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1、AReference number ISO 13398:1997(E) INTERNATIONAL STANDARD ISO 13398 First edition 1997-12-01 Refrigerated light hydrocarbon fluids Liquefied natural gas Procedure for custody transfer on board ship Hydrocarbures lgers rfrigrs Gaz naturels liqufis Procdure de transfert de garde bord des navires Copy
2、right International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 02:43:39 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 13398:1997(E) ISO 1997 All rights reserved. Unl
3、ess 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 CH-1211 Gen
4、ve 20 Switzerland Internetcentraliso.ch X.400c=ch; a=400net; p=iso; o=isocs; s=central Printed in Switzerland ii ContentsPage 1Scope 1 2Normative references .1 3Definitions .1 4Gauging instruments .2 5Precautions .3 6Custody transfer .4 7Calculation 5 8Sampling .6 9Analysis 6 Annexes ACalculation pr
5、ocedures of correction tables .7 BSafety precautions 11 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 02:43:39 MDTNo reproduction or networking permitted without license from I
6、HS -,-,- ISOISO 13398:1997(E) iii Foreword ISO (the International Organization 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 int
7、erested in a subject for 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. ISO collaborates closely with the International Electrotechni
8、cal 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.
9、International Standard ISO 13398 was prepared by Technical Committee ISO/TC 28, Petroleum products and lubricants, Subcommittee SC 5, Measurement of light hydrocarbon fluids. Annex A forms an integral part of this International Standard. Annex B is for information only. Copyright International Organ
10、ization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 02:43:39 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 13398:1997(E) ISO iv Introduction Loading and discharging of LNG to/from
11、 an LNG carrier is a closed cycle operation performed by providing a vapour return line linking the tanks on board and on shore. This avoids displacement of vapour to the atmosphere. In addition, it may involve two or more shore tanks for easier cargo operation. Therefore, it is normal practice to i
12、mplement the custody transfer on board the LNG carrier to ensure more accurate volumetric determination. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 02:43:39 MDTNo reproducti
13、on or networking permitted without license from IHS -,-,- INTERNATIONAL STANDARD ISOISO 13398:1997(E) 1 Refrigerated light hydrocarbon fluids Liquefied natural gas Procedure for custody transfer on board ship 1 Scope This International Standard specifies methods of custody transfer of LNG on board s
14、hip, using a level gauge for determination of liquid level, thermometers for determination of liquid and/or vapour temperature and pressure gauges for determination of vapour pressure in cargo tanks. 2 Normative references The following standards contain provisions which, through reference in this t
15、ext, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent ed
16、itions of the standards indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 6568:1981, Natural gas Simple analysis by gas chromatography. ISO 6578:1991, Refrigerated light hydrocarbon liquids Static measurement Calculation procedure. ISO 8309:19
17、91, Refrigerated light hydrocarbon fluids Measurement of liquid levels in tanks containing liquefied gases Electrical capacitance gauges. ISO 8310:1991, Refrigerated light hydrocarbon fluids Measurement of temperature in tanks containing liquefied gases Resistance thermometers and thermocouples. ISO
18、 8311:1989, Refrigerated light hydrocarbon fluids Calibration of membrane tanks and independent prismatic tanks in ships Physical measurement. ISO 8943:1991, Refrigerated light hydrocarbon fluids Sampling of liquefied natural gas Continuous method. ISO 10574:1993, Refrigerated light hydrocarbon flui
19、ds Measurement of liquid levels in tanks containing liquefied gases Float-type level gauges. 3 Definitions For the purposes of this International Standard, the following definitions apply. 3.1 “boil-off” gas (BOG): Vapour generated from LNG which is stored under nearly atmospheric pressure condition
20、s at low temperatures (under the influence of heat transfer a certain amount of LNG will evaporate or “boil-off”). Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 02:43:39 MDTNo
21、reproduction or networking permitted without license from IHS -,-,- ISO 13398:1997(E) ISO 2 3.2 closing custody transfer: Custody transfer implemented after loading and discharging LNG, at the loading and discharging ports respectively. 3.3 custody transfer: Measurement of liquid level, liquid and v
22、apour temperature, vapour pressure and analysis of the composition of LNG to be delivered to/from a tank, by which volume and other data are determined to be a basis of payment of cost or assessment of the duty. 3.4 custody transfer system on board ship: A system consisting of a level gauge, thermom
23、eter and pressure gauge, which are used for measurement of liquid level, temperature and pressure of the cargo in tanks for the purpose of custody transfer. 3.5 opening custody transfer: Custody transfer implemented before loading and discharging LNG, at the loading and discharging ports respectivel
24、y. 3.6 thermal correction factor: A factor used to correct the volume of LNG at an arbitrary temperature in a cargo tank to that at the reference temperature. 4 Gauging instruments 4.1 Level gauges 4.1.1 The number of level gauges Each cargo tank shall be equipped with two sets of level gauges, pref
25、erably of different measuring principle: e.g. a float level gauge and a capacitance level gauge. 4.1.2 Installation The level gauges shall be installed at the locations having little effect of sloshing of LNG, and they shall also be calibrated to indicate the depth of the liquid from the tanks lowes
26、t point irrespective of the shape of the cargo tank. The gauge reference point shall be set as low as possible to facilitate measurement of liquid level after discharge at the discharging port, and before loading at the loading port. 4.2 Temperature sensors 4.2.1 The number of temperature sensors To
