ASTM G8-96(2003)e1
(Test Method)Standard Test Methods for Cathodic Disbonding of Pipeline Coatings
Standard Test Methods for Cathodic Disbonding of Pipeline Coatings
SCOPE
1.1 These test methods cover accelerated procedures for simultaneously determining comparative characteristics of insulating coating systems applied to steel pipe exterior for the purpose of preventing or mitigating corrosion that may occur in underground service where the pipe will be in contact with inland soils and may or may not receive cathodic protection. They are intended for use with samples of coated pipe taken from commercial production and are applicable to such samples when the coating is characterized by function as an electrical barrier.
1.2 This test method is intended for testing coatings submerged or immersed in the test solution at room temperature. When it is impractical to submerge or immerse the test specimen, Test Method G 95 may be considered where the test cell is cemented to the surface of the coated pipe specimen. If higher temperatures are required, see Test Method G 42. If a specific test method is required with no options, see Test Method G 80.
1.3 The values stated in SI units to 3 significant decimals are to be regarded as the standard. The values given in parentheses are for information only.
This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: G8 – 96 (Reapproved 2003)
Standard Test Methods for
Cathodic Disbonding of Pipeline Coatings
This standard is issued under the fixed designation G8; the number immediately following the designation indicates the year of original
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
´ NOTE—An editorial correction was made to Disbonded Equivalent Circle Diameter in Fig. 6 in October 2007.
1. Scope G12 Test Method for Nondestructive Measurement of Film
Thickness of Pipeline Coatings on Steel
1.1 These test methods cover accelerated procedures for
G42 Test Method for Cathodic Disbonding of Pipeline
simultaneously determining comparative characteristics of in-
Coatings Subjected to Elevated Temperatures
sulating coating systems applied to steel pipe exterior for the
G80 Test Method for Specific Cathodic Disbonding of
purposeofpreventingormitigatingcorrosionthatmayoccurin
Pipeline Coatings
underground service where the pipe will be in contact with
G95 Test Method for Cathodic Disbondment Test of Pipe-
inland soils and may or may not receive cathodic protection.
line Coatings (Attached Cell Method)
They are intended for use with samples of coated pipe taken
from commercial production and are applicable to such
3. Summary of Test Methods
samples when the coating is characterized by function as an
3.1 Both of the two test methods described subject the
electrical barrier.
coating on the test specimen to electrical stress in a highly
1.2 This test method is intended for testing coatings sub-
conductive, alkaline electrolyte. Electrical stress is obtained
merged or immersed in the test solution at room temperature.
either by means of a sacrificial magnesium anode or from an
When it is impractical to submerge or immerse the test
impressed current system. The coating is perforated before
specimen, Test Method G95 may be considered where the test
starting the test.
cell is cemented to the surface of the coated pipe specimen. If
3.1.1 In Method A, a magnesium anode is used with no
higher temperatures are required, see Test Method G42.Ifa
electrical monitoring during the test period. The results are
specific test method is required with no options, see Test
determined by physical examination after the test period is
Method G80.
concluded.
1.3 ThevaluesstatedinSIunitsto3significantdecimalsare
3.1.2 In Method B, either a magnesium anode or an im-
toberegardedasthestandard.Thevaluesgiveninparentheses
pressedcurrentsystemmaybeused.Electricalinstrumentation
are for information only.
is provided for measuring the current in the cell circuit. The
1.4 This standard does not purport to address all of the
electrical potential is also measured, and upon conclusion of
safety concerns, if any, associated with its use. It is the
the test period, the test specimen is physically examined.
responsibility of the user of this standard to establish appro-
3.1.3 In both test methods physical examination is con-
priate safety and health practices and determine the applica-
ducted by comparing the extent of loosened or disbonded
bility of regulatory limitations prior to use.
coating at the perforations in the immersed area with extent of
2. Referenced Documents loosened or disbonded coating at a newtest hole in the coating
2 made in an area that was not immersed.
2.1 ASTM Standards:
4. Significance and Use
4.1 Breaksorholidaysinpipecoatingsmayexposethepipe
These test methods are under the jurisdiction of ASTM Committee D01 on
Paint and Related Coatings, Materials, and Applications and are the direct
to possible corrosion, since after a pipe has been installed
responsibility of Subcommittee D01.48 on Durability of Pipeline Coating and
underground, the surrounding earth will be more or less
Linings.
moisture-bearing and it constitutes an effective electrolyte.
Current edition approved Dec. 1, 2003. Published December 2003. Originally
Damage to pipe coating is almost unavoidable during trans-
approved in 1969. Last previous edition approved in 1996 as G8–96. DOI:
10.1520/G0008-96R03E01.
portation and construction. Normal soil potentials as well as
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
applied cathodic protection potentials may cause loosening of
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
the coating, beginning at holiday edges, in some cases increas-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. ing the apparent size of the holiday. Holidays may also be
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959, United States.
