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1、 CGA C-172008 (EIGA Doc 62/05) METHODS TO AVOID AND DETECT INTERNAL GAS CYLINDER CORROSION 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 C-172008 (EIGA DOC 62/
2、05) PREFACE As a part of a program of harmonization of industry standards, the Compressed Gas Association (CGA) has adopted the original European Industrial Gases Association (EIGA) document 62/05, Methods to Avoid and Detect Internal Gas Cylinder Corrosion. This standard is intended as an internati
3、onal harmonized standard for the worldwide use and application by all members of the Asia Industrial Gases Association, Compressed Gas Association, European Industrial Gases Association, and Japan Industrial and Medical Gases Association. The CGA edition has the same technical content as the EIGA ed
4、ition, however, there are editorial changes primarily in formatting, units used, and spell- ing. Also, references to European regulatory requirements have been replaced with the relevant North Ameri- can requirements. PLEASE NOTE: The information contained in this document was obtained from sources
5、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 severally, make no guarantee of the results and assume no liability or responsibility
6、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 contained within, or that abnormal or unusual circumstances may not warrant or suggest
7、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. In connection with such review, any such comments or suggestions will be fully review
8、ed 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 federal, state, provincial, or municipal specifications or regulations; insurance requir
9、ements; 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 publications, audiovisual programs, safety and technical bulletins, and safety posters is ava
10、ilable via the Internet at our website at . For more information contact CGA at Phone: 703-788-2700, ext. 799. E-mail: Work Item 05-154 Cylinder Specifications Committee FIRST EDITION: 2008 2008 The Compressed Gas Association, Inc. All rights reserved. All materials contained in this work are prote
11、cted by United States and international copyright laws. No part of this work may be reproduced or transmitted in any form or by any means, electronic or mechanical including photocopying, recording, or any informa- tion storage and retrieval system without permission in writing from The Compressed G
12、as Association, Inc. All requests for permission to reproduce material from this work should be directed to The Compressed Gas Association, 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 C-172008 C
13、OMPRESSED GAS ASSOCIATION, INC. PAGE iii (EIGA DOC 62/05) Contents Page 1 Introduction.1 2 Scope and purpose1 3 Definitions.1 3.1 Corrosion.1 3.2 Corrosive gas 1 3.3 Hydraulic test.1 4 Bibliography1 5 Corrosion1 6 Sources of moisture contamination2 6.1 Water from manufacturers hydraulic test2 6.2 Wa
14、ter from product / filling operation.2 6.3 Water feedback during use .2 6.4 Water ingress 2 6.5 Water from periodic inspection of cylinders.2 7 Avoidance of cylinder corrosion .3 7.1 Material selection and cylinder design.3 7.2 Avoidance of water ingress .4 7.3 Moisture detection methods 4 7.4 Corro
15、sion detection methods.5 7.5 Special recommendations for some types of applications.5 8 Guidance for moisture acceptance levels 6 9 Conclusions6 This page is intentionally blank. -,-,- CGA C-172008 COMPRESSED GAS ASSOCIATION, INC. PAGE 1 (EIGA DOC 62/05) 1 Introduction There are a number of reasons
16、for a cylinder to fail while in service such as from abuse, misuse, manufac- turing flaws, and internal corrosion. A number of gases can react with moisture to produce corrosive media that possibly could react with the cylinder material and lead to a cylinder failure. The number of incidents resulti
17、ng from internal corrosion is relatively small compared to the number of cylinders in service because the industry follows procedures to reduce moisture in cylinders. 2 Scope and purpose This publication provides guidance to help prevent and detect internal corrosion of compressed gas cylin- ders. I
18、t applies to gas cylinders and bundles, including cylinder installations at customer sites. Its main emphasis is for steel cylinders containing oxygen/oxygen mixtures and carbon dioxide/carbon di- oxide mixtures in the presence of moisture. Certain aspects of this document can also apply to other co
