Corrosion Failure Study Of Heat Exchanger Of Styrene Plant And Selection Of Corrosion Resistant Materials

The heat exchangers of styrene plant are facing severe corrosion in the process of production. 20 steel that is usually used cannot meet the requirements of production. The corrosion fail of heat exchanger of styrene plant is studied in this paper and the corrosion fail mechanism is determined. The corrosion behaviors of 20 steel,Cr13 steel,316 L steel and amorphous coating are tested by electrochemical methods. The corrosion behaviors of 20 steel in corrosion environments containing different ions are analyzed, and corrosion resistant material that is appropriate for the production is selected. The immersion tests are carried out by high temperature and high pressure reaction kettle to verify the results of electrochemical tests.The corrosion fail mechanism is determined by analyzing a leaking pipeline of the heat exchanger. The results show that the corrosion sort of the inner wall is uniform, the inner wall is in light corrosion level. The corrosion sort of the outer wall of the pipeline is local corrosion. There are many corrosion pits on the outer wall, which is the main cause of the leakage. Oxygen ions and Chlorine ions in the corrosion environment lead to the pitting corrosion of the outer wall. The binding force of the corrosion products and steel is weak and the corrosion products can be lifted off, which lead to corrosion and perforation.The 20 steel has the characteristics of active polarization in the environment containing different ions and the corrosion resistance of the 20 steel is the worst. Cr13 steel, 316 L steel and amorphous coating have the characteristics of passive polarization and their corrosion resistance are excellent. The corrosion resistance of 316 L steel and amorphous coating are better than Cr13 steel.The surface of 20 steel is cover by corrosion products in the corrosion environment containing Cl-, the corrosion products are porous and the protective effect of it is poor, the surface of 20 steel has little corrosion products in the corrosion environment containing S^2-, the corrosion rate of 20 steel is the highest in different corrosion environment. The surfaces of Cr13 steel, 316 L steel and amorphous have little corrosion products in different corrosion environments. The surface of amorphous coating is uneven because of spraying process, which lead to higher corrosion rate. The corrosion rate of 316 L steel is the least in different environments.