1、Designation: G 199 09Standard Guide forElectrochemical Noise Measurement1This standard is issued under the fixed designation G 199; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses
2、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. Within the limitation
3、s 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 that are useful in
4、 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 measurement are inclu
5、ded 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 limitations prior to
6、 use.2. Referenced Documents2.1 ASTM Standards:2G1 Practice for Preparing, Cleaning, and Evaluating Cor-rosion Test SpecimensG3 Practice for ConventionsApplicable to ElectrochemicalMeasurements in Corrosion TestingG4 Guide for Conducting Corrosion Tests in Field Appli-cationsG5 Reference Test Method
7、 for Making Potentiostatic andPotentiodynamic Anodic Polarization MeasurementsG15 Terminology Relating to Corrosion and CorrosionTestingG16 Guide forApplying Statistics toAnalysis of CorrosionDataG31 Practice for Laboratory Immersion Corrosion Testingof MetalsG46 Guide for Examination and Evaluation
8、 of PittingCorrosionG59 Test Method for Conducting Potentiodynamic Polar-ization Resistance MeasurementsG61 Test Method for Conducting Cyclic PotentiodynamicPolarization Measurements for Localized Corrosion Sus-ceptibility of Iron-, Nickel-, or Cobalt-Based AlloysG96 Guide for Online Monitoring of C
9、orrosion in PlantEquipment (Electrical and Electrochemical Methods)G 102 Practice for Calculation of Corrosion Rates andRelated Information from Electrochemical MeasurementsG 106 Practice for Verification ofAlgorithm and Equipmentfor Electrochemical Impedance Measurements3. Terminology3.1 Definition
10、sThe terminology used herein, if not spe-cifically defined otherwise, shall be in accordance with Termi-nology G15. Definitions provided herein and not given inTerminology G15are limited only to this guide.3.2 Definitions of Terms Specific to This Standard:3.2.1 coupling current, nmeasured current f
11、lowing 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 ammeter (ZRA) or cur
12、rent-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 potential signals.3.2
13、.5 electrochemical potential noise measurement,nelectrochemical noise measurement using an electrochemi-cal potential signal.3.2.6 Fourier transform, ntransformation of a time do-main signal into the frequency domain.1This guide is under the jurisdiction of ASTM Committee G01 on Corrosion ofMetals a
14、nd is the direct responsibility of Subcommittee G01.11 on ElectrochemicalMeasurements in Corrosion Testing.Current edition approved March 15, 2009. Published April 2009.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annua
15、l Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.7 galvanostat, ndevice used for automatically main-taining a controlled c
16、urrent between two electrodes.3.2.8 noise impedance, |Zn|, V, nratio of the amplitudeof potential noise to current noise, in the frequency domain, ata specified frequency.3.2.9 noise resistance, Rn,V, nstandard deviation ofpotential noise divided by the standard deviation of currentnoise.3.2.10 pit
17、indicator, nstandard deviation of current noisedivided by the mean of the coupling current.3.2.11 pitting 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 me
18、ans.3.2.12 pitting index, nstandard deviation of current noisedivided by the root mean square of the 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
19、.1 DiscussionIdeally, one of these electrodes isunder study and the other is a reference electrode; 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 controlle
20、d voltage difference between an electrodeunder study and a reference electrode in which a thirdelectrode, 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
21、 noise measurements.3.2.16 sample period, ntime between the first and lastdata collection during electrochemical 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 s
22、ampleperiod at a typical sample interval in electrochemical noisemeasurement.3.2.19 zero resistance 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
23、 noise measurement is used for moni-toring of localized corrosion processes such as pitting (1, 2).34.2 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 occu
24、r as aresult of spontaneous changes in the instantaneous corrosionrate (4). The fluctuations may 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), adsor
25、ption/desorption processes, surface coverage (9), diffusion (10),variation of film thickness (11), 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 (
26、white)noise (caused by thermal effects in which noise power isdirectly proportional to the measured bandwidth), Johnsonnoise (produced by the measurement instrumentation), andshot noise (in electrical circuits caused by the quantized natureof the electronic charge) (16-18). However, the electrochemi
27、calnoise signals generated may have characteristics similar tothose stated in the preceding sentence.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 apply
28、ing any external perturbation.4.6 Method AZRA-Based Current and PotentialMeasurementTwo nominally identical electrodes arecoupled through a ZRA, which maintains a 0-V potentialdifference between them by injecting (measured) current. Thepotential between the couple and a third (reference) electrodeis
29、 also measured. The reference electrode may be either aconventional reference electrode such as a saturated calomelelectrode (SCE) or simply be a third electrode identical inmaterial to the coupled electrodes (19, 20).4.7 Method BPotentiostatic Current Measurement withStandard Reference ElectrodeRef
30、erence Test Method G5provides practice for making potentiostatic measurements. Theworking electrode 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 req
31、uired to maintain potentialcontrol (21, 22).NOTE 1Noise on the reference electrode will result 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 po
32、tential between thereference 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 solution resista
33、nce.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 There are severa
34、l 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 capabilities. The info
35、rmation is not intended to be all-inclusive.3The boldface numbers in parentheses refer to the list of references at the end ofthis standard.G1990925. Significance and Use5.1 Use of this guide is intended to provide information onelectrochemical noise to monitor corrosion on a continuousbasis.5.2 Thi
36、s guide is intended for conducting electrochemicalnoise measurements, both in the laboratory 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 actio
37、nbefore significant damage occurs to process equipment (37).5.4 This technique is also 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
38、 process equipment requiresknowledge of the rate or mechanism of attack on an ongoingbasis. 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 e
39、lement (elec-trode). When first introduced into a system, corrosion rates ona probe element 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
40、to minimize noisefrom other sources.6.3 Probe elements by their nature are consumable. Hazard-ous situations may occur if probes are left in service forextended periods beyond their probe life. In some configura-tions, crevice corrosion can cause damage or leaks at theinterface between the element a
41、nd its sealing surface that cancause false readings.6.4 Electrical contact between probe 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 e
42、rroneous readings.7. Apparatus7.1 Electronics:7.1.1 The input impedance of the device should be highenough to minimize current drawn from the electrodes, suchthat the electrodes are not polarized by the measuring device.Practice G 106 provides guidelines for verification of algo-rithm and equipment
43、for electrochemical impedance measure-ments.7.1.2 The potential range of the device depends on 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
44、 10 V or lower).7.1.4 The device should be capable of maintaining an offsetpotential between 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 res
45、ponse so thatsignal transients are not distorted. Note that the signal that oneis attempting 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 b
46、eingmeasured. The wide dynamic ranges seen in passive-to-activetransitions (nA to mA) may require 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
47、the device should be belowthe electrochemical current or potential noise being measured.High-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 req
48、uirements in 7.1.1-7.1.8 do not include allpossible combinations of instrumentation and electrode 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
49、 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 air or an inert gas.7.2.3 A thermometer or thermocouple holder.7.2.4 The test cell shall be constructed from materials thatwill not corrode, deteriorate, or otherwise contaminate thesolution. Practice G31provides st
