Corrosion testing spray

Sa.lt Spray Tests. One of the older accelerated corrosion tests is the salt spray test (40). Several modifications of this imperfect test have been proposed, some of which are even specified for particular appHcations. The neutral salt spray test persists, however, especially for coatings that are anodic to the substrate and for coatings that are dissolved or attacked by neutral salt fog. For cathodic coatings, such as nickel on steel, the test becomes a porosity test, because nickel is not attacked by neutral salt fog. Production specifications that call for 1000 hours salt spray resistance are not practical for quahty acceptance tests. In these cases, the neutral salt spray does not qualify as an accelerated test, and faster results from different test methods should be sought. 

The CASS Test. In the copper-accelerated acetic acid salt spray (CASS) test (42), the positioning of the test surface is restricted to 15 2°, and the salt fog corrosivity is increased by increasing temperature and acidity, pH about 3.2, along with the addition of cupric chloride dihydrate. The CASS test is used extensively by the U.S. automobile industry for decorative nickel—chromium deposits, but is not common for other deposits or industries. Exposure cycle requirements are usually 22 hours, rarely more than 44 hours. Another corrosion test, now decreasing in use, for decorative nickel—chromium finishes is the Corrodkote test (43). This test utilizes a specific corrosive paste combined with a warm humidity cabinet test. Test cycles are usually 20 hours. 

Corrosion Tests of Flame Sprayed Coated Steel-19 Year Report, American Welding Society. Miami (1974)... 

The accelerated corrosion test in most general use is the CASS test in which the articles are sprayed intermittently with a solution made up as follows ... 

The most widely used accelerated tests are based on salt spray, and are covered by several Government Specifications. BS 1391 1952 (recently withdrawn) gives details of a hand-atomiser salt-spray test which employs synthetic sea-water and also of a sulphur-dioxide corrosion test. A continuous salt-spray test is described in ASTM B 117-61 and BS AU 148 Part 2(1969). Phosphate coatings are occasionally tested by continuous salt spray without a sealing oil film and are expected to withstand one or two hours spray without showing signs of rust the value of such a test in cases where sealing is normally undertaken is extremely doubtful. 

For additional information on some of the features of the salt spray test and its limitations in respect of certain of the purposes for which it may be used, reference should be made to the book Corrosion Testing for Meta Finishing prepared by the Institute of Metal Finishing. 

Specification for electroplated coatings of 65/35 tin/nickel alloy Method for the evaluation of results of accelerated corrosion tests on metallic coatings Methods of test for paints Cross-cut test Pull-off test for adhesion Resistance to artificial weathering (enclosed carbon arc) and Addendum No. 1 Resistance to continuous salt spray Notes for guidance on the conduct of natural weathering test... 

Corrosion tests in artificial atmospheres salt spray tests... 

Corrosion Testing. Salt spray testing (ASTM-B-117-52,54) was used to determine durability of adhesive bond in corrosive environment. Lap shear samples were exposed to salt spray for 14 days and then immediately tested for lap shear strength. 

For standards, see Table 1 ( Corrosion testing NaCl ). Materials and apparatus spray chamber, test solutions (5 % NaCl solutions). 

If suitable field sites are not available or lack controlled conditions, then corrosion tests must be conducted in the laboratory. Cabinets are constructed in which the atmosphere is controlled and high humidity and temperature can be used to help accelerate the tests. Marine environments are simulated by salt spray and industrial environments by sulphur dioxide or nitrogen dioxide. Figure 18 shows a salt-spray cabinet and the arrangement of test panels. Periodic changes of temperature within the cabinet can be used to simulate night and day. Addition of other aggressive salts or acid into the sprayed solution is further used to accelerate the test. 

All specimen are fully wetted (Fig. 5) by the corrosive test fluid (exception R = -1 probes which were only sprayed). The surface quality of the specimen - honed resp. polished - is well comparable to the finish of real pump components. 

L-23398, which contained corrosion inhibitors, survived the four test cycles in salt spray cabinet and sulphurous acid corrosion testing, whereas a MIL-L-81329 coating without a corrosion inhibitor survived only one cycle. 

After completing corrosion testing exposure, the panels were rinsed with distilled water and visual observations were made. The panels were then subjected to Turco 5469 paint stripper solution to strip off the E-coat or spray primers (including the controls) from the scribed surface, so that the effect of corrosion beneath the coatings and away from the scribes could be viewed. These panels were then used to estimate the average corrosion creep widths, in order to compare the corrosion performance of the different sample systems [5]. 

Figures 28.3 and 28.4 depict corrosion tests results obtained for 2024-T3 and 7075-T-6 respectively. The first picture (from left), CC Deft, represents the control sample prepared by chromate conversion coating and chromated spray primer (Deft). The second sample, CC E-coat, is prepared by the same procedure for the CC Deft except that E-coat replaced Deft primer. The third sample is prepared by applying the same E-coat directly (without chromate conversion coating) on the...

