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Short Note on Bathtub Curve
  • Difficulty Level : Basic
  • Last Updated : 26 Oct, 2020

Bathtub Curve is generally graph that is used to graphically demonstrate run-to-failure maintenance strategy. This curve simply represents overall life cycle of assets and failure rate of overall population of assets over time. Bathtub curve is usually considered to be one of most useful and essential graphical representations of reliability of assets.

Assets are usually equipment, components, or parts of equipment, etc. With help of such graph, one can determine and predict when failure usually happens and then identify root causes. After identifying root causes, one can prevent failure from occurrence by simply fixing root causes. It is being named bathtub curve simply because curve resembles longitudinal section of bathtub.

Different Sections of Curve :
Bathtub curve is basically divided into three different sections. Asset generally faces these three sections all over their lifetime. Three different sections of bathtub curve are given below –


  • Infant Mortality Section :
    Infant mortality section is simply referred to as early failure period. By seeing curve, one can easily understand that in this section, asset is beginning with its usage for first time. Initially, failure rate i.e. probability of failure occurrence is very high and with increasing time, there is a gradual decrease in failure rate. In this section, failures are usually occurred due to manufacturing defects, installation issues, design issues, material defects, or improper start-up procedures, etc.

  • Normal Life Section :
    Normal life section is simply referred to as usual life period or steady-state operation. It can also be said that this section represents normal operating life of assets. By seeing curve, one can easily understand that in this section, asset is still experiencing failure but at normal and low rate. In this section, failures are usually occurred due to overloading, hidden defects, collision with other objects, mistakes of personnel, etc.

    Failure occurrence generally depends upon function and condition of particular asset. Therefore, for different asses, failure rate can be different. In this period or section, an asset can be remaining unchecked for some time as chances of failure occurrence is low during this period and therefore resources can be used wherever required. Failure rate is almost constant in this phase. One can say that failures generally occur due to random events.

  • Wear-out Section :
    Wear-out section is simply referred to as aging period. By seeing curve, one can easily understand that in this section, there is gradual increase in failure rate of assets with increasing time. Number of failures occurrence experienced by assets generally increases with time. In this section, failures are usually occurred due to fatigue, wear, gradual deterioration, corrosion, etc. This period simply represents end of life cycle of assets.
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