ASTM G192-08(2014)

Standard Test Method for Determining the Crevice Repassivation Potential of Corrosion-Resistant Alloys Using a Potentiodynamic-Galvanostatic-Potentiostatic Technique

SIGNIFICANCE AND USE
5.1 The THE test method is designed to provide highly reproducible crevice repassivation potentials for corrosion–resistant alloys (for example, Alloy 22) in a wide range of environments from non-aggressive to highly aggressive. In conditions of low environmental aggressiveness (such as low temperature or low chloride concentration), corrosion–resistant alloys such as Alloy 22 will resist crevice corrosion initiation and the cyclic potentiodynamic polarization test (Test Method G61) may fail to promote crevice corrosion mainly because it drives the alloy into transpassive dissolution instead of nucleating crevice corrosion. The THE test method provides a more controlled way of applying the electrical charge to the test electrode, which may induce crevice corrosion without moving it into transpassive potentials.  
5.2 The more noble this crevice corrosion repassivation potential (ER,CREV) value, the more resistant the alloy is to crevice corrosion in the tested electrolyte. This is similar to other test methods to measure localized corrosion resistance such as Test Method G61 and Test Methods G48. The results from this test method are not intended to correlate in a quantitative manner with the rate of propagation that one might observe in service when localized corrosion occurs.  
5.3 This test method may be used to rank several alloys by using the same testing electrolyte and temperature. It can also be used to determine the response of a given alloy when the environmental conditions (such as electrolyte composition and temperature) change.
SCOPE
1.1 This test method covers a procedure for conducting anodic polarization studies to determine the crevice repassivation potential for corrosion–resistant alloys. The concept of the repassivation potential is similar to that of the protection potential given in Reference Test Method G5.  
1.2 The test method consists in applying successively potentiodynamic, galvanostatic, and potentiostatic treatments for the initial formation and afterward repassivation of crevice corrosion.  
1.3 This test method is a complement to Test Method G61.  
1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.  
1.5 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.

General Information

• Status: Historical
• Publication Date: 31-Oct-2014
• ICS: 77.060 - Corrosion of metals
• Technical Committee: G01 - Corrosion of Metals
• Drafting Committee: G01.11 - Electrochemical Measurements in Corrosion Testing

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: G192 − 08 (Reapproved 2014)
Standard Test Method for
Determining the Crevice Repassivation Potential of
Corrosion-Resistant Alloys Using a Potentiodynamic-
Galvanostatic-Potentiostatic Technique
This standard is issued under the fixed designation G192; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Determine the Precision of a Test Method
G1Practice for Preparing, Cleaning, and Evaluating Corro-
1.1 This test method covers a procedure for conducting
sion Test Specimens
anodic polarization studies to determine the crevice repassiva-
G5Reference Test Method for Making Potentiodynamic
tionpotentialforcorrosion–resistantalloys.Theconceptofthe
Anodic Polarization Measurements
repassivation potential is similar to that of the protection
G15Terminology Relating to Corrosion and CorrosionTest-
potential given in Reference Test Method G5.
ing (Withdrawn 2010)
1.2 The test method consists in applying successively
G48Test Methods for Pitting and Crevice Corrosion Resis-
potentiodynamic, galvanostatic, and potentiostatic treatments
tance of Stainless Steels and Related Alloys by Use of
for the initial formation and afterward repassivation of crevice
Ferric Chloride Solution
corrosion.
G61Test Method for Conducting Cyclic Potentiodynamic
Polarization Measurements for Localized Corrosion Sus-
1.3 This test method is a complement to Test Method G61.
ceptibility of Iron-, Nickel-, or Cobalt-Based Alloys
1.4 The values stated in SI units are to be regarded as the
G78Guide for Crevice Corrosion Testing of Iron-Base and
standard. The values given in parentheses are for information
Nickel-Base Stainless Alloys in Seawater and Other
only.
