1、 Reference number ISO/TR 13086-1:2011(E) ISO 2011TECHNICAL REPORT ISO/TR 13086-1 First edition 2011-09-01 Gas cylinders Guidance for design of composite cylinders Part 1: Stress rupture of fibres and burst ratios related to test pressure Bouteilles gaz Directives pour la conception des bouteilles en
2、 matire composite Partie 1: Fracture sous contrainte des fibres et indice dclatement relatifs la pression dessai ISO/TR 13086-1:2011(E) COPYRIGHT PROTECTED DOCUMENT ISO 2011 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by a
3、ny means, electronic or mechanical, 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
4、 copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2011 All rights reservedISO/TR 13086-1:2011(E) ISO 2011 All rights reserved iiiContents Page Foreword iv Introduction . v 1 Scope 1 2 Normative reference 1 3 Terms and definitions . 1 4 Factors of safety related to stress rupture . 2
5、4.1 Stress ratio . 2 4.2 Field experience and background . 3 4.3 Stress rupture test programs . 3 4.4 Stress rupture field experience 6 4.5 Other discussion . 7 4.6 Summary 7 5 Factors of safety related to test pressure . 8 5.1 General . 8 5.2 Burst . 8 5.3 Cyclic fatigue . 8 5.4 Stress rupture reli
6、ability . 9 5.5 Damage tolerance 9 5.6 Evaluation of burst ratios . 10 5.7 Summary 12 6 Technical Report Summary 13 Annex A (informative) Verification of stress ratios using strain gauges 14 Bibliography 15 ISO/TR 13086-1:2011(E) iv ISO 2011 All rights reservedForeword ISO (the International Organiz
7、ation 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 established
8、 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. I
9、nternational Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publ
10、ication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. In exceptional circumstances, when a technical committee has collected data of a different kind from that which is normally published as an International Standard (“state of the art”, for exa
11、mple), it may decide by a simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely informative in nature and does not have to be reviewed until the data it provides are considered to be no longer valid or useful. Attention is drawn to the possib
12、ility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO/TR 13086-1 was prepared by Technical Committee ISO/TC 58, Gas cylinders, Subcommittee SC 3, Cylinder design. ISO/TR 13086-1:2011(
13、E) ISO 2011 All rights reserved vIntroduction Composite reinforced cylinders have been used in commercial service for about 40 years. In the first years of use, glass fibres were the reinforcement of choice. Design guidelines, including safety factors, were established when these cylinders were firs
14、t developed. Additional fibres for reinforcing composite cylinders have become available in following years, including aramid and carbon. Different design configurations have been established over the years, including hoop wrapped, full wrapped with a metal liner, and full wrapped with a non-metalli
15、c liner. Different applications have developed, including breathing cylinders, emergency inflation cylinders, fuel tanks for vehicles powered by compressed natural gas or hydrogen, accumulators, and many other uses. Standards for these composite cylinders have developed in different ways. Some are d
16、esign based, others are performance based. Some were developed for a single fibre or application. Some of these have remained static, while others evolved as materials and designs changed. Other standards were developed with a broad scope of materials and applications. Safety factors have been treat
17、ed differently in these different standards. The entire industry, including manufacturers, customers, and regulatory bodies, would benefit from a cohesive foundation of the technical issues from which safety factors for composite cylinders are developed, so that a consistent approach to safety facto
18、rs is taken in composite cylinder standards. The elements of foundation currently exist, but need to be collected and organized for maximum benefit. This foundation will also serve as a base for evaluating new materials, designs, and applications that develop in the future. A foundation of the techn
19、ical issues supporting safety factors for composite cylinders will be built under this part of ISO/TR 13086. Elements involving the composite cylinder materials, designs, and applications will be incorporated. This Technical Report will be updated with additional topics periodically and can be refer
