1、Designation: B 826 03Standard Test Method forMonitoring Atmospheric Corrosion Tests by ElectricalResistance Probes1This standard is issued under the fixed designation B 826; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method provides a means for monitoringcorrosivity of environmental tests that involve exposure tocorrosi
3、ve gases.1.2 This test method uses a resistance monitor (RM) probefabricated from a chosen metal conductor, with one conductorsegment uncovered to permit exposure of the chosen metalconductor to the corrosive gas mixture and the second conduc-tor segment covered to protect the metal conductor of thi
4、ssegment from direct attack by the corrosive gas mixture. Thecovered conductor segment provides a reference for evaluatingchanges in the uncovered segment. The ratio of the resistanceof the exposed segment to that of the covered segment providesa measure of the amount of metal conductor that has rea
5、ctedwith the corrosive gas test environment to form poorly con-ducting corrosion product, thus providing a measure of testcorrosivity.1.3 Resistance monitoring is applicable to a broad range oftest conditions by selection of the appropriate metal conductorand initial metal thickness.1.4 This method
6、is similar in intent to Test Methods B 808.1.5 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 become familiarwith all hazards including those identified in the appropriateMaterial Safety Da
7、ta Sheet for this product/material as pro-vided by the manufacturer, to establish appropriate safety andhealth practices, and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:B 808 Test Method for Monitoring of Atmospheric Corro-sion Chamber
8、s by Quartz Crystal Microbalances2B 810 Test Method for Calibration of Atmospheric Corro-sion Test Chambers by Change in Mass of Copper Cou-pons2B 827 Practice for Conducting Mixed Flowing Gas (MFG)Environmental Tests2G 96 Guide for On-Line Monitoring of Corrosion in PlantEquipment (Electrical and E
9、lectrochemical Methods)33. Summary of Test Method3.1 The corrosivity of an atmospheric corrosion test such asa mixed flowing gas (MFG) type test is measured by monitor-ing the loss in electrical conductivity of a metal element whosesurface corrodes to form poorly conducting corrosion product.This co
10、rrosion product consumes metal from a conduction pathcausing an increase in electrical resistance. The resistance ofthe degraded conduction path is compared with a similar pathwhose surface is covered to prevent corrosion. This compari-son resistance also provides a temperature correction reference.
11、The ratio of the electrical resistance of the path exposed to thecorrosive gases to that of the covered path is monitored duringthe test and compared to an expected ratio-versus-time curve toestablish the relationship of the test corrosivity to expected testcorrosivity. Alternatively, the ratio-vers
12、us-time curve for agiven atmosphere can be compared with the behavior of othercorrosive atmospheres to evaluate the relative corrosivity of thevarious atmospheres.4. Significance and Use4.1 Corrosivity monitoring of test environments provides ameans to monitor an integrated value of test corrosivity
13、 whichcannot be evaluated from test parameters themselves, such astemperature, humidity, and gas concentration. As such themonitor value can be used for specification purposes such astest validation. Electrical resistance monitoring of conductorsexposed to corrosive media is a well-established pract
14、ice.4,5,6,74.2 The resistance method assumes uniform corrosion overthe entire surface of the exposed metal conductor segment.1This test method is under the jurisdiction of ASTM Committee B02 onNonferrous Metals and Alloys and is the direct responsibility of SubcommitteeB02.11 on Electrical Contact T
15、est Methods.Current edition approved June 10, 2003. Published July 2003. Originallyapproved in 1997. Last previous edition approved in 1997 as B 826 - 97.2Annual Book of ASTM Standards, Vol 03.04.3Annual Book of ASTM Standards, Vol 03.02.4ASTM G 96, Guide for On-Line Monitoring of Corrosion in Plant
16、 Equipment(Electrical and Electrochemical Methods).1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Local corrosion such as pitting, crevice, or grain boundarycorrosion may provide invalid estimates of test corrosivity.Marked changes
17、in slope of the curve of electrical resistanceratio versus time may indicate undesired processes which canbe due to deficiencies in the test atmosphere or in the monitoritself.4.3 Because of limitations of the diffusion process withinthe corrosion product formed on the metal conductor segmentof the
18、RM probe when passivating corrosion films are formed,resistance monitoring may not be useful for test chambermonitoring purposes for very long test exposures. Chambermonitoring is dependent on detecting changes in the rate ofcorrosion of the RM as an indicator signal that specified gasconcentrations
19、 must be reverified. However, low corrosionrates limit the absolute value of the rate of change of corrosionrate with change of test conditions; for parabolic film growthprocesses, the growth rate decreases with time limiting thesensitivity of the RM at extended test times.4.4 Since corrosion rate c
20、an be a complex function of testparameters in MFG tests with any given metal primarilyresponsive to a subset of the gases in the MFG environment,more than one type metal resistance probe is required in orderto assist in maintenance of relative gas concentrations. Forsuch test specifications, values
21、of resistance ratios must bereferred to ratios obtained under known test conditions assupplied by the test specifier. Information relating to thesensitivity of various metals to various corrodants has beenpublished.8,94.5 RM probes can be useful from 1 % of thickness con-sumed upward to 50 % of thic
22、kness consumed by the corrosionfilm growth. Conductor thicknesses between 25 nm and 0.2mm are commercially available.105. Interferences5.1 Resistance monitor probes are generally constructedfrom thin film metal coatings on dielectric substrates in theform of a serpentine pattern or loop to provide a
23、 long conductorpath so as to increase the ease of detection of a resistancechange. With such configurations, formation of a corrosionproduct, which grows out from the edges of the conductorpaths, can contact adjacent paths; when such contacting cor-rosion films are formed from conducting corrosion p
24、roductssuch as some copper sulfides, abrupt changes in probe resis-tance can be observed due to shorting of the current path. Suchshorting of the current path can also occur if condensationoccurs on the probe, especially in the presence of gases thatdissolve in the condensed film to form an electrol
25、yte. Suchshorting behavior is seen as an anomalous resistance decreaseand indicates that corrosion of the RM is not predictable fromits electrical resistance.5.2 Corrosive gas permeation through the protective cover-ing of the reference conductor can lead to corrosion of thereference conductor, thus
26、 reducing the apparent resistance ratiobetween the exposed conductor and the reference conductor.Excess resistance change of the reference conductor above thatexpected for any observed temperature change of the RM is anindication of this possible interference. The RM should beexamined after the test
27、 for discoloration of the referenceconductor as a signal of possible corrosion of the referenceconductor when such excess resistance change is observed.Presence of corrosion of the reference conductor invalidatesthe estimate of atmosphere corrosivity based on the observedresistance ratio-versus-time
28、 curve.5.3 Thermal gradients across the RM probe as a result of thepresence of local heat sources such as lamps or powered testdevices can produce an anomalous resistance ratio change.Such effects can be verified by shutting off the local heat sourceand remeasuring the resistance ratio.5.4 Scratches
29、 or other localized conductor thickness varia-tions can produce anomalous resistance ratios after reducedcorrosion exposures. This behavior can be detected by abruptincreases in apparent rate of corrosion which occur when thethinned region corrodes through to the dielectric substrate.Such abrupt cha
30、nges indicate the end of useful data from theRM.5.5 Contaminant films on the surface of the exposed con-ductor can inhibit corrosion or accelerate corrosion. Care mustbe taken to assure freedom from fingerprints, spittle, oil, orother surface contamination prior to installation in the testchamber. I
31、f a cleaning procedure is used, it should be appro-priately evaluated and consistently applied to avoid differinginitial conditions on the RM. The exposed metal conductor ofthe probe should be examined after the test exposure to ensureuniformity of corrosion film growth. Clumps of corrosionproduct i
32、ndicate undesirable conditions and potential problemsinterpreting resistance changes.5.6 Since in-situ electrical resistance measurements requireelectrical access to the probe being measured, defects in theelectrical access system, for example, cables and sockets, canaffect the resistance values bei
33、ng measured. Protection of theelectrical access system from the deleterious effects of expo-sure to corrosive gases is required to ensure a reliable moni-toring system.5.7 Most interferences are detectable when multiple probesare used in a single test by comparison of one probe to another.6. Apparat
34、us6.1 The apparatus consists of two elements, a probe that isresponsive to the corrosive environment and a means toelectrically measure the resistance of the probe.106.1.1 Resistance Monitor (RM) Probe, consists of twoelements of identical material in thermal contact with eachother. One element is c
35、apable of interaction with a corrosive5Allen, R. C. and Trzeciak, M. J., “Measuring Environmental Corrosivity,”Institute of Electrical and Electronic Engineers, Components, Hybrids, and Manu-facturing Technology Transaction, Vol CHMT-3, 1, March 1980, pp. 67-70.6Murcko, R., Corrosion-Indicating Devi
36、ce, IBM Technical Disclosure Bulletin,Vol 32, No.10A, March 1990, p. 25.7Sproles, E. S., “Electrical Resistance of Wires Used as a Corrosion RateMonitor,” Corrosion of Electronic and Magnetic Materials, ASTM STP 1148,P.J.Peterson, Ed., American Society for Testing and Materials, 1992, pp. 11-20.8Ric
37、e, D., et. al., “Atmospheric Corrosion of Copper and Silver,” Journal ofElectrochemical Society, Vol 128, No. 2, February 1981, pp. 275-284.9Rice, D., et al., “Indoor Corrosion of Metals,” Journal of ElectrochemicalSociety, Vol 127, No. 4, April 1980, pp. 891-901.10Resistance monitor system manufact
38、ured by Rohrback Cosasco Systems, Inc.,11841 E. Smith Ave., Santa Fe Springs, CA 90670, United States, have been foundto be satisfactory for corrosivity monitoring of airborne corrosion agents; see ModelCK-3 Corrosometer.B826032gas environment and is the detector of test chamber corrosivity.The seco
39、nd element is protected from interaction with thecorrosive gases from the chamber by means of an imperviousovercoat such as epoxy or other polymer and serves as areference. The electrical properties of the elements are chosenwith regard to the expected amount of corrosion to be detected.Mildly corro
40、sive environments would be monitored by meansof thinner conductors than would be employed in stronglycorrosive environments so as to be more sensitive to thedecreased amount of corrosion expected.6.1.2 Resistance monitor probes are measured with standardelectrical resistance measurement equipment or
41、 with suitablecommercial systems.10A Kelvin bridge or a potentiometershall be used when measuring resistance less than 10 V.AWheatstone bridge may be used with resistances greater than10 V. The resistance shall be measured with an accuracy of0.1 %. The measuring current shall be so small that theres
42、istance being measured changes by less than 0.1 % due totemperature rise.6.2 It is highly desirable that a means for continuousmonitoring of the probe be available so that a record ismaintained during times when the test facility is unattended.7. Calibration7.1 Calibrate electrical resistance measur
43、ing apparatus inaccordance with the manufacturers instructions once every sixmonths or more frequently if drift indicates that the require-ments of 0.1 % accuracy cannot be met with semiannualcalibration.8. Procedure8.1 Store probes in a glass desiccator after fabrication, freefrom exposure to plast
44、ic materials that emit volatile plasticizersor other organic vapors. Handle and store commercial probes10in accordance with the manufacturers instructions. Take careto ensure that the exposed metal conductor of the proberemains free of contaminants prior to use in the test chamberfor corrosivity mon
45、itoring. Some commercial probes10havebeen supplied with a removable protective film covering theconductor that is to be exposed to the corrosive gases. Usersare cautioned that such film have been reported to leave aresidue that affects the initial sensitivity to a corrosive envi-ronment. If such a f
46、ilm is present, remove this film just beforeinstallation of the RM probe in the gaseous corrosion testchamber or other location where corrosivity is to be monitored.8.2 Install probes in the corrosive gas stream within the testchamber between 4 and 6 cm from the test samples beingevaluated in the te
47、st chamber. The RM probes and the testsamples shall all be in a single plane that is perpendicular to thegas flow direction. Probes shall not be behind any gas flowobstruction such as a test sample or test sample support rack,nor shall they obstruct the gas flow to any test sample. Theplane of the m
48、etal conductor of the RM probe shall be parallelto the gas flow with the exposed metal conductor closest to thesource of the gas flow and the protected reference metalconductor downstream from the exposed metal conductor. Thelong axis of the probe shall be perpendicular to the gas flowdirection. The
49、 RM probe may be mounted with the plane of theconductor vertical or horizontal for the case of horizontal gasflow; for vertical gas flow, the plane of the conductor shall bevertical. In some cases, it may be desired that the conductor befacing downward to avoid settling of particulate material on theface of the conductor. See Fig. 1.8.3 Installation of the probes shall be consistent with instal-lation of the test samples in accordance with Practice B 827.Alternatively, if it is desired to use resistance probes as acomplement to weight gain for corrosion chamber calibration,probe placeme