19、rro- sive gases e.g., hydrogen chloride. 3 Definitions For the purpose of this publication, the following definitions apply. 3.1 Corrosion Reaction of the cylinder material with certain aqueous media (e.g., carbonic acid formed from carbon diox- ide and water). 3.2 Corrosive gas Gas in a cylinder th
20、at will interact with the cylinder material in an oxidizing manner in the presence of mois- ture. 3.3 Hydraulic test Test performed on the cylinder using an aqueous solution, such as a test to check for leaks (proof test) or an expansion test (hydrostatic test). 4 Bibliography EIGA Doc 83/02, Recomm
21、endation for safe filling of carbon dioxide cylinders and bundles, European In- dustrial Gases Association, Avenue des Arts 3-5, B-1210 Brussels, Belgium. www.eiga.org EN 1968, Transportable gas cylindersPeriodic inspection and testing of seamless steel gas cylinders, European Committee for Standard
22、ization, 36, rue de Stassart, B-1050 Brussels, Belgium. www.cenorm.be CGA G-6.3, Carbon Dioxide Cylinder Filling and Handling Procedures, Compressed Gas Association, Inc., 4221 Walney Rd., 5th Floor, Chantilly, VA 20151. CGA G-6.8, Transfilling and Safe Handling of Small Carbon Dioxide Cylinders, C
23、ompressed Gas Associa- tion, Inc., 4221 Walney Rd., 5th Floor, Chantilly, VA 20151. CGA P-57, Avoidance of Failure of Carbon Monoxide and of Carbon Monoxide/Carbon Dioxide Mixtures Cylinders (EIGA Doc 95/07), Compressed Gas Association, Inc., 4221 Walney Rd., 5th Floor, Chantilly, VA 20151. 5 Corr
24、osion There are mainly two mechanisms that promote corrosion. These are: a) Acidic corrosion, possibly caused by gases such as carbon dioxide and sulfur dioxide, which form ac- ids when combined with water. Visual indications include area corrosion, line corrosion, or pitting cor- rosion in local ar
25、eas; and -,-,- PAGE 2 COMPRESSED GAS ASSOCIATION, INC. CGA C-172008 (EIGA DOC 62/05) b) Oxidizing gas corrosion, which may be caused by gases such as oxygen when combined with water. This corrosion is generally widespread over the internal surface of the cylinder. 6 Sources of moisture contamination
26、 Free moisture contamination can occur from several different sources, i.e., manufacture, filling, use, valv- ing, storage, and maintenance. 6.1 Water from manufacturers hydraulic test As part of a cylinders acceptance procedure, a mandatory hydraulic test is performed. It is absolutely es- sential
27、that subsequent emptying and drying of the cylinder is undertaken, so there is no free moisture left in the cylinder. Once achieved, it is essential that this internal condition is maintained (see also 6.5). 6.2 Water from product / filling operation It is possible to fill cylinders with products co
28、ntaining moisture. Additionally, some filling operations may introduce moisture into cylinders, e.g., if water lubricated compressors or water-ring vacuum pumps are used without adequate precautions to prevent water carry over. 6.3 Water feedback during use Aqueous feedback into cylinders may occur
29、whenever the cylinder is at a lower pressure than the applica- tion (involving a fluid) to which it is connected. 6.4 Water ingress 6.4.1 Rainwater Rainwater could enter the cylinder if the valve is left open after use, or if an unvalved cylinder is inade- quately protected while in storage or trans
30、portation. 6.4.2 Water immersion When cylinders are immersed in water (e.g., seawater, freshwater, etc.) and when the external pressure exceeds the internal pressure of the compressed gas, there is a chance that the aqueous material will enter the cylinder and contribute to corrosion. Some users suc
31、h as fish farms, shipyards, etc., immerse cylinders either during or after use. If the valve is not shut tightly, then water will enter the cylinder, once the cylinder is empty. Suppliers and users should take proper precautions and give special attention to cylinders in these applica- tions. 6.4.3
32、Atmospheric humidity Cylinders stored with their valves open or devalved cylinders that are inadequately protected against mois- ture ingress will “breathe.“ This involves the possible condensation of moisture from the atmosphere into the cylinder when the temperature drops, e.g. at night. This mois
33、ture will result in internal contamination following several such “air ingress cycles,“ though this will rarely result in a large quantity of water. 6.5 Water from periodic inspection of cylinders As part of the periodic inspection and test, cylinders are usually hydraulically tested, (unless a suit
34、able al- ternative is permitted). It is absolutely essential that subsequent emptying and drying of the cylinder is un- dertaken, such that there is no free moisture left in the cylinder. Once achieved, it is essential that this in- ternal condition is maintained until re-use. To confirm the absence
