EN ISO 4256:1998

SLOVENSKI STANDARD
01-november-1999
1DGRPHãþD
SIST EN ISO 4256:1998
8WHNRþLQMHQLQDIWQLSOLQL'RORþHYDQMHSDUQHJDWODND0HWRGD813,62
Liquefied petroleum gases - Determination of gauge pressure - LPG method (ISO
4256:1996)
Flüssiggase - Bestimmung des Dampfdruckes - LPG-Verfahren (ISO 4256:1978)
Gaz de pétrole liquéfiés - Détermination de la pression de vapeur - Méthode GPL (ISO
4256:1978)
Ta slovenski standard je istoveten z: EN ISO 4256:1998
ICS:
75.160.30 Plinska goriva Gaseous fuels
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

INTERNATIONAL
STANDARD
Second edition
1996-I O-l 5
Liquefied petroleum gases -
Determination of gauge vapour pressure -
LPG method
DBtermination de la pression de vapeur
Gaz de p&role liqu@fi& -
Mkthode GPL
relative -
Reference number
IS0 4256: 1996(E)
IS0 4256: 1996(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide fed-
eration of national standards bodies IS0 member bodies). The work of
preparing International Standards is normally carried out through IS0
body interested in a subject for
technical committees. Each membe
which a technical committee has been established has the right to be
represented on that committee. International organizations, governmental
and non-governmental, in liaison with ISO, also take part in the work. IS0
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard IS0 4256 was prepared by Technical Committee
lSO/lC 28, Petroleum products and lubricants.
This second edition cancels and replaces the first edition (IS0 4256:1978),
which has been technically revised.
Annexes A and B form an integral part of this International Standard.
0 IS0 1996
All rights reserved. Unless otherwise specified, no part of this publication may be
reproduced or utilized in any form or by any means, electronic or mechanical, including
photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland
ii
INTERNATIONAL STANDARD @ IS0 IS0 4256: 1996(E)
Liquefied petroleum gases - Determination of gauge
vapour pressure - LPG method
WARNING - The use of this International Standard may involve hazardous materials, operations and
equipment. This standard does not purport to address all of the safety problems associated with its use. It
is the responsibility of the user of this International Standard to establish appropriate safety and health
practices and determine the applicability of regulatory limitations prior to use.
of IEC and IS0 maintain registers of currently valid In-
1 Scope
ternational Standards.
This International Standard describes a method for the
IS0 3007: 1986, Petroleum products - Determination
determination of gauge vapour pressures of liquefied
of vapour pressure - Reid method.
petroleum gas products (see clause 3) at temper-
atures within the approximate range of 35 “C to 70 “C.
IS0 4257:1988, Liquefied petroleum gases - Method
of sampling.
NOTES
I Information on the vapour pressure of liquefied petro-
leum gases is required for the selection of properly de-
signed storage vessels, shipping containers and customer
3 Definitions
utilization equipment, to ensure the safe handling of these
products, and to ensure that maximum operating design
For the purposes of this International Standard, the
pressures are not exceeded under the foreseen ambient
following definitions apply.
operating conditions.
2 The vapour pressure of liquefied petroleum gases is an
3.1 vapour pressure: Pressure exerted by the va-
indirect measure of the lowest temperature at which initial
pour of a liquid when in equilibrium with the liquid.
vaporization can be expected to occur. It may also be con-
sidered to be an indirect indication of the most volatile con-
stituent present in the product.
In this International Standard, the term “vapour press-
ure” shall be understood as gauge vapour pressure,
which is absolute vapour pressure minus atmospheric
pressure.
