1、Designation:G896(Reapproved 2003)e1Standard Test Methods forCathodic Disbonding of Pipeline Coatings1This standard is issued under the fixed designation G 8; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revision
2、.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon (e) indicates an editorial change since the last revision or reapproval.e1NOTEAn editorial correction was made to Disbonded Equivalent Circle Diameter in Fig. 6 in October 2007.1. Scope1.1 These test methods cover acce
3、lerated procedures forsimultaneously determining comparative characteristics of in-sulating coating systems applied to steel pipe exterior for thepurpose of preventing or mitigating corrosion that may occur inunderground service where the pipe will be in contact withinland soils and may or may not r
4、eceive cathodic protection.They are intended for use with samples of coated pipe takenfrom commercial production and are applicable to suchsamples when the coating is characterized by function as anelectrical barrier.1.2 This test method is intended for testing coatings sub-merged or immersed in the
5、 test solution at room temperature.When it is impractical to submerge or immerse the testspecimen, Test Method G95may be considered where the testcell is cemented to the surface of the coated pipe specimen. Ifhigher temperatures are required, see Test Method G42.Ifaspecific test method is required w
6、ith no options, see TestMethod G80.1.3 The values stated in SI units to 3 significant decimals areto be regarded as the standard. The values given in parenthesesare for information only.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is th
7、eresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2G12 Test Method for Nondestructive Measurement of FilmThickness of Pipeline Coatings o
8、n SteelG42 Test Method for Cathodic Disbonding of PipelineCoatings Subjected to Elevated TemperaturesG80 Test Method for Specific Cathodic Disbonding ofPipeline CoatingsG95 Test Method for Cathodic Disbondment Test of Pipe-line Coatings (Attached Cell Method)3. Summary of Test Methods3.1 Both of the
9、 two test methods described subject thecoating on the test specimen to electrical stress in a highlyconductive, alkaline electrolyte. Electrical stress is obtainedeither by means of a sacrificial magnesium anode or from animpressed current system. The coating is perforated beforestarting the test.3.
10、1.1 In Method A, a magnesium anode is used with noelectrical monitoring during the test period. The results aredetermined by physical examination after the test period isconcluded.3.1.2 In Method B, either a magnesium anode or an im-pressed current system may be used. Electrical instrumentationis pr
11、ovided for measuring the current in the cell circuit. Theelectrical potential is also measured, and upon conclusion ofthe test period, the test specimen is physically examined.3.1.3 In both test methods physical examination is con-ducted by comparing the extent of loosened or disbondedcoating at the
12、 perforations in the immersed area with extent ofloosened or disbonded coating at a new test hole in the coatingmade in an area that was not immersed.4. Significance and Use4.1 Breaks or holidays in pipe coatings may expose the pipeto possible corrosion, since after a pipe has been installedundergro
13、und, the surrounding earth will be more or lessmoisture-bearing and it constitutes an effective electrolyte.Damage to pipe coating is almost unavoidable during trans-portation and construction. Normal soil potentials as well asapplied cathodic protection potentials may cause loosening ofthe coating,
14、 beginning at holiday edges, in some cases increas-ing the apparent size of the holiday. Holidays may also be1These test methods are under the jurisdiction of ASTM Committee D01 onPaint and Related Coatings, Materials, and Applications and are the directresponsibility of Subcommittee D01.48 on Durab
15、ility of Pipeline Coating andLinings.Current edition approved Dec. 1, 2003. Published December 2003. Originallyapproved in 1969. Last previous edition approved in 1996 as G896.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. Fo
16、r Annual Book of ASTMStandards volume information, 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.caused by such potentials. While apparently loosened coatingand cathod
17、ic holidays may not result in corrosion, this testprovides accelerated conditions for loosening to occur andtherefore gives a measure of resistance of coatings to this typeof action.4.2 The effects of the test may be evaluated by eitherphysical examination or monitoring the current drawn by thetest
18、specimen and both of these two. Usually there is nocorrelation between the two methods of evaluation but bothmethods are significant. Physical examination consists ofassessing the effective contact of the coating with the metalsurface in terms of observed differences in the relative adhesivebond. It
