Strategic Role of Diagnostics in Asset Management under Ageing, Climate Change & Earthquake

Abstract

The present paper discusses probability and diagnostics from a hazard rate bathtub curve perspective. We employed a basic bathtub model representing a single teething, random and wear-out phenomenon. The teething and wear-out processes lead to extreme hazard rates at the start and end of product life. Customers are supposed to endure none of these. The extremes are prevented by quality control (burn-in and testing) respectively timely servicing and replacement. Often Period and Condition Based Maintenance (PBM, CBM) are applied to plan servicing or replacement before failures occur. Hazard rates play a key role in PBM and CBM. These are different hazard rates. PBM uses the actual hazard rate of the asset group failure distribution. In contrast, CBM focuses on individual assets and employs diagnostics to estimate their individual failure probability. The employed prognostic hazard rate is based not only on the
asset itself, but also on the particular diagnostic and interpretation of the results. If diagnostics and interpretation can forecast a reasonably accurate time until failure, the prognostic hazard rate is increasing with time. In other cases, a degradation is unambiguously detected, but the method does not allow to forecast a time (well). The prognostic is viewed as more or less constant suggesting random failure. The relationship between Asset Health Index (AHI) and the prognostic failure probability and hazard rate is discussed. From this, it can be shown that the AHI needs a definition on probability in addition to time to failure. Furthermore, three scenarios were studied: normal ageing; accelerated ageing associated with severe conditions like climate change; and disruptive ageing by an impact as with natural phenomena like earthquakes. Finally, the methodology of hazard rate curves deserves more credit than to be seen as a carrier of doom and gloom. The present paper made abundant use of the hazard rate and the bathtub curve to demonstrate the concept and its utility for understanding PBM, CBM and associated diagnostics.