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|Probability of Failure (PoF)
likelihood, based on realistic
an asset will reach functional failure ("F")
at a point in time (usually within in a particular calendar
year), which is expressed along a probability
The probability that an asset will fail during a particular age interval, given that it survives to enter that age.
The probability that performance will be maintained into the future
PoF is established by deterioration models wherein there are two primary methods for graphically representing the PoF along a curve:
PoF can be expressed in a variety of linguistic scales (low, medium, high) or numerical scales (1,2,3,...) relative to a particular year.
Listed below is an example of a five-tiered linguistic scale:
In order to establish PoF, we need several pieces of information, including: typical service life, consumed life and remaining life, PF interval, FMEA. Some of this information is empirical and some is statistical in nature.
Listed below are some of the key elements to establish the PoF for a single asset:
The PoF can be applied in a variety of useful ways to the manageement of assets:
The PoF is directly affected by various factors, including the following:
The PoF is utilized in development of the following asset management principles, tools and techniques:
Fig. Risk-based decision making is at the heart of asset management and this requires mindful consideration of the relationship between the probability of failure (PoF) and the consequences of failure (CoF). The complexities of these correlations can sometimes be captured on a risk matrix.
Fig. Some of the key statistical elements of an asset survivor curve.
Fig. The whole life of assets can be divided into life stages - early life, mid-life and late-life, with different maintenance strategies at each life stage.
Fig. Probability of Failure (PoF) expressed as survivor curves with either positive or negative skewness.
Fig. Probability of Failure (PoF) expressed as a degradation curve (performance curve) relative to the points of Potential Failure ("P") and Functional Failure ("F").
Fig. PoF represented on the horizontal (x-axis) of a criticality/risk matrix.
Fig. I. Care is oblivious to the extraordinary events that can totally wipe out his assets and upset the delicate order of things, such as force majeure and acts of God.
Fig. Relationship between Probability of Failure (PoF) and the horizontal axis of a risk matrix.
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