e7.4 - Systems failures and system reliability

Question 1

System

Answer 1

A system refers to all of the components, processes and interactions between the parts of a complex process.

A ‘hard’ system is a piece of equipment.

A ‘soft’ system is a management or software system.

Question 2

Reliability is…

Answer 2

…In engineering terms -

‘The ability of a system or component to perform its required function under stated conditions for a specific period of time’

In general, the more components in, or more complex a system, the more unreliable it becomes.

Question 3

Holistic approach

Answer 3

Holistic approach examines the system as a whole.

The malfunction of a component and the hazard it creates is considered in terms of the effect on the system as a whole.

An example of a holistic approach would be a HAZOP study.

Question 4

Reductionist approach

Answer 4

A reductionist approach divides the system into its individual components.

An individual component is isolated and examined

The reductionist approach identifies failure of each component within the system. An example of this technique is Failure Mode and Effects Analysis.

Question 5

‘Bathtub curve’

Answer 5

Failure probability for a device typically follows a bathtub curve with three distinct regions -

Infant mortality (burn-in) period

Useful life period

Wear out (end-of-life) period

Question 6

Infant mortality (burn-in) Period

Answer 6

High probability of failure related to manufacturing defects

Question 7

Useful life period

Answer 7

Minimum, almost constant, low failure rate

Question 8

Wear out (end-of-life) period

Answer 8

Due to wear out or fatigue mechanisms, probability of failure increases