ASTM D6676/D6676M-21

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Designation: D6676/D6676M − 13 D6676/D6676M − 21
Standard Test Method for
Cathodic Disbonding of Exterior Pipeline Coatings at
Elevated Temperatures Using Interior Heating
This standard is issued under the fixed designation D6676/D6676M; the number immediately following the designation indicates the
year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last
reapproval. A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method describes an accelerated procedure for determining comparative characteristics of coating systems applied
to the exterior of steel pipe for the purpose of preventing or mitigating corrosion that may occur in underground or immersion
where the pipe is carrying heated media and is under cathodic protection. This test method is intended for use with samples of
coated pipe, or with a specimen cut from the section of coated pipe or flat plates,plates and is applicable to such samples when
the coating is characterized by function as an electrical barrier.
1.2 This test method is intended to simulate conditions when external coatings are exposed to high temperature inside the pipe
and to an ambient temperature outside, and thus are subjected to temperature gradient. If elevated temperatures are required but
without temperature gradient, see Test Method G42.
1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each
system are not necessarily exact equivalents; therefore, to ensure conformance with the standard, each system shall be used
independently of the other, and values from the two systems shall not be combined.
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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
G8D7091 Test Methods for Cathodic Disbonding of Pipeline CoatingsPractice for Nondestructive Measurement of Dry Film
Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to
Non-Ferrous Metals
G12 Test Method for Nondestructive Measurement of Film Thickness of Pipeline Coatings on Steel (Withdrawn 2013)
G42 Test Method for Cathodic Disbonding of Pipeline Coatings Subjected to Elevated Temperatures
This test method is under the jurisdiction of ASTM Committee D01 on Paint and Related Coatings, Materials, and Applications and is the direct responsibility of
Subcommittee D01.48 on Durability of Pipeline Coating and Linings.
Current edition approved Nov. 1, 2013Nov. 1, 2021. Published November 2013December 2021. Originally approved in 2001. Last previous edition approved in 20012013
ε1
as D6676 – 01D6676/D6676M – 13. which was withdrawn January 2010 and reinstated in November 2013. DOI: 10.1520/D6676_D6676M-13.DOI: 10.1520/D6676_
D6676M-21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D6676/D6676M − 21
G62 Test Methods for Holiday Detection in Pipeline Coatings
G95 Test Method for Cathodic Disbondment Test of Pipeline Coatings (Attached Cell Method)
3. Summary of Test Method
3.1 The test method described, subjects the coating on the test specimen to electrical stress in a highly conductive alkaline
electrolyte. Electrical stress is obtained from an impressed direct- current direct-current system. An intentional holiday is to be
made in the coating prior to starting of test.
3.1.1 Electrical instrumentation is provided for measuring the current and the potential throughout the test cycle. At the conclusion
of the test period, the test specimen is physically examined.
3.1.2 Physical examination is conducted by comparing the extent of loosened or disbonded coating at the intentional holiday in
the immersed area with extent of loosened or disbonded coating at a reference holiday made in the coating in an area that was not
immersed.
3.1.3 The cathodic stress is applied under conditions of a constant temperature gradient, simulating a heated pipeline with 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 as tape) for maximum cathodic disbondment resistance. Cut coupons or
flat plates must not be used.
4. Significance and Use
4.1 Damage to a pipe coating is almost unavoidable during transportation and construction. Breaks or holidays in pipe coatings
may expose the pipe to possible corrosion since, after a pipe has been installed underground, the surrounding earth will be
moisture-bearing and will constitute an effective electrolyte. Applied cathodic protection potentials may cause loosening of the
coating, beginning at holiday edges. Spontaneous holidays may also be caused by such potentials. Usually exterior pipeline
coatings applied over pipes carrying hot media (oil, gas) are exposed to high temperature inside the pipe and low temperature
outside and subjected to temperature gradient. Heat flux is directed from metal (substrate) to the coating. This test method provides
accelerated conditions for cathodic disbondment to occur under simulated heating and provides a measure of resistance of coatings
to this type of action.
4.2 The effects of the test are to be evaluated by physical examinations and monitoring the current drawn by the test specimens.
Usually there is no correlation between the two methods of evaluation, but both methods are significant. Physical examination
consists of assessing the effective contact of the coating with the metal surface in terms of observed differences in the relative
adhesive bond. It is usually found that the cathodically disbonded area propagates from an area where adhesion is zero to an area
where adhesion reaches the original level. An intermediate zone of decreased adhesion may also be present.
FIG. 1 Pipe Specimen Heated Inside
D6676/D6676M − 21
FIG. 2 Flat Specimen Heated Over Hot Plate
4.3 Assumptions associated with test results include:
4.3.1 Maximum adhesion, or bond, is found in the coating that was not immersed in the test liquid, and
4.3.2 Decreased adhesion in the immersed test area is the result of cathodic disbondment.
4.4 Ability to resist disbondment is a desired quality on a comparative basis, but disbondment in this test method is not necessarily
an adverse indication of coating performance. The virtue of this test method is that all dielectric-type coatings now in common
use will disbond to some degree, thus providing a means of comparing one coating to another.
4.5 The amount of current flowing in the test cell is a relative indicator of the extent of areas requiring protection against corrosion;
however, the current density appearing in this test is much greater than that usually required for cathodic protection in natural,
inland soil environments.
4.6 Test voltages higher than those recommended may result in the formation of chlorine gas. The subsequent chemical effects
on the coating could cast doubt on the interpretation of the test results. Filter tube with fritted diskdisc (see Test Method G95) or
layer of sand (40 mesh) put on the coated surface may reduce this effect.
