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Designation G42 − 11 Reapproved 2019´1Standard Test Method forCathodic Disbonding of Pipeline Coatings Subjected toElevated Temperatures1This standard is issued under the fixed designation G42; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon ´ indicates an editorial change since the last revision or reapproval.ε1NOTEEditorial changes were made throughout in July 2019.1. Scope1.1 This test method describes an accelerated procedure fordetermining comparative characteristics of insulating coatingsystems applied to steel pipe exterior for the purpose ofpreventing or mitigating corrosion that may occur in under-ground service where the pipe will be exposed to hightemperatures and is under cathodic protection. This test methodis intended for use with samples of coated pipe taken fromcommercial production and is applicable to such samples whenthe coating is characterized by function as an electrical barrier.1.2 This test method is intended for testing coatings sub-merged or immersed in the test solution at elevated tempera-ture. When it is impractical to submerge or immerse the testspecimen, Test Method G95 may be considered where the testcell is cemented to the surface of the coated pipe specimen. Ifroom temperatures are required, see Test Methods G8.Ifaspecific test method is required with no options, see TestMethod G80.1.3 The values stated in SI units to three significant deci-mals are to be regarded as the standard. The values given inparentheses are for information only.1.4 WarningMercury has been designated by EPA andmany state agencies as a hazardous material that can causecentral nervous system, kidney, and liver damage. Mercury, orits vapor, may be hazardous to health and corrosive tomaterials. Caution should be taken when handling mercury andmercury-containing products. See the applicable product Ma-terial Safety Data Sheet MSDS for details and EPA’s websitehttp//www.epa.gov/mercury/faq.htm for additional informa-tion. Users should be aware that selling mercury or mercury-containing products, or both, in your state may be prohibited bystate law.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade TBT Committee.2. Referenced Documents2.1 ASTM Standards2G8 Test Methods for Cathodic Disbonding of Pipeline Coat-ingsG12 Test Method for Nondestructive Measurement of FilmThickness of Pipeline Coatings on Steel Withdrawn20133G80 Test Method for Specific Cathodic Disbonding of Pipe-line Coatings Withdrawn 20133G95 Test Method for Cathodic Disbondment Test of PipelineCoatings Attached Cell MethodE1 Specification for ASTM Liquid-in-Glass ThermometersE2251 Specification for Liquid-in-Glass ASTM Thermom-eters with Low-Hazard Precision Liquids3. Summary of Test Method3.1 This test method subjects the coating on the test speci-men to electrical stress in a highly conductive electrolyte. Thecoating is artificially perforated before starting the test. Theelectrical stress is produced by connecting the test specimen tothe negative terminal of a source of direct current and byconnecting an anode to the positive terminal. Electrical instru-mentation is provided for measuring the current flowing in the1This test method is under the jurisdiction of ASTM Committee D01 on Paintand Related Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.48 on Durability of Pipeline Coating and Linings.Current edition approved July 1, 2019. Published July 2019. Originally approvedin 1975. Last previous edition approved in 2011 as G42 – 11. DOI 10.1520/G0042-11R19E01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade TBT Committee.1cell.The electrical potential is also measured, and the specimenis physically examined at intervals during the test period andupon conclusion of the test.3.1.1 The cathodic stress is applied under conditions of aconstant-elevated temperature.4. Significance and Use4.1 Damage to pipe coating is almost unavoidable duringtransportation and construction. Breaks or holidays in pipecoatings may expose the pipe to possible corrosion since, aftera pipe has been installed underground, the surrounding earthwill be moisture-bearing and will constitute an effectiveelectrolyte. Applied cathodic protection potentials may causeloosening of the coating, beginning at holiday edges. Sponta-neous holidays may also be caused by such potentials. This testmethod provides accelerated conditions for cathodic disbond-ment to occur and provides a measure of resistance of coatingsto this type