Chloride-Containing Aqueous Environments
1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3. Terminology
responsibility of the user of this standard to establish appro-
3.1 Definitions—For definitions of corrosion-related terms
priate safety and health practices and determine the applica-
used in this test method, see Terminology G15.
bility of regulatory limitations prior to use.
4. Summary of Test Method
2. Referenced Documents
4.1 This anodic polarization test method combines tech-
2.1 ASTM Standards:
niques such as potentiodynamic, galvanostatic, and potentio-
B575 Specification for Low-Carbon Nickel-Chromium-
static polarization methods. This test method is called the
Molybdenum, Low-Carbon Nickel-Chromium-
Tsujikawa-Hisamatsu Electrochemical (THE) test method to
Molybdenum-Copper, Low-Carbon Nickel-Chromium-
honor the two precursors of this technique (see 1 and 2). The
Molybdenum-Tantalum, Low-Carbon Nickel-Chromium-
new technique will be called the THE test method. This new
Molybdenum-Tungsten, and Low-Carbon Nickel-
THE test method is more time-consuming than the already
Molybdenum-Chromium Alloy Plate, Sheet, and Strip
well-established cyclic potentiodynamic polarization (CPP)
D1193Specification for Reagent Water
described in Test Method G61.
E691Practice for Conducting an Interlaboratory Study to
4.2 The THE test method can be used with any corrosion-
–resistant alloy, but it was developed by studying Alloy 22
This test method is under the jurisdiction of ASTM Committee G01 on
(UNSN06022).ThecompositionandotherpropertiesofAlloy
Corrosion of Metals and is the direct responsibility of Subcommittee G01.11 on
22 are given in Specification B575.Alloy 22 is a nickel–based
Electrochemical Measurements in Corrosion Testing.
alloy containing approximately 22wt% Cr, 13wt% Mo, 3wt%
Current edition approved Nov. 1, 2014. Published November 2014. Originally
approved in 2008. Last previous edition approved in 2008 as G192–08. DOI:
10.1520/G0192-08R14.
2 3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or The last approved version of this historical standard is referenced on
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM www.astm.org.
Standards volume information, refer to the standard’s Document Summary page on The boldface numbers in parentheses refer to a list of references at the end of
the ASTM website. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G192 − 08 (2014)
W and 3wt% Fe. The THE test method is a complement to the other test methods to measure localized corrosion resistance
cyclic potentiodynamic polarization (CPP) described in Test such as Test Method G61 and Test Methods G48. The results
MethodG61.CPPmaybeusedasafirstfastscreeningmethod from this test method are not intended to correlate in a
andTHEtestmethodforfine-tuningtherepassivationpotential quantitativemannerwiththerateofpropagationthatonemight
for crevice corrosion when the environment is not highly observe in service when localized corrosion occurs.
aggressive(3-6).TheTHEtestmethodhasalsobeenappliedto
5.3 This test method may be used to rank several alloys by
other highly corrosion–resistant alloys, such asTitanium grade
using the same testing electrolyte and temperature. It can also
7 (Ref 7).
be used to determine the response of a given alloy when the
4.3 The THE test method can be used with any electrolyte environmental conditions (such as electrolyte composition and
solution. A standard 1 M NaCl solution at 90°C or lower temperature) change.
temperature may be used to compare alloys of interest. The
6. Apparatus
round robin described in Section 15 was carried out in 1 M
NaCl solution at 90°C.
6.1 Cell—The polarization cell should be similar to the one
described in ReferenceTest Method G5 andTest Method G61.
4.4 Thetestinvolvesinpolarizingthetestelectrodeinthree
Other polarization cells may be equally suitable. The cell
steps:
should have a capacity of about 1 L and should have suitable
4.4.1 Step 1—The test electrode is polarized potentiody-
necksorsealstopermittheintroductionofelectrodes,gasinlet
namically at a rate of 0.168 mV/s (as in Test Method G61)
and outlet tubes, and a thermometer or thermocouple. The
starting at or slightly below the corrosion potential until a
Luggin probe-salt bridge separates the bulk solution from the
preset current (or current density) is reached (for example,
saturated calomel or saturated silver chloride reference elec-
2µA⁄cm ).After this initial potentiodynamic polarization, the
trode.
polarization control is changed to galvanostatic mode (Step 2).
