ASTM B827-05(2009)e1
(Practice)Standard Practice for Conducting Mixed Flowing Gas (MFG) Environmental Tests
Standard Practice for Conducting Mixed Flowing Gas (MFG) Environmental Tests
SIGNIFICANCE AND USE
Mixed flowing gas (MFG) tests are used to simulate or amplify exposure to environmental conditions which electrical contacts or connectors can be expected to experience in various application environments (1, 2).
Test samples which have been exposed to MFG tests have ranged from bare metal surfaces, to electrical connectors, and to complete assemblies.
The specific test conditions are usually chosen so as to simulate, in the test laboratory, the effects of certain representative field environments or environmental severity levels on standard metallic surfaces, such as copper and silver coupons or porous gold platings (1, 2).
Because MFG tests are simulations, both the test conditions and the degradation reactions (chemical reaction rate, composition of reaction products, etc.) may not always resemble those found in the service environment of the product being tested in the MFG test. A guide to the selection of simulation conditions suitable for a variety of environments is found in Guide B 845.
The MFG exposures are generally used in conjunction with procedures which evaluate contact or connector electrical performance such as measurement of electrical contact resistance before and after MFG exposure.
The MFG tests are useful for connector systems whose contact surfaces are plated or clad with gold or other precious metal finishes. For such surfaces, environmentally produced failures are often due to high resistance or intermittences caused by the formation of insulating contamination in the contact region. This contamination, in the form of films and hard particles, is generally the result of pore corrosion and corrosion product migration or tarnish creepage from pores in the precious metal coating and from unplated base metal boundaries, if present.
The MFG exposures can be used to evaluate novel electrical contact metallization for susceptibility to degradation due to environmental exposure to the test corrosive gases.
The MFG exposures can be u...
SCOPE
1.1 This practice provides procedures for conducting environmental tests involving exposures to controlled quantities of corrosive gas mixtures.
1.2 This practice provides for the required equipment and methods for gas, temperature, and humidity control which enable tests to be conducted in a reproducible manner. Reproducibility is measured through the use of control coupons whose corrosion films are evaluated by mass gain, coulometry, or by various electron and X-ray beam analysis techniques. Reproducibility can also be measured by in situ corrosion rate monitors using electrical resistance or mass/frequency change methods.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 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 become familiar with all hazards including those identified in the appropriate Material Safety Data Sheet (MSDS) for this product/material as provided by the manufacturer, to establish appropriate safety and health practices, and determine the applicability of regulatory limitations prior to use. See 5.1.2.4.
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´1
Designation:B827–05(Reapproved2009)
Standard Practice for
Conducting Mixed Flowing Gas (MFG) Environmental Tests
This standard is issued under the fixed designation B827; 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 (´) indicates an editorial change since the last revision or reapproval.
´ NOTE—Note 3 and the notes in Table 1 were removed editorially in October 2009.
1. Scope B542 Terminology Relating to Electrical Contacts and
Their Use
1.1 This practice provides procedures for conducting envi-
B765 Guide for Selection of Porosity and Gross Defect
ronmental tests involving exposures to controlled quantities of
Tests for Electrodeposits and Related Metallic Coatings
corrosive gas mixtures.
B808 Test Method for Monitoring of Atmospheric Corro-
1.2 This practice provides for the required equipment and
sion Chambers by Quartz Crystal Microbalances
methods for gas, temperature, and humidity control which
B810 Test Method for Calibration of Atmospheric Corro-
enable tests to be conducted in a reproducible manner. Repro-
sion Test Chambers by Change in Mass of Copper Cou-
ducibility is measured through the use of control coupons
pons
whose corrosion films are evaluated by mass gain, coulometry,
B825 Test Method for Coulometric Reduction of Surface
or by various electron and X-ray beam analysis techniques.
Films on Metallic Test Samples
Reproducibility can also be measured by in situ corrosion rate
B826 Test Method for Monitoring Atmospheric Corrosion
monitors using electrical resistance or mass/frequency change
Tests by Electrical Resistance Probes
methods.
