ASTM B827-2005(2009)e2 Standard Practice for Conducting Mixed Flowing Gas (MFG) Environmental Tests《传导混流气的环境试验的标准实施规程》.pdf

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1、Designation: B827 05 (Reapproved 2009)2Standard Practice forConducting Mixed Flowing Gas (MFG) Environmental Tests1This standard is issued under the fixed designation B827; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year o

2、f 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 2009.2NOTEFootnote 6 was added editorially in May 2010.

3、1. Scope1.1 This practice provides procedures for 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 r

4、eproducible manner. Repro-ducibility is measured 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

5、 or mass/frequency changemethods.1.3 The values 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 o

6、f 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 limitations pr

7、ior to use. See 5.1.2.4.2. Referenced Documents2.1 ASTM Standards:2B542 Terminology Relating to Electrical Contacts andTheir UseB765 Guide for Selection of Porosity and Gross DefectTests for Electrodeposits and Related Metallic CoatingsB808 Test Method for Monitoring of Atmospheric Corro-sion Chambe

8、rs by Quartz Crystal MicrobalancesB810 Test Method for Calibration of Atmospheric Corro-sion Test Chambers by Change in Mass of Copper Cou-ponsB825 Test Method for Coulometric Reduction of SurfaceFilms on Metallic Test SamplesB826 Test Method for Monitoring Atmospheric CorrosionTests by Electrical R

9、esistance ProbesB845 Guide for Mixed Flowing Gas (MFG) Tests forElectrical ContactsD1193 Specification for Reagent WaterD2912 Test Method for Oxidant Content of the Atmosphere(Neutral KI)3D2914 Test Methods for Sulfur Dioxide Content of theAtmosphere (West-Gaeke Method)D3449 Test Method for Sulfur D

10、ioxide in Workplace At-mospheres (Barium Perchlorate Method)3D3464 Test Method for Average Velocity in a Duct Using aThermal AnemometerD3609 Practice for Calibration Techniques Using Perme-ation TubesD3824 Test Methods for Continuous Measurement of Ox-ides of Nitrogen in the Ambient or Workplace Atm

11、osphereby the Chemiluminescent MethodD4230 Test Method of Measuring Humidity with Cooled-Surface Condensation (Dew-Point) HygrometerE902 Practice for Checking the Operating Characteristics ofX-Ray Photoelectron Spectrometers1This practice is under the jurisdiction of ASTM Committee B02 on Nonferrous

12、Metals and Alloys and is the direct responsibility of Subcommittee B02.11 onElectrical Contact Test Methods.Current edition approved Oct. 1, 2009. Published October 2009. Originallyapproved in 1992. Last previous edition approved in 2005 as B827 - 05. DOI:10.1520/B0827-05R09E02.2For referenced ASTM

13、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.3Withdrawn. The last approved version of this historical standard is referencedon

14、www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.G91 Practice for Monitoring Atmospheric SO2Using theSulfation Plate Technique3. Terminology3.1 Definitions relating to electrical contacts are in accor-dance with Terminolo

15、gy B542.4. Significance and Use4.1 Mixed flowing gas (MFG) tests are used to simulate oramplify exposure to environmental conditions which electricalcontacts or connectors can be expected to experience in variousapplication environments (1, 2).44.2 Test samples which have been exposed to MFG testsha

16、ve ranged from bare metal surfaces, to electrical connectors,and to complete assemblies.4.3 The specific test conditions are usually chosen so as tosimulate, in the test laboratory, the effects of certain represen-tative field environments or environmental severity levels onstandard metallic surface

17、s, 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 degradation reactions (chemical reaction rate,composition of reaction products, etc.) may not always re-semble those found in the service environment of the pro

18、ductbeing tested in the MFG test. A guide to the selection ofsimulation conditions suitable for a variety of environments isfound in Guide B845.4.5 The MFG exposures are generally used in conjunctionwith procedures which evaluate contact or connector electricalperformance such as measurement of elec

19、trical contact resis-tance before and after MFG exposure.4.6 The MFG tests are useful for connector systems whosecontact surfaces are plated or clad with gold or other preciousmetal finishes. For such surfaces, environmentally producedfailures are often due to high resistance or intermittencescaused

20、 by the formation of insulating contamination in thecontact region. This contamination, in the form of films andhard particles, is generally the result of pore corrosion andcorrosion product migration or tarnish creepage from pores inthe precious metal coating and from unplated base metalboundaries,

21、 if present.4.7 The MFG exposures can be used to evaluate novelelectrical contact metallization for susceptibility to degradationdue to environmental 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 abar

22、rier to the ingress of corrosive gases.4.9 The MFG exposures can be used to evaluate thesusceptibility of other connector materials such as 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 Gui

23、de B765.4.11 The MFG tests are generally not applicable where thefailure mechanism is other than pollutant gas corrosion such asin tin-coated separable contacts.5. Apparatus5.1 Apparatus required to conduct MFG tests are dividedinto four major categories, corrosion test chamber, gas supplysystem, ch

24、amber monitoring system, and chamber operatingsystem.5.1.1 Corrosion Test Chamber:5.1.1.1 The chamber shall consist of an enclosure made ofnonreactive, low-absorbing, nonmetallic materials containedwithin a cabinet or oven capable of maintaining the tempera-ture to a maximum tolerance of 61C with a

