Frequently Asked Questions

Q-FOG Cyclic Corrosion Testers

Q: What is Cyclic Corrosion Testing?

Cyclic corrosion testing is intended to be a more realistic way to perform salt spray tests than traditional, steady state exposures. Because actual atmospheric exposures usually include both wet and dry conditions, it makes sense to pattern accelerated laboratory tests after these natural cyclic conditions. Research indicates that, with cyclic corrosion tests, the relative corrosion rates, structure and morphology are more similar to those seen outdoors. Consequently, cyclic tests usually give better correlation to outdoors than conventional salt spray tests. They are effective for evaluating a variety of corrosion mechanisms, including general, galvanic, and crevice corrosion.

Cyclic corrosion testing is intended to produce failures representative of the type found in outdoor corrosive environments. CCT tests expose specimens to a series of different environments in a repetitive cycle. Simple exposures like Prohesion may consist of cycling between salt fog and dry conditions. More sophisticated automotive methods call for multi-step cycles that may incorporate immersion, humidity, condensation, along with salt fog and dry-off. Originally, these automotive test procedures were designed to be performed by hand. Laboratory personnel manually moved samples from salt spray chambers to humidity chambers to drying racks, etc. More recently, microprocessor controlled chambers have been used to automate these exposures and reduce variability.

See Technical Bulletin LF-8144 for more information

Q: Why is an air preconditioner used with the Q-FOG CRH Cyclic Corrosion Tester?

Q-Lab includes an air preconditioner as a standard accessory with every Q-FOG CRH tester. Not all manufacturers do this, so we often are asked why it is necessary. In short, the Q-FOG CRH air preconditioner ensures reliable, stable, repeatable chamber conditions and precise control of  transitions. These are necessary elements for achieving reliable corrosion test results.

There are three major benefits of the air preconditioner:

  1. Cooling and dehumidifying laboratory air ensures consistent compliance with “ambient” dry-off conditions in standards such as VW PV1210 and GMW 14872.
  2. The air-preconditioner reduces the dew point of air entering the chamber by drying the air. This allows the tester to comply with the Renault ECC1 cycle or others with low dew points.
  3. Control of the air entering the chamber enables very precise linear transitions between conditions, which promotes test repeatability.

The graph below is an example of how the drying and cooling action shifts the range of available tester conditions. This example is for a well-controlled lab environment but a similar improvement is realized in hot, humid laboratories. The preconditioner shifts the incoming air dew point from the dotted black line to the solid blue line, making available the region shaded in green. This region includes several key “ambient” setpoints from major corrosion standards.

The air preconditioner removes repeatability issues associated with corrosion testing. Since the air coming from the air preconditioner to the tester has consistent temperature and relative humidity conditions, the Q-FOG CRH enables precise control of test conditions and linear ramping that is consistent from test to test.

Preconditioner Graph




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