Cristiano Alexandre Virgínio Cavalcante

A multi-criteria decision model to determine inspection intervals of condition monitoring based on delay time analysis

In periodic monitoring, the main problem is determining the inspection interval of condition monitoring. For this problem, the decision variable is represented by the time of next inspection of condition monitoring. There are several studies that deal with prescribing inspection intervals. But only a few of these allow the decision maker to observe simultaneously more than one aspect. This does not accord with the natural tendency of the decision maker who desires to see the decision problem from a broader perspective, by having different viewpoints or dimensions of choices. Therefore, the main objective of this paper is to propose a decision model, which can simultaneously determine inspection intervals for condition monitoring regarding the failure behavior of equipment to be inspected, features of maintainability and decision maker preferences about cost and downtime.

Multicriteria and Multiobjective Models for Risk, Reliability and Maintenance Decision Analysis

Multiobjective and Multicriteria Problems and Decision Models.- Multiobjective and Multicriteria Decision Processes and Methods.- Basic Concepts on Risk Analysis, Reliability and Maintenance.- Multidimensional Risk Analysis.- Preventive Maintenance Decisions.- Decision Making in Condition-Based Maintenance.- Decision on Maintenance Outsourcing.- Spare Parts Planning Decisions.- Decision on Redundancy Allocation.- Design Selection Decisions.- Decisions on Priority Assignment for Maintenance Planning.- Other Risk, Reliability and Maintenance Decision Problems.

Imperfect inspection and replacement of a system with a defective state: A cost and reliability analysis

We consider a system with three possible states, good, defective and failed. Failures are detected as soon as they occur; the defective state, which is only revealed by inspection, does not prevent the system from fulfilling the function for which it was designed. We present a maintenance model consisting of periodic inspections to check the state of the system, in which inspections are subject to error. At a false positive inspection the system is unnecessarily replaced; at a false negative inspection a defect remains unrevealed with reliability implications for future operation. The model is illustrated with an example from the railways. In this context, we suppose that system lifetime is heterogeneous so that the time the system spends in the defective state is a random variable from a mixed distribution. We determine under what circumstances the cost of maintenance cannot be justified by its efficacy, and suggest that when there is the possibility that replacement is poorly executed (lifetime heterogeneity) the natural response to imperfect inspection of increasing the inspection frequency can be counter-productive.

Maintenance scheduling of a protection system subject to imperfect inspection and replacement

An inspection and replacement policy for a protection system is described in which the inspection process is subject to error, and false positives (false alarms) and false negatives are possible. We develop two models: one in which a false positive implies renewal of the protection system; the other not. These models are motivated by inspection of a protection system on the production line of a beverage manufacturer. False negatives reduce the efficiency of inspection. Another notion of imperfect maintenance is also modelled: that of poor installation of a component at replacement. These different aspects of maintenance quality interact: false alarms can, in a worst case scenario, lead to the systematic and unnecessary replacement of good components by poor components, thus reducing the availability of the system. The models also allow situations in which maintenance quality differs between alternative maintainers to be investigated.

Hybrid block replacement and inspection policies for a multi-component system with heterogeneous component lives

Novel replacement policies that are hybrids of inspection maintenance and block replacement are developed for an n identical component series system in which the component parts used at successive replacements arise from a heterogeneous population. The heterogeneous nature of components implies a mixed distribution for time to failure. In these circumstances, a hybrid policy comprising two phases, an early inspection phase and a later wear-out replacement phase, may be appropriate. The policy has some similarity to burn-in maintenance. The simplest policy described is such a hybrid and comprises a block-type or periodic replacement policy with an embedded block or periodic inspection policy. We use a three state failure model, in which a component may be good, defective or failed, in order to consider inspection maintenance. Hybrid block replacement and age-based inspection, and opportunistic hybrid policies will also arise naturally in these circumstances and these are briefly investigated. For the simplest policy, an approximation is used to determine the long-run cost and the system reliability. The policies have the interesting property that the system reliability may be a maximum when the long-run cost is close to its minimum. The failure model implies that the effect of maintenance is heterogeneous. The policies themselves imply that maintenance is carried out more prudently to newer than to older systems. The maintenance of traction motor bearings on underground trains is used to illustrate the ideas in the paper.

