Investigation of corrosion resistance of steel used in beet sugar processing juices

In this study, corrosion behaviors of materials used in diffusion units and equipment used in juice clarification steps and tubes in evaporators at Ankara Sugar Factory were investigated in terms of juice production and juice clarification processes as well as juice medium at evaporation stages. The measurements have been performed by comparing steel types used in these units and alternative types of steels that can also be used during the study. For this purpose, pH and Brix (Bx, refractometric dry matter) values of raw juice, thin juice and juice taken from evaporator have been measured during 2009-2010, 2010-2011, and 2011-2012 campaign periods of Ankara Sugar Factory. In addition to these measurements, traditional weight loss and electrochemical tests such as Linear Polarization Resistance (LP), Tafel Extrapolation (TP), Electrochemical Impedance Spectroscopy (EIS) were performed to measure and compare the corrosion rate of the metals used in different juice mediums. The metals included in the study were AISI 316L, AISI 304L grade stainless steel, St 37.2 grade carbon steel and nickel-coated St 37.2. The highest and the lowest corrosion rates were recorded for raw juice and thin juice, respectively. St 37.2 steel had the fastest corrosion rate, whereas the stainless steel AISI 316L has the slowest corrosion rate. However, AISI 316L shows only slightly higher corrosion resistance compared to the corrosion resistance of AISI 304L in different juices. Therefore, AISI 304L steel, which is cheaper than AISI 316L, can be selected as a substation of St 37.2 steel.