ASTM B826-97
(Test Method)Standard Test Method for Monitoring Atmospheric Corrosion Tests by Electrical Resistance Probes
Standard Test Method for Monitoring Atmospheric Corrosion Tests by Electrical Resistance Probes
SCOPE
1.1 This test method provides a means for monitoring corrosivity of environmental tests that involve exposure to corrosive gases.
1.2 This test method employs a resistance monitor (RM) probe fabricated from a chosen metal conductor, with one conductor segment uncovered to permit exposure of the chosen metal conductor to the corrosive gas mixture and the second conductor segment covered to insulate the metal conductor of this segment from exposure to the corrosive gas mixture. The covered conductor segment provides a reference for evaluating changes in the uncovered segment. The ratio of the resistance of the exposed segment to that of the covered segment provides a measure of the amount of metal conductor which has reacted with the corrosive gas test environment to form poorly conducting corrosion product, thus providing a measure of test corrosivity.
1.3 Resistance monitoring is applicable to a broad range of test conditions by selection of the appropriate metal conductor and initial resistance value.
1.4 This method is similar in intent to Test Methods B808.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
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Designation: B 826 – 97
Standard Test Method for
Monitoring Atmospheric Corrosion Tests by Electrical
Resistance Probes
This standard is issued under the fixed designation B 826; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope Absence of Heat Transfer (Electrical Methods)
1.1 This test method provides a means for monitoring
3. Summary of Test Method
corrosivity of environmental tests that involve exposure to
3.1 The corrosivity of an atmospheric corrosion test such as
corrosive gases.
a mixed flowing gas (MFG) type test is measured by monitor-
1.2 This test method uses a resistance monitor (RM) probe
ing the loss in electrical conductivity of a metal element whose
fabricated from a chosen metal conductor, with one conductor
surface corrodes to form poorly conducting corrosion product.
segment uncovered to permit exposure of the chosen metal
This corrosion product consumes metal from a conduction path
conductor to the corrosive gas mixture and the second conduc-
causing an increase in electrical resistance. The resistance of
tor segment covered to protect the metal conductor of this
the degraded conduction path is compared with a similar path
segment from direct attack by the corrosive gas mixture. The
whose surface is covered to prevent corrosion. This compari-
covered conductor segment provides a reference for evaluating
son resistance also provides a temperature correction reference.
changes in the uncovered segment. The ratio of the resistance
The ratio of the electrical resistance of the path exposed to the
of the exposed segment to that of the covered segment provides
corrosive gases to that of the covered path is monitored during
a measure of the amount of metal conductor that has reacted
the test and compared to an expected ratio-versus-time curve to
with the corrosive gas test environment to form poorly con-
establish the relationship of the test corrosivity to expected test
ducting corrosion product, thus providing a measure of test
corrosivity. Alternatively, the ratio-versus-time curve for a
corrosivity.
given atmosphere can be compared with the behavior of other
1.3 Resistance monitoring is applicable to a broad range of
corrosive atmospheres to evaluate the relative corrosivity of the
test conditions by selection of the appropriate metal conductor
various atmospheres.
and initial metal thickness.
1.4 This method is similar in intent to Test Methods B 808.
4. Significance and Use
1.5 This standard does not purport to address all of the
4.1 Corrosivity monitoring of test environments provides a
safety concerns, if any, associated with its use. It is the
means to monitor an integrated value of test corrosivity which
responsibility of the user of this standard to establish appro-
cannot be evaluated from test parameters themselves, such as
priate safety and health practices to determine the applicability
temperature, humidity, and gas concentration. As such the
of regulatory limitations prior to use.
monitor value can be used for specification purposes such as
test validation. Electrical resistance monitoring of conductors
2. Referenced Documents
exposed to corrosive media is a well-established prac-
2.1 ASTM Standards:
, , , ,
4 5 6 7 8
tice.
B 808 Test Method for Monitoring of Atmospheric Corro-
2 4.2 The resistance method assumes uniform corrosion over
sion Chambers by Quartz Crystal Microbalances
the entire surface of the exposed metal conductor segment.
B 810 Test Methods for Calibration of Atmospheric Corro-
sion Test Chambers by Change in Mass of Copper Cou-
pons Discontinued; see 1990 Annual Book of ASTM Standards, Vol 03.02.
ASTM D 2776, Standard Test Methods for Corrosivity of Water in the Absence
B 827 Practice for Conducting Mixed Flowing Gas (MFG)
of Heat Transfer (Electrical Methods).
Environmental Tests
Allen, R. C. and Trzeciak, M. J., “Measuring Environmental Corrosivity,”
D 2776 Methods of Test for Corrosivity of Water in the
Institute of Electrical and Electronic Engineers, Components, Hybrids, and Manu-
facturing Technology Transaction, Vol CHMT-3, 1, March 1980, pp. 67-70.
