1、| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | BRITISH STANDARD AEROSPACE SERIES BS 4N 10
2、0-6: 1999 ICS 49.090 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW Aircraft oxygen systems and equipment Part 6: Guidance and recommendations on the selection of materials for use with oxygenThis British Standard, having been prepared under the direction of the Engineering S
3、ector Committee, was published under the authority of the Standards Committee and comes into effect on 15 October 1999 BSI 10-1999 The following BSI references relate to the work on this standard: Committee reference ACE/38 Draft for comment 96/706267 DC ISBN 0 580 29546 X BS 4N 100-6:1999 Amendment
4、s issued since publication Amd. No. Date Comments Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee ACE/38, Aircraft oxygen equipment, upon which the following bodies were represented: British Airways British Compressed Gas
5、es Association Civil Aviation Authority Health and Safety Executive Ministry of Defence Society of British Aerospace Companies Limited South Bank UniversityBS 4N 100-6:1999 BSI 10-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Normative references 1 3 Selectio
6、n of metallic materials 1 4 Selection of non-metallic materials 3 5 Selection of combinations of materials 4 Bibliography 5 Table 1 Typical test results 6ii BSI 10-1999 BS 4N 100-6:1999 Foreword This Part of BS 4N 100 has been prepared by Technical Committee ACE/38 and specifies general requirements
7、 for oxygen systems and equipment for use on aircraft and ground support equipment. It partially supersedes BS 3N100 which is withdrawn upon publication of all seven parts. BS 4N 100 consists of the following parts: Part 1: Design and installation; Part 2: Tests for the compatibility of materials in
8、 the presence of oxygen; Part 3: Testing of equipment and systems; Part 4: Guide to the physiological factors; Part 5: Guide to fire and explosion hazards associated with oxygen; Part 6: Guidance and recommendations on the selection of materials for use with oxygen; Part 7: Guide to cleaning, labell
9、ing and packaging. This part of BS N 100 is classed as a guide and provides guidance and recommendations on the selection of materials for use with oxygen to minimize the risk of ignition and combustion. NOTE The latest revision of an aerospace series standard is indicated by a prefix number. A Brit
10、ish Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a fron
11、t cover, an inside front cover, pages i and ii, pages 1 to 5 and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued. BSI 10-1999 1 BS 4N 100-6:1999 1 Scope This part of BS N 100 provides guidance and recommendations on the selection of mater
12、ials for use with oxygen to minimize the risk of ignition and combustion. The guidance and recommendations may be used equally well in non-aerospace applications. 2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions
13、of this part of this British Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply, for undated references the latest edition of the publication referred to applies. BS 4 N 100-2, Aircraft oxygen systems and equipment Tests for the compatib
14、ility of materials in the presence of oxygen. 3 Selection of metallic materials 3.1 The selection of metals to minimize the risk of ignition and the effects of fire depends on several factors as follows: a) the working regime i.e. gas flow conditions, rapid state changes; b) the working environment
15、i.e. pressure velocity, mass flow rate and temperature; c) the level of filtration and/or the chance of particle creation within the system; d) the nature of combustion and ability to self- quench. When heated in 100 % oxygen under pressure, alloys of iron (steel, stainless steel) and aluminium (inc
16、luding aluminium bronze) evolve large quantities of energy and burn vigorously once ignitions occur. Under some circumstances, burning continues even if the pressurized oxygen is replaced by ambient air. At much higher temperatures, copper and nickel alloys (including brass, tin-bronze, cupro-nickel
17、, monel) will ignite but rapidly extinguish once the ignition source is removed. Any metal that can be ignited in ambient air (magnesium, titanium for example) should never be selected. 3.2 Since 1985, various test methods have been investigated to assist with the ranking of metals for selection. Tw
