Multifactorial study of erosion-corrosion mechanisms in the wear of a low carbon steel by slurry of copper tailing

Abstract

The hydraulic transport of solids (hydro-transport) in the form of slurry is an essential technology for transporting large volumes of raw, process and waste materials in several industries such as oil and gas, metallurgy and mining. However, although this type of transport system is considered safe compared to other alternatives, corrosion and erosion have constituted an essential threat to the integrity of the slurry transport system. Erosion-corrosion (E-C) of metallic materials describe the material degradation process where mechanical wear by solid particles interact with the electrochemical corrosion process. A major issue in approaching the understanding of E-C material loss processes is the large number of variables involved since multiple factors can act simultaneously or interact between them, affecting considerably the type of material removal mechanisms involves in the wear process. Thereby, a comprehensive understanding of the erosion-corrosion mechanisms is of practical importance to establish the mitigation strategy. This research focuses on quantifying and characterizing the effects of selected factors and their interactions on the E-C wear in conventional pipe steel, API 5L X65, by a synthetic copper tailing slurry. The studied parameters are velocity, particle concentration, temperature, pH, dissolved oxygen and copper ions. The study by experimental design was conducted using a rotating cylinder electrode to induce the E-C damage. The contribution and statistical significance of each studied parameter in the wear process were determined using statistical tools while the wear mechanism affected by the main factors and interactions was analyzed using surface characterization techniques and electrochemical analysis. The statistical analysis revealed that three main effects and two interactions explain the increment in wear rate. These are slurry velocity, dissolved oxygen, and temperature, and interactions between velocity/dissolved oxygen and particle/copper ions content. In addition, it is concluded that increment in particle energy and frequency of impact are the main contributors in removing the material at higher particle velocity. Whereas, the availability of dissolved oxygen prevents the formation of a work-hardened layer in the sub-surface of the steel and promotes localized-type corrosion by a mechanism dominated by erosion-enhanced corrosion. The remaining main effects and interactions can be described regarding the same mechanism.