4.4.2 Step 2—The preset current of 2 µA/cm is kept 6.2 Test Electrode (Specimen) Holder—The test electrode
constant for a 2-h period to develop and grow a crevice
holder and the mounting rod should be similar to the one
corroded area (if any develops). During the galvanostatic Step described in Figure 5 in Reference Test Method G5 (repro-
2, the potential output is monitored.
duced in Fig. 1). A leakproof PTFE compression gasket, as
4.4.3 Step 3—The polarization control is shifted to the described in subsection 4.6.1 in Reference Test Method G5,is
potentiostatic mode. The potential at the end of the galvanos-
also necessary.
tatic hold (Step 2) is read, and then 10 mV are subtracted. The
6.3 Potentiostat and Output Potential and Current Measur-
resultingvalueofpotentialisappliedfora2-hperiodwhilethe
ing Instruments—The potentiostat and other instruments
current output is monitored. Then successive potentiostatic
should be similar to the ones specified in Test Method G61.
treatments are applied, each time at 10 mV lower than the
Mostcommercialpotentiostatandrelatedinstrumentsmeetthe
previous treatment. A total of 10-15 potentiostatic treatments
specific requirements for these types of measurements.
are usually required to finish Step 3.
6.4 Electrodes—The standard recommended working or
4.5 The crevice repassivation potential (ER,CREV) is the
testing electrode is shown in Fig. 1, which is a prismatic
highest potential in Step 3 for which current density does not
measuring 0.75 by 0.75 by 0.375-in. thick (approximately 20
increase as a function of time. It is understood that at a
by20by10mm).Ithasadrilledandtappedholeontopforthe
potential below ER,CREV the alloy will not develop crevice
connecting rod (as in Reference Test Method G5). The elec-
corrosion under the tested conditions.
trodes also have a 7-mm diameter hole in the center for
mounting two crevice formers, one at each side using a bolt.
5. Significance and Use
The test electrode could be cut from any plate or extruded bar.
5.1 The THE test method is designed to provide highly It is recommended that the creviced faces of the test electrode
reproducible crevice repassivation potentials for corrosion–re- correspondtotherollingorextrudeddirection.Incertaintested
sistant alloys (for example, Alloy 22) in a wide range of conditions the test electrode may show end grain attack in the
environments from non-aggressive to highly aggressive. In short transverse direction, but generally the crevice former
conditions of low environmental aggressiveness (such as low provides a more active path for corrosion than the freely
temperatureorlowchlorideconcentration),corrosion–resistant exposed surfaces.
alloys such as Alloy 22 will resist crevice corrosion initiation
6.5 Crevice Former or Crevice Washer—Thecreviceformer
and the cyclic potentiodynamic polarization test (Test Method
is a multiple crevice assembly (MCA), and it is described in
G61) may fail to promote crevice corrosion mainly because it
subsection 5.4 of Test Methods G48, in subsection 9.2.2 in
drives the alloy into transpassive dissolution instead of nucle-
Guide G78, and in Ref 8. This MCAcrevice former should be
ating crevice corrosion. The THE test method provides a more
fabricated using a hard non-conductive ceramic material such
controlled way of applying the electrical charge to the test
as alumina or mullite (Fig. 2). Before mounting on the test
electrode,whichmayinducecrevicecorrosionwithoutmoving
electrode (specimen), the crevice washers should be covered
it into transpassive potentials.
with a PTFE tape.This tape is 1.5-in. wide and 0.003-in. thick
5.2 The more noble this crevice corrosion repassivation (standard military grade MIL-T-27730A). A corrosion–resis-
potential (ER,CREV) value, the more resistant the alloy is to tant fastener is used to secure the two MCA washers, one on
crevice corrosion in the tested electrolyte. This is similar to each side of the test electrode. Crevice formers made of solid
G192 − 08 (2014)
FIG. 1 Prismatic Test Electrode (0.75 by 0.75 by 0.375 in. or approximately 20 by 20 by 10 mm)
PTFE such as in Test Methods G48 or Guide G78 are not as counter electrode be twice as large as the one of the working
effective,sincetheydonotformacrevicegaptightenoughfor electrode (test electrode or specimen).
