EUROPEAN STANDARD EN 50290-2-24NORME EUROPÉENNE EUROPÄISCHE NORMJanuary 2002CENELECEuropean Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung Central Secretariat: rue de Stassart 35, B - 1050 Brussels© 2002 CENELEC -All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.Ref. No. EN 50290-2-24:2002 EICS 29.035.20; 33.120.10Supersedes HD 624.4 S1:1996English versionCommunication cablesPart 2-24: Common design rules and construction –PE sheathingCâbles de communicationPartie 2-24: Règles de conception communes et construction –Polyéthylène pour gainageKommunikationskabelTeil 2-24: Gemeinsame Regeln für Entwicklung und Konstruktion –PE-MantelmischungenThis European Standard was approved by CENELEC on 2001-11-01. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions.CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic,Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands,Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.EN 50290-2-24:2002- 2 -ForewordThis European Standard was prepared by a joint working group of the Technical Committees CENELEC TC 46X, Communication cables, and CENELEC TC 86A, Optical fibres and optical fibre cables.The text of the draft was submitted to the Unique Acceptance Procedure and was approved by CENELEC as EN 50290-2-24 on 2001-11-01.This European Standard supersedes HD 624.4 S1:1996.The following dates were fixed:–latest date by which the EN has to be implementedat national level by publication of an identicalnational standard or by endorsement(dop)2002-08-01–latest date by which the national standards conflictingwith the EN have to be withdrawn(dow)2004-08-01Annexes designated "normative" are part of the body of the standard.In this standard, annexes A, B and C are normative.This European Standard has been prepared under the European Mandate M/212 given to CENELEC by the European Commission and the European Free Trade Association._________- 3 -EN 50290-2-24:20021ScopeThis Part 2-24 of EN 50290 gives specific requirements for PE sheathing compounds used in communication cables.It is to be read in conjunction with Part 2-20 of EN 50290.2Normative referencesThis European Standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply to this European Standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies (including amendments).EN 60811-1-1:1995Insulating and sheathing materials of electric and optical cables - Commontest methods -- Part 1-1: General application - Measurement of thickness andoverall dimensions - Tests for determining the mechanical properties(IEC 60811-1-1:1993)EN 60811-1-2:1995Insulating and sheathing materials of electric cables - Common test methodsPart 1-2: General application -- Thermal ageing methods(IEC 60811-1-2:1985 + corr. May 1986 + A1:1989)EN 60811-1-3:1995Insulating and sheathing materials of electric and optical cables - Commontest methods -- Part 1-3: General application - Methods for determining thedensity - Water absorption tests - Shrinkage test (IEC 60811-1-3:1993)EN 60811-1-4:1995Insulating and sheathing materials of electric and optical cables - Commontest methods -- Part 1-4: General application - Tests at low temperature(IEC 60811-1-4:1985 + corr. May 1986 + A1:1993)EN 60811-4-1:1995Insulating and sheathing materials of electric cables - Common test methods- - Part 4: Methods specific to polyethylene and polypropylene compounds - -Section 1: Resistance to environmental stress cracking - Wrapping test afterthermal ageing in air - Measurement of the melt flow index - Carbon blackand/or mineral content measurement in PE (IEC 60811-4-1:1985)EN 60811-4-2:1999Insulating and sheathing materials of electric and optical fibre cables -Common test methods - - Part 4: Methods specific to polyethylene andpolypropylene compounds Section 2: Tensile strength and elongation at breakafter pre-conditioning - Wrapping test after thermal ageing in air -Measurement of mass increase – Long - term stability test - Test method forcopper - catalysed oxidative degradation(IEC 60811-4-2:1990, mod.)3RequirementsIn case of specific applications, additional performances could be needed. Relevant test methods and requirements shall be included in the detail specifications of the cables.EN 50290-2-24:2002- 4 -Table 1 - Black PE sheathing compoundsCharacteristicsTest method Unit Grades 1)LD/MD HD LLD1Maximum rated temperature atcable for which the compound canbe used° C702)80802Density 