ASTM B827-2005(2009)e1 Standard Practice for Conducting Mixed Flowing Gas (MFG) Environmental Tests.pdf

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1、Designation: B 827 05 (Reapproved 2009)1Standard Practice forConducting Mixed Flowing Gas (MFG) Environmental Tests1This standard is issued under the fixed designation B 827; 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 () indicates an editorial change since the last revision or reapproval.1NOTENote 3 and the notes in Table 1 were removed editorially in October 2009.1. Scope1.1 This practice provides procedures fo

3、r conducting envi-ronmental tests involving exposures to controlled quantities ofcorrosive gas mixtures.1.2 This practice provides for the required equipment andmethods for gas, temperature, and humidity control whichenable tests to be conducted in a reproducible manner. Repro-ducibility is measured

4、 through the use of control couponswhose 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 ratemonitors using electrical resistance or mass/frequency changemethods.1.3 The values

5、stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.4 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 hazar

6、ds 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 limitations prior to use. See 5.1.2.4.2. Referenced Documents2

7、.1 ASTM Standards:2B 542 Terminology Relating to Electrical Contacts andTheir UseB 765 Guide for Selection of Porosity and Gross DefectTests for Electrodeposits and Related Metallic CoatingsB 808 Test Method for Monitoring of Atmospheric Corro-sion Chambers by Quartz Crystal MicrobalancesB 810 Test

8、Method for Calibration of Atmospheric Corro-sion Test Chambers by Change in Mass of Copper Cou-ponsB 825 Test Method for Coulometric Reduction of SurfaceFilms on Metallic Test SamplesB 826 Test Method for Monitoring Atmospheric CorrosionTests by Electrical Resistance ProbesB 845 Guide for Mixed Flow

9、ing Gas (MFG) Tests forElectrical ContactsD 1193 Specification for Reagent WaterD 2912 Test Method for Oxidant Content of the Atmo-sphere (Neutral KI)3D 2914 Test Methods for Sulfur Dioxide Content of theAtmosphere (West-Gaeke Method)D 3449 Test Method for Sulfur Dioxide in Workplace At-mospheres (B

10、arium Perchlorate Method)3D 3464 Test Method forAverage Velocity in a Duct Using aThermal AnemometerD 3609 Practice for Calibration Techniques Using Perme-ation TubesD 3824 Test Methods for Continuous Measurement of Ox-ides of Nitrogen in the Ambient or Workplace Atmosphereby the Chemiluminescent Me

11、thodD 4230 Test Method of Measuring Humidity with Cooled-Surface Condensation (Dew-Point) HygrometerE 902 Practice for Checking the Operating Characteristicsof X-Ray Photoelectron SpectrometersG91 Practice for Monitoring Atmospheric SO2Using theSulfation Plate Technique3. Terminology3.1 Definitions

12、relating to electrical contacts are in accor-dance with Terminology B 542.1This practice is under the jurisdiction of ASTM Committee B02 on NonferrousMetals and Alloys and is the direct responsibility of Subcommittee B02.11 onElectrical Contact Test Methods.Current edition approved Oct. 1, 2009. Pub

13、lished October 2009. Originallyapproved in 1992. Last previous edition approved in 2005 as B 827 - 05.2For 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

14、Document Summary page onthe ASTM website.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4. Significance and Use4.1 Mixed flowing gas (MFG) tests are used to simulate oramplify exposure to environmental conditions which el

15、ectricalcontacts or connectors can be expected to experience in variousapplication environments (1, 2).44.2 Test samples which have been exposed to MFG testshave ranged from bare metal surfaces, to electrical connectors,and to complete assemblies.4.3 The specific test conditions are usually chosen s

16、o as tosimulate, in the test laboratory, the effects of certain represen-tative field environments or environmental severity levels onstandard metallic surfaces, such as copper and silver couponsor porous gold platings (1, 2).4.4 Because MFG tests are simulations, both the test con-ditions and the d

17、egradation reactions (chemical reaction rate,composition of reaction products, etc.) may not always re-semble those found in the service environment of the productbeing tested in the MFG test. A guide to the selection ofsimulation conditions suitable for a variety of environments isfound in Guide B

18、845.4.5 The MFG exposures are generally used in conjunctionwith procedures which evaluate contact or connector electricalperformance such as measurement of electrical contact resis-tance before and after MFG exposure.4.6 The MFG tests are useful for connector systems whosecontact surfaces are plated

