• Estimation of shutdown schedule to remove fouling layers of heat exchangers using risk-based inspection (RBI)

      Elwerfalli, A.; Alsadaie, S.; Mujtaba, Iqbal M. (2021-12-02)
      Oil and Gas plants consist of a set of heat exchangers, which are used in recovering the waste heat from product streams to preheat the oil. The heat transfer coefficient of exchangers declines considerably during the operation period due to fouling. Fouling in heat exchangers is a complex phenomenon due to the acceleration of many layers of chemical substances across tubes of heat exchangers resulting from chemical reactions and surface roughness. In this paper, the fouling process was determined as a critical failure in the heat exchanger. Failure is an accelerated fouling layer across the heat exchanger tubes, which can be the reason for the clogging of tubes. Hence, a risk assessment was conducted using the Risk-Based Inspection (RBI) approach to estimate the probability of fouling in heat exchangers. The results showed that the RBI approach can be used successfully to predict the suitable time to shut down the plant and conduct the fouling cleaning process.
    • Genetic algorithms for scheduling generation and maintenance in power systems

      Aldridge, C.J.; Dahal, Keshav P.; McDonald, J.R. (1999)
    • Maintenance cost models in deregulated power systems under opportunity costs.

      Al-Arfaj, Khalid A.; Dahal, Keshav P.; Azaiez, M.N. (2007)
      Maintenance costs in deregulated power systems play an important role. This mainly includes direct costs associated with material and labor costs; and indirect costs associated with spare parts inventory, shipment, test equipment cost, indirect labor, and opportunity costs. The cost function is used as the sole or main component of the objective function in maintenance scheduling and planning activities. The cost has been modeled in literature with several representations for centralized power systems. With deregulation of power industries in many countries the costs representation to be used within the maintenance model in the decentralized power systems has become an important research question. This paper presents modeling of different components of maintenance costs that can be used within the main objective function of the maintenance scheduling and planning problem for the deregulated environment.
    • Maintenance Scheduling With Delay-time Modelling - An Overview

      Du, Jing-Yu; Li, Jian-Ping; Hu, Yim Fun; Guan, X.; Si, M.; Liu, B. (2021-09-01)
      Effective maintenance is a key for infrastructures’ high operational reliability. The integration of corrective repairs and schedule-based failure preventions has been a mainstream of modern maintenance, and an associated policy-making technique, delay-time modelling, is overviewed in this paper for optimising the maintenance cost-efficiency in different practical scenarios, including imperfect, opportunistic and nested maintenance. A few typical examples of its applications in minimising maintenance operating expenses are discussed in this paper and their results are explained to better demonstrate the benefits of the technique. This work aims to prepare for the future applications of the delay-time modelling in railway maintenance policy making.
    • Marginal cost analysis of single-item maintenance policies with several decision variables

      Csenki, Attila (2004)
      The marginal cost approach for the analysis of repair/replacement models was introduced by Berg in 1980 and has since been applied to many maintenance policies of various complexity. All models hitherto analysed in the literature by the marginal cost approach have one single decision variable only, this being, typically, the age of the current item at the time of ordering or replacement. This paper is concerned with the extension of the marginal cost technique to maintenance policies with several decision variables. After addressing the general framework appropriate for the multi-parameter case, we exemplify the workings of the technique by analysing a two-variable maintenance model involving replacement and minimal repair. We demonstrate that the marginal cost approach is an attractive and intuitively appealing technique also for models with several decision variables. Just as in the single-parameter situation, the approach is amenable to economic interpretation, a welcome feature for users of maintenance models with a prime interest in its economic (rather than its mathematical) aspects. As an added bonus of the marginal cost approach, in our example, some otherwise necessary tools from the theory of stochastic processes are dispensable.
    • Organisational learning model for utility asset management using knowledge engineering approach.

      Chandarasupsang, T.; Chakpitak, N.; Dahal, Keshav P. (International Conference on Condition Monitoring and Diagnosis., 2006)
      Under the evolving environment, a utility company is required to improve the operation and maintenance of its physical assets usually in the forms of an asset management program. This paper proposes an organisational learning model for the utility companies with respect to the asset management activities. CommonKADS is utilised as a tool to capture the knowledge associated with managing the assets from the learning processes of the utility company. A case study of Bangpakong power plant in Thailand is presented. The results show that by applying the proposed methodologies, the learning processes within the utility companies can be categorised and explained by five major learning steps of breakdown, corrective, preventive, predictive, and proactive maintenances.