Effects of failure severity and critical failure modes on reliability and availability

Unexpected failures in process industries lead to production loss and an increase in the cost of maintenance as well. Reliability, Availability, and Maintainability (RAM) analysis is a helpful tool in reducing the number of failures. Also, it helps to increase the mean time between failures by carrying out necessary design modifications with an appropriate improvement in the maintenance schedule. The present study examines the effect of critical failure modes on the reliability of the Effluent Treatment and Injection plant (ETIP) of an oil field. The essential equipment of the plant is identified, which upon failure could result in downtime of the facility. Based on the field data and OREDA database, probable failure rates in each critical mode and mean active repair time are developed with the help of Reliability Block Diagrams (RBD) using the BLOCKSIM™ tool. Using Monte Carlo approach, performance of the system is analyzed in the critical failure modes over the lifetime. It is seen that the reliability of the chosen process plant decreases with time in the critical failure modes while the combined effect of all critical failures on the reliability is about 5%. While criticality of the analysis depends on estimates of failure rates and the repair time of essential equipment, the mean availability of the plant is estimated to be 97.62%.