ASTM G199-09(2020)e1

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.
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Designation: G199 − 09 (Reapproved 2020)
Standard Guide for
Electrochemical Noise Measurement
This standard is issued under the fixed designation G199; 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.
ε NOTE—Replaced Terminology G15 with Terminology G193, and other editorial changes made throughout in Dec. 2020.
1. Scope G1 Practice for Preparing, Cleaning, and Evaluating Corro-
sion Test Specimens
1.1 This guide covers the procedure for conducting online
G3 Practice for Conventions Applicable to Electrochemical
corrosion monitoring of metals by the use of the electrochemi-
Measurements in Corrosion Testing
cal noise technique. Within the limitations described, this
G4 Guide for Conducting Corrosion Tests in Field Applica-
techniquecanbeusedtodetectlocalizedcorrosionactivityand
tions
to estimate corrosion rate on a continuous basis without
G5 Reference Test Method for Making Potentiodynamic
removal of the monitoring probes from the plant or experimen-
Anodic Polarization Measurements
tal cell.
G16 Guide for Applying Statistics to Analysis of Corrosion
1.2 This guide presents briefly some generally accepted
Data
methods of analyses that are useful in the interpretation of
G31 Guide for Laboratory Immersion Corrosion Testing of
corrosion test results.
Metals
1.3 This guide does not cover detailed calculations and G46 Guide for Examination and Evaluation of Pitting Cor-
methods;ratheritcoversarangeofapproachesthathavefound rosion
application in corrosion testing. G59 Test Method for Conducting Potentiodynamic Polariza-
tion Resistance Measurements
1.4 The values stated in SI units are to be regarded as
G61 Test Method for Conducting Cyclic Potentiodynamic
standard. No other units of measurement are included in this
Polarization Measurements for Localized Corrosion Sus-
standard.
ceptibility of Iron-, Nickel-, or Cobalt-Based Alloys
1.5 This standard does not purport to address all of the
G96 Guide for Online Monitoring of Corrosion in Plant
safety concerns, if any, associated with its use. It is the
Equipment (Electrical and Electrochemical Methods)
responsibility of the user of this standard to establish appro-
G102 Practice for Calculation of Corrosion Rates and Re-
priate safety, health, and environmental practices and deter-
lated Information from Electrochemical Measurements
mine the applicability of regulatory limitations prior to use.
G106 Practice for Verification of Algorithm and Equipment
1.6 This international standard was developed in accor-
for Electrochemical Impedance Measurements
dance with internationally recognized principles on standard-
G193 Terminology and Acronyms Relating to Corrosion
ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
3. Terminology
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee. 3.1 Definitions—The terminology used herein, if not spe-
cifically defined otherwise, shall be in accordance with Termi-
2. Referenced Documents
nology G193. Definitions provided herein and not given in
Terminology G193 are limited only to this guide.
2.1 ASTM Standards:
3.2 Definitions of Terms Specific to This Standard:
3.2.1 coupling current, n—measured current flowing be-
This guide is under the jurisdiction ofASTM Committee G01 on Corrosion of
tween two electrodes in an electrolyte coupled by an external
Metals and is the direct responsibility of Subcommittee G01.11 on Electrochemical
Measurements in Corrosion Testing.
circuit.
Current edition approved Nov. 1, 2020. Published December 2020. Originally
3.2.2 current measuring device, n—device that is capable of
approved in 2009. Last previous edition approved in 2014 as G199 – 09 (2014).
DOI: 10.1520/G0199-09R20E01.
measuring the current flow across the electrode/electrolyte
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
interface or the coupling current of a pair of electrodes, usually
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
a zero resistance ammeter (ZRA) or current-to-voltage con-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. verter.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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G199 − 09 (2020)
3.2.3 electrochemical current noise measurement, 4. Summary of Guide
n—electrochemical noise measurement using an electrochemi-
4.1 Electrochemical noise measurement is used for moni-
cal current signal.
toring of localized corrosion processes such as pitting (1, 2).
3.2.4 electrochemical noise measurement (ENM),
4.2 Electrochemical noise measurement may be used to
n—technique involving the acquisition and analysis of electro-
estimate a general corrosion rate (3).
chemical current and potential signals.
