Definition:
Useful Life is the period during which a component operates with a relatively constant failure rate before degradation significantly increases risk.
Key Points:
- After useful life, the failure rate rises sharply.
- SIS components should be replaced before useful life ends.
- It is similar to but distinct from Lifetime.
Example:
A solenoid valve with a useful life of 10 years under expected service conditions.
See Also: lifetime
Cited Source:
- IEC 61508-2:2010, Clause 7.6.3
- Power Quality Blog – related to power distribution but the same concepts hold – here