Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers



Last updated: August 15, 2017

What Does Potentiostep Mean?

Potentiostep is a technique in which an electrode is polarized in a series of potential increments or decrements.

This method can provide useful information regarding corrosion mechanisms, corrosion rates and susceptibility of specific materials to corrosion in designated environments. The potentiostep technique is used in the potentiostaircase method for corrosion testing. Pit nucleation can be determined by the potentiostep technique.

The best way to follow the logic of the corrosion rate measurement is to follow stepwise the determination of a polarization curve.

Electrochemical current noise can be measured by the potentiostep technique to clarify the passivation and the depassivation mechanisms of steel in concrete.


Corrosionpedia Explains Potentiostep

In contrast to normal polarization, potentiostep is performed over an extended time period. This permits the time-dependent development of corrosion with crevices and pores. In contrast to normal, accelerated anodic polarization, stepwise polarization can reveal the crevice effect of pores.

For example, steel in concrete is normally protected against corrosion due to a thin and dense passive layer formed in the alkaline medium of the pore solution of concrete. In the presence of chloride at the steel’s surface, the passive layer breaks down and corrosion is initiated. Potentiostep tests of steel electrodes in solution at different chloride concentrations have been conducted by simultaneously measuring the electrochemical current noise to clarify the passivation and the depassivation mechanisms.

In order to obtain qualitative correlation with neutral salt spray testing of sintered stainless steels of various densities, stepwise polarization must be employed. The slower polarization rate in stepwise polarization enables the time-consuming buildup of localized attack in the pores, analogous to the mechanism of crevice corrosion.

The detrimental effect of small pores, causing increased crevice corrosion at densities of approximately 6.7g/cm3 and higher, does not show up in a lower pitting potential because of the fast scanning normally employed in potentiodynamic polarization tests. The stepwise potential registers lower potential values that decrease with increasing metal density.


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