Optimal Replacement Time Research Articles

On some discounted replacement models of a series system

Series system is having the shortest optimal replacement time among the other systems. And sometimes, the components (similar or non-similar) that formed the series system may have different failure rates due to some factors. In this paper, we considered a series system with six components, such that, all the six components are subjected to two types of failures, which are type I and type II failures. Therefore, we can say the system is also subjected to two types of failures (type I and type II). If the system fails due to type I, the system is minimal repair. But if the system fails due to type II, the system is replaced completely with a new one. We developed a discounted age replacement models with minimal repair for a series system. Two discounted age replacement model with minimal repair based on two decisions are proposed in the study. Finally, some numerical examples are given to obtain the optimal replacement times for the series system from the three replacement models constructed.

Cartridge filter selection and replacement: Optimization of produced water quantity, quality, and cost

In this study at a full-scale desalination installation seven types of commercially available cartridge filter (CF) elements were evaluated in terms of: (i) water production volume (m3), (ii) produced water quality, and (iii) operational cost (€cent/m3). The cost of optimal CF replacement time relative to increased CF pressure drop was determined for three electricity tariffs (0.05, 0.15, and 0.25 €/kWh) to assess further cost reduction. CF 1 was able to achieve the highest water production rate, the lowest produced water SDI, and the lowest cost of operation. The total costs of cartridge filtration varied between 1.22 and 1.70 €cents/m3 produced water, depending on the CF type. Replacing the worst-performing CF type by the best-performing CF type would reduce operational CF costs by about 39.3%, enabling a cost saving of 0.48 €cents/m3 produced water, emphasizing that selection of the right CF enables a large reduction of cartridge filtration costs. Moreover, depending on the electricity tariff an additional 2–16% cost reduction can be achieved by replacing CFs at an optimal time. At high energy cost, it may be more economical to replace cartridge elements more often to reduce the increased cost associated with the required higher pressure.

Extended age maintenance models and its optimization for series and parallel systems

In this paper, extended preventive replacement models for series and parallel system with n independent non-identical components are proposed. It is assumed that the system suffers from two types of failure. One is repairable (type-I) failure, at that time the system can be rectified by minimal repair. Another is non-repairable (type-II) failure, then the whole system is replaced. In the proposed models, the system is replaced at the planned time, at random working time, or at the time when type-II failure occurs, with options whichever occurs first or whichever occurs last. The average cost rate (ACR) function and the failure rate function (FRF) of the series and parallel system under the different cases are obtained respectively. Moreover, the optimal preventive replacement time of models based on minimization of the ACR function is obtained theoretically. Numerical examples are presented to evaluate the cost of the system and verify the performance of our results.

Optimization of drill bit replacement time in open-cast coal mines

To gain a competitive edge within the international and competitive setting of coal markets, coal producers must find new ways of reducing costs. Increasing bench drilling efficiency and performance in open-cast coal mines has the potential to generate savings. Specifically, monitoring, analyzing, and optimizing the drilling operation can reduce drilling costs. For example, determining the optimal drill bit replacement time will help to achieve the desirable penetration rate. This paper presents a life data analysis of drill bits to fit a statistical distribution using failure records. These results are then used to formulate a cost minimization problem to estimate the drill bit replacement time using the evolutionary algorithm. The effect of cost on the uncertainty associated with replacement time is assessed through Monte-Carlo simulation. The relationship between the total expected replacement cost and replacement time is also presented. A case study shows that the proposed approach can be used to assist with designing a drill bit replacement schedule and minimize costs in open-cast coal mines.

Reliability and optimal replacement policy for a k-out-of-n system subject to shocks

Consider a k-out-of-n system which is subject to shocks that occur at random times. Each shock causes failure of random number of components, and hence the system’s lifetime corresponds to one of the arrival times of shocks. The reliability and mean time to failure of the system are studied when the times between shocks follow a phase type distribution. The optimal replacement time problem which is concerned with the minimization of the total long-run average cost per unit time is also defined and studied.

