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Manufacturers use corrosion tests to determine the most cost-effective materials for outdoor use.
Customers also test products for contract compliance and consumer safety. Corrosion testing provides data to assess the probable degree of material degradation. Variable environments preclude a universal corrosion test. To predict service life and find the most economical means to achieve it, environmental conditions should be duplicated in cyclic corrosion tests. This article presents steps to select a cyclic corrosion cabinet.
Two types of lab corrosion tests have been developed over the past 70 years-- Traditional Salt Spray (Fog), and Cyclic. Cyclic testing is divided into two types of tests-Basic and Advanced (Figure 1).
The popularity of cyclic testing comes primarily from the improved reliability of results that can be correlated with outdoor exposures. Coatings and other protective systems can be developed and tested more rapidly, giving design engineers a competitive advantage for bringing superior products to market.
Cyclic Testing
Cyclic testing replicates varying end-use environments. In the early 1970s, a prototype was developed that inserted a dry-off period between episodes of saturated humidity. The reason for the drying period was the observation that most corrosion takes place during transition from wet to dry, rather than when an item is continuously wet.
During the early days of cyclic testing, samples were placed in a cabinet that had a specific condition-such as corrosive fog. When the prescribed time ended, the sample was moved to the next condition: an oven for dry heat, a lab bench for ambient temperature, a sink for complete wetting, etc.
Such manual sample movement no longer is necessary. Advanced cyclic cabinets bring multiple environments to the sample, providing repeatable test conditions, reduced operator error, time savings, and much-improved reproducibility. A cabinet can create up to 14 environmental cycles in any order, replicating the wide variety of outdoor conditions.
Operating Cycles
An advanced cabinet can create all 14 cycles (Table 1), reducing the need for several cabinets to perform different tasks. Advanced cabinets can do all types of tests and provide for future testing needs.
Comparisons Among Cabinets
EXPOSURE ZONE AND FREE SETING OF FOG A 30-ft^sup 3^ (850-L) chamber from one manufacturer may actually be smaller than a 20-ft^sup 3^ (565-L) chamber from another because some manufacturers...