The environmental conditions that must be simulated and the degree of acceleration that is required often determine the choice of a laboratory test. In immersion testing, acceleration is achieved principally by: (reference)
Once the environmental conditions have been determined, and the test designed, then it should be repeated a sufficient number of times to determine whether it meets the desired standard for reproducibility. Immersion tests can be divided into two categories:
Simple immersion tests: basically small sections of the candidate material are exposed to the test medium and the loss of weight of the material is measured for a period of time. Immersion testing remains the best method of screening and eliminating from further consideration those materials that should not be considered for specific applications. But while these tests are the quickest and most economical means for providing a preliminary selection of best suited materials, there is no simple way to extrapolate the results obtained from these simple tests to the prediction of system lifetime.
Alternate immersion tests: another variation of the immersion test is the cyclic test procedure where a test specimen is immersed for a period of time in a test environment, then removed and dried before being re-immersed to continue the cycle. Normally hundreds of these cycles are completed during the course of a test program.