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G8 – 96 (2003)
caused by such potentials. While apparently loosened coating 5.1.2 Magnesium Anode—The anode shall be made of a
and cathodic holidays may not result in corrosion, this test magnesium alloy having a solution potential of −1.45 to −1.55
provides accelerated conditions for loosening to occur and V with respect to a CuCuSO reference electrode in the
therefore gives a measure of resistance of coatings to this type electrolyte given in 6.1. It shall have a surface area not less
of action. than one third that of the total specimen area exposed to
4.2 The effects of the test may be evaluated by either electrolyte (outside area exposed only). The anode shall be
physical examination or monitoring the current drawn by the provided with a factory-sealed, 4107-cmil (14-gage Awg),
test specimen and both of these two. Usually there is no minimum,insulatedcopperwire.Anodeswithoutafactoryseal
correlation between the two methods of evaluation but both may be used if the magnesium extends above the cover.
methods are significant. Physical examination consists of
5.1.3 Connectors—Wiring from anode to test specimen
assessing the effective contact of the coating with the metal
shallbe4107-cmil(14-gageAwg),minimum,insulatedcopper.
surfaceintermsofobserveddifferencesintherelativeadhesive
Attachmenttothetestspecimenshallbebysoldering,brazing,
bond. It is usually found that the electrically stressed area
orboltingtothenonimmersedend,andtheplaceofattachment
propagates from the holiday to a boundary where the loosened
shall be coated with an insulating material. A junction in the
coating leaves off for the more effective contact or bond
connectingwireispermitted,providedthatitismadebymeans
attributed to an original condition throughout the specimen
of a bolted pair of terminal lugs soldered or mechanically
beforeelectricalstressingwasapplied.Assumptionsassociated
crimped to clean wire ends.
with test results include the following:
5.1.4 Holiday Tools—Holidays shall be made with conven-
4.2.1 Attempting to loosen or disbond the coating at a new
tional drills of the required diameter. For use in preparing
test hole made in the coating in an area that was not immersed
small-diameter pipe specimens such as 19.05 mm (0.750 in.)
represents maximum adhesion or bond as measured by the
nominal diameter pipe, the use of a drill modified by substan-
lifting technique used, and that the same lifting technique can
tially grinding away the sharp cone point has been found
be used at a test hole that was immersed thereby providing a
effectiveinpreventingperforationofthemetalwallofthepipe.
means of comparing relative resistance to lifting.
Asharp-pointed knife with a safe handle is required for use in
4.2.2 Any relatively lesser bonded area at the immersed test
making physical examinations.
holes in the coating was caused by electrical stressing and was
5.1.5 High-Resistance Voltmeter, for direct current, having
not attributable to an anomaly in the application process.
an internal resistance of not less than 10 MV and having a
Ability to resist disbondment is a desired quality on a com-
rangefrom0.01to5Vformeasuringpotentialtothereference
parative basis, but disbondment per se in this test is not
electrode.
necessarily an adverse indication. The virtue of this test is that
5.1.6 Reference Electrode, saturated CuCuSO of conven-
alldielectrictypecoatingsnowincommonusewilldisbondto
tional glass or plastic tube with porous plug construction,
some degree thus providing a means of comparing one coating
preferably not over 19.05 mm (0.750 in.) in diameter, having a
with another. Bond strength is more important for proper
potential of −0.316 V with respect to the standard hydrogen
functioning of some coatings than others and the same mea-
electrode.Acalomel electrode may be used, but measurements
sured disbondment for two different coating systems may not
made with it shall be converted to the CuCuSO reference for
represent equivalent loss of corrosion protection.
reporting by adding−0.072 V to the observed reading.
4.2.3 The amount of current in the test cell is a relative
5.1.7 Thickness Gage, for measuring coating thickness in
indicator of the extent of areas requiring protection against
accordance with Test Method G12.
corrosion;however,thecurrentdensityappearinginthistestis
5.1.8 Thermometer, for measuring electrolyte temperature,
much greater than that usually required for cathodic protection
general lab type, 1° subdivisions, 76.2 mm (3 in.) immersion.
in natural, inland soil environments.
5.2 Additional Apparatus for Method B:
5. Apparatus
5.2.1 High-Resistance Voltmeter, for direct current, having
5.1 Apparatus for Both Methods:
an internal resistance of not less than 10 MV and capable of
5.1.1 Test Vessel—A nonconducting material shall be used
measuring as low as 10 µVpotential drop across a shunt in the
for the vessel or as a lining in a metallic vessel. Dimensions of
test cell circuit.
the vessel shall permit the following requirements:
5.2.2 Precision Wire-Wound Resistor,1-V6 1%, 1-W
5.1.1.1 Test specimens shall be suspended vertically in the
(minimum), to be used in the test cell circuit as a shunt for
vesselwithatleast25.4-mm(1-in.)clearancefromthebottom.
current.
