UNDERSTAND THE CONCEPT
Reliability is the probability of performing the required function for a stated time under stated conditions. In the exponential model, R(t) = exp(−λt), where λ is a constant failure rate and t is mission duration. With a compatible mean-time estimate M, λ = 1/M.
For a repairable asset, using an MTBF estimate in this model assumes stable, comparable behaviour and a constant rate. The mission calculation asks about no failure during the mission; it does not credit repairs within that mission. Ageing, common causes and changing duty can invalidate this simple model.
TRY THE MODEL
Reliability, over time.
Change the inputs to explore a constant-failure-rate scenario. All times are in hours.
Learning model only. The mission calculation assumes a constant failure rate and no repair credit during the mission. Inherent availability is a separate steady-state measure; it excludes planned downtime and logistics or administrative delays. This calculator does not validate a plant design.
Questions to take back to your team
- Are the failure definition and operating duty consistent?
- Is the constant-rate assumption defensible?
- Is the mission duration clearly stated?
Further reading
Explore the primary references below. Requirements and applicability depend on your organization and jurisdiction.
