ASTM G59-23

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Designation: G59 − 97 (Reapproved 2020) G59 − 23
Standard Test Method for
Conducting Potentiodynamic Polarization Resistance
Measurements
This standard is issued under the fixed designation G59; 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 an experimental procedure for polarization resistance measurements which can be used for the
calibration of equipment and verification of experimental technique. The test method can provide reproducible corrosion potentials
and potentiodynamic polarization resistance measurements.
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, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.4 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.
2. Referenced Documents
2.1 ASTM Standards:
G3 Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing
G5 Reference Test Method for Making Potentiodynamic Anodic Polarization Measurements
G102 Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements
3. Significance and Use
3.1 This test method can be utilized to verify the performance of polarization resistance measurement equipment including
reference electrodes, electrochemical cells, potentiostats,potentiost-
ats, scan generators, and measuring and recording devices. The test method is also useful for training operators in sample
preparation and experimental techniques for polarization resistance measurements.
3.2 Polarization resistance can be related to the rate of general corrosion for metals at or near their corrosion potential, E .
corr
Polarization resistance measurements are an accurate and rapid way to measure the general corrosion rate. Real time Real-time
corrosion monitoring is a common application. The technique can also be used as a way to rank alloys, inhibitors, and so forth
in order of resistance to general corrosion.
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 Nov. 1, 2020June 1, 2023. Published November 2020June 2023. Originally approved in 1978. Last previous edition approved in 20142020 as
G59G59 – 97 (2020). – 97 (2014). DOI: 10.1520/G0059-97R20.DOI: 10.1520/G0059-23.
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 the ASTM website.
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G59 − 23
3.3 In this test method, a small potential scan, ΔE(t), defined with respect to the corrosion potential (ΔE = E – E ), is applied
corr
to a metal sample. The resultant currents are recorded. The polarization resistance, R , of a corroding electrode is defined from
P
Eq 1 as the slope of a potential versus current density plot at i = 0 (1-4):
] ΔE
R 5 (1)
S D
p
] i
i50, dE/dt→0
The current density is given by i. The corrosion current density, i , is related to the polarization resistance by the Stern-Geary
corr
coefficient, B.(3),
B
i 5 10 (2)
corr
R
p
2 2
The dimension of R is ohm-cm , i is muA/cm , and B is in V. The Stern-Geary coefficient is related to the anodic, b , and
p corr a
cathodic, b , Tafel slopes as per in accordance with Eq 3.
c
b b
a c
B 5 (3)
2.303~b 1b !
a c
The units of the Tafel slopes are V. The corrosion rate, CR, in mm per year can be determined from Eq 4 in which EW is the
equivalent weight of the corroding species in grams and ρ is the density of the corroding material in g/cm .
i EW
corr
CR 5 3.27 ×10 (4)
ρ
Refer to Practice G102 for derivations of the above equations and methods for estimating Tafel slopes.
3.4 The test method may not be appropriate to measure polarization resistance on all materials or in all environments. See 8.2 for
a discussion of method biases arising from solution resistance and electrode capacitance.
4. Apparatus
4.1 The apparatus is described in Test Method G5. It includes a 1 L 1 L round bottom flask modified to permit the addition of inert
gas, thermometer, and electrodes. This standard cell or an equivalent cell can be used. An equivalent cell must be constructed of
inert materials and be able to reproduce the standard curve in Test Method G5.
4.2 A potentiostat capable of varying potential at a constant scan rate and measuring the current is needed.
4.3 A method of recording the varying potential and resulting current is needed.
5. Test of Electrical Equipment
5.1 Before the polarization resistance measurement is made, the instrument system (potentiostat, X-Y recorder or data acquisition
system) must be tested to ensure proper functioning. For this purpose, connect the potentiostat to a test electrical circuit (5). While
more complex dummy cells are sometimes needed in electrochemical studies, the simple resistor shown in Fig. 1 is adequate for
the present application.
FIG. 1 Arrangement for Testing of Electrical Equipment (Potentiostat, X-Y Recorder)
The boldface numbers in parentheses refer to the list of references at the end of this standard.
G59 − 23
5.2 Use R = 10.0 Ω. Set the applied potential on the potentiostat to E = –30.0 mV and apply the potential. The current should be
3.0 mA by Ohm’s Law, I = E/R.
NOTE 1—When polarization resistance values are measured for systems with different corrosion currents, the value of R should be chosen to cover the
current range of the actual polarization resistance measurement. Expected corrosion currents in the microampere range require R = 11 kΩ to 10 kΩ.
5.3 Record the potentiodynamic polarization curve at a scan rate of 0.6 V/h from ΔE = –30 mV to ΔE = +30 mV and back to ΔE
= –30 mV. The plot should be linear, go through the origin, and have a slope 10 Ω. The curves recorded for the forward and reverse
scans should be identical.
5.4 If the observed results are different than expected, the electrochemical equipment may require calibration or servicing in
accordance with the manufacturer’s guidelines.
6. Experimental Procedure
6.1 The 1.0 N H SO test solution should be prepared from American Chemical Society reagent grade acid and distilled water as
2 4
described in Test Method G5. The standard test cell requires 900 mL of test solution. The temperature must be maintained at 30 °C
within 1°.
6.2 The test cell is purged at 150 cm /min with an oxygen-free gas such as hydrogen, nitrogen, or argon. The purge is started at
least 30 min before specimen immersion. The purge continues throughout the test.
6.3 The working electrode should be prepared
...