Direct Maintenance Costs Research Articles

Preventive Maintenance Scheduling

In this work, the effectiveness of preventive maintenance scheduling (PMS) decisions was reported based on a techno-economic model that reflects cost objective function for ship maintenance activities. With a potential to impact on both transportation businesses and users of transportation services, the model provides an alternative to the combined classical literature problems of spare-parts inventory management and control, failure prediction and reliability. The PMS model developed incorporates separate and combined functions of indirect, direct and factor maintenance costs. Idleness period for various formulated schedules are evaluated and compared. First, a general form of the preventive maintenance cost function incorporating unit cost of maintaining ships, a set of cost function parameters and variables was developed. The operations research framework for the problem is then applied to obtain test cases in which cost parameter(s) was/were used for scheduling decisions. Monte Carlo simulation is applied to generate additional test problems. Practical data were used to validate the model. For each problem, optimal schedules based on one to four cost parameters were determined. For each schedule, the total maintenance cost, cost of idleness, total ship idle period and total ship operation period were computed under inflation, opportunity and combined opportunity and inflation and compared with the values corresponding to maintenance cost parameter using t-test (p<0.05). Thus, the use of combined data from maintenance, opportunity and inflation for preventive maintenance scheduling of a fleet of ships is more effective than direct maintenance cost approach.

Resistência à erosão por cavitação de aços inoxidáveis austeníticos CrMnSiN depositados por PTA

A erosão por cavitação deteriora componentes em serviço, tais como partes metálicas de bombas de água, válvulas e, em especial, pás de turbinas hidráulicas, sendo nesse último caso responsável por elevados prejuízos ligados tanto aos custos da manutenção direta, como sobretudo às perdas por interrupção na geração de energia elétrica. Dentre os materiais aplicados no reparo por soldagem de danos por cavitação incluem-se aços inoxidáveis tradicionais tipo AISI 308 e 309, aços inoxidáveis ao Co e ligas à base de Co (stellites), caracterizando-se essas últimas pela maior sensibilidade a trincas, dificuldade de esmerilhamento e pelo mais alto custo. Nesse contexto este trabalho buscou formular, depositar e analisar o desempenho de aços inoxidáveis austeníticos CrMnSiN, soldados pelo processo PTA. A resistência à erosão por cavitação foi avaliada segundo a norma ASTM G 32-92. A microestrutura foi caracterizada por microscopia ótica e microscopia eletrônica de varredura e a formação de martensitas α' e ε, induzida pela cavitação, foi avaliada por difração de raios-X. A integridade da superfície dos depósitos foi controlada por END, além disso a dureza e a facilidade de acabamaneto por esmerilhamento serviram como critérios para avaliar os revestimentos soldados. Verificou-se que os revestimentos aplicados por PTA eram livres de trincas de solidificação, com baixa porosidade, boa molhabilidade e adequado acabamento superficial. A melhor liga inoxidável austenítica elaborada (0,03%C; 0,35% N; 13,2%Cr; 11,8% Mn; 2,8%Si; bal %Fe) mostrou uma resistência à erosão por cavitação próxima aquela das principais ligas comerciais.

Searching for Gas Turbine Maintenance Schedules

Preventive maintenance schedules occurring in industry are often suboptimal with regard to maintenance coal-location, loss-of-production costs and availability. We describe the implementation and deployment of a software decision support tool for the maintenance planning of gas turbines, with the goal of reducing the direct maintenance costs and the often costly production losses during maintenance downtime. The optimization problem is formally defined, and we argue that the feasibility version is NP-complete. We outline a heuristic algorithm that can quickly solve the problem for practical purposes and validate the approach on a real-world scenario based on an oil production facility. We also compare the performance of our algorithm with results from using integer programming, and discuss the deployment of the application. The experimental results indicate that downtime reductions up to 65% can be achieved, compared to traditional preventive maintenance. In addition, the use of our tool is expected to improve availability with up to 1% and reduce the number of planned maintenance days by 12%. Compared to a integer programming approach, our algorithm is not optimal, but is much faster and produces results which are useful in practice. Our test results and SIT AB’s estimates based< on operational use both indicate that significant savings can be achieved by using our software tool, compared to maintenance plans with fixed intervals.

An estimation method for direct maintenance cost of aircraft components based on particle swarm optimization with immunity algorithm

A particle swarm optimization (PSO) algorithm improved by immunity algorithm (IA) was presented. Memory and self-regulation mechanisms of IA were used to avoid PSO plunging into local optima. Vaccination and immune selection mechanisms were used to prevent the undulate phenomenon during the evolutionary process. The algorithm was introduced through an application in the direct maintenance cost (DMC) estimation of aircraft components. Experiments results show that the algorithm can compute simply and run quickly. It resolves the combinatorial optimization problem of component DMC estimation with simple and available parameters. And it has higher accuracy than individual methods, such as PLS, BP and v-SVM, and also has better performance than other combined methods, such as basic PSO and BP neural network.