4.3 Electrochemical noise measurement operates on the
3.2.5 electrochemical potential noise measurement,
principle that fluctuations in potential and current occur as a
n—electrochemical noise measurement using an electrochemi-
result of spontaneous changes in the instantaneous corrosion
cal potential signal.
rate (4). The fluctuations may be due to one or more of several
3.2.6 Fourier transform, n—transformation of a time do-
phenomena that include: initiation (5) and propagation of
main signal into the frequency domain.
localized corrosion (6), Faradaic currents (7), double-layer
3.2.7 galvanostat, n—device used for automatically main-
capacitance discharge, gas bubble formation (8), adsorption/
taining a controlled current between two electrodes.
desorption processes, surface coverage (9), diffusion (10),
3.2.8 noise impedance, |Zn|, [Ω],n—ratio of the amplitude
variation of film thickness (11), mobility of charge carrier (12),
of potential noise to current noise, in the frequency domain, at passivity breakdown (13), and temperature variations (14, 15).
a specified frequency.
4.4 The noise fluctuations associated with corrosion phe-
3.2.9 noise resistance, R , [Ω],n—standard deviation of
n nomena can usually be distinguished from thermal (white)
potential noise divided by the standard deviation of current
noise (caused by thermal effects in which noise power is
noise.
directly proportional to the measured bandwidth), Johnson
noise (produced by the measurement instrumentation), and
3.2.10 pit indicator, n—standard deviation of current noise
divided by the mean of the coupling current. shot noise (in electrical circuits caused by the quantized nature
oftheelectroniccharge) (16-18).However,theelectrochemical
3.2.11 pitting factor, n—standard deviation of the current
noise signals generated may have characteristics similar to
noise divided by the general corrosion current.
those stated in the preceding sentence.
3.2.11.1 Discussion—The general corrosion current is nor-
mally estimated by a secondary electrochemical means.
4.5 The electrochemical noise method of corrosion mea-
surement may help to evaluate the corrosion mechanism of
3.2.12 pitting index, n—standard deviation of current noise
metals in electrolytes. Its particular advantage is in continuous
divided by the root mean square of the coupling current
monitoring without applying any external perturbation.
calculated over the same sample period.
3.2.13 potential measuring device, n—a high impedance 4.6 Method A—ZRA-Based Current and Potential
digital voltmeter or electrometer used to measure the potential
Measurement—Twonominallyidenticalelectrodesarecoupled
between two electrodes. through a ZRA, which maintains a 0-V potential difference
3.2.13.1 Discussion—Ideally, one of these electrodes is
between them by injecting (measured) current. The potential
understudyandtheotherisareferenceelectrode;however,the
between the couple and a third (reference) electrode is also
measurements may be made between two nominally identical
measured. The reference electrode may be either a conven-
electrodes manufactured from the material being studied.
tional reference electrode such as a saturated calomel electrode
(SCE) or simply be a third electrode identical in material to the
3.2.14 potentiostat, n—device used for automatically main-
coupled electrodes (19, 20).
taining a controlled voltage difference between an electrode
under study and a reference electrode in which a third
4.7 Method B—Potentiostatic Current Measurement with
electrode,thecounter(orauxiliary)electrode,isusedtosupply
Standard Reference Electrode—Reference Test Method G5
a current path from the electrode under study back to the
provides practice for making potentiostatic measurements.The
potentiostat.
working electrode potential is controlled with respect to the
3.2.15 sample interval, n—time delay between successive referenceelectrodeataprescribedvalue.Thecurrentmeasured
electrochemical noise measurements. (flowing between the working (Test 1) and auxiliary or counter
(Test 2) electrodes) is that required to maintain potential
3.2.16 sampleperiod,n—timebetweenthefirstandlastdata
control (21, 22).
collection during electrochemical noise measurement.
NOTE1—Noiseonthereferenceelectrodewillresultinacorresponding
3.2.17 time domain analysis, n—direct evaluation of time
current noise signal; therefore, the reference electrode needs to be
series data, for example, using statistical descriptions of the
relatively noise free. The potential measurement can only be made across
data. the auxiliary and working electrodes, as the potential between the
referenceandtheworkingisheldconstantbythepotentiostat.Thevoltage
3.2.18 time record, n—dataset obtained over a sample pe-
developed across the auxiliary and working electrodes is a function of the
riod at a typical sample interval in electrochemical noise
currentflowingthroughthecellandtheimpedancecausedbytheauxiliary
measurement. electrode, the working electrode, and the solution resistance.
3.2.19 zero resistance ammeter (ZRA), n—electronic device
used to measure current without imposing a significant IR drop
by maintaining close to 0-V potential difference between the
The boldface numbers in parentheses refer to the list of references at the end of
inputs. this standard.
