Electrochemical behavior of stainless steel W.Nr. 1.4301 in the malic acid and sulfur dioxide solution

In our earlier investigation on stainless steel W.Nr. 1.4301, corrosion damage was observed when the steel was in the contact with fruit pulps and pectin which had been conserved with SO2. In order to understand the corrosion behavior of stainless steel W.Nr. 1.4301, which is used in equipment for the production and the conservation of fruit pulps, the electrochemical behavior of the steel in an electrolyte which contained SO2 and malic acid (which is the most abundant fruit acid in fruit pulp) was studied. It was shown that, in the presence of malic acid, at potentials close to the corrosion potential, the stainless steel is completely passive in 0.1 M Na2SO4 and, at potentials more positive than 0.7 V, two parallel processes occur: dissolution of the steel and anodic oxidation of malic acid into acetaldehyde. It was already observed that, in the presence of malic acid and sulfur dioxide, the anodic process of stainless steel dissolution is accelerated and has a pitting form. In the presence of SO2, some acceleration of the cathodic process on stainless steel occurs as a consequence of SO2 reduction. The obtained results indicate that the observed corrosion of process equipment made of stainless steel W.Nr. 1.4301 is caused mainly by the presence of SO2 in the fruit pulp.