1、Designation: G199 09 (Reapproved 2014)Standard Guide forElectrochemical Noise Measurement1This standard is issued under the fixed designation G199; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、 in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide covers the procedure for conducting onlinecorrosion monitoring of metals by the use of the electrochemi-cal noise technique. Withi
3、n the limitations described, thistechnique can be used to detect localized corrosion activity andto estimate corrosion rate on a continuous basis withoutremoval of the monitoring probes from the plant or experimen-tal cell.1.2 This guide presents briefly some generally acceptedmethods of analyses th
4、at are useful in the interpretation ofcorrosion test results.1.3 This guide does not cover detailed calculations andmethods; rather it covers a range of approaches that have foundapplication in corrosion testing.1.4 The values stated in SI units are to be regarded asstandard. No other units of measu
5、rement are included in thisstandard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limi
6、tations prior to use.2. Referenced Documents2.1 ASTM Standards:2G1 Practice for Preparing, Cleaning, and Evaluating Corro-sion Test SpecimensG3 Practice for Conventions Applicable to ElectrochemicalMeasurements in Corrosion TestingG4 Guide for Conducting Corrosion Tests in Field Applica-tionsG5 Refe
7、rence Test Method for Making PotentiodynamicAnodic Polarization MeasurementsG15 Terminology Relating to Corrosion and Corrosion Test-ing (Withdrawn 2010)3G16 Guide for Applying Statistics to Analysis of CorrosionDataG31 Guide for Laboratory Immersion Corrosion Testing ofMetalsG46 Guide for Examinati
8、on and Evaluation of Pitting Cor-rosionG59 Test Method for Conducting Potentiodynamic Polariza-tion Resistance MeasurementsG61 Test Method for Conducting Cyclic PotentiodynamicPolarization Measurements for Localized Corrosion Sus-ceptibility of Iron-, Nickel-, or Cobalt-Based AlloysG96 Guide for Onl
9、ine Monitoring of Corrosion in PlantEquipment (Electrical and Electrochemical Methods)G102 Practice for Calculation of Corrosion Rates and Re-lated Information from Electrochemical MeasurementsG106 Practice for Verification of Algorithm and Equipmentfor Electrochemical Impedance Measurements3. Termi
10、nology3.1 DefinitionsThe terminology used herein, if not spe-cifically defined otherwise, shall be in accordance with Termi-nology G15. Definitions provided herein and not given inTerminology G15 are limited only to this guide.3.2 Definitions of Terms Specific to This Standard:3.2.1 coupling current
11、, nmeasured current flowing be-tween two electrodes in an electrolyte coupled by an externalcircuit.3.2.2 current measuring device, ndevice that is capable ofmeasuring the current flow across the electrode/electrolyteinterface or the coupling current of a pair of electrodes, usuallya zero resistance
12、 ammeter (ZRA) or current-to-voltage con-verter.3.2.3 electrochemical current noise measurement,nelectrochemical noise measurement using an electrochemi-cal current signal.3.2.4 electrochemical noise measurement (ENM),ntechnique involving the acquisition and analysis of electro-chemical current and
13、potential signals.1This guide is under the jurisdiction of ASTM Committee G01 on Corrosion ofMetals and is the direct responsibility of Subcommittee G01.11 on ElectrochemicalMeasurements in Corrosion Testing.Current edition approved May 1, 2014. Published May 2014. Originallyapproved in 2009. Last p
14、revious edition approved in 2009 as G199- 09. DOI:10.1520/G0199-09R14.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM
15、 website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.5 electrochemical potential noise measurement,nelectrochemical noise measurement using an
16、 electrochemi-cal potential signal.3.2.6 Fourier transform, ntransformation of a time do-main signal into the frequency domain.3.2.7 galvanostat, ndevice used for automatically main-taining a controlled current between two electrodes.3.2.8 noise impedance, |Zn|, ,nratio of the amplitudeof potential
17、noise to current noise, in the frequency domain, ata specified frequency.3.2.9 noise resistance, Rn, ,nstandard deviation ofpotential noise divided by the standard deviation of currentnoise.3.2.10 pit indicator, nstandard deviation of current noisedivided by the mean of the coupling current.3.2.11 p
18、itting factor, nstandard deviation of the currentnoise divided by the general corrosion current.3.2.11.1 DiscussionThe general corrosion current is nor-mally estimated by a secondary electrochemical means.3.2.12 pitting index, nstandard deviation of current noisedivided by the root mean square of th
