ASTM G61-86(2009)
(Test Method)Standard Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements for Localized Corrosion Susceptibility of Iron-, Nickel-, or Cobalt-Based Alloys
Standard Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements for Localized Corrosion Susceptibility of Iron-, Nickel-, or Cobalt-Based Alloys
SIGNIFICANCE AND USE
An indication of the susceptibility to initiation of localized corrosion in this test method is given by the potential at which the anodic current increases rapidly. The more noble this potential, obtained at a fixed scan rate in this test, the less susceptible is the alloy to initiation of localized corrosion. The results of this test are not intended to correlate in a quantitative manner with the rate of propagation that one might observe in service when localized corrosion occurs.
In general, once initiated, localized corrosion can propagate at some potential more electropositive than that at which the hysteresis loop is completed. In this test method, the potential at which the hysteresis loop is completed is determined at a fixed scan rate. In these cases, the more electropositive the potential at which the hysteresis loop is completed the less likely it is that localized corrosion will occur.
If followed, this test method will provide cyclic potentiodynamic anodic polarization measurements that will reproduce data developed at other times in other laboratories using this test method for the two specified alloys discussed in 3.4. The procedure is used for iron-, nickel-, or cobalt-based alloys in a chloride environment.
A standard potentiodynamic polarization plot is included. These reference data are based on the results from five different laboratories that followed the standard procedure, using specific alloys of Type 304 stainless steel, UNS S30400 and Alloy C-276, UNS N10276. Curves are included which have been constructed using statistical analysis to indicate the acceptable range of polarization curves.
The availability of a standard test method, standard material, and standard plots should make it easy for an investigator to check his techniques to evaluate susceptibility to localized corrosion.
SCOPE
1.1 This test method covers a procedure for conducting cyclic potentiodynamic polarization measurements to determine relative susceptibility to localized corrosion (pitting and crevice corrosion) for iron-, nickel-, or cobalt-based alloys in a chloride environment. This test method also describes an experimental procedure which can be used to check one's experimental technique and instrumentation.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 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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Standards Content (Sample)
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Designation: G61 − 86(Reapproved 2009)
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 whichtheanodiccurrentincreasesrapidly.Themorenoblethis
potential, obtained at a fixed scan rate in this test, the less
1.1 This test method covers a procedure for conducting
susceptible is the alloy to initiation of localized corrosion.The
cyclic potentiodynamic polarization measurements to deter-
resultsofthistestarenotintendedtocorrelateinaquantitative
mine relative susceptibility to localized corrosion (pitting and
manner with the rate of propagation that one might observe in
crevicecorrosion)foriron-,nickel-,orcobalt-basedalloysina
service when localized corrosion occurs.
chloride environment. This test method also describes an
experimental procedure which can be used to check one’s 3.2 Ingeneral,onceinitiated,localizedcorrosioncanpropa-
experimental technique and instrumentation. gate at some potential more electropositive than that at which
the hysteresis loop is completed. In this test method, the
1.2 The values stated in SI units are to be regarded as
potential at which the hysteresis loop is completed is deter-
standard. No other units of measurement are included in this
mined at a fixed scan rate. In these cases, the more electro-
standard.
positive the potential at which the hysteresis loop is completed
1.3 This standard does not purport to address all of the
the less likely it is that localized corrosion will occur.
safety concerns, if any, associated with its use. It is the
3.3 If followed, this test method will provide cyclic poten-
responsibility of the user of this standard to establish appro-
tiodynamic anodic polarization measurements that will repro-
priate safety and health practices and determine the applica-
duce data developed at other times in other laboratories using
bility of regulatory limitations prior to use.
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 Potentiostatic and
using specific alloys of Type 304 stainless steel, UNS S30400
Potentiodynamic Anodic Polarization Measurements
and Alloy C-276, UNS N10276. Curves are included which
2.2 ASTM Adjuncts:
have been constructed using statistical analysis to indicate the
Standard Samples (set of two)
acceptable range of polarization curves.
3.5 The availability of a standard test method, standard
3. Significance and Use
material, and standard plots should make it easy for an
3.1 An indication of the susceptibility to initiation of local-
investigator to check his techniques to evaluate susceptibility
ized corrosion in this test method is given by the potential at
to localized corrosion.
This test method is under the jurisdiction of ASTM Committee G01 on
4. Apparatus
Corrosion of Metals and is the direct responsibility of Subcommittee G01.11 on
Electrochemical Measurements in Corrosion Testing.
4.1 The polarization cell should be similar to the one
Current edition approved May 1, 2009. Published May 2009. Originally
described in Reference Test Method G5. Other polarization
´1
approvedin1986.Lastpreviouseditionapprovedin2003asG61–86(2003) .DOI:
cells may be equally suitable.
10.1520/G0061-86R09.
4.1.1 The cell should have a capacity of about 1 L and
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
should have suitable necks or seals to permit the introduction
Standards volume information, refer to the standard’s Document Summary page on
of electrodes, gas inlet and outlet tubes, and a thermometer.
the ASTM website.
3 The Luggin probe-salt bridge separates the bulk solution from
Available from ASTM International Headquarters. Order Adjunct No.
ADJG0061. Original adjunct produced before 1995. thesaturatedcalomelreferenceelectrode.Theprobetipshould
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G61 − 86 (2009)
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 .
4.5 Current-Measuring Instruments (Note 1)—An instru-
mentthatiscapableofmeasuringacurrentaccuratelytowithin
1%oftheabsolutevalueoveracurrentrangebetween1.0and
10 µAshouldbeused.Manycommercialunitshaveabuild-in
instrument with an output as a voltage, which is preferred for
recording purposes. For the purpose of the present test a
FIG. 1 Schematic Diagram of Specimen Holder (see Footnotes 3
and 4)
logarithmic output is desirable.
4.6 Anodic Polarization Circuit—Ascanning potentiostat is
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(Note1)—Apotentiostatthatwillmaintain
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
5 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 polarization plot.
commerically available. Precautions should be taken to ensure
4.4 Potential-Measuring Instruments (Note 1)—The
that it is maintained in the proper condition. The potential of
potential-measuring circuit should have a high input imped-
thecalomelelectrodeshouldbecheckedatperiodicintervalsto
11 14
ance on the order of 10 to 10 Ω to minimize current drawn
ensure the accuracy of the electrode.
from the system during measurements. Instruments should
have sufficient sensitivity and accuracy to detect a change in 5. Reagents and Materials
potential of 61 mV, usually included in commercial poten-
5.1 Purity
...
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