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G199 − 09 (2020)
4.8 Method C—Galvanostatic Potential Measurement—An 7.1.1 The input impedance of the device should be high
electrode is supplied with current from a galvanostat at a enough to minimize current drawn from the electrodes, such
prescribed current value. The potential difference between the that the electrodes are not polarized by the measuring device.
electrode and a reference electrode is measured. An auxiliary Practice G106 provides guidelines for verification of algorithm
electrode is used to carry the return current. and equipment for electrochemical impedance measurements.
7.1.2 The potential range of the device depends on the
4.9 There are several methods by which the electrochemical
maximum potential difference between the two electrodes
noise data can be obtained (23-26) and analyzed, and some
(typically <1 V).
methods of interpreting the data are given in Appendix X1
7.1.3 The potential resolution of the device should be
(27-35). These analyses are included to aid the individual in
adequate to discriminate the signal to within the required
understandingtheelectrochemicalnoisetechniqueandsomeof
accuracy (typically 10 µV or lower).
its capabilities. The information is not intended to be all-
7.1.4 The device should be capable of maintaining an offset
inclusive.
potential between the two electrodes of less than 1 mV.
5. Significance and Use
7.1.5 The frequency response of the device should be flat
(within the desired accuracy) across the frequency range of the
5.1 Use of this guide is intended to provide information on
analysis.Thedeviceshouldhaveafastenoughresponsesothat
electrochemical noise to monitor corrosion on a continuous
signal transients are not distorted. Note that the signal that one
basis.
is attempting to measure may be below the resolution of the
5.2 This guide is intended for conducting electrochemical
instrument.
noise measurements, both in the laboratory and in-service
environments (36). NOTE 2—The offset voltage will appear as a current offset in the
measurement with no electrodes connected.
5.3 This technique is useful in systems in which process
7.1.6 The current range depends on the system being
upsets or other problems can create corrosive conditions. An
measured. The wide dynamic ranges seen in passive-to-active
early warning of corrosive attack can permit remedial action
transitions (nA to mA) may require auto-ranging circuits.
before significant damage occurs to process equipment (37).
7.1.7 The bias current of the device should be within the
5.4 This technique is also useful when inhibitor additions
required accuracy of the measurement. Otherwise it may cause
are used to control the corrosion of equipment. The indication
an error in the measured current.
of increasing corrosion activity can be used to signal the need
7.1.8 The background noise of the device should be below
for additional inhibitor (38).
the electrochemical current or potential noise being measured.
5.5 Control of corrosion in process equipment requires
High-impedance reference electrode inputs may pick up extra-
knowledge of the rate or mechanism of attack on an ongoing
neous noise from the environment and shielding may be
basis. This technique can be used to provide such information
required. An independent measurement of the background
in a digital format that is easily transferred to computers for
noise level should be performed.
analysis (39).
7.1.9 The requirements in 7.1.1 – 7.1.8 do not include all
possible combinations of instrumentation and electrode ar-
6. Limitations and Interferences
rangements. The instrument, cell, and analysis requirements
6.1 Results are representative of the probe element (elec-
should be determined by the particular test being undertaken.
trode). When first introduced into a system, corrosion rates on
7.2 Test Cell—The test cell should be constructed to allow
a probe element may be different from that of the structure.
the following items to be inserted into the solution chamber:
6.2 Noise can originate from thermal, electrical, and me-
7.2.1 Three identical electrodes, two of which comprise the
chanical factors. Since the interest is only on the noise from
coupled electrodes and the third electrode acts as a reference.
Faradaic processes, care should be exercised to minimize noise
Alternatively,insteadofthethirdidenticalelectrode,aLuggin-
from other sources.
Haber capillary with salt bridge connection for a reference
6.3 Probe elements by their nature are consumable. Hazard-
electrode may be used.
ous situations may occur if probes are left in service for
7.2.2 An inlet and an outlet for air or an inert gas.
extended periods beyond their probe life. In some
7.2.3 A thermometer or thermocouple holder.
configurations, crevice corrosion can cause damage or leaks at
7.2.4 The test cell shall be constructed from materials that
the interface between the element and its sealing surface that
will not corrode, deteriorate, or otherwise contaminate the
can cause false readings.
solution. Guide G31 provides standard practice for conducting
immersion corrosion testing.