AN APPLICATION OF PHASE-TYPE DISTRIBUTIONS IN A RELIABILITY SHOCK MODEL

Phase-type distributions have been found to be very useful in reliability, queueing theory, and some other operational research applications. In this work, we de_ne a new mixed shock model and study lifetime properties of the corresponding system using phase-type distributions. The system under concern fails upon the occurrence of k consecutive shocks of size at least d1 or a single large shock of size at least d2, d1 < d2. In particular, using closure properties of phase-type distributions, we obtain survival function and mean time to failure of the system. Optimal replacement time is also studied.

Optimal Timing for Peripheral Intravenous Cannula Replacement

Background:Current literature indicates the optimal replacement time of an intravenous catheter, ranges from when “clinically indicated” (i.e.signs of complications such as infection, occlusion, and/or phlebitis) to three days. The time constraint is designed to prevent infection(s) and phlebitis, as well as to decrease the costs of healthcare, and the time spent by nurses, on patient care.Aim:To evaluate the impact ofroutineremoval and re-siting of the peripheral intravenous catheter removal, compared to removal when “clinically indicated” by adults and/or pediatrics.Search Strategy:A search for literature was conductedviaCochrane Review and Web of Sciences™ Core Collection, MEDLINE, and PubMed to summarise the optimal timing for peripheral intravenous cannula replacement. One reviewer individually evaluated the trial(s), review(s), quality of the guidelines, and then, extracted the data.Selection Criteria:Criteria included guideline(s); randomized controlled trial(s); and reviews; all of which matched routine removal of peripheral intravenous cannulation, with re-sited when “clinically indicated”, only in patients in the hospital, partaking in intravenous medication and/or fluids. Articles of relevance to the topic, published in English, French, or Portuguese, prior to 2018, were reviewed.Conclusion:The effective implementation of evidence-based, guideline-based practice can decrease the catheter-related infection risk. While larger multi-site trials are required, present-day evidence asserts: the repetitive inserting of a peripheral intravenous device may raise the patient’s level of discomfort, increase the costs of healthcare, and does not decrease complications associated with peripheral intravenous devices.Implications for Practice:The clinically indicated intravenous catheter replacement procedure is cost-effective, compared with the recurring replacement procedure, which recurs every 72 hours; it has been suggested that healthcare institution(s) and hospital(s) have considered revising the policy, whereby intravenous catheters are replaced, if clinically indicated, only.

Age Replacement Policies with Shortage and Excess Costs

It has been proposed in recent literatures that if replacement time is planned too early prior to failure time, a waste of operation cost, i.e., excess costs, would incur because the system might run for an additional period of time to complete critical operations; and if the replacement time is too late after failure, a great failure cost, i.e., shortage cost, is incurred due to the delay in time of the carelessly scheduled replacement. The above notion of shortage and excess costs are taken into consideration for the replacement first, replacement last and replacement overtime models in this paper. We obtain the expected cost rates and their optimum replacement times. Comparisons among these optimum times are made analytically and numerically.

Optimizing replacement time for mining shovel teeth using reliability analysis and Markov chain Monte Carlo simulation

PurposeThe purpose of this paper is twofold: an approach is proposed to determine the optimum replacement time for shovel teeth; and a risk-quantification approached is developed to derive a confidence interval for replacement time.Design/methodology/approachThe risk-quantification approach is based on a combination of Monte Carlo simulation and Markov chain. Monte Carlo simulation whereby the wear of shovel teeth is probabilistically monitored over time is used.FindingsResults show that a proper replacement strategy has potential to increase operation efficiency and the uncertainties associated with this strategy can be managed.Research limitations/implicationsThe failure time distribution of a tooth is assumed to remain “identically distributed and independent.” Planned tooth replacements are always done when the shovel is not in operation (e.g. between a shift change).Practical implicationsThe proposed approach can be effectively used to determine a replacement strategy, along with the level of confidence level, for preventive maintenance planning.Originality/valueThe originality of the paper rests on developing a novel approach to monitor wear on mining shovels probabilistically. Uncertainty associated with production targets is quantified.

