ASTM G50-2010 Standard Practice for Conducting Atmospheric Corrosion Tests on Metals《大气对金属腐蚀试验的实施标准操作规程》.pdf

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1、Designation: G50 10Standard Practice forConducting Atmospheric Corrosion Tests on Metals1This standard is issued under the fixed designation G50; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of last revision. A number i

2、n parentheses indicates the year of last reapproval. A superscriptepsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice covers and defines conditions for exposureof metals and alloys to the weather. It sets forth the generalprocedures that should b

3、e followed in any atmospheric test. Itis presented as an aid in conducting atmospheric corrosion testsso that some of the pitfalls of such testing may be avoided. Assuch, it is concerned mainly with panel exposures to obtaindata for comparison purposes.1.2 The values stated in inch-pound units are t

4、o be regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of

5、 whoever uses this standard to consult andestablish appropriate safety and health practices and deter-mine the applicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A380 Practice for Cleaning, Descaling, and Passivation ofStainless Steel Parts, Equipment, an

6、d SystemsD2010/D2010M Test Methods for Evaluation of Total Sul-fation Activity in the Atmosphere by the Lead DioxideTechniqueG1 Practice for Preparing, Cleaning, and Evaluating Corro-sion Test SpecimensG33 Practice for Recording Data from Atmospheric Corro-sion Tests of Metallic-Coated Steel Specime

7、nsG46 Guide for Examination and Evaluation of PittingCorrosionG84 Practice for Measurement of Time-of-Wetness on Sur-faces Exposed to Wetting Conditions as in AtmosphericCorrosion TestingG91 Practice for Monitoring Atmospheric SO2Using theSulfation Plate TechniqueG92 Practice for Characterization of

8、 Atmospheric Test SitesG140 Test Method for Determining Atmospheric ChlorideDeposition Rate by Wet Candle Method3. Significance and Use3.1 The procedures described herein can be used to evaluatethe corrosion resistance of metals when exposed to the weather,as well as to evaluate the relative corrosi

9、vity of the atmosphereat specific locations. Because of the variability and complexityof weather effects and the industrial and natural factorsinfluencing the atmospheric corrosivity of a test site, a multi-year exposure period should be considered to minimize theirinfluence.Also, as corrosivity may

10、 vary at a site from season toseason, exposures should be made either at the same time ofthe year to minimize variability or these differences should beestablished by multiple exposures.3.2 Control specimens should always be employed inweathering tests. The control specimens should be from amaterial

11、 having established weathering characteristics. A sub-stantial amount of corrosion data shall have been accumulatedfor the control specimens. It is also good practice to retainsamples of all materials exposed so that possible effects oflong-term aging can be measured.4. Test Sites4.1 Test sites shou

12、ld be chosen at a number of locationsrepresentative of the atmospheric environments where themetals or alloys are likely to be used. If such information is notavailable, the selection should include sites typical of indus-trial, rural, and marine atmospheres. Test site characterization,if needed, sh

13、all be conducted in accordance with Practice G92.4.2 Exposure racks should be located in cleared, well-drained areas such that the exposed specimens will be sub-jected to the full effects of the atmosphere at the location of thetest site. Shadows of trees, buildings, or structures should notfall on

14、the specimens, and local contamination of the atmo-sphere should be avoided, unless the specific influences of suchconditions are intended to be assessed.1This practice is under the jurisdiction of ASTM Committee G01 on Corrosionof Metals and is the direct responsibility of Subcommittee G01.04 on At

15、mosphericCorrosion.Current edition approved Sept. 1, 2010. Published October 2010. Originallyapproved in 1976. Last previous edition approved in 2003 as G5076(2003). DOI:10.1520/G0050-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at servicea

16、stm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United

17、States.4.3 In special cases, the exposure racks may be partiallysheltered to allow accumulation of corrosive materials from theair but at the same time prevent washing by rain. If shelteringis used, its purpose and configuration should be described indetail.4.4 If local pollution effects are to be i

18、nvestigated, thesamples should be exposed at different distances from thesource and at different elevations. Where it is particularlyimportant to obtain corrosion rates involving a micro-environment, samples should be mounted directly on thestructure involved. Suitable attachment must be devised for