An Age-Based Inspection and Replacement Policy for Heterogeneous Components

This paper considers a hybrid maintenance policy for a single component from a heterogeneous population. The component is placed in a socket, and the component and socket together comprise the system. The s-population of components consists of two sub-populations with different failure characteristics. By supposing that a component may be in a defective but operating state, so that there exists a delay time between defect arrival and component failure, we consider a novel maintenance policy that is a hybrid of inspection and replacement policies. There are similarities in this approach with the concept of ldquoburn-inrdquo maintenance. The policies are investigated in the context of traction motor bearing failures. Under certain circumstances, particularly when the mixture parameter is large, and the distribution of lifetimes for the two component types are well separated, the hybrid policy has significant cost savings over the standard age-based replacement policy, and over the pure inspection policy. In addition to the cost metric, the mean time between operational failures of the system under the hybrid policy can be used to guide decision-making. This maintenance policy metric is calculated using simulation, and using an approximation which assumes that operational failures occur according to a Poisson process with a rate that can be calculated in a straightforward way. The simulation results show good agreement with the approximation.

A study of a two-phase inspection policy for a preparedness system with a defective state and heterogeneous lifetime

This paper considers an inspection policy for a single component protection or preparedness system, in which the component arises from a heterogeneous population. At any point in time, the system may be in one of three states, good, defective or failed. The system is only required in an emergency, and in order to ensure high availability of the system on-demand, the system undergoes a sequence of inspections. Inspection determines the system state, so that if a transition from the good state occurs between inspections it is not revealed until subsequent inspection. When a defect or failure is revealed, the component is replaced. At the final inspection the component is replaced. We suppose that a component may be either weak or strong, so that the time in the good state has a distribution that is a mixture. In these circumstances, the efficacy of a two-phase inspection policy, with an anticipated high inspection frequency in early life and low inspection frequency in later life, is considered using availability and cost criteria. The policy is investigated in the context of a valve in a natural gas supply network. If the lifetime distributions in the mixture are quite distinct, then cost savings of the order of 5% can be achieved by using the two-phase policy in place of the simpler single phase policy. Furthermore, only if the mean time in the defective state is small or the required availability is very high does the two-phase policy tend to mimic a burn-in policy.

Priorização de áreas de controle de perdas em redes de distribuição de água

The water supply systems for its complexity and own characteristics embed a certain index of water losses in the production. Besides, an old infrastructure, common in the Brazilian water supply systems, propitiates an accelerated process of deterioration, giving as consequence larger maintenance problems, especially elevating the indexes of water losses due to the resulting effects of the negligence to the conservation activities. In consequence, the Water Companies have the problem of high revenue losses when wasting fresh water by lack of an appropriate management. Furthermore, the managers need a new posture front to the decision making process, regarding to the action to be implemented, for a better efficiency of the system operational control, in order to avoid the losses. The objective of this work is to present a multicriteria model based on the PROMETHEE I method to support the manager in ranking the critical areas of losses, seeking to allocate investment of time and resources in the water supply systems in a more efficient way, focus on its efforts in the most critical areas.

Modelo multicritério de apoio a decisão para o planejamento de manutenção preventiva utilizando PROMETHEE II em situações de incerteza

As a strategic tool to reduce costs and increment the availability of the plant, Preventive Maintenance has become quite popular over the last years due to the significant increase of its application in industries. Despite the great quantity of models that deal with that problem, these are less than satisfactory in many situations when failure data are inexistent or not too reliable and when the observation of the conduct of more than one aspect is desirable to establish the periodicity of Preventive Maintenance. In such context, this article offers a model of decision by making use of the multicriteria method PROMETHE II and the Bayesian analysis, which allows to establish the periodicity of the Preventive Maintenance, observing the costs and reliability parameter and also permitting the lack of data not to be an impediment in the stipulation of those timings.

The Effect of Maintenance Quality on Spare Parts Inventory for a Fleet of Assets

This paper considers the effect of fleet size on a joint policy of maintenance and spare parts inventory when spare parts are of varying quality. We consider N identical one-component systems subject to age-based replacement, and with a single echelon periodic review spare-parts policy. The joint policy is optimised with regard to the long-run total cost per unit time, where the cost components include both replacement and inventory related costs. In particular, we are interested in the effect of spare parts quality and the size of the fleet on the variability in the demand for spare parts. Furthermore, the effects of changing lead time, different failure characteristics, and simultaneous deployment of the N systems over a finite horizon on the optimal joint policy are investigated. We develop a stochastic simulation model to investigate these effects. We find that the scale effect varies with the quality of spare parts: the poorer the quality of spare parts, the smaller the scale effect. Our approach allows the value (e.g. cost of poor quality spare parts) in spare parts provisioning for maintenance to be quantified.