B845 Guide for Mixed Flowing Gas (MFG) Tests for
1.3 The values stated in SI units are to be regarded as
Electrical Contacts
standard. No other units of measurement are included in this
D1193 Specification for Reagent Water
standard.
D2912 Test Method for Oxidant Content of theAtmosphere
1.4 This standard does not purport to address all of the
(Neutral KI)
safety concerns, if any, associated with its use. It is the
D2914 Test Methods for Sulfur Dioxide Content of the
responsibility of the user of this standard to become familiar
Atmosphere (West-Gaeke Method)
with all hazards including those identified in the appropriate
D3449 Test Method for Sulfur Dioxide in Workplace At-
Material Safety Data Sheet (MSDS) for this product/material
mospheres (Barium Perchlorate Method)
as provided by the manufacturer, to establish appropriate
D3464 Test Method forAverage Velocity in a Duct Using a
safety and health practices, and determine the applicability of
Thermal Anemometer
regulatory limitations prior to use. See 5.1.2.4.
D3609 Practice for Calibration Techniques Using Perme-
2. Referenced Documents
ation Tubes
D3824 Test Methods for Continuous Measurement of Ox-
2.1 ASTM Standards:
ides of Nitrogen in theAmbient orWorkplaceAtmosphere
by the Chemiluminescent Method
This practice is under the jurisdiction ofASTM Committee B02 on Nonferrous D4230 Test Method of Measuring Humidity with Cooled-
Metals and Alloys and is the direct responsibility of Subcommittee B02.11 on
Surface Condensation (Dew-Point) Hygrometer
Electrical Contact Test Methods.
E902 PracticeforCheckingtheOperatingCharacteristicsof
Current edition approved Oct. 1, 2009. Published October 2009. Originally
X-Ray Photoelectron Spectrometers
approved in 1992. Last previous edition approved in 2005 as B827 - 05. DOI:
10.1520/B0827-05R09E01.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Withdrawn. The last approved version of this historical standard is referenced
the ASTM website. on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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B827–05 (2009)
G91 Practice for Monitoring Atmospheric SO Using the 5. Apparatus
Sulfation Plate Technique
5.1 Apparatus required to conduct MFG tests are divided
into four major categories, corrosion test chamber, gas supply
3. Terminology
system, chamber monitoring system, and chamber operating
3.1 Definitions relating to electrical contacts are in accor-
system.
dance with Terminology B542.
5.1.1 Corrosion Test Chamber:
5.1.1.1 The chamber shall consist of an enclosure made of
4. Significance and Use
nonreactive, low-absorbing, nonmetallic materials contained
4.1 Mixed flowing gas (MFG) tests are used to simulate or
within a cabinet or oven capable of maintaining the tempera-
amplify exposure to environmental conditions which electrical
ture to a maximum tolerance of 61°C with a preferred
contactsorconnectorscanbeexpectedtoexperienceinvarious
tolerance held to 60.5°C within the usable chamber working
application environments (1, 2).
space accordance with 7.3, with a means to introduce and
4.2 Test samples which have been exposed to MFG tests
exhaust gases from the chamber.
have ranged from bare metal surfaces, to electrical connectors,
5.1.1.2 The chamber isolates the reactive gases from the
and to complete assemblies.
external environment. Chamber materials that are not low-
4.3 The specific test conditions are usually chosen so as to
absorbing can affect test conditions by absorbing or emitting
simulate, in the test laboratory, the effects of certain represen-
reactive gases, leading to control and reproducibility problems.
tative field environments or environmental severity levels on
Thechamberconstructionshallbesuchthattheleakrateisless
standard metallic surfaces, such as copper and silver coupons
than 3 % of the volume exchange rate.
or porous gold platings (1, 2).
