Abstract
A unique patented laboratory test chamber has been devised to simulate environmental exposure. This device automatically cycles test specimens through alternating immersion and heat-UV exposures. The difference between the new accelerated test chamber and existing test cabinets is that the failure and defects obtained on the new chamber are more visually representative of failures that occur in actual field environments. Rusting, chalking, blistering, cracking, and peeling failures have been successfully duplicated.
NACE defines corrosion as the deterioration of a material under the influence of an environment. The environment is undefined, and is infinitely variable. It may consist of predominantly weathering, with exposure to sun, rain, and temperature change. Northern environments will include freeze/thaw, and chemical environments are contaminated by chemical ion species. Materials exposed in these naturally occurring environments deteriorate under these and perhaps other influences. The best test to establish a material's resistance to a given environment is exposure in that environment over a sufficiently long period of time. Unfortunately, such "natural" environmental corrosion testing is prohibitively expensive and time-consuming. Furthermore, relatively small changes in a given environment (such as differences in wet time, chloride ion, sulfate, oxygen concentrations, temperature, etc.) may cause failure of a material that otherwise would be considered "corrosion resistant". Thus, no one naturally occurring environment is the same as any other.
However, certain of the more predominating environmental influences may be sufficient to generally characterize an environment. As an example, a "marine" environment connotates damp salt air and sea water wetting. This obviously is different than an inland environment, where such influences are not present. Similarly, an "immersion" environment is different than an atmospheric environment. A "high temperature" environment may induce material failures that otherwise would not occur at ambient temperatures. Accordingly, many material researchers, in order to reduce the time necessary to evaluate materials in an environment, have tried to characterize the most influential attributes of various environments, and incorporate them in laboratory testing devices to accelerate "natural" failures. The simulated environmental variables are chosen in order to be reasonably representative of the predominating influences in the actual environment.
For most organic materials (plastics, fabrics, wood, coatings, etc.), the influence of water and solar radiation are probably the most detrimental. In immersion or chemical environments, water and the presence of the various chemical species are the most influential. In most cases, it is believed that a dynamic condition is more severe than a stable condition. For example, alternate wetting and drying is more severe than either the completely dry or a completely wet environment. Similarly, thermal cycling (alternately hot and cold) is more detrimental than a stable temperature condition (either hot or cold). Finally, the ability to easily adjust or change the predominating environmental influences in order to more closely simulate a dynamic condition, or to provide failure acceleration, is essential. All of these considerations led to the design of a new environmental test cabinet for material evaluation.