Enhancing a company's profitability and competitiveness using integrated vibration-based maintenance: A case study

In this paper a model is developed for identifying, monitoring and improving the economic impact of vibration-based maintenance (VBM). This model provides an additional possibility of identifying where, why and how much capital should be invested, and judges whether or not the investment was cost-effective. The model is further utilised to develop relevant maintenance performance measures. When the model was tested in a Swedish paper mill, the main results were: the average yearly maintenance profit achieved using integrated VBM was at least 3.58 million Swedish kronor (SEK) (approximately US$0.358 million), and average potential savings (economic losses) were around SEK 30 million (US$3 million). Furthermore, the model facilitated identification of problem areas and recognition of where investments should be made. The major conclusion is that the better the data coverage and quality, the greater control is possible over direct maintenance costs, savings and further profits in maintenance. Moreover, using the model it would be easier and more reliable to detect deviations in the maintenance performance and eliminate their causes at an early stage.

Life-cycle oriented optimization of maintenance costs for drainage systems in traffic tunnels - by (further) developing a new calcification reduction method

For quite some time, many operators of drained tunnels have been faced with the problem of cost-intensive maintenance measures to counteract the phenomenon of scaling in tunnel drainage systems. In view of the severe worsening of this problem in the numerous tunnels on its high-speed railway link between Hanover and Wurzburg, Deutsche Bahn AG, the German railway company, decided to conduct a research project together with the Institute for Construction Engineering and Management of the Swiss Federal Institute of Technology Zurich. On the one hand, the project aims to investigate the cause-and-effect relationships that explain the scaling phenomena in those tunnels that are influenced by descending ground water, since the tunnels on the high-speed routes only have a low depth of coverage on average. On the other hand, the research project was to be used to test and improve the application of a new preventive method for stabilizing water hardness. For a long time, the causes of scaling in tunnel drainage systems were unknown. Although there was clearly a connection with more recent tunneling methods and the materials used, the actual mechanisms remained unexplored. The findings of the first investigation phase of the research project showed that the enrichment of the descending seepage and ground water with carbon dioxide was a principal natural cause of the formation of scale, especially in low covered tunnels, and that, in conjunction with the materials used, this resulted in the - in part - considerable occurrences of scaling. And although such scaling as a result of natural causes cannot be prevented entirely, an intelligent choice of building materials and method of constructing the tunnel are possible and necessary to alleviate the effects. Thus measures must be taken in tunnel drainage systems to counter the adjustment to deeper chemical equilibriums and, in doing so, to reduce the formation of stable salt deposits. The water, enriched with lime and carbonic acid above atmospheric conditions must be drained out of the tunnel relatively uninfluenced and, as such, without any significant traces of scaling. This can only be achieved with an adequate design and construction of the entire drainage system. For example, the water falls - which are still to this day a common feature - where the pipes flow into the manholes need to be abolished since the drainage water is aerated and carbon dioxide degraded at this point, leading to reduced lime solubility and the formation of - in part - massive lime deposits. A further element of maintenance, which helps to reduce the formation of deposits on the one hand, whilst at the same time ensuring that the inevitable deposits are much softer than before, is the stabilization of water hardness. This is a process originally derived from nature whereby molecules that are rich in aspartic acid control the formation of inorganic skeletal material, for example in crustaceans. The active agent of hardness stabilization, polyaspartic acid, is a nature-related substance, which is therefore fully decomposed by micro-organisms and regarded as environmentally unproblematic. By adsorbing the hardness-forming ions in the drainage system, polyaspartic acid prevents, disrupts or delays the formation of hard scale. As an overall result, the right use of hardness stabilization in connection with constructional modifications can result in longer cleaning intervals and a substantial reduction in the scope of cleaning works in the pipes, which in turn generally leads to a considerable extension in the life cycle of the tunnel drainage system and lower direct maintenance costs together with increased availability of the traffic routes. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.

Methods to reduce direct maintenance costs for commercial aircraft

Direct maintenance costs (DMC) of commercial aircraft make a significant contribution to an aircraft's cost of ownership. The aim of our research is to find out some methods to reduce DMC. The paper first points out that design and fault diagnosis are the key factors to influence DMC, disregarding factors unique to a particular airline. A new concept of R&M design – maintenance free operating period and fault diagnosis expert system are discussed in this paper, in order to reduce DMC.

Civil aircraft maintenance and support Fault diagnosis from a business perspective

Aircraft maintenance down times together with maintenance activity durations and associated man‐hour expenditure are extremely important factors contributing to two major yardsticks of airline and civil aircraft performance: despatch reliability and direct maintenance costs, and have important cost implications. In maintaining an aircraft there is a need to predict fault diagnosis activities in quantitative terms of time. Traditionally estimating maintenance, in particular fault diagnosis, in terms of time has received scant attention. This paper identifies the need to evaluate all maintenance activity times. In addition, an approach is offered to estimate fault diagnosis activity times using knowledge‐based systems. Finally, the paper offers a vision outline in applying the technology and techniques to provide cost‐effective and timely fault diagnosis.