20、enced in the development of standards for composite cylinders. TECHNICAL REPORT ISO/TR 13086-1:2011(E) ISO 2011 All rights reserved 1Gas cylinders Guidance for design of composite cylinders Part 1: Stress rupture of fibres and burst ratios related to test pressure 1 Scope This part of ISO/TR 13086 g
21、ives guidance for the design of composite cylinders, relating to stress rupture reliability and burst ratio as a function of test pressure. Related issues, such as cyclic fatigue of the liner and composite, damage tolerance, environmental exposure, and life extension will be addressed in subsequent
22、parts. The topics covered by this part of ISO/TR 13086 are to support the development and revision of standards for fibre composite reinforced pressurized cylinders. 2 Normative reference The following referenced documents are indispensable for the application of this document. For dated references,
23、 only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 10286:2007, Gas cylinders Terminology 3 Terms and definitions For the purposes of this document, the terms and definitions given in ISO 10286:2007, Annex A,
24、and the following apply. 3.1 autofrettage pressure pressure to which a metal lined composite pressure vessel is taken, prior to the test pressure cycle, in order to yield the liner, and therefore establish a compressive stress in the liner at zero pressure 3.2 burst ratio the ratio of the minimum re
25、quired burst pressure and the working pressure 3.3 stress ratio the ratio of the minimum strength of the fibre, as determined through burst testing of a pressure cylinder, divided by the stress in the fibre at working pressure 3.4 stress rupture phenomenon by which a reinforcing fibre can fail under
26、 an applied tensile load over time, and is dependent on the stress level ISO/TR 13086-1:2011(E) 2 ISO 2011 All rights reservedNOTE Temperature level can affect stress rupture as predicted by the Arrhenius rate equation. Resin properties can affect stress rupture. If the temperature level of the resi
27、n exceeds its glass transition temperature, this can also affect stress rupture. 4 Factors of safety related to stress rupture 4.1 General This clause addresses stress rupture and related reliability for composite cylinder reinforcements, including glass, aramid (aromatic polyamide), and carbon fibr
28、es. Stress rupture is directly related to stress in the fibre. Stress in the fibre is related to pressure in the cylinder, but not necessarily linearly. Stress rupture, which is the possibility that the reinforcing fibre fail under continuous loading, will be addressed as a function of the reinforci
29、ng fibre, including glass, aramid (aromatic polyamide), and carbon fibres. Reliability versus time under load will be addressed. The term “safety factor” has more than one meaning. It is often used to be the ratio of the burst pressure to the working pressure or to the maximum expected operating pre
30、ssure. It may also be used as the ratio between any ultimate failure level compared with an operating level, such as with cyclic fatigue of a liner or of the composite reinforcement. 4.2 Stress ratio The term “stress ratio” is often used with composite pressure vessels to address a fibre characteris
31、tic known as stress rupture. Stress ratio is the ratio of the minimum strength of the fibre, as determined through burst testing of a pressure cylinder, divided by the stress in the fibre at working pressure. Stress ratio has more validity than a burst ratio in predicting reliability associated with
32、 stress rupture. The difference in the ratios occurs because in composite cylinders with metallic liners, the load sharing between the composite and liner is not linear with pressure. In these vessels, the stress ratio, and therefore reliability prediction, can be affected by variables including the
33、 liner and fibre modulus of elasticity, liner and fibre thickness, liner yield strength, and autofrettage pressure. As an example, consider a Type 3 cylinder with a load sharing liner. The cylinder is first subjected to an autofrettage cycle, which yields the liner, and puts it in compression at zer
34、o pressure. The composite, therefore, will have some pre-load that is added to the stress at working pressure. As the cylinder is taken up to burst pressure, the liner yields above the autofrettage pressure, therefore the composite takes a higher percentage of the added load. The end result is that
35、stress ratio and burst ratio will not be equal. Calculation of stress versus load is necessary in order to meet stress ratio requirements. Note that for a cylinder with a non-loadsharing liner, the stress ratio and burst ratio are equal. Stresses may be calculated by finite element analysis that inc
