Steels outdoor tests

Rust Layers in Steels Submitted to Outdoor Tests... 

In the 1970s, in order to facilitate the comparison of results, corrosion experts started to calibrate their outdoor testing stations on the basis of measurements taken on identical specimens of several metals and alloys such as steel, zinc, copper and aluminium. They were exposed in each participating testing station. These stations were thus classified based on their aggressiveness and the results compared. 

Effect of mass The rate of rusting of steel in the atmosphere is affected to some extent by the mass of the part concerned, because this determines the speed at which the surface temperature adjusts itself to fluctuations in the ambient temperature, the amount of condensation during humid periods, and the time during which dew or rain remains in contact with the steel. For example, in a test over 12 months at the National Chemical Laboratory under sheltered conditions outdoors, thick steel plates rusted more than thin ones as is shown below. 

Table 11(A). Outdoor and laboratory tests of paint coatings applied over ASa 3 steel panels.

D6675—01(2011) Standard Practice for Salt-Accelerated Outdoor Cosmetic Corrosion Testing of Organic Coatings on Automotive Sheet Steel... 

Blekkenhorst et al. (1991) have developed a 10-week cyclic test that has good accord with practice but some anomalies. Goodwin et al. of British Steel (1991) have, however, concentrated on developments in outdoor weathering tests in view of the limitations of cyclic tests. 

At Canadian Electrolytic Zinc, Valleyfield, Quebec, the main pollutant is sulfur-based gases. Three indoor and two outdoor sites are being tested, and 2-year results are given in Table 2.34 (except for the roaster, which has 5-KX) ppm SO2, traces of SO3, and dust, but is dry and has a known lower corrosion rate from tests on zinc-coated steels). Qualitatively, the results were comparable to those in the acid areas of the pulp and paper plant. 

Biestek, T. (1961a). Comparative outdoor exposure tests of electrodeposited zinc and cadmium coatings of steel in a natural industrial atmosphere. 1st. Int Congress on Metallic Corrosion, London, pp. 269-275 or preprint 455-460. 

Davidson, D. D., Soreide, L. E., and Stephens, M. L. (1989). Assessment of the Chrysler chipping corrosion test using laboratory scab and long-term outdoor exposure testing. Galvatech 89, Iron and Steel Institute, Japan, pp. 536-544. 

Johansson, E., and Rendahl, B. (1991). Field exposure and outdoor. scab-testing of different pre-coated steels. 3rd Int. Zinc-Coated Steel Sheet Conf., S3A/1-9. 

The automotive industry has taken a lead role in the development of cyclic corrosion tests that can produce results that better correlate with field exposure. In 1984, a joint effort. Automotive Corrosion and Prevention Committee, began between the Corrosion Task Force of the American Iron and Steel Institute and the Society of Automotive Engineers. Nearly 20 years later, and after considering over 130 available laboratory, proving ground, and outdoor corrosion tests, SAE Surface Vehicle Standard, J2334, Cosmetic Corrosion Lab Test, was published in June 1998 [20],... 

The addition of acetic acid to the salt solution used in the salt spray tests was introduced first in 1945 and is currently Annex A1 of ASTM G 85 [Practice for Modified Salt Spray (Fog) Testing]. The acidified test is much more corrosive than the normal salt spray test and is capable of producing a pattern of attack similar to that developed in outdoor service for decorative chromium plate on steel or zinc. It is much slower than the copper-accelerated acetic acid-salt spray (CASS) test in ASTM B 368 [Method for Copper-Accelerated Acetic Acid-Salt Spray (Fog) Testing (CASS Test)], [77] which resembles it in effect. 

The corrosion behavior of stainless steels in outdoor exposure tests near the shore in a marine atmosphere is also described in DIN 81249, part 4 (1997). The information given relates to a distance of 25 m from the waterline outside the splash line. Table 1-10 lists the corrosion rate and susceptibility to pitting or crevice corrosion. CrNi steels containing molybdenum are passive and have good corrosion resistance. 

Testers may be tempted to force quicker corrosion testing by increasing the amount of chemical stress. Steel that corrodes in a 0.05% sodium chloride (NaCl) solution will corrode even more quickly in 5% NaCl solution the same is true for zinc-coated steel. The problem is that the amount of acceleration is different for the two metals. An increase in NaCl content has a much more marked effect for zinc-coated substrates than for carbon steel substrates. Strom and Strom [1] have demonstrated this effect in a test of weakly accelerated outdoor exposure of painted zinc-coated and carbon steel samples. In this weakly accelerated test, commonly known as the Volvo Scab test, samples are exposed outdoors and sprayed twice a week with a salt solution. Table 7.1 gives the results after 1 year of this test, using different levels of NaCl for the twice-weekly spray. 

The most widely used simulated service test for static atmospheric testing is described in ASTM G 50, Practice for Conducting Atmospheric Corrosion Tests on Metals. It is used to test coated sheet steels for a variety of outdoor applications. Test materials, which are in the form of flat test panels mounted in a test rack (Fig. 16), are subjected to the cyclic effects of the weather, geographical influences, and bacteriological factors that cannot be realistically duplicated in the laboratory. Test durations can last from several months up to many years. Some zinc-coated steel specimens have undergone testing for more than 30 years. 

J.P. MOTan, P.R. Ziiiian, and M.W. Egbert, Cosmetic CoiTOsion of Painted Alumimun and Steel Automotive Body Sheet Results from Outdoor and Accelerated Laboratory Test Methods, Corrosion and Corrosion Control of Aluminum and Steel in Ughtweight Automotive Applicatbns, E.N. Soepenberg, Ed., NACE International, 1995, paper 374, p 374-1 to 374-22... 

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