Investigation of the corrosion behavior of Q345 steel under ammonium chloride concentration gradient based on electrochemical technology

Abstract

Preventing ammonium salt corrosion is a key problem for ensuring the stable operation of continuous production, which is of great importance for the chemical industry. This study examines the ambient-temperature corrosion of Q345 steel with NH4Cl solution (with concentrations of 0.01, 1, and saturated mol/L over 200, 500, and 1000 h) using electrochemical methods. This study aims to reveal ammonium salt corrosion in refining facilities and provide support for high-temperature corrosion research. The results show that as the NH4Cl concentration increases, the EIS Nyquist diagram shows a weakened capacitive arc and a transition to Warburg impedance. This indicates Cl− diffusion-controlled corrosion is significantly enhanced. High concentration and long corrosion time lead to a weakened protective effect of the rust layer and a decrease in charge transfer resistance, resulting in the maximum self-corrosion rate in saturated NH4Cl solution at 1000 h. Exposure in high concentration for a short time is preferred to induce local corrosion, while exposure in low concentration for a short time may cause passivation. This study reveals the key role of Cl− diffusion in the long-term corrosion of Q345 steel in an NH4Cl environment and the corrosion behavior under high and low concentrations, providing experimental support for corrosion assessment and protection.