1、Designation: G42 11Standard 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
2、 of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes an accelerated procedure fordetermining comparative characteristics of insulating coatingsy
3、stems 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 p
4、roduction 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
5、, 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-mal
6、s 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
7、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 EPAs website(http:/www.epa.gov/mercury/faq.htm) for additional informa-tion. Users should be aware that selling mercu
8、ry 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 and health practices
9、 and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2G8 Test Methods for Cathodic Disbonding of PipelineCoatingsG12 Test Method for Nondestructive Measurement of FilmThickness of Pipeline Coatings on SteelG80 Test Method for Specific Cat
10、hodic Disbonding ofPipeline CoatingsG95 Test Method for Cathodic Disbondment Test of Pipe-line Coatings (Attached Cell Method)E1 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
11、 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
12、 and byconnecting an anode to the positive terminal. Electrical instru-mentation is provided for measuring the current flowing in thecell. 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 cat
13、hodic 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
14、 underground, the surrounding earth1This 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 Nov. 15, 2011.
15、Published January 2012. Originallyapproved in 1975. Last previous edition approved in 2003 as G42 96 (2003). DOI:10.1520/G0042-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume informat
16、ion, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.will be moisture-bearing and will constitute an effectiveelectrolyte. Applied cathodic protection potentials may cau
17、seloosening 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 a
18、re 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 surfac
19、e 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 ass
20、ociated with test results include:4.3.1 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,
21、 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 appe
22、aring 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 ap
23、plication 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
24、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 m
25、uch 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
26、. Apparatus5.1 Test VesselAsuitable nonreactive vessel shall be used,capable of withstanding internal heating at not less than 60Cand 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
27、.) 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
28、 heater can beimmersed in the heat transfer medium to effectively control thetemperature of the sample. Dimensions of the vessel shallpermit the following requirements:5.1.1 Test specimens shall be suspended vertically in thevessel with at least 25 mm (1 in.) clearance from the bottom.5.1.2 Test spe
29、cimens shall be separated by not less than 38mm (112 in.), and a vertically suspended anode can be placedat an equal distance from each specimen not less than theseparation distance.5.1.3 Test specimens shall be separated from any wall of thevessel by not less than 13 mm (12 in.).5.1.4 Depth of elec
30、trolyte shall permit the test length of thespecimen to be immersed as required in 7.4.5.1.5 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 (112 in.).5.2 AnodeThe anode shall be provided with a factory-s
31、ealed, insulated copper wire lead.35.3 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 nonimmersed end, and the place of attachmentshall be coated with an insulating materia
32、l. 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
33、specimens such as 19-mm (34-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 examina
34、tions.5.5 Multimeters:5.5.1 Multimeter, for direct current, having an internalresistance of not less than 10 MV 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 MV and capable
35、of measuring aslow as 10 V 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
36、 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 25C will3Duriron, a material found suitable for this purpose is av
37、ailable from DurironCo., Inc., Dayton, OH.G42112read 1.53 V at 60C, a scale increase of 0.03 V.5.6.1 A saturated calomel electrode at 25C is converted toCu CuSO4by adding 0.07 V to the observed reading. If thesaturated calomel electrode reads 1.43 V at 25C, it will read1.46 V at 60C, a scale increas
38、e of 0.03 V. It follows that asaturated calomel electrode reading of 1.46 V at 60C is equalto a saturated Cu CuSO4reading of 1.50 V at 25C.5.6.2 A0.1 normal calomel electrode at 25C is converted toCu CuSO4by subtracting 0.02 V from the observed reading.Since the potential change due to an increase f
39、rom 25C to60C is negligible, it follows that a 0.1 normal calomelelectrode reading 1.52 V at 60C is equal to a saturated CuCuSO4reading of 1.50 V at 25C.5.7 Thermometers, two, mercury-filled type or liquid-in-glass, accurate to 61C. One shall be of the full-immersiontype for measuring temperature ne
40、ar 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 thermoc
41、ouple or equal or betteraccuracy may be used.5.8 Combination Heater Plate, with built-in magnetic stir-rer, or equivalent, shall be used for heating and stirring theelectrolyte. The heater shall be adjustable to produce andcontrol a temperature of 60 6 1C in the test vessel.5.9 Direct-Current Rectif
42、ier, 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,1V61 %, 1 W (min), to be used inthe test cell circuit as a shunt
43、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 with
44、alligator 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 deminerali
45、zed 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 Vcm at room temperature
46、.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 v
47、essel 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 representative piece o
48、fproduction-coated pipe. One end shall be plugged, sealed, orcapped.7.2 One holiday shall be made in the middle of the im-mersed length by drilling a radial hole through the coating sothat the angular cone point of the drill will fully enter the steelwhere the cylindrical portion of the drill meets
49、the steelsurface. The drill diameter shall be not less than three times thecoating thickness, but it shall never be less than 6 mm (14 in.)in diameter. The steel wall of the pipe shall not be perforated.With small-diameter pipes, where there is danger of perforatingthe pipe, the holiday shall be started with a standard 60 conepoint and finished with a drill that has had a substantial portionof the cone point ground away.NOTE 3Before making the holiday, see 7.5.7.3 The end of the pipe which will protrude above theimmersion line shall be pro
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