19、 or clad with gold or other preciousmetal finishes. For such surfaces, environmentally producedfailures are often due to high resistance or intermittencescaused by the formation of insulating contamination in thecontact region. This contamination, in the form of films andhard particles, is generally

20、 the result of pore corrosion andcorrosion product migration or tarnish creepage from pores inthe precious metal coating and from unplated base metalboundaries, if present.4.7 The MFG exposures can be used to evaluate novelelectrical contact metallization for susceptibility to degradationdue to envi

21、ronmental exposure to the test corrosive gases.4.8 The MFG exposures can be used to evaluate theshielding capability of connector housings which may act as abarrier to the ingress of corrosive gases.4.9 The MFG exposures can be used to evaluate thesusceptibility of other connector materials such as

22、plastichousings 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 thefailure mechanism is other than pollutant gas corrosion such asin tin-coat

23、ed separable contacts.5. Apparatus5.1 Apparatus required to conduct MFG tests are dividedinto four major categories, corrosion test chamber, gas supplysystem, chamber monitoring system, and chamber operatingsystem.5.1.1 Corrosion Test Chamber:5.1.1.1 The chamber shall consist of an enclosure made of

24、nonreactive, low-absorbing, nonmetallic materials containedwithin a cabinet or oven capable of maintaining the tempera-ture to a maximum tolerance of 61C with a preferredtolerance held to 60.5C within the usable chamber workingspace accordance with 7.3, with a means to introduce andexhaust gases fro

25、m the chamber.5.1.1.2 The chamber isolates the reactive gases from theexternal environment. Chamber materials that are not low-absorbing can affect test conditions by absorbing or emittingreactive gases, leading to control and reproducibility problems.The chamber construction shall be such that the

26、leak rate is lessthan 3 % of the volume exchange rate.5.1.1.3 The chamber shall have provision for maintaininguniformity of the average gas flow velocity within 620%ofaspecified value or of the chamber average when the chamber isempty. For chambers with a dimension of more than 0.5 m,measurement poi

27、nts shall be in accordance with Test MethodB 810. For chambers with all dimensions of less than 0.5 m, aminimum of five points shall be measured at locations in theplane of sample exposure (perpendicular to the expected flowdirection) that are equidistant from each other and the walls ofthe chamber.

28、After all five or more data values are recorded, allmeasurements shall be repeated a second time. After the twosets of measurements are recorded, a third complete set shall berecorded. The arithmetic average of the 15 or more measure-ments shall be the chamber average. See 7.5 and 7.6.8.Ifahotwire a

29、nemometer is used for gas velocity measurements, itshall be made in accordance with Test Method D 3464, withthe exception that sample sites shall be in accordance with TestMethod B 810.5.1.1.4 A sample access port is desirable. This should bedesigned such that control coupons can be removed or repla

30、cedwithout interrupting the flow of gases. Corrosion test chambercorrosion rates have been shown to be a function of thepresence or absence of light (3, 4). Provision for controlling thetest illumination level in accordance with a test specificationshall be made.5.1.1.5 Examples of test chamber syst

31、ems are diagrammedin Figs. 1-3. They are not to be considered exclusive examples.5.1.2 Gas Supply System:5.1.2.1 Description and RequirementsThe gas supply sys-tem consists of five main parts: a source of clean, dry, filteredair; a humidity source; corrosive gas source(s); gas deliverysystem; and co

32、rrosive gas concentration monitoring system(s).Total supply capacity must be such as to meet requirements forcontrol of gas concentrations. The minimum number of volumechanges is determined by the requirement that the concentra-tion of corrosive gases be maintained within 615 % betweengas inlet and

33、outlet. This is verified by measurement of the gasconcentrations near the gas inlet upstream of the usablechamber working volume and comparing with gas concentra-tions measured downstream of the usable chamber workingvolume just prior to the chamber exhaust; these values shall bewithin 615 % (see 7.