4.4 Because MFG tests are simulations, both the test con- 5.1.1.3 The chamber shall have provision for maintaining
ditions and the degradation reactions (chemical reaction rate, uniformity of the average gas flow velocity within 620%ofa
composition of reaction products, etc.) may not always re- specified value or of the chamber average when the chamber is
semble those found in the service environment of the product empty. For chambers with a dimension of more than 0.5 m,
measurement points shall be in accordance with Test Method
being tested in the MFG test. A guide to the selection of
simulation conditions suitable for a variety of environments is B810. For chambers with all dimensions of less than 0.5 m, a
found in Guide B845. minimum of five points shall be measured at locations in the
4.5 The MFG exposures are generally used in conjunction plane of sample exposure (perpendicular to the expected flow
with procedures which evaluate contact or connector electrical direction) that are equidistant from each other and the walls of
performance such as measurement of electrical contact resis- the chamber.After all five or more data values are recorded, all
tance before and after MFG exposure. measurements shall be repeated a second time. After the two
4.6 The MFG tests are useful for connector systems whose setsofmeasurementsarerecorded,athirdcompletesetshallbe
contact surfaces are plated or clad with gold or other precious recorded. The arithmetic average of the 15 or more measure-
metal finishes. For such surfaces, environmentally produced ments shall be the chamber average. See 7.5 and 7.6.8.Ifahot
failures are often due to high resistance or intermittences wire anemometer is used for gas velocity measurements, it
caused by the formation of insulating contamination in the shall be made in accordance withTest Method D3464, with the
contact region. This contamination, in the form of films and exception that sample sites shall be in accordance with Test
hard particles, is generally the result of pore corrosion and Method B810.
corrosion product migration or tarnish creepage from pores in
5.1.1.4 A sample access port is desirable. This should be
the precious metal coating and from unplated base metal
designedsuchthatcontrolcouponscanberemovedorreplaced
boundaries, if present.
without interrupting the flow of gases. Corrosion test chamber
4.7 The MFG exposures can be used to evaluate novel
corrosion rates have been shown to be a function of the
electricalcontactmetallizationforsusceptibilitytodegradation
presenceorabsenceoflight(3,4).Provisionforcontrollingthe
due to environmental exposure to the test corrosive gases.
test illumination level in accordance with a test specification
4.8 The MFG exposures can be used to evaluate the
shall be made.
shielding capability of connector housings which may act as a
5.1.1.5 Examples of test chamber systems are diagrammed
barrier to the ingress of corrosive gases.
in Figs. 1-3.They are not to be considered exclusive examples.
4.9 The MFG exposures can be used to evaluate the
5.1.2 Gas Supply System:
susceptibility of other connector materials such as plastic
5.1.2.1 Description and Requirements—Thegassupplysys-
housings to degradation from the test corrosive gases.
tem consists of five main parts: a source of clean, dry, filtered
4.10 The MFG tests are not normally used as porosity tests.
air; a humidity source; corrosive gas source(s); gas delivery
For a guide to porosity testing, see Guide B765.
system; and corrosive gas concentration monitoring system(s).
4.11 The MFG tests are generally not applicable where the
Total supply capacity must be such as to meet requirements for
failure mechanism is other than pollutant gas corrosion such as
controlofgasconcentrations.Theminimumnumberofvolume
in tin-coated separable contacts.
changes is determined by the requirement that the concentra-
tion of corrosive gases be maintained within 615 % between
gas inlet and outlet. This is verified by measurement of the gas
The boldface numbers in parentheses refer to the list of references at the end of
this standard. concentrations near the gas inlet upstream of the usable
´1
B827–05 (2009)
absolute variations no greater than 63 % relative humidity
from the specified value.
5.1.2.4 Corrosive Gas Sources—Corrosive (test) gases,
such as nitrogen dioxide, hydrogen sulfide, chlorine, sulfur
dioxide, etc. shall be of chemically pure grade or better. Such
gasesarefrequentlysuppliedindrycarriergassuchasnitrogen
or air. (Warning—This practice involves the use of hazardous
materials, procedures, and equipment. The gas concentrations
in the test chamber may be within permissible exposure limits
(PEL). However, concentrations in the compressed gas cylin-
ders or permeation devices are often above the PEL, and may
exceed the immediately dangerous to life and health level
(IDHL).This practice does not address safety issues associated
with MFG testing.)