2 Normative references
The following standards contain provisions which, 3.2 liquefied petroleum gas (LPG): Hydrocarbon
gas that can be stored and/or handled in the liquid
through reference in this text, constitute provisions of
this International Standard. At the time of publication, phase under moderate conditions of pressure and at
ambient temperature. It consists essentially of C3 and
the editions indicated were valid. All standards are
CJ alkanes or alkenes, or a mixture of these, contains
subject to revision, and parties to agreements based
on this International Standard are encouraged to in- generally less than 5 % by liquid volume of material of
higher carbon number, and has a gauge vapour pres-
vestigate the possibility of applying the most recent
sure not exceeding approximately 1 600 kPa at 40 “C.
editions of the standards indicated below. Members
IS0 4256: 1996(E) @ IS0
designated as the upper and lower chambers, comply-
4 Principle
ing with the requirements of 5.1 .I to 5.1.7. If the “air
chamber” and the “20 % lower chamber” of the
The test apparatus, equipped with a pressure gauge,
method described in IS0 3007 are used, which are
is purged and then filled completely with an aliquot of
interchangeable with the corresponding chambers in
the test sample. A given volume of the liquid content
this method, the apparatus assembly shall pass a hy-
of the apparatus is withdrawn, and the apparatus im-
drostatic test (7.3) before being used for testing lique-
mersed in a water bath maintained at the test tem-
fied petroleum gases.
perature. The observed gauge pressure at equilibrium,
corrected for gauge error and ambient barometric
pressure, is recorded.
The volume ratios of the chambers shall be deter-
mined in accordance with annex A of IS0 3007:1986.
5 Apparatus
5.1 Vapour
pressure apparatus, constructed as
illustrated in figure 1 d consisting of two chambers,
Gauge
Straight-through valve
T
Gauge couplin
Lower chamber
Bleeder-valve
coupling
\ Inlet valve
Upper chamber
Figure 1 - Typical apparatus for measuring LPG vapour pressure
@ IS0 IS0 4256: 1996(E)
NOTE - Any method of coupling the chambers may be
51.1 Upper chamber, consisting of a cylindrical
employed provided that the volumetric requirements are
vessel of inside dimensions 51 mm & 3 mm in diam-
met and that the assembly is free from leaks under the
eter and 254 mm + 3 mm in length, with the inner sur-
conditions of the test.
faces of the ends slightly sloped to provide complete
drainage from either end when held in a vertical pos-
ition. At one end of the upper chamber, a suitable
5.2 Pressure gauge
bleeder-valve coupling shall be provided to receive the
bleeder-valve assembly and the pressure gauge. At
A Bourdon-type spring gauge of test gauge quality
the other end of the chamber, an opening approxi-
114 mm to 140 mm in diameter, provided with a
mately 13 mm in diameter shall be provided for
nominal 6 mm male thread connection with a pass-
coupling with the lower chamber. Care shall be taken
ageway not less than 5 mm in diameter from the
that the connections to the end openings do not pre-
Bourdon tube to the atmosphere.
vent the chamber from draining completely.
The range and graduations of the pressure gauge
used shall be governed by the vapour pressure of the
5.12 Lower chamber, 33 1/3 %, a cylindrical vessel
sample being tested, as shown in table 1.
of volume such that the ratio of the volume of the up-
per chamber to the volume of the lower chamber is
The observed gauge readings shall be corrected for
2 + 0,03 (see note 1, 5.1.3).
“gauge error” in accordance with 9.2, either by direct
calibration against a dead-weight tester (5.5), or by the
use of a second gauge certified by a recognized offi-
5.1.3 Lower chamber, 20 %, a cylindrical vessel of
cial body.
volume such that the ratio of the volume of the upper
chamber to the volume of the lower chamber is
Table 1 - Specifications for pressure gauges
4 + 0,05 (see notes 1 and 2).
Gauge specifications
LPG
NOTES
vapour
Scale Maximum Maximum
1 In determining the volumetric capacities of the cham-
pressure
range numbered intermediate
bers, the vo.1um.e of the lower chamber is considered as
intervals
graduations
that which is Mow the “straight-through” valve closure.
kPa kPa
The volume above the “straight-through” valve closure, in-
cluding the portion of the coupling attached to the upper
chamber, is considered as part of the upper chamber vol- 70 3,5
s 655 0 to 700
ume.
0 to 2 000 175
620 to 1 730
2 The apparatus requirements for this method, excluding
0 to 3 500 350
1 660 to 3 460
the bleeder-valve assembly, are identical with those of
IS0 3007 with the exception of the 33 1/3 % lower cham-
ber. Although the test procedure details are different, the
5.3 Vapour pressure bath, of dimensions such that
air and liquid chambers of IS0 3007 may be used in the
the bleeder-valve assembly is completely immersed
present method provided that they are of sufficient
when the vapour pressure apparatus is inserted in an
strength to withstand the higher test pressures (7.3).
upright position.
