Cabinet corrosion tests

Cabinet corrosion tests have been used since the early 1900s as a means of evaluating the performance of coatings as a quality control tool for monitoring processes, and in some cases, as a method for accelerating corrosive activity. 

A cabinet corrosion test is one in which a test chamber (or cabinet) is used to produce an environment that will cause the occurrence of a corrosion product on a test sample. Some common corrosive environments produced in a test chamber are salt fog, humidity, hot and cold temperatures, ultraviolet exposure, and corrosive gases. These environments may be used individually or in combination with each other. 

The most commonly used cabinet corrosion test is the Salt Spray (Fog) Test. Although originally adopted as a test method, ASTM B 117 is actually a practice—Standard Practice for Operating Salt Spray (Fog) Apparatus [7]. 

Cabinet corrosion tests can be a useful tool in determining the production quality or suitability of given material. 

Cyclic Cabinet Corrosion Testing, STP 1238, G. S. Haynes, Ed., ASTM, West Conshohocken, PA, 1995. 

Suga, S., and Suga, S., Cyclic Corrosion Tests in Japanese Industries, in Ha5mes, G. S. and Tellefsen, K., Cyclic Cabinet Corrosion Testing, STP 1238, Philadelphia, American Society for Testing and Materials, 1994, pp. 99-112. 

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. 

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. 

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. 

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. 

Corrosion tests in artificial atmospheres [1, 2, 3] are used as comparative tests for the evaluation of corrosivity of metals and metal alloys and corrosion protection capability of various corrosion protection means by metal plating, varnishing and paint coating as well as anodic and conversion coating. Therefore, it is essential to know precisely the corrosivity of the test cabinet environment. 

The standard method for the test cabinet corrosivity determination is described in ISO 92271 [1] but we failed to find any information about the validation of this method or its metrological parameter evaluation. On the other hand, it is necessary to determine from the experimental point of view whether this technique is reliable enough as a standard method. A procedure is described in ISO... 

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. 

Evaluation of cabinet corrosivity. In order to determine the corrosivity of the corrosion cabinet environment eight tests were performed [5] according to the standard method of the neutral salt spray test (Table 1). The results of corrosion rate of RS and the main statistical parameters such as the number of reference samples n, average RS mass m and RS mass loss Am of each RS, average RS surface area S and surface area of each RS Sn, mean averages of all eight experiments and their standard deviations are presented in Table 2a and 2b. 

Table 2a Primary data (n) of salt spry test cabinet corrosivity evaluation in eight experiments as corrosion rate (v, mg/m2) of RS (average mass m=31225 mg) mass loss (Am, mg) from their geometric surface area (S, mm2) (first four experiments)...

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 corrosion duration. In the standard method normal corrosion test duration is indicated as 96 h, and this means that the measurement accuracy is 1 h. Our experiments were performed with 0.2 h accuracy since the corrosion cabinet was opened for several minutes every 24 h to check the quantity of the collected... 

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. 

Experimental possibilities and technical conditions of the corrosion test cabinet allow us to present preliminary... 

For a more comprehensive evaluation of corrosivity measurement uncertainty, it is necessary (1) to carry out an experimental investigation of the influence of each particular factor of corrosion test cabinet environment and experimental procedure and (2) construct a more detailed measurement model. 

Fig. 1.18. Scheme of corrosion cabinet for testing inhibited film materials by Kanzaki s method (1) aluminum tube, (2) rubber washer, (3) plastic cap, (4) glass jar, (5) insulating polymer tube, (6) metal sample, (7) strips of studied material... 

The laboratory accelerated corrosion test practiced at Cortec Co. includes exposure of cold-rolled steel plates wrapped in packets of inhibited films and subjected to thermal-humid atmosphere in special cabinets at 54° C temperature and 95% humidity for 21 days (504 h). Upon the termination of the test the corrosion damage of the samples is estimated. 

A dilTerent approach is used in UTE C20-453 [120], where specimens are burned in an enclo.sed cabinet and the change in resistance of a copper wire or other electrical circuits contained in the cabinet measured. Tests of this type appear to be more realistic, since they directly assess the corrosive effects of fire gases on actual components, but the acid gas type of test described above is simpler. 

One-year test results on zinc and cadmium are in Table 2.22. The results of long-term atmospheric corrosion tests on zinc and cadmium coatings (Fig. 2.35) are compared with those of accelerated corrosion tests (Fig. 2.36) on the same coatings in three cabinets warm and humid, SO2 gas, and sea mist (Strekalov and Berukshtis, 1965). 

Corrosion test cabinets have evolved from homemade water-and-spray tanks that operated at fixed or ambient temperatures and humidity to computer-controlled, multi-environmental laboratory apparatus that are not only functional, but are also an attractive addition to the laboratory. Sizes range from small benchtop units to large walk-in and drive-in chambers capable of testing hill vehicles or other large specimens. ISO requirements have led to the use of NIST traceable devices for measurement of temperature, humidity, and/or other critical conditions to enhance the accuracy and repeatability of the test conditions. A Ust of commonly used cabinet tests is shown in Table 1. 

Electronics corrosion is a unique subject because it occurs largely indoors or inside packages or cabinets. Therefore, classical corrosion tests do not generally apply. In addition, many failure mechanisms are unique to these systems and therefore are not treatable by classic corrosion kinetic fundamentals. This chapter therefore describes the various corrosion mechanisms important in electronics and lists the various test methods that are used in the industry. 

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