35、 of free moisture, an internal visual in- spection after drying is recommended. Organizations undertaking hydraulic testing should have a quality assurance system to ensure cylinders are adequately dried after the hydraulic test. It should be noted that a cylinder warmed or hot from the drying proce
36、ss can condense moisture inside as it cools if the drying process used moist, hot gas. CGA C-172008 COMPRESSED GAS ASSOCIATION, INC. PAGE 3 (EIGA DOC 62/05) 7 Avoidance of cylinder corrosion Several methods are available to reduce the likelihood of corrosion. The different methods are based upon mat
37、erial selection, design criteria, prevention and detection methods. These methods can be applied as single measures or in combination depending upon the application. 7.1 Material selection and cylinder design 7.1.1 Material selection Aluminum Alloys: Aluminum alloy cylinders are widely used in the g
38、as industry. Their high corrosion resistance makes them suitable for carbon dioxide and its mixtures and for oxygen and its mixtures, even in the presence of water. However, care shall be taken to minimize ingress of fluids into the cylinder when in the presence of certain contaminants, e.g., chlori
39、des or soft drink syrups, as it should not be assumed that the alloy will protect entirely against all corrosion mechanisms. Carbon Steels and Low Alloy Steels: Cylinders made from low alloy or carbon steels are very widely used for carbon dioxide and its mixtures and for oxygen and its mixtures. In
40、 the presence of water, internal corrosion will occur, and the rate of cor- rosion will depend on the gas, gas pressure and the amount of water and contaminants present. Stainless Steels: Stainless steel cylinders are corrosion resistant for a wide variety of products. However, due to the very high
41、cost, their use is limited to very special applications, e.g., ultra high purity gases. They are very sensi- tive to chloride contamination, and care shall be taken, e.g., with the water quality for any marine applica- tions and the hydraulic test to ensure chloride levels are compatible with the gr
42、ade of stainless steel used. Internal Coating and Surface Treatments: Some cylinders, particularly those used in the diving industry, have been internally coated/treated. While the experience with internal coatings, e.g., plastic linings, has not been entirely satisfactory, encour- aging results hav
43、e been obtained for internal surface treatments, e.g., phosphate treatment. Steels with Improved Toughness: Improving the toughness of the steel increases the chance of a leak instead of a burst (leak before break). This approach does not prevent corrosion but may limit the consequences should a fai
44、lure occur. With the steels available today, only limited progress can be made in this area. The chance of a leak instead of a burst is increased when the pressure at the time of failure is low compared with the test pressure. 7.1.2 Cylinder design Corrosion Allowance: Cylinder specifications such a
45、s ISO 9809 do not contain a corrosion allowance, unlike some stationary pressure vessel codes. For steel cylinders, because of the potentially high corrosion rates, a normal corro- sion allowance of approximately 1 mm to 2 mm is of little benefit to extend the cylinders life and conse- quently is no
46、t recommended by the industry. Good Design in Welded Cylinders: For some gas applications welded cylinders are used. Welded cylinders should be designed and manufac- tured in such a way that joggle joints do not retain water. -,-,- PAGE 4 COMPRESSED GAS ASSOCIATION, INC. CGA C-172008 (EIGA DOC 62/05
47、) 7.2 Avoidance of water ingress 7.2.1 Single cylinders There are different methods for protecting single cylinders from water ingress. These methods include but are not limited to: closing the valve at the valve manufacturers recommended torques; returning the cylinder with residual gas pressure to
48、 the filler; using a residual pressure valve that retains a residual positive gas pressure inside the cylinder; and using a nonreturn valve that is designed to prevent back flow from a process. 7.2.2 Bundle design Bundles shall have at least one main valve even if individual cylinders are valved. For protecting the bundle from water ingress, follow the methods listed in 7.2.1 for the main valve of the bundle. 7.2.3 Customer installation Customer installations should provide a nonreturn valve in their process if the possibility of water ingress exists. 7.2.4 Filling operation