1)(without carbon black)EN 60811-1-3clause 8g/cm3£ 0,940> 0,940£ 0,9403Melt flow index 1) (see note 1)EN 60811-4-1clause 10g/10 min£ 0,4£ 2,53)£ 1,0£ 2,04Mechanical characteristics EN 60811-1-19.24.1 4.11In state of deliveryTensile strength- median, minMPa1018164.12Elongation at break- median, min%300300500 4.2After ageing EN 60811-1-28.1Ageing conditions- temperature - duration ° Ch100 ± 224 x 10100 ± 224 x 10100 ± 224 x 10Elongation at break- median, min%300300500 5Shrinkage3)EN 60811-1-3clause 11Test conditions- sample length(if not otherwise specifed)- temperature- durationResult to be obtained- shrinkage, max mm° Ch%2004)4)4)2004)4)4)2004)4)4)1)to be given by the supplier2)80 °C for MD3)for special application4)in the relevant cable specification- 5 -EN 50290-2-24:2002 Table 1 - Black PE sheathing compounds (Cont'd)Characteristics Test method Unit Grades 1)LD/MD HD LLD6Performances afterpre-conditioning(for sheath in direct contact withfilling compound)Annex ATest conditions- temperature - duration ° Ch60/70 ± 27 x 2460/70 ± 27 x 2460/70 ± 27 x 246.11Result to be obtainedTensile strength- median, minMPa1018166.12Elongation at break- median, min%3003005007Carbon black content5)EN 60811-4-1clause 11%2,5 ± 0,52,5 ± 0,52,5 ± 0,5 8Carbon black dispersion5)Annex B To meet To meet To meet9Stress cracking5) (see note 2)EN 60811-4-1clause 8Procedure BTo meet To meet To meet5) For inner sheath applications, non black PE compounds can be used, then items 7, 8, 9 may not apply.NOTE 1 If required, MFI may be measured on sheath with other values to be specified.NOTE 2Stress cracking test on raw material may not be sufficient to guarantee a stress cracking performance on finished product. Therefore an additional test has to be performed either on complete cable or on a piece of sheath taken from complete cable, in accordance with the test methods described in annex C.EN 50290-2-24:2002- 6 -Table 2 - Coloured PE sheathing compoundsCharacteristics Test method Unit Grades 1)LD/MD HD LLD 1Maximum rated temperature atcable for which the compound canbe used° C702)80802Density1)EN 60811-1-3clause 8g/cm3£ 0,940> 0,940£ 0,9403Melt flow index 1) (see note 1)EN 60811-4-1clause 10g/10 min£ 0,4£ 2,53)£ 1,0£ 2,04Mechanical characteristics EN 60811-1-19.24.1 4.11In state of deliveryTensile strength- median, minMPa1018164.12Elongation at break- median, min%300300500 4.2After ageing EN 60811-1-28.1Ageing conditions- temperature - duration ° Ch100 ± 224 x 10100 ± 224 x 10100 ± 224 x 10Elongation at break- median, min%300300500 5Shrinkage 3)EN 60811-1-3clause 11Test conditions- sample length(if not otherwise specifed) - temperature- durationResult to be obtained- shrinkage, max mm° Ch%2004)4)4)2004)4)4)2004)4)4)1)to be given by the supplier on the basic resin2) 80 °C for MD3)for special application4) in the relevant cable specification- 7 -EN 50290-2-24:2002 Table 2 - Coloured PE sheathing compounds (Cont'd)Characteristics Test method Unit Grades 1)LD/MD HD LLD6Performances afterpre-conditioning(for sheath in direct contact withfilling compound)Annex ATest conditions- temperature - duration ° Ch60/70 ± 27 x 2460/70 ± 27 x 2460/70 ± 27 x 24Result to be obtainedTensile strength- median, minMPa101816Elongation at break- median, min%3003005007Stress cracking 5) (see note 2)EN 60811-4-1clause 8Procedure BTo meet To meet To meet5)For inner sheath applications, item 7 may not apply – Natural grades can be usedNOTE 1 If required, MFI may be measured on sheath with other values to be specified.NOTE 2 Stress cracking test on raw material may not be sufficient to guarantee a stress cracking performance on finished product. Therefore an additional test has to be performed either on complete cable or on a piece of sheath taken from complete cable, in accordance with the test methods described in annex C.Guidance to use:Natural or coloured polyolefin cable sheaths, containing conventional antioxidant stabilisers degrade rapidly when subjected to natural daylight weathering through photocatalysed oxidation (actinic degradation). Degradation is manifested by discolouration of the sheath followed immediately by loss of mechanical properties and spontaneous cracking.This ageing process is accelerated in situations where the sheath is physically stressed, for example at sharp bends. Under temperate European climates failure can occur within two years of exposure. Ageing will not only