BS EN 12814-3:2014 BSI Standards Publication Testing of welded joints in thermoplastics semi-finished products Part 3: Tensile creep test BS EN 12814-3:2014 BRITISH STANDARD National foreword This British Standard is the UK implementation of EN 12814-3:2014 It supersedes BS EN 12814-3:2000 which is withdrawn The UK participation in its preparation was entrusted to Technical Committee PRI/80, Welding thermoplastics A list of organizations represented on this committee can be obtained on request to its secretary This publication does not purport to include all the necessary provisions of a contract Users are responsible for its correct application © The British Standards Institution 2014 Published by BSI Standards Limited 2014 ISBN 978 580 78955 ICS 25.160.40 Compliance with a British Standard cannot confer immunity from legal obligations This British Standard was published under the authority of the Standards Policy and Strategy Committee on 28 February 2014 Amendments issued since publication Date Text affected BS EN 12814-3:2014 EN 12814-3 EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM February 2014 ICS 25.160.40 Supersedes EN 12814-3:2000 English Version Testing of welded joints in thermoplastics semi-finished products - Part 3: Tensile creep test Essais des assemblages soudés sur produits semi-finis en thermoplastiques - Partie 3: Essai de fluage en traction Prüfen von Schweißverbindungen aus thermoplastischen Kunststoffen - Teil 3: Zeitstand-Zugversuch This European Standard was approved by CEN on 30 November 2013 CEN 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 CEN-CENELEC Management Centre or to any CEN 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 CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom EUROPEAN COMMITTEE FOR STANDARDIZATION COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels © 2014 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members Ref No EN 12814-3:2014 E BS 12814-3:2014 ENEN 12814-3:2014 (E) Contents Page Foreword Introduction Scope Normative references Terms and definitions Symbols and designations 5 Principle of the test 6 Sampling procedures 7 Dimensions of test specimens .7 Cutting and preparation of test specimens 9 Mechanical testing 10 10 Test equipment 10 11 Determination of the long-term welding factor 11 12 Test report 13 Annex A (informative) Resistance to slow crack growth 15 Annex B (informative) Whole pipe tensile creep rupture test 18 Annex C (informative) Minimum creep rupture time of the parent material (ttm) for applicability of the long-term welding factor 21 Annex D (informative) Testing of socket joints 22 Bibliography 25 BS EN 12814-3:2014 EN 12814-3:2014 (E) Foreword This document (EN 12814-3:2014) has been prepared by Technical Committee CEN/TC 249 “Plastics”, the secretariat of which is held by NBN This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by August 2014, and conflicting national standards shall be withdrawn at the latest by August 2014 Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights This document supersedes EN 12814-3:2000 The main changes with respect to the previous edition are listed below: a) addition of a NOTE for an alternative test using a whole pipe welded sample (Clause 5) making reference to Annex B (informative), Whole pipe tensile creep rupture test; b) addition of a NOTE for the sampling procedures (Clause 6) in case of socket joints with reference to Annex D (informative), Testing of socket joints EN 12814, Testing of welded joints of thermoplastics semi-finished products, is divided into the following parts: — Part 1: Bend test; — Part 2: Tensile test; — Part 3: Tensile creep test (the present document); — Part 4: Peel test; — Part 5: Macroscopic examination; — Part 6: Low temperature tensile test; — Part 7: Tensile test with waisted test specimens; — Part 8: Requirements According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom BS 12814-3:2014 ENEN 12814-3:2014 (E) Introduction The design of welded thermoplastics constructions under static load is based on the long-term creep rupture with behaviour, specifically the resistance to slow crack growth of the thermoplastics material and the welds For design purposes, the relevant characteristic values for the welded joints are the “long-term tensile welding factors” to which this European Standard provides the test method The long-term tensile welding factors are normally used in conjunction with the creep rupture curve of the parent material, given for example in EN 1778, when designing welded semi-finished products under static load The long-term tensile welding factor(s), the crack behaviour and the appearance of the fracture surface provide information on the quality of the weld NOTE The behaviour of the failure obtained during the tensile creep test can be related to the notch sensitivity of the parent material An example of a test to provide information about the notch sensitivity of parent material is given in Annex A BS EN 12814-3:2014 EN 12814-3:2014 (E) Scope This European Standard specifies the dimensions, the method of sampling and the preparation of the test specimens, and the conditions for performing the tensile creep test perpendicular to the weld in order to determine the long-term tensile welding factor A