ASTM G61-86(1998)

NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: G 61 – 86 (Reapproved 1998)
Standard Test Method for
Conducting Cyclic Potentiodynamic Polarization
Measurements for Localized Corrosion Susceptibility of
Iron-, Nickel-, or Cobalt-Based Alloys
This standard is issued under the fixed designation G 61; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope ositive the potential at which the hysteresis loop is completed
the less likely it is that localized corrosion will occur.
1.1 This test method gives a procedure for conducting cyclic
3.3 If followed, this test method will provide cyclic poten-
potentiodynamic polarization measurements to determine rela-
tiodynamic anodic polarization measurements that will repro-
tive susceptibility to localized corrosion (pitting and crevice
duce data developed at other times in other laboratories using
corrosion) for iron-, nickel-, or cobalt-based alloys in a
this test method for the two specified alloys discussed in 3.4.
chloride environment. This test method also describes an
The procedure is used for iron-, nickel-, or cobalt-based alloys
experimental procedure which can be used to check one’s
in a chloride environment.
experimental technique and instrumentation.
3.4 A standard potentiodynamic polarization plot is in-
1.2 This standard does not purport to address all of the
cluded. These reference data are based on the results from five
safety concerns, if any, associated with its use. It is the
different laboratories that followed the standard procedure,
responsibility of the user of this standard to establish appro-
using specific alloys of Type 304 stainless steel, UNS S30400
priate safety and health practices and determine the applica-
and Alloy C-276, UNS N10276. Curves are included which
bility of regulatory limitations prior to use.
have been constructed using statistical analysis to indicate the
2. Referenced Documents
acceptable range of polarization curves.
3.5 The availability of a standard test method, standard
2.1 ASTM Standards:
material, and standard plots should make it easy for an
D 1193 Specification for Reagent Water
investigator to check his techniques to evaluate susceptibility
G 3 Practice for Conventions Applicable to Electrochemical
to localized corrosion.
Measurements in Corrosion Testing
G 5 Reference Test Method for Making Potentiostatic and
4. Apparatus
Potentiodynamic Anodic Polarization Measurements
4.1 The polarization cell should be similar to the one
3. Significance and Use described in Practice G 5. Other polarization cells may be
equally suitable.
3.1 An indication of the susceptibility to initiation of local-
4.1.1 The cell should have a capacity of about 1 L and
ized corrosion in this test method is given by the potential at
should have suitable necks or seals to permit the introduction
which the anodic current increases rapidly. The more noble this
of electrodes, gas inlet and outlet tubes, and a thermometer.
potential, obtained at a fixed scan rate in this test, the less
The Luggin probe-salt bridge separates the bulk solution from
susceptible is the alloy to initiation of localized corrosion. The
the saturated calomel reference electrode. The probe tip should
results of this test are not intended to correlate in a quantitative
be adjustable so that it can be brought into close proximity with
manner with the rate of propagation that one might observe in
the working electrode.
service when localized corrosion occurs.
4.2 Specimen Holder:
3.2 In general, once initiated, localized corrosion can propa-
4.2.1 Specimens should be mounted in a suitable holder
gate at some potential more electropositive than that at which
designed for flat strip, exposing 1 cm to the test solution (Fig.
the hysteresis loop is completed. In this test method, the
1). Such specimen holders have been described in the litera-
potential at which the hysteresis loop is completed is deter-
,
5 6
ture. It is important that the circular TFE-fluorocarbon gasket
mined at a fixed scan rate. In these cases, the more electrop-
be drilled and machined flat in order to minimize crevices.
This test method is under the jurisdiction of ASTM Committee G01 on
These standard samples are available as a set of one of each type from ASTM
Corrosion of Metals and is the direct responsibility of Subcommittee G01.11 on Headquarters at a nominal cost Order PCN ADJG0061.
Electrochemical Measurements in Corrosion Testing. France, W. D., Jr., Journal of the Electrochemical Society, Vol 114, 1967, p.
Current edition approved Nov. 28, 1986. Published January 1987. 818.
2 6
Annual Book of ASTM Standards, Vol 11.01. Myers, J. R., Gruewlar, F. G., and Smulezenski, L. A., Corrosion, Vol 24, 1968,
Annual Book of ASTM Standards, Vol 03.02. p. 352.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
G61
0.625-in. (14-mm) diameter disks. The chemical compositions
of the alloys used in the round robin are listed in Table 1.
4.7.2 Counter Electrodes—The counter electrodes may be
prepared as described in Practice G 5 or may be prepared from
high-purity platinum flat stock and wire. A suitable method
would be to seal the platinum wire in glass tubing and
introduce the platinum electrode assembly through a sliding
seal. Counter electrodes should have an area at least twice as
large as the test electrode.
4.7.3 Reference Electrode —A saturated calomel electrode
with a controlled rate of leakage (about 3 μL/h) is recom-
mended. This type of electrode is durable, reliable, and
commerically available. Precautions should be taken to ensure
that it is maintained in the proper condition. The potential of
the calomel electrode should be checked at periodic intervals to
ensure the accuracy of the electrode.
5. Reagents and Materials
5.1 Purity of Reagents—Reagent grade chemicals shall be
used in all tests. Unless otherwise indicated, it is intended that
all reagents shall conform to the specifications of the Commit-
tee on Analytical Reagents of the American Chemical Society,
4,5
FIG. 1 Schematic Diagram of Specimen Holder where such specifications are available. Other grades may be
used, provided it is first ascertained that the reagent is of
4.3 Potentiostat (Note 1)—A potentiostat that will maintain
sufficiently high purity to permit its use without lessening the
an electrode potential within 1 mV of a preset value over a
accuracy of the determination.
wide range of applied currents should be used. For the type and
5.2 Purity of Water—The water shall be distilled or deion-
size of standard specimen supplied, the potentiostat should
ized conforming to the purity requirements of Specification
have a potential range of − 1.0 to + 1.6 V and an anodic current
5 D 1193, Type IV reagent water.
output range of 1.0 to 10 μA. Most commercial potentiostats
5.3 Sodium Chloride (NaCl).
meet the specific requirements for these types of measure-
5.4 Samples of Standard Type 304 stainless steel (UNS
ments.
S30400) and the Alloy C-276 (UNS N10276) used in obtaining
NOTE 1—These instrumental requirements are based upon values typi-
the standard reference plot are available for those who wish to
cal of the instruments in the five laboratories that have provided the data
check their own test procedure and equipment.
used in determining the standard polarization plot.
4.4 Potential-Measuring Instruments (Note 1)—The
potential-measuring circuit should have a high input imped- 7
Ives, D. J., and Janz, G. J., Reference Electrodes, Theory and Practice,
11 14
ance on the order of 10 to 10 V to minimize current drawn
Academic Press, New York, NY 1961.
Reagent Chemicals, American Chemical Society Specifications, Am. Chemical
from the system during measurements. Instruments should
Soc., Washington, DC. For suggestions on the testing of reagents not listed by the
have sufficient sensitivity and accuracy to detect a change in
American Chemical Society, see Analar Standards for Laboratory Chemicals, BDH
potential of 61 mV, usually included in commercial poten-
Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and National
tiostats. An output as a voltage is preferred for recording Formulary, U.S. Pharmacopeial Covention, Inc. (USPC), Rockville, MD.”
purposes.
4.5
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