under constant operating conditions on identical test material,would in the long run,in the normal and correct operation of the test method,exceed the values in Table 4only in one case in
twenty.
FIG.2Hydrometer Scale Reading for Opaque Fluids
TABLE 3Example PMT Table Numbers
Material
Density at 15°C kg/m 3Density at 20°C kg/m 3Relative Density at 60/60°F
°API
Crude petroleum 53A 59A 23A 5A Petroleum products 53B 59B 23B 5B Lubricating oils
53D
59D
–
5D
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