certain high end corrosion–resistant materials. This may result
6.7 Reference Electrode—Reference electrodes could be
in higher and poorly reproducible repassivation potential
commercially available saturated calomel or silver-silver chlo-
values. Two standard metal washers are used as well (Figs. 1
ride. These electrodes are durable and reliable; however, they
and2).ThestandardpressureontheMCAcreviceformersmay
shouldbemaintainedintheproperconditions.Thepotentialof
vary (depending of the study underway) but a minimum of
thereferenceelectrodesshouldbecheckedatperiodicintervals
30-in.·lb (3.4-N·m) torque may be needed to form a tight
to ensure their accuracy.
crevice. Use a calibrated torque wrench to apply the torque.
Electricalcontactbetweentheboltandthetestelectrodeshould
7. Reagents and Materials
be avoided. Effective insulation may be provided by the use of
7.1 Purity of Reagents—Reagent grade chemicals should be
nonmetallic sleeves or by wrapping the assembly bolt with
used in all tests.
PTFE tape.
7.2 Purity of Water—The water should be distilled or
6.6 Counter Electrode—The counter electrodes may be
deionized conforming to the requirements of Specification
prepared as in Reference Test Method G5 or may be prepared
D1193, Type IV reagent water.
from high-purity platinum flat stock and wire. Counter elec-
trodescouldbeeasilyfabricatedbyspotweldingplatinumwire 7.3 Sodium Chloride (NaCl)—To prepare 1 L of 1 M NaCl
to a platinum foil, which could be curved to adapt to the cell solution, dissolve 58.45 g of NaCl in purified water to obtain a
geometry. It is recommended that the area of the platinum total volume of solution of 1 L.
G192 − 08 (2014)
FIG. 1 Prismatic Test Electrode (0.75 by 0.75 by 0.375 in. or approximately 20 by 20 by 10 mm) (continued)
7.4 Purging Gas—Ifdeaerationisnecessary,nitrogengasof with regard to reproducing crevice conditions and the preven-
a minimum 99.99 purity should be used. Tests could also be tion of possible fracture of the ceramic devices.
run under normal aeration conditions or under any other
9.3 The test electrodes could be prepared using wrought or
atmosphere.
cast material, or machined weld metal.
7.5 Prismatic-Shaped Test Electrodes of the Corrosion–Re-
9.4 The bolt, nut, and flat washer must be made of a
sistant Alloy—Other type of creviced test electrodes may also
corrosion–resistant material. It is recommended to use Ti Gr 2
be used, depending on the specific study being performed.
(UNS R52400). Fastening devices can also be fabricated using
other readily available materials such asAlloys C-276 and 625
8. Hazards
(UNS N10276 and N06625, respectively). The crevice former
8.1 Normal precautions for handling hot liquids should be
is manufactured using a ceramic material according to the
observed.
12-tooth design in Test Methods G48, Guide G78, and Ref 8
8.2 Personal protective equipment for handling hot liquids
(Fig. 2). The ceramic washer is covered by a wide PTFE tape
should be used. 1.5-in. wide and 0.003-in. thick (standard military grade
MIL-T-27730A).
