Titanium-Clad Ignition Studies in Simulated Pressure Oxidation Leaching Environments

摘要

For large Pressure Acid Leaching (PAL) autoclaves as used for the nickel industry, titanium-clad steel construction offers significant capital and maintenance cost reduction benefits compared to refractory-lined steel construction. Titanium has become the material of choice from the corrosion perspective. The exceptional corrosion resistance of titanium and its alloys in this lean sulfuric acid environment has been demonstrated over several decades. Pressure Oxidation Leaching (POX) extractive metallurgy processes also operate under acidic conditions but with high oxygen partial pressures. Titanium can be subject to ignition in the oxygen-rich environment if damage to titanium's protective oxide layer occurs in conjunction with the other well-known components of the "Fire Triangle." When solid or monolithic titanium components are used, ignition can result in complete burning of the component and sometimes drastically unsafe conditions. This experience has limited the acceptance of solid titanium as well as titanium-clad autoclaves in this service (except for several small- and medium-sized laboratory units). To provide increased confidence in these applications, a study of the effects of the substrate metal upon the outcome of an ignition event is undergoing. The objective is to compare the ignition result of solid titanium, titanium clad onto carbon steel and clad onto stainless steel base metals, and titanium clad onto carbon steel with an oxidation-resistant and chilling interlayer metal between the titanium and steel backer. Preliminary testing was performed using conventional oxy-fuel cutting equipment. More definitive testing is being performed at Southwest Research Institute using a small test autoclave. This report presents results to-date of the ongoing work.