19、e coupling currentcalculated over the same sample period.3.2.13 potential measuring device, na high impedancedigital voltmeter or electrometer used to measure the potentialbetween two electrodes.3.2.13.1 DiscussionIdeally, one of these electrodes isunder study and the other is a reference electrode;
20、 however, themeasurements may be made between two nominally identicalelectrodes manufactured from the material being studied.3.2.14 potentiostat, ndevice used for automatically main-taining a controlled voltage difference between an electrodeunder study and a reference electrode in which a thirdelec
21、trode, the counter (or auxiliary) electrode, is used to supplya current path from the electrode under study back to thepotentiostat.3.2.15 sample interval, ntime delay between successiveelectrochemical noise measurements.3.2.16 sample period, ntime between the first and last datacollection during el
22、ectrochemical noise measurement.3.2.17 time domain analysis, ndirect evaluation of timeseries data, for example, using statistical descriptions of thedata.3.2.18 time record, ndataset obtained over a sample pe-riod at a typical sample interval in electrochemical noisemeasurement.3.2.19 zero resistan
23、ce ammeter (ZRA), nelectronic deviceused to measure current without imposing a significant IR dropby maintaining close to 0-V potential difference between theinputs.4. Summary of Guide4.1 Electrochemical noise measurement is used for moni-toring of localized corrosion processes such as pitting (1, 2
24、).44.2 Electrochemical noise measurement may be used toestimate a general corrosion rate (3).4.3 Electrochemical noise measurement operates on theprinciple that fluctuations in potential and current occur as aresult of spontaneous changes in the instantaneous corrosionrate (4). The fluctuations may
25、be due to one or more of severalphenomena that include: initiation (5) and propagation oflocalized corrosion (6), Faradaic currents (7), double-layercapacitance discharge, gas bubble formation (8), adsorption/desorption processes, surface coverage (9), diffusion (10),variation of film thickness (11)
26、, mobility of charge carrier (12),passivity breakdown (13), and temperature variations (14, 15).4.4 The noise fluctuations associated with corrosion phe-nomena can usually be distinguished from thermal (white)noise (caused by thermal effects in which noise power isdirectly proportional to the measur
27、ed bandwidth), Johnsonnoise (produced by the measurement instrumentation), andshot noise (in electrical circuits caused by the quantized natureof the electronic charge) (16-18). However, the electrochemicalnoise signals generated may have characteristics similar tothose stated in the preceding sente
28、nce.4.5 The electrochemical noise method of corrosion mea-surement may help to evaluate the corrosion mechanism ofmetals in electrolytes. Its particular advantage is in continuousmonitoring without applying any external perturbation.4.6 Method AZRA-Based Current and PotentialMeasurementTwo nominally
29、 identical electrodes are coupledthrough a ZRA, which maintains a 0-V potential differencebetween them by injecting (measured) current. The potentialbetween the couple and a third (reference) electrode is alsomeasured. The reference electrode may be either a conven-tional reference electrode such as
30、 a saturated calomel electrode(SCE) or simply be a third electrode identical in material to thecoupled electrodes (19, 20).4.7 Method BPotentiostatic Current Measurement withStandard Reference ElectrodeReference Test Method G5provides practice for making potentiostatic measurements. Theworking elect
31、rode potential is controlled with respect to thereference electrode at a prescribed value. The current measured(flowing between the working (Test 1) and auxiliary or counter(Test 2) electrodes) is that required to maintain potentialcontrol (21, 22).NOTE 1Noise on the reference electrode will result
32、in a correspondingcurrent noise signal; therefore, the reference electrode needs to berelatively noise free. The potential measurement can only be made acrossthe auxiliary and working electrodes, as the potential between the4The boldface numbers in parentheses refer to the list of references at the
33、end ofthis standard.G199 09 (2014)2reference and the working is held constant by the potentiostat. The voltagedeveloped across the auxiliary and working electrodes is a function of thecurrent flowing through the cell and the impedance caused by the auxiliaryelectrode, the working electrode, and the
34、solution resistance.4.8 Method CGalvanostatic Potential MeasurementAnelectrode is supplied with current from a galvanostat at aprescribed current value. The potential difference between theelectrode and a reference electrode is measured. An auxiliaryelectrode is used to carry the return current.4.9