9. Sampling, Test Electrodes, and Test Units
9.1 Recommended test electrodes (specimens) are 10. Preparation of Apparatus
prismatic-shaped as shown in Fig. 1. The thickness of the
10.1 The testing cell and test electrode holder are described
material for the test electrodes is not essential, but it should be
in Reference Test Method G5.
enough to handle the mounting rod mechanism. Thicker
10.2 The potentiostat and other instruments should be simi-
materials are easier to prepare (polish).Afresh (or 1 h prior to
lartotheonesspecifiedinTestMethodG61.Mostcommercial
testing) finish wet grinding of 600 grit silicon carbin
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: G192 − 08 G192 − 08 (Reapproved 2014)
Standard Test Method for
Determining the Crevice Repassivation Potential of
Corrosion-Resistant Alloys Using a Potentiodynamic-
Galvanostatic-Potentiostatic Technique
This standard is issued under the fixed designation G192; 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 covers a procedure for conducting anodic polarization studies to determine the crevice repassivation
potential for corrosion–resistant alloys. The concept of the repassivation potential is similar to that of the protection potential given
in Reference Test Method G5.
1.2 The test method consists in applying successively potentiodynamic, galvanostatic, and potentiostatic treatments for the
initial formation and afterward repassivation of crevice corrosion.
1.3 This test method is a complement to Test Method G61.
1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
B575 Specification for Low-Carbon Nickel-Chromium-Molybdenum, Low-Carbon Nickel-Chromium-Molybdenum-Copper,
Low-Carbon Nickel-Chromium-Molybdenum-Tantalum, Low-Carbon Nickel-Chromium-Molybdenum-Tungsten, and Low-
Carbon Nickel-Molybdenum-Chromium Alloy Plate, Sheet, and Strip
D1193 Specification for Reagent Water
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
G1 Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
G5 Reference Test Method for Making Potentiodynamic Anodic Polarization Measurements
G15 Terminology Relating to Corrosion and Corrosion Testing (Withdrawn 2010)
G48 Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride
Solution
G61 Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements for Localized Corrosion Susceptibility of
Iron-, Nickel-, or Cobalt-Based Alloys
G78 Guide for Crevice Corrosion Testing of Iron-Base and Nickel-Base Stainless Alloys in Seawater and Other Chloride-
Containing Aqueous Environments
3. Terminology
3.1 Definitions—For definitions of corrosion-related terms used in this test method, see Terminology G15.
This test method is under the jurisdiction of ASTM Committee G01 on Corrosion of Metals and is the direct responsibility of Subcommittee G01.11 on Electrochemical
Measurements in Corrosion Testing.
Current edition approved May 1, 2008Nov. 1, 2014. Published May 2008November 2014. Originally approved in 2008. Last previous edition approved in 2008 as
G192–08. DOI: 10.1520/G0192-08.10.1520/G0192-08R14.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. 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
G192 − 08 (2014)
4. Summary of Test Method
4.1 This anodic polarization test method combines techniques such as potentiodynamic, galvanostatic, and potentiostatic
polarization methods. This test method is called the Tsujikawa-Hisamatsu Electrochemical (THE) test method to honor the two
precursors of this technique (see 1 and 2). The new technique will be called the THE test method. This new THE test method is
more time-consuming than the already well-established cyclic potentiodynamic polarization (CPP) described in Test Method G61.
4.2 The THE test method can be used with any corrosion–resistant alloy, but it was developed by studying Alloy 22 (UNS
N06022). The composition and other properties of Alloy 22 are given in Specification B575. Alloy 22 is a nickel–based alloy
containing approximately 22wt% Cr, 13wt% Mo, 3wt% W and 3wt% Fe. The THE test method is a complement to the cyclic
potentiodynamic polarization (CPP) described in Test Method G61. CPP may be used as a first fast screening method and THE
test method for fine-tuning the repassivation potential for crevice corrosion when the environment is not highly aggressive (3-6).
The THE test method has also been applied to other highly corrosion–resistant alloys, such as Titanium grade 7 (Ref 7).
4.3 The THE test method can be used with any electrolyte solution. A standard 1 M NaCl solution at 90°C or lower temperature
may be used to compare alloys of interest. The round robin described in Section 15 was carried out in 1 M NaCl solution at 90°C.
4.4 The test involves in polarizing the test electrode in three steps:
4.4.1 Step 1—The test electrode is polarized potentiodynamically at a rate of 0.168 mV/s (as in Test Method G61) starting at
or slightly below the corrosion potential until a preset current (or current density) is reached (for example, 2 μA ⁄cm ). After this
initial potentiodynamic polarization, the polarization control is changed to galvanostatic mode (Step 2).