tensile creep test may be used in conjunction with other tests (e.g bend test, tensile test, macrographic examination, …) to assess the performance of welded assemblies, made from thermoplastics materials The test is applicable to welded assemblies made from thermoplastics materials filled or unfilled such as tubes and fittings, sheets, plates and profiles, but not reinforced, irrespective of the welding process used Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application For dated references, only the edition cited applies For undated references, the latest edition of the referenced document (including any amendments) applies EN 13100-1, Non destructive testing of welded joints of thermoplastics semi-finished products — Part 1: Visual examination EN ISO 899-1, Plastics — Determination of creep behaviour — Part 1: Tensile creep (ISO 899-1) Terms and definitions For the purposes of this document, the following terms and definitions apply 3.1 test temperature temperature of the medium surrounding the test specimen during the test 3.2 test stress test load divided by the minimum cross sectional area of the test specimen 3.3 creep rupture curve regression curve through the geometric mean values of failure times 3.4 minimum failure time ttm creep rupture time of the parent material to ensure that the test method is applicable 3.5 ductile fracture large scale deformation of material from fracture surfaces 3.6 brittle fracture little or no deformation of material from fracture surfaces Symbols and designations Symbols and designations are given in Table BS 12814-3:2014 ENEN 12814-3:2014 (E) Table — Symbols and designations Designations Symbols a Minimum measured thickness of test specimen within calibrated and parallel length mm an Nominal thickness of test piece mm b Width of calibrated and parallel length of the test specimen mm b1 Width of shoulder of the test specimen mm c Depth of the notch mm Nominal outside diameter of the tube mm Dn fl Long-term tensile welding factor Fs Value of the force applied to the welded test specimen calculated from the chosen value of σs N Ft Value of the force applied to the unwelded test specimen calculated from the chosen value of σt N L Total length of the test specimen mm Lj Minimum distance between the clamping jaws mm L0 Calibrated and parallel length of the test specimen mm Maximum width of the weld bead of the test specimen mm Radius of shoulder of the test specimen mm Lw a r a Units ttm Minimum failure time σs Value of stress of the welded test specimens used in the calculation of fl N/mm σt Reference stress Value of stress of the unwelded test specimens, used in the calculation of fl N/mm h For extrusion and hot gas welds only Principle of the test The test involves subjecting a test specimen to a constant load until fracture occurs The time to fracture is measured and recorded NOTE Annex B An alternative test using a whole pipe welded sample rather that a test specimen cut form the weld is given in BS EN 12814-3:2014 EN 12814-3:2014 (E) The tests are carried out over a range of temperatures and loads, and in a test medium Only such media shall be used which cause no swelling or degradation of the polymer Examples of available test media are air, water or solutions of demineralised water with detergents Care should be taken to ensure that the condition of the test medium does not influence the results of the test The applicability of the long-term tensile welding factor for design purposes requires a minimum creep rupture time for the parent material (ttm) Before determining the long-term welding factor for the materials mentioned in Annex C, a tensile creep test should be carried out on the parent material at one of the test conditions given in Table C.1 The values of creep rupture time should be at least that quoted in Table C.1 Application standards may prescribe higher values for these rupture times depending upon the semi-finished product and material Sampling procedures Welded and unwelded test specimens shall be taken from the same test piece NOTE In the case of socket joints, see Annex D The test specimens (welded and unwelded) shall be cut perpendicular to the welded joint at least eight hours after welding For sheets where the extrusion direction is different on either side of the weld, the unwelded test specimens shall be taken from the side of the test piece which has the lowest creep rupture time Each test specimen shall be marked in order to identify its original position within the test piece No heat treatment or mechanical straightening operations shall be carried out on the test specimen Dimensions of test specimens The dimensions of test specimens according to Figure are given in Table and those according to Figure are given in Table Profiles can be tested if test specimens are in accordance with the dimensions given in Table or Table For tubes having nominal outside diameter less than 20 mm, the whole tube shall be tested In this case, the minimum distance between the clamps shall be 200 mm BS 12814-3:2014 ENEN 12814-3:2014 (E) Key Lj = L0 + (2xb) Figure — Type test specimen for flat and tubular assemblies Figure — Type test specimen for flat and tubular assemblies BS 12814-3:2014 ENEN 12814-3:2014 (E) w) calculated value of the long-term tensile welding