ASTM G42-96(2003)
(Test Method)Standard Test Method for Cathodic Disbonding of Pipeline Coatings Subjected to Elevated Temperatures
Standard Test Method for Cathodic Disbonding of Pipeline Coatings Subjected to Elevated Temperatures
SCOPE
1.1 This test method describes an accelerated procedure for 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 exposed to high temperatures and is under cathodic protection. This test method is intended for use with samples of coated pipe taken from commercial production and is 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 elevated 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 room temperatures are required, see Test Methods G 8. If a specific test method is required with no options, see Test Method G 80.
1.3 The values stated in SI units to three significant decimals are to be regarded as the standard. The values given in parentheses are for information only.
1.4 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:G42–96(Reapproved2003)
Standard Test Method for
Cathodic Disbonding of Pipeline Coatings Subjected to
Elevated Temperatures
ThisstandardisissuedunderthefixeddesignationG42;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope G12 Test Method for Nondestructive Measurement of Film
Thickness of Pipeline Coatings on Steel
1.1 This test method describes an accelerated procedure for
G80 Test Method for Specific Cathodic Disbonding of
determining comparative characteristics of insulating coating
Pipeline Coatings
systems applied to steel pipe exterior for the purpose of
G95 Test Method for Cathodic Disbondment Test of Pipe-
preventing or mitigating corrosion that may occur in under-
line Coatings (Attached Cell Method)
ground service where the pipe will be exposed to high
temperaturesandisundercathodicprotection.Thistestmethod
3. Summary of Test Method
is intended for use with samples of coated pipe taken from
3.1 This test method subjects the coating on the test speci-
commercialproductionandisapplicabletosuchsampleswhen
men to electrical stress in a highly conductive electrolyte. The
the coating is characterized by function as an electrical barrier.
coating is artificially perforated before starting the test. The
1.2 This test method is intended for testing coatings sub-
electrical stress is produced by connecting the test specimen to
merged or immersed in the test solution at elevated tempera-
the negative terminal of a source of direct current and by
ture. When it is impractical to submerge or immerse the test
connecting an anode to the positive terminal. Electrical instru-
specimen, Test Method G95 may be considered where the test
mentation is provided for measuring the current flowing in the
cell is cemented to the surface of the coated pipe specimen. If
cell.Theelectricalpotentialisalsomeasuredandthespecimen
room temperatures are required, see Test Methods G8.Ifa
is physically examined at intervals during the test period and
specific test method is required with no options, see Test
upon conclusion of the test.
Method G80.
3.1.1 The cathodic stress is applied under conditions of a
1.3 The values stated in SI units to three significant deci-
constant-elevated temperature.
mals are to be regarded as the standard. The values given in
parentheses are for information only.
4. Significance and Use
1.4 This standard does not purport to address all of the
4.1 Damage to pipe coating is almost unavoidable during
safety concerns, if any, associated with its use. It is the
transportation and construction. Breaks or holidays in pipe
responsibility of the user of this standard to establish appro-
coatings may expose the pipe to possible corrosion since, after
priate safety and health practices and determine the applica-
a pipe has been installed underground, the surrounding earth
bility of regulatory limitations prior to use.
will be moisture-bearing and will constitute an effective
2. Referenced Documents electrolyte. Applied cathodic protection potentials may cause
2 loosening of the coating, beginning at holiday edges. Sponta-
2.1 ASTM Standards:
neousholidaysmayalsobecausedbysuchpotentials.Thistest
G8 Test Methods for Cathodic Disbonding of Pipeline
method provides accelerated conditions for cathodic disbond-
Coatings
ment to occur and provides a measure of resistance of coatings
to this type of action.
This test method is under the jurisdiction of ASTM Committee D01 on Paint
4.2 The effects of the test are to be evaluated by physical
and Related Coatings, Materials, andApplications and is the direct responsibility of
examinations and monitoring the current drawn by the test
Subcommittee D01.48 on Durability of Pipeline Coating and Linings.
specimen. Usually there is no correlation between the two
Current edition approved Dec. 1, 2003. Published December 2003. Originally
methods of evaluation, but both methods are significant.
approved in 1975. Last previous edition approved in 1996 as G42–96. DOI:
10.1520/G0042-96R03.
