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1、 CGA P-592008 (EIGA Doc 151/08) PREVENTION OF OVERPRESSURE DURING FILLING OF CRYOGENIC VESSELS FIRST EDITION COMPRESSED GAS ASSOCIATION, INC. 4221 Walney Road, 5th Floor Chantilly, VA 20151 Phone: 703-788-2700 Fax: 703-961-1831 E-mail: PAGE ii COMPRESSED GAS ASSOCIATION, INC. CGA P-592008 EIGA DOC
2、151/08 PREFACE As a part of a program of harmonization of industry standards, the Compressed Gas Association (CGA) and the European Industrial Gases Association (EIGA) have consolidated four documents on overpressurization of transportable and static cryogenic pressure vessels during filling into on
3、e document. The CGA version, P-59 Prevention of Overpressure During Filling of Cryogenic Vessels has the same technical content as the EIGA version, EIGA Doc 151/08 Prevention of excessive pressure during filling of cryogenic vessels. However, there are editorial differences in formatting and spelli
4、ng. PLEASE NOTE: The information contained in this document was obtained from sources believed to be reliable and is based on technical information and experience currently available from members of the Compressed Gas Association, Inc. and others. However, the Association or its members, jointly or
5、severally, make no guarantee of the results and assume no liability or responsibility in connection with the information or suggestions herein contained. Moreover, it should not be assumed that every acceptable commodity grade, test or safety procedure or method, precaution, equipment or device is c
6、ontained within, or that abnormal or unusual circumstances may not warrant or suggest further requirements or additional procedure. This document is subject to periodic review, and users are cautioned to obtain the latest edition. The Associa- tion invites comments and suggestions for consideration.
7、 In connection with such review, any such comments or suggestions will be fully reviewed by the Association after giving the party, upon request, a reasonable op- portunity to be heard. Proposed changes may be submitted via the Internet at our web site, . This document should not be confused with fe
8、deral, state, provincial, or municipal specifications or regulations; insurance requirements; or national safety codes. While the Association recommends reference to or use of this document by government agencies and others, this document is purely voluntary and not binding. A listing of all publica
9、tions, audiovisual programs, safety and technical bulletins, and safety posters is available via the Internet at our website at . For more information contact CGA at Phone: 703-788-2700, ext. 799. E-mail: Work Item 06-110 Bulk Distribution Equipment and Standards Committee NOTEAppendix A (informati
10、ve) is for information only. FIRST EDITION: 2008 2008 The Compressed Gas Association, Inc. All rights reserved. All materials contained in this work are protected by United States and international copyright laws. No part of this work may be reproduced or transmitted in any form or by any means, ele
11、ctronic or mechanical including photocopying, recording, or any informa- tion storage and retrieval system without permission in writing from The Compressed Gas Association, Inc. All requests for permis- sion to reproduce material from this work should be directed to The Compressed Gas Association,
12、Inc., 4221 Walney Road, Suite 500, Chantilly VA 20151. You may not alter or remove any trademark, copyright or other notice from this work. CGA P-592008 COMPRESSED GAS ASSOCIATION, INC. PAGE iii EIGA DOC 151/08 Contents Page 1 Introduction.1 2 Scope and purpose1 2.1 Scope 1 2.2 Purpose.1 3 Definitio
13、ns.2 3.1 Definitions2 3.2 Background .2 4 Transport tanks 3 4.1 Filling operation.3 4.2 Preventative measures4 4.3 Recommendations.5 5 Static tanks.5 5.1 Equipment and procedures .5 5.2 Principles for overpressure protection.6 5.3 Examples of overpressure protection6 5.4 Recommendations.7 6 General
14、recommendations.7 6.1 Existing installations8 6.2 Applicable principles and techniques 8 6.3 The role of driver-monitored procedures.8 Appendix Appendix AExample of Fly Wire System (Informative)9 This page is intentionally blank. CGA P-592008 COMPRESSED GAS ASSOCIATION, INC. PAGE 1 EIGA DOC 151/08 1
15、 Introduction This document details the methods that can be used to prevent the overpressurization of both transportable and static cryogenic pressure vessels during filling. It replaces guidance given in two separate and earlier EIGA documents, EIGA Doc 59/98 Prevention of excessive pressure in cry
16、ogenic tanks during filling and EIGA Doc 77/01 Protection of cryogenic transportable tanks against excessive pressure during filling. This document re- places the CGA publications PS-8, Protection of Cryogenic Storage Tanks from Overpressure During Operator- Attended Refill and PS-14, Protection of
17、Cryogenic Transport Vessels from Overpressurization During Opera- tor-Attended Refill. 2 Scope and purpose 2.1 Scope This document is intended to provide guidance to the filler/owner of either transportable or static cryo- genic tanks, detailing the systems and procedures that can be used to prevent
18、 them being over pressur- ized, during filling e.g., causing a catastrophic failure by excessive pressure. Vessels for which the upper pressure limit (UPL) cannot be exceeded by the maximum allowable pump feed pressure (MAPFP) do not require any additional protection. It is intended to address the i