occur on installed cables but also on cables stored externally on drums or reels where the cables have been inadequately protected from solar radiation.Ultraviolet stabilisation systems may be incorporated in the sheath compound to extend the induction period before the onset of failure. Such systems will permit prolonged external storage of cables but their performance does not approach that of conventional sheaths containing a minimum of 2 % of carbon black. Consequently they are unsuitable for external use where long service lives are required, especially where the cable will be installed in exacting climatic conditions such as aerial cablesEN 50290-2-24:2002- 8 -Annex A(normative)Performances after pre-conditioningTo perform the test, use EN 60811-4-2 with the following modifications1:1 Scope - Second paragraphReplace "...elongation at break..." by "...tensile strength and elongation at break...".6 Pre-conditioningReplace the existing title by the following new title:6 Conditioning8 Elongation at break after pre-conditioningReplace the existing title and text of this clause by the following new title and text:8 Tensile strength and elongation at break after pre-conditioning8.1 GeneralThis text is intended for filled cables for polyolefin insulations with a wall thickness of more than 0,8 mm and for polyolefin sheaths in direct contact with filling compound.8.2 Pre-conditioning procedureA sample of complete cable of sufficient length shall be pre-conditioned in air (i.e. suspended in an oven). The duration of the test and the temperature of the air maintained continuously shall be as follows:-7 x 24 h at 60 °C for filling compound having a nominal drop-point above 50 °C and up to an including70 °C.-7 x 24 h at 70 °C for filling compound having a nominal drop-point above 70 °C.After pre-conditioning, the cable sample shall be left at ambient temperature for at least 16 h without being exposed to direct sunlight. Then the sheath and cores to be tested shall be taken from the cable and shall be cleaned by suitable means.8.3 Tensile strength and elongation tests after pre-conditioningTensile strength and/or elongation tests, with respect to requirements in the cable standard, on test pieces according to 8.2 shall be performed in accordance with clause 9 of EN 60811-1-1 without any further ageing treatment.1) The modifications listed are intended for revision of EN 60811-4-2 (IEC 60811-4-2).- 9 -EN 50290-2-24:2002 9 Wrapping test after pre-conditioning9.2 Test procedureReplace the existing title and text of the subclause by the following new title and text:9.2 Pre-conditoning procedureThe pre-conditiong shall be carried out in accordance with 8.2 of this standard. Then the cores to be tested shall be taken from the cable and shall be cleaned by suitable means.9.3 Evaluation of resultsReplace the existing title and text of the subclause by the following new title and text:9.3 Test procedureTest pieces according to 9.2 shall be subjected to a winding test in accordance with the method specified in 10.5.2.For cellular insulations including foam-skin having a wall thickness below or equal to 0,2 mm the pull exerted on the exposed conductor shall be reduced to about 7,5 N/mm2 with respect to the conductor cross-section.Add a new subclause:9.4 Evaluation of resultsAfter cooling down to ambient temperature, the test pieces shall show no cracks when examined with normal or corrected vision without magnification. The test may be repeated once only if one test piece fails.10.5 Test procedureReplace the existing text by the following new text, inserting two subclauses:10.5.1 Test pieces according to 10.3 shall be subjected, after ageing in accordance with 10.4, to a winding test at ambient temperature.10.5.2 The conductor shall be laid bare at one end. A weight shall be applied to the exposed conductor end, exerting a pull of about 15 N/mm2 ± 20 % with respect to the conductor cross-section. Ten windings shall be made on the other end of the test piece by means of a winding device in accordance with 10.2.2 on a metal mandrel at a speed of about one revolution per 5 s. The winding diameter shall be 1 to 1,5 times the test piece diameter. Subsequently, the test pieces wound on the mandrel shall be removed from the latter and shall be kept in their helical form for 24 h at 70 ± 2 °C in the vertical position, substantially in the middle of the heating