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1、Reference number ISO 4257:2001(E) ISO 2001 INTERNATIONAL STANDARD ISO 4257 Second edition 2001-07-15 Liquefied petroleum gases Method of sampling Gaz de ptrole liqufis Mthode dchantillonnage Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aram
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5、r bodies. In the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below. ISO 2001 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 mec
6、hanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs member body in the country of the requester. ISO copyright office Case postale 56 ? CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.ch Web www.
7、iso.ch Printed in Switzerland ii ISO 2001 All rights reserved Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/23/2007 08:51:51 MDTNo reproduction or networking permitted without license from IHS -,-,- IS
8、O 4257:2001(E) ISO 2001 All rights reservediii ContentsPage Foreword.iv 1Scope 1 2Term and definition .1 3Principle1 4General considerations for obtaining a representative sample .1 5Safety precautions.2 6Apparatus.3 7Preparing the sample container.4 8Procedure.4 Bibliography7 Copyright Internationa
9、l Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/23/2007 08:51:51 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 4257:2001(E) iv ISO 2001 All rights reserved Foreword ISO (the International Organ
10、ization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been establish
11、ed 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. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
12、 International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3. 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
13、the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. International Standard ISO 4257 was prepared by Techn
14、ical Committee ISO/TC 28, Petroleum products and lubricants, Subcommittee SC 3, Static petroleum measurement. This second edition cancels and replaces the first edition (ISO 4257:1988), of which it constitutes a technical revision. Copyright International Organization for Standardization Provided by
15、 IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/23/2007 08:51:51 MDTNo reproduction or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARDISO 4257:2001(E) ISO 2001 All rights reserved1 Liquefied petroleum gases Method of sampling WARNING The use of
16、 this International Standard may involve hazardous materials, operations and equipment. This International Standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health and enviro
17、nment protection practices and determine the applicability of regulatory limitations prior to use. 1Scope This International Standard specifies the procedure to be used for obtaining samples of unrefrigerated liquefied petroleum gases (LPG). It is suitable for sampling from bulk containers, to provi
18、de samples for laboratory testing of products covered by ISO 9162. This International Standard is applicable for the provision of samples for compositional analysis by ISO 7941. It is not applicable for the provision of samples for trace analysis of low-boiling components. If trace analysis of low-
19、boiling components is required, a variable-volume receiver such as that described in ASTM D 3700 should be used. 2Term and definition For the purposes of this International Standard, the following term and definition applies. 2.1 liquefied petroleum gases LPG petroleum gases that can be stored and/o
20、r handled in the liquid phase under moderate conditions of pressure and at ambient temperature NOTEThese gases consist predominantly of propane, propene, butanes and butenes, with small proportions of ethane, ethene and/or pentanes and pentenes. They are normally described in terms of the predominan
21、t hydrocarbon, e.g. commercial butane or commercial propane. 3Principle A liquid sample is transferred from the source into a sample container through a transfer line by purging the container and filling it with liquid, then providing a liquid ullage so that 80 % (V/V) of the container volume remain
22、s filled with liquid. NOTEFor the purposes of this International Standard, the term “% (V/V)“ is used to represent the volume fraction. 4General considerations for obtaining a representative sample Great care is required to obtain a representative sample, especially if the material to be sampled is
23、a mixture of liquefied gases. The following factors shall be taken into account. a)Take samples from the liquid phase only. b)Avoid sampling from the bottom of a vessel. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not
24、for Resale, 04/23/2007 08:51:51 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 4257:2001(E) 2 ISO 2001 All rights reserved c)The contents of tanks can be non-homogeneous. Homogeneity can be improved by circulating the contents prior to sampling. A waiting period of 30
25、min is recommended after circulation before sampling to permit settling of any aqueous material and to allow dissipation of any static charge that may have developed. d)When sampling from pipelines under flow conditions, the pressure in the line needs to be above vapour pressure to avoid two-phase c
26、onditions. 5Safety precautions 5.1General Because of the hazards involved, liquefied gases shall be sampled only by, or under the supervision of, persons familiar with the necessary safety precautions. Three areas of safety shall be considered: a)safety at the sampling point; b)safety of the contain
27、er; c)safety during transport. 5.2Safety at the sampling point Care shall be taken to avoid contact by liquid LPG with the skin. Protective gloves and goggles shall be worn, and care shall be taken to avoid breathing vapours. Discharge of LPG can give rise to static electricity. Equipment shall be e
28、lectrically grounded or bonded to the LPG tank before commencing and throughout the sampling operations. During purging and ullaging, safe means for disposal of waste vapours and liquids shall be provided. Compliance with local safety requirements and environmental regulations is necessary. 5.3Safet
29、y of the container Sample containers for use under pressure shall have been pressure-tested and shall be in accordance with national or local regulations, and the maximum safe operating pressure shall be marked on the container. Sampling operators shall ensure that the pressure rating of the contain
30、er is suitable for use with the product to be sampled and the conditions under which it is to be handled. Containers shall have been checked for gas tightness. Containers shall not be overfilled. There shall always be sufficient ullage space to allow liquid expansion under all storage and transport
31、conditions. Carefully follow the procedure in clause 8, especially 8.4. Before use, check that the valves and pressure cylinder are not damaged. It is recommended that a frame collar, preferably square-shaped, be fitted around each valve to protect it from accidental damage during use, transport and
32、 storage. Containers shall be placed in a cool location, shaded from direct sunshine, as soon as possible after taking the sample. Keep the sample cool until testing is completed or provide a means of avoiding excessive variation in its temperature. 5.4Safety during transport Precautions shall be ta
33、ken to protect the integrity of the container by packing the container in a crate in accordance with regulatory requirements and by using a protective cap on the valves so that accidental unseating of the valves or tampering with them is prevented. It is recommended that valves should always be capp
34、ed. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/23/2007 08:51:51 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 4257:2001(E) ISO 2001 All rights reserved3 6Apparatus 6.
