1、Designation: G 95 07Standard Test Method forCathodic Disbondment Test of Pipeline Coatings (AttachedCell Method)1This standard is issued under the fixed designation G 95; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of
2、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 covers accelerated procedures forsimultaneously determining comparative characteristics ofcoating system
3、s applied to steep pipe exterior for the purposeof preventing or mitigating corrosion that may occur inunderground service where the pipe will be in contact withnatural soils and will receive cathodic protection. They areintended for use with samples of coated pipe taken fromcommercial production an
4、d are applicable to such sampleswhen the coating is characterized by function as an electricalbarrier.1.2 This test method is intended to facilitate testing ofcoatings where the test cell is cemented to the surface of thecoated pipe specimen. This is appropriate when it is impracti-cal to submerge o
5、r immerse the test specimen as required byTest Methods G8, G42,orG80. Coating sample configura-tion such as flat plate and small diameter pipe may be used,provided that the test procedure remains unchanged.21.3 This test method allows options that must be identifiedin the report.1.4 The values state
6、d in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.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
7、 health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3G8 Test Methods for Cathodic Disbonding of PipelineCoatingsG12 Test Method for Nondestructive Measurement of FilmThickness of Pipeline Coatings on SteelG42 Test Method
8、 for Cathodic Disbonding of PipelineCoatings Subjected to Elevated TemperaturesG62 Test Methods for Holiday Detection in Pipeline Coat-ingsG80 Test Method for Specific Cathodic Disbonding ofPipeline Coatings3. Summary of Test Method3.1 The test method described subjects the coating on thetest specim
9、en to electrical stress in a highly conductive alkalineelectrolyte. Electrical stress is obtained from an impresseddirect-current system. An intentional holiday is to be made inthe coating prior to starting of test.3.1.1 Electrical instrumentation is provided for measuringthe current and the potenti
10、al throughout the test cycle. At theconclusion of the test period, the test specimen is physicallyexamined.3.1.2 Physical examination is conducted by comparing theextent of loosened or disbonded coating at the intentionalholiday in the immersed area with extent of loosened ordisbonded coating at a r
11、eference holiday made in the coating inan area that was not immersed.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 under
12、ground, 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 c
13、onditions 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 two1This test
14、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, 2007. Published July 2007. Originally approvedin 1987
15、. Last previous edition approved in 1998 as G 95 - 87 (1998)e1which waswithdrawn March 2007 and reinstated in July 2007.2For other cathodic disbondment testing procedures, consult Test Methods G8,G42, and G80.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Custom
16、er Service at serviceastm.org. For 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.methods of evaluation, but both metho
17、ds 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 propogates from an areawhere adhesion is zero to an area whe
18、re adhesion reaches theoriginal level.An intermediate zone of decreased adhesion mayalso be present.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 Decreased adhesion in the immersed test
19、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
20、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.5. Apparatus5.1 Test VesselA transparent plastic or glass tube tha
21、t iscentered over the intentional holiday and sealed to the testsample surface with a waterproof sealing material. The cylin-der is to be 101.6 mm (4.0 in. nominal diameter) and ofsufficient height to contain 127.0 mm (5.0 in.) of electrolyte.Fig. 1 and Fig. 2 apply to this entire section.NOTE 1Size
22、 of vessel shall remain unchanged. Sealing proceduremust be altered to accommodate specimen having a diameter less than101.60 mm (4 in.).5.2 Filter TubeAnode assembly shall be constructed uti-lizing an immersion tube with fritted disk. Length of the tubewill be 180 mm (7 in.) and 8 mm (0.315 in.) in
23、 diameter. Thefritted-disk section shall be 30 mm (1.18 in.) in diameter witha pore size of 10 to 15 m.5.3 Impressed-Current AnodeAnode shall be of the plati-num wire type, 0.51 mm (0.020 in.) - 24 gage diameter. It shallbe of sufficient length to extend outside the confines of the testcell and shal
24、l be connected to the wire from the power sourcewith a bolted or compression fitting.FIG. 1 Typical Test Set UpG950725.4 Anode AssemblyAnode shall be suspended inside thetest vessel so that the tip of the anode assembly closest to theholiday is 25.4 mm (1 in.) above, and the edge of the anodeassembl
25、y is 12.7 mm (12 in.) offset from the holiday.5.5 Reference ElectrodeSaturated Cu-CuSO4of conven-tional glass or plastic tube with porous plug construction,preferably not over 19.05 mm (0.750 in.) in diameter, having apotential of 0.316 V with respect to the standard hydrogenelectrode. A saturated c
26、alomel electrode may be used, butmeasurements made with it shall be converted to the Cu-CuSO4reference for reporting by adding 0.072 V to theobserved reading.5.6 Reference Electrode PlacementSubmerge the tip ofthe reference electrode 25.4 mm (1 in.) into the electrolyte.5.7 High-Impedence Multimeter
27、For making direct-current and voltage measurements. Multimeter must have aninternal resistance of not less than 10 M V and be capable ofmeasuring current as low as 1 mA, and voltage up to 10 V.5.8 Direct-Current Power SupplyCapable of supplyinglow-ripple voltage at 3.0, 60.01, V, as measured between
28、 thetest specimen and reference electrode.5.9 Precision Wire-Wound Resistor1 V,61 %, 1-W(minimum) to be used in the test cell circuit as a shunt formeasuring current.5.10 Thickness GageFor measuring coating thickness inaccordance with Test Method G12.5.11 Holiday DetectorFor locating holidays in the
