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1、BRITISH STANDARD BS 7816-2: 1997 IEC 1244-2: 1996 Determination of long-term radiation ageing in polymers Part 2: Procedures for predicting ageing at low dose rates ICS 29.035.20 Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 12:03:13 GMT+00:00 2006, Uncontroll
2、ed Copy, (c) BSI BS 7816-2:1997 This British Standard, having been prepared under the direction of the Electrotechnical Sector Board, was published under the authority of the Standards Board and comes into effect on 15 March 1997 BSI 01-1999 The following BSI references relate to the work on this st
3、andard: Committee reference GEL/15/5 Draft for comment 94/212330 DC ISBN 0 580 26629 X Committees responsible for this British Standard The preparation of this British Standard was entrusted by Technical Committee GEL/15, Insulating materials, to Subcommittee GEL/15/5, Methods of test, upon which th
4、e following bodies were represented: Adhesive Tape Manufacturers Association British Capacitor Manufacturers Association British Industrial Ceramic Manufacturers Association British Telecom plc Electrical and Electronic Insulation Association (BEAMA Ltd.) Electricity Association Rotating Electrical
5、Machines Association (BEAMA Ltd.) The following bodies were also represented in the drafting of the standard, through subcommittees and panels: AEA Technology British Cable Makers Confederation British Plastics Federation ERA Technology Ltd. Transmission and Distribution Association (BEAMA Ltd.) Uni
6、versity of Manchester Amendments issued since publication Amd. No.DateComments Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 12:03:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7816-2:1997 BSI 01-1999i Contents Page Committees responsibleInside front cover
7、National forewordii Introduction1 1General2 2Power law extrapolation method2 3Superposition of time dependent data4 4Superposition of DED data6 5Conclusions8 Annex A (informative) BibliographyInside back cover Figure 1 Schematic illustrating the types of dose rate effects which can occur in radiatio
8、n-aged polymeric materials9 Figure 2 Interpolation of the end-point dose Schematic10 Figure 3 Extrapolation of end-point dose to lower dose rates Schematic10 Figure 4a Limitations Extrapolation of DED near thermal ageing limit11 Figure 4b Limitations Extrapolation of DED in a polymer with type III b
9、ehaviour11 Figure 5 Elongation at break of polypropylene irradiated in air (from 7)12 Figure 6 Extrapolation of end-point dose from data in Figure 512 Figure 7 Extrapolation of end-point dose for XLPE (from 7)13 Figure 8 Example where extrapolation of end-point dose is not feasible13 Figure 9 Schema
10、tic Superposition principle for thermal ageing and combined thermal-radiation ageing14 Figure 10a Determining shift factors b(T) for thermal ageing15 Figure 10b Superposition of data to yield master curve15 Figure 11 Determination of activation energy E16 Figure 12 Determination of shift factors a(T
11、, D) for combined thermal-radiation ageing16 Figure 13 Fitting experimental values of a(T, D) to the empirical model-equation (3)17 Figure 14 Calculated DED using equation (3)17 Figure 15 Experimental data for EPDM elastomer fitted to the superposition model18 Figure 16 Calculated DED for 50 % compr
12、ession set18 Figure 17 Calculated DED for 50 % compression set19 Figure 18 Calculated DED for e/eo = 0,519 Figure 19 DED values under combined thermal-radiation conditions Schematic20 Figure 20 Superposition of DED data Schematic20 Figure 21 Superposition of DED data for neoprene cable jacket materi
13、al (O heterogeneous oxidation, homogeneous oxidation)21 Figure 22 Superposition of DED for Hypalon cable jacket material Homogeneous oxidation data only21 Figure 23 Superposition of DED data for PVC showing type III behaviour Homogeneous oxidation data only22 Licensed Copy: London South Bank Univers
14、ity, London South Bank University, Fri Dec 08 12:03:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7816-2:1997 ii BSI 01-1999 National foreword This Part of BS 7816 has been prepared by Subcommittee GEL/15/5. It is identical with IEC 1244-2:1996 Determination of long-term radiation ageing in polym
15、ers, Part 2: Procedures for predicting ageing at low dose rates, published by the International Electrotechnical Commission (IEC). IEC 1244-2:1996 was issued in the type 2 technical report series of publications (according to G.4.2.2 of Part 1 of the IEC/ISO Directives) as a “prospective standard fo
16、r provisional application” in the field of insulating materials because there was an urgent requirement for guidance on how standards in this field should be used to meet an identified need. IEC 1244-2:1996 is not to be regarded as an “International Standard”. It is proposed for provisional applicat
