Technical System Maintenance

Chapter includes an introduction to the maintenance theory. The main definitions connected with the analysed research area are presented and discussed. Later, the author discusses the main maintenance problems being investigated in the recent literature. She focuses on the three main research categories: maintenance theories, mathematical models and management models. A broader view of mathematical modelling is provided. In this area the factors that influence the process of optimal maintenance policy selection are presented. Moreover, the classification of known maintenance strategies is presented and briefly analysed. The main classification criterion is connected with a failure occurrence in a technical system. Following this, Corrective Maintenance, Time-Based Maintenance, Preparedness Maintenance, Condition-Based Maintenance, Predictive Maintenance, and Reliability Centred Maintenance are overviewed. At the end, the aim of this book and its scope is also presented.

There are analysed and summarized the results of preventive maintenance, one of the most commonly used maintenance strategy. The reviewed literature is classified into two main groups of models for one-unit and multi-unit systems. For single-unit systems the author investigates age-replacement policies, block-replacement policies, sequential preventive maintenance policies, failure limit policies and repair limit policies. The optimum policies are discussed, and their several modified and extended models are presented. The main extensions include imperfect maintenance implementation, shock modelling, or finite/infinite time horizon modelling cases. The classification also includes optimality criterion and used modelling method. For multi-component systems maintenance case there are analysed the main replacement policies for systems with and without components dependence. First, the simplest models are analysed, i.e. age-replacement and block-replacement policies. Later, the maintenance policies for systems with components dependence are introduced. The author summarizes the latest developments for group maintenance, opportunistic maintenance, and cannibalization maintenance models. The discussion of models bases on criteria, among others, planning horizon, modelling method, and optimization criterion. The main development directions in preventive maintenance modelling are presented in a graphical form. The brief summary of the conducted literature review is provided with indicating the main research gaps in this modelling area.

The objective of this chapter is to present a literature review on inspection maintenance modelling issues. The discussed maintenance models are classified into two main groups—form single- and multi-unit systems. For single-unit systems the reviewed research works include such modelling issues like optimum and nearly optimum inspection policies, shock occurrence, information uncertainty, sequential inspection, multi-state objects, or imperfect inspection performance. The classification also includes optimality criterion, planning horizon, and used modelling method. The maintenance models for multi-unit systems regard to the two types of technical objects—protective devices (or standby units) and operational units. The main extensions of the developed models are discussed and summarized. Moreover, the main development directions in inspection maintenance modelling are presented in a graphical form. The brief summary of the conducted literature review is provided with indicating the main research gaps in this modelling area.

The chapter presents a literature review on delay-time modelling for single- and multi-unit (complex) systems. First, there are introduced the main definitions connected with this maintenance approach. Later, there is presented the analysis of known maintenance models being developed in this research area. The maintenance models for single-unit systems assume two-stage or three-stage failure processes implementation. The optimum policies are discussed, and their several modified and extended models are presented. The main extensions include imperfect inspection implementation, postponed replacement performance, or different types of failures investigation. The classification also includes optimality criterion, planning horizon, and used modelling method. In the case of complex systems, the discussed problems regard to e.g. models’ parameters estimation issues, case studies analysis, or hybrid modelling approach implementation. The main extensions of the developed models are discussed and summarized. At last, the main development directions in delay-time-based maintenance modelling are presented in a graphical form. The brief summary of the conducted literature review is provided with indicating the main research gaps in this modelling area.

The objective of this Chapter is to present delay-time based maintenance models for multi-unit systems performing in various reliability structures (series, parallel, n_k-out-of-n types) for the two cases of perfect and imperfect inspection performance. First, the necessity of the DT modelling for multi-unit systems performing in various reliability structures is discussed. The research gap is underlined and structure of the Chapter is presented. Moreover, preliminary simulation DT models are characterized. They focus on availability and maintenance costs of technical systems performing in series and non-series structures with perfect and imperfect inspection. Their sensitivity analysis is carried out and main results are discussed. Moreover, first decision rules for maintenance managers are specified. Later, the short overview of recent developments on delay-time based maintenance modelling for systems in non-series reliability structures is presented and structure for the next Sections is given. In Sect. 5.2 new analytical delay-time maintenance models are developed. The implemented maintenance policy bases on Block Inspection policy implementation and the analytical model is presented for the perfect inspection case. The solution is based on renewal reward theory use and is given for the first inspection cycle. The main decision variable is the time period between successive system inspection actions performance Tin, while the purpose of the developed model is to estimate the expected maintenance cost per unit of system time. As a result, the main assumptions for the DT models are defined. This gives the possibility to obtain the main reliability functions for the modelled system performing in various reliability structures. Later, the expected maintenance cost model is introduced. Section 5.3 provides the reader with extended delay-time maintenance models for systems performing in two reliability structures—series and parallel ones. The analysed system is a two-component system (including component A and component B). The main assumptions are defined and compatible with the ones determined in Sect. 5.2. The main difference is connected with the possibility of planned and unplanned inspection actions performance during the time interval (0, T_in). First, the number of event scenarios is presented and analysed. Later, the probability functions of system failure and preventive replacement are presented. This gives the possibility to obtain the expected maintenance cost model. In the next Sections the author discusses and analyses the possibilities of use of the obtained simple delay-time based maintenance models for determining the best inspection time interval. First, the convergence of the chosen analytical model with the simulation model is given. Later, the optimization modelling issues are discussed and the new cost coefficient is proposed. The Chapter is completed by concluding remarks that contain the most important conclusions obtained from the performed research developments.

This chapter is focused on a problem of developed maintenance models implementation for real-life technical systems implementation. First, there are investigated the issues of models’ parameters estimation process and its uncertainty. The conducted analysis bases on simulation modelling use and is focused on economic and reliability consequences of improper selection/estimation of modelling parameters. Later, the research analysis focused on analytical delay-time models (given in Sect. 5.​2) and regards to, among others, definition of simple decision rules for the best inspection period determining. In the next section the author presents a simple methodology of applying delay-time analysis to a maintenance and inspection department. The defined algorithm is aimed at estimation of optimal inspection interval basing on the DT models developed in Chap. 5 and results obtained from the modelling parameters estimation analysis. Finally, two case studies are proposed to investigate the optimal inspection interval for two-unit systems performing in series and parallel structures. The models used to analyse the given systems are based on the results of Chap. 5 and Sect. 6.2. The first example regards to engine equipment maintenance (v-ribbed belt with belt tensioner), the second example presents the maintenance of left and right steering dumpers that are used in wheel loaders. In order to obtain the optimal inspection interval the author focuses on cost optimisation. The third example regards to the problem of maintenance policy selection based on the available operational and maintenance data from a company.

The book is completed by the Conclusions and future research chapter that contains the summary of the presented results, the formulation of open problems concerned with delay-time based maintenance modelling, and definition of the main directions for further research. The author also summarizes the main contribution of this book.