1、STD-BSI BS EN 728-ENGL 1777 Lb24bb7 Ob23b08 77T BRITISH STANDARD Plastics piping and ducting systems - Polyolefin pipes and fittings - Determination of oxidation induction time The European Standard EN 728 : 1997 has the status of a British Standard ICs 23.040.20 NO COPYING WITHOUT BSI PERMISSION EX
2、CEPT AS PERMITTED BY COPYRIGHT LAW BS EN 728 : 1997 BS 2782 : Part 11 : Method 1103D : 1997 STD=BSI BS EN 728-ENGL 1777 m Lb24bb9 Ob23b07 bOb m I BS EN 728 : 1997 This British Standard, having been prepared under the direction of the Sector Board for Materiais and Chemicals, was published under the
3、authority of the Standards Board and comes into effect on 15 July 1997 O BSI 1997 Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee PRI61, Phtics piping systems and components, upon which the following bodies were represent
4、ed: British Gas plc British Plastics Federation British Plumbing Fittjngs Manufacturers Association British Valve and Actuator Manufactures Association Chartered Institution of Water and Environment Management Department of the Environment (British Board of Agrement) Department of the Environment (B
5、uilding Research Establishment) Department of liansport Electricity Association Health and Safety Executive Institute of Building Control Institute of Materials Institution of Civil Engineers Institution of Gas Engineers National Association of Plumbing, Heating and Mechanical Services Contractors P
6、ipeline Industries Guild Plastics Land Drajnage Manufacturers Association Society of British Gas Industries Society of British Water Industries Water Companies Association Water Services Association of England and Wales The following bodies were also represented in the clrafthg of this standard, thr
7、ough subcommittees and panels ERA Technology Ltd. Engineering Equipment and Materials Users Association wA Technology Ltd. Amendments issued since publication AmdNo. Date I Te*affectd The following BSI references relate to the work on this standard Committee reference PRV61 Draft for comment 92/4137
8、9 DC ISBN O 580 27392 X - STD.BSI BS EN 728-ENGL L777 Lb24bb7 Ob23bLO 328 BS EN 728 : 1997 Contents COmmittRes responsible Nationai foreword page Inside front cover ii Foreword Method 1 Scope 2 Normative references 3 Principle 4 Materials 5 Apparatus 6 Testpieces 7 Procedure 8 Interpretation of resu
9、its 9 Testreport 2 3 3 3 3 3 3 5 5 6 6 Figures 1 - test parametem, except those common to all plastics, are omiw, - no materialdependent requirements are given; - editorial changes have been introduced The material-dependent parameters andor performance requirements are incorporated in the System st
10、andard(s) concerned. This standard is one of a series of standards on test methods which support System Standards for plastics piping systems and ducting systms. According to the CENKENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement t
11、his European standard: Austria, Belgium, Denmark, Fnland, Fiance, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom. O BSI 1997 STD-BSI BS EN 728-ENGL 1977 Lb29bbS Ob23b14 T73 m x x Ln 1 scope This standard species
12、a method for measuring the oxidation induction time in oxygen at a specified temperature of polyolen marials for or from pipes or fittings. It may be used for assessing the thermal stability of either raw materials or finished products. 2 Normative references This standard incorporates by dated or u
13、ndated reference, provisions from other publications. These nonnative references are cited at the appropriate places in the text and the publications are listed hereafteE For dated references, subsequent amendments to or revisions of any of these publications apply to this standard oniy when incorpo
14、rated in it by amendment or revision. For undated references the latest edition of the publication referred to applies. 3 Principle It is assumed that a polyolen material for manufacture of pipe and/or fittings will incorporate an additive package which includes one or more antioxidants or other sta
15、biieis. The time for which the material, with its additive package consisting of antioxidant, stabilizers and other additives present in a test piece, inhibits oxidation is measured while the test piece is held isothemdy at a specified temperaime in a stream of oxygen. The progress of the oxidation
16、is monitored by measuring the difference in energy flow (AQ) or temperature (An between the test piece pan and reference pan of a thermal analyser and recording this difference agajnst time. The oxidation induction time (Om is then derived hm this record as the period during which the difference in
17、energy flow or temperature remains constant (see figure 2) between the test piece pan and reference pan. This time can be indicative of the effective residual antioxidant level and reflects the time the test piece can be exposed in pure oxygen at the test temperature before the onset of thermal degr