34、6). Alternative methods of demonstratingcompliance with the maximum allowable concentration gradi-ent are acceptable. Normally, a conditioned chamber equili-brates within several hours after sample loading and start of the4The boldface numbers in parentheses refer to the list of references at the en

35、d ofthis standard.B 827 05 (2009)12corrosive gas supply. Times longer than 2 h shall be reported inthe test report; see Section 8. A guide to estimating supplyrequirements is provided in Appendix X1.NOTE 1Guidance: when inlet to outlet concentrations vary by morethan 615 %, it usually indicates an o

36、verloaded chamber.5.1.2.2 Clean, Dry, Filtered Air SourceGases other thanoxygen and nitrogen that are present in the dry air source shallbe less than or equal to those defined by OHSA Class D limitswith the following additional constraint. Gases other thannitrogen, oxygen, carbon dioxide, noble gase

37、s, methane, ni-trous oxide, and hydrogen shall be less than 0.005 (ppm) byvolume total and shall be High Efficiency ParticulateArrestants(HEPA) filtered.5.1.2.3 Humidity SourceThe humidity source shall usedistilled or deionized water, Specification D 1193, Type 1 orbetter, and shall introduce no ext

38、raneous material. The humid-ity source shall be maintained equivalent to SpecificationD 1193 Type II or better, with the exception that electricalresistivity shall be maintained equivalent to SpecificationD 1193 Type IV. The time averaged value of humidity shall bewithin 61 % relative humidity of th

39、e specified value withabsolute variations no greater than 63 % relative humidityfrom the specified value.5.1.2.4 Corrosive Gas SourcesCorrosive (test) gases,such as nitrogen dioxide, hydrogen sulfide, chlorine, sulfurdioxide, etc. shall be of chemically pure5grade or better. Suchgases are frequently

40、 supplied in dry carrier gas such as nitrogenor air. (WarningThis practice involves the use of hazardousmaterials, procedures, and equipment. The gas concentrationsin the test chamber may be within permissible exposure limits(PEL). However, concentrations in the compressed gas cylin-ders or permeati

41、on devices are often above the PEL, and mayexceed the immediately dangerous to life and health level(IDHL). This practice does not address safety issues associatedwith MFG testing.)5.1.2.5 Gas Delivery SystemThe gas delivery system iscomprised of three main parts: gas supply lines, gas controlvalves

42、 and flow controllers, and a mixing chamber. The gasdelivery system shall be capable of delivering gases at therequired concentrations and rates within the test chamber.(1) All materials used for the gas transport system must notinteract with the gases to the extent that chamber gas concen-trations

43、are affected.(2) Gases, make-up air, and water vapor must be thor-oughly mixed before gas delivery to the samples under test inthe chambers. Care must be taken to ensure absence of aerosolformation in the mixing chamber whereby gases are consumedin the formation of particulates which may interfere w

44、ith gasconcentration control and may introduce corrosion processeswhich are not representative of gaseous corrosion mechanisms.Aerosol formation may be detected by the presence of a visiblefilm or deposit on the interior surface of the gas system wherethe gases are mixed.(3) Any fogging of the tubin

45、g walls or mixing chamberwalls can be taken to be an indication of a loss of corrosivegases from the atmosphere. Final mixing of the specified gasesshould occur inside a separate area of, or as close as possibleto, the test chamber so as to ensure thermal equilibration withthe test chamber.(4) Flow

46、measurement capability is required at the inlet ofthe chamber and also at the exhaust of negative pressurechambers to ensure the absence of uncalibrated gas streams.5.1.2.6 Corrosive Gas Concentration Monitoring SystemStandard measurement systems for very low level gas concen-trations are listed in

47、Table 1, which provides for gases incommon use in present mixed flowing gas systems, for testingelectrical contact performance.(1) Each instrument must be characterized for interferencewith the gases specified, both individually and mixed.(2) Depending on the exact equipment set used, it may notbe p

48、ossible to accurately measure the concentration of somegases, such as chlorine, in combination with any of the othergases.(3) The analytic instruments shall be maintained andcalibrated electronically in accordance with the manufacturersrecommendations. Standard gas sources shall also be calibrated5C

49、hemically Pure and Pre-Purified are designations of Matheson Gas Co., EastRutherford, NJ, for specific grades of purity of gas. Other vendors such as AIRCOhave equivalent gas purities available sold under different terminology.FIG. 1 Schematic Flow-Through Mixed Flowing Gas (MFG) TestSystemB 827 05 (2009)13in accordance with the manufacturers specifications, or inaccordance with Practice D 3609. Gas concentration analyzersshall be calibrated to standard gas sources in accordance withthe manufacturers recommendations. They shall be calibratedbefore and after each te