chamber in accordance with 10.2.3.EN 50290-2-24:2002- 10 -Annex B(normative)2)Test methods for the assessment of carbon black dispersion inpolyethylene using a microscopeB.1 IntroductionThe methods below describe procedures for assessing the uniformity of dispersion of carbon black in a compound or extrusion.B.2 ScopeThese methods describe procedures for assessing the carbon black dispersion in polyethylene using a microscope.Procedure A is primarily intended for use with polyethylene compounds but may be used for extrusions.Procedure B is intended for use with polyethylene extrusions or moundings only.B.3 PrincipleProcedure AA small sample of the material is squeezed into a thin layer 20 m m to 30 m m thick between two microscope slides heated to either 170 °C to 210 °C, or a higher temperature if specified in the material specification.The pressed sample is examined microscopically by transmitted light. The frequency and size distribution of particles and agglomerates is measured and graded by comparison with Table B.1.The uniformity of dispersion is assessed by comparison with the photomicrographs of Table B.2.Procedure BA microtome section of the material, 10 m m to 20 m m thick, is examined as per procedure A.B.4 ApparatusThe following apparatus is required.B.4.1 Hot plateCapable of being controlled at the required temperature.B.4.2 Microscope slidesB.4.3 MicroscopeCalibrated and capable of at least X 200 magnification. The circular field of view at X 100 magnification shall be 0,7 mm ± 0,07 mm.2) Based on ISO document at draft stage, as ISO/DIS 18553.- 11 -EN 50290-2-24:2002 B.4.4 MicrotomeB.5 ProcedureB.5.1 Preparation of specimensProcedure APlace two of the clean microscope slides on the hotplate maintained at 170 °C to 210 °C, or other higher temperature, as specified in the material specification. Choose six separate granules of compound, or six separate parts of an extruded article, to be as representative as possible of the whole batch. Cut a specimen of approximate mass 0,2 mg from the interior of each granule or part. Place the six specimens on one of the hot microscope slides so that each one is approximately equidistant from its neighbour(s) and from adjacent edge(s) of the slide.Place the second slide over the first, and press the specimens out by applying even pressure for 1 minute to 2 minutes to the whole area of the face of the upper slide. Exert an amount of pressure for a period necessary for each specimen to be pressed out to a thickness of between 20 m m and 30 m m.After the specimens have been placed on the slide, the latter shall in no case remain on the hotplate for more than 3 minutes.Remove the slide from the hotplate and allow it to cool.NOTE Shims of metal or some other suitable material may be used to achieve the required specimen thickness and uniformity of thickness. Procedure BCut six microtome sections of thickness between 10 m m and 20 m m each approximately of mass 0,25 mg, from different parts of the extrusion or moulding.B.5.2 Assessment of dispersionAgglomeratesExamine the six specimens in turn under the microscope under transmitted light with a magnification of at least X 100.For each specimen examine the agglomerates checking that they are really pigment by varying the light intensity and using transmitted and reflected light if possible. Measure and record the largest dimension of each agglomerate, ignoring those less than 5 m m. Rate according to the size categories given in Table B.1. Examine the whole of the specimen.NOTE If larger sample sizes are used to prepare the specimens the number of for a 1,25 mg sample mass.For some pigments no particles or agglomerates greater than 5 m m may be visible, hence a grading of 0 is obtained from Table B.1.AppearanceExamine each of the specimens in turn under the microscope under transmitted light at a magnification X 100 ± 10.Compare each specimen with the micrographs in the Table B.2 for uniformity of appearance taking into account smears and streaks.EN 50290-2-24:2002- 12 -B.6 Expression of resultsB.6.1 Grading of agglomeratesUsing Table B.1, determine the highest grade for each sample. Calculate the arithmetic mean of the six gradings obtained, and express the result to a single decimal point, rounded up to its higher value (see the examples given in Table B.3).B.6.2 Rating of appearanceExpress the appearance as the highest comparative rating with the photomicrographs in Table B.2.B.7 RequirementsThe mean agglomerate grading shall not be greater than 4,0.The appearance rating shall not be worse than photomicrograph C2.