18、adation. in normal atmospheric conditions this time will be longer. O Page 3 EN 728 : 1997 Depending upon the material and the pipe or fitting processing, dimensions and service conditions, the methods of sample and test piece preparation may be crucial to the consistency of the resuits and their si
19、gnificance. NOTE. It is assumed that the following test parameters are set by the standard making reference to this standard a) the test temperature, b) the methods of sample and test piece preparation (see 6.2) and, if applicable, the moulding temperature see a) of 6.11; c) the number of test piece
20、s (see 6.3). for the reference pan (see 6.1); It is recommended to choose a temperature which normally results in induction times of at least 10 min. 4 Materials 4.1 Oxygen An oxygen supply with a purity of at least 99,5 96 4.2 Nitrogen A nitrogen supply with a purity of 99,998 %. 4.3 Reference mate
21、rials %o or more temperature reference matmiais (calibration standards) of high purity metal having melting temperatures in the vicinity of the testing temperatwe, T see a) of the note to clause 31. When T lies between 190 “C and 220 “C (typical for testing polyolens), the calibration metals shall b
22、e as follow - indium (melting point 156,6 “C) with a purity grade of at least 99,99 %, - tin (melting point 231,9 “C) with a purity grade of at least %,99 %, where the melting point is derived from the onset in the DSC diagram (shown as A in figure 1). 4.4 Solvent A solvent of appropriate compositio
23、n (see 7.2), analytical grade. 5 Apparatus 6.1 Lhflmtid scanning calorimeter (DSC) or dkrent2al ULemLal analyser (DTA), capable of: O a) recording the difference in energy flow, AQ , or in temperature, AT, between the test piece pan and the reference pan against time (see clause 7); b) exposing a te
24、st piece in an open or ventilated duminium pan to a flow of50 nmin f 10% of nitrogen and 50 mlhnin 10 % of oxygen in turn so that each gas changeover is effected in not more than 1 min. The pan shall have a flat, smooth base capable of making good contact with the cell base and with a test piece res
25、pectively; O BSI 1997 I STDOBSI BS EN 728-ENGL 1777 W Lb24bb7 Ob23b15 70T W Page 4 EN 728 : 1997 as I I I I I I r-c D- A,$ Difference in energy flow A Onset temperature (melting point) C Melting point D Temperature Figure 1. Typical calibration curve c) increasing the temperature over the range of 1
26、40 “C to 250 “C at a rate of (1 0,l) Wmin when the cell contallis either a temperature calibration device or a calibration metal (see 4.3 and 7.1); d) increasing the test piece pan temperature T over the range from 50 “C to the test temperature at a rate of (20 f 2) Wmin (see 7.2); e) stabdizhg the
27、temperature at (T f 0,3) “C within 3 min of nrst reaching (T f 0,3) OC; f) maintaining the test temperature, for the duration of the test (see 7.2). within f 0,3 “C NOTE. The design of the instrument oven should ensure that the test piece comparhnent is exposed to the required gas flow i see bll. 6.
28、2 Tmpemture memurernent device, capable of continuously monitoring the test piece pan temperature with a resolution of 0,l “C. NOTE 1. Test piece pan temperatures are used as the values for test resuts. NOTE 2. This device can be integrai with the DSC or DTA apparatus (see 6.1), but this is not esse
29、ntiai. A high impedance digitai voltmeter with a resolution of 1 mV has been found suitable when connected to a thermocouple and the associated cold junction, or cold compensator, of the thermai anaiyser. 6.3 Analytical balance, capable of weighing a tst piece (see clause 6) to a iimt of error of 0,
30、l mg. 6.4 Gasflow control anal ?aeasung clevices, capable of providing the required flow rate (see 7.1 and 7.2). Rotameters are suitable, if they are calibrated against a positive volume displacement device, e.g. a soap bubble flowmeter or equivalent. 6.6 Z?iw, comprishg a stopwatch or equivalent O
31、BSI 1997 STD-BSI BS EN 728-ENGL 1797 m LbZLibbS Ob23bLb 84b m 6 Bst pieces 6.1 Preparation of test piece from raw materials Cut one or more test pieces (see 6.3), each having a mass of (15 f 2) mg, from a melt flow extrudate obtained in accordance with IS0 1133, or prepare one or more test pieces as
32、 follows: a) prepare a compression-moulded piaque in accordance with IS0 293. Limit heating to 2 min at the moulding temperature specified by the referring b) cut a cyhdrical sample with a diameter not less than half the inside diameter of the test piece pan; standat. NOTE. It is recommended to use
33、test pieces with a diameter of approximately 6 mm. c) cut a test piece from the cyiinder to give a test piece mass of (15 f 2) mg. 6.2 Preparation of test pieces from a pipe or fitting Cut samples from the pipe or fitting in accordance with the referring standard, so as to obtain one or more test pi
34、eces (see 6.3) each having a mass of (15 f 2) mg. NOTE. For testing of thick-walled polyethylene pipe or fittings the following method has been found suitable. Recommended procedure for test piece preparation for pipes and fittings. Obtain a cross section of the wall of the pipe and/or fitting by us
