Modified salt spray testing

Alternative atmospheric cabinet simulation tests are available, including ASTM G 87, Practice for Conducting Moist SO2 Tests and ASTM G 85, Practice for Modified Salt Spray Testing. Service in environments where humidity or moisture varies may be simulated by cyclic humidity or alternate immersion tests. See ASTM G 60, Test Method for Conducting Cyclic Humidity Tests and ASTM G 44, Practice for Exposure of Metals and Alloys by Alternate Immersion in Neutral 3.5 % Sodium Chloride Solution. 

Organic coatings are commonly evaluated using salt water immersion, salt fog or spray, modified salt exposure tests (e.g., salt fog with added SO2), and various cyclic exposure tests. Humidity exposure and water immersion, and, for many applications, physical resistance tests (adhesion, impact resistance, etc.) are widely used preliminary tests. Standard methods for most of these tests are given in compilations of standard tests such as the Annual Book of ASTM Standards (16). Test methods have been extensively reviewed (e.g., 17-23). 

Panels of high strength aluminum alloy (7075-T6) were used in this study. The panels were approximately 10 x 3 x 0.032 inch (25 x 7.5 x 0.08 cm) in size. The test environments for coating evaluation were (1) a 5% NaCl spray (fog) chamber according to ASTM Standard Method of Salt Spray (Fog) Testing (B117-73), and (2) a modified 5% NaCl/S02 spray (fog) chamber with SO gas introduced periodically - ASTM Standard Practice for Modified Salt Spray (Fog) Testing (G85-84(A4)). In the latter case, a constant spray of 5% NaCl was maintained in the chamber and SO2 was introduced for one hour four tines a day (every 6 hours)( ). Coated test panels were examined for corrosion after one- and two- eek exposure periods. 

Figures 31.20 and 31.21 show the scanned images of SO2 and Prohesion salt spray-tested panels of [2B], respectively. Visual observation of these images reveals that panels that were only acetone wiped and E-coated ([2B](Ace)/E) provided poor corrosion resistance. In contrast, the plasma-modified [2B] panels showed excellent corrosion resistance even after 12 weeks of exposure to Prohesion salt spray,...

Figures 31.23 and 31.24 show typical scanned images of SO2 and Prohesion salt spray-tested [7B] panels, respectively. Visual observation of these images reveals that the plasma-modified panels of [7B] have outperformed both control panels in the SO2 salt spray test. These plasma film combinations were prepared on deoxidized [7B] surfaces without any plasma cleaning pretreatment. Figure 31.23 also shows an image of a panel that had simply been deoxidized prior to the application of E-coat, which performed excellently in the SO2 salt spray test. Figure 31.25 compares the corrosion width obtained by the two methods. The comparisons shown in Figures 31.19, 31.22, and 31.25 indicates that the results obtained by the two methods do not match, partly due to the different duration of tests, and that samples which show good results in one test do not do as well in the other test.

ASTM G85 describes modified versions of salt spray testing in which the spray solution is acidified with acetic acid, SO2 is added, or the test conditions are cycled. These modifications result in a more corrosive environment than the standard salt spray test. 

ASTM G85-11, Standard practice for modified salt spray (fog) testing, in Annual Book of ASTM Standards, vol. 03.02, ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA, 2002. 

ASTM G85-85 (1985) Standard Practice for Modified Salt Spray (Fog) Testing. 

ASTM G85-02el Standard practice for modified salt spray (fog) testing. 

Both (PPy)s and (PPyXn films were prepared in the galvanostatic mode (j = 4 mA/cm ) and had thickness between 3 and 10 pm. The (PPyXn films heated at 180°C for 30 min in order to achieve polycondensation of the modified polymer chains. Both samples were over-coated with cath horetic paints (total thicloiess about 28 pm) and then compared in salt spray tests with phosphated steels covered with the same thickness of cataphoretic paint These tests were performed for 500 h, after which adherence was checked. It is found that the adherence properties are similar for all samples. The main difference is that corrosion propagation around the streaks is twice as small for (PPy)m than as for (PPy), ch shows behavior identical with tfiat of the phosphat steel system 02). 

A compilation of modified salt fog tests, ASTM G 85, includes five annexes. The first. Acetic Acid Salt Spray (Fog) Testing, was originally published as ASTM B 287. In this annex, the salt solution is prepared in accordance with B 117, then tidjusted to a pH in the 3.1-3.3 range with the acetic acid. The acetic acid salt spray test is used for decorative chromium plating on steel [4]. The test duration is typically 144-240 h. 

Salt Spray (Fog) Tests—Three different cyclic acidified Scilt spray tests have been widely used for exfoliation testing in the aluminum and aircraft industries. These are described in Annexes A2, A3, and A4 in ASTM G 85, Practice for Modified Salt Spray (Fog) Testing. The three practices are not equivalent, and the user should determine which one is best suited for the alloy and application under investigation. The following notes were t en from the ASTM G 112, which contains additional details regarding their usage ... 

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 most widely used cabinet test is the neutral salt spray (Fog) test (ASTM B 117), which consists of a fog of 5 % sodium chloride within the chamber at 35 C [46. Controversy exists over the validity of B 117 as a performance test because corrosion mechanisms are not always the same as those observed in automobile service. Also, not all materials can be successfully evaluated in the test. However, the value of the salt spray test as a quality assurance test is well documented [46]. Several modifications to the salt spray test have been developed including acetic acid salt spray (ASTM G 85, Annex 1), copper accelerated acetic acid salt spray (ASTM B 368), acidified synthetic seawater fog (ASTM G 43, Method of Acidified Synthetic Seawater (Fog) Testing), and modified salt spray (ASTM G 85). ASTM G 85 also includes cyclic tests. 

Laboratory exposure tests are usually conducted in chambers similar to that described in ASTM B 117, Test Method of Salt Spray (Fog) Testing. Because the environment is more corrosive than the salt fog described in ASTM B 117, the variations described in ASTM G 85, Practice for Modified Salt Spray (Fog) Testing, are often used. Some investigators have used a modified procedure in which the test coupons are mounted over holes on the outside wall of the exposure chamber so that they can be subjected to a thermal gradient [35]. Outside mounting of the coupons also affords the opportunity to conduct in situ electrochemical impedance measurements. 

Standard Practice for Measurement of Time-of-Wetness on Surfaces Exposed to Wetting Conditions as in Atmospheric Corrosion Testing Standard Practice for Modified Salt Spray (Fog) Testing Standard Practice for Conducting Moist SO2 Tests... 

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