An Optimal Condition-Based Replacement Method for Systems With Observed Degradation Signals

Condition-based maintenance for a degrading system has been attached great importance in reducing unexpected failures and enabling the safe operation of the system. In this paper, we consider a condition-based replacement problem with observed degradation signals for the determination of the optimal replacement time of the system. The observed degradation signals contain some health related information of the system so that the system's health state may be more accurately estimated and the future degradation progression of the system can be predicted. Based on the predicted degradation state, the concerned replacement problem is formulated in the framework of the Markov decision process and then a new degradation-modeling framework based on maximum likelihood estimation is proposed to analyze the degradation signals and to predict the future degradation state of the system. To solve the proposed condition-based replacement decision problem, we analyze structural properties of the optimal replacement policy and an optimal monotonic control limit solution policy is developed for condition-based replacement. Finally, a case study is provided to illustrate the proposed optimal replacement method.

Note on History of Age Replacement Policies

This paper tries to trace our research history briefly from Barlow and Proschan to attain general replacement models. We begin with a random age replacement policy that is planned at a random time Y and call it as random replacement. When the distribution of Y becomes a degenerate distribution placing unit mass at T, age replacement is formulated. We obtain the general formulas for optimum replacement times. We next suppose the unit works for a job with random works, and replacement policies with N cycles are discussed. As follows, we combine age and random replacement models and discuss replacement first, replacement last, replacement overtime, replacement overtime first and replacement overtime last. By formulating the distributions of replacement times with n variables, general replacement models with n replacement times are obtained.

The number of failed components in a k-out-of-n system consisting of multiple types of components

The number of failed components in a failed or operating system is a very useful quantity in terms of replacement and maintenance strategies. These quantities have been studied in several papers for a system consisting of identical components. In this paper, the number of failed components at the time when the system fails and the number of failed components when the system is working are considered for a well-known and widely applicable k-out-of-n structure. The system is assumed to have multiple types of components. That is, the system consists of components having nonidentical failure time distributions. Optimization problems are also formulated to find optimal values of the number of components of each type, and the optimal replacement time.

Reliability analysis of the aircrafts normal braking system

An identified component of Airbus A-330 aircraft which should be maintained properly is the normal braking system. The objectives of this study are to: (1) identify the critical component of the normal braking system; and (2) determine the optimal replacement time interval of replacement of the normal braking system component. This study is conducted in Garuda Maintenance Facility Aero Asia company. Primary data in this study are the components replacement data of normal braking system in period January 2015 - January 2017. The life distribution such as Mean Time to Failure (MTTF), reliability, probability density function, cumulative distribution function, and failure rate are obtained by the Weibull++ software. Results show that the critical component of the normal braking system is the brake unit assembly. Meanwhile, the life distribution analysis show that the reliability of importance value of the normal breaking system IR is 74.07 percent which occurs at MMTF and system reliability are 4365.5 hours and 55.58 percent, respectively. These values indicate that optimal replacement time interval of the Brake Unit Assembly is 5599.7 hours.

Environmental performance of alternative end-of-life scenarios for electrical and electronic equipment: A case study for vacuum cleaners

Extending the product life span of electrical and electronic equipment is considered an optimal strategy for resource conservation as consuming new resources to produce new appliances is avoided, and the amount of generated waste is reduced. However with energy-using products, the energy efficiency of equipment and other user-related behaviour variables play a key role when determining the best end-of-life scenario from an environmental viewpoint. This research aimed to identify the optimal replacement time by considering two main situations from an environmental perspective. In Situation 1 (equipment does not need repairing during its life span), two scenarios are compared: using equipment until the end of its life span versus replacing it with more energy-efficient equipment. In Situation 2 (equipment breaks and needs repairing during its life span), two scenarios are compared: repairing equipment and using it until the end of its life span versus not repairing and replacing it with more energy-efficient equipment.To this end, the life cycle assessment methodology is applied. The definition of the life cycle of each scenario combines the energy class of the initial appliance and the energy class of the replacing one, as well as their years of use. Apart from this, different consumer use behaviours are also considered, based on the equipment’s frequency of use. Finally according to an analysis of main failures, different repair requirements are also considered in each scenario.The results, after taking a domestic vacuum cleaner as the case study, show that consumer use behaviour is the variable that most affects the environmental impact when selecting the scenario with less environmental impact for each situation. According to the consumer profile, for consumers who use vacuum cleaners occasionally, using and repairing (if required) them until the end of their life span is the most recommendable option. However, for other consumer use behaviours (those who vacuum often), replacement with a more energy-efficient vacuum cleaner is recommendable when the difference between the initial and the replacing energy efficiency class of vacuum cleaner exceeds two levels.