The bath shall be capable of maintaining the test tem-
5.1.4 Bleeder-valve assembly.
perature within the following limits:
The bleeder-valve for purging the apparatus shall be a
a) for test temperature G 50 “C: + 0,l “C;
nominal 6 mm valve fitted into the side of the bleeder-
valve coupling. The lower end shall be threaded to fit
b) for test temperature > 50 “C: + 0,3 “C.
into the end fitting of the upper chamber, and the
upper end shall be threaded to receive the gauge
coupling.
5.4 Temperature sensor, either a thermometer
conforming to the specifications given in annex A, or a
5.1.5 Valves and coupling.
suitably calibrated electronic measuring device of
equivalent accuracy.
At one end of the lower chamber, an opening ap-
proximately 19 mm in diameter shall be provided to
The thermometer shall be positioned in the bath in
receive a suitable straight-through valve having a
such a manner that it can be viewed throughout the
minimum internal channel of 13 mm diameter. The
test and adjusted so that it is immersed to the test
other end of the chamber shall be equipped with a
temperature graduation mark.
nominal 6 mm inlet valve.
@ IS0
IS0 4256: 1996(E)
7.3 Hydrostatic test
5.4.1 Low-range thermometer, for indicating test
temperatures between 35 “C and 40 “C.
The assembled chambers shall be certified by the
manufacturer to withstand approximately 7 000 kPa
5.42 Middle-range thermometer, for indicating test
gauge hydrostatic pressure without permanent de-
temperatures between 41 “C and 50 “C.
formation.
5.4.3 High-range thermometer, for indicating test
7.4 Leak test
temperatures between 51 “C and 80 “C.
Before placing new apparatus in service, and each
time the apparatus is used after a period of at least a
5.5 Dead-weight tester, of satisfactory range, as a
week of nonutilization, the assembled vapour press-
means of checking the accuracy of vapour pressure
ure apparatus shall be checked for freedom from
gauges.
leaks by filling it with air, natural gas, nitrogen, or
other similar gases, to 3 500 kPa gauge pressure, and
NOTE - If the second gauge (5.2) is certified by a recog-
then completely immersing it in a water bath. Only
nized official body, this apparatus is unnecessary.
apparatus that will withstand this test without leaking
shall be used.
6 Sampling and sample handling
8 Procedure
6.1 Obtain and store samples in accordance with
IS0 4257 unless the test samples are taken directly
8.1 General
from the source of the material to be tested.
For specific hazard statements, see annex B.
6.2 Use any convenient method of coupling the va-
If necessary, chill the apparatus with a portion of the
pour pressure apparatus to the sample source.
material under test to facilitate transfer, either for
purging (8.2) or for introduction of test sample (8.3).
A minimum length of tubing, 6 mm to 7 mm in diam-
Close the inlet valve and open the bleeder-valve to its
eter, of grade appropriate to the pressure range in-
wide-open position. Allow the contained sample to
volved in the test, and made of material corrosion-
evaporate until the apparatus is cooled to well below
resistant to the products being sampled, is satisfac-
the temperature of the sample source. Expel any re-
tory for this purpose. If a flexible tubing connection is
sidual material remaining after this operation from the
used, the tubing shall be made of an electrically con-
apparatus through the bleeder-valve by inverting the
ductive material or constructed with a built-in earth
assembly. Close the bleeder-valve. Return the chilled
(ground) connection to minimize the effect of static
apparatus to its normal upright position, and take the
electricity.
test sample in the manner outlined below.
6.3 Additional safety precautions for the handling of
8.2 Purging
liquefied petroleum gases, given in annex B, shall be
meticulously observed during all the following oper-
ations.
With the assembled apparatus (7.2) in an upright pos-
ition, connect the inlet valve of the lower chamber to
the sample source using the sampling connection
7 Preparation of apparatus (6.2). Open the sample source valve to the apparatus.
Cautiously open the bleeder-valve on the upper cham-
ber, permitting the apparatus to fill with liquid (see
7.1 C
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