5.1.1.2 Eachtestspecimenshallbeseparatedfromtheother
5.2.3 Volt-Ohm-Meter,forinitialtestingofapparentcoating
specimens, from the anodes and from the walls of the test
resistance.
vessel by at least 38.1 mm (1.500 in.).
5.2.4 Metallic Electrode, used temporarily with the volt-
5.1.1.3 Depth of electrolyte shall permit the test length of
ohm-meter to determine apparent initial holiday status of the
the specimen to be immersed as required in 7.4.
test specimen.
5.1.1.4 If electrical monitoring is to be performed as re-
5.2.5 Additional Connecting Wires, 4107-cmil (14-gage
quired in Method B, the reference electrode may be placed
Awg), minimum, insulated copper.
anywhere in the vessel, provided it is separated from the
specimen and from the anode by not less than 38.1 mm (1.500 5.2.6 Brass Studs, used at a terminal board, together with
in.). alligator clips or knife switches, for making and breaking
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G8 – 96 (2003)
FIG. 1 Modification of Method B (Fig. 5) Using Impressed Current to Test More than One Specimen
circuits. Alligator clips shall not be used to connect to dowels introduced through holes in the top ends of test
electrodes or specimens at the top location of test cells. specimens have been found suitable for suspending test speci-
5.2.7 Zero-ResistanceAmmeter,capableofmeasuringdirect mens from the vessel cover.
current as low as 10 µAmay be used in the alternative method
given in 9.1.3 and substituted for the apparatus described in
7. Test Specimen
5.2.1 and 5.2.2.
7.1 The test specimen shall be a representative piece of
5.2.8 Direct-Current Rectifier, capable of supplying con-
production-coated pipe. One end shall be plugged or capped,
stant voltage at a voltage of 1.50 6 0.01 V, as measured
and sealed.
between the specimen and reference electrode.
7.2 One or three holidays shall be made in each specimen.
5.2.9 Impressed Current Anode, shall be of the nonconsum-
Three holidays are recommended. Recommended dimensions
able type provided with a factory sealed, insulated copper
are given in Fig. 2.Aspecimen with one holiday shall have it
wire.
drilled in the middle of the immersed length. If three holidays
5.2.10 Voltage Divider, 100-V, 25-W rheostat, to be used if
are used, they shall be drilled 120° apart with one in the center
more than one specimen is to be tested as shown in Fig. 1.
and the other two at locations one fourth the distance from top
and bottom of the immersed test length. Each holiday shall be
6. Reagent and Materials
drilledsothattheangularconepointofthedrillwillfullyenter
6.1 The electrolyte shall consist of potable tap water with
the steel where the cylindrical portion of the drill meets the
the addition of 1 mass% of each of the following technical-
steel surface. The drill diameter shall be not less than three
gradesalts,calculatedonananhydrousbasis:sodiumchloride,
times the coating thickness, but it shall never be smaller than
sodium sulfate, and sodium carbonate. Use freshly prepared
6.35mm(0.250in.)indiameter.Thesteelwallofthepipeshall
solution for each test.
not be perforated. With small-diameter pipes, where there is
6.2 Materials for sealing the ends of coated pipe specimens
dangerofperforatingthepipe,theholidayshallbestartedwith
may consist of bituminous products, wax, epoxy, or other
a standard 60° cone point and finished with a drill that has had
materials, including molded elastomeric or plastic end caps.
a substantial portion of the cone point ground away.
6.3 Plywood or plastic material has been found suitable for
the construction of test vessel covers and for the support
NOTE 1—Before making the holiday, see 8.1.
through apertures of test specimens and electrodes. Wood
7.3 The end of the pipe which will protrude above the
immersion line shall be provided with suitable supporting
means and a separate wire connection for electrical purposes,
Durion,amaterialfoundsuitableforthispurposeisavailablefromDurionCo.,
Inc., Dayton OH. soldered, brazed, or bolted to the pipe. The protruding end,
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G8 – 96 (2003)
Dimension mm (in.)
490.22 6 12.7 (19.300 6 0.500)
B 245.11 6 12.7 ( 9.6506 0.500)
C 120.65 6 6.35 ( 4.7506 0.250)
D 114.3 6 6.35 ( 4.500 6 0.250)
E 233.363, min ( 9.1875, min)
F 19.05, min ( 0.750, min)
G 762, min (30, min)
FIG. 2 Recommended Dimensions for Specimen
including hanger and wire connections, shall be protected and Measure the apparent resistance in ohms, making two deter-
sealed with an insulating coating material. minations: one with the specimen connected to the positive
7.4 The specimen test area shall consist of the area between terminal of the multimeter; and one with the specime
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