5.1.2.5 Gas Delivery System—The gas delivery system is
comprised of three main parts: gas supply lines, gas control
valves and flow controllers, and a mixing chamber. The gas
delivery system shall be capable of delivering gases at the
required concentrations and rates within the test chamber.
(1) All materials used for the gas transport system must not
interact with the gases to the extent that chamber gas concen-
trations are affected.
(2) Gases, make-up air, and water vapor must be thor-
oughly mixed before gas delivery to the samples under test in
the chambers. Care must be taken to ensure absence of aerosol
formation in the mixing chamber whereby gases are consumed
in the formation of particulates which may interfere with gas
FIG. 1 Schematic Flow-Through Mixed Flowing Gas (MFG) Test
concentration control and may introduce corrosion processes
System
whicharenotrepresentativeofgaseouscorrosionmechanisms.
Aerosol formation may be detected by the presence of a visible
film or deposit on the interior surface of the gas system where
chamber working volume and comparing with gas concentra-
the gases are mixed.
tions measured downstream of the usable chamber working
(3) Any fogging of the tubing walls or mixing chamber
volume just prior to the chamber exhaust; these values shall be
walls can be taken to be an indication of a loss of corrosive
within 615 % (see 7.6).Alternative methods of demonstrating
gases from the atmosphere. Final mixing of the specified gases
compliance with the maximum allowable concentration gradi-
should occur inside a separate area of, or as close as possible
ent are acceptable. Normally, a conditioned chamber equili-
to, the test chamber so as to ensure thermal equilibration with
brateswithinseveralhoursaftersampleloadingandstartofthe
the test chamber.
corrosivegassupply.Timeslongerthan2hshallbereportedin
(4) Flow measurement capability is required at the inlet of
the test report; see Section 8. A guide to estimating supply
the chamber and also at the exhaust of negative pressure
requirements is provided in Appendix X1.
chambers to ensure the absence of uncalibrated gas streams.
NOTE 1—Guidance: when inlet to outlet concentrations vary by more
5.1.2.6 Corrosive Gas Concentration Monitoring System—
than 615 %, it usually indicates an overloaded chamber.
Standard measurement systems for very low level gas concen-
5.1.2.2 Clean, Dry, Filtered Air Source—Gases other than
trations are listed in Table 1, which provides for gases in
oxygen and nitrogen that are present in the dry air source shall
common use in present mixed flowing gas systems, for testing
be less than or equal to those defined by OHSAClass D limits
electrical contact performance.
with the following additional constraint. Gases other than
(1) Each instrument must be characterized for interference
nitrogen, oxygen, carbon dioxide, noble gases, methane, ni-
with the gases specified, both individually and mixed.
trous oxide, and hydrogen shall be less than 0.005 (ppm) by
(2) Depending on the exact equipment set used, it may not
volumetotalandshallbeHighEfficiencyParticulateArrestants
be possible to accurately measure the concentration of some
(HEPA) filtered.
gases, such as chlorine, in combination with any of the other
5.1.2.3 Humidity Source—The humidity source shall use
gases.
distilled or deionized water, Specification D1193,Type1or
(3) The analytic instruments shall be maintained and
better, and shall introduce no extraneous material. The humid-
calibrated electronically in accordance with the manufacturers’
ity source shall be maintained equivalent to Specification
D1193 Type II or better, with the exception that electrical
resistivity shall be maintained equivalent to Specification
Chemically Pure and Pre-Purified are designations of Matheson Gas Co., East
D1193 Type IV. The time averaged value of humidity shall be
Rutherford, NJ, for specific grades of purity of gas.
...
This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation:B827–97(Reapproved2003) Designation:B827–05(Reapproved2009)
Standard Practice for
Conducting Mixed Flowing Gas (MFG) Environmental Tests
This standard is issued under the fixed designation B 827; 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 (´) indicates an editorial change since the last revision or reapproval.
´ NOTE—Note 3 and the notes in Table 1 were removed editorially in October 2009.
1. Scope
1.1 This practice provides procedures for conducting environmental tests involving exposures to controlled quantities of
corrosive gas mixtures.
