Pitting corrosion of surgical instruments in disinfectant environments

The reusable surgical instruments are subject by law to treatments of disinfection and decontamination. Corrosion, although minimal, during these treatments is inacceptable and therefore it is necessary to pay great attention to the choice of materials with which the tools are built and in the composition of disinfecting agents. The main constituents of detergents for disinfecting and decontamination of surgical instruments are quaternary ammonium salts, and organic acids such as peracetic acid. The reusable surgical instruments are manufactured, according to the standard specification DIN EN ISO 7153-1, with stainless steels 304,316 and 420. However the chloride ions present in disinfecting solutions can produce pitting corrosion on stainless steel surgical instruments. This study is a collaboration between the Department of Industrial Engineering of the University of Padua and a company in Padua that produce detergents and disinfectants bactericidal and virucidal. The main goal of the work is to determine the corrosive action of various formulations of detergent and to seek an appropriate inhibitor, compatible with the disinfectant, which is effective in increasing the resistance to pitting corrosion. Two different formulations called F1 and F2 were after compared. The first, called F1, contain chlorides and an various amounts of an inhibitor, while in the second, called F2 the chlorides have been replaced with the amines and no inhibitors were added. The results show that the presence of the inhibitor cause an increase in the resistance to pitting corrosion but also that the best choice is to replace the chloride ions with amines. Corrosion resistance was evaluated with potentiodynamic polarization tests, immersion tests and electrochemical impedance spectroscopy (EIS) tests.