With the application of cathodic protection to high strength steels and alloys there is an increasing need to determine the acceptable negative limit for a particular alloy / environment combination, which can only be determined by laboratory testing.

This paper will summarize the issues associated with determining negative limit, describe the different laboratory test methods (constant strain, constant load, slow strain rate, stepped load, stepped potential etc), and the issues associated with determining the specific acceptance criteria.  Examples of test data from a number of different steels and alloys and exposure environments will be present to illustrate the problems.