17、ion so that information and experience of its use in practice may be gathered. A review of the technical report, IEC 1244-2:1996, will be carried out not later than three years after its publication, with the options of either extension for a further three years, or conversion to an International St
18、andard, or withdrawal. This British Standard implements IEC 1244-2:1996, and as such it is a technical report and is not to be considered to be a “provisional standard” subject to the outcome of the above mentioned review. Any comments on the content of this British Standard should be sent to the Br
19、itish Standards Institution, marked for the attention of the Secretary to Technical Committee GEL/15. A British 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 Standar
20、d does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 22, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporat
21、ed. This will be indicated in the amendment table on the inside front cover. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 12:03:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7816-2:1997 BSI 01-19991 Introduction The behaviour of polymers under irradiation
22、is strongly influenced by the atmosphere in which they are irradiated, particularly the presence of oxygen. When polymers are irradiated in oxygen-containing atmospheres, it is often observed that the irradiation dose required to reach a particular level of degradation changes with dose rate. The ex
23、istence of such dose rate effects in the radiation ageing of polymeric materials has been recognised for many years but only recently has a sufficient understanding been achieved of the processes involved to enable predictive methodologies to be developed. The types of dose rate effects which are se
24、en in polymers are illustrated schematically in Figure 1 11), where DED (dose to equivalent damage) is defined as the dose required to reach a specific level of a damage parameter (such as elongation at break, tensile strength, compression set, etc.). Figure 1 illustrates behaviour that is commonly
25、seen in most, but not all, polymers. In an inert atmosphere, represented by curve I, degradation is independent of dose rate over a wide range of dose rates. When dose rates are small enough for thermal degradation effects to dominate, curve I will approach the line representing thermal ageing under
26、 inert conditions. On a log-log plot like Figure 1, this thermal ageing will be represented by a straight line of slope equal to one. In the presence of oxygen, dose rate effects can arise from several processes including diffusion-limited oxidation and time-dependent chemical reactions. At high dos
27、e rates, diffusion limited oxidation becomes important (Figure 1); in this region DED tends to increase with increasing dose rate. It should be noted that Figure 1 is schematic and is only indicative of the types of behaviour that can occur. The diffusion-limited region in particular is very depende
28、nt on the type of polymer, its thickness, the permeation rate for oxygen and the sensitivity of the material to surface properties. The observed degradation is strongly influenced by the thickness of the oxidation layer. At high enough dose rates, oxidation will only occur in a thin surface layer wh
29、ich does not affect the bulk properties of most polymers. In this case, the degradation observed is similar to that seen in an inert atmosphere and DED approaches the inert ageing line. The dose rate above which heterogeneous oxidation occurs can be determined theoretically or by the use of profilin
30、g techniques. These procedures are discussed in detail in report IEC 1244-1. In the homogeneous oxidation region, dose rate effects are reduced for many polymers; the slope of the log-log DED versus dose rate plot remains constant or nearly constant with decreasing dose rate (curve II in Figure 1),
31、until the dose rate is sufficiently low for thermal degradation to become dominant. In type II behaviour, the slope of the DED plot against dose rate is determined by the reaction rate of the dominant chemical reaction. If the reaction rate is high relative to the initiation rate, the slope is small
32、 and may approach zero; whereas at low reaction rates, the slope is higher but 1. 1) Figures in square brackets refer to annex A. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 12:03:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7816-2:1997 2 BSI 01-1999 In
33、a few polymers irradiated in oxygen-containing environments, more complex dose rate effects are observed in the homogeneous oxidation region (e.g. curve III in Figure 1). A well documented example of type III behaviour is seen in PVC; this is believed to arise from the breakdown of intermediate hydr
