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Wide Dispersion

The variation in probability of the failure of an asset is not closely tied to the median service life.

Listed below are some of the key attributes of assets with a wide dispersion pattern:

  • The confidence interval for the modal year of functional failure is high.
  • The life (critical year) of these assets may be difficult to predict.
  • The renewal cycles may occur at either fixed intervals or variable intervals.
  • The failure patterns may be stochastic and therefore difficult to predict.
  • There are many years or decades between the early start year and the late start year.

Assets with a wide dispersion may exhibit varying degrees of skewness in their distribution, as follows:

There is generally a strong correlation between long life assets and a wide dispersion.

Listed below are some examples of assets with a wide dispersion patterns:

  • Windows
  • Wall cladding
  • Sanitary storm collection piping
  • Plumbing service piping
Many of the distribution assets within the mechanical system and electrical system fall into the wide dispersion class.

Management Principles
Listed below are some principles for consideration in the management of asset with wide dispersion patterns.
  • Recognize that the asset may provide many years of warning prior to functional failure. That is, the P-F Interval may be long.
  • Arrange for an inspection of the asset at the appropriate time before failure is forecast.
  • Ensure that adequate funds are on hand for renewal of the asset by making annual contributions to a long range reserve account.
  • These types of asset are best suited to a preventive replacement strategy based upon inspection replacement principles.
Fig. Histogram for an asset with a wide dispersion pattern.

Comparison of narrow and wide dispersion in a probability distribution.
Fig. Comparison of narrow and wide dispersions in a probability distribution.

Fig. Wood siding generally exhibits a wide dispersion pattern around 30 years.

I. Care is trying to connect the dots in order to reveal the patterns in the data that underpins his assets, including trends.
Fig. I. Care is trying to connect the dots to reveal the patterns in the data that underpin his assets.

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