Comparison of Asphalt Extraction Procedures: Implications of Hidden Environmental and Liability Costs

In the past, asphalt extractions were performed using toxic solvents; alternative, less polluting methods have been developed that can replace the traditional solvent extraction method. Accordingly, five potential asphalt extraction methods were compared for the Nebraska Department of Roads Bituminous Laboratory: solvent extraction using trichloroethylene (TCE), solvent extraction using an alternative solvent, solvent extraction using TCE and a solvent recovering reclaimer, ignition oven, and an ignition oven and solvent combination. To compare the total cost of each option, the direct capital costs, operating and maintenance costs, as well as the hidden environmental, health, and safety costs were considered. Because the hidden costs can be difficult to quantify, a total cost assessment approach was used. To represent the uncertainties in the cost and design data, fuzzy set theory was used. A traditional economic analysis, including only the capital, and operating and maintenance costs, found that the three least-cost options were within the range of uncertainty of the analysis; these three options were the ignition oven (most environmentally friendly option), ignition oven with solvents, and solvent reclaimer. However, when the hidden costs related to the environmental, health, and safety aspects for an asphalt extraction procedure were incorporated into the cost analysis, the cost comparison changed significantly; the most environmentally friendly option, ignition oven, was shown to be by far the least-cost option. Accordingly, the quantification of environmental, health, and safety costs that are difficult to assess is very important when evaluating environmentally friendly processes.

Operation of Milwaukee's Major Treatment Plants as an Integrated System, U.S.A.

Milwaukee has integrated the operation of its two large secondary treatment plants in a manner similar to that of an industrial complex. Raw materials, intermediate and final products are interchanged between its plants to optimize process capacity, O/M costs and product delivered. The key materials interchanged have been raw wastewater, thickened waste activated sludge and digested sludge. Detailed direct operating and maintenance costs are kept for each process. Indirect costs are also allocated to each process in proportion to its direct costs. Since early 1982 it has been advantageous to transfer waste activated sludge and digested sludge from the plant producing a liquid sludge, AGRI-LIFE, for agricultural application to the plant that produces a heat dried sludge, Milorganite, for commercial sale. The interplant transfer has been by truck, however, the District is now designing a 12 mile pipeline to connect the two plants. Operations and maintenance costs are presented for each of Milwaukee's processes.

Overhaul Life Development and Early Failure Detection of Aircraft Gas Turbines

In a modern gas turbine‐powered aircraft, engine material cost is the major single contributor to direct maintenance and overhaul cost. Due to the large expenditures involved, even a small percentage improvement in this field will result in the achievement of large savings. By concentrating on the reduction of both scheduled and unscheduled removals, this cost can be minimized. An analysis of the experience gained with the application (o gas turbine engines, of traditional overhaul life development programmes shows that these are of no benefit in determining the limitations of the engine. Experience and control of the total time or take‐off cycles of components, rather than time between overhaul, is the most important factor in the operational development of gas turbine engines. Overhaul life development can be divided into two phases: the initial programme applied to new engines with little operational background, and the developed programme applied to engines with substantial operating experience. In the initial programme, the sampling of two engines every 100 hours from a declared plateau can provide the required information and produces the required stagger in total time of components. In the developed programme large steps in overhaul life can be declared without further sampling. Life development of critical engine components cannot be done in service and requires manufacturer's cyclic testing ahead of airline experience until fail‐safe designs are achieved. Early failure detection of gas turbine engines is a Held of great potential return which to date has been only barely explored. Both engine manufacturers and operators need to develop tools and techniques for effective early failure detection quickly, to gain the large benefits which this field offers. Examples of the application of some early failure detection designs and techniques in Trans‐Canada Air Lines (T.C.A.) are given. These are in the field of visual examination with increased access to the engine, X‐ray examination of flame tubes with the engine installed in the aircraft, more effective use of the oil system to give warning of failure, engine vibration monitoring and automatic flight performance recording.

Plant Management and Other Factors Affecting Maintenance Costs in Steam-Generating Stations

Abstract Although direct maintenance costs in thermal power stations comprise only a small percentage of the total cost of production, replacement power costs while a generating unit is out of service for maintenance are also chargeable to the over-all cost of the job. This may amount to considerably more than the entire cost of the repairs. The control of maintenance costs is concerned principally with those factors which influence the ability of the plant to stay on the line, and this includes a wide variety of problems relating to equipment design, plant layout, types of fuels, manpower utilization, and other management problems. The limited statistical value of the term “operating availability” is discussed, and the concept of “relative mechanical availability” is introduced. Increasing technical and physical complications, together with larger unit sizes and greatly expanded generating systems, suggests the need for a redistribution of responsibilities at the plant level. This has created a demand for higher-grade engineering graduates with academic qualifications more suited to the special problems of thermal-power production, and a larger degree of co-operative effort between the utilities and the universities.