Abstract
Potentiodynamic measurements are used to determine key potentials to classify certain corrosion properties. The material selection for components (e.g. shafts) in corrosive environments is widely based upon these potentiodynamic measurements. Criticism for using these potentials for component design has been expressed in literature. Potentiostatic measurements are known to represent the long term corrosive impact experienced by components in a more realistic manner but are prone to scatter. Therefore a statistical approach called staircase method was adapted to the given electrochemical problem. With using this staircase method, a reliable value for the median potential (threshold potential) can be determined. This potential defines the threshold between anodic dissolution and cathodic protection. For the first time, this newly defined potentiostatic threshold potential is offering a validated median potential value for corrosion prediction in a given corrosion system based on potentiostatic measurements. Threshold potentials for the stainless steel grades 1.4057 and 1.4542 were investigated in aerated electrolytes at 25°C with different chloride ion concentrations.
Highlights
Potentiodynamic measurements are used to determine key potentials such as corrosion potential, pitting potential and repassivation potential
Conducting a sequence of independent potentiostatic tests by using the staircase method led to the findings exemplarily given in figure 3
The diagram shows the conducted sequences of consecutive potentiostatic tests in accordance with the sequence of operation
Summary
Potentiodynamic measurements are used to determine key potentials such as corrosion potential, pitting potential and repassivation potential. Failure cases have been described for components designed according to these standards Criticism for using these potentials (e.g. the repassivation potential) for component design has been expressed repeatedly in literature [1,2,3]. One major point of criticism is that the long term corrosion prediction is based on a short term dynamically measured potential value which is barely taking the kinetics of chemical reactions into account. To minimize the number of experiments necessary for gaining reliable results, a statistical approach was chosen. This approach is called up-and-down method and is known as staircase method [4]
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