18、o of these methods are reported in ASTM special technical publications (STP) (see bibliography) and represent “in-use” modes of ignition as follows: a) Particle impact (P.I.) 2,000mm aluminium particle in a supersonic oxygen flow at 27.6 MPa impacts a heated target of the test material at right angl
19、es. The ranking criterion is the maximum temperature at which ignition and consumption of the target does not occur. b) Promoted combustion (P.C.) Test material specimen subjected to the heat released by a burning aluminium promoter in oxygen at pressure. The ranking criteria are as follows: 1) the
20、minimum oxygen pressure required to support self-sustained combustion; 2) the propagation rate. Based on the results reported, the following table shows the relative performance of common metals used in oxygen systems. (Results obtained using samples of solid section uniform proportions).2 BSI 10-19
21、99 BS 4N 100-6:1999 Table 1 Typical test results Metal Type P.I. temp. 8C P.C. pressure MPa Aluminium alloy 6061 -33 0.7 Aluminium bronze 7 % Al 312 1.4 Carbon/Alloy steel 9 % Ni 202 3.5 Ductile cast iron 3.5 Stainless steel 17-4 PH 6.9 14-5 PH 31 13-4 PH 33 304 47 6.9 316 52 6.9 Copper alloys Brass
22、 (CZ grades) 347 48.3 Tin bronze 307 48.3 Copper(pure) 55.2 Nickel alloys Inconel 718 202 3.5 Inconel 600 332 6.9 Nickel (pure) 357 68.9 Monel 400 55.2 Generally, the temperature limit is defined by non- metals being used in the system: the pressure is the maximum developed in the system under consi
23、deration i.e. the pressure developed at maximum operating temperature, or the setting of any protection devices (relief valve or bursting disc). Whilst the information reflects the best data available, it is recognized that many metals have been in use for years at pressure conditions well in excess
24、 of those listed, without compromising safety. Two particular factors are involved and make a significant effect i.e. systems design and temperature/ pressure combinations experienced. Aluminium particularly (and other metals that similarly form an oxide film) can safely be used at conditions well a
25、bove P.I. and P.C. values provided that the oxide film is not breached. Typical causes are friction rubbing, impact or adjacent ignition source. Temperature/pressure combinations, i.e. the working conditions, rarely approach the limits investigated during testing. The objective data that is availabl
26、e at the moment, coupled with product experience, shows that reduced temperature and/or pressure conditions during testing will enhance results. Therefore, an aluminium alloy at 14 MPa/708C may be used for a valve body or carbon/alloy steel at 42 MPa/708C for a pressure vessel, subject to the proper
27、ties of other parts, the overall design and absence of contaminating particles. System design is most important. Low velocity gas flow is inherently safer than supersonic; avoid dramatic changes of pressure (e.g. adiabatic conditions): sudden changes of gas flow direction (abrupt right angle drillin
28、gs) or passage configurations (sharp edges) cause local heating and gas turbulence. Filtration is essential, not forgetting metallic debris that may be caused during assembly: absolute cleanliness is paramount at all times. Ensure that any non-metal in the system that can be directly exposed to the
29、oxygen flow (e.g. valve seat) is kept to a minimum and is housed in a metal with P.I. temperature and P.C. pressure as high as possible. 3.3 No metals should be used for service in an oxygen environment before being tested (see 3.2)o r compared with the ranking table. Objectivity may only be obtaine
30、d by testing specific metals in a representative system to conditions offering a suitable safety margin over the proposed duty. 3.4 Metals chosen for valves and valve seats shall be non-shattering under maximum loading conditions to avoid particle contamination of the system. 3.5 Shedding caused by
31、the rubbing of two surfaces shall be avoided by choosing metals with widely differing hardness for the two surfaces. Certain metals can cold-weld e.g. nickel; intimate contact of these metals should be avoided for moving parts. Ensure that metals chosen for mating threads will not cold-weld or gall.
