ASTM G61-86(2018)

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.
Designation: G61 − 86 (Reapproved 2018)
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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2.2 ASTM Adjuncts:
Standard Samples (set of two)
1.1 This test method covers a procedure for conducting
cyclic potentiodynamic polarization measurements to deter-
3. Significance and Use
mine relative susceptibility to localized corrosion (pitting and
3.1 An indication of the susceptibility to initiation of local-
crevicecorrosion)foriron-,nickel-,orcobalt-basedalloysina
chloride environment. This test method also describes an ized corrosion in this test method is given by the potential at
whichtheanodiccurrentincreasesrapidly.Themorenoblethis
experimental procedure which can be used to check one’s
experimental technique and instrumentation. potential, obtained at a fixed scan rate in this test, the less
susceptible is the alloy to initiation of localized corrosion.The
1.2 The values stated in SI units are to be regarded as
resultsofthistestarenotintendedtocorrelateinaquantitative
standard. No other units of measurement are included in this
manner with the rate of propagation that one might observe in
standard.
service when localized corrosion occurs.
1.3 This standard does not purport to address all of the
3.2 Ingeneral,onceinitiated,localizedcorrosioncanpropa-
safety concerns, if any, associated with its use. It is the
gate at some potential more electropositive than that at which
responsibility of the user of this standard to establish appro-
the hysteresis loop is completed. In this test method, the
priate safety, health, and environmental practices and deter-
potential at which the hysteresis loop is completed is deter-
mine the applicability of regulatory limitations prior to use.
mined at a fixed scan rate. In these cases, the more electro-
1.4 This international standard was developed in accor-
positive the potential at which the hysteresis loop is completed
dance with internationally recognized principles on standard-
the less likely it is that localized corrosion will occur.
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom- 3.3 If followed, this test method will provide cyclic poten-
mendations issued by the World Trade Organization Technical
tiodynamic anodic polarization measurements that will repro-
Barriers to Trade (TBT) Committee. duce data developed at other times in other laboratories using
this test method for the two specified alloys discussed in 3.4.
2. Referenced Documents The procedure is used for iron-, nickel-, or cobalt-based alloys
in a chloride environment.
2.1 ASTM Standards:
D1193Specification for Reagent Water 3.4 A standard potentiodynamic polarization plot is in-
G3Practice for Conventions Applicable to Electrochemical
cluded.These reference data are based on the results from five
Measurements in Corrosion Testing different laboratories that followed the standard procedure,
G5Reference Test Method for Making Potentiodynamic
using specific alloys of Type 304 stainless steel, UNS S30400
Anodic Polarization Measurements
and Alloy C-276, UNS N10276. Curves are included which
have been constructed using statistical analysis to indicate the
acceptable range of polarization curves.
This test method is under the jurisdiction of ASTM Committee G01 on
3.5 The availability of a standard test method, standard
Corrosion of Metals and is the direct responsibility of Subcommittee G01.11 on
material, and standard plots should make it easy for an
Electrochemical Measurements in Corrosion Testing.
investigator to check his techniques to evaluate susceptibility
Current edition approved May 1, 2018. Published June 2018. Originally
approvedin1986.Lastpreviouseditionapprovedin2014asG61–86(2014).DOI:
to localized corrosion.
10.1520/G0061-86R18.
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 Available from ASTM International Headquarters. Order Adjunct No.
the ASTM website. ADJG0061. Original adjunct produced before 1995.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G61 − 86 (2018)
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
Nickel balance 8.74
Phosphorus 0.018 0.029
Silicon 0.05 0.60
Sulfur 0.006 0.014
Vanadium 0.20 .
Tungsten 3.62 .
4.4 Potential-Measuring Instruments (Note 1)—The
potential-measuring circuit should have a high input imped-
11 14
ance on the order of 10 to 10 Ω to minimize current drawn
from the system during measurements. Instruments should
have sufficient sensitivity and accuracy to detect a change in
FIG. 1 Schematic Diagram of Specimen Holder (see Footnotes 3
potential of 61 mV, usually included in commercial poten-
and 4)
tiostats. An output as a voltage is preferred for recording
purposes.
4. Apparatus
4.5 Current-Measuring Instruments (Note 1)—An instru-
mentthatiscapableofmeasuringacurrentaccuratelytowithin
4.1 The polarization cell should be similar to the one
1%oftheabsolutevalueoveracurrentrangebetween1.0and
described in Reference Test Method G5. Other polarization
10 µAshouldbeused.Manycommercialunitshaveabuild-in
cells may be equally suitable.
instrument with an output as a voltage, which is preferred for
4.1.1 The cell should have a capacity of about 1 L and
recording purposes. For the purpose of the present test a
should have suitable necks or seals to permit the introduction
logarithmic output is desirable.
of electrodes, gas inlet and outlet tubes, and a thermometer.
The Luggin probe-salt bridge separates the bulk solution from
4.6 Anodic Polarization Circuit—Ascanning potentiostat is
thesaturatedcalomelreferenceelectrode.Theprobetipshould
used for potentiodynamic measurements. Potential and current
beadjustablesothatitcanbebroughtintocloseproximitywith
are plotted continuously using an X-Y recorder and a logarith-
the working electrode.
mic converter (contained in the potentiostat or incorporated
into the circuit) for the current. Commercially available units
4.2 Specimen Holder:
are suitable.
4.2.1 Specimens should be mounted in a suitable holder
designed for flat strip, exposing 1 cm to the test solution (Fig.
4.7 Electrodes:
1). Such specimen holders have been described in the litera-
4.7.1 The standard Type 304 stainless steel (UNS S30400)
ture. It is important that the circular TFE-fluorocarbon gasket
andAlloy C-276 (UNS N10276) should be machined into flat
be drilled and machined flat in order to minimize crevices.
0.625-in. (14-mm) diameter disks. The chemical compositions
of the alloys used in the round robin are listed in Table 1.
4.3 Potentiostat (Note 1)—Apotentiostat that will maintain
4.7.2 Counter Electrodes—The counter electrodes may be
an electrode potential within 1 mV of a preset value over a
prepared as described in ReferenceTest Method G5 or may be
widerangeofappliedcurrentsshouldbeused.Forthetypeand
prepared from high-purity platinum flat stock and wire. A
size of standard specimen supplied, the potentiostat should
suitable method would be to seal the platinum wire in glass
have a potential range of−1.0 to+1.6 V and an anodic current
tubing and introduce the platinum electrode assembly through
output range of 1.0 to 10 µA. Most commercial potentiostats
a sliding seal. Counter electrodes should have an area at least
meet the specific requirements for these types of measure-
twice as large as the test electrode.
ments.
4.7.3 Reference Electrode —A saturated calomel electrode
NOTE 1—These instrumental requirements are based upon values
with a controlled rate of leakage (about 3 µL/h) is recom-
typical of the instruments in the five laboratories that have provided the
mended. This type of electrode is durable, reliable, and
data used in determining the standard
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