We’ll further the discussion from our recent post “DON'T BASE YOUR RELIABILITY STRATEGIES ON YOUR ORIGINAL ESTIMATES ONLY. YOU HAVE TO BE "DYNAMIC"!”
Last time we talked about moving Pf on the Pf-Ff Curve and why that happens.
Today, I’d like to explain how the entire Pf-Ff Curve changes dynamically to move left and right on the X-axis (Age). In the figure below, we have both the Pe-Fe Estimate Curve (Grey) and the Pf-Ff Forecast Curve (dotted). The slope at the current point on the estimate curve is compared to the current slope of the forecast curve over a short interval toward the past; this factor is user selected. Another slope is measured from Installation to Now. Through use of an algorithm that mathematically compares these slopes against each other to determine a value called the “Decay Rate”. Depending on whether the Decay Rate is positive or negative, the forecast curve may move toward the RED High Stress curve, or toward the GREEN Low Stress curve respectively. As time or cycles pass by, the Pf-Ff Forecast Curve becomes more and more confident and thus, Point Pf (Potential Failure Forecast) becomes more stable and permanent in its location. Barring any catastrophic external anomalies resulting in failure, we will now be able to plan and schedule our maintenance activities.