Reliability Centered Maintenance is a widely used method to optimize preventive maintenance tasks for dynamic equipment. This methodology was first used in the aircraft industry in the 1980s to achieve safety and reliability from cost-efficient and cost-effective operations, then used in other industries including nuclear power plants, and offshore oil & gas industry. Research on maintenance cost optimization in RCM based on failure rate is very rare, so it is necessary to study the effect of failure rate on maintenance cost optimization at RCM. In this study, maintenance cost optimization in RCM based on failure rate has been done by utilizing Duelist Algorithm. The purpose of this studies is to get the lowest maintenance cost value. The lowest maintenance cost was achieved by seeking the optimum failure rate and time interval. The reliability constraint based on oil and gas standard is 0.95. The optimization results show the optimal failure rate is 0.52 Ã— 10-6 per-hour and time interval of 94940 hours. It saves as much as 1819 USD during 5 years on flash gas compression system.