Modeling the Effects of Maintenance on the degradation of a Water-feeding Turbo-pump of a Nuclear Power Plant

International audienceThis work addresses the modelling of the effects of maintenance on the degradation of an electric power plant component. This is done within a modelling framework previously proposed by the authors, of which the distinguishing feature is the characterization of the component living conditions by influencing factors (IFs), i.e. conditioning aspects of the component life that influence its degradation. The original fuzzy logic-based modelling framework includes maintenance as an IF; this requires one to jointly model its effects on the component degradation together with those of the other influencing factors. This may not come natural to the experts who are requested to provide the if-then linguistic rules at the basis of the fuzzy model linking the IFs with the component degradation state. An alternative modelling approach is proposed in this work, which does not consider maintenance as an IF that directly impacts on the degradation but as an external action that affects the state of the other IFs. By way of an example regarding the propagation of a crack in a water-feeding turbo-pump of a nuclear power plant, the approach is shown to properly model the maintenance actions based on information that can be more easily elicited from experts

The Economy of Preventive Maintenance of Concrete Bridges Due to Corrosion

The current practice for physical evaluation and delayed maintenance of deteriorated concrete bridge is fundamentally wrong. This research presents a new approach for the evaluation of the condition states of steel reinforced concrete bridge members, which is based on their chemical conditions instead of the physical deficiencies such as cracks and delamination. Using the proposed chemical based inspection approach, a more effective and economic preventive maintenance plan could be achieved. The available non-destructive evaluation (NDE) methods and preventive maintenance measure are identified. Since the chloride induced corrosion is the major factor that dictates the service life of the steel reinforced bridge element, a refined equation for estimation of the diffusion coefficient of chloride ions into concrete is proposed. A Finite Element Analysis (FEA) model that accounts for time-dependent and temperature-dependent diffusion coefficient was developed and verified against experimental data produced by several researchers. The results of the numerical analysis showed good agreement with experimental data. After validation against experimental data, the FEA model was used to evaluate the effectiveness of the preventive maintenance measures, such as surface sealers and overlays. The chloride profiles derived from the FEA model was then used as an indicator to select appropriate preventive maintenance measures at the right time based on the chloride concentration at the surface of the steel. A simplified concrete bridge deck element is selected to compare the life-cycle cost of a bridge deck with different concrete mix design and different maintenance strategies under various exposure conditions. For cost-effective management of concrete highway bridges, the following measures should be taken, depending on the exposure conditions: 1. For severe exposure conditions, such as coastal area or cold regions that require a large amount of deicing salt, carbon steel reinforced bridge decks have a short service life. Therefore, a well-planned preventive maintenance strategy needs to be implemented in order to postpone or eliminate the needs of major rehabilitation and replacement. In such case, the use of stainless steel could be the most economical solution for the long run. In addition, the use of integrated overlay made of high performance concrete or cathodic protection systems may reduce the life-cycle cost based on a 75-year expected service life. 2. For moderate exposures, the use of overlays and surface sealers has been deemed cost-effective. However, the life-cycle cost is very sensitive for sealer application since it needs to be reapplied frequently. Thus, the effectiveness of the sealer should be closely monitored by the Non-destructive Evaluation (NDE) methods. 3. For mild exposures, the corrosion may not be the most critical deterioration mechanism for the bridge deck element. The riding surface of the bridge deck needs to be replaced periodically due to other deterioration mechanisms such as erosion, fatigue cracks, etc. In conclusion, this research shows that it is not only economical, but also necessary to allocate more funds to perform in-depth, chemical oriented non-destructive tests and active preventive maintenance

Optimal Periodic Inspection of a Stochastically Degrading System

This thesis develops and analyzes a procedure to determine the optimal inspection interval that maximizes the limiting average availability of a stochastically degrading component operating in a randomly evolving environment. The component is inspected periodically, and if the total observed cumulative degradation exceeds a fixed threshold value, the component is instantly replaced with a new, statistically identical component. Degradation is due to a combination of continuous wear caused by the component\u27s random operating environment, as well as damage due to randomly occurring shocks of random magnitude. In order to compute an optimal inspection interval and corresponding limiting average availability, a nonlinear program is formulated and solved using a direct search algorithm in conjunction with numerical Laplace transform inversion. Techniques are developed to significantly decrease the time required to compute the approximate optimal solutions. The mathematical programming formulation and solution techniques are illustrated through a series of increasingly complex example problems

Bridge maintenance to enhance corrosion resistance and performance of steel girder bridges

