Accelerated cyclic corrosion test

Figure 55. Positive SSIMS spectra from each side of the metal-paint interface on a hot-dip galvanized steel surface after accelerated cyclic corrosion testing [1871 A) Metal B) Paint...

Yau, Y.-H., Hinnerschietz, S.J. and Fountoulakis, S.G., Performance of organic/metal-lic composite coated sheet steels in accelerated cyclic corrosion tests, in Proc. Corrosion 95, NACE, Houston, 1995, Paper 396. 

The number of available cyclic corrosion tests are too many to outline. ASTM Subcommittee D 01.27, Accelerated Test Methods, has formalized a document on laboratory corrosion tests that is published as ASTM D 6899. 

Correlation of the test methods to actual field performance is forming the basis of selection of the most predictive accelerated tests. This work led to the development of SAE J2334, a new standard accelerated laboratory cyclic corrosion test that accurately predicts the cosmetic corrosion performance of automotive coated steel sheet. The results of this study are described in a series of publications [37,35,36,55]. 

Lance, Accelerated cyclic oxidation testing protocols for thermal barrier coatings and alumina-forming alloys and coatings. Mater. Corrosion, 57 (2006), 1-13. 

Accelerated Corrosion Tests. There are as many as a dozen methods (salt fog, Kesternich, etc.) that are currently being used to investigate corrosion resistance of coating systems and a need to develop a better and more dependable method to predict in-use service. A severe drawback of all these tests is that their results often compare unsatisfactorily with practical experience. One reason for the discrepancies is assumed to be the variability of natural exposure conditions. Accordingly, cyclic testing procedures have been developed with which exposure conditions, especially temperature and humidity. 

Various conditions of accelerated corrosion testing are summarized in Table 1.10. According to ISO 14993 [85], water condensation on the test specimens should not occur under wet conditions. The methods of testing organic coatings on metallic materials according to ISO 11997-1 under cyclic corrosion conditions include condensation of water on the test surface during the period of humidity [87]. 

ISO TC 156 WG7/N137, Accelerated corrosion testing involving cyclic exposure to salt mist, dry and wet conditions. Draft International Standard, International Organization for Standardization, 1998. 

N.D. Cremer, Cyclic methods of accelerated corrosion testing, Polym. Paint Col. J. 180 (1990)... 

Another commonly used cyclic corrosion laboratory test is GM9540P, Accelerated Corrosion Test [22]. The operating conditions are as follows ... 

The current salt spray test, in which the plated specimen is exposed to a spray or fog of sodium chloride solution, is the most widely used accelerated corrosion test for coatings, and various procedures have acceptance tests in standard specifications in numerous countries. Over the years, the procedure has employed sodium chloride solutions of concentrations between 3 and 20 %, sometimes with the addition of hydrochloric acid or hydrogen peroxide. The salt spray test [ASTM B 117, Test Method of Salt Spray (Fog) Testing] has largely fallen into disrepute because of the recognition that its reproducibility and correlation with outdoor exj>osure were often poor. Cyclic salt spray testing as well as alternate electrolytes such as the "prohesion test solution have been found to produce more realistic results. 

Electrochemical tests provide a means to understand the corrosion process, simulate service conditions, or accelerate evaluation of a material [27]. ASTM G 3, Practice for Conventions Applicable to Electrochemical Measurements in Corrosion Testing ASTM G 5, Standard Reference Test Method for Making Potentiostatic and Potentiodynamic Polarization Measurements and ASTM G 61, Standard Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements for Localized Corrosion Susceptibility of Iron-, Nickel-, or Cobalt-Based Alloys provide background in some of these techniques. 

Hundreds of test methods are used to accelerate the aging of coatings. Several of them are widely used, such as salt spray and ultraviolet (UV) weathering. A review of all the corrosion tests used for paints, or even the major cyclic tests, is beyond the scope of this chapter. It is also unnecessary because this work has been presented elsewhere the reviews of Goldie [1], Appleman [2], and Skerry and colleagues [3] are particularly helpful. 

