LIQUEFIED PETROLEUM GAS SAMPLING PROCEDURES First Edition 2010 Copyright of SIGTTO, Bermuda ISBN: 978 1 905331 99 4 British Library Cataloguing in Publication Data Society of International Gas Tanker & Terminal Operators Limited. Bermuda. Liquefied Petroleum Gas Sampling Procedures Notice of Terms of Use While the advice given in this document has been developed using the best information currently available, it is intended purely as guidance to be used at the owner’s own risk. No responsibility is accepted by the Society of International Gas Tanker and Terminal Operators Ltd, or by any person, firm, corporation or organisation who or which has been in any way concerned with the furnishing of information or data, the compilation, publication or authorised translation, for the accuracy of any information or advice given herein or for any omission herefrom or for any consequences whatsoever resulting directly or indirectly from the compliance with or adoption of guidance contained herein even if caused by a failure to exercise reasonable care. Published by Witherby Seamanship International Ltd 4 Dunlop Square, Livingston Edinburgh, EH54 8SB Scotland, UK Tel No: +44(0)1506 463 227 Fax No: +44(0)1506 468 999 Email: info@emailws.com www.witherbyseamanship.com Printed and bound in Great Britain by Bell & Bain Ltd, Glasgow III CONTENTS Taking Samples of Liquefied Gas Cargoes ????????????????????????????????????????????????????????????????????????????????????????????????????????1 Summary ???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????3 1. The Basic Reasons why Cargo Samples are Taken ..............................................................4 2. Sampling Systems – ‘Open Loop’ or ‘Closed Loop’ Systems ...................................5 3. The Standard Type of Containers Used to Obtain and Transport Samples ........................................................................................................................................................9 4. Standard for Sampling Connection Fittings ..............................................................................10 5. The Procedures Involved in Taking Samples .............................................................................13 Bibliography ?????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????16 5 Taking Samples of Lique?ed Gas Cargoes 2? Sampling Systems – ‘Open Loop’ or ‘Closed Loop’ Systems Ships’ cargo tanks are normally fitted with several sample connections so that samples may be taken at several different levels. ‘Top’, ‘middle’ and ‘bottom’ samples are common, and these are of great assistance when checking vapour displacement operations, such as inerting or ‘gassing up’ for example. The lower connections can also be used to take liquid samples if there is a suitable pressure in the cargo tanks. This is not possible with fully refrigerated cargoes, where it is necessary to take samples using the cargo pump, usually recirculating product back to the same tank. Liquid sampling connections should be fitted with two valves to ensure isolation should one be blocked by ice or hydrates, etc, and terminate in a standard connection. The recommended design is shown on page 10. During sampling, venting to atmosphere should always be minimised, although it is recognised that a small, controlled amount of cargo vapour may be released during purging of sample points and when creating an ullage in sample containers. Any such purging, venting or ullaging of sample containers must be carried out in a safe location, taking into account the properties of the product, wind and weather conditions, and proximity of sources of ignition and ventilation intakes, etc. 6 Taking Samples of Lique?ed Gas Cargoes If the sample system has only an inlet connection to the sample container, it will always be necessary to vent small quantities of cargo to atmosphere. This is known as an ‘open loop’ system. If a second connection is provided so that product can be returned to the cargo tanks, this arrangement is known as a ‘closed loop’ system and, if used with a sample container with inlet and outlet connections, minimises the amount of product vented to atmosphere. If the main hazard from the product to be sampled is its flammability, open sampling may be used provided that due care is taken to reduce the amount of product release to an absolute minimum. However, if the cargo has toxic risks, eg VCM or butadiene, then SIGTTO recommends the use of ‘closed loop’ sampling to avoid release of the material to atmosphere. The return path of this closed loop should also be fitted with double shut-off valves. These return valve(s) should be operated full open or closed and should not be used for throttling/flow control during the sampling process.