4.4.2 Step 2—The preset current of 2 μA/cm is kept constant for a 2-h period to develop and grow a crevice corroded area (if
any develops). During the galvanostatic Step 2, the potential output is monitored.
4.4.3 Step 3—The polarization control is shifted to the potentiostatic mode. The potential at the end of the galvanostatic hold
(Step 2) is read, and then 10 mV are subtracted. The resulting value of potential is applied for a 2-h period while the current output
is monitored. Then successive potentiostatic treatments are applied, each time at 10 mV lower than the previous treatment. A total
of 10-15 potentiostatic treatments are usually required to finish Step 3.
4.5 The crevice repassivation potential (ER,CREV) is the highest potential in Step 3 for which current density does not increase
as a function of time. It is understood that at a potential below ER,CREV the alloy will not develop crevice corrosion under the
tested conditions.
5. Significance and Use
5.1 The THE test method is designed to provide highly reproducible crevice repassivation potentials for corrosion–resistant
alloys (for example, Alloy 22) in a wide range of environments from non-aggressive to highly aggressive. In conditions of low
environmental aggressiveness (such as low temperature or low chloride concentration), corrosion–resistant alloys such as Alloy 22
will resist crevice corrosion initiation and the cyclic potentiodynamic polarization test (Test Method G61) may fail to promote
crevice corrosion mainly because it drives the alloy into transpassive dissolution instead of nucleating crevice corrosion. The THE
test method provides a more controlled way of applying the electrical charge to the test electrode, which may induce crevice
corrosion without moving it into transpassive potentials.
5.2 The more noble this crevice corrosion repassivation potential (ER,CREV) value, the more resistant the alloy is to crevice
corrosion in the tested electrolyte. This is similar to other test methods to measure localized corrosion resistance such as Test
Method G61 and Test Methods G48. The results from this test method are not intended to correlate in a quantitative manner with
the rate of propagation that one might observe in service when localized corrosion occurs.
5.3 This test method may be used to rank several alloys by using the same testing electrolyte and temperature. It can also be
used to determine the response of a given alloy when the environmental conditions (such as electrolyte composition and
temperature) change.
6. Apparatus
6.1 Cell—The polarization cell should be similar to the one described in Reference Test Method G5 and Test Method G61. Other
polarization cells may be equally suitable. The cell should have a capacity of about 1 L and should have suitable necks or seals
to permit the introduction of electrodes, gas inlet and outlet tubes, and a thermometer or thermocouple. The Luggin probe-salt
bridge separates the bulk solution from the saturated calomel or saturated silver chloride reference electrode.
6.2 Test Electrode (Specimen) Holder—The test electrode holder and the mounting rod should be similar to the one described
in Figure 5 in Reference Test Method G5 (reproduced in Fig. 1). A leakproof PTFE compression gasket, as described in subsection
4.6.1 in Reference Test Method G5, is also necessary.
The boldface numbers in parentheses refer to a list of references at the end of this standard.
G192 − 08 (2014)
FIG. 1 Prismatic Test Electrode (0.75 by 0.75 by 0.375 in. or approximately 20 by 20 by 10 mm)
6.3 Potentiostat and Output Potential and Current Measuring Instruments—The potentiostat and other instruments should be
similar to the ones specified in Test Method G61. Most commercial potentiostat and related instruments meet the specific
requirements for these types of measurements.
6.4 Electrodes—The standard recommended working or testing electrode is shown in Fig. 1, which is a prismatic measuring
0.75 by 0.75 by 0.375-in. thick (approximately 20 by 20 by 10 mm). It has a drilled and tapped hole on top for the connecting
rod (as in Reference Test Method G5). The electrodes also have a 7-mm diameter hole in the center for mounting two crevice
formers, one at each side using a bolt. The test electrode could be cut from any plate or extruded bar. It is recommended that the
creviced faces of the test electrode correspond to the rolling or extruded direction. In certain tested conditions the test electrode
may show end grain attack in the short transverse direction, but generally the crevice former provides a more active path for
corrosion than the freely exposed surfaces.