of action.4.2 The effects of the test are to be evaluated by physicalexaminations and monitoring the current drawn by the testspecimen. Usually there is no correlation between the twomethods of evaluation, but both methods are significant.Physical examination consists of assessing the effective contactof the coating with the metal surface in terms of observeddifferences in the relative adhesive bond. It is usually foundthat the cathodically disbonded area propagates from an areawhere adhesion is zero to an area where adhesion reaches theoriginal level.An intermediate zone of decreased adhesion mayalso be present.4.3 Assumptions associated with test results include4.3.1 Maximum adhesion, or bond, is found in the coatingthat was not immersed in the test liquid, and4.3.2 Decreased adhesion in the immersed test area is theresult of cathodic disbondment.4.4 Ability to resist disbondment is a desired quality on acomparative basis, but disbondment in this test method is notnecessarily an adverse indication of coating performance. Thevirtue of this test method is that all dielectric-type coatings nowin common use will disbond to some degree, thus providing ameans of comparing one coating to another.4.5 The current density appearing in this test method ismuch greater than that usually required for cathodic protectionin natural environments.4.6 That any relatively lesser bonded area was caused byelectrical stressing in combination with the elevated and ordepressed temperature and was not attributable to an anomalyin the application process. Ability to resist disbondment is adesired quality on a comparative basis, but most insulatingmaterials will disbond to some extent under the acceleratedconditions of this test. Bond strength is more important forproper functioning of some coatings than others and the samemeasured disbondment for two different coating systems maynot represent equivalent loss of corrosion protection.4.6.1 The amount of current flowing in the test cell may bea relative indicator of the extent of areas requiring protectionagainst corrosion; however, the current density appearing inthis test is much greater than that usually required for cathodicprotection in natural, inland soil environments.4.6.2 Test voltages higher than those recommended mayresult in the formation of chlorine gas. The subsequent chemi-cal effects on the coating could cast doubt on the interpretationof the test results.5. Apparatus5.1 Test VesselAsuitable nonreactive vessel shall be used,capable of withstanding internal heating at not less than 60°Cand suitable for continuous circulation of the electrolyte.A 19-L 5-gal cylindrical glass vessel has been found suitable,having an approximate diameter of 300 mm 12 in. and adepth of 300 mm. A flat bottom is required for operation of amagnetic stirring rod. An alternate means of heating the testsample can be provided by internally heating. The pipe samplemay be filled with a suitable heat transfer material oil, steelshot, etc.. A thermocouple or thermometer and heater can beimmersed in the heat transfer medium to effectively control thetemperature of the sample. Dimensions of the vessel shallpermit the following requirements5.1.1 Test specimens shall be suspended vertically in thevessel with at least 25 mm 1 in. clearance from the bottom.5.1.2 Test specimens shall be separated by not less than38 mm 11⁄2 in., and a vertically suspended anode can beplaced at an equal distance from each specimen not less thanthe separation distance.5.1.3 Test specimens shall be separated from any wall of thevessel by not less than 13 mm 1⁄2 in..5.1.4 Depth of electrolyte shall permit the test length of thespecimen to be immersed as required in The reference electrode may be placed anywhere inthe vessel, provided it is separated from the specimen and fromthe anode by not less than 38 mm 11⁄2 in..5.2 AnodeThe anode shall be provided with a factory-sealed, insulated copper wire lead.45.3 ConnectorsWiring from anode to test specimen shallbe 4107 cmil 14-gage Awg, minimum, insulated copper.Attachment to the test specimen shall be by soldering orbrazing to the non-immersed end, and the place of attachmentshall be coated with an insulating material. A junction in theconnecting wire is permitted, provided that it is made by meansof a bolted pair of terminal lugs soldered or mechanicallycrimped to clean wire ends.5.4 Holiday ToolsHolidays shall be made with conven-tional drills of the required diameter. For use in preparingsmall-diameter