Physicalexaminationconsistsofassessingtheeffectivecontact
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
of the coating with the metal surface in terms of observed
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
differences in the relative adhesive bond. It is usually found
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. that the cathodically disbonded area propagates from an area
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
G42–96 (2003)
where adhesion is zero to an area where adhesion reaches the 5.1.4 Depth of electrolyte shall permit the test length of the
originallevel.Anintermediatezoneofdecreasedadhesionmay specimen to be immersed as required in 7.4.
also be present. 5.1.5 The reference electrode may be placed anywhere in
4.3 Assumptions associated with test results include: thevessel,provideditisseparatedfromthespecimenandfrom
4.3.1 Maximum adhesion, or bond, is found in the coating the anode by not less than 38 mm (1 ⁄2 in.).
that was not immersed in the test liquid, and 5.2 Anode—The anode shall be provided with a factory-
4.3.2 Decreased adhesion in the immersed test area is the sealed, insulated copper wire lead.
result of cathodic disbondment. 5.3 Connectors—Wiring from anode to test specimen shall
4.4 Ability to resist disbondment is a desired quality on a be 4107 cmil (14-gage Awg), minimum, insulated copper.
comparative basis, but disbondment in this test method is not Attachment to the test specimen shall be by soldering or
necessarily an adverse indication of coating performance. The brazing to the nonimmersed end, and the place of attachment
virtueofthistestmethodisthatalldielectric-typecoatingsnow shall be coated with an insulating material. A junction in the
in common use will disbond to some degree, thus providing a connectingwireispermitted,providedthatitismadebymeans
means of comparing one coating to another. of a bolted pair of terminal lugs soldered or mechanically
4.5 The current density appearing in this test method is crimped to clean wire ends.
much greater than that usually required for cathodic protection 5.4 Holiday Tools—Holidays shall be made with conven-
in natural environments. tional drills of the required diameter. For use in preparing
4.6 That any relatively lesser bonded area was caused by small-diameterpipespecimenssuchas19-mm( ⁄4-in.)nominal
electrical stressing in combination with the elevated and or diameter pipe, the use of a drill modified by substantially
depressed temperature and was not attributable to an anomaly grinding away the sharp cone point has been found effective in
in the application process. Ability to resist disbondment is a preventing perforation of the metal wall of the pipe. A
desired quality on a comparative basis, but most insulating sharp-pointed knife with a safe handle is required for use in
materials will disbond to some extent under the accelerated making physical examinations.
conditions of this test. Bond strength is more important for 5.5 Multimeters:
proper functioning of some coatings than others and the same 5.5.1 Multimeter, for direct current, having an internal
measured disbondment for two different coating systems may resistanceofnotlessthan10MVandhavingarangefrom0.01
not represent equivalent loss of corrosion protection. to 5 V for measuring potential to the reference electrode.
4.6.1 The amount of current flowing in the test cell may be 5.5.2 Multimeter, for direct current, having an internal
a relative indicator of the extent of areas requiring protection resistance of not less than 11 MV and capable of measuring as
against corrosion; however, the current density appearing in low as 10 µV potential drop across a shunt in the test cell
this test is much greater than that usually required for cathodic circuit.
protection in natural, inland soil environments. 5.5.3 Multimeter, for initial testing of apparent coating
4.6.2 Test voltages higher than those recommended may resistance.
result in the formation of chlorine gas. The subsequent chemi- 5.6 Reference Electrode—Saturated Cu CuSO electrode
cal effects on the coating could cast doubt on the interpretation having a potential of−0.316 V with respect to the standard
of the test results. hydrogen electrode shall be the standard of reference in these
test methods. Other electrodes may be used but measurements
5. Apparatus
thusobtainedshallbeconvertedtotheCuCuSO referencefor
5.1 TestVessel—Asuitablenonreactivevesselshallbeused,
reporting by making the proper correction.
capable of withstanding internal heating at not less than 60°C
NOTE 1—A saturated Cu CuSO electrode reading−1.50 V at 25°C
and suitable for continuous circulation of the electrolyte.
will read−1.53 V at 60°C, a scale increase of 0.03 V.
A19-L(5-gal) cylindrical glass vessel has been found suitable,
5.6.1 Asaturated calomel electrode at 25°C is converted to
having an approximate diameter of 300 mm (12 in.) and a
Cu CuSO by adding−0.07 V to the observed reading. If the
depth of 300 mm. A flat bottom is required for operation of a 4
saturated calomel electrode reads−1.43 V at 25°C, it will
magnetic stirring rod. An alternate means of heating the test
read−1.46Vat60°C,ascaleincreaseof0.03V.Itfollowsthat
sample can be provided by internally heating.The pipe sample
a saturated calomel electrode reading of−1.46 V at 60°C is
may be filled with a suitable heat transfer material (oil, steel
equal to a saturated Cu CuSO reading of−1.50 V at 25°C.
shot, etc). A thermocouple or thermometer and heater can be
5.6.2 A0.1normalcalomelelectrodeat25°Cisconvertedto
immersedintheheattransfermediumtoeffectivelycontrolthe
Cu CuSO by subtracting−0.02 V from the observed reading.
temperature of the sample. Dimensions of the vessel shall
Since the potential change due to an increase from 25°C to
permit the following requirements:
60°C is negligible, it follows that a 0.1 normal calomel
5.1.1 Test specimens shall be suspended vertically in the
electrode reading−1.52 V at 60°C is equal to a saturated Cu
vessel with at least 25 mm (1 in.) clearance from the bottom.
