Evaluation of the corrosion resistance of selected stainless steels to an environment simulating biological corrosion

Abstract

ABSTRACT Stainless steels are widely used materials due to their excellent corrosion resistance, mechanical properties, and aesthetic appeal. Ferritic stainless steels are a subclass of stainless steels that are widely used in various industrial applications, including the construction of water storage tanks. These materials are susceptible to various forms of corrosion, including microbial induced corrosion (MIC), which is a significant concern in industrial settings. This thesis provides a comprehensive overview of stainless steels, with particular emphasis on ferritic stainless steels and their susceptibility to biological corrosion. Theoretical aspects of different corrosion mechanisms and their impact on the microstructure and corrosion resistance of the material are discussed in detail. The practical part of the thesis describes the experimental investigation carried out to evaluate the corrosion properties of DIN 1.4521 ferritic stainless steel. The testing methods used to assess the corrosion resistance of the material included electrochemical potentiodynamic polarization testing and double-loop electro potentiokinetic reactivation (EPR DL) methods, determination of corrosion parameters as well as sensitization of the material. Four different concentrations of NaCl (0.9%, 3.5%, 10%, and 20%) and three different concentrations of H2SO4 (1%, 2%, and 5%) were selected for testing. The NaCl solutions were selected to simulate the corrosion properties of contaminated water stored in water storage tanks, while the H2SO4 solutions were used to simulate the corrosive environment created by bacteria during microbial induced corrosion (MIC). The results showed that the corrosion resistance of stainless steel is influenced by the composition of the corrosive environment, with the highest corrosion rates observed in 5% H2SO4. The SEM analysis provided valuable information about the types of corrosion and their effects on the microstructure of the stainless steel samples. Furthermore, it was found that the concentration of H2SO4 at the level of 5% increases the corrosion rate by up to three orders of magnitude. These findings indicate that the presence of sulfuric acid-metabolizing bacteria on the surfaces of ferritic stainless steel water tanks may have a significant effect on their corrosion behaviour.