plantavailability

Plant availability is a reliability metric that expresses the proportion of time a plant—such as a manufacturing facility or power plant—is able to operate at its specified capacity during a defined period. It is used to assess how effectively a plant is ready for production and to guide maintenance and investment decisions.

Common definitions distinguish inherent, operational, and achieved availability. Inherent availability, A_inh, is calculated as MTBF / (MTBF + MTTR), where MTBF is mean time between failures and MTTR is mean time to repair. Operational or achieved availability, A_op, measures the fraction of scheduled time that the plant is actually online, often expressed as (Total time − downtime) / Total time. Effective availability may adjust for planned shutdowns, ramp times, or other non-operational intervals.

Calculations require time-based data on failures, repairs, and planned maintenance. Availability is influenced by maintenance quality, preventive maintenance practices, component aging, redundancy or spare parts, and the reliability of subsystems. Higher availability typically improves capacity, throughput, and return on investment but may require balancing maintenance costs and risk of failure.

Applications include manufacturing, energy generation, and processing industries where uninterrupted operation is critical. Plant availability is related to, but distinct from, related metrics such as reliability, maintainability, and overall equipment effectiveness (OEE). See also MTBF, MTTR, and OEE for related concepts.