5. Apparatus
5.1 Test Vessel for Pipe Specimen (Fig. 4)—A suitable nonreactive vessel shall be used, capable of withstanding internal heating
at test temperature and suitable to accommodate a test specimen, an anode. Heating the test sample can be provided by internally
heating. The pipe sample may be filled with a suitable heat transfer material (oil, steel, shot, sand, copper chips, etc.) A
thermocouple or thermometer and heater can be immersed in the heat transfer medium to effectively control the temperature of
the sample. Dimensions of the vessel shall permit the following requirements:
5.1.1 Test specimen shall be suspended vertically in the vessel with at least 25 mm [1 in.] clearance from the bottom.
5.1.2 Test specimen shall be separated by not less than 38 mm [1 ⁄2 in.], and a vertically suspended anode can be placed at an equal
distance from each specimen not less than the separation distance.
5.1.3 Test specimen shall be separated from any wall of the vessel by not less than 13 mm [ ⁄2 in.].
5.1.4 Depth of electrolyte shall permit the test length of the specimen to be immersed as required in 7.4.
5.1.5 The reference electrode may be placed anywhere in the vessel, provided it is separated from the specimen and from the anode
by not less than 38 mm [1 ⁄2 in.].
5.2 Test Vessel for Flat or Cut From Pipe Specimens (Fig. 3)—A transparent plastic ofor glass tube that is centered over the
intentional holiday and sealed to the test sample surface with a waterproof sealing material. The cylinder is to be 101.6 mm [4.0
in.] nominal diameter and of sufficient height to contain 127.0 mm [5.0 in.] of electrolyte.
D6676/D6676M − 21
FIG. 3 Test Set-Up for Cathodic Disbonding Test with Coated Pipe Coupon (or Flat Coupon) Heated Over Hot Plate
5.3 Impressed-Current Anode—Anode shall be of the platinum wire type, 0.51 mm [0.020 in.]–24 gauge diameter. It shall be of
sufficient length to extend outside the confines of the test cell and shall be connected to the wire from the power source with a
bolted or compressed fitting.
5.4 Anode Assembly—Anode shall be suspended inside the test vessel so that the tip of the anode assembly closest to the holiday
is 25.4 mm [1 in.] above, and the edge of the anode assembly is 12.7 mm [ ⁄2 in.] above, and the edge of the anode assembly is
12.7 mm [ ⁄2 in.] offset from the holiday.
5.5 Reference Electrode—Saturated Cu-CuSO of conventional glass or plastic tube with porous plug construction, preferably not
over 19.05 mm [0.750 in.] in diameter, having a potential of –0.316 V with respect to the standard hydrogen electrode. A saturated
calomel electrode may be used, but measurements made with it shall be converted to the Cu- CuSO reference for reporting by
adding -0.072–0.072 V to the observed reading.
5.6 Reference Electrode Placement—Submerge the tip of the reference electrode 25.4 mm [1 in.] into the electrolyte.
5.7 High-Impedance Multimeter—For making direct current and voltage measurements. Multimeter must have an internal
resistance of not less than 10 MΩ and be capable of measuring as low as 10 μ V potential drop across a shunt in the test cell circuit,
and voltage up to 10 V.
D6676/D6676M − 21
FIG. 4 Test Set-Up for Cathodic Disbonding Test at Elevated Temperature
5.8 Direct-Current Power Supply—Capable of supplying low-ripple voltage at 1.5, 60.01, V, as measured between the test
specimen and reference electrode.
5.9 Precision Wire-Wound Resistor—1 Ω 6 1 % 1-W (mimimum)(minimum) to be used in the test cell circuit as a shunt for
measuring current.
5.10 Thickness Gauge—for measuring coating thickness in accordance with Practice D7091 or Test Method G12.
5.11 Holiday Detector—for locating holidays in the coating of the test specimen in accordance with Test Method G62.
5.12 Connections—Wiring from current source to the specimen shall be by either soldering, brazing, or bolting to the
non-immersed area of the specimen. A junction in the connection wire is not desirable but, if necessary, may be made by means
of a bolted pair of terminal lugs, soldering or mechanically crimping to clean wire ends.
5.13 Additional Connecting Wires—If additional wiring is necessary, it shall be stranded, insulated copper and not less than 1.75
mm [0.069 in.]–15 gauge diameter.
5.14 Holiday Tools—A drill and a suitable drill bit that will accomplish drilling of test hole, as described in 9.2.
5.15 Heaters: Heaters—A method to heat the test specimen to 80 6 1°C (or other temperature as specified) shall be used.
5.15.1 Pipe Specimens—Liquid Heat Exchange Medium—Circulating bath with built-in heater shall be used for heating the heat
transfer medium (silicone oil or other) to produce and control temperature of 80°80 6 1°C (or other temperature as specified)
inside of the coated pipe samples connected with the bath by the hoses.
5.15.2 Pipe Specimens—Solid Heat Exchange Medium—Heaters suitable for controlling temperature at 80°80 6 1°C or as
otherwise specified shall be employed inside the coated pipe.
5.15.3 Flat Plates—Heater plate, or equivalent, shall be used for heating coated samples. The heater shall be adjustable to produce
and control a temperature of 80°80 6 1°C or other specified temperature on the uncoated surface of testing panel.
D6676/D6676M − 21
5.16 Thermometers or Thermocouples, to measure temperature of heat transfer medium or on the
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