1、Designation: D6676/D6676M 13Standard Test Method forCathodic Disbonding of Exterior Pipeline Coatings atElevated Temperatures Using Interior Heating1This standard is issued under the fixed designation D6676/D6676M; the number immediately following the designation indicates theyear of original adopti
2、on or, in the case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes an accelerated procedure fordetermining compara
3、tive characteristics of coating systemsapplied to the exterior of steel pipe for the purpose ofpreventing or mitigating corrosion that may occur in under-ground or immersion where the pipe is carrying heated mediaand is under cathodic protection. This test method is intendedfor use with samples of c
4、oated pipe, or with a specimen cutfrom the section of coated pipe or flat plates, and is applicableto such samples when the coating is characterized by functionas an electrical barrier.1.2 This test method is intended to simulate conditionswhen external coatings are exposed to high temperature insid
5、ethe pipe and to an ambient temperature outside, and thus aresubjected to temperature gradient. If elevated temperatures arerequired but without temperature gradient, see Test MethodG42.1.3 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values
6、stated ineach system may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Combiningvalues from the two systems may result in non-conformancewith the standard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its
7、use. It is theresponsibility 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:2G8 Test Methods for Cathodic Disbonding of Pipeline Coat-ingsG12 Test Met
8、hod for Nondestructive Measurement of FilmThickness of Pipeline Coatings on SteelG42 Test Method for Cathodic Disbonding of PipelineCoatings Subjected to Elevated TemperaturesG62 Test Methods for Holiday Detection in Pipeline Coat-ingsG95 Test Method for Cathodic Disbondment Test of PipelineCoatings
9、 (Attached Cell Method)3. Summary of Test Method3.1 The test method described, subjects the coating on thetest specimen 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 c
10、oating prior to starting of test.3.1.1 Electrical instrumentation is provided for measuringthe current and the potential 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
11、or disbonded coating at the intentionalholiday in the immersed area with extent of loosened ordisbonded coating at a reference holiday made in the coating inan area that was not immersed.3.1.3 The cathodic stress is applied under conditions of aconstant temperature gradient, simulating a heated pipe
12、linewith an exterior coating.3.1.4 Specimens that can be used are: (a) piece of pipe (Fig.1)or(b) samples cut from pipe or flat plate (Fig. 2 and Fig. 3).3.1.4.1 Some coatings rely on application tension (such astape) for maximum cathodic disbondment resistance. Cutcoupons or flat plates must not be
13、 used.4. Significance and Use4.1 Damage to a 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 wil
14、l constitute an effectiveelectrolyte. Applied cathodic protection potentials may cause1This 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 a
15、nd Linings.Current edition approved Nov. 1, 2013. Published November 2013. Originallyapproved in 2001. Last previous edition approved in 2001 as D6676 011whichwas withdrawn January 2010 and reinstated in November 2013. DOI: 10.1520/D6676_D6676M-13.2For referenced ASTM standards, visit the ASTM websi
16、te, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
17、1loosening of the coating, beginning at holiday edges. Sponta-neous holidays may also be caused by such potentials. Usuallyexterior pipeline coatings applied over pipes carrying hotmedia (oil, gas) are exposed to high temperature inside the pipeand low temperature outside and subjected to temperatur
18、egradient. Heat flux is directed from metal (substrate) to thecoating. This test method provides accelerated conditions forcathodic disbondment to occur under simulated heating andprovides a measure of resistance of coatings to this type ofaction.4.2 The effects of the test are to be evaluated by ph
19、ysicalexaminations and monitoring the current drawn by the testspecimens. 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 observedd
20、ifferences 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 resul
21、ts 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, but disbondment in thi
22、s 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 amount of current flowing in the test cell
23、is arelative 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 Test voltages higher than those recommended mayresult in
24、the formation of chlorine gas. The subsequent chemi-cal effects on the coating could cast doubt on the interpretationof the test results. Filter tube with fritted disk (see Test MethodG95) or layer of sand (40 mesh) put on the coated surface mayreduce this effect.5. Apparatus5.1 Test Vessel for Pipe
25、 Specimen (Fig. 4)A suitablenonreactive vessel shall be used, capable of withstandinginternal heating at test temperature and suitable to accommo-date a test specimen, an anode. Heating the test sample can beprovided by internally heating. The pipe sample may be filledwith a suitable heat transfer m
26、aterial (oil, steel, shot, sand,copper chips, etc.) A thermocouple or thermometer and heatercan be immersed in the heat transfer medium to effectivelycontrol the temperature of the sample. Dimensions of thevessel shall permit the following requirements:5.1.1 Test specimen shall be suspended vertical
