Equipment and piping in Oil Sands operations are subject to erosion, abrasion and impact wear while handling dry ore and wet slurry. Wear resistant overlays play a very important role in extending the service life of various equipment and piping in Oil Sands production operations. Tungsten carbide overlays and chromium carbide overlays are widely used to increase the wear resistance of equipment and piping. Bonding with the base material, overlay chemistry, carbide distribution, carbide volume fraction, dilution, and through thickness hardness are all important factors in determining the wear resistance and service life of overlays. Qualification and production testing are necessary to ensure the quality of the overlays. Service life of overlays depend on the quality control process adopted during the fabrication process.
Wear resistant overlays have been in use for a very long time. Lots of work has been done in the last 10 years to increase the service life of overlays and minimize unexpected premature failures. A significant part of this work was focused on quality control and testing requirements of the overlays. This resulted in new testing methodologies and improved inspection requirements.
Canadian Oil Sands mining operations have been producing oil from sand ore from the early 1960s. Oil Sands mainly consists of high hardness quartz, silica, bitumen and water. Bitumen production processes include mining the sand, washing it with hot water, slurry transportation, tailing disposal and bitumen production. Abrasion, gouging wear, impact wear, erosion and erosion-corrosion are predominant degradation mechanisms in Oil Sand mining operations. Dry and wet operations dealing with Oil Sands, cause significant wear and corrosion issues on carbon steel materials. Carbon steel is widely used for the equipment, piping, and pipelines due to relatively low cost, ease of fabrication and availability. However, carbon steel has marginal wear, erosion, corrosion resistance, and a relatively short service life. Oil Sands production operators are continuously looking for wear resistant materials. High alloy steels, cast white irons, wear resistant overlays, and non-metallic lining materials are widely used in fabrication of various equipment to improve erosion and corrosion resistance properties. Chromium Carbide Overlays (CCO), and Tungsten Carbide Overlays (WCO) are two typical wear resistant overlay materials widely used in Oil Sand production operations. High hardness, proper chemical composition, metallurgical bond between carbon steel and overlay are required for WCO and CCO to resist severe wear, erosion, and/or corrosion. However, the industry had seen a number of premature failures on overlaid equipment and piping due to inferior quality of the overlays. Typical deficiencies of CCO and WCO overlays include low hardness, spallation, insufficient carbide volume fraction, carbide segregation, base metal dilution, and low through-thickness hardness, etc. These deficiencies resulted in pre-mature failures of the overlays, loss of primary containment (LOPC), production losses, and safety/environmental impact to the oil sand production operators. Seeing the premature failures, Oil Sand operators had worked hard to establish strict overlay standards and requirements to acquire quality overlay products. This paper describes typical wear mechanisms in Oil Sands production operations, field premature failures due to the poor overlay quality, importance of quality control and testing requirements during the fabrication, and overlay qualification. It would also summarize the recent improvements on quality control of WCO and CCO in order to increase the service life and reduce premature failures. Finally, it describes the benefits from implementing company specific overlay standards, overlay qualification & production testing, and quality control.
