Newmont Cadia’s Concentrator 1 40 ft semi-autogenous grinding (SAG) mill has undergone numerous liner redesigns since commissioning in 1998. SAG mill liner design has been driven primarily by the need to handle increased ball charges, a shift resulting from the finer feed sizes produced by the upstream high-pressure grinding rolls (HPGR). The SAG mill currently operates at a 22 per cent ball charge and 2 per cent ore filling. This has resulted in recurrent feed end (FE) and discharge end (DE) bolt breakages, as well as DE grate bar fractures which directly reduce overall plant availability. Comminution and Transportation Tech Inc (CTTI) was engaged to support the site’s comprehensive and ongoing root cause analysis (RCA) process using coupled Discrete Element Modelling (DEM) and Finite Element Analysis (FEA) to identify the contributing factors behind the ongoing bolting and grate bar failures. The investigation revealed that a combination of factors caused a significant drop in bolt clamping force. This loss of pretension allowed the FE and DE liners to shift radially outwards, generating a point load on the inner end of the tapered bolt head that exceeded its fatigue limit. Systematically addressing this failure sequence has allowed the site to return from a 13 week stopgap bolt campaign life to match the 26 week liner campaign life. The grate bars primarily failed because of low Charpy impact toughness due to elevated levels of phosphorus and, in one case, residual aluminium. The failures were exacerbated by infrequent, high-energy impacts from 140 mm balls. These bars were already peened and weakened by 60 mm media becoming socketed in the pebble ports and projecting onto the grate from the top of the mill. Each of the steps in this failure sequence has been addressed, and no further grate bar failures have occurred. The successful elimination of these bolt and grate reliability issues demonstrates the value of advanced simulation techniques in solving complex engineering failures and stabilising plant availability.