1、 CEN EN*ISO*3993 95 3404589 OLL9082 LB7 M BRITISH STANDARD Liquefied petroleum gas and light hydrocarbons - Determination of density or relative density - Pressure hydrometer method The European Standard EN IS0 3993 : 1995 has the status of a British Standard ICs 75.200 NO COPYING WITHOUT BSI PERMIS
2、SION EXCEPT AS PERMITTED BY COPYRIGHT LAW BS EN IS0 3993 : 1996 - CEN EN*ISO*3993 95 3YOY589 OLL9083 Dl13 BS EN IS0 3993 : 1996 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee PlV12, Petroleum measurement and sampiing, up
3、on which the following bodies were represented: Department of Energy (Gas and Oil Measurement Branch) Department of We and Industry (National Engineering Laboratory) Institute of Petroleum Salvage Association The following was also represented in the drafhng of the standard through subcommittees and
4、 panels GAMBICA (BEAMA Ltd.) This British Standard, having been prepared under the direction of the Sector Board for Materiais and Chemicals, was published under the authority of the Standards Board and comes into effect on 15 February 1996 O BSI 1996 Amendments issued since publication Amd.No* ID 1
5、0s Pa = 1 bar = 1,019 72 kgf/cn? 21 At present at the sage of draft. CEN EN*ISO*3993 95 3404589 0339089 531 1500 to 580 kgld 570 to 650 kg/d Alternative ranges Subdivisions 1 kg/d Figured every 5 or 10 kglm3 Page 4 EN IS0 3993 : 1995 0.500 to 0.580 gim1 0,570 to 0,650 g/ml 0.500 to 0.580 0,570 to 0,
6、650 0.001 g/ml 0.001 0,005 or 0,010 g/ml 0,005 or 0,010 4 Apparatus Overall length Bulb diameter Bulb wall thickness Stem diameter Stem wall rhickness Scale length 4.1 Hydrometers, made of glass, graduated in density or relative density, with the appropriate range and conforming to the dimensions gi
7、ven in table 1. 330 mm max. 18 to 20 mm 0.4 to 0.6 mm 8to9mm 0.3 to 0.35 mm 110 to 130 mm NOTE - For the use of thermohydrometers see the annex. Use a certified hydrometer, or calibrate the hydrometers in ac- cordance with clause 7. Calibration corrections should be ap- plied if the scale errors are
8、 in excess of 0,5 of a subdivision of the scale. 4.2 Thermometer, having a sensitivity of at least 2.7 mm/l OC (1.5 mm/l OF) calibrated for total immersion and of suitable dimensions to fit inside the hydrometer cylinder (4.3). A thermometer conforming to ISO/R 653, STL/O.Z/ - 151 +45 is recommended
9、. The thermometer shall be held firmly inside the hydrometer cylinder by means of a suitable clip in such a position as not to interfere with the free motion of the hydrometer. 4.3 Hydrometer cylinder, constructed of glass or trans- parent plastics, for example polymethylmethacrylate or equiv- alent
10、 material, conforming to the design and dimensions given in the figure. The ends shall be tightly sealed by means of chloroprene gaskets and metal end-plates as shown. CAUTlON - As a precautionary measure a protective shield shall be placed around the plastics or glass cylinder. Replace any cylinder
11、s that show any fogging, crazing, cracking, or etching. NOTE - Certain compounds attack plastics and cloud the inner sur- face of the cylinder, making it difficult or impossible to read the hydrometer. Tests have shown no attack by ethane, ethylene, pro- pane, propylene, butane, isobutane, normal bu
12、tylenes, isobutyiene, pentane and isopentane and no attack is expected from butadiene. Users are cautioned, however, always to clean the cylinder thoroughly after each determination. Ketones and alcohols must not be used for cleaning as they attack and weaken plastics whilst aromatics also tend to a
13、ttack the surface of plastics and should similarly not be used. The liquid inlet valve and the liquid outlet valve shall be tightly connected to a base plate which shall be so bored as to give both valves a common inlet to the cylinder. The vapour vent valve shalt be similarly connected to the top p
14、late. All valves shall be 6 mm or equivalent needle valves. The cylinder shall not be operated at a gauge pressure greater than 1.4 MPa i14 bar). 4.4 Water bath, fitted with a thermostat or other means of maintaining the bath at a constant temperature of 15 f 0,2 Oc or 20 k 0.2 OC or 60 I 0.5 OF, an
15、d of such dimensions that the hydrometer cylinder (4.3) can be completely immersed. 5 Reference liquids The following reference liquids are required for calibration of the hydrometer if a certified hydrometer is not available. 5.1 density. NOTE - Propane of densin, 507,6 kglrd (0,507 6 g/ml) at 15 O
16、C or 500.0 kg/m3 10.500 O g/ml) at 20 DC or a relative densiry W OF of 0,507 3 is suitable. Pure propane, having a certified density or relative 5.2 Pure butane. having a certified density or relative densitv. NOTE - Butane of density 584.5 kg/m3 (0.584 5 g/mli at 15 OC or 578.8 kg/m3 (0.578 8 g/ml)
17、 at 20 OC or a relative density 60/60 OF of 0,584 4 is suitable. Table 1 - Ranges and dimensional specification for pressure hydrometers CEN EN*IS0*3993 95 3404587 OLL7090 253 Page 5 EN IS0 3993 : 1995 Dimensions in millimetres as in A) Figure - Pressure hydrometer cylinder CEN EN*ISO*3993 95 340458
