Bathtub Curve & Maintenance Policies
Bathtub curves are used regularly in engineering applications.
The bathtub curve is used primarily in engineering to describe the process by which engineered components fail. The curve can have other applications outside of engineering as well, but that is the primary field in which it is used. The curve refers to the rate of failure of various components in relation to time. This is usually expressed in relation to the number of hours the component has been in service.

  1. Theory

The bathtub curve theory is more of an analogy than a theory, but it is often described in more theoretical terms. The rate of decay or failure with which engineered components occur is likened to the curve of the interior of a typical bathtub. In the earliest phase of a system's implementation, the rate of failure decreases sharply over time because any initial failures or problems are overcome with a solution. During the next phase, the bottom of the bathtub's curve, the failure rate becomes more constant over the course of time as the system's components are in relatively good shape. Toward the end of its life span, the curve goes back up sharply, like the wall of the bathtub, as failures occur at an increasing rate. This is similar to an old car that has one problem after another the older it gets.
The bathtub theory can be used by engineering firms and other companies to anticipate problems that may develop. Doing so can create the opportunity to anticipate such problems in advance and rapidity at which they will occur. This allows companies the opportunity to have ample staff and other resources on hand to attack problems proactively, as they occur or in advance of their occurrence. This can help eliminate additional costs in the long run. Scheduled maintenance at regular intervals will help eliminate unexpected maintenance issues.
Anticipating problems is only possible to an extent. Unexpected problems are likely to occur in the long run. If the bathtub curve theory holds correct though, these should occur at a fairly constant or at least a slower rate throughout the middle part of a system's life span. As problems arise, they have to be dealt with in a timely fashion so that additional problems do not begin to accumulate and snowball out of control. Having maintenance policies established to ensure timely completion of problems will keep this from occurring.
At some point, the amount of money spent maintaining mechanical and other types of equipment will outweigh the cost of replacement. Plus, the number of problems that occur will do so at an increasing rate, making it difficult to engage in preventive and routine maintenance. This final curve of the bathtub represents the period in which companies must decide when and how much maintenance should continue versus engaging in full-scale replacement.