Figure 31.17 shows typical scanned images of SO2 salt spray-tested panels, two controls and two plasma polymer-treated panels. By visual observation, one can easily see that the corrosion performance of the plasma polymer-treated panels, [2A](Ace/0/N)/TN/E and [2A](Dox/AH)/TH/E, is far better than that of the control panels, [2A]CC/E and [2A]CC/A. Figure 31.18 shows typical scanned images of the surfaces of controls and plasma interface-engineered systems of [2A](Ace/0)/TH/E and [2A](Ace/0)/TN)/E after Prohesion salt spray corrosion testing and subsequent... 

E-coat stripping. Both plasma-treated panels show excellent corrosion protection performance as compared to the control panels. All [2A] panels with different plasma treatments and plasma polymer coatings, which were corrosion tested in both SO2 and Prohesion salt spray tests, were similarly scanned, and the corrosion width was evaluated by using a scanned image and computer calculation of the corroded area. Figure 31.19 compares the corrosion width obtained by the two methods. 

Figure 31.29 summarizes the corrosion widths along the scribed lines that were calculated from (1) SO2 salt spray-tested and (2) Prohesion salt spray-tested A1 alloy panels and their corresponding control panels. As seen from Fig. 31.29, the corrosion test results showed that the plasma coating systems based on the chromate-free spray primers provided excellent corrosion protection for the A1 alloys studied. 

The corrosion widths of Prohesion salt spray-tested IVD Al-coated Al panels were calculated and are summarized in Figure 32.6. As is evident from the data, after 12 weeks of Prohesion salt spray testing, IVD/plasma polymer/spray paint systems showed better corrosion protection overall than IVD/plasma polymer/E-coat systems. All the IVD/plasma polymer/spray paint systems outperformed the cathodic E-coated controls and showed corrosion test results comparable to those of the Deft primer oated controls. 

Eugenija Ramoskiene Validation of salt spray corrosion test... 

Abstract Quality control of corrosion test results implies the validation of the corrosion test method and estimation of the uncertainty of corrosion rate measurement. The corrosion test in an artificial atmosphere of the salt spray mist needs evaluation of corrosivity of the test cabinet by reference specimens. Such calibration of corrosion environment raises very strict requirements for the method description and details of all procedures and used specimens. Reliable corrosion measurements by spray tests require validation of the experimental device together with the experimental procedure and determination of corrosivity uncertainty of the test cabinet environment. 

Our aim was to present an experimental evaluation of the corrosivity of the salt spray corrosion test cabinet, to indicate the gaps in the description of the corrosion test method according to ISO 9227 and to estimate the main components of the uncertainty of the corrosivity measurement. 

ISO 9227 [1] does not specify in detail many necessary parameters and does not determine the precision of such a test method. The precision and accuracy of corrosion determination are influenced by many factors preparation of specimens, conditioning, removal of corrosion products, cleaning, drying, etc. In literature on the corrosion tests we failed to find any information concerning the quality of corrosion tests results. The aim of this paper is to call attention to the problems in the corrosion measurement data quality and the necessity to evaluate the uncertainty for measurement results. We attempted to show the main components of uncertainty of the result in such a measurement on the basis of the experimental evaluation of the corrosivity of the spray test corrosion cabinet by means of reference specimens. 

Ordinary statistical analysis of the corrosivity tests showed that the mean of corrosion rate v=lll g/m2of eight experiments means and its standard deviation j-4.1 g/m2 estimate of neutral salt spray test cabinet corrosivity as 111 3 g/m2 (confidence 95%) shows that corrosivity of our corrosion cabinet meets the requirements of ISO 9227, which states that the average value and its data scattering should be 140 40 g/m2. 

Uncertainty of mass loss measurement. The standard method of the neutral salt spray test does not indicate the mass of RS. Mass loss was found as a difference between the RS prepared for the corrosion test and the RS after the corrosion test and corrosion product stripping as well as protective coating removal from the RS (Table 1). Such a mass loss determination is based on three components (1) mass loss determination by weighing (accuracy 0.5 mg and standard deviation 0.3 mg) before the neutral salt spray test and after it, (2) determination of difference and (3) cor-... 

It was assumed that the uncertainty of corrosion test duration comprised two components (1) accuracy which was indirectly indicated in standard method description and (2) our experimental possibility to keep the total duration of corrosion process in the neutral salt spray environment within limits of 0.2 h. 

Additional specifications from other corrosion test standards [2, 3] are required for the standard method of the accelerated corrosion test in the neutral salt spray test cabinet at 35 2 °C within 96 h. For the evaluation of corrosion data quality, the test should be performed according to the requirements of contemporary standards such as ISO/IEC 17025 [9] and, therefore, the corrosion test data uncertainty must be determined. 

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