Trend Analysis
The main objective of trend analysis is directed to know whether the equipment is deteriorating or improving. This can be known by analyzing the past failure data in terms of TBF (in case of repairable equipment) or TTF (in case of non-repairable equipment). From the analysis, one of the following three conclusions may be drawn.
Positive trend implies that the machine is improving with time. This may be due to the machine is new or in infant stage, i.e. First stage of bathtub curve or effective maintenance. It is observed by gradual decrease in failure times or Decreasing Failure Rate (DFR)
If the machine is showing a negative trend, it implies that machine is deteriorating with time. In other words, the equipment is subjected to frequent or long failures. It is indicated by gradual increase of failure times. It can be considered that machine showing negative trend is in the third stage of machine life cycle or old age. It is due to worn out parts or inherent failures or inappropriate maintenance system. Whatever the reason may be, this situation disrupts the production and affects the productivity. Therefore such equipment is of more concern to maintenance as well as production engineers. These failure patterns are categorized by Increasing Failure Rate (IFR).
This is one of critical situations, maintenance engineers face. If failure times are neither increasing nor decreasing, it may lead to conclusion that the equipment is experiencing constant Failure Rate (CFR). But this is true in some cases only, which means that the no trend situation need not be Youth of machine (Random failures) with Constant Failure Rate. However the no trend situation implies that the failure behaviour is independent of time. It may be in random failure stage or typical increasing failure rate due to independent and identical distribution (IID) of failure times. Therefore, this rate is to be further analyzed to know this fact.