19、each case.5. Exposure Racks and Frames5.1 Test racks and frames should be constructed of amaterial that will remain intact for the entire proposed periodof exposure. Galvanized pipe has been found adequate for rackconstruction in most environments (Note 1). Type 304 stainlesssteel is adequate as a f

20、rame material for all environments. Formarine exposures, alloy 400 UNS No. N04400 or Type 316stainless steel has also been successfully used. Aluminum(5052 and 6061-T6) and copper frames also have givensatisfactory service in a wide range of environments. Careshould be observed in the use of copper

21、frames, as corrosionproducts splashed during rainfall might affect the corrosion ofother metals such as aluminum or magnesium.NOTE 1If galvanized pipe is field-threaded, thread areas must beprotected to ensure joint integrity for long exposure periods. In severeenvironments, additional coatings may

22、be required to provide corrosion-free service.5.2 Racks and frames also may be constructed of wood.Insulators may be attached to wooden frames with aluminumbronze, alloy 400, or stainless steel screws. In such a case, nowood sections should be used with dimensions less than 2 by4 in. (50 by 100 mm),

23、 and at least two coats of an exteriorgrade paint or enamel over a suitable primer must be applied.Periodic maintenance will be required on all wood construc-tion.5.3 Solid, glazed, electrical insulator knobs should be usedto hold the specimens on the frames, using stainless steel, alloy400, aluminu

24、m, nylon, or bronze bolts and nuts. Specimensshall be mounted in the grooves of these insulators. In selectingfasteners for use on specific frame materials, care should betaken to avoid unfavorable galvanic relationships.5.4 A suitable frame for mounting the insulators is shown inFig. 1. This frame

25、will accommodate 70 standard 4 by 6-in.(100 by 150-mm) specimens; other sizes can be mounted byrearranging the insulators in the holes provided. It is acceptableto slot the holes in the frames in such a manner that themounting frames are adjustable for specimens of other sizes.This is a convenience

26、when it is not possible to preparespecimens of a preplanned size, and it is often helpful in fittingthe specimens snugly into the frames.5.5 The racks should be designed to give exposure to aslarge an area of the underside of the specimens as possible.Structural members of the rack should not be loc

27、ated directlyunder the specimens where they would shelter the underside ofthe specimens.5.6 As most published data on atmospheric corrosion ofmetals are based on an exposure angle of 30 from thehorizontal, facing south, it is recommended that this angle beused. Racks should be designed so that the l

28、owest specimensare at least 30 in. (760 mm) above the ground. See Notes 2 and3.NOTE 2Maximum exposure to the sun may be obtained by exposingspecimens facing south (for the northern hemisphere) at an angle equal tothe latitude of the test site. Exposure at this angle will yield the lowestcorrosion ra

29、tes for most materials. Although these corrosion rates willchange at other angles of exposure, the order of merit established for eachmaterial will be the same.NOTE 3In special instances, it may be desirable to orient racks andframes in the direction of a specific corrodent source, for example, theo

30、cean, for marine environments. Also, this practice should not beconstrued as prohibiting special orientation of test frames for specific testpurposes, but it is strongly suggested that in such cases testing also bedone in accordance with this practice so that a basis point for comparisonwith availab

31、le data is determined. Any special orientation or preferentialsource of corrosion should be specifically identified in the exposure sitedescription.5.7 Arack of the design and dimensions shown in Fig. 2 willgive the correct exposure angle and can support the specimenframe described in 5.4.5.8 The gr

32、ound under the racks should be kept free ofweeds, bushes, and debris. Organic herbicides, defoliants, orpesticides should not be used for this purpose.6. Test Specimens6.1 When the material to be tested is in sheet form, aspecimen size of 4 by 6 in. (100 by 150 mm) is appropriate.Specimens may be la

33、rger, for example, 4 by 8 in. (100 by 200mm), to suit a particular test; however, the specimens prefer-ably should not be smaller than 4 by 6 in.6.2 To assure adequate rigidity of the specimens on the rack,a minimum thickness of 0.030 in. (0.75 mm) is suggested. Itmay be difficult to accommodate thi

34、cknesses greater than 0.250in. (6.25 mm) in the insulator grooves. (Special deep-throatedinsulators can be obtained to accommodate thicker specimens,or the edges of thicker specimens can be machined to fitstandard insulators.)6.3 When it is desired to test samples of odd shapes, such asbolts, nuts,

