ASTM G3-89(2010)
(Practice)Standard Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing
Standard Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing
SIGNIFICANCE AND USE
This practice provides guidance for reporting, displaying, and plotting electrochemical corrosion data and includes recommendations on signs and conventions. Use of this practice will result in the reporting of electrochemical corrosion data in a standard format, facilitating comparison between data developed at different laboratories or at different times. The recommendations outlined in this standard may be utilized when recording and reporting corrosion data obtained from electrochemical tests such as potentiostatic and potentiodynamic polarization, polarization resistance, electrochemical impedance and admittance measurements, galvanic corrosion, and open circuit potential measurements.
SCOPE
1.1 This practice covers conventions for reporting and displaying electrochemical corrosion data. Conventions for potential, current density, electrochemical impedance and admittance, as well as conventions for graphical presentation of such data are included.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. See also 7.4.
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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Designation: G3 − 89(Reapproved 2010)
Standard Practice for
Conventions Applicable to Electrochemical Measurements
1
in Corrosion Testing
This standard is issued under the fixed designation G3; the number immediately following the designation indicates the year of original
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope impedance and admittance measurements, galvanic corrosion,
and open circuit potential measurements.
1.1 This practice covers conventions for reporting and
displaying electrochemical corrosion data. Conventions for
4. Sign Convention for Electrode Potential
potential, current density, electrochemical impedance and
4.1 The Stockholm sign invariant convention is recom-
admittance, as well as conventions for graphical presentation
mended for use in reporting the results of specimen potential
of such data are included.
measurements in corrosion testing. In this convention, the
1.2 The values stated in SI units are to be regarded as
positivedirectionofelectrodepotentialimpliesanincreasingly
standard. No other units of measurement are included in this
oxidizing condition at the electrode in question. The positive
standard. See also 7.4.
direction has also been denoted as the noble direction because
1.3 This standard does not purport to address all of the
thecorrosionpotentialsofmostnoblemetals,suchasgold,are
safety concerns, if any, associated with its use. It is the
more positive than the nonpassive base metals. On the other
responsibility of the user of this standard to establish appro-
hand,thenegativedirection,oftencalledtheactivedirection,is
priate safety and health practices and determine the applica-
associated with reduction and consequently the corrosion
bility of regulatory limitations prior to use.
potentials of active metals, such as magnesium. This conven-
tionwasadoptedunanimouslybythe1953InternationalUnion
2. Referenced Documents
of Pure and Applied Chemistry as the standard for electrode
2 3
2.1 ASTM Standards:
potential (1).
IEEE/ASTM SI 10Standard for Use of the International
4.2 In the context of a specimen electrode of unknown
System of Units (SI) (the Modern Metric System)
potential in an aqueous electrolyte, consider the circuit shown
in Fig. 1 with a reference electrode connected to the ground
3. Significance and Use
terminal of an electrometer. If the electrometer reads on scale
3.1 This practice provides guidance for reporting,
when the polarity switch is negative, the specimen electrode
displaying, and plotting electrochemical corrosion data and
potential is negative (relative to the reference electrode).
includes recommendations on signs and conventions. Use of
Conversely, if the electrometer reads on scale when polarity is
this practice will result in the reporting of electrochemical
positive, the specimen potential is positive. On the other hand,
corrosion data in a standard format, facilitating comparison
if the specimen electrode is connected to the ground terminal,
between data developed at different laboratories or at different
the potential will be positive if the meter is on scale when the
times. The recommendations outlined in this standard may be
polarity switch is negative, and vice versa.
utilized when recording and reporting corrosion data obtained
NOTE 1—In cases where the polarity of a measuring instrument is in
from electrochemical tests such as potentiostatic and potentio-
doubt, a simple verification test can be performed as follows: connect the
dynamic polarization, polarization resistance, electrochemical
measuring instrument to a dry cell with the lead previously on the
referenceelectrodetothenegativebatteryterminalandtheleadpreviously
1 on the specimen electrode to the positive battery terminal. Set the range
This practice is under the jurisdiction ofASTM Committee G01 on Corrosion
switchtoaccommodatethedrycellvoltage.Themeterdeflectionwillnow
ofMetalsandisthedirectresponsibilityofSubcommitteeG01.11onElectrochemi-
show the direction of positive potential.
cal Measurements in Corrosion Testing.
Also, the corrosion potential of magnesium or zinc should be negative
Current edition approved May 1, 2010. Published May 2010. Originally
ina1 N NaCl solution if measured against a saturated standard calomel
approved in 1968. Last previous edition approved in 2004 as G3–89(2004). DOI:
10.1520/G0003-89R10. electrode (SCE).
2
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
3
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. th
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