ASTM G50-20

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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.
Designation: G50 − 10 (Reapproved 2015) G50 − 20
Standard Practice for
Conducting Atmospheric Corrosion Tests on Metals
This standard is issued under the fixed designation G50; 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.
1. Scope
1.1 This practice covers and defines conditions for exposure of metals and alloys to the weather. It sets forth the general procedures
that should be followed in any atmospheric test. It is presented as an aid in conducting atmospheric corrosion tests so that some
of the pitfalls of such testing may be avoided. As such, it is concerned mainly with panel exposures to obtain data for comparison
purposes.
1.2 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of whoever uses this standard to consult and establish appropriate safety safety, health, and healthenvironmental practices and
determine the applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
A380A380/A380M Practice for Cleaning, Descaling, and Passivation of Stainless Steel Parts, Equipment, and Systems
D2010/D2010M Test Methods for Evaluation of Total Sulfation Activity in the Atmosphere by the Lead Dioxide Technique
G1 Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
G33 Practice for Recording Data from Atmospheric Corrosion Tests of Metallic-Coated Steel Specimens
G46 Guide for Examination and Evaluation of Pitting Corrosion
G84 Practice for Measurement of Time-of-Wetness on Surfaces Exposed to Wetting Conditions as in Atmospheric Corrosion
Testing
G91 Practice for Monitoring Atmospheric SO Deposition Rate for Atmospheric Corrosivity Evaluation
G92 Practice for Characterization of Atmospheric Test Sites
G140 Test Method for Determining Atmospheric Chloride Deposition Rate by Wet Candle Method
3. Significance and Use
3.1 The procedures described herein can be used to evaluate the corrosion resistance of metals when exposed to the weather, as
This practice is under the jurisdiction of ASTM Committee G01 on Corrosion of Metals and is the direct responsibility of Subcommittee G01.04 on Atmospheric
CorrosionCorrosion of Metals in Natural Atmospheric and Aqueous Environments.
Current edition approved Nov. 1, 2015Nov. 1, 2020. Published December 2015November 2020. Originally approved in 1976. Last previous edition approved in 20102015
as G50G50–10(2015).–10. DOI: 10.1520/G0050-10R15.10.1520/G0050-20.
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’sstandard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G50 − 20
well as to evaluate the relative corrosivity of the atmosphere at specific locations. Because of the variability and complexity of
weather effects and the industrial and natural factors influencing the atmospheric corrosivity of a test site, a multi-year exposure
period should be considered to minimize their influence. Also, as corrosivity may vary at a site from season to season, exposures
should be made either at the same time of the year to minimize variability or these differences should be established by multiple
exposures.
3.2 Control specimens should always be employed in weathering tests. The control specimens should be from a material having
established weathering characteristics. A substantial amount of corrosion data shall have been accumulated for the control
specimens. It is also good practice to retain samples of all materials exposed so that possible effects of long-term aging can be
measured.
4. Test Sites
4.1 Test sites should be chosen at a number of locations representative of the atmospheric environments where the metals or alloys
are likely to be used. If such information is not available, the selection should include sites typical of industrial, rural, and marine
atmospheres. Test site characterization, if needed, shall 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 subjected to the full
effects of the atmosphere at the location of the test site. Shadows of trees, buildings, or structures should not fall on the specimens,
and local contamination of the atmosphere should be avoided, unless the specific influences of such conditions are intended to be
assessed.
4.3 In special cases, the exposure racks may be partially sheltered to allow accumulation of corrosive materials from the air but
at the same time prevent washing by rain. If sheltering is used, its purpose and configuration should be described in detail.
4.4 If local pollution effects are to be investigated, the samples should be exposed at different distances from the source and at
different elevations. Where it is particularly important to obtain corrosion rates involving a micro-environment, samples should be
mounted directly on the structure involved. Suitable attachment must be devised for each case.
5. Exposure Racks and Frames
5.1 Test racks and frames should be constructed of a material that will remain intact for the entire proposed period of exposure.
Galvanized pipe has been found adequate for rack construction in most environments (Note 1). Type 304 stainless steel is adequate
as a frame material for all environments. For marine exposures, alloy 400 UNS No. N04400 or Type 316 stainless steel has also
been successfully used. Aluminum (5052 and 6061-T6) and copper frames also have given satisfactory service in a wide range of
environments. Care should be observed in the use of copper frames, as corrosion products splashed during rainfall might affect the
corrosion of other metals such as aluminum or magnesium.
NOTE 1—If galvanized pipe is field-threaded, thread areas must be protected to ensure joint integrity for long exposure periods. In severe environments,
additional coatings may 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 aluminum bronze, alloy
400, or stainless steel screws. In such a case, no wood sections should be used with dimensions less than 22 in. by 4 in. (50(50 mm
by 100 mm), and at least two coats of an exterior grade paint or enamel over a suitable primer must be applied. Periodic
maintenance will be required on all wood construction.
5.3 Solid, glazed, electrical insulator knobs should be used to hold the specimens on the frames, using stainless steel, alloy 400,
aluminum, nylon, or bronze bolts and nuts. Specimens shall be mounted in the grooves of these insulators. In selecting fasteners
for use on specific frame materials, care should be taken to avoid unfavorable galvanic relationships.
5.4 A suitable frame for mounting the insulators is shown in Fig. 1. This frame will accommodate 70 standard 44 in. by 6-in.
(1006 in. (100 mm by 150-mm)150 mm) specimens; other sizes can be mounted by rearranging the insulators in the holes
provided. It is acceptable to slot the holes in the frames in such a manner that the mounting frames are adjustable for specimens
of other sizes. This is a convenience when it is not possible to prepare specimens of a preplanned size, and it is often helpful in
fitting the specimens snugly into the frames.
G50 − 20
FIG. 1 Suitable Test Frame
5.5 The racks should be designed to give exposure to as large an area of the underside of the specimens as possible. Structural
members of the rack should not be located directly under the specimens where they would shelter the underside of the specimens.
5.6 As most published data on atmospheric corrosion of metals are based on an exposure angle of 30° from the horizontal, facing
south, it is recommended that this angle be used. used in conjunction with an orientation facing the Equator. Racks should be
designed so that the lowest specimens are at least 30 in. (760 mm) above the ground. See Notes 2 and 3.
NOTE 2—Maximum exposure to the sun may be obtained by exposing specimens facing south (for the northern hemisphere) the Equator at an angle equal
to the latitude of the test site. Exposure at this angle will yield the lowest corrosion rates for most materials. Although these corrosion rates will change
at other angles of exposure, the order of merit established for each material will be the same.
G50 − 20
NOTE 3—In special instances, it may be desirable to orient racks and frames in the direction of a specific corrodent source, for example, the ocean, for
marine environments. Also, this practice should not be construed as prohibiting special orientation of test frames for specific test purposes, but it is
strongly suggested that in such cases testing also be done in accordance with this practice so that a basis point for comparison with available data is
determined. Any special orientation or preferential source of corrosion should be specifically identified in the exposure site description.
5.7 A rack of the design and dimensions shown in Fig. 2 will give the correct exposure angle and can support the specimen frame
described in 5.4.
5.8 The ground under the racks should be kept free of weeds, bushes, and debris. Organic herbicides, defoliants, or pesticides
should not be used for this purpose.
6. Test Specimens
6.1 When the material to be tested is in sheet form, a specimen size of 44 in. by 6 in. (100(100 mm by 150 mm) is appropriate.
Specimens may be larger, for example, 44 in. by 8 in. (100(100 mm by 200 mm), to suit a particular test; however, the specimens
preferably should not be smaller than 44 in. 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. It may
be difficult to accommodate thicknesses greater than 0.250 in. (6.25 mm) in the insulator grooves. (Special deep-throated insulators
can be obtained to accommodate thicker specimens, or the edges of thicker specimens can be machined to fit standard insulators.)
6.3 When it is desired to test samples of odd shapes, such as bolts, nuts, pipes, angles, assemblies, and structures, etc., a means
of supporting them in the test racks must be devised. It is important that the specimens be electrically insulated from their
respective supports and from each other to prevent unintentional galvanic corrosion. However, if desired, galvanic couples of
dissimilar metals can be exposed on these frames. Efforts should be made to minimize crevices between specimens and support
materials.
NOTE 1—Items 1, 2, 3, 4, 5, and 8 are 1 ⁄4-in. (31.8-mm) in. (31.8 mm) hot-dip galvanized pipe.
NOTE 2—Fill all legs with concrete to about 6 in. (152 mm) above ground line.
Metric Equivalents
ft-in. m ft-in. m Req.
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