Application of gamma process model to estimate the lifetime of photovoltaic modules

The analysis of long term data for degradation of PV modules suffers from volatility and uncertainty due to intrinsic and extrinsic factors. The low rate of degradation causes analysis complexity and ambiguity. In this study, methods used to estimate the PV module lifetimes were reviewed in terms of degradation of power output with time. Under the assumption that degradation is continuous, gradual, and monotonic, the gamma process model can explain the sampling and temporal uncertainties of lifetime data. Examples are provided to demonstrate the use of gamma process model for long term and accelerated lifetime test (ALT) data. Three types of lifetime estimation method were compared for long term operation data. Although they all gave similar estimated lifetime, the gamma process model gave the most applicable results to determine warranty life. The gamma process model can also express the condition variation at inspection and the lifetime variation at failure level as probability distributions. A method to determine warranty life is proposed using an age based replacement policy. For ALT data, we estimated the lifetime from degradation data using the Arrhenius equation for standard environmental conditions and applied the gamma process model to obtain time varying probability distributions for condition and lifetime. Service life was estimated as the median, while warranty life was estimated as the minimum rate of increase of optimal replacement time.

Moment-based approach for some age-based replacement problems

In this paper we develop statistical inference approaches for three age replacement policies; classical age replacement, opportunity-based age replacement first and opportunity-based age replacement last, when the failure time distribution of an item is unknown. More specifically, we utilize the sample moments of the failure time distribution and estimate the optimal age replacement times for three problems above. Further, we derive the upper and lower bounds of the expected cost functions per unit time for respective age-based replacement problems, under the assumption that the failure time has an arbitrary IFR (increasing failure rate) distribution function with finite moments. Finally, we investigate the inference performance of our moment-based approaches in numerical examples, and the applicability of them under the partial information on the failure time distribution.

Optimal Replacement Time of Electrical Components Based on Constant-Interval Replacement Model: Equipment Inspection Method and Weibull Analysis

The operation of distribution system with the components in deteriorating condition makes the system reliability worsen. It is important to find the solution for balancing failure cost and maintenance benefits such as down-time and reliability. In this paper, time to replace the components in optimum condition based on constant-interval replacement mode is investigated. The optimal replacement time is mainly depended on component’s reliability and the cost ration of preventive replacement and failure replacement. In this paper, equipment inspection method and Weibull Analysis is applied to obtain the accurate reliability estimation. Weibull Analysis is applied with constant-interval replacement model to investigate the optimum replacement time for each component considering the different cost ratios. According to the quantitative results, the determination of the optimal replacement time (OPT) can minimize the total downtime and failure cost. Consequently, the reliability of the system is maximized and estimation also becomes more accurate due to sufficient approach.

Computing optimal replacement time and mean residual life in reliability shock models

In this paper, matrix-based methods are presented to compute the optimal replacement time and mean residual lifetime of a system under particular class of reliability shock models. The times between successive shocks are assumed to have a common continuous phase-type distribution. The system’s lifetime is represented as a compound random variable and some properties of phase-type distributions are utilized. Extreme shock model, run shock model, and generalized extreme shock model are shown to be the members of this class. Graphical illustrations and numerical examples are presented for the run shock model when the interarrival times between shocks follow Erlang distribution.

Comparisons of Individual and Group Replacement Policies for a Two-machine Series System

This paper studies the comparisons of individual and group replacement policies for a two-machine series system. Suppose that manufacturer's production system which consists of two machines in series. For two machines, when any machine fails within the operating time, minimal repair is performed for machines by the manufacturer. Due to the inevitable deterioration of the machine, the machine may fail more frequently as its age or usage increases. Therefore, an appropriate preventive replacement (PR) of the machine may be suitable for reducing the number of failures and maintains the operation of the machine normally. When a PR action is performed, it incurs a replacement cost and a downtime cost. Hence, when the replacement cost is high, it might be worthwhile replacing both machines at the same time (called group replacement policy; GRP) instead of replacing them separately (called individual replacement policy; IRP). Under these maintenance policies, the maintenance cost rate models of individual and group replacement for a series system is derived and further, optimal preventive replacement time is obtained such that the expected total cost rate is minimized. Finally, some numerical examples are given to illustrate the influences of individual and