CuSO reading of−1.50 V at 25°C.
5.1.2 Test specimens shall be separated by not less than 38
5.7 Thermometers, two, mercury-filled type, accurate to
mm (1 ⁄2 in.), and a vertically suspended anode can be placed
61°C. One shall be of the full-immersion type for measuring
at an equal distance from each specimen not less than the
separation distance.
5.1.3 Testspecimensshallbeseparatedfromanywallofthe
Duriron, a material found suitable for this purpose is available from Duriron
vessel by not less than 13 mm ( ⁄2 in.). Co., Inc., Dayton, OH.
G42–96 (2003)
NOTE 3—Before making the holiday, see 7.5.
temperature near the bottom of the vessel, and a second
thermometer shall be of the partial-immersion type for mea-
7.3 The end of the pipe which will protrude above the
suring temperature near the top of the vessel.
immersion line shall be provided with suitable supporting
5.8 Combination Heater Plate, with built-in magnetic stir-
means and a separate wire connection for electrical purposes,
rer, or equivalent, shall be used for heating and stirring the
soldered, or brazed to the pipe. The protruding end, including
electrolyte. The heater shall be adjustable to produce and
hanger and wire connections, shall be protected and sealed
control a temperature of 60 6 1°C in the test vessel.
with an insulating coating material.
5.9 Direct-Current Rectifier, capable of supplying constant
7.4 The specimen test area shall consist of the area between
currentatavoltageof1.50 60.01V,asmeasuredbetweenthe
the edge of the bottom end seal and the immersion line. The
specimen and reference cell.
bottom end seal area shall not be considered part of the area
5.10 Thickness Gage, for measuring coating thickness in
tested. Coated specimens of any suitable diameter and length
accordance with Test Method G12.
of pipe may be used, but the immersed area shall be not less
2 2 2 2
5.11 PrecisionResistor,1V61%,1W(min),tobeusedin
than 23 200 mm (36 in. ).An area of 92 900 mm (1 ft ) has
the test cell circuit as a shunt for current.
been found preferable when convenient.
5.12 Carbon or Stainless Steel Electrode, used temporarily
7.5 The continuity of the coating and efficiency of the end
with the volt-ohm-meter to determine apparent initial holiday
sealshallbetestedbeforemakingartificialholidaysasfollows:
status of the test specimen.
7.5.1 Immerse the test specimen and a carbon or stainless
5.13 Additional Connecting Wires, 4107 cmil (14-gage
steel electrode in the electrolyte. Connect one terminal of the
Awg), minimum, insulated copper.
ohmmeter to the test specimen and the other terminal to the
5.14 Brass Studs, used at a terminal board, together with
carbon or stainless steel electrode. Measure the apparent
alligator clips or knife switches, for making and breaking
resistance in ohms, making two determinations: one with the
circuits. Alligator clips shall not be used to connect the
specimen connected to the positive terminal of the ohmmeter,
electrodes or specimens at the top location of test cells.
and one with the specimen connected to the negative terminal.
The lowest of the two readings should be not less than 1000
6. Reagents and Materials
MV, however, the test may be conducted with a low reading
6.1 The electrolyte shall consist of potable tap water or
less than 1000 MV, provided that the condition is taken into
higher purity water (distilled or demineralized water is satis-
account in evaluating results.
factory) with the addition of 1 weight% of each of the
following technical-grade salts, calculated on an anhydrous
8. Procedure
basis: sodium chloride, sodium sulfate, and sodium carbonate.
8.1 Immersethetestspecimenintheelectrolyteandconnect
ittotheanodeasshowninFig.1.Adjusttherectifierorvoltage
NOTE 2—The resulting solution has a pH of 10 or higher and a
resistivity of 25 to 50 V·cm at room temperature.
divider so that the potential between specimen and reference
cell is−1.50 6 0.01 V at 25°C (−1.53 6 0.01 V at 60°C) (see
6.2 Materials for sealing the ends of coated pipe specimens
Fig. 2). The holiday may be positioned facing the anode or
may consist of bituminous products, wax, epoxy, or other
facing away from the anode as described in Test Methods G8.
materials, including molded elastomeric or plastic end caps,
Spa
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