29、 coatingof the test specimen in accordance with Test Methods G62.5.12 ConnectionsWiring from current source to the speci-men shall be by either soldering, brazing, or bolting to thenon-immersed area of the specimen. A junction in the connec-tion wire is not desirable but, if necessary, may be made b
30、ymeans of a bolted pair of terminal lugs, soldering or mechani-cally crimping to clean wire ends.5.13 Additional Connecting WiresIf additional wiring isnecessary, it shall be stranded, insulated copper and not lessthan 1.75 mm (0.069 in. -14 gage) diameter.5.14 Holiday ToolsA drill and a suitable dr
31、ill bit that willaccomplish drilling of test hole, as described under 8.2.Asharp-pointed knife, with a safe handle is required for use inmaking physical examination.6. Reagent and Materials6.1 The electrolyte shall consist of distilled or deionizedwater with the addition of 3 mass % of technical gra
32、de sodiumchloride. Use freshly prepared solution for each test.7. Test Specimen7.1 During the coating operation, the applicator may bedirected to cut a section of coated pipe of sufficient length forlaboratory evaluation of the coating. Precautions are to betaken when cutting the pipe so that spatte
33、r will not harm thecoating where testing will be done. Wet rags shall be placed oneach side of the torch-cut area to minimize thermal changesand spatter damage to the coating. Test sample shall be takenat least 76.2 mm (3 in.) from any torch-cut edge. Specialprecautions are to be taken so that coati
34、ng is not damaged inhandling, transporting, or further cutting. The test specimensmay be a cut coupon, flat plate, or a ring specimen. The testmay also be performed on an actual inservice pipeline, or anyother appropriate coated surface.8. Procedure8.1 Verify the coating integrity in the area to be
35、tested inaccordance with Test Methods G62. Discard specimen foundto contain holidays. Measure and record the maximum andminimum coating thickness measured in the area subjected totest in accordance with Test Method G12.8.2 One intentional holiday shall be made in each specimento be tested. The holid
36、ay shall be drilled so that the angularcone point of the drill will fully enter the steel where thecylindrical portion of the drill meets the steel surface. The drillshall be 3.2 mm (0.125 in.) in diameter.8.3 Electrical connection is then made to the test specimen,(see 5.12).8.4 Attach the test cyl
37、inder to the test specimen, (see 5.1).Take care to ensure that the cylinder satisfactorily fits thecurvature of the pipe sample and that it is centered over theintentional holiday.8.5 Add the electrolyte solution to the specified level in thetest cylinder. Record the pH of the solution. Check the le
38、vel ofthe electrolyte each day and maintain by adding distilled ordeionized water.8.6 Place the fritted glass filter tube into the electrolytesolution as described in 5.4. Support the fritted glass filter tube.8.7 Insert the platinum anode into the fritted glass tube,down to within 5 mm (2 in.) of t
39、he bottom.8.8 Attach the positive lead of the current source to theplatinum anode and the negative lead to the cathode (pipe). AFIG. 2 Anode AssemblyG95073potential of 3 V DC with respect to a copper-copper sulphatereference electrode is to be impressed across the test cell.8.9 Conduct the test at a
40、 room temperature of 21 to 25C (70to 77F). Tests to be run for a period of 90 days.8.10 At least twice each week, place a reference CuSO4electrode in the electrolyte between the anode and the holiday.Read the voltage and adjust the power supply output, ifrequired, so that a negative 3 V DC potential
41、 is maintainedbetween the reference electrode and the test sample.9. Examination9.1 At the end of the 90 day test period, disassemble the celland rinse the test area with warm tap water. Immediately wipethe sample dry and visually examine the entire test area for anyevidence of unintentional holiday
42、s and loosening of coating atthe edge of all holidays, including the intentional holiday, andrecord coating condition, for example, color, blisters, cracking,crazing, adhering deposits, etc.9.2 Drill a new reference holiday in the coating in an areathat was not immersed. Follow the same drilling pro
43、cedure asdescribed in 8.2.9.3 Make radial 45 cuts through the coating intersecting atthe center of both the intentional holiday and the referenceholiday with a sharp, thin-bladed knife.Take care to ensure thatcoating is cut completely through to the steel substrate.9.4 Attempt to lift the coating at
44、 both the reference holidayand the intentional holiday with the point of a sharp, thin-bladed knife. Use the bond at the reference holiday as areference for judging the quality of the bond at the intentionalholiday. Measure and record the total area of disbonded coatingat the intentional holiday.10.
45、 Report10.1 The report of results shall include the following.10.1.1 Complete identification of the test specimen, includ-ing:10.1.1.1 Name and code number of the coating,10.1.1.2 Size and wall thickness of pipe,10.1.1.3 Applicator, production date, and production runnumber of coating,10.1.1.4 Minim
46、um-maximum coating thickness, averagethickness, and the thickness at the holiday,10.1.1.5 Size of initial holidays,10.1.1.6 Dates of starting and termination of test,10.1.1.7 Cell diameter and depth of electrolyte,10.1.1.8 Salt composition and concentration,10.1.1.9 Cell voltage,10.1.1.10 Length of
47、test period, and10.1.1.11 Other data that may be pertinent.10.2 Report the test results by measuring the total area ofdisbondment by planimeter, square counting, or other precisemethod. Subtract the initial holiday area and calculate anequivalent circle diameter.411. Precision and Bias11.1 Precision
48、For between-laboratory testing data iswithin 625 % of the mean for represented samples. Sampleswere taken from one length of production run coated 16 in.pipe.11.2 BiasNo statement of bias is made since sampleswere all obtained from one length of pipe and all participatinglaboratories utilized equipm
49、ent and procedures as outlined inthis test method.12. Keywords12.1 anode; attached cell; cathodic; disbondment; electricalstress; electrolyte; salt bridgeASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical
