1、Designation: B826 09Standard Test Method forMonitoring Atmospheric Corrosion Tests by ElectricalResistance Probes1This standard is issued under the fixed designation B826; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、 last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () 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 tocorrosive
3、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 thisse
4、gment 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 reacte
5、dwith 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 is
6、similar in intent to Test Methods B808.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the
7、user of this standard to become familiarwith all hazards including those identified in the appropriateMaterial Safety Data Sheet (MSDS) for this product/materialas provided by the manufacturer, to establish appropriatesafety and health practices, and determine the applicability ofregulatory limitati
8、ons prior to use.2. Referenced Documents2.1 ASTM Standards:2B808 Test Method for Monitoring of Atmospheric Corro-sion Chambers by Quartz Crystal MicrobalancesB810 Test Method for Calibration of Atmospheric Corro-sion Test Chambers by Change in Mass of Copper Cou-ponsB827 Practice for Conducting Mixe
9、d Flowing Gas (MFG)Environmental TestsG96 Guide for Online Monitoring of Corrosion in PlantEquipment (Electrical and Electrochemical Methods)3. 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
10、 electrical conductivity of a metal element whosesurface corrodes to form poorly conducting corrosion product.This corrosion product consumes metal from a conduction pathcausing an increase in electrical resistance. The resistance ofthe degraded conduction path is compared with a similar pathwhose s
11、urface is covered to prevent corrosion. This compari-son resistance also provides a temperature correction reference.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
12、curve toestablish the relationship of the test corrosivity to expected testcorrosivity. Alternatively, the ratio-versus-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
13、Use4.1 Corrosivity monitoring of test environments provides ameans to monitor an integrated value of test corrosivity whichcannot be evaluated from test parameters themselves, such astemperature, humidity, and gas concentration. As such themonitor value can be used for specification purposes such as
14、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 Test Methods.Current edition approved Oct. 1, 2009. Published December 2009. Originallyapproved in 1997. Last previous edition
15、 approved in 2003 as B826 - 03. DOI:10.1520/B0826-09.2For 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 website.1Copyrig
16、ht ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.test validation. Electrical resistance monitoring of conductorsexposed to corrosive media is a well-established practice.3,4,5,64.2 The resistance method assumes uniform corrosion overthe entir
17、e surface of the exposed metal conductor segment.Local corrosion such as pitting, crevice, or grain boundarycorrosion may provide invalid estimates of test corrosivity.Marked changes in slope of the curve of electrical resistanceratio versus time may indicate undesired processes which canbe due to d
18、eficiencies 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 RM probe when passivating corrosion films are formed,resistance monitoring may not be useful for test chambermonitori
19、ng 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 must be reverified. However, low corrosionrates limit the absolute value of the rate of change of corrosionrate with
20、 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 can be a complex function of testparameters in MFG tests with any given metal primarilyresponsive to a subset of the g
21、ases 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 of resistance ratios must bereferred to ratios obtained under known test conditions assupplied by the test specifier.
22、 Information relating to thesensitivity of various metals to various corrodants has beenpublished.7,84.5 RM probes can be useful from 1 % of thickness con-sumed upward to 50 % of thickness consumed by the corrosionfilm growth. Conductor thicknesses between 25 nm and 0.2mm have been reported and comm
23、on sizes are availablecommercially.5. 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 long conductorpath so as to increase the ease of detection of a resistancechange. W
24、ith 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 productssuch as some copper sulfides, abrupt changes in probe resis-tance can be obse
25、rved 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 electrolyte. Suchshorting behavior is seen as an anomalous resistance decreaseand indicates
26、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 reducing the apparent resistance ratiobetween the exposed conductor and the referen
27、ce 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 for discoloration of the referenceconductor as a signal of possible corrosion of th
28、e 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 curve.5.3 Thermal gradients across the RM probe as a result of thepresence of local
29、 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 or other localized conductor thickness varia-tions can produce anomalous resistance
30、 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 changes indicate the end of useful data from theRM.5.5 Contaminant films on the surface
31、 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. If a cleaning procedure is used, it should be appro-priately evaluated and consistent
32、ly 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 indicate undesirable conditions and potential problemsinterpreting resistance changes
33、.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 being measured. Protection of theelectrical access system from the deleterious effects
34、of expo-sure to corrosive gases is required to ensure a reliable moni-toring system.5.7 Problems due to interferences can be reduced by usingmultiple probes in a single test and comparing outcomesagainst one another.3ASTM G96, Guide for On-Line Monitoring of Corrosion in Plant Equipment(Electrical a
35、nd Electrochemical Methods).4Allen, 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. 67-70.5Murcko, R., Corrosion-Indicating Device, IBM Te
36、chnical Disclosure Bulletin,Vol 32, No.10A, March 1990, p. 25.6Sproles, 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. 11-20.7Rice, D., et.
37、 al., “Atmospheric Corrosion of Copper and Silver,” Journal ofElectrochemical Society, Vol 128, No. 2, February 1981, pp. 275-284.8Rice, D., et al., “Indoor Corrosion of Metals,” Journal of ElectrochemicalSociety, Vol 127, No. 4, April 1980, pp. 891-901.B826 0926. Apparatus6.1 The apparatus consists
38、 of two elements, a probe that isresponsive to the corrosive environment and a means toelectrically measure the resistance of the probe.6.1.1 Resistance Monitor (RM) Probe, consists of twoelements of identical material in thermal contact with eachother. One element is capable of interaction with a c
39、orrosivegas environment and is the detector of test chamber corrosivity.The second 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 c
40、hosenwith regard to the expected amount of corrosion to be detected.Mildly corrosive 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
41、 probes are measured with standardelectrical resistance measurement equipment or with suitablecommercial systems. A Kelvin bridge or a potentiometer shallbe used when measuring resistance less than 10 V. A Wheat-stone bridge may be used with resistances greater than 10 V.The resistance shall be meas
42、ured with an accuracy of 0.1 %.The measuring current shall be so small that the resistancebeing measured changes by less than 0.1 % due to temperaturerise.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 te
43、st facility is unattended.7. Calibration7.1 Calibrate electrical resistance measuring 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.
44、1 Store probes in a glass desiccator after fabrication, freefrom exposure to plastic materials that emit volatile plasticizersor other organic vapors. Handle and store commercial probes inaccordance with the manufacturers instructions. Take care toensure that the exposed metal conductor of the probe
45、 remainsfree of contaminants prior to use in the test chamber forcorrosivity monitoring. Some commercial probes have beensupplied with a removable protective film covering the con-ductor that is to be exposed to the corrosive gases. Users arecautioned that such film have been reported to leave a res
46、iduethat affects the initial sensitivity to a corrosive environment. Ifsuch a film is present, remove this film just before installationof the RM probe in the gaseous corrosion test chamber or otherlocation where corrosivity is to be monitored.8.2 Install probes in the corrosive gas stream within th
47、e testchamber between 4 and 6 cm from the test samples beingevaluated in the test 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
48、rack,nor shall they obstruct the gas flow to any test sample. Theplane of the metal 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.
49、 Thelong axis of the probe shall be perpendicular to the gas flowdirection. The 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 B827.Alternatively, if it is desired to use resistance pr
