Corrosion Behavior of Multi-ion Recombination on Q235 Carbon Steel During Transportation of Reclaimed Water in Heating Pipes

Abstract

Purposes The study was focused on the corrosion behavior of heating pipes during the transportation of reclaimed water, where the corrosion factors and interactions amoug these factors were considered. Methods Specifically, the comprehensive effects of multiple ions (Cl-, SO42-, HCO3-, Ca2+) and pH on Q235 carbon steel (main materials used in heating pipes) were researched by electrochemistry methods. Meanwhile, weight loss method was also applied for the verification of the reliability and practicability of the electrochemistry method. Findings The results indicated that O and Cl- are the key factors to the corrosion of Q235, which could be inhibited or promoted by other ions with different ionic properties and concentrations. For SO42-, the corrosion of Cl- on Q235 could be suppressed (50~100 mg/L) owing to the competitive adsorption between Cl- and SO42- or promoted (150~250 mg/L) owing to the improved electrical conductivity of solutions, which is depended on the ion concentrations. A small amount of HCO3- could lead to the improvement of corrosion on Q235, though excess H+ from high concentrations of HCO3- (100~200 mg/L) could restrain the corrosion of Cl-. Because of the increase of electrical conductivity, addition of Ca2+ at low concentrations (less than 150 mg/L) would facilitate the corrosion of pipes, while the Ca(OH)2 precipitates derived from the reaction between high concentrations (150~200 mg/L) of Ca2+ and OH- prevented Q235 from being corroded by Cl-. Moreover, the different surface states of materials would result in different corrosion morphologies according to the analyses of SEM and EDS. Conclusions The combination of electrochemistry method based on laboratory tests and weight loss method from the actual corrosion status would have significant practicality. The study provides a theoretical basis and data for the pretreatment of reclaimed water when it is transported by the heating pipe networks, which is of practical importance.

Keywords

• heating pipes
• reclaimed water
• corrosion behavior
• electrochemistry method
• multi-ion recombination