Fouling influence on pitting corrosion of stainless steel heat exchanging surface

In this work the influence of surface deposits, namely rust and scale, on pitting corrosion of the AISI 316 steel was investigated. The rust from the mild steel corrosion in NaCl aqueous solution was deposited on the stainless steel surface. The scale carbonate layer was formed using electrochemical scaling technique. Potentiodynamic polarization was used to evaluate the pitting potential of the steel covered with rust or scale deposits. It was established that iron corrosion products can accumulate chloride ions, but the local concentration of the latter appeared to be insufficient to reduce the resistance of AISI 316 steel to pitting in solutions with NaCl concentration up to 2.8 g/L. The scale layer while being able to reduce the oxygen supply to the surface 10 times does not affect pitting resistance of the steel in 35 g/L NaCl solution either. The acidic media inside the pits was found to be responsible for the dissolution of the calcium carbonate over and around the pits. Pitting resistance depends only on the chloride content in water and neither rust nor scale deposition influence pitting corrosion of AISI 316 stainless steel.