1、Designation: G 42 96 (Reapproved 2003)Standard Test Method forCathodic Disbonding of Pipeline Coatings Subjected toElevated Temperatures1This standard is issued under the fixed designation G 42; the number immediately following the designation indicates the year of originaladoption or, in the case o
2、f revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes an accelerated procedure fordetermining comparative characteristics of
3、 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 t
4、aken 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 imm
5、erse the testspecimen, Test Method G95may 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
6、significant deci-mals are to be regarded as the standard. The values given inparentheses are for information only.1.4 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 s
7、afety and health practices 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 Te
8、st Method for Specific Cathodic Disbonding ofPipeline CoatingsG95 Test Method for Cathodic Disbondment Test of Pipe-line Coatings (Attached Cell Method)3. Summary of Test Method3.1 This test method subjects the coating on the test speci-men to electrical stress in a highly conductive electrolyte. Th
9、ecoating 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 f
10、lowing 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 cathodic stress is applied under conditions of aconstant-elevated temperature.4. Significance and Use4.1 Damage to pipe coa
11、ting 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 cathodi
12、c 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 actio
13、n.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 th
14、e 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
15、 be present.1This 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 Dec. 1, 2003. Published December 2003.
16、 Originallyapproved in 1975. Last previous edition approved in 1996 as G 42 96.2For 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 standards Document Summary page o
17、nthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.3 Assumptions associated 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 Decreas
18、ed 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 diele
19、ctric-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 bo
20、nded 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 exten
21、t 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 te
22、st 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
23、 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 60Cand suitable for c
24、ontinuous circulation of the electrolyte.A19-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 provi
25、ded 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 foll
26、owing 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 specimens 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
27、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 electrolyte 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 vess
28、el, 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-sealed, insulated copper wire lead.35.3 ConnectorsWiring from anode to test specimen shallbe 4107 cmil (14-gage Awg), minimum, insulated copper.Attach
29、ment to the test specimen shall be by soldering orbrazing to the nonimmersed 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
30、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 (34-in.) nominaldiameter pipe, the use of a drill modified by substantiallygrinding away the sharp cone point has been found
31、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 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 fo
32、r measuring potential to the reference electrode.5.5.2 Multimeter, for direct current, having an internalresistance of not less than 11 MV and capable 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.
33、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
34、by making the proper correction.NOTE 1A saturated Cu CuSO4electrode reading 1.50 V at 25Cwill read 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 2
35、5C, it willread 1.46 V at 60C, a scale increase of 0.03 V. It follows thata saturated calomel electrode reading of 1.46 V at 60C isequal to 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.S
36、ince the potential change due to an increase from 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, accurate to61C. One shall be of the full-immersion type f
37、or measuringtemperature near the bottom of the vessel, and a second3Duriron, a material found suitable for this purpose is available from DurironCo., Inc., Dayton, OH.G 42 96 (2003)2thermometer shall be of the partial-immersion type for mea-suring temperature near the top of the vessel.5.8 Combinati
38、on 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 Rectifier, capable of supplying constantcurrent at a voltage of
39、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 for current.5.12 Carbon or Stainless Steel Electrode, used
40、 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 breaking
41、circuits. 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
42、% 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.6.2 Materials for sealing the ends of coated pipe specime
43、nsmay 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
44、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 ofproduction-coated pipe. One end shall be plugged, sealed,
45、 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 the steelsurface. The drill diameter shall be not less tha
46、n 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 dril
47、l 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 provided with suitable supportingmeans and a separate wire connection for electrical purposes,soldered, or brazed to
48、 the pipe. The protruding end, includinghanger and wire connections, shall be protected and sealedwith an insulating coating material.7.4 The specimen test area shall consist of the area betweenthe edge of the bottom end seal and the immersion line. Thebottom end seal area shall not be considered pa
49、rt of the areatested. Coated specimens of any suitable diameter and lengthof pipe may be used, but the immersed area shall be not lessthan 23 200 mm2(36 in.2). An area of 92 900 mm2(1 ft2) hasbeen found preferable when convenient.7.5 The continuity of the coating and efficiency of the endseal shall be tested before making artificial holidays as follows:7.5.1 Immerse the test specimen and a carbon or stainlesssteel electrode in the electrolyte. Connect one terminal of theohmmeter to the test specimen and the other terminal to thecarb