19、 is usually found that the electrically stressed areapropagates from the holiday to a boundary where the loosenedcoating leaves off for the more effective contact or bondattributed to an original condition throughout the specimenbefore electrical stressing was applied.Assumptions associatedwith test
20、 results include the following:4.2.1 Attempting to loosen or disbond the coating at a newtest hole made in the coating in an area that was not immersedrepresents maximum adhesion or bond as measured by thelifting technique used, and that the same lifting technique canbe used at a test hole that was
21、immersed thereby providing ameans of comparing relative resistance to lifting.4.2.2 Any relatively lesser bonded area at the immersed testholes in the coating was caused by electrical stressing and wasnot attributable to an anomaly in the application process.Ability to resist disbondment is a desire
22、d quality on a com-parative basis, but disbondment per se in this test is notnecessarily an adverse indication. The virtue of this test is thatall dielectric type coatings now in common use will disbond tosome degree thus providing a means of comparing one coatingwith another. Bond strength is more
23、important for properfunctioning of some coatings than others and the same mea-sured disbondment for two different coating systems may notrepresent equivalent loss of corrosion protection.4.2.3 The amount of current in the test cell is a relativeindicator of the extent of areas requiring protection a
24、gainstcorrosion; however, the current density appearing in this test ismuch greater than that usually required for cathodic protectionin natural, inland soil environments.5. Apparatus5.1 Apparatus for Both Methods:5.1.1 Test VesselA nonconducting material shall be usedfor the vessel or as a lining i
25、n a metallic vessel. Dimensions ofthe vessel shall permit the following requirements:5.1.1.1 Test specimens shall be suspended vertically in thevessel with at least 25.4-mm (1-in.) clearance from the bottom.5.1.1.2 Each test specimen shall be separated from the otherspecimens, from the anodes and fr
26、om the walls of the testvessel by at least 38.1 mm (1.500 in.).5.1.1.3 Depth of electrolyte shall permit the test length ofthe specimen to be immersed as required in 7.4.5.1.1.4 If electrical monitoring is to be performed as re-quired in Method B, the reference electrode may be placedanywhere in the
27、 vessel, provided it is separated from thespecimen and from the anode by not less than 38.1 mm (1.500in.).5.1.2 Magnesium AnodeThe anode shall be made of amagnesium alloy having a solution potential of 1.45 to 1.55V with respect to a CuCuSO4reference electrode in theelectrolyte given in 6.1. It shal
28、l have a surface area not lessthan one third that of the total specimen area exposed toelectrolyte (outside area exposed only). The anode shall beprovided with a factory-sealed, 4107-cmil (14-gage Awg),minimum, insulated copper wire.Anodes without a factory sealmay be used if the magnesium extends a
29、bove the cover.5.1.3 ConnectorsWiring from anode to test specimenshall be 4107-cmil (14-gageAwg), minimum, insulated copper.Attachment to the test specimen shall be by soldering, brazing,or bolting to the nonimmersed end, and the place of attachmentshall be coated with an insulating material. A junc
30、tion 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.5.1.4 Holiday ToolsHolidays shall be made with conven-tional drills of the required diameter. For use in preparingsmall-diameter pipe specime
31、ns such as 19.05 mm (0.750 in.)nominal diameter pipe, the use of a drill modified by substan-tially grinding away the sharp cone point has been foundeffective in preventing perforation of the metal wall of the pipe.A sharp-pointed knife with a safe handle is required for use inmaking physical examin
32、ations.5.1.5 High-Resistance Voltmeter, for direct current, havingan internal resistance of not less than 10 MV and having arange from 0.01 to 5 V for measuring potential to the referenceelectrode.5.1.6 Reference Electrode, saturated CuCuSO4of conven-tional glass or plastic tube with porous plug con
33、struction,preferably not over 19.05 mm (0.750 in.) in diameter, having apotential of 0.316 V with respect to the standard hydrogenelectrode.Acalomel electrode may be used, but measurementsmade with it shall be converted to the CuCuSO4reference forreporting by adding 0.072 V to the observed reading.5
34、.1.7 Thickness Gage, for measuring coating thickness inaccordance with Test Method G12.5.1.8 Thermometer, for measuring electrolyte temperature,general lab type, 1 subdivisions, 76.2 mm (3 in.) immersion.5.2 Additional Apparatus for Method B:5.2.1 High-Resistance Voltmeter, for direct current, havin
