Titanium Corrosion in Distillation Columns

Summary

The separation of hydrogen cyanide (HCN) from water is accomplished by distillation with live steam stripping. The environment in the distillation column is highly corrosive, especially in the stripping section, due to the use of SO₂ and dilute H₂SO₄ to inhibit HCN polymerization. Several organic impurities are also present. Various materials of construction have been used for different parts of the columns in this service, including 316 SS, Monel, Haveg 60, and Hastelloy B. Titanium was selected for the stripping sections of two badly corroded columns on the basis of a series of corrosion tests which indicated no measurable corrosion of titanium. However, catastrophic corrosion of the first titanium replacement section occurred immediately after startup. A program was quickly undertaken to alter the chemical environment, and the corrosion was completely halted in about a week. Localized corrosion later occurred in each column but appears to have been checked.