34、operoxide species produced by irradiation 2-4; this is illustrated in more detail in 4.5. 1 General 1.1 Scope and object This part of IEC 1244 is a technical report of type 2 which applies to procedures for predicting ageing at low dose rates. The object of this report is to present three methods wh
35、ich have been used to extrapolate data obtained from high dose rate experiments to the low dose rates typical of service conditions. These methods assume that homogeneous oxidation has been achieved under the test conditions. The techniques described in the following clauses are research methods whi
36、ch have been found to be useful for a range of elastomeric and thermoplastic materials and some thermosets, and are subject to continuing research. The procedures require a considerable number of test data to enable predictions to be made under low dose rate conditions. The power law extrapolation m
37、ethod (clause 2) has mainly been used for isothermal data whereas the superposition methods (clauses 3 and 4) can make use of data obtained over a range of temperatures. 1.2 Normative references The following normative documents contain provisions which, through reference in this text, constitute pr
38、ovisions of this part of IEC 1244. At the time of publication, the editions indicated were valid. All normative documents are subject to revision, and parties to agreements based on this part of IEC 1244 are encouraged to investigate the possibility of applying the most recent editions of the normat
39、ive documents indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. IEC 544-1:1994, Guide for determining the effects of ionizing radiation on insulating materials Part 1: Radiation interaction and dosimetry. IEC 544-2:1991, Guide for determining the
40、effects of ionizing radiation on insulating materials Part 2: Procedures for irradiation and test. IEC 544-4:1985, Guide for determining the effects of ionizing radiation on insulating materials Part 4: Classification system for service in radiation environments. IEC 1244-1:1993, Determination of lo
41、ng-term radiation ageing in polymers Part 1: Techniques for monitoring diffusion-limited oxidation. 2 Power law extrapolation method 2.1 Introduction This method is based on the extrapolation of test data obtained under isothermal conditions in air or in oxygen overpressure over a range of dose rate
42、s. The upper limit to the dose rate is such that homogeneous oxidation conditions are achieved (but see 2.4). The test data obtained at the different dose rates are used to determine endpoint criteria which are extrapolated graphically to the service dose rate. 2.2 Test procedure The maximum dose ra
43、te at which homogeneous oxidation will occur in the test material shall be assessed. Information in the literature may be used to estimate the maximum dose rate, or the oxidation layer thickness may be calculated (IEC 1244-1). Once the maximum dose rate has been established, at least two (preferably
44、 three) other dose rates should be selected, each dose rate being at least one order of magnitude lower than the previous value. The general guidelines of IEC 544-2 should be used in the selection of specimen types, radiation source, dosimetry, and temperature control. All irradiations should be car
45、ried out in air or at constant oxygen overpressure, although as noted in IEC 1244-1, oxygen overpressure techniques entail some risk of over-ageing the samples. The homogeneity of oxidation through the specimen thickness should be checked using profiling techniques such as those described in IEC 124
46、4-1. The test report should include details of the irradiation source, dose rate, atmosphere, temperature, sample type and thickness. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 12:03:13 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 7816-2:1997 BSI 01-19993
47、2.3 Evaluation and extrapolation For the types of materials for which this procedure is recommended (i.e. elastomers and thermoplastics), elongation at break e is generally the property measured; for some materials, tensile strength or other criteria may be more useful. Using elongation as the measu
48、red parameter, to establish the endpoints at each dose rate, the relative elongation e/eo is plotted against absorbed dose (eo is the initial value of the elongation at break). A number of endpoint criteria can be interpolated from the graph (Figure 2); typical endpoint criteria might be e/eo = 0,75
49、, 0,5 or 0,4. A sufficient number of absorbed doses shall be used to enable the endpoint criterion to be established without extrapolation. The dose at which the endpoint criterion is reached, i.e. the dose to equivalent damage DED, is plotted against the dose rate in a log/log plot (Figure 3). This plot is found to be linear in some materials, e.g. some polyolefins, enabling extrapolation to lower dose rates. The endpoint dose is then given by where is the dose rate; K and n are empirica