Cyclic humidity tests

G 60 Test Method for Conducting Cyclic Humidity Tests... 

Chip Resistance of Surface Coatings Laboratory Cyclic Corrosion Test Method for Conducting Cyclic Humidity Tests Method for Conducting Moist SO Tests Cyclic Corrosion Test (CCT)... 

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. 

D 2803 Guide for testing filiform corrosion resisfance of organic coatings on metol D 2933 Test method for corrosion resistance of coated steel specimens (cyclic method) G 60 Method for conducfing cyclic humidity tests... 

There are numerous options for the production of fog and humidity testing in cabinets in order to asses the corrosion resistance of a broad spectrum of products. The basic humidity test is most commonly used to evaluate the corrosion behavior of materials or the effects of residual contaminants. Cyclic humidity tests are conducted to simulate exposure to high humidity and heat typical of tropical environments. 

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). 

Cyclic polarisation test carried out in 2.5 % NaHCOs + 0.5 % NaCl + 0.1 % CaCl2 solution on MS and WS after exposed in humid SO2 environment for 9 m. The polarisation plots are given in Fig. 3.49 along with corrosion rate Icon) in Table 3.23. 

In cyclic immersion tests the sample is periodically immersed in an electrolyse, for example by attaching it to a partially submerged wheel that slowly turns. With this method, it is easy to simulate the humidity cycles, but there is a major drawback during the immersion phase, the corrosion products can dissolve, in contrast to what happens normally in true atmospheric corrosion. This procedure therefore simulates atmospheric corrosion only in an imperfect way. 

The cyclic immersion test and the stressed high-humidity (sustained load durability) test are particularly aggressive and are both discriminating tests for adhesive durability performance. 

Typical cyclic corrosion tests include one or more steps of salt solution exposure, humidity, drying, and/or ambient conditions. A list of commonly used cyclic tests is included in Table 1. 

Applicable test methods include [28] Continuous Salt Spray Tests (ASTM B 117), Neutral Salt Spray Test (ASTM B 117), Acetic Acid Salt Spray Test, Copper-Accelerated Salt Spray Test (CASS) (ASTM B 368), Cyclic Salt Spray Tests, the Copper Development Association (CDA) Test, the Hitachi Salt Spray Test, Climate Tests, The Humidity Test, The International Electrotechnical Commission/Intemational Organization for Standardization (lEC/ISO) Test and Mud Test. 

The durability for a bonded system can be tested by applying cyclic loads on either simple lap shear specimens, more sophisitcated H-specimens or on the whole bonded structure (e.g., the whole car body). It is recommended to run a corrosion test or at least a high humidity test... 

Lab exposure—cyclic corrosion test (CCT-IV) This is a cyclic test method, consisting of three environments salt spray (per ASTM B 117), diyoff (60 °C, or 140 °F, ambient relative humidity), and high-humidity (60 °C, 95% relative humidity). Salt spray was tqtplied for 10 min, followed by 155 min at d off, followed by 75 min of humidity. Five repetitive cycles of 160 min dryoff and 80 min humidity complete the 24 h cycle. Exposure time was 50 cycles (5 cycles per week, weekends at ainbient). Results are shown in Fig. 3(f). 

Lab exposure—General Motors cyclic corrosion test method GM 9540P-Method B This is a four-part test The first part involved 8 h exposure to anibient conditions, with a 5 min salt spray period at the first four 90 min time intervals. Salt environment consisted of 1% NaCl, 0.1% CaCl, and 0.25% NaHC03. Spray was applied manually using a spray bottle. The second part was a high-humidity exposure (49 °C, or 120 °F, 95% relative humidity) for 8 h. The third part, defined as a dryoff environment, provided an 8 h exposure at 60 °C (140 °F), less than 30% relative humidity. Exposure period was 40 cycles (5 cycles per week weekends at ambient lab conditions). Results are shown in Fig. 

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. 

There are several accelerated tests which differ in the selection of light source and cyclic exposure to varying degrees of humidity. Some accelerated tests include salt spray, heat, cold, and other weather factors. 

The moisture excluding efficiency of coatings decreases rapidly with time, relative humidity cycling, and weathering exposure. When cyclic or weathering tests are extended for periods of a year or more moisture exclusion is practically eliminated. 

The adhesive should be selected on the basis of durability as defined by slow cyclic testing in a hot and humid environment. 

Environmental aging is usually less severe in service (laboratory tests tend to accelerate aging so that the testing can be completed in a reasonable time). However, the effects of the actual service environment are generally more complex. For example, there may be simultaneous exposure to cyclic stress, cyclic temperature, and humid environments. 

The final engineering tests with the civilian mask offered some interesting problems which had not been encountered before. Prior to this test no item of like materials and like construction had been subjected to such severe environmental conditions at Dugway Proving Ground. The tests consisted of storing the masks for 9 weeks in chambers at —65°F. (arctic), +165°F. (desert), and -fll3°F. and maximum humidity (tropic). In addition, masks were stored for 3 weeks under each of these climatic conditions in succession (cyclic). Upon completion of this surveillance, the masks were compared with controls as to physical condition, gas life, and aerosol penetration. 

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]. 

For a number of years the following desiccator method of corrosive tests was used at MPRI NASH [49-51,98]. Metallic samples in the form of plates 50 X 50 X 2 in size are wrapped in an inhibited film and placed into the desiccator inside which 98 2% relative air humidity is maintained by aqua solution of glycerin, and are subjected to cyclic heating-cooling. One cycle consists of the endurance of the samples in the same humidity at a temperature of 55 2°C for 8h and at a similar humidity and a temperature of 20 2°C for 16 h. The protective ability of the films is estimated by the corrosion resistance of metallic samples after 21 test cycles (Table 1.11). 

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