18、9 OLL909L L9T Page 6 EN IS0 3993 : 1995 6 Sampling The procedure for sampling for calibration of the apparatus and for subsequent testing is described below. 6.1 Carefully clean and dry the hydrometer (4.11, the ther- mometer 4.21 and the inside wall of the pressure cylinder (4.3). Insert the hydrom
19、eter in the pressure cylinder and attach the thermometer and cover plate. 6.2 Connect the source of supply of the liquid to be tested to the inlet valve by suitable fittings so that a representative sample can be introduced into the cylinder (4.3); ascertain that these connections are free from leak
20、s. Open the outlet valve and purge the sampling connections by opening the inlet valve slightly, permitting the product to flow through the outlet valve at the bottom of the cylinder. 6.3 When the connections have been purged, close the outlet and vent valves and open the inlet valve, permitting the
21、 liquid to enter the cylinder until it is full. If necessary, the vent valve may be opened slightly to permit complete filling of the cylinder, after which it shall be closed. At no time shall the pressure in the cylinder be allowed to rise above a gauge pressure of 1,4 MPa (14 bar). 6.4 When the cy
22、linder has been filled, close the inlet valve and open the outlet valve, permitting the contents of the cylinder to be withdrawn completely and the pressure inside the cylinder to be reduced to that of the atmosphere. 6.5 Close the outlet valve and open the inlet valve, filling the cylinder to a lev
23、el at which the enclosed hydrometer floats freely. If it is necessary to accomplish this filling by venting vapour through the vent valve, repeat the purging to cool the cylinder sufficiently to permit its being filled without the necessity of venting. 6.6 With all valves closed, examine the apparat
24、us for leaks; if leaks are detected, discard the sample, rwuce the pressure to atmospheric and repair the leaks. Repeat the sampling pro- cedure. 7 Calibration of apparatus 7.1 If a hydrometer having a calibration certificate issued by an approved laboratow is not used, the hydrometer shall be calib
25、rated using one of the alternative procedures specified in 7.2 or 7.3 before densities are determined. 7.2 Take three or more samples having different densities in the range of the hydrometer to be tested. Using the procedure specified in clause 8 determine in duplicate for each sample the hydromete
26、r reading on a certified hydrometer. Average the two values for each sample if these do not differ by more than 0.5 kg/m2, or the equivalent. If the duplicate results differ by more than 0.5 kg/m2, or the equivalent, repeat the determina tions. Then obtain the average of duplicate hydrometer reading
27、s on the hydrometer being calibrated following the same procedure. Ensure that the maximum difference in temperature for all these determinations is not more than 0.4 OC (1 OF). Compare the hydrometer readings obtained on the two hydrometers and record any differences as corrections to be applied to
28、 hydrometer readings on the hydrometer being calibrated. 7.3 Use the procedure in clause 8 to determine the density of one of the reference liquids of certified density (see clause 5) at a temperature within f 0.2 OC (0.5 OF) of the certification temperature. Make duplicate determinations and averag
29、e the two results if these do not differ by more than OS kg/mJ, or the equivalent. Deduct the average from the certified density of the reference liquid to obtain the correction to be applied. If the two results differ by more than 0.5 kg/m3, or the equivalent, repeat the determinations. NOTE - This
30、 method provides a check of the hyorometer at only one point on the scale, but this IS often acceptable for routine tening. 8 Procedure 8.1 be tested as specified in clause 6. Prepare the apparatus and take a sample of the liquid to 8.2 Disconnect the cylinder from the source of supply of liquid and
31、 place it in the water bath (4.4) maintained at 15 ? 0,2 OC, 20 I 0,2 OC or 60 k 0.5 OF until thermal equilibrium has been obtained. To accelerate thermal adjust- ment, occasionally remove the cylinder from the water bath, swirl it gently a few times to ensure mixing, and replace it in the water bat
32、h. Exercise care to prevent damage to the hydrometer and thermometer. Measure the temperature of the water bath using a ther- mometer outside the cylinder in order to avoid the effects of pressure on the thermometer inside the cylinder. Use the ther- mometer inside the cylinder to ensure that the li
33、quid under test has reached constant temperature and that the temperature of the liquid does not vary significantly during the determination. 8.3 Remove the cylinder from the water bath (see the notei, stand it on a fim level surface and, while the hydrometer is floating freely, take the hydrometer
