From measurement collection to remaining useful life estimation : defining a diagnostic-prognostic frame for optimal maintenance scheduling of choke valves undergoing erosion
Condition Based Maintenance (CBM) aims at regulating maintenance scheduling based on data analyses and system condition monitoring. Clear advantages of optimizing maintenance scheduling include relevant cost savings and improved safety and plant availability. A critical aspect is the integration of CBM strategies with condition monitoring technologies for handling a wide range of information sources and eventually making optimal decisions on when and what to repair. In this work, a practical case study concerning maintenance of choke valves in offshore oil platforms has been investigated. Choke valves used in offshore oil platforms undergo erosion caused by the sand grains transported by the oil-water-gas mixture extracted from the well. Erosion is a critical problem which can affect the correct functioning of the valves, result in revenue losses and cause environmental hazards. In this respect, this work proposes a diagnostic-prognostic scheme for assessing the actual health state of a choke va lv and eventually estimating its Remaining Useful Life (RUL). In particular, the focus has been on th e identification of those parameters which contribute to the actual erosion of the choke valve, the development of a model-based approach for calculating a reliable indicator of the choke valve health state, the actual estimation of the choke RU L based on that indicator using statistical approache s and, finally, the investigation of methods to reduc e the uncertainty of the RUL estimation by adding highly meaningful knowledge on the erosion state of the choke valve .
Failure prediction using personalized models and an application to heart failure prediction
Background To reduce disruptions of processes and the cost of maintenance, predicting the onset of failure (or a similar event) of a physical system (or components of a physical system) has become important. Prediction of onset of failure would allow appropriate corrective actions at the right time. In this paper, we present a method to predict the “onset” of failure (the start of a degradation process or similar types of events) of a physical system that minimizes data collection and personalizes it for the physical system. The method applies to situations where one monitors the operating characteristics of the physical system at regular time intervals by means of attached sensors and other measurement instruments. It creates a model of the physical system, during normal operations, using the time-series data produced by the sensors and measurement instruments. However, it does not create or use any time-series models. It simply examines the distribution of time-series data across different time periods. It uses this model of normal operations in subsequent time periods to monitor the physical system for deviations from normality. Results We illustrate this method with an application to predict the “onset” of subsequent decompensated heart failures for patients already treated for a heart failure at a hospital. As part of an NIH study, these heart failure patients received two ECG patches, an accelerometer and a bio-impedance measurement device for regular monitoring for a period after their release from the hospital. Conclusions When dealing with non-homogenous, disparate physical systems, personalized models can be better predictors of a phenomenon compared to generalized models based on data collected from an assortment of such physical systems. In medicine such models can be a powerful addition to the set of medical diagnostic tools. And such personalized models can be built rather quickly without waiting for extensive data collection.
Relative Erosion Resistance of Several Materials
Over 200 materials were screened by a high-velocity sandblast-type erosion test to determine their suitability for application in coal gasifier valves. Most metals had relatively similar and low erosion resistances. Ceramics and cermets such as boron carbide (B 4 C), tungsten carbide (WC), silicon carbide (SiC), silicon nitride (Si 3 N 4 ), and titanium diboride (TiB 2 ), if manufactured to minimize porosity, had more than four times the erosion resistance of metals. Several coatings such as boronized molybdenum and tungsten carbide, chemical vapor-deposited titanium carbon nitride (TiCN), and electrodeposited TiB 2 also proved highly erosion resistant when applied in sufficient thicknesses. Additional findings confirmed that cermet binder content and ceramic porosity are related to erosion resistance.