The Porgera Gold Mine in Papua New Guinea placed its Processing Plant under care and maintenance in April 2020, leaving four large autoclave reactors offline. A proactive preservation program was implemented: autoclaves were safely drained and filled with a low-density acidic solution of pH<4 and held at atmospheric pressure and temperature for over two years. the introduction of steam-boiler heating to maintain internal temperatures of 20–30°c was applied after inspection in 2022. this approach preserved brick hydration and sustained chemical passivation of linings, while preventing thermal shock and corrosion during the idle period. conditions were closely monitored through routine inspections and temperature logging, and final inspections and minor repairs were completed before recommissioning and start-up. recommissioning commenced in december 2023, after more than three years of care and maintenance. a carefully sequenced ramp-up was executed across all units, following equipment supplier protocols for brick curing as well as internal operational procedures. a gradual, controlled increase in vessel pressure and temperature was applied to each autoclave, mitigating risks during start-up. operator refresher training was undertaken ahead of the restart to ensure safe execution. the outcome was exceptional: all four autoclaves were successfully recommissioned with zero brick lining failures and no major relining or structural repairs required. the pressure oxidation circuit was restored to normal operation on schedule and within budget in july 2024, achieving design throughput shortly after restart. this case study highlights the effectiveness of structured preservation and recommissioning strategies in autoclave operations. by maintaining controlled thermal and chemical conditions throughout care and maintenance, porgera demonstrated that long-term idle autoclaves can be safely and efficiently restarted. the lessons learned provide a benchmark for future shutdowns of operating plants and recommissioning projects in high-sulfide gold processing environments.>