35、gan internal resistance of not less than 10 MV and capable ofmeasuring as low as 10 V potential drop across a shunt in thetest cell circuit.5.2.2 Precision Wire-Wound Resistor,1-V61 %, 1-W(minimum), to be used in the test cell circuit as a shunt forcurrent.5.2.3 Volt-Ohm-Meter, for initial testing o
36、f apparent coatingresistance.5.2.4 Metallic Electrode, used temporarily with the volt-ohm-meter to determine apparent initial holiday status of thetest specimen.5.2.5 Additional Connecting Wires, 4107-cmil (14-gageAwg), minimum, insulated copper.5.2.6 Brass Studs, used at a terminal board, together
37、withalligator clips or knife switches, for making and breakingG896 (2003)e12circuits. Alligator clips shall not be used to connect toelectrodes or specimens at the top location of test cells.5.2.7 Zero-Resistance Ammeter, capable of measuring directcurrent as low as 10 A may be used in the alternati
38、ve methodgiven in 9.1.3 and substituted for the apparatus described in5.2.1 and 5.2.2.5.2.8 Direct-Current Rectifier, capable of supplying con-stant voltage at a voltage of 1.50 6 0.01 V, as measuredbetween the specimen and reference electrode.5.2.9 Impressed Current Anode, shall be of the nonconsum
39、-able type provided with a factory sealed, insulated copperwire.35.2.10 Voltage Divider, 100-V, 25-W rheostat, to be used ifmore than one specimen is to be tested as shown in Fig. 1.6. Reagent and Materials6.1 The electrolyte shall consist of potable tap water withthe addition of 1 mass % of each of
40、 the following technical-grade salts, calculated on an anhydrous basis: sodium chloride,sodium sulfate, and sodium carbonate. Use freshly preparedsolution for each test.6.2 Materials for sealing the ends of coated pipe specimensmay consist of bituminous products, wax, epoxy, or othermaterials, inclu
41、ding molded elastomeric or plastic end caps.6.3 Plywood or plastic material has been found suitable forthe construction of test vessel covers and for the supportthrough apertures of test specimens and electrodes. Wooddowels introduced through holes in the top ends of testspecimens have been found su
42、itable for suspending test speci-mens from the vessel cover.7. Test Specimen7.1 The test specimen shall be a representative piece ofproduction-coated pipe. One end shall be plugged or capped,and sealed.7.2 One or three holidays shall be made in each specimen.Three holidays are recommended. Recommend
43、ed dimensionsare given in Fig. 2. A specimen with one holiday shall have itdrilled in the middle of the immersed length. If three holidaysare used, they shall be drilled 120 apart with one in the centerand the other two at locations one fourth the distance from topand bottom of the immersed test len
44、gth. Each holiday shall bedrilled so that the angular cone point of the drill will fully enterthe steel where the cylindrical portion of the drill meets thesteel surface. The drill diameter shall be not less than threetimes the coating thickness, but it shall never be smaller than6.35 mm (0.250 in.)
45、 in diameter.The steel wall of the pipe shallnot be perforated. With small-diameter pipes, where there isdanger of perforating the pipe, the holiday shall be started witha standard 60 cone point and finished with a drill that has hada substantial portion of the cone point ground away.NOTE 1Before ma
46、king the holiday, see 8.1.7.3 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, brazed, or bolted to the pipe. The protruding end,3Durion, a material found suitable for this
47、 purpose is available from Durion Co.,Inc., Dayton OH.FIG. 1 Modification of Method B (Fig. 5) Using Impressed Current to Test More than One SpecimenG896 (2003)e13including hanger and wire connections, shall be protected andsealed with an insulating coating material.7.4 The specimen test area shall
48、consist of the area betweenthe edge of the bottom end seal and the immersion line. Thebottom end seal area shall not be considered part of the areatested.Any suitable diameter and specimen length of pipe maybe used, but the immersed area shall be not less than 23 227mm2(36 in.2). An area of 92 900 m
49、m2(1 ft2) has been foundpreferable when convenient.8. Specimen Preparation8.1 Before making artificial holidays, verify the continuityof the coating and the effectiveness of the end-cap seal asfollows:8.1.1 Immerse the test specimen and a metallic electrode inthe electrolyte. Connect one terminal of the multimeter to thetest specimen and the other terminal to the metallic electrode.Measure the apparent resistance in ohms, making two deter-minations: one with the specimen connected to the positiveterminal of the multimeter; and one with the specimen con-nected to the neg
