DETERMINATION OF THE SYNERGISM BETWEEN EROSION AND CORROSION IN POTASH-SAND SLURRY CORROSION OF CARBON STEEL

Abstract

Erosion-corrosion is a common problem in the mining and mineral processing industries, both in Saskatchewan and other parts of the world. The combination of erosion and corrosion in flow systems may lead to severe material wear in pipelines and equipment. When erosion and corrosion interact, a synergy may occur between them. Erosion-corrosion synergism may cause more or less material loss beyond the effects of pure erosion and pure corrosion. Experiments were performed using saturated sand-potash slurries over a wide range of solids concentrations, velocities, and two particle sizes. A flow loop apparatus circulated the slurry through an AISI 1018 carbon steel elbow. An additional apparatus was developed to apply cathodic protection to the inside surface of the elbow. The research conditions aimed to mimic those found in the potash industry. Experiments focused on determining the effect of solids concentration, flow velocity, and particle size on the protection current density (iprot) and corrosion rate (CR) within the elbow. A complex relationship was oberserved between iprot and slurry concentration. As the slurry concentration was increased, iprot increased up to a critical slurry concentration between 4 – 10 wt.%. Above the critical slurry concentration, iprot decreased with increasing slurry concentrations. This relationship was consistent regardless of the flow velocity. Particle sizes of 0.55 mm and 1.05 mm were both examined in this research. It was observed that the elbow required a larger iprot when smaller sand particles were used, relative to when larger particles were used. In all experiments, enhanced corrosion material loss caused by erosion-corrosion synergy was quantified. Enhanced corrosion was shown to increase the total corrosion rate by as much as 52% over varying slurry concentrations. Additionally, the smaller sand particle size increased the enhanced corrosion by an average of 12.5% across the conditions examined. All the observed changes in enhanced corrosion and iprot were most likely caused by slurry concentration, flow velocity, and particle size altering mass transfer rates of oxygen. From the phase IV research, a linear correlation was developed relating the CR to iprot. The linear relationship was consistent for all flow velocities and slurry concentrations tested. This suggests that corrosion rates could potentially be predicted from the measurement of iprot for carbon steel – potash slurry systems, and possibly others.