Bathtub curve of Engineering System Failures

Understanding the risk of failure of an engineering system is very important to avoid catastrophic accidents from happening due to the failure of safety critical items of an engineering system.

The following bathtub curve gives a general idea on expected failure potential through the life cycle of a system. The expected risk level will also behave accordingly, if necessary risk management practices are not followed ( including increased testing, observations, risk assessments, etc.).

As indicated in the “Bathtub curve”, the early phase of high failure risk can be due to many reasons such as  improper designs, untested technologies, use of unsuitable materials, lack of operator experience, etc. ).

Bath tub curve

Then the system enters a long period of reduced and steady risk level region where the system is quite safe as long as it is kept undisturbed (by not making significant changes).

Eventually the system will enter a rapidly increasing failure rate region. This is due to the aging of components and subsystems which are failed by wear, fatigue, corrosion, end of design life, or inability to properly maintain due to the old technologies or out of production parts. Manufacturers often end their warranty period before their product reaches this region.

While doing risk assessments, it is important to understand this general bathtub curve behavior of the engineering systems.