Not all kraft mills have corrosion concerns in black liquor environments despite operating with similar temperatures, sulphidity and caustic content. There is reason to believe this change in liquor corrosivity is due to the presence of softwood extractives. This study used a synthetic solution to simulate weak black liquor environments (5 g/L sodium hydroxide and 20 g/L sodium sulphide) at 160°C to perform laboratory experiments. These experiments used a K02700 (A516 grade 70 carbon steel) working electrode to perform potentiodynamic, open circuit potential and immersion experiments to determine how liquor corrosivity changes in the presence of 1 or 5 g/L catechol, tannic acid or sodium citrate. These experiments were repeated in the presence of 1 g/L chloride in an attempt to increase the kinetics of corrosion. The catechol and tannic acid increased liquor corrosivity; however, the influence of 1 g/L chloride in the presence of an extractive was less clear. The reduced corrosion rate measured in the immersion studies in the presence of catechol, tannic acid and chloride is thought to do with the chloride interfering or binding with the chelates in solution rendering it less corrosive.
Key words: black liquor, carbon steel, K02700 extractives, catechol, tannic acid, sodium citrate, potentiodynamic, open circuit potential, autoclave