1.2 Thispracticeprovidesfortherequiredequipmentandmethodsforgas,temperature,andhumiditycontrolwhichenabletests
to be conducted in a reproducible manner. Reproducibility is measured through the use of control coupons whose corrosion films
are evaluated by mass gain, coulometry, or by various electron and X-ray beam analysis techniques. Reproducibility can also be
measured by in situ corrosion rate monitors using electrical resistance or mass/frequency change methods.
1.3The values stated in SI units are to be regarded as the standard.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 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 become familiar with all hazards including those identified in the appropriate Material Safety Data
Sheet (MSDS) for this product/material as provided by the manufacturer, to establish appropriate safety and health practices, and
determine the applicability of regulatory limitations prior to use. See 5.1.2.4.
2. Referenced Documents
2.1 ASTM Standards:
B 542 Terminology Relating to Electrical Contacts and Their Use
B 765 Guide for Selection of Porosity and Gross Defect Tests for Electrodeposits and Related Metallic Coatings
B 808 Test Method for Monitoring of Atmospheric Corrosion Chambers by Quartz Crystal Microbalances
B 810 Test Method for Calibration of Atmospheric Corrosion Test Chambers by Change in Mass of Copper Coupons
B 825 Test Method for Coulometric Reduction of Surface Films on Metallic Test Samples
B 826 Test Method for Monitoring Atmospheric Corrosion Tests by Electrical Resistance Probes
B 845 Guide for Mixed Flowing Gas (MFG) Tests for Electrical Contacts
D 1193 Specification for Reagent Water
D1607Test Method for Nitrogen Dioxide Content of the Atmosphere (Griess-Saltzman Reaction) Specification for Reagent
Water
D 2912 Test Method for Oxidant Content of the Atmosphere (Neutral KI)
D 2914 Test Methods for Sulfur Dioxide Content of the Atmosphere (West-Gaeke Method)
D 3449 Test Method for Sulfur Dioxide in Workplace Atmospheres (Barium Perchlorate Method)
D 3464 Test Method for Average Velocity in a Duct Using a Thermal Anemometer
D 3609 Practice for Calibration Techniques Using Permeation Tubes
D 3824 Test Methods for Continuous Measurement of Oxides of Nitrogen in the Ambient or Workplace Atmosphere by the
Chemiluminescent Method
D 4230 Test Method of Measuring Humidity Withwith Cooled-Surface Condensation (Dew-Point) Hygrometer
E 902 Practice for Checking the Operating Characteristics of X-Ray Photoelectron Spectrometers
G91 Practice for Monitoring Atmospheric SO Using the Sulfation Plate Technique
This practice is under the jurisdiction ofASTM Committee B02 on Nonferrous Metals andAlloys and is the direct responsibility of Subcommittee B02.11 on Electrical
Contact Test Methods.
Current edition approved June 10, 2003. Published July 2003. Originally approved in 1992. Last previous edition approved in 1997 as B827-97.
Current edition approved Oct. 1, 2009. Published October 2009. Originally approved in 1992. Last previous edition approved in 2005 as B 827 - 05.
For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
, Vol 02.04.volume information, refer to the standard’s Document Summary page on the ASTM website.
Withdrawn.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
´1
B827–05 (2009)
3. Terminology
3.1 Definitions relating to electrical contacts are in accordance with Terminology B 542.
4. Significance and Use
4.1 Mixed flowing gas (MFG) tests are used to simulate or amplify exposure to environmental conditions which electrical
contacts or connectors can be expected to experience in various application environments (1, 2).
4.2 Test samples which have been exposed to MFG tests have ranged from bare metal surfaces, to electrical connectors, and
to complete assemblies.
4.3 The specific test conditions are usually chosen so as to simulate, in the test laboratory, the effects of certain representative
fieldenvironmentsorenvironmentalseveritylevelsonstandardmetallicsurfaces,suchascopperandsilvercouponsorporousgold
platings (1, 2).
4.4 Because MFG tests are simulations, both the test conditions and the degradation reactions (chemical reaction rate,
compositionofreactionproducts,etc.)maynotalwaysresemblethosefoundintheserviceenvironmentoftheproductbeingtested
in the MFG test. A guide to the selection of simulation conditions suitable for a variety of environments is found in Guide
B845.B 845.
