A roof should be inspected annually but could be more than that. One should inspect his roof for damage after high winds, hail, or other events that could damage structures.
Daily
before use
For fish tanks, weekly, at a minimum.
Septic tank drains should be inspected and cleaned every 3-5 years to ensure they are functioning properly.
The whole vehicle should have a safety inspection every service.
Fire extinguishers should be inspected annually - by a suitably qualified person.
Physical damage to a cylinder is seldom repaired. More often the motor is replaced.
Radiator hoses and heater hoses should be inspected yearly and replaced when neccessary.
The error rate is less taht 1%. You should have your valves inspected often.
The contents of any emergency kit should be routinely inspected, depending on the anticipated necessity and/or the current disaster "season." Depending on where you are, it should be inspected and replenished every 6-15 months, if not more frequently.
They are inspected at least once a year. Inspections are random - and without warning.