Murcko, R., Corrosion-Indicating Device, IBM Technical Disclosure Bulletin,
This test method is under the jurisdiction of ASTM Committee B-2 on
Vol 32, No.10A, March 1990, p. 25.
Nonferrous Metals and Alloys and is the direct responsibility of Subcommittee
ASTM G 96, Guide for On-Line Monitoring of Corrosion in Plant Equipment
B02.11 on Electrical Contact Test Methods.
(Electrical and Electrochemical Methods).
Current edition approved May 10, 1997. Published December 1997.
Sproles, E. S., “Electrical Resistance of Wires Used as a Corrosion Rate
Annual Book of ASTM Standards, Vol 03.04.
Monitor,” Corrosion of Electronic and Magnetic Materials, ASTM STP 1148,P.J.
Peterson, Ed., American Society for Testing and Materials, 1992, pp. 11-20.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
B 826
Local corrosion such as pitting, crevice, or grain boundary ing of the reference conductor can lead to corrosion of the
corrosion may provide invalid estimates of test corrosivity. reference conductor, thus reducing the apparent resistance ratio
Marked changes in slope of the curve of electrical resistance between the exposed conductor and the reference conductor.
ratio versus time may indicate undesired processes which can Excess resistance change of the reference conductor above that
be due to deficiencies in the test atmosphere or in the monitor expected for any observed temperature change of the RM is an
itself. indication of this possible interference. The RM should be
4.3 Because of limitations of the diffusion process within examined after the test for discoloration of the reference
the corrosion product formed on the metal conductor segment conductor as a signal of possible corrosion of the reference
of the RM probe when passivating corrosion films are formed, conductor when such excess resistance change is observed.
resistance monitoring may not be useful for test chamber Presence of corrosion of the reference conductor invalidates
monitoring purposes for very long test exposures. Chamber the estimate of atmosphere corrosivity based on the observed
monitoring is dependent on detecting changes in the rate of resistance ratio-versus-time curve.
corrosion of the RM as an indicator signal that specified gas 5.3 Thermal gradients across the RM probe as a result of the
concentrations must be reverified. However, low corrosion presence of local heat sources such as lamps or powered test
rates limit the absolute value of the rate of change of corrosion devices can produce an anomalous resistance ratio change.
rate with change of test conditions; for parabolic film growth Such effects can be verified by shutting off the local heat source
processes, the growth rate decreases with time limiting the and remeasuring the resistance ratio.
sensitivity of the RM at extended test times. 5.4 Scratches or other localized conductor thickness varia-
4.4 Since corrosion rate can be a complex function of test tions can produce anomalous resistance ratios after reduced
parameters in MFG tests with any given metal primarily corrosion exposures. This behavior can be detected by abrupt
responsive to a subset of the gases in the MFG environment, increases in apparent rate of corrosion which occur when the
more than one type metal resistance probe is required in order thinned region corrodes through to the dielectric substrate.
to assist in maintenance of relative gas concentrations. For Such abrupt changes indicate the end of useful data from the
such test specifications, values of resistance ratios must be RM.
referred to ratios obtained under known test conditions as 5.5 Contaminant films on the surface of the exposed con-
supplied by the test specifier. Information relating to the ductor can inhibit corrosion or accelerate corrosion. Care must
sensitivity of various metals to various corrodants has been be taken to assure freedom from fingerprints, spittle, oil, or
9,10
published. other surface contamination prior to installation in the test
4.5 RM probes can be useful from 1 % of thickness con- chamber. If a cleaning procedure is used, it should be appro-
sumed upward to 50 % of thickness consumed by the corrosion priately evaluated and consistently applied to avoid differing
film growth. Conductor thicknesses between 25 nm and 0.2 initial conditions on the RM. The exposed metal conductor of
mm are commercially available. the probe should be examined after the test exposure to ensure
uniformity of corrosion film growth. Clumps of corrosion
5. Interferences
product indicate undesirable conditions and potential problems
5.1 Resistance monitor probes are generally constructed
interpreting resistance changes.
from thin film metal coatings on dielectric substrates in the
5.6 Since in-situ electrical resistance measurements require
form of a serpentine pattern or loop to provide a long conductor
electrical access to the probe being measured, defects in the
path so as to increase the ease of detection of a resistance
electrical access system, for example, cables and sockets, can
change. With such configurations, formation of a corrosion
affect the resistance values being measured. Protection of the
product, which grows out from the edges of the conductor
electrical access system from the deleterious effects of expo-
paths, can contact adjacent paths; when such contacting cor-
sure to corrosive gases is required to ensure a reliable moni-
rosion films are formed from conducting corrosion products
toring system.
such as some copper sulfides, abrupt changes in probe resis-
5.7 Most interferences are detectable when multiple probes
tance can be observed due to shorting of the current path. Such
are used in a single test by comparison of one probe to another.
shorting of the current path can also occur if condensation
6. Apparatus
occurs on the probe, especially in the presence of gases that
dissolve in the condensed film to fo
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