- 13 -EN 50290-2-24:2002 Table B.1 (normative) - Grading table for agglomeratesDimensions(m)5to112131415161718191101111121131141 102030405060708090100110120130140150Grades000,5101£3+101,5£6+£3+102£ 12+£6+£3+102,5> 12+£ 12+£6+£3+103> 12+£ 12+£6+£3+103,5> 12+£ 12+£6+£3+104> 12+£ 12+£6+£3+104,5> 12+£ 12+£6+£3+105> 12+£ 12+£6+£3+105,5< 12+£ 12+£6+£3+106> 12+£ 12+£6+£3+106,5> 12+£ 12+£6+£3+107> 12+£ 12+£6+£3+10 NOTE 7 m m corresponds to 0,7 spc mm under a magnification of 100; similarly 60 m m corresponds to 6 spc mm under a magnification of 100.EN 50290-2-24:2002- 14 -Table B.2 (normative) - Photomicrographs for rating the appearance of dispersions- 15 -EN 50290-2-24:2002EN 50290-2-24:2002- 16 -Table B.3 (informative) - Examples of grading of agglomeratesTable B.3.1 - Example 1Dimension samples(m m)5to10112021303140415051606170Grading for the sampleSample 1321Grade 2,0 Sample 2351Grade 2,5 Sample 31421Grade 3,0 Sample 4322Grade 2,5 Sample 5324Grade 3,0 Sample 631257Grade 3,5Incidence of agglomerates by sizeTable B.3.1 shows the number of agglomerates, classed by size, in each sample.Gradings:(2,0 + 2,5 + 3,0 + 2,5 + 3,0 + 3,5) / 6 = 2,75Hence the mean grade = 2,8- 17 -EN 50290-2-24:2002 Table B.3 (informative) - Examples of grading of agglomerates (Cont’d)Table B.3.2 - Example 2Dimension samples(m m)5to1011202130314041505160Grading of the sampleSample 173931Grade 3,0 Sample 27393Grade 3,0 Sample 37353Grade 2,5 Sample 41951Grade 2,5 Sample 51952Grade 3,0 Sample 61Grade 3,0Incidence of agglomerates by sizeTable B.3.2 shows the number of agglomerates, classed by size, in each sample.Gradings:(3,0 + 3,0 + 2,5 + 2,5 + 3,0 + 3,0) / 6 = 2,8333Hence the mean grading = 2,9EN 50290-2-24:2002- 18 -Annex C(normative)Resistance to environmental stress cracking on cable sheathC.1 PurposeThe purpose of this annex is to describe methods to evaluate the resistance to stress cracking of the polyethylene cable jackets.C.2 Method A - Test on complete cableC.2.1 GeneralThis test method is applicable for all sizes of cable.A test specimen comprising a length of cable is submitted both to a constant deformation and to a surface-active liquid heated at 50 °C.C.2.2 ApparatusC.2.2.1 Metallic half-circular bends whose diameter is 12 times the cable diameter.C.2.2.2 A climatic circulating air oven whose dimensions are sufficient to accept bends with test specimens to be tested. The temperature shall be regulated (70 ± 1) °C.C.2.2.3 Surface-active liquid whose volume is sufficient and regulated (50 ± 1) °C.The surface-active liquid used is an aqueous solution containing 1 % of polyethanol-nonyl-phenol (Igepal CO-630 or Antarox CO-630 or equivalent).This reagent is bio-degradable, the bath shall be regenerated after a maximum 10 days of use.C.2.3 SpecimenTest specimens shall constitute cable lengths whose dimensions comply with the relevant bend diameter. These specimens shall form a semi-circle and shall be secured on the mandrel with metallic clamps or polyamide bonds, located at the end of the bend.A minimum length of one metre, for each cable, consisting of one or several specimens, shall be tested. C.2.4 ProcedureC.2.4.1 The bent cable on the mandrel is placed in the climatic oven for 4 hours; at a temperature of(70 ± 2) °C.C.2.4.2 The cable and the mandrel are then removed from the oven and kept at ambient temperature for a minimum duration of 4 hours.C.2.4.3 The specimen is removed from the mandrel, straightened and then bent in the reverse direction on the same mandrel.C.2.4.4 The specimen and the mandrel are then immersed in the bath of surface-actve liquid, heated to(50 ± 2) °C for 72 hours.