25、preferredtolerance held to 60.5C within the usable chamber workingspace accordance with 7.3, with a means to introduce andexhaust gases from 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 conditio

26、ns by absorbing or emittingreactive gases, leading to control and reproducibility problems.The chamber construction shall be such that the 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

27、620%ofaspecified value or of the chamber average when the chamber isempty. For chambers with a dimension of more than 0.5 m,measurement points shall be in accordance with Test MethodB810. For chambers with all dimensions of less than 0.5 m, aminimum of five points shall be measured at locations in t

28、heplane of sample exposure (perpendicular to the expected flowdirection) that are equidistant from each other and the walls ofthe chamber.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

29、 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 anemometer is used for gas velocity measurements, itshall be made in accordance with Test Method D3464, with theexception that sample sites shall be in accordance

30、with TestMethod B810.5.1.1.4 A sample access port is desirable. This should bedesigned such that control coupons can be removed or replacedwithout interrupting the flow of gases. Corrosion test chambercorrosion rates have been shown to be a function of thepresence or absence of light (3, 4). Provisi

31、on for controlling thetest illumination level in accordance with a test specificationshall be made.5.1.1.5 Examples of test chamber systems 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

32、consists of five main parts: a source of clean, dry, filteredair; a humidity source; corrosive gas source(s); gas deliverysystem; and corrosive gas concentration monitoring system(s).Total supply capacity must be such as to meet requirements forcontrol of gas concentrations. The minimum number of vo

33、lumechanges is determined by the requirement that the concentra-tion of corrosive gases be maintained within 615 % betweengas inlet and outlet. This is verified by measurement of the gasconcentrations near the gas inlet upstream of the usable4The boldface numbers in parentheses refer to the list of

34、references at the end ofthis standard.B827 05 (2009)22chamber 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 7.6). Alternative methods of demonstratingcompliance w

35、ith the maximum allowable concentration gradi-ent are acceptable. Normally, a conditioned chamber equili-brates within several hours after sample loading and start of thecorrosive gas supply. Times longer than 2 h shall be reported inthe test report; see Section 8. A guide to estimating supplyrequir

36、ements is provided in Appendix X1.NOTE 1Guidance: when inlet to outlet concentrations vary by morethan 615 %, it usually indicates an overloaded 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 tho

37、se defined by OHSA Class D limitswith the following additional constraint. Gases other thannitrogen, oxygen, carbon dioxide, noble gases, 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 Humi

38、dity SourceThe humidity source shall usedistilled or deionized water, Specification D1193,Type1orbetter, and shall introduce no extraneous material. The humid-ity source shall be maintained equivalent to SpecificationD1193 Type II or better, with the exception that electricalresistivity shall be mai

39、ntained equivalent to SpecificationD1193 Type IV. The time averaged value of humidity shall bewithin 61 % relative humidity of the specified value withabsolute variations no greater than 63 % relative humidityfrom the specified value.5.1.2.4 Corrosive Gas SourcesCorrosive (test) gases,such as nitrog

40、en dioxide, hydrogen sulfide, chlorine, sulfurdioxide, etc. shall be of chemically pure5grade or better. Suchgases are frequently supplied in dry carrier gas such as nitrogenor air. (WarningThis practice involves the use of hazardousmaterials, procedures, and equipment. The gas concentrationsin the

41、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 mayexceed the immediately dangerous to life and health level(IDHL). This practice does not address safety issues associatedwith MFG

42、 testing.)5.1.2.5 Gas Delivery SystemThe gas delivery system iscomprised of three main parts: gas supply lines, gas controlvalves and flow controllers,6and a mixing chamber. The gasdelivery system shall be capable of delivering gases at therequired concentrations and rates within the test chamber.(1

43、) All materials used for the gas transport system must notinteract 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 inthe chambers. Care must be taken to ensure a

44、bsence of aerosolformation in the mixing chamber whereby gases are consumedin the formation of particulates which may interfere with gasconcentration control and may introduce corrosion processeswhich are not representative of gaseous corrosion mechanisms.Aerosol formation may be detected by the pre

45、sence of a visiblefilm or deposit on the interior surface of the gas system wherethe gases are mixed.(3) Any fogging of the tubing 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 s

46、eparate area of, or as close as possibleto, the test chamber so as to ensure thermal equilibration withthe test chamber.(4) Flow 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.

47、6 Corrosive Gas Concentration Monitoring SystemStandard measurement systems for very low level gas concen-trations are listed in Table 1, which provides for gases incommon use in present mixed flowing gas systems, for testingelectrical contact performance.(1) Each instrument must be characterized fo

48、r interferencewith the gases specified, both individually and mixed.(2) Depending on the exact equipment set used, it may notbe possible to accurately measure the concentration of somegases, such as chlorine, in combination with any of the othergases.(3) The analytic instruments shall be maintained

49、andcalibrated electronically in accordance with the manufacturers5Chemically 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.6Mass flow controllers are recommended for best results.FIG. 1 Schematic Flow-Through Mixed Flowing Gas (MFG) TestSystemB827 05 (2009)23recommendations. Standard gas sources shall also be calibratedin accordance with the manufacturers specifications, or inaccordance with Prac