35、e of a core drill directed raially through the wall, so that the diameter of the core preferably is just less than the inner diameter of the test pan for the test instrument see note to item b) of 6.11 and care is taken not to overheat the sample during the cuting operation. Cut from the core test p
36、ieces of the specified mass in the form of discs as follows. Select at least the inner-waii surface zone, outer-wall surface zone and mid-wall zone as the sample points from the core which are to be tested individually, unless surface effects are of prime interest. in such cases cut the discs only f
37、rom the inner and outer surfaces and test them with surface side uppermost. 6.3 Number of test pieces The number of test pieces shall be as specified in the referring standard. 7 Procedure 7.1 Calibration 7.1.1 General Carry out the procedures given in 7.1.2 and 7.1.3 each at the frequency necessary
38、 to ensure that results obtained in accordance with 7.2 are obtained under the specified conditions. 7.1.2 lkmperature calibration 7.1.2.1 bure that the oven is properly clean, e.g. by heating up in a nitrogen atmosphere at a temperatwe of approximately 500 “C to 550 “C for at least 10 min followed
39、after cooling by a cleaning with a cloth, if necessary Page 6 EN 728 : 1997 Establish an oxygen flow of 50 mlmiin f 10 % through the apparatus at a temperature of at least 10 “C below the expected melting point of one of the calibration metals, e.g. indium or tin (see 4.3). Heat the calibration meta
40、i in a sealed aluminium pan at a rate of 1 Wmin untji the melting endotherm is recorded, using an empty sealed aluminium pan as reference. Obtain a plot of AT or AG against temperature (e.g. see figure 1). If the apparatus does not automaticdy do so, mark the indicated temperature on a chart at inte
41、rvals in the region of the endotherm so that the melting point can be determined with a precision of f O,i “C. Take the melting point of the metal to be the temperature given by the intercept of the extended baseline and the extended tangent to the first slope of the endotherm, i.e. the onset temper
42、ature shown as A 7.1.2.2 Repeat the procedure given in 7.1.2.1 using a piece of the other calibration metai. 7.1.2.3 Adjust the apparatus so that the indicated melting point of indium lies within (156,6 f 0,3) “C and that of tin lie within (231,9 f 0,3) “C. NOTE. The described dynamic cabbration pro
43、cedure according to 7.1.2.3 is expected to correspond to the isothermal calibration within the experimental error. 7.1.3 lme calibration For a chart output, use a timer (6.6) to check that the pen moves along the abscissa at a known rate. 7.4 Measurement of oxidation induction time Before their use,
44、 ensure that the test piece pan(s) and reference pan are clean, e.g. by cleaning with an appropriate solvent (see 4.4) such as hexane. Establish a nitrogen flow of 50 mlhnin f 10 % through the DSC or DTA Check that when a switchover to oxygen is made, the gas flow will continue at that rate. Revert
45、to a nitrogen flow of 50 dmin 10 %. Put a test piece into the test piece pan, ensuring as good initial contact with the pan as possible. If the test piece includes the inner or outer surface of the source pipe or fitting (see clause 3), place it in the pan with that surface uppermost. Introduce an o
46、pen or ventilated aluminium pan conmg a test piece and an empty aluminium reference pan into the instrument. Purge the instrument oven with nilxogen for 3 min to expel any oxygen. Set the instrument both to raise the temperature from an ambient start temperature of 50 “C at a rate of 20 Wmin and to
47、run isothermally at T “C until the temperature has Mied. Start to record the thermogram as a plot of the energy flow difference (A c) the position(s) in the pipe or fitting wall cross section hm which the test pieces were derived; d) the mass of the test piece, in milligrams; e) the oxidation induct
48、ion time, t, of each test piece, and, if applicable, the mean, maximum and minimum values and a copy of the thermogram(s); f) the test temperature, g) manufacture, model and type SC or DTA) of instrument used, h) details of any changes in the test piece appearance (see 8.2); i) any factors which may
49、 have affected the results, such as any incidents or any operating details not j) the date of test. in degrees Celsius; specified in this standard O BSI 1997 STD=BSI BS EN 728-ENGL 2777 Lb24bb7 Ob23bZB bL7 W BS EN 728 : 1997 List of references See national foreword. * tn * O BSI 1997 BS EN 728 : 1997 BS 2782 : Part 11 : Method 1103D : 1997 BSI 389 Chiswick High Road London w4 4AL BSI - British Standards Institution BSI is the independent nationai body responsible for preparing British Standards. It presents the UK view on standards in Europe and at
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