As most mining projects around the world operate in harsh environments, one of the constant threats facing the sector is the wear and tear of on-site metal equipment and structures.
Mine sites suffer from a wide range of abrasion, impact and corrosion issues, with the equipment being affected including – but not restricted to large excavators, pumps and valves. Since project proponents are constantly facing increasing economic pressures, they must plan a truly sustainable approach in order to increase operational efficiencies, keeping an eye firmly on reducing maintenance expenditures whenever possible.
Fortunately, evolving technologies allow operators to effectively address variations in the size of the abrasive media as well as its velocity and impact. Economic technologies such as thermal spray metal systems, ceramics, reinforced epoxies and urethanes are valuable when it comes to highly abrasive and corrosive applications.
Technology selection
A few things to consider when selecting which technology to apply include cost and ease of application, the average time between failure performance, characterisation of potential failure that could significantly impact equipment or overall plant output, in addition to dry service conditions, which may involve higher grinding and gouging wear. Moreover, wet service (slurry) applications can help negate scratching abrasion and corrosion.
Effective corrosion management can result in lower maintenance costs, decreased inspection/monitor expenses, an improved ability to meet production goals, a fall in product loss, asset preservation, fewer environmental releases as well as related fines (that in turn improves public relations and a drop in worker injuries). Gouging, which primarily affects drag line buckets, excavators and crushers is of particular concern.
Over time, a mine’s surface becomes plastically deformed and work-hardened by the abrasive forces. Under these circumstances, deteriorating equipment will fail to work efficiently, resulting in additional expense and the need for enhanced labour protection. Miners looking for new equipment are advised to obtain equipment made of wear-resistant material such as stronger martensitic steel, or purchase a lower grade austenitic alloy and accept a higher wear rate.
For plant already impacted by gouging, it is possible to repair or extend its life with protective coatings at a fraction of the replacement cost using weld overlay of selected alloy rod or a thermal spray coating. Meanwhile, high distress grinding abrasion occurs when an abrasive surface is crushed between opposing faces, after which the fracturing stress is transferred to the metal surface, resulting in micro-cutting and furrowing.
Generally, high stress grinding abrasion affects the milling and grinding phases used to liberate the valuable ore from the waste, with the metal loss of these systems directly impacting yield and output. Then there’s low stress scratching, which affects the movement of slurry and other systems where particles move freely across a surface.
Unless the metal is hard enough to resist, these particles cut micro-furrows and grooves into the surface, with chutes, gravity classifiers, screens and pneumatic conveying systems experiencing this form of wear. When it comes to carrying out repairs using coatings, there are usually three choices – alumina ceramic tile inserts affixed by chemical adhesives, pre-moulded rubber elastomers and ceramicreinforced polymers (which provides the wear resistance of ceramic tile and the ductility of a rubber elastomer).
Ultimately, to gain the best possible outcome, the remediation process should begin with an assessment of current asset maintenance practices and create a prioritised list of critical equipment and gauge their performance. Following this, an evaluation of their impact on overall plant productivity is required. Once this is completed, a strategy to establish best practices by using subject matter expertise, along with a well-planned technology rollout, is ideal. This should then be followed by periodic inspections and refinements.
