ASTM G61-86(2003)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:G61–86(Reapproved2003)
Standard Test Method for
Conducting Cyclic Potentiodynamic Polarization
Measurements for Localized Corrosion Susceptibility of
Iron-, Nickel-, or Cobalt-Based Alloys
ThisstandardisissuedunderthefixeddesignationG61;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.2 Ingeneral,onceinitiated,localizedcorrosioncanpropa-
gate at some potential more electropositive than that at which
1.1 This test method covers a procedure for conducting
the hysteresis loop is completed. In this test method, the
cyclic potentiodynamic polarization measurements to deter-
potential at which the hysteresis loop is completed is deter-
mine relative susceptibility to localized corrosion (pitting and
mined at a fixed scan rate. In these cases, the more electrop-
crevicecorrosion)foriron-,nickel-,orcobalt-basedalloysina
ositive the potential at which the hysteresis loop is completed
chloride environment. This test method also describes an
the less likely it is that localized corrosion will occur.
experimental procedure which can be used to check one’s
3.3 If followed, this test method will provide cyclic poten-
experimental technique and instrumentation.
tiodynamic anodic polarization measurements that will repro-
1.2 This standard does not purport to address all of the
duce data developed at other times in other laboratories using
safety concerns, if any, associated with its use. It is the
this test method for the two specified alloys discussed in 3.4.
responsibility of the user of this standard to establish appro-
The procedure is used for iron-, nickel-, or cobalt-based alloys
priate safety and health practices and determine the applica-
in a chloride environment.
bility of regulatory limitations prior to use.
3.4 A standard potentiodynamic polarization plot is in-
2. Referenced Documents
cluded.These reference data are based on the results from five
different laboratories that followed the standard procedure,
2.1 ASTM Standards:
using specific alloys of Type 304 stainless steel, UNS S30400
D1193 Specification for Reagent Water
and Alloy C-276, UNS N10276. Curves are included which
G3 PracticeforConventionsApplicabletoElectrochemical
have been constructed using statistical analysis to indicate the
Measurements in Corrosion Testing
acceptable range of polarization curves.
G5 Reference Test Method for Making Potentiostatic and
3.5 The availability of a standard test method, standard
Potentiodynamic Anodic Polarization Measurements
material, and standard plots should make it easy for an
3. Significance and Use
investigator to check his techniques to evaluate susceptibility
to localized corrosion.
3.1 An indication of the susceptibility to initiation of local-
ized corrosion in this test method is given by the potential at
4. Apparatus
whichtheanodiccurrentincreasesrapidly.Themorenoblethis
4.1 The polarization cell should be similar to the one
potential, obtained at a fixed scan rate in this test, the less
described in Practice G5. Other polarization cells may be
susceptible is the alloy to initiation of localized corrosion.The
equally suitable.
resultsofthistestarenotintendedtocorrelateinaquantitative
4.1.1 The cell should have a capacity of about 1 L and
manner with the rate of propagation that one might observe in
should have suitable necks or seals to permit the introduction
service when localized corrosion occurs.
of electrodes, gas inlet and outlet tubes, and a thermometer.
The Luggin probe-salt bridge separates the bulk solution from
thesaturatedcalomelreferenceelectrode.Theprobetipshould
This test method is under the jurisdiction of ASTM Committee G01 on
beadjustablesothatitcanbebroughtintocloseproximitywith
Corrosion of Metals and is the direct responsibility of Subcommittee G01.11 on
the working electrode.
Electrochemical Measurements in Corrosion Testing.
Current edition approved October 1, 2003. Published October 2003. Originally
approved in 1986. Last previous edition approved in 1998 as G 61–86 (1998).
2 4
Annual Book of ASTM Standards, Vol 11.01. These standard samples are available as a set of one of each type fromASTM
Annual Book of ASTM Standards, Vol 03.02. Headquarters at a nominal cost Order PCN ADJG0061.
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G61–86 (2003)
4.2 Specimen Holder: 10 µAshouldbeused.Manycommercialunitshaveabuild-in
4.2.1 Specimens should be mounted in a suitable holder instrument with an output as a voltage, which is preferred for
designed for flat strip, exposing 1 cm to the test solution (Fig. recording purposes. For the purpose of the present test a
1). Such specimen holders have been described in the litera- logarithmic output is desirable.
4.6 Anodic Polarization Circuit—Ascanning potentiostat is
used for potentiodynamic measurements. Potential and current
are plotted continuously using an X-Y recorder and a logarith-
mic converter (contained in the potentiostat or incorporated
into the circuit) for the current. Commercially available units
are suitable.
4.7 Electrodes:
4.7.1 The standard Type 304 stainless steel (UNS S30400)
andAlloy C-276 (UNS N10276) should be machined into flat
0.625-in. (14-mm) diameter disks. The chemical compositions
of the alloys used in the round robin are listed in Table 1.
TABLE 1 Chemical Composition of Alloys Used in the Round
Robin, Weight %
Type 304
Alloy C-276
Element Stainless Steel
(UNS N10276)
(UNS S30400)
Carbon 0.003 0.060
Chromium 15.29 18.46
Cobalt 2.05 .
Columbium . 0.11
Copper . 0.17
Iron 5.78 balance
Manganese 0.48 1.43
Molybdenum 16.03 0.17
4,5
Nickel balance 8.74
FIG. 1 Schematic Diagram of Specimen Holder
Phosphorus 0.018 0.029
Silicon 0.05 0.60
Sulfur 0.006 0.014
ture. It is important that the circular TFE-fluorocarbon gasket
Vanadium 0.20 .
be drilled and machined flat in order to minimize crevices.
Tungsten 3.62 .
4.3 Potentiostat (Note 1)—Apotentiostat that will maintain
an electrode potential within 1 mV of a preset value over a
widerangeofappliedcurrentsshouldbeused.Forthetypeand
4.7.2 Counter Electrodes—The counter electrodes may be
size of standard specimen supplied, the potentiostat should
prepared as described in Practice G5 or may be prepared from
have a potential range of−1.0 to+1.6 V and an anodic current
5 high-purity platinum flat stock and wire. A suitable method
output range of 1.0 to 10 µA. Most commercial potentiostats
would be to seal the platinum wire in glass tubing and
meet the specific requirements for these types of measure-
introduce the platinum electrode assembly through a sliding
ments.
seal. Counter electrodes should have an area at least twice as
NOTE 1—These instrumental requirements are based upon values typi-
large as the test electrode.
cal of the instruments in the five laboratories that have provided the data
4.7.3 Reference Electrode —A saturated calomel electrode
used in determining the standard polarization plot.
with a controlled rate of leakage (about 3 µL/h) is recom-
4.4 Potential-Measuring Instruments (Note 1)—The
mended. This type of electrode is durable, reliable, and
potential-measuring circuit should have a high input imped-
commerically available. Precautions should be taken to ensure
11 14
ance on the order of 10 to 10 V to minimize current drawn
that it is maintained in the proper condition. The potential of
from the system during measurements. Instruments should
thecalomelelectrodeshouldbecheckedatperiodicintervalsto
have sufficient sensitivity and accuracy to detect a change in
ensure the accuracy of the electrode.
potential of 61 mV, usually included in commercial poten-
tiostats. An output as a voltage is preferred for recording
5. Reagents and Materials
purposes.
5.1 Purity of Reagents—Reagent grade chemicals shall be
4.5 Current-Measuring Instruments (Note 1)—An instru-
used in all tests. Unless otherwise indicated, it is intended that
mentthatiscapableofmeasuringacurrentaccuratelyt
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