6.4 Electrical contact between probe elements should be
avoided. In certain situations (for example, sour corrosion in 7.2.5 OnetypeofsuitablecellisdescribedinReferenceTest
the presence of hydrogen sulfide), the corrosion products can Method G5. Cells are not limited to that design. For example,
lead to apparent electrical shorting of the probe elements a 1 L round-bottom flask can be modified for the addition of
leading to erroneous readings. various necks to permit the introduction of electrodes, gas inlet
and outlet tubes, and the thermometer holder.ALuggin-Haber
7. Apparatus
capillaryprobecouldbeusedtoseparatethebulksolutionfrom
7.1 Electronics: the reference electrode. The capillary tip can be adjusted to
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G199 − 09 (2020)
bring it into close proximity to the working electrode. The 7.6.2.2 The potential of a reference electrode should be
minimum distance should be no less than two capillary checked at periodic intervals to ensure the accuracy of the
diameters from the working electrode. electrode. For other alloy-electrolyte combinations, a different
referenceelectrodemaybepreferredtoavoidcontaminationof
7.3 Electrode Holder—The auxiliary and working elec-
the reference electrode or the electrolyte.
trodes can be mounted in the manner shown in Reference Test
7.6.2.3 Any reference electrode may be used instead of a
Method G5.Assembly precautions described in ReferenceTest
standard reference electrode. The reference electrode should
Method G5 should be followed.
ideally have noise characteristics that are less than the magni-
7.4 Potentiostat—The potentiostat shall be of the type that
tude of the potential noise signal that is to be measured. Noble
allows application of a potential sweep as described in Refer-
metal electrodes (for example, platinum or gold) are generally
ence Test Method G5 and Test Method G59. The potentiostat
unsuitable because of their high-impedance characteristics.
shallhaveoutputsintheformofvoltageversusgroundforboth
NOTE 4—A saturated silver/silver chloride electrode with a controlled
potential and current.
rate of leakage (about 3 µL/h) has been found to be suitable. It is durable,
reliable, and commercially available. Precautions shall be taken to ensure
7.5 Collection and Analysis of Current-Voltage Response—
that the electrode is maintained in the proper condition.
The potential and current measuring circuits shall have the
7.7 Recording Device—Thepotentialandcurrentsignalsare
characteristics described in Reference Test Method G5.
recorded continuously using a personal computer (PC) or a
7.6 Electrodes:
digital data recorder. In the former case, either a combination
7.6.1 Electrode preparation should follow Reference Test
of current and potential measuring instruments or a scanning
Method G5, which involves drilling and tapping the speci-
potentiostat should be interfaced with the PC. The PC should
men(s) and mounting on the electrode holder. The working
be equipped with appropriate hardware and software to collect
electrode or working electrode pair should be constructed from
and analyze data from the peripheral instruments. The storage
the material to be tested. If a pair, the electrodes should be
requirements for some electrochemical noise data may be
prepared from the same piece of strip or rod. If a three
substantial and should be considered.
“identical” electrode arrangement is to be used, the electrodes
7.8 Signal Transformation and Recording:
should be prepared from the same piece of strip or rod. The
7.8.1 Theelectrochemicalsignalsareusuallysampledinthe
electrode surface area should be chosen such that the current
time domain using analog-to-digital conversion techniques.
measurement will neither saturate (electrodes too large) nor be
The sampling rate has a direct bearing on the resolution of the
at the limits of resolution of the current measurement (too
analog-to-digital conversion. Sampling frequency is typically
small). A good starting point is 10 cm ; adjustments are:
once per second, but faster or slower conversions may be
smaller electrodes for large currents and larger electrodes for
appropriate.
small currents. Care should be taken in mounting the elec-
7.8.2 Analog-to-digital conversion also entails a sampling
trode(s) to avoid the likelihood of crevice corrosion.
resolution error. Analog-to-digital converters have finite reso-
7.6.2 Reference electrode type and usage should follow
lution that, in turn, results in a round-off error that is math-
Reference Test Method G5. A low-impedance, low-noise
ematically equivalent to noise.They may also contribute to the
reference electrode is recommended. The reference and bridge
noise over and above this error caused by non-idealities in the
shall not contaminate the electrolyte and shall be suitable for a
converter.
given combination of alloy and electrolyte. The most appro-
7.8.2.1 The process of converting from continuous to dis-
priate reference electrode and bridge for a given environment
crete time signals causes another form of error known as
will vary. If a reference electrode of the same material as the
aliasing.When a high-frequency component ~f$f /2! is present
working electrode(s) is adopted, the user should be aware that s
in the continuous signal, the process of sampling will cause
the noise characteristics of the reference electrode will be
that component to appear at lower frequencies. This limit, f /2,
similar to the working electrode(s). s
is known as the Nyquist limit. Once a component has been
NOTE 3—A low-impedance reference electrode is recommended be-
aliased into a lower frequency, it is impossible to differentiate
cause high-impedance reference electrodes tend to be more susceptible to
between it and the component originally at that frequency. To
electrostatic pi
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