Study of Corrosion of Super Martensitic Stainless Steel Under Alternating Current in Artificial Sea Water

Acknowledgement to Statoil Forsknings-senter, Trondheim, Norway, for supporting this research

 

Corrosion occurs when AC is conducted between a metal and an electrolyte. Alternating the current produces cyclic changes in the polarity of the electrode. Each half-cell reaction occurring during this cyclic polarization has different accumulative effects. For instance, the anodic half cycle when the current is anodic can lead to corrosion or pitting whereas the cathodic half cycle can lead to hydrogen charging and possibly cracking.

AC produces a shift in the electrode potential, however the direction and magnitude of the shift depends on the intensity of the AC. Pitting is usually observed after sufficient time.

Studies have been conducted to explain the phenomena and the possible implications on the design of corrosion protection systems like cathodic protection.

EIS and cyclic polarization have been used to determine the effect of different modes of conduction of AC and induced magnetic fields. Characterization of hydrogen content and scanning electron microscopy of the surface has also been used.

By studying the true wave form response of the metal under AC and DC, and by relating the response of the hydrogen charging and corrosion it will be possible to achieve a better understanding of the AC enhanced corrosion phenomena.

 

Key words: AC corrosion, waveform, pitting, hydrogen charging, potential shift