19、ssue of receiving vessels greater than 265 gallons (1000 liters) water capac- ity for liquid argon, nitrogen, oxygen, natural gas, helium, hydrogen, or ethylene. This document should also be used for receiving vessels under 265 gallons (1000 liters) that are not designed for transport when full. Thi
20、s document can also be used as guidance for other products and other transfer systems. It does not consider the hazardous nature of any product release, only the prevention of a failure of the tank due to pressure. Protective measures that prevent the overpressurization of receiving vessels in servi
21、ce e.g., by failure of the vacuum, pressure raising, flame engulfment etc. are detailed in other codes and standards and are not considered further here. 2.2 Purpose In 1996 a serious accident focused the attention of the gas industry on the fact that a cryogenic storage tank can be pressurized abov
22、e its bursting pressure during filling. If a high pressure or high flow pump is used to fill a low pressure tank and if the safety measures are not appropriate or do not work, then an un- safe situation can arise. This was the first significant incident of this type in an industry that has operated
23、safely and reliably with an estimated several million filling operations carried out per year. However, due to recent technical de- velopments in pumping equipment (increasing delivery pressures and flow rates), the safety margin the tanks have against failure may be reduced unless the protective me
24、asures against such an event occur- ring have not been upgraded simultaneously. It is an essential management task to systematically control any changes to product transfer systems to ensure that the integrity of the tanks being filled is not jeopardized. Pressure vessels are used in the distributio
25、n and site storage of cryogenic liquids on customer sites. This in- cludes those involved in the transport of cryogenic fluids (transportable pressure vessels) e.g., road tankers, railroad tank cars transferring product from the production facility to the customers site and those on the cus- tomer s
26、ite itself (static pressure vessels) that provide on site storage for the cryogenic fluids. Overpressurization avoidance has been effected through operator procedures and training. This training in- cludes for example: an initial and practical training verified by a qualification test, a re-examinat
27、ion and requalification verified by a selected driver inspector. PAGE 2 COMPRESSED GAS ASSOCIATION, INC. CGA P-592008 EIGA DOC 151/08 The safety record of filling operations today indicates that the training of the personnel has been exemplary based on historical performance. In order to accommodate
28、 the continuously improving capability of pumping systems, the objective is now to further improve overall safety by applying the principles of this document and by introducing an additional safety protection system when required. 3 Definitions 3.1 Definitions MAWP Maximum Allowable Working Pressure
29、. The maximum pressure a tank is designed for during normal operation. A vessels pressure relief devices are normally set to open at the MAWP. MAPFP Maximum Allowable Pump Feed Pressure. The maximum pressure that a receiver tanks fill coupling, fill valves and pipe work and any connected circuit are
30、 designed for. It is typically between 220 psig and 650 psig (15 bar and 45 bar). It is normally higher than the MAWP of the tank, to allow for pressure drop in the inlet system dur- ing the filling. UPL Upper Pressure Limit. The highest pressure it is acceptable to allow a tank to reach under abnor
31、mal conditions (e.g., test pressure). WP Working Pressure. The pressure at which the vessel is set to operate. It is the set pressure of the pressure con- trol devices (The pressure build up and the economizer regulators). Fly wire system A standardized wire connection between the receiving tank and
32、 the pump control system used to transfer sig- nal during the filling. MDP Maximum Delivery Pressure. The maximum pressure that can be produced by a given pump or pressure trans- fer system used to fill a receiver tank. Transport tank Transport tank includes fixed tanks (of tank vehicles or tank wag
33、ons), demountable tanks, tank containers and swap bodies for cryogenic fluids Cryogenic storage tank Typically a static (stationary) vacuum-insulated vessel also known as the receiver tank Cryogenic fluid A refrigerated liquefied gas that is partly liquid because of its low temperature. Pressurized
34、loading systems Any system used to transfer product via a gravity, pressure, or mechanical means (e.g., ground pump, transfer pump). Receiving vessel Covers both cryogenic storage tank and transport tank. 3.2 Background 3.2.1 Transport tanks Transport tanks for cryogenic fluids are normally low pres
35、sure tanks (typically with a design pressure of less than 45 psig 3 bar) that are designed manufactured and used in accordance with the applicable transport regulations. CGA P-592008 COMPRESSED GAS ASSOCIATION, INC. PAGE 3 EIGA DOC 151/08 In many cases these tanks are filled from a pressure source (
36、at the production facility) with a pressure that ex- ceeds the MAWP of the transport tanker. Typically the applicable transport regulations do not cover methods for filling and withdrawal. To discharge the cryogenic fluid in to the receiver tank, the road tanker is fitted with a centrifugal pump. 3.