4.5 The MFG exposures are generally used in conjunction with procedures which evaluate contact or connector electrical
performance such as measurement of electrical contact resistance before and after MFG exposure.
4.6 The MFG tests are useful for connector systems whose contact surfaces are plated or clad with gold or other precious metal
finishes. For such surfaces, environmentally produced failures are often due to high resistance or intermittences caused by the
formationofinsulatingcontaminationinthecontactregion.Thiscontamination,intheformoffilmsandhardparticles,isgenerally
the result of pore corrosion and corrosion product migration or tarnish creepage from pores in the precious metal coating and from
unplated base metal boundaries, if present.
4.7 The MFG exposures can be used to evaluate novel electrical contact metallization for susceptibility to degradation due to
environmental exposure to the test corrosive gases.
4.8 The MFG exposures can be used to evaluate the shielding capability of connector housings which may act as a barrier to
the ingress of corrosive gases.
4.9 The MFG exposures can be used to evaluate the susceptibility of other connector materials such as plastic housings to
degradation from the test corrosive gases.
4.10 The MFG tests are not normally used as porosity tests. For a guide to porosity testing, see Guide B 765.
4.11 The MFG tests are generally not applicable where the failure mechanism is other than pollutant gas corrosion such as in
tin-coated separable contacts.
5. Apparatus
5.1 ApparatusrequiredtoconductMFGtestsaredividedintofourmajorcategories,corrosiontestchamber,gassupplysystem,
chamber monitoring system, and chamber operating system.
5.1.1 Corrosion Test Chamber:
5.1.1.1 The chamber shall consist of an enclosure made of nonreactive, low-absorbing, nonmetallic materials contained within
a cabinet or oven capable of maintaining the temperature to a maximum tolerance of 61°C with a preferred tolerance held to
60.5°C within the usable chamber working space accordance with 7.3, with a means to introduce and exhaust gases from the
chamber.
5.1.1.2 The chamber isolates the reactive gases from the external environment. Chamber materials that are not low-absorbing
can affect test conditions by absorbing or emitting reactive gases, leading to control and reproducibility problems. The chamber
construction shall be such that the leak rate is less than 3 % of the volume exchange rate.
5.1.1.3 The chamber shall have provision for maintaining uniformity of the average gas flow velocity within 620%ofa
specified value or of the chamber average when the chamber is empty. For chambers with a dimension of more than 0.5 m,
measurement points shall be in accordance with Test Method B 810. For chambers with all dimensions of less than 0.5 m, a
minimum of five points shall be measured at locations in the plane of sample exposure (perpendicular to the expected flow
direction) that are equidistant from each other and the walls of the chamber. After all five or more data values are recorded, all
measurements shall be repeated a second time. After the two sets of measurements are recorded, a third complete set shall be
recorded. The arithmetic average of the 15 or more measurements shall be the chamber average. See 7.5 and 7.6.8. If a hot wire
anemometer is used for gas velocity measurements, it shall be made in accordance with Test Method D 3464, with the exception
that sample sites shall be in accordance with Test Method B 810.
5.1.1.4 A sample access port is desirable. This should be designed such that control coupons can be removed or replaced
without interrupting the flow of gases. Corrosion test chamber corrosion rates have been shown to be a function of the presence
or absence of light (3, 4). Provision for controlling the test illumination level in accordance with a test specification shall be made.
Annual Book of ASTM Standards, Vol 11.01.
The boldface numbers in parentheses refer to the list of references at the end of this standard.