34、reading as promptly as possible in the following manner : Observe a point slightly below the plane of the liquid surface and then raise the line of vision until this surface, seen as an ellipse, becomes a straight line. The point where this line cuts the hydrometer scale is the reading of the instru
35、ment. A white card held behind the cylinder just below the liquid level will im- prove the visibility of the surface. Estimate the hydrometer reading to the nearest one-fifth of a subdivision of the scale. NOTE - The cylinder may be left in the water bath, provided thar the hydrometer reading can be
36、 clearly observed in accordance with the re- mainder of this sub-clause. Read the temperature in the cylinder to the nearest 0.2 OC 0,5 OF) immediately before and after reading the hydrometer. If these temperatures differ by more than 0.4 OC (1 OF), repeat the determination. CEN EN*IS0*3993 95 34045
37、89 OLL9092 O26 Hydrometer type Density at 15 OC Density at 20 OC Relative density 60/60 OF 8.4 Immediately after each determination, empty the liquid from the cylinder and vent to reduce the pressure to at- mospheric. Highly volatile liquids and liquefied petroleum gases must not be left in the appa
38、ratus since, at high ambient temperatures, they might generate sufficient pressure to burst the cylinder. a 1,215 7 1,911 x 10-3 1,234 6 1,910 x 10-3 6,753 9 x 10-4 5,898 x 10-7 8.5 This method may be used for measurements in the field at ambient temperatures, with the realisation that the results a
39、re less precise and the precision data in clause 9 may not apply. CAUTION - If so used, the cylinder must be vented and the test discontinued if the pressure in the cylinder rises above a gauge pressure of 1,4 MPa (14 bar). 8.6 Apply hydrometer corrections, if any, to the result. If determinations a
40、re not carried out at the reference temperature correct the results in accordance with the petroleum measure- ment tables referred to in IS0 911) (see notes 1 and 2). NOTES 1 Table 53A should be used for the correction of densities to 15 Oc for corrected densities down to 612 kg/m3 and table 23A for
41、 the cor- rection of reiative densities to 60/80 OF for corrected relative densities down to 0,612; for values below these ranges and down to the equivalent of 500 kg/m3 10.500 glrnl) at 15 OC, reference should be made to the corresponding tables in the 1952 edition of API 2540. ASTM D 1250 and IPj.
42、M), and to tables 33 and 34 of ASTM D 1250-80; table A in the Addendum to ISO/R 912) should be used for the correction of density to n) OC. 2 Suitable conversions of corrected hydrometer readings with buta- diene from test temperature 1-20 to 60 OC) to reference temperature are given by the equation
43、 et = hydrometer reading + altl - I) + (i1 - fi2 or d, = hydrometer reading + a(rl - f) + Bitt - f)2 where Q is the density in kilograms per cubic metre at 15 OC or 20 OC; f is the reference temperature of 15 OC, 20 OC M 60 OF; i1 is the temperature at which the hydrometer reading was taken; a and ,
44、 are the coefficients taken from table 2, corresponding to the type of soda-lime3) glass hydrometer usad; d, is the relative density 60/60 OF. Page 7 EN IS0 3993 : 1995 9 Precision The precision of the method, as obtained by statistical ex- amination of interlaboratory test results, is as follows :
45、9.1 Repeatability The difference between successive test results, 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 following value only in on
46、e case in twenty : densin/ 1 kg/d or 0.001 g/ml relative density 0,001 9.2 Reproducibility The difference between two single and independent results, obtained by different operators working in different laboratories on identical test material, would in the long run, in the normal and correct operati
47、on of the test method, exceed the following value only in one case in twenty : density 3 kg/d or O,G3 g/ml relative density 0,003 10 Test report The test report shall contain the following information a) reference to this International Standard; b) the value of the corrected reading, to the nearest
48、1 kg/rn3, or equivafent; C) whether the value reported is density or relative density: d) if density, the unit and temperature (see 2.1 i; e) if relative density, the temperatures I, and r2 (see 2.21; f) the method used for hydrometer calibration !see clause 71. 1) IS0 91, Petroleum measurement fabl
49、es. 2) In course of revision as IS0 91 12. 3) Calculate for glass having a thermal cubic expansion coefficient of 25 x 10-6 K-1. CEN EN*IS0*3993 95 = 3404589 OLL9093 Tb2 = Page 8 EN IS0 3993 : 1995 Annex Use of thermohydrometers (Forms part of the Standard.) In certain circumstances, in particular for measurements in the field, thermahydrometers may be more convenient to use. Thermohydrometers of suitable range and of dimensions such that they float freely within the pressure cylinder (minimum clearances : at walls 5 mm, at top and bottom