35、There are several methods by which the electrochemicalnoise data can be obtained (23-26) and analyzed, and somemethods of interpreting the data are given in Appendix X1(27-35). These analyses are included to aid the individual inunderstanding the electrochemical noise technique and some ofits capabi
36、lities. The information is not intended to be all-inclusive.5. Significance and Use5.1 Use of this guide is intended to provide information onelectrochemical noise to monitor corrosion on a continuousbasis.5.2 This guide is intended for conducting electrochemicalnoise measurements, both in the labor
37、atory and in-serviceenvironments (36).5.3 This technique is useful in systems in which processupsets or other problems can create corrosive conditions. Anearly warning of corrosive attack can permit remedial actionbefore significant damage occurs to process equipment (37).5.4 This technique is also
38、useful when inhibitor additionsare used to control the corrosion of equipment. The indicationof increasing corrosion activity can be used to signal the needfor additional inhibitor (38).5.5 Control of corrosion in process equipment requiresknowledge of the rate or mechanism of attack on an ongoingba
39、sis. This technique can be used to provide such informationin a digital format that is easily transferred to computers foranalysis (39).6. Limitations and Interferences6.1 Results are representative of the probe element (elec-trode). When first introduced into a system, corrosion rates ona probe ele
40、ment may be different from that of the structure.6.2 Noise can originate from thermal, electrical, and me-chanical factors. Since the interest is only on the noise fromFaradaic processes, care should be exercised to minimize noisefrom other sources.6.3 Probe elements by their nature are consumable.
41、Hazard-ous situations may occur if probes are left in service forextended periods beyond their probe life. In someconfigurations, crevice corrosion can cause damage or leaks atthe interface between the element and its sealing surface thatcan cause false readings.6.4 Electrical contact between probe
42、elements should beavoided. In certain situations (for example, sour corrosion inthe presence of hydrogen sulfide), the corrosion products canlead to apparent electrical shorting of the probe elementsleading to erroneous readings.7. Apparatus7.1 Electronics:7.1.1 The input impedance of the device sho
43、uld be highenough to minimize current drawn from the electrodes, suchthat the electrodes are not polarized by the measuring device.Practice G106 provides guidelines for verification of algorithmand equipment for electrochemical impedance measurements.7.1.2 The potential range of the device depends o
44、n themaximum potential difference between the two electrodes(typically 1 V).7.1.3 The potential resolution of the device should beadequate to discriminate the signal to within the requiredaccuracy (typically 10 V or lower).7.1.4 The device should be capable of maintaining an offsetpotential between
45、the two electrodes of less than 1 mV.7.1.5 The frequency response of the device should be flat(within the desired accuracy) across the frequency range of theanalysis. The device should have a fast enough response so thatsignal transients are not distorted. Note that the signal that oneis attempting
46、to measure may be below the resolution of theinstrument.NOTE 2The offset voltage will appear as a current offset in themeasurement with no electrodes connected.7.1.6 The current range depends on the system beingmeasured. The wide dynamic ranges seen in passive-to-activetransitions (nA to mA) may req
47、uire auto-ranging circuits.7.1.7 The bias current of the device should be within therequired accuracy of the measurement. Otherwise it may causean error in the measured current.7.1.8 The background noise of the device should be belowthe electrochemical current or potential noise being measured.High-
48、impedance reference electrode inputs may pick up extra-neous noise from the environment and shielding may berequired. An independent measurement of the backgroundnoise level should be performed.7.1.9 The requirements in 7.1.1 7.1.8 do not include allpossible combinations of instrumentation and elect
49、rode ar-rangements. The instrument, cell, and analysis requirementsshould be determined by the particular test being undertaken.7.2 Test CellThe test cell should be constructed to allowthe following items to be inserted into the solution chamber:7.2.1 Three identical electrodes, two of which comprise thecoupled electrodes and the third electrode acts as a reference.Alternatively, instead of the third identical electrode, a Luggin-Haber capillary with salt bridge connection for a referenceelectrode may be used.7.2.2 An inlet and an outlet for ai