factor (fl) with information about the reference stress of the parent material; x) identification of the laboratory; y) date of the test; z) name and signature of the responsible person for the test report 14 BS EN 12814-3:2014 EN 12814-3:2014 (E) Annex A (informative) Resistance to slow crack growth A.1 Full notch creep test (FNCT) A.1.1 Principle The resistance to slow crack growth of the parent material can be determined using the Full Notch Creep Test The applied stress chosen should be such that it induces a brittle fracture surface Values for test stress and test temperature are given in Table C.1 For thermoplastics, lower temperatures will increase the time to failure of the test piece A.1.2 Preparation of the test specimens The test specimens for the FNCT shall be cut from the parent material perpendicular to the welded joint from the same test piece used for the tensile creep test The test specimens for the FNCT shall be cut with parallel sides as shown in Figure A.1 The minimum distance between the clamps and the notch shall be x an A.1.3 Test specimen notching The test specimen shall be notched on all four sides in the same plane The depth of the notch, c, shall be 17 % ± % of the measured thickness, a A notch is produced by pressing a razor blade or a similar tool, which gives an identical result, into the test specimen It is important to make all the notches coplanar Test specimens shall be notched at a room temperature of 23 °C ± °C To ensure consistency of results, the razor blade shall be periodically changed A.1.4 Mounting and conditioning The test specimen shall be loaded free from external torsion and bendings effects The whole test specimen shall be immersed in the test medium The test specimen shall be conditioned to the test temperature before loading A.1.5 Calculation of the test load (Ft) Ft = A x σ where Ft is the test load (N); A is the ligament area of the test specimen after notching (mm ); σ is the tensile stress according to Table C.1 (N/mm ) 2 15 BS 12814-3:2014 ENEN 12814-3:2014 (E) Key clamp notch a measured thickness of test specimen b width of test specimen c depth of the notch, where 0,95 x a ≤ b ≤ 1,05 x a Figure A.1 — FNCT test specimen A.2 Two notch creep test (2NCT) A.2.1 Principle The resistance to slow crack growth of parent material with a wall thickness of less than 10 mm can be determined using the Two Notch Creep Test The applied stress chosen should be such that it induces a brittle fracture surface The minimum thickness of the test specimens should be 3,0 mm Values for test stress and test temperature are given in Table C.1 For thermoplastics, lower temperatures will increase the time to failure of the test piece A.2.2 Preparation of the test specimens The test specimens for the 2NCT shall be cut from the parent material perpendicular to the welded joint from the same test piece used for the tensile creep test The test specimens for the 2NCT shall be cut with parallel sides as shown in Figure A.2 The minimum distance between the clamps and the notch shall be x an A.2.3 Test specimen notching The test specimen shall be notched on two sides in the same plane The depth of the notch, c, shall be 17 % ± % of the measured width, b A notch is produced by pressing a razor blade or a similar tool, which gives an identical result, into the test specimen It is important to make both notches coplanar Test specimens shall be notched at a room temperature of 23 °C ± °C To ensure consistency of results, the razor blade shall be periodically changed 16 BS EN 12814-3:2014 EN 12814-3:2014 (E) A.2.4 Mounting and conditioning The test specimen shall be loaded free from external torsion and bendings effects The whole test specimen shall be immersed in the test medium The test specimen shall be conditioned to the test temperature before loading A.2.5 Calculation of the test load (Ft) Ft = A x σ where Ft is the test load (N); A is the ligament area of the test specimen after notching (mm ); σ is the tensile stress according to Table C.1 (N/mm ); 2 Key load notch sheet: a measured thickness of test specimen b width of test specimen c depth of the notch with a ≥ 1,7 mm pipe Figure A.2 — 2NCT test specimen 17 BS 12814-3:2014 ENEN 12814-3:2014 (E) Annex B (informative) Whole pipe tensile creep rupture test B.1 General This test is applicable to welded pipe assemblies made from thermoplastics materials, irrespective of the welding process used It has the advantage that it tests the whole welded joint The test results can be used for comparative purposes and can be used to optimise the welding process B.2 Principle The test involves subjecting a welded length of pipe to a constant load at a constant elevated temperature until fracture occurs The time to fracture is measured and recorded B.3 Mounting and conditioning The test sample shall be loaded free from external torsion and bending The whole sample between the end fittings shall be immersed in the test medium The test sample shall be conditioned to the test temperature before loading B.4 Mechanical testing Figure B.1 shows an example of the test equipment for the whole pipe tensile creep rupture test 18 BS EN 12814-3:2014 EN 12814-3:2014 (E) Key hydraulic jack supporting plate water line top end fitting push rod weld pipe test sample