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B827–05 (2009)
5.1.1.5 Examples of test chamber systems are diagrammed in Figs. 1-3. They are not to be considered exclusive examples.
5.1.2 Gas Supply System:
5.1.2.1 Description and Requirements —The gas supply system consists of five main parts: a source of clean, dry, filtered air;
a humidity source; corrosive gas source(s); gas delivery system; and corrosive gas concentration monitoring system(s). Total
supply capacity must be such as to meet requirements for control of gas concentrations.The minimum number of volume changes
is determined by the requirement that the concentration of corrosive gases be maintained within 615 % between gas inlet and
outlet.Thisisverifiedbymeasurementofthegasconcentrationsnearthegasinletupstreamoftheusablechamberworkingvolume
and comparing with gas concentrations measured downstream of the usable chamber working volume just prior to the chamber
exhaust; these values shall be within 615 % (see 7.6). Alternative methods of demonstrating compliance with the maximum
allowable concentration gradient are acceptable. Normally, a conditioned chamber equilibrates within several hours after sample
loading and start of the corrosive gas supply. Times longer than 2 h shall be reported in the test report; see Section 8. A guide to
estimating supply requirements is provided in Appendix X1.
NOTE 1—Guidance: when inlet to outlet concentrations vary by more than 615 %, it usually indicates an overloaded chamber.
5.1.2.2 Clean, Dry, Filtered Air Source—Gases other than oxygen and nitrogen that are present in the dry air source shall be
less than or equal to those defined by OHSA Class D limits with the following additional constraint. Gases other than nitrogen,
oxygen, carbon dioxide, noble gases, methane, nitrous oxide, and hydrogen shall be less than 0.005 (ppm) by volume total and
shall be High Efficiency Particulate Arrestants (HEPA) filtered.
5.1.2.3 Humidity Source—The humidity source shall use distilled or deionized water, Specification D 1193, Type 1 or better,
and shall introduce no extraneous material. The humidity source shall be maintained equivalent to Specification D 1193 Type II
or better, with the exception that electrical resistivity shall be maintained equivalent to Specification D 1193Type IV. The time
averaged value of humidity shall be within 61 % relative humidity of the specified value with absolute variations no greater than
63 % relative humidity from the specified value.
5.1.2.4 Corrosive Gas Sources—Corrosive (test) gases, such as nitrogen dioxide, hydrogen sulfide, chlorine, sulfur dioxide, etc.
shall be of chemically puregrade or better. Such gases are frequently supplied in a carrier gas such as nitrogen which shall be of
10 5
Pre-Purified grade or better. ( grade or better. Such gases are frequently supplied in dry carrier gas such as nitrogen or
air. (Warning—This practice involves the use of hazardous materials, procedures, and equipment. The gas concentrations
Annual Book of ASTM Standards, Vol 11.03.
FIG. 1 Schematic Flow-Through Mixed Flowing Gas (MFG) Test
System
´1
B827–05 (2009)
FIG. 2 Schematic Vertical Recirculating Mixed Flowing Gas (MFG) Test System
FIG. 3 Schematic Horizontal Recirculating Mixed Flowing Gas (MFG) Test System
in the test chamber may be within permissible exposure limits (PEL). However, concentrations in the compressed gas
cylindersorpermeationdevicesareoftenabovethePEL,andmayexceedtheimmediatelydangeroustolifeandhealthlevel
(IDHL). This practice does not address safety issues associated with MFG testing.)
5.1.2.5 Gas Delivery System—The gas delivery system is comprised of three main parts: gas supply lines, gas control valves
and flow controllers, and a mixing chamber. The gas delivery system shall be capable of delivering gases at the required
concentrations and rates within the test chamber.
(1)Allmaterialsusedforthegastransportsystemmustnotinteractwiththegasestotheextentthatchambergasconcentrations
are affected.
Chemically Pure and Pre-Purified are designations of Matheson Gas Co., East Rutherford, NJ, for specific grades of purity of gas. Other vendors such as AIRCO have
equivalent gas purities available sold under different terminology.
´1
B827–05 (2009)
(2) Gases, make-up air, and water vapor must be thoroughly mixed before gas delivery to the samples under test in the
chambers. Care must be taken to ensure absence of aerosol formation in the mixing chamber whereby gases are consumed in the
formation of particulates which may interfere with gas concentration control and may introduce corrosion processes which are not
representative of gaseous corrosion mechanisms. Aerosol formation may be detected by the presence of a visible film or deposit
on the interior surface of the gas system where the gas
...
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