35、1Sample container Use metal sampling containers and fittings of a type that ensure maximum safety and are corrosion-resistant to the product being sampled. A suitable material is stainless steel; an aluminium sample container shall not be used. The size of the container depends upon the amount of sa
36、mple required for the laboratory tests that are to be made. If the container is to be transported, it shall conform to national or international regulations for the transportation of hazardous materials. The sampling container shall be of the two-valve type with an ullage tube as shown in Figure 1.
37、The end of the container at which the ullage tube is fitted shall be clearly and indelibly marked. The length of the tube is such that the volume V1(see Figure 1) represents 20 % (V/V) of the total capacity of the container. Total capacity = V1?V2, with V2= 4?V1. Single-valve containers shall not be
38、 used (see note 1 hereafter). Clearly label the cylinder with the following information: ?cylinder number; ?place at which the sample was taken; ?ships name (if appropriate); ?ships tank number (if appropriate); ?shore tank number (if appropriate); ?method of sampling; ?date and time of sampling; ?d
39、escription of the product; ?initials or other identifying mark of the operator; ?destination of the cylinder; ?any further information relevant to the laboratory concerning the sample and the condition of the cylinder. NOTE 1The single-valve containers present the following disadvantages: ?without u
40、llage tube, safety is not ensured; ?with ullage tube, they cannot be purged and cleaned adequately with solvents. NOTE 2The valves can be of the same type as those which fit commercially available LPG cylinders. 6.2Sample transfer line Transfer lines shall be made of a material, preferably metal, th
41、at is impervious to the product to be sampled and capable of withstanding without leakage the pressure to which it is exposed in the procedure. They shall be equipped with two valves in addition to that at the product source and those on the container: a control valve (designated A in Figure 2) and
42、a vent valve (designated B in Figure 2). Between valves A and B, a pressure relief valve shall be installed, which shall be vented to a safe place. The transfer line between the T-union directly above the vent valve B which connects to the sample container at valve C in Figure 2 shall be constructed
43、 from “armoured flexible tubing“. 6.3Connection to sample container Use metal sample connectors. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=Aramco HQ/9980755100 Not for Resale, 04/23/2007 08:51:51 MDTNo reproduction or networking permitte
44、d without license from IHS -,-,- ISO 4257:2001(E) 4 ISO 2001 All rights reserved 7Preparing the sample container 7.1If the sample container (6.1) has been used for sampling an uncontaminated product, drain the sample container and proceed as indicated in 7.3. 7.2If the sample container (6.1) has bee
45、n used for sampling a contaminated product, or if the previous use of the sample container is unknown, carry out the operations below in strict order: a)drain the sample container (6.1); b)clean it with volatile solvents (see note hereafter); c)dry it under vacuum; d)purge the air from the container
46、 with clean, dry gaseous propane and maintain this condition by closing the valves. NOTEAs volatile solvents, acetone followed by pentane are preferred. 7.3After being connected to the sample transfer line, the sample container (6.1) shall be purged using procedure 8.2. 8Procedure 8.1Purging the sam
47、ple transfer line Connect the ends of the transfer line to the product source and to the valve C of the container. Close the control valve A, vent valve B and the valve C (see Figure 1). Open the valve at the product source and purge the transfer line by opening the control valve A and the vent valv
48、e B. 8.2Purging the sample container With the container (6.1) in an upright position and its valve D fitted with an ullage tube at the top, close vent valve B and valve C, and open control valve A. Open valve C, and partly fill the container with sample by slowly opening the valve D. Close the control valve A, and allow part of the sample to escape in the vapour phase through valve D. Close valve D and swing the sample container through 180 into the reverse vertical position. Return the container to the upright position with valve D on the