bottom end fitting Figure B.1 — Example of test equipment for whole pipe tensile creep rupture tests The test conditions shall be chosen such that at least 30 % of the wall thickness at the location of the failure has undergone brittle fracture, as shown in Figure B.2 19 BS 12814-3:2014 ENEN 12814-3:2014 (E) Figure B.2 — Typical fracture surface at the location of failure B.5 Evaluation In order to evaluate the test results, the geometric mean value shall be calculated from the individual rupture times This value shall be used for comparative purposes only The determination of the long-term tensile welding factor is not required B.6 Test report The test report shall be as defined in Clause 12, except for the calculated value of the long-term tensile welding factor (fl) 20 BS EN 12814-3:2014 EN 12814-3:2014 (E) Annex C (informative) Minimum creep rupture time of the parent material (ttm) for applicability of the long-term welding factor Table C.1 — ttm values for some thermoplastics materials a a Material Stress MPa Temperature °C ttm h PP-H 95 400 PP-H 3,5 95 600 PE 80 500 These values were determined in a test medium of demineralised water containing % of nonyl-phenoxy (ethyleneoxy) ethanol with 10 ethyleneoxide molecules 21 BS 12814-3:2014 ENEN 12814-3:2014 (E) Annex D (informative) Testing of socket joints D.1 General This test is valid for heated tool socket and electrofusion fittings welded to pipes with a minimum wall thickness of mm The test results can be used for comparative purposes and can be used to optimise, e.g the welding process or the construction of the fitting The comparison between electrofusion and heated tool socket fitting systems is not possible without additional analysis D.2 Sampling procedure The test specimens shall be cut perpendicular to the welded joint at least eight hours after welding At least six pre-test specimens shall be cut from each side of the welded joint, except for electrofusion fittings that have had both sides welded simultaneously, where three specimens from each side are sufficient However, if the results are significantly different between the two sides, the number of test specimens shall be increased to six per side D.3 Dimensions of test specimens The dimensions of the pre-test specimens are given in Figure D.1 Dimensions in millimetres Figure D.1 — Dimensions of pre-test specimen The dimensions of the final test specimen are given in Figure D.2 22 BS EN 12814-3:2014 EN 12814-3:2014 (E) Dimensions in millimetres Key pre-test specimen d = 16 mm L0 ≥ 2d Figure D.2 — Dimensions of final test specimen D.4 Cutting and preparation of test specimens Pre-test specimens shall be cut from the welded joint using, for example, a hole-driller The specimens shall be taken from the middle of the fusion length, as shown in Figure D.3 a) heated tool socket weld b) electrofusion weld Figure D.3 — Position of the pre-test specimen in the welded joint for Pre-test specimens cut from electrofusion joints shall contain at least three wires and shall contain no voids In order to produce the final test specimen, extension bars shall be welded (using, for example, heated tool butt welding) to the pre-test specimen, as shown in Figure D.4 The surfaces of the pre-test specimens shall be machined flat prior to welding 23 BS 12814-3:2014 ENEN 12814-3:2014 (E) Dimensions in millimetres Key pre-test specimen extension bar Figure D.4 — Welding extension bars to the pre-test specimen The material for the extension bars shall be the same as that of the pre-test specimen During welding of the extension bars, heating of the fusion line between the pipe and socket in the pre-test specimen shall be minimized If necessary, the test specimens can be quenched directly after welding of the extension bars D.5 Mechanical testing The recommended test parameters for PE joints are given in Table D.1 ) Table D.1 — Recommended test stresses and temperatures for PE joints Joint types Test stress N/mm Test temperature °C Heated tool socket 80 Electrofusion 80 For electrofusion joints, the reduction of the cross-section due to the wires shall not be taken into account when calculating the test load D.6 Evaluation In order to evaluate the test results, the geometric mean value shall be calculated from the individual rupture times This value shall be used for comparative purposes only The determination of the long-term tensile welding factor is not required Only test specimens that not fail in the extension bars or in the butt welds between the pre-test specimens and the extension bars and are free of voids around the heating wire shall be used in the evaluation If it is not possible to obtain pre-test specimens that are void-free, this test shall not be used D.7 Test report The test report shall be as defined in Clause 12, except for the calculated value of the long-term tensile welding factor (fl) 1) 24 There are insufficient data for other materials BS EN 12814-3:2014 EN 12814-3:2014 (E) Bibliography [1] EN 1778, Characteristic values for welded thermoplastics constructions — Determination of allowable stresses and moduli for design of thermoplastics equipment 25 This page deliberately left blank This page deliberately left blank NO COPYING WITHOUT BSI PERMISSION 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