Home About Services Blog Subscribe Contact 

PF Interval


The
PF interval represents the second (middle) phase in a
threephase life cycle
model and deterioration
model of assets.
The three phases are identified as follows
The time, or cycles, from when a "Potential Failure" ("P") is first detected on an asset, or component, until the asset or component has reached "Functional Failure" ("F"). Also sometimes referred to as the leading indicators to failure of an asset or the failure development period.The pattern of the PF Interval is reflected on a PF Curve. and is used to express the probability of failure (PoF) of an asset within a particular calender year. The phrase PF interval was coined by J. Moubray.A type of deterioration model that utilizes a graph to represent the relationship between potential failure ("P") and functional failure ("F"). PF curves are used to map and avert failures. An understanding of the PF curve helps the owner determine which types of asset replacement policy is most appropriate to their tolerance for risk. Examples of PF Intervals for Assets Listed below are some examples to illustrate the application of the PF interval:
Identifying the Points on the PF Interval PF intervals are determined through a variety of techniques to gather empirical data on the condition of an asset, including:
Establishing the Patterns of the PF Interval The longer the PF interval, the more time the owner has to make a good decision by planning an appropriate course of action and raising the necessary funds for renewal of the asset. It is therefore helpful to understand the pattern of the interval in order to map and avert failures. For more information about the identification of the points along the PF interval, refer to:
Application of the PF interval: The PF interval is a useful concept for establishing appropriate asset management strategies at different stages in the lifecycle of an asset. It provides insight for the physical analysis of a reserve study. Included below are three key concepts. A. Shift from TimeBased Maintenance (TbM) to ConditionBased Maintenance (CbM) Reliabilitycentered maintenance principles state that the frequency with which a predictive maintenance task should be performed on an asset is determined by the PF Interval for that asset. Three types of indicators
C. Development of Replacement Policy An understanding of the PF interval helps the owner determine which types of asset replacement policy is most appropriate to their tolerance for risk. The PF Interval Relative to the Forces of Retirement: Listed below are some examples of how the PF interval can be mapped against the six replacement drivers of assets:

Fig. Decisions should consider the whole life of assets, including the IP interval and the PF interval. Fig. The whole life of assets can be divided into life stages  early life, midlife and latelife. Fig. An example of the progression of deterioration from potential failure ("P") to functional failure ("F") along the PF interval. Fig. The PF interval illustrated with asphalt paving along the curve. Fig. The risk spectrum extending along the PF interval to illustrate the varying strategies in the PreP and PreF periods. For example, a shift from TimeBased Maintenance (TbM) to ConditionBased Maintenance (CbM). Fig. Fixed interval events mapped onto the PF curve to illustrate the relationship between time and resistance to failure. Fig. Variable interval events mapped onto the PF curve to illustrate the relationship between time and condition. Fig. The forces of retirement mapped onto the PF curve. Fig. Asset replacement policies mapped onto the PF interval to illustrate their relationship to functional failure ("F"). Fig. Proximity to Potential Failure ("P") and Functional Failure ("F") along the PF curve. Fig. Left: multiple points P on the PF curve; and Right: Leading indicators, lagging indicators and coincident indicators on a PF Curve (right). Fig. Premature failure on the PF interval, where both potential failure ("P") and functional failure ("F") occur earlier than intended. Fig. A generic survivor curve overlaid with the points of potential failure (P) and functional failure (F) of the same asset at two buildings to draw the correlation between the global maxima (the class) and the local minima (the site conditions). 

See also:

Fig. Comparison of the PF Curves of two assets. 
(c) Copyright Asset Insights, 20002013, All Rights Reserved  "Insight, foresight and oversight of assets" 
Google