The integrity and efficiency of any national highway system relies on the condition of the various components. Bridges are fundamental elements of a highway system, representing an important investment and a strategic link that facilitates the transport of persons and goods. The cost to rehabilitate or replace a highway bridge represents an important expenditure to the owner, who needs to evaluate the correct time to assume that cost. Among the several factors that affect the condition of steel highway bridges, corrosion is identified as the main problem. In the USA corrosion is the primary cause of structurally deficient steel bridges. The benefit of regular high-pressure superstructure washing and spot painting were evaluated as effective maintenance activities to reduce the corrosion process. The effectiveness of steel girder washing was assessed by developing models of corrosion deterioration of composite steel girders and analyzing steel coupons at the laboratory under atmospheric corrosion for two alternatives: when high-pressure washing was performed and when washing was not considered. The effectiveness of spot painting was assessed by analyzing the corrosion on steel coupons, with small damages, unprotected and protected by spot painting. A parametric analysis of corroded steel girder bridges was considered. The emphasis was focused on the parametric analyses of corroded steel girder bridges under two alternatives: (a) when steel bridge girder washing is performed according to a particular frequency, and (b) when no bridge washing is performed to the girders. The reduction of structural capacity was observed for both alternatives along the structure service life, estimated at 100 years. An economic analysis, using the Life-Cycle Cost Analysis method, demonstrated that it is more cost-effective to perform steel girder washing as a scheduled maintenance activity in contrast to the no washing alternativ

Integration of structural health monitoring information to reliability based condition assessment and life cycle costing of bridges

According to Transportation Association of Canada (TAC), the rough estimate of number of bridges in Canada is 80,000 with the replacement value of $35 billion. A large number of bridges will need replacement during 2005 to 2015 which will result in 50% annual increase in replacement cost. Recent alarming incidents of the Laval De la Concorde Overpass collapse (2006), Canada and the I-35W Mississippi River bridge collapse (2007), USA show the gravity of the situation. One of the main factors responsible for this situation is the present available techniques of the bridge condition monitoring and rehabilitation are not able to cope up with the drastic deterioration and ageing of the bridges. The widely employed method for bridge inspection is visual inspection, and it lacks the reliability-based assessment of bridge and its components. The instrumentation of the bridge with Structural Health Monitoring (SHM) systems and assessment of the bridge condition and behaviour based on the information obtained from SHM systems is one of the promising solutions of the present problem. The main focus of the current research is to integrate SHM data with traditional information (e.g. visual inspection), develop a reliability based structural condition index using the updated information on a structures operational performance, and assessing the value of information for SHM in regard to the overall lifecycle cost of a structure. This study develops a methodology for a reliability based assessment of the bridge components using SHM system information, and information updating by fusing SHM data with traditional information for precise evaluation of expected life cycle cost. The methods developed herein have been demonstrated through a case study based on an existing bridge namely, the Crowchild Bridge in Calgary, Alberta. A finite element model of the bridge has been developed and validated against the field data. This validated model has been used to simulate the static load test on the bridge, deterioration in the bridge and to study the bridge response under the different loading conditions. The artificial neural network (ANN) technique has been used for the diagnosis of the SHM data, and then the reliability index of the bridge deck has been calculated using the Monte Carlo Simulation technique. A method for updating the bridge deck repair strategy is introduced based on the reliability index calculation. The maintenance and rehabilitation strategy is updated based on the hypothetical results. The results of updated strategy are compared with un-updated one using the Bayesian Theorem. The expected life cycle cost is evaluated considering the capital cost, maintenance and rehabilitation cost, user cost, and failure cost. Capital cost is treated as deterministic while maintenance and rehabilitation cost, and user cost are considered probabilistic. Each individual cost and then total cost is calculated per m 2 . The value of information is also discussed

Post-Sale Cost Modeling and Optimization Linking Warranty and Preventive Maintenance

Ph.DDOCTOR OF PHILOSOPH

Remaining useful life estimation in heterogeneous fleets working under variable operating conditions

The availability of condition monitoring data for large fleets of similar equipment motivates the development of data-driven prognostic approaches that capitalize on the information contained in such data to estimate equipment Remaining Useful Life (RUL). A main difficulty is that the fleet of equipment typically experiences different operating conditions, which influence both the condition monitoring data and the degradation processes that physically determine the RUL. We propose an approach for RUL estimation from heterogeneous fleet data based on three phases: firstly, the degradation levels (states) of an homogeneous discrete-time finite-state semi-markov model are identified by resorting to an unsupervised ensemble clustering approach. Then, the parameters of the discrete Weibull distributions describing the transitions among the states and their uncertainties are inferred by resorting to the Maximum Likelihood Estimation (MLE) method and to the Fisher Information Matrix (FIM), respectively. Finally, the inferred degradation model is used to estimate the RUL of fleet equipment by direct Monte Carlo (MC) simulation. The proposed approach is applied to two case studies regarding heterogeneous fleets of aluminium electrolytic capacitors and turbofan engines. Results show the effectiveness of the proposed approach in predicting the RUL and its superiority compared to a fuzzy similarity-based approach of literature

30th International Conference on Condition Monitoring and Diagnostic Engineering Management (COMADEM 2017)

Proceedings of COMADEM 201

Aeronautical Engineering: A special bibliography with indexes, supplement 64, December 1975

This bibliography lists 288 reports, articles, and other documents introduced into the NASA scientific and technical information system in November 1975