27、ly in thevessel with at least 25 mm 1 in. clearance from the bottom.5.1.2 Test specimen 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 specimen shall be separated
28、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 vessel, provided it is separated from the specimen and fromthe anode by not less
29、 than 38 mm 112 in.5.2 Test Vessel for Flat or Cut From Pipe Specimens (Fig.3)A transparent plastic of glass tube that is centered over theintentional holiday and sealed to the test sample surface with awaterproof sealing material. The cylinder is to be 101.6 mm4.0 in. nominal diameter and of suffic
30、ient height to contain127.0 mm 5.0 in. of electrolyte.5.3 Impressed-Current AnodeAnode shall be of the plati-num wire type, 0.51 mm 0.020 in.24 gauge diameter. It shallbe of sufficient length to extend outside the confines of the testcell and shall be connected to the wire from the power sourcewith
31、a bolted or compressed fitting.5.4 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 anodeFIG. 1 Pipe Specimen Heated InsideFIG. 2 Flat Specimen Heated Over Hot PlateD6676/D6676M 132ass
32、embly is 12.7 mm 12 in. above, and the edge of the anodeassembly 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 wi
33、th respect to the standard hydrogenelectrode. A saturated calomel 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 m
34、m 1 in. into the electrolyte.5.7 High-Impedance MultimeterFor making direct currentand voltage measurements. Multimeter must have an internalresistance of not less than 10 M and be capable of measuringas low as 10 V potential drop across a shunt in the test cellcircuit, and voltage up to 10 V.5.8 Di
35、rect-Current Power SupplyCapable of supplyinglow-ripple voltage at 1.5, 60.01, V, as measured between thetest specimen and reference electrode.5.9 Precision Wire-Wound Resistor1 6 1 % 1-W(mimimum) to be used in the test cell circuit as a shunt formeasuring current.5.10 Thickness Gaugefor measuring c
36、oating thickness inaccordance with Test Method G125.11 Holiday Detectorfor locating holidays in the coatingof the test specimen in accordance with Test Method G62.5.12 ConnectionsWiring from current source to the speci-men shall be by either soldering, brazing, or bolting to thenon-immersed area of
37、the specimen. A junction in the connec-tion wire is not desirable but, if necessary, may be made bymeans 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
38、and not lessthan 1.75 mm 0.069 in.15 gauge diameter.5.14 Holiday ToolsA drill and a suitable drill bit that willaccomplish drilling of test hole, as described in 9.2.5.15 Heaters:FIG. 3 Test Set-Up for Cathodic Disbonding Test with Coated Pipe Coupon (or Flat Coupon) Heated Over Hot PlateD6676/D6676
39、M 1335.15.1 Pipe SpecimensLiquid Heat Exchange MediumCirculating bath with built-in heater shall be used for heatingthe heat transfer medium (silicone oil or other) to produce andcontrol temperature of 80 6 1C (or other temperature asspecified) inside of the coated pipe samples connected with thebat
40、h by the hoses.5.15.2 Pipe SpecimensSolid Heat Exchange MediumHeaters suitable for controlling temperature at 80 6 1C or asotherwise specified shall be employed inside the coated pipe.5.15.3 Flat PlatesHeater plate, or equivalent, shall beused for heating coated samples. The heater shall be adjustab
41、leto produce and control a temperature of 80 6 1C or otherspecified temperature on the uncoated surface of testing panel.5.16 Thermometers or Thermocouples, to measure tempera-ture of heat transfer medium or on the uncoated surface ofpanel over hot plate and in electrolyte.5.17 Sharp-Pointed Knife,
42、with a safe handle is required foruse in making physical examination.6. Reagents and Materials6.1 Portable Tap Water or Higher Purity Water(distilledor demineralized water is satisfactory) with 1 weight percent ofeach of the following technical-grade salts, calculated on ananhydrous basis: sodium ch
43、loride, sodium sulfate, and sodiumcarbonate.NOTE 1The resulting solution has a pH of 10 or higher and aresistivity of 25 to 50 CM at room temperature.6.2 Materials, bituminous products, wax, epoxy, or othermaterials, including molded elastomeric or plastic end caps,capable of withstanding the test t
44、emperature, for sealing theends of coated pipe specimens.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
45、found suitable for suspending test specimens from thevessel cover.6.4 Hoses, capable of withstanding the test temperature of80 6 1C for connection of the plastic end caps in pipespecimens with circulating bath.6.5 Sand, (40 mesh), to be used over hot plate for moreconsistent better uniform heating o
46、f flat panels.7. Test Specimen (Coated Pipes)7.1 The test specimen shall be a representative piece ofcoated pipe. Each end shall be plugged, sealed, or capped withinlet and outlet nozzles connected with circulating bath.7.2 One holiday shall be made in the middle of the im-mersed length by drilling
47、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 than three times thecoating thickness, but it shall never be less than 6 mm 14 in.in diameter
48、. 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 2Before making the ho
49、liday, see 7.5.7.3 The end of the pipe, which will protrude above theimmersion line, shall be provided with suitable supportingFIG. 4 Test Set-Up for Cathodic Disbonding Test at Elevated TemperatureD6676/D6676M 134means and a separate wire connection for electrical purposes,soldered, or brazed to 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
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