27、 measure liquid and vapour temperatures of LNG, each cargo tank shall be equipped with five or more temperature sensors. These temperature sensors shall be supported by spare sensors, for emergency use, which are mounted adjacent the temperature sensors. 4.2.2 Installation Two sensors including spar
28、es shall be installed at the tank bottom and the tank top, in order to constantly measure the temperatures of liquid and vapour respectively. The remaining sensors including spares shall be installed at equally spaced distances between the tank bottom and top. All the sensors shall be mounted such t
29、hat they are not affected by the spray of LNG when the spray pumps are in operation. 4.3 Pressure gauges The pressure gauges which measure vapour pressure in the cargo tanks shall be either of the type consisting of a transmitter and receiver or the type with local display. Copyright International O
30、rganization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 02:43:39 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO ISO 13398:1997(E) 3 4.3.1 The number of pressure gauges Each cargo t
31、ank shall be equipped with a pressure gauge of the transmitter type or of the local display type. If a pressure gauge, of either type, has been mounted on the vapour header, this can also be used for the purpose of the custody transfer. 4.3.2 Installation A pressure gauge shall be set at an appropri
32、ate position on the vapour dome and/or the vapour header to accurately measure vapour pressure in the cargo tank. A pressure gauge of the local display type or the pressure transmitter shall be mounted in an appropriate container to shelter it from direct spray of seawater. 5 Precautions This clause
33、 outlines the precautions to be taken prior to berthing an LNG carrier at a loading or discharging port in order to ensure smooth and accurate custody transfer. 5.1 Maintenance To implement custody transfer with an expected precision, the custody transfer system shall always be maintained in good or
34、der and condition. 5.2 Preliminary function test The custody transfer system shall be functionally tested by means of an appropriate measure such as a test-run just before commencement of the custody transfer. 5.3 Operation The custody transfer system shall be operated by a skilled ships officer. 5.
35、4 Use of a VHF radio Unless the custody transfer system control panels are protected by a barrier there is a risk of electrical disturbance which may cause malfunctioning of the system. In this case VHF radios shall not be used near the system control panels when they are in operation. 5.5 Precautio
36、ns against malfunctioning of float level gauge Floats which are wound home at the top of their housing during the voyage shall be put into serviceable condition by lowering the float on to the liquid surface to allow thermal stability before commencement of the custody transfer. 5.6 Condition of the
37、 ship at the time of custody transfer 5.6.1 Pipe lines 5.6.1.1 Delivery lines to be used for loading and/or discharging shall be in volumetrically identical condition at the opening and closing of custody transfer. 5.6.1.2 Vapour lines which are connected to the vapour header line shall be opened to
38、 make the vapour pressure in all cargo tanks the same. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 02:43:39 MDTNo reproduction or networking permitted without license from IH
39、S -,-,- ISO 13398:1997(E) ISO 4 5.6.2 Cargo facilities In advance of the custody transfer, various cargo facilities such as spray pumps in cargo tanks, BOG compressors, etc., which may affect the results of the custody transfer shall be stopped. 5.6.3 Trim and list Trim and list of the ship shall be
40、 kept unchanged while the custody transfer is performed. 6 Custody transfer 6.1 Method This clause sets out the method of custody transfer by using a capacitance level gauge or a float level gauge. It is recommended, in principle, to use the same method for opening and closing custody transfer. If t
41、he level gauge normally used is inoperative at the time of opening custody transfer, necessitating use of the alternative level gauge, the latter shall be used again at the time of closing custody transfer even when the level gauge normally used has been corrected. 6.2 Measurement of liquid level Pr
42、ior to measurement of the liquid level, observe the ships draughts on the fore, aft, port and starboard side by draught marks or other suitable means. This will verify the ships trim and list and whether trim and list corrections are required: make sure that the ships vapour lines to the boilers and
43、 shore tanks have been closed. 6.2.1 Capacitance level gauge (see ISO 8309) The liquid level in each cargo tank shall be measured at least five times at appropriate intervals which have been programmed into the processor unit, or by manual operation where the system has no automatic scanning program
44、me. 6.2.2 Float level gauge (see ISO 10574) 6.2.2.1 The liquid level in each cargo tank shall be measured at least five times. 6.2.2.2 The liquid level in the cargo tank shall be kept higher than the floating point of the float level gauge, at the time of the opening custody transfer at the loading
45、and the closing custody transfer at the discharging ports, respectively. 6.2.2.3 Before measurements, the float shall be wound up to the top storage position and the maximum indication compared to that noted at the time of the last inspection to ascertain that the float level gauge is functioning pr
46、operly. 6.2.3 Determination of the corrected liquid level 6.2.3.1 Where the capacitance level gauge is used for measurement of the liquid level in cargo tanks, apply the trim corrections and the list corrections as required to its arithmetic mean value to obtain the true level. 6.2.3.2 Where the flo
47、at level gauge is used, in addition to the above corrections, apply a thermal correction factor to correct the measurement error due to contraction of the floats suspending tape or wire. If the liquid density of the LNG to be measured is different from that on which the immersion level of the float
48、has been adjusted, apply the corrected immersion level to correct measurement error due to a change in the floats immersion level. See A.6.1 and A.6.2. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=NASA Technical Standards 1/9972545001 Not for Resale, 04/21/2007 02:43:39 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO ISO 13398:1997(E) 5