36、orporates material non-linearities, or by closed form analysis that accounts for material non-linearities. Alternatively, strains can be verified using strain gages on the composite in accordance with the guidelines in ISO 11439:2000, Annex G 1 . See Annex A. Table 1 lists stress ratios commonly use
37、d in newer composite standards that consider stress rupture reliability for the various reinforcing materials and configurations used in the cylinder standards. These stress ratios are intended to provide a reliability of 0,999999 over the cylinder lifetime; that is, less than 1 failure in 1,000,000
38、 cylinder lifetimes. Other standards may use higher stress ratios or safety factors, in part to address damage tolerance, environment, or unknown issues. ISO/TR 13086-1:2011(E) ISO 2011 All rights reserved 3Table 1 Fibre Stress Ratios to achieve 0,999999 reliability Fibre Material Hoop Wrapped, Meta
39、l Lined (Type 2) Fully Wrapped, Metal Lined (Type 3) Fully Wrapped, Non-metal Lined (Type 4) Glass 2,65 3,50 3,50 Aramid 2,25 3,00 3,00 Carbon 2,25 2,25 2,25 NOTE 1 Values of 2,35, 2,35, and 2,75 are used on carbon, aramid, and glass respectively for Type 2 cylinders in standards for CNG where settl
40、ed temperature is 15 C. NOTE 2 Values of 2,35, 3,1, and 3,65 are used on carbon, aramid, and glass, respectively, for Types 3 and 4 in some standards for CNG where settled temperature is 15 C. NOTE 3 Values of 2,00 are used for carbon for Types 2, 3, and 4 in ISO/TS 15869 for pressures greater than
41、or equal to 350 bar. Standards that use these stress ratios include ISO 11439, ECE R-110, ISO/TS 15869, ANSI/CSA NGV2, CSA B-51 Part 2, ASME Section X Class III, and KHK Technical Standard #9. 4.3 Field experience and background Metal pressure vessels have historically had a 2,25-2,5 burst ratio for
42、 high pressure transportable cylinders. Burst ratios in this range addressed margins for overfilling, temperature compensation during fill, material variability, and strength loss due to corrosion. As glass reinforcing fibres were being introduced for use in pressure vessels, stress rupture was inve
43、stigated. A higher stress ratio was required for glass fibre reinforced cylinders in order to provide adequate reliability and avoid stress rupture. A higher stress ratio for glass fibre solved the problem with stress rupture, and the resultant thicker wall also provided good damage tolerance and du
44、rability. Several million glass fibre reinforced cylinders with the higher stress ratio are in service worldwide and have an excellent safety record. When aramid fibres were introduced, they were used in cylinders almost immediately because of their lower weight. Today, the characteristics of aramid
45、 fibres are well understood, and lower stress ratios than glass are accepted and appropriate for many applications. The use of carbon fibre as a reinforcing material for composite pressure vessels grew significantly in the early 1990s, and it was recognized that carbon fibre had superior stress rupt
46、ure characteristics, allowing safe reductions in stress ratios. However, specifying a stress ratio only addresses stress rupture and cyclic fatigue of the reinforcing materials. It is also necessary to specify testing which reflects the environment to which the pressure vessel is exposed. The enviro
47、nmental conditions should address temperature extremes, fluid and chemical exposure, and mechanical damage, at a minimum. 4.4 Stress rupture test programs Test programs evaluating the stress rupture characteristics of glass, aramid, and carbon fibres were conducted 8910111214 . These references disc
48、uss the background of the test programs, offer assessments of reliability, and discuss issues related to the results. Robinson 13presents an analytical basis for comparing the reliability of the various fibres. The reliability for glass, aramid, and carbon fibres, when used at the stress ratios give
49、n in Table 1, will all be greater than 0,999999 over the lifetime specified for composite pressure vessels (15-30 years) when held at ISO/TR 13086-1:2011(E) 4 ISO 2011 All rights reservedthe rated working pressure (see Figures 1, 2, and 3). The risk of a pressure vessel failing due to stress rupture is less than 1 in a million over its lifetime. It is seen that carbon fibre is far superior to glass fibre in stress rupture using Robinsons evaluation. If the fibres were stressed to 80 % of their average ultimate st