pipe specimens such as 19-mm 3⁄4-in. nominaldiameter pipe, the use of a drill modified by substantiallygrinding away the sharp cone point has been found effective inpreventing perforation of the metal wall of the pipe. Asharp-pointed knife with a safe handle is required for use inmaking physical examinations.5.5 Multimeters4Duriron, a material found suitable for this purpose is available from DurironCo., Inc., Dayton, OH.G42 − 11 2019´125.5.1 Multimeter, for direct current, having an internalresistance of not less than 10 MΩ and having a range from 0.01to 5 V for measuring potential to the reference electrode.5.5.2 Multimeter, for direct current, having an internalresistance of not less than 11 MΩ and capable of measuring aslow as 10 µV potential drop across a shunt in the test cellcircuit.5.5.3 Multimeter, for initial testing of apparent coatingresistance.5.6 Reference ElectrodeSaturated Cu CuSO4electrodehaving a potential of −0.316 V with respect to the standardhydrogen electrode shall be the standard of reference in thesetest methods. Other electrodes may be used but measurementsthus obtained shall be converted to the Cu CuSO4reference forreporting by making the proper correction.NOTE 1Asaturated Cu CuSO4electrode reading −1.50 V at 25°C willread −1.53 V at 60°C, a scale increase of 0.03 V5.6.1 A saturated calomel electrode at 25°C is converted toCu CuSO4by adding −0.07 V to the observed reading. If thesaturated calomel electrode reads −1.43 V at 25°C, it will read−1.46 V at 60°C, a scale increase of 0.03 V. It follows that asaturated calomel electrode reading of −1.46 V at 60°C is equalto a saturated Cu CuSO4reading of −1.50 V at 25°C.5.6.2 A0.1 normal calomel electrode at 25°C is converted toCu CuSO4by subtracting −0.02 V from the observed reading.Since the potential change due to an increase from 25°C to60°C is negligible, it follows that a 0.1 normal calomelelectrode reading −1.52 V at 60°C is equal to a saturated CuCuSO4reading of −1.50 V at 25°C.5.7 Thermometers, two, mercury-filled type or liquid-in-glass, accurate to 61°C. One shall be of the full-immersiontype for measuring temperature near the bottom of the vessel,and a second thermometer shall be of the partial-total-immersion type for measuring temperature near the top of thevessel. Liquid-in-glass thermometers shall conform to Speci-fications E1 or E2251. Electronic temperature reading devicessuch as RTDs, thermistors or thermocouple of equal or betteraccuracy may be used.5.8 Combination Heater Plate, with built-in magneticstirrer, or equivalent, shall be used for heating and stirring theelectrolyte. The heater shall be adjustable to produce andcontrol a temperature of 60 6 1°C in the test vessel.5.9 Direct-Current Rectifier, capable of supplying constantcurrent at a voltage of 1.50 6 0.01 V, as measured between thespecimen and reference cell.5.10 Thickness Gage, for measuring coating thickness inaccordance with Test Method G12.5.11 Precision Resistor, 1Ω 6 1 , 1 W min, to be used inthe test cell circuit as a shunt for current.5.12 Carbon or Stainless Steel Electrode, used temporarilywith the volt-ohm-meter to determine apparent initial holidaystatus of the test specimen.5.13 Additional Connecting Wires, 4107 cmil 14-gageAwg, minimum, insulated copper.5.14 Brass Studs, used at a terminal board, together withalligator clips or knife switches, for making and breakingcircuits. Alligator clips shall not be used to connect theelectrodes or specimens at the top location of test cells.6. Reagents and Materials6.1 The electrolyte shall consist of potable tap water orhigher purity water distilled or demineralized water is satis-factory with the addition of 1 weight of each of thefollowing technical-grade salts, calculated on an anhydrousbasis sodium chloride, sodium sulfate, and sodium carbonate.NOTE 2The resulting solution has a pH of 10 or higher and aresistivity of 25 to 50 Ω·cm at room temperature.6.2 Materials for sealing the ends of coated pipe specimensmay consist of bituminous products, wax, epoxy, or othermaterials, including molded elastomeric or plastic end caps,capable of withstanding the test temperature.6.3 Plywood has been found suitable for the construction ofnonconductive test vessel covers and for the support throughapertures of test specimens and electrodes. Wood dowelsintroduced through holes in the top ends of test specimens havebeen found suitable for suspending test specimens from thevessel cover.7. Test Specimen7.1 The test specimen shall be a repres