The extent of adhesive bond failure under corrosive environments is greatly accelerated when cyclic mechanical stresses are imposed on the adhesive bond during exposure. Three to four orders of magnitude reduction in fatigue life of adhesive bonds is observed for bonds exposed to environment prior to fatigue testing. 

ISO 14993 2001. Corrosion of Metals and Alloys - Accelerated Testing Involving Cyclic Exposure to Salt Mist, Dry and Wet Conditions. Geneva, ISO Copyright Office, 2001. 

Chemical and Corrosion Resistance The corrosion resistance of CCCs depends on thickness and coating age. Corrosion resistance has been observed to scale with total chromium content [153]. Some studies have found that corrosion resistance does scale with Cr(VI) content [154], while others have found no such correlation [155]. Corrosion resistance is evaluated by continuous or cyclic accelerated exposure testing and electrochemical methods. On aluminum alloys, heavy CCCs will resist pitting for as long as 400 to 1000 h [156]. CCC-coated surfaces will exhibit total impedances of 1 to 2 Mf2 cm after exposure to aerated 0.5 M NaCl solution for 24 h. Such coatings can be expected to withstand 168 h of salt spray exposure without serious pitting [157]. CCCs usually perform well in mild neutral environments, but do not fare as well under... 

It was tried to recreate the parameters of field tests at the accelerated laboratory tests where the effect of humidity, chloride ions and presence of SO2 were considered. Comparison of Table 3.22 (lab test) and 3.3 (field test) reveals that the corrosion rate of as received MS and WS in 3.5 % NaCl is lower than the exposed panels. Eaya of as received panels are also greater. However, corrosion rate in cyclic polarisation of MS and WS after SO2 exposure is comparable to cyclic polarisation of coated panels after 18 m exposed at P3 as can be seen from Tables 3.23 and 3.4 and Figs. 3.39 and 3.8. Both plots show passivity. In general, the trend WS is more corrosion resistant than MS as seen in both field and laboratory tests. 

A second key to choosing an accelerated test is a good understanding of the materitil/materials being tested. In the subsection titled Specific Systems, a discussion of the way in which several coated sheet products provide corrosion protection was presented. Selection of a cyclic test that will yield good predictive information must take these factors into account. If the materitJ of interest is known to provide barrier protection due to the formation of a psissive film on the coating surface in the exposure environment of concern. 

Categories of laboratory (accelerated) tests are electro-chemictd, immersion, cabinet, cyclic, and proving grounds. These accelerated tests require (1) selection of environmental and physical conditions representative of service exposure, (2) accelerated corrosion rates without a change in the mechanism, (3) reproducibility of results, and (4) acceleration factors which relate to service performance. 

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. 

Protection against corrosion of iron and steel in structures—Zinc and aluminium coatings—Guidelines Corrosion of metals and alloys— Accelerated testing involving cyclic exposure to salt mist, dry" and "wet conditions... 

Mallon, K. et al., Accelerated test program utilizing a cyclical test method and analysis of methods to correlate with field testing, in Proc. Corrosion 92, NACE, Houston, 1992, Paper 331. 

For metals, FDA regulations specify ASTM F2129 (standard test method for conducting cyclic potentiodynamic polarization measurements to determine the corrosion susceptibility of small implant devices). Some devices may also require testing for stress corrosion (failure due to corrosion accelerated by tensile stress). There are many test methods for fatigue fracture, so it is incumbent on the manufacturer to select the most appropriate one(s) for device in question. Pacemaker leads, for example, are often tested in a fixture that flexes them 90 over a specified radius at twice the typical cardiac cycle rate (Fig. 10) [31]. Presently, FDA requires satisfactory performance over 4 hundred million cycles (equivalent to about 10 years in human use). 

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