35、pipes, angles, assemblies, and structures, etc., ameans of supporting them in the test racks must be devised. Itis important that the specimens be electrically insulated fromtheir respective supports and from each other to preventunintentional galvanic corrosion. However, if desired, galvaniccouples

36、 of dissimilar metals can be exposed on these frames.Efforts should be made to minimize crevices between speci-mens and support materials.6.4 The total number of test specimens required should bedetermined from a knowledge of the duration of the test and theplanned removals of the specimens for inte

37、rmediate evalua-tions. Usually it should not be necessary to remove specimensprior to completing one years exposure, unless specific dataare required for corrosion occurring during earlier stages ofexposure. For reliable results, sufficient specimens should beused for multiple removals at each expos

38、ure period. Triplicatespecimens for each examination period will usually satisfy thisrequirement. A suggested suitable removal schedule is 1, 2, 4,G501028, and 16 years. Removal schedules for tests of differentperiods of total exposure should be adjusted accordingly.6.5 Included with each series of

39、test specimens should be anappropriate number of control specimens, as defined in 3.2.7. Preparation of Test Specimens7.1 Specimens should be identified in a manner that willendure for the life of the test. A good method is the use of aseries of edge notches or drilled holes in the body of thespecim

40、en arranged according to some desired code. Anothermethod is to attach a stainless steel tag by means of aninsulated cord and a suitably located hole. Numbers stampedon the back of the specimen and further protected by coveringwith a good grade of electrical tape is a suitable technique forshort-ter

41、m exposure tests. For materials that do not exhibitsignificant atmospheric corrosion (copper, aluminum, stainlesssteels, etc.), it is sufficient to stamp the identification on theface of the panel.7.2 Oil, grease, and dirt should be removed by degreasingwith a solvent cleaner or scrubbing, or both,

42、to removeinsoluble soils (see Practice G1). Any mill scale or rust shouldbe removed from all ferrous specimens unless it is specificallydesired to perform the test with the mill scale intact. Picklingwith inhibited acid as well as blasting with sand or grit areFIG. 1 Suitable Test FrameG50103accepta

43、ble descaling methods. If acid pickling is used, caremust be taken to stop the pickling action as soon as the millscale and rust have been removed. Stainless steels should bepickled in accordance with Practice A380 to ensure surfacesfree of iron contamination.7.3 Specimens should be weighed to at le

44、ast the nearest 0.01g before exposure. More corrosion-resistant materials arefrequently weighed to the nearest 0.1 mg. When deemedappropriate, the specimens should be photographed to take intoaccount pre-exposure surface defects. Records should be keptof the weight, dimensions, and appearance of eac

45、h specimen atthe beginning of the test. Data to be recorded prior to exposureare explicitly outlined in Practice G33. Changes in the physicalappearance and any corrosion losses of the specimens due toweathering can then be determined. If information on changesin mechanical properties is desired, ini

46、tial measurementsshould be determined on materials in test (see also 3.2). Formaterials that change their mechanical properties on aging atthe temperature of the test site, mechanical properties shall bedetermined on separate specimens stored at that temperaturebut protected from corrosion.8. Proced

47、ure8.1 Mount the specimens on the racks so that they aresupported by the insulators and do not make electrical contactwith each other or with the supporting racks.8.2 Atmospheric factors such as time of wetness of thespecimens, temperature of the specimens, and the concentra-tion of atmospheric cont

48、aminants such as sulfur dioxide andchlorides in the local environment have a great influence on thecorrosion rate of many metals, particularly in the early stagesof exposure. Therefore, if possible, expose the test materials inan environment similar to that to which they will be subjectedin actual u

49、se. Measurement of sulfate levels shall be made inaccordance with Practice G91. Measurement of chloride levelsshall be made in accordance with Practice G140. Measure oftime-of-wetness shall be measured in accordance with PracticeG84.8.3 Periodic observations of weather factors and a means fordetermining atmospheric variables may be incorporated in thetest.3Also see Test Method D2010/D2010M.8.4 Make periodic evaluations as to the conditions of boththe top (skyward) and the bottom (groundward) surfaces,noting whether or not any oxide coating is tightly adhering orif it continues t