- 19 -EN 50290-2-24:2002 C.2.5 Evaluation of resultsExamination for presence of cracks, with normal or corrected vision without magnification.C.2.6 Test reportThe test report shall mention- the type of cable;- the cable diameter;- the diameter of the bend used;- the number of specimens tested and their length;- any other observations;- the result obtained.C.3 method B - Test on pieces of sheathC.3.1 GeneralThis method can be used for cable diameter greater than 10 mm and sheath thickness greater than 1,6 mm.C.3.2 ApparatusC.3.2.1 An apparatus to achieve test pieces with two smooth and parallel surfaces by cutting.C.3.2.2 Electrically heated air ovenC.3.2.3 Clean, sharp, undamaged blanking die with blanking press suitable for cutting test pieces(38,0 ± 2,5) mm x (13,0 ± 0,8) mm or other suitable devices.In case of sheath thickness greater than 2,0 mm the sample thickness must be reduced by suitable means to the value specified in C.3.3.C.3.2.4 Dial gauge, with spherical measuring inset (ball-diameter: at least 3 mm) pressure of 0,3 N to 1,5 N.C.3.2.5 Notching device as in Figure C.1 with blades as in Figure C.2.C.3.2.6 Bending clamp assembly as in Figure C.3 with vice or other suitable device ensuring the symmetrical closing of the clamping jaws.C.3.2.7 Transfer tool assembly as in Figure C.4 for shifting in one operation the bent test piece(s) from the bending clamp to the brass channel.C.3.2.8 Brass channel specimen holder as in Figure C.5 for accommodating ten bent test pieces.C.3.2.9 Hard glass test tubes 200 mm x 32 mm for accommodating the brass channel specimen holder with the bent test specimens. The tubes are plugged by suitable aluminium foil wrapped corks (see Figure C.6).C.3.2.10 Reagent: 10 % aqueous solution of Igepal CO-630 or Antarox CO-630 or equivalent reagent.The reagent shall be used only once.C.3.2.11 A heated container of sufficient size and depth to accept racks which will hold the filled test tubes (Figure C.6). The temperature shall be maintained at (50 ± 0,5) °C by means of suitable equipment. The thermal capacity shall be high enough to ensure that the temperature does not drop below 49 °C even when the test tubes are inserted.EN 50290-2-24:2002- 20 -C.3.3 SamplesExamination of the PE cable sheaths. The surfaces shall not show any swellings, dents or holes.The apparatus as in C.3.2.1 is used to prepare strips with two parallel surfaces from the cable sheath. The samples should be taken in direction of the cable axis and approximately in the middle of the test piece, with a thickness of 1,8 mm, and from these strips 10 test pieces are prepared as in C.3.2.3. The thickness of these test pieces, measured using the dial gauge as in C.3.2.4, shall be (1,8 ± 0,2) mm.The surfaces of the test pieces shall be at right angles to each other, as oblique edges can lead to erroneous results. The test pieces are kept in a straight condition for at least 16 hours in the oven as in C.3.2.2 at a temperature of (70 ± 2) °C and then cooled to room temperature.C.3.4 ProcedureShortly before placing into the reagent, each of the test pieces shall be given a notch in the middle of the test piece surface (Figure C.7) using the notching devices as in C.3.2.5.The notch depth shall be 0,30 mm to 0,40 mm.NOTE The blade shall be neither dull nor damaged and, therefore, shall be replaced as required. Even under favourable conditions it should not be used for more than 100 notches.Ten test pieces are then placed , with the notch up, in the bending clamp as in C.3.2.6. The clamp is closed for 30 s to 35 s by means of a vice or a motor-driven arbor press at a constant speed.The bent test pieces are lifted with the transfer tool as in C.3.2.7 from the bending clamp and placed in the brass channel as in C.3.2.8. If some test pieces are riding too high in the holder they shall be forced down by manual pressure.The holder is inserted in a tube as in C.3.2.9, 5 min to 10 min after the test pieces have been bent. The test tube is filled with the appropriate reagent as in C.3.2.10 until all the test pieces are covered by the liquid, and shall be closed by a cork.The filled test tube shall be placed immediately in a rack in the heated container as in C.3.2.11. Care shall be taken that the test pieces do not touch the test tube during the test. The moment of insertion in the heated container shall be noted.The holder with the test tubes and the test pieces shall be maintained for 48 hours in the heated container at(50 ± 2) °C.C.3.5 Evaluation of resultsAfter removal from the heated container, the 10 test pieces are examined for cracks with normal or corrected vision without magnification.The test is considered as passed when none of ten test pieces shows a crack.If only one test piece fails, the test shall be repeated with 10 new test pieces from the cable sheath. Then only the test pieces of the repeated test will be considered. The test is considered as passed if no test piece fails.NOTE In general the stress cracks originate perpendiculary from the notch.。
