795 post-commissioning tension checks, are essential for achieving reliable long-term mill operation. This requires each bolt to be tensioned to its specified elongation and verified using ultrasonic bolt-tension measurements under the supervision of an experienced mill installer. When the bolted connection design is robust, routine re-tensioning is generally unnecessary once operational loads have stabilised; however, it remains best practice to periodically spot-check a selection of fasteners as part of standard maintenance procedures. In recent years, online fastener-monitoring systems have become increasingly accessible, providing a practical means for continuous remote monitoring and risk mitigation. Washout is the localised loss of material from a mill component caused by slurry flowing between or beneath the protective liners. It most commonly results from incorrectly installed liner or poor maintenance. Once slurry passes between liner segments, it erodes a groove, channel, or cavity in the underlying component. The resulting reduction in wall thickness increases local stresses in and around the damaged area. Depending on its location, this elevated stress can significantly reduce equipment life or, in severe cases, lead to catastrophic failure. In most cases, washout can be prevented with diligent liner monitoring practices. This should include regular in-situ liner scans, liner wear reports, and Discrete Element Method (DEM) based liner wear prediction and optimization. Two examples of fatigue failure are detailed below. While no root-cause analysis has been conducted by the author, these cases are presented to demonstrate common fatigue mechanisms and highlight mitigation strategies that could have reduced the likelihood of failure. Figure 2 shows a crack propagating through a mill shell end flange at the connection between the shell and the mill head. The crack initiates immediately adjacent to the head radial flange split. This is relevant as the head flange creates a stiffness discontinuity, which would not have been captured in an axisymmetric finite element analysis. The left side of the figure shows stress behavior accurately captured in a detailed finite element model. Additional contributors could include the location of the intra-flange radial weld seams, and the condition of the flange connection (including fastener preload, flange opening and connection utilization). Figure 2 – Mill shell crack at circumferential flange, adjacent to radial head flange This failure has been seen in several very large ball mills around the world, including some 28ft diameter ball mills. Figure 3. In this case the crack propagates through the cast mill head, with its initiation originating at the termination of the head radial flange near the outer diameter of the trunnion flange. As with the shell failure, this critical stress location would not have been identified if the radial-flange stress concentration
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