Corrosion failure of titanium tubes of a heat exchanger for the heating of dissolving lye

Corrosion of titanium heat exchangers in the processing of sylvinite ore is undesirable from economic, safety, and process sustainability perspectives. Triggered by an industrial case, we investigated the extent of corrosion during simulated contact with sylvinite ore (in dissolving lye) in relevant conditions. Detailed characterization of the failed tubes and corrosion products was carried out to understand the mechanism of failure. Corrosion of titanium (Grade 2) tubes was investigated at room temperature, 60, 70, 80, and 90 degrees C. After electrochemical and surface morphology analysis, we found that pitting corrosion of the titanium tube material sharply increased above 80 degrees C in the simulated sylvinite ore environment (pH 7.1). The failure analysis revealed extensive degradation by transgranular cracking through both the oxide and metal matrix, likely caused by a combination of the high temperature, pressure, possible vibrations, the build-up of lye deposits causing crevices, the high salt content of the lye, and possibly metal (copper, iron, zinc) impurities/deposits in or on the titanium metal, which can catalyze hydrogen evolution.