37、2.2 Static tanks Static cryogenic tanks provide gas or liquid for customer use and have a WP ranging from a few atmospheres up to in excess of 500 psig (35 bar). During filling this WP must be kept constant in order not to disturb the users process. The pressurized loading systems (e.g., transport t
38、ank pump) used to fill the static cryogenic vessel must have: an output pressure that at least matches the highest WP in the range of tanks to be filled (at various cus- tomer sites). and produce additional pressure to overcome the frictional pressure drop of the cryogenic fluid flowing into the tan
39、k. This means that pressurized loading systems can produce a maximum pressure that exceeds the MAWP of the receiver tank. 4 Transport tanks 4.1 Filling operation Transport tanks are normally filled with closed vents to reduce losses. In order to make the transfer of product into the transport tank p
40、ossible without depressurization, the pressure source of the filling station may exceed the MAWP of the transport tank. Detecting when the maximum level of liquid is reached in the tank is done by various methods throughout the gas industry e.g., by observing when liquid flows from a try-cock, by we
41、ight, or by measurement of flow. 4.1.1 Filling by pump It is common to fill a transport tank using a pumping system, via a single filling hose. To obtain sufficient flow rates, the pump has a possible maximum discharge pressure in excess of the receiving vessels MAWP. The standard filling procedure
42、requires the operator to continuously monitor and control the receiving tank pressure below MAWP by adjustment of the top and bottom fill balance. Automatic systems using flow meters or weight scales may be used. Filling is complete when the intended amount of liquid is transferred or the maximum fi
43、ll level is reached. In situations where the operator either fails to end the fill process when the maximum filling level is reached or fails to control the tank pressure during fill, the pressure in the transport tank will increase and may reach the MAWP, causing the relief devices to open. If the
44、flow of the pump is greater than the capacity of the relief sys- tem, the pressure in the transport tank may rise to the pump MDP. 4.1.2 Filling with pressure balance This method of filling involves hose connections between the gas phase and the liquid phase of the receiver and storage tank. The dif
45、ferential pressure requirement of the transfer system will be reduced as the pressure of the transport tank and the storage tank will be equalized before/during filling. This method may also be used to reduce loss of gaseous product from the gas phase of the transport tank. PAGE 4 COMPRESSED GAS ASS
46、OCIATION, INC. CGA P-592008 EIGA DOC 151/08 The product may be transferred by a pump or by the liquid head of the storage tank. The filling procedure is normally controlled by an operator who may be supported by automatic systems. Any potential overpressurization of the storage tank will be reduced
47、when using this two hose transfer method as the pressure can balance. 4.1.3 Pressure transfer Transport tanks may be filled without pumps by pressure transfer if the pressure of the storage tank exceeds the pressure of the transport tank. The necessary pressure difference for the liquid product tran
48、sfer may be produced by increasing the pressure in the gas phase of the storage tank by operating a pressure build up system. Other methods may be used e.g., using the liquid head of the storage tank. The filling procedure is normally controlled by an operator who may be supported by automatic syste
49、ms. If the operator fails to stop the filling procedure at the maximum fill level the transport tank may be pressurized up to the MAWP of the static storage tank, plus the liquid head. 4.2 Preventative measures In reviewing the possible methods and devices to protect transport tanks against overpressurization during fill- ing, the following principles shall be considered: methods that are independent of the filling station or trans