32、 BSI 10-1999 3 BS 4N 100-6:1999 3.6 Promoted combustion tests (see 3.2) conducted using thin sections or meshes demonstrate that there is a mass/surface area effect which tends to reduce the pressures compared with those obtained from solid samples. Only pure nickel, for example, has demonstrated a
33、similar performance. 3.7 It should be ensured that the electro-motive series potential between differing metals in contact is as small as possible. Where dissimilar metals are to be in contact, they should be insulated with gaskets or coatings of suitable material, conforming to BS N 100-2. 3.8 Corr
34、osion is unlikely to occur where parts will only come into contact with pure, dry oxygen. Wherever moisture can occur, appropriate protective treatment, conforming to BS N 100-2, should be applied or enhanced; for example, anodizing aluminium or passivating stainless steel. Selection should take int
35、o account the corrosion effects under stress of certain metals, for example season cracking of copper/zinc alloys. WARNING NOTE Certain protective treatments can cause toxicity problems if used in breathing systems, e.g. cadmium plating. 3.9 Where non-corrosion resistant metals are used for oxygen c
36、ylinders, the surfaces should be examined for the presence of corrosion after manufacture and at re-lifing /overhaul. 4 Selection of non-metallic materials 4.1 The selection of non-metals has historically been based on an interpretation of results from three tests known as “Pot”, “Bomb” and “Impact”
37、 (see BS N 100-2). More recently, the bomb test method has been completely revised and extended, resulting in the better repeatability of the results and hence improved accuracy (see BS N 100-2). However, the demonstration of compatibility with oxygen at the desired conditions of temperature and pre
38、ssure achieved using these methods does not, take into account either time based effects (soaking in oxygen/absorbed gas) or gas flow effects. Additional testing may be necessary to explore these factors. 4.2 Certain non-metallic materials, especially elastomers, degrade by contact with oxygen. Befo
39、re use in oxygen systems, it should be demonstrated that the selected material is suitable for the conditions likely to occur in use. This may be achieved by reference to manufacturers data, or by the use of artificial ageing processes. 4.3 Oxidation will occur to varying degrees, dependent on the s
40、usceptibility of the material and the temperature experienced during exposure of the material to oxygen. The oxidation will often cause an embrittling of the substance, flexible materials are likely to become embrittled more readily than rigid materials. Embrittlement originates at the surface expos
41、ed to oxygen and progresses with time through the material until the whole structure has changed. Embrittlement of materials occurring in gaseous oxygen as the result of an oxidation process is experienced as a hardening of the material which reduces its resilience and its resistance to impact and b
42、ending. Visually, the embrittlement is associated with slight surface crazing which develops into deeper cracks and a darkening in the colour of the material. 4.4 Some non-metallic materials are prone to the absorption of oxygen when continuously exposed to the gas under pressure. This will cause a
43、lowering of the spontaneous ignition temperature (S.I.T.), BS N 100-2 refers. Consideration should be given to testing such materials both prior to, and after long term exposure to oxygen. 4.5 Materials chosen for valve-seats shall be non-shattering under maximum loading conditions to avoid particle
44、 contamination of the system. 4.6 Materials chosen for use where relative movement between surfaces is experienced during manufacture/assembly or in use, shall resist shedding and delamination to avoid risks of particle contamination of the system. 4.7 In general, non-metallic materials have lower P
45、.I. and P.C. values than metals. However, the heat of combustion is often sufficient to ignite adjacent metals. Consequently, non- metallic materials should be kept to an essential minimum in any system. An exception to this is often found with ceramic or similar materials, where the risk is often a
46、ssociated with its brittleness and hence generation of system contaminating particles. 4.8 Non-metallic materials used in high-risk areas of systems (e.g. valve-seats) should be kept to as small a quantity as practical, and should be housed within a metal/non-metal of significantly higher ignition t
47、emperature.4 BSI 10-1999 BS 4N 100-6:1999 5 Selection of combinations of materials 5.1 In addition to the effect of electro-motive series potential between different metals in contact (see 3.7), dissimilar non-metallic materials, especially elastomers and polymers, can dissociate in such a way that
48、constituent parts migrate across surface boundaries if in contact. For instance, over a relatively short period of time in a components life (a few months) plasticizer has been known to leach from bromobutyl rubber and migrate to the surface of nylon plastic in contact to the extent that a bond was
49、formed. Such effects can cause changes in physical properties as well as affecting the results of oxygen compatibility testing. 5.2 Stress, such as the shearing stress of a valve spindle on a seat, can give rise to a reaction between certain otherwise relatively inert materials. One particularly good example is fluorinated-hydrocarbon/aluminium reaction. 5.3 Materials and/or metals in combination, such as coatings and plating, have not been widely tested. Generally, it is recommended that each different material/metal is taken on its individual merits for th
