Abstract
We report an investigation of the corrosion susceptibility of welded S32550 Duplex stainless steel in the presence of tritiated hydrogen peroxide, chloride and carbonate, which are found in radioactive aqueous solutions. It is well known that a structure transformation occurs during welding, this could lead to localized corrosion of the welded zone. The electrochemical behavior of welded S32550 steel was studied using cyclic voltammetry and electrochemical impedance spectroscopy to provide an indication of mechanisms and oxide layer modifications. Increasing hydrogen peroxide concentration produces several effects. Although the corrosion potential does not change, the prepassive current is higher and, depending on passive potentials and hydrogen peroxide concentration, the passive oxide layer and its characteristics change showing the importance of the radiolytic species in passivity. Also, the breakdown potential shifts towards more positive values on increasing 3H 2O 2 concentration. Thicker passive oxide layers should limit localized corrosion. Examination of the impedance spectra indicates ionic diffusion in the outer oxide passive layer and a diffusion barrier effect for the inner oxide. As the hydrogen peroxide concentration is further increased, these effects appear more pronounced. Carbonate ions should keep the alkaline buffer pH constant giving protection from localized corrosion, and 3H 2O 2 should enhance the characteristics of the inner passive oxide layer. Due to the effects of these two parameters: alkaline pH kept constant at the electrode surface and enhancement of the characteristics of the inner oxide layer by 3H 2O 2, no pitting is observed in presence of chloride ions. Also, an equation, giving the pitting potential limit is derived. The ability of the nucleation sites to propagate as metastable pits is limited by the presence of the 3H 2O 2 and CO 2− 3 buffers.
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