6.5 Crevice Former or Crevice Washer—The crevice former is a multiple crevice assembly (MCA), and it is described in
subsection 5.4 of Test Methods G48, in subsection 9.2.2 in Guide G78, and in Ref 8. This MCA crevice former should be fabricated
using a hard non-conductive ceramic material such as alumina or mullite (Fig. 2). Before mounting on the test electrode
(specimen), the crevice washers should be covered with a PTFE tape. This tape is 1.5-in. wide and 0.003-in. thick (standard
military grade MIL-T-27730A). A corrosion–resistant fastener is used to secure the two MCA washers, one on each side of the test
electrode. Crevice formers made of solid PTFE such as in Test Methods G48 or Guide G78 are not as effective, since they do not
form a crevice gap tight enough for certain high end corrosion–resistant materials. This may result in higher and poorly
reproducible repassivation potential values. Two standard metal washers are used as well (Figs. 1 and 2). The standard pressure
G192 − 08 (2014)
FIG. 1 Prismatic Test Electrode (0.75 by 0.75 by 0.375 in. or approximately 20 by 20 by 10 mm) (continued)
on the MCA crevice formers may vary (depending of the study underway) but a minimum of 30-in.·lb (3.4-N·m) torque may be
needed to form a tight crevice. Use a calibrated torque wrench to apply the torque. Electrical contact between the bolt and the test
electrode should be avoided. Effective insulation may be provided by the use of nonmetallic sleeves or by wrapping the assembly
bolt with PTFE tape.
6.6 Counter Electrode—The counter electrodes may be prepared as in Reference Test Method G5 or may be prepared from
high-purity platinum flat stock and wire. Counter electrodes could be easily fabricated by spot welding platinum wire to a platinum
foil, which could be curved to adapt to the cell geometry. It is recommended that the area of the platinum counter electrode be twice
as large as the one of the working electrode (test electrode or specimen).
6.7 Reference Electrode—Reference electrodes could be commercially available saturated calomel or silver-silver chloride.
These electrodes are durable and reliable; however, they should be maintained in the proper conditions. The potential of the
reference electrodes should be checked at periodic intervals to ensure their accuracy.
7. Reagents and Materials
7.1 Purity of Reagents—Reagent grade chemicals should be used in all tests.
7.2 Purity of Water—The water should be distilled or deionized conforming to the requirements of Specification D1193, Type
IV reagent water.
7.3 Sodium Chloride (NaCl)—To prepare 1 L of 1 M NaCl solution, dissolve 58.45 g of NaCl in purified water to obtain a total
volume of solution of 1 L.
7.4 Purging Gas—If deaeration is necessary, nitrogen gas of a minimum 99.99 purity should be used. Tests could also be run
under normal aeration conditions or under any other atmosphere.
7.5 Prismatic-Shaped Test Electrodes of the Corrosion–Resistant Alloy—Other type of creviced test electrodes may also be
used, depending on the specific study being performed.
8. Hazards
8.1 Normal precautions for handling hot liquids should be observed.
8.2 Personal protective equipment for handling hot liquids should be used.
G192 − 08 (2014)
NOTE 1—Includes Fig. 5 from Reference Test Method G5 to describe how the test electrode is attached to the specimen holder.
FIG. 2 Crevice Formers for the Test Electrode
G192 − 08 (2014)
9. Sampling, Test Electrodes, and Test Units
9.1 Recommended test electrodes (specimens) are prismatic-shaped as shown in Fig. 1. The thickness of the material for the
test electrodes is not essential, but it should be enough to handle the mounting rod mechanism. Thicker materials are easier to
prepare (polish). A fresh (or 1 h prior to testing) finish wet grinding of 600 grit silicon carbine paper is recommended. If surface
effects are being studied, other surface finishing may be considered.
9.2 If other than mill finishes are investigated, the test electro
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