Atmospheric exposure tests

Table 3.21A Atmospheric exposure test, Sheffield, 5 years. Results loss weight (g/m ) ...

An extensive compilation of atmospheric exposure test data on zinc is now available and complements the slightly earlier critical study by Schikorr . 

In order to secure information as to changes in corrosion rates with time, as in atmospheric exposure tests, it is necessary to expose sufficient specimens to allow sets to be taken from test after at least three time intervals. 

In view of possible or probable variations in mechanical properties among different specimens of the same metal cut from different sheets or other pieces, or even from different sections of the same sheet or piece, it is necessary to pay careful attention to the initial sampling of stock to be used for control, as well as exposure, specimens. An interesting case in which several of these considerations were involved was provided by the long-time atmospheric exposure tests of non-ferrous metals carried out by Subcommittee VI of ASTM Committee B-3 on Corrosion of Non-Ferrous Metals and Alloys in which changes in tensile properties were used as one of the means of measuring the extent of corrosion. 

Media considerations. SCC tests can be divided into those conducted in natural environments, such as atmospheric exposure tests and seawater immersion tests, and those which are conducted under laboratory conditions or other fabricating operations. The principal disadvantage of atmospheric exposure tests is the comparatively long time required for their completion however, they are reliable since they can reflect the projected use. There is a standard practice for evaluating stress-corrosion cracking resistance of metals and alloys by alternate immersion in a solution of NaCl 3.5%, pH 6.5. For spray testing, ASTM B-117, 2003 states the relevant conditions for conducting the test. (ASTM G44)4... 

Hence, high-temperature atmospheric exposure tests were necessary to evaluate damage morphology and service life related to oxidation. The test samples were cylindrical with the dimensions of 10 X 70 mm. 

Media Considerations SCC tests are conducted in (i) natural atmospheres (ii) seawater immersion, and (iii) laboratory or other fabrication conditions. Atmospheric exposure tests take a long exposure time, but are reliable as they... 

Atmospheric tests on 0.3% copper steel, 7 i -year exposure, from C. Larrabee, Corrosion 9,259 (1953). Atmospheric rates for zinc and copper, 10-year exposure, from Symposium on Atmospheric Exposure Tests on Non-Ferrous Metals, ASTM, 1946. Seawater data from Corrosion Handbook, H. H. Uhlig, editor, Wiley, New York, 1948. Soil data for steel are averaged for 44 soils, 12-year exposure for zinc, 12 soils, 11-year exposure for copper, 29 soils, 8-year exposure from Underground Corrosion, M. Romanoff, Circ. 579, National Bureau of Standards, Washington, D.C. 1957. 

American Society for Testing and Materials. (1957). Report of Subcommittee XV on Atmospheric Exposure Tests of Wire and Wire Products. Proc. ASTM, 34 pp. 

Clarke, S. G., and Longhurst, E. E. (1962). The corrosion behaviour of metals and protective coatings in tropical atmosphere exposure tests. 1st Int. Congress on Metallic Corrosion, Butterworths, London, pp. 254-268. 

TABLE 14—NACE International Standards relating to atmospheric exposure tests. 

Laboratory corrosion tests for exfoliation corrosion susceptibility are a necessary tool for research and quality control engineers however, the validity of such accelerated tests depends on their relationship to realistic service conditions and their sensitivity to various degrees of susceptibility. The tests must be discriminating and yet not so severe as to be unrealistic. For the majority of engineered structures, exposure to outdoor atmospheres provides a baseline that is representative of many service conditions, except for structures that are subjected to unusual chemical environments. Experience has shown that seacoast conditions are more corrosive to aluminum alloys than inland urban and industrial conditions (see Fig. 2), and seacoast atmospheric exposure tests have been particularly useful for the validation of accelerated exfoliation tests [9]. 

Sprowls, D. O., Sitmmerson, T. J., and Loftin, F. E., Exfoliation Corrosion Testing of 7075 and 7178 Aluminum AUoys-Interim Report on Atmospheric Exposure Tests, Corrosion in Natural Environments, ASTM STP 558, ASTM International, West Conshohocken, PA, 1974, pp. 99-113. 

YEAR INSPECTION RESULTS OF ATMOSPHERIC EXPOSURE TESTS ON METALLIZED ALUMINUM COATED CARBON STEEL PANELS... 

Campbell H., CIDA. Anodized aluminum, atmospheric exposure tests. Euston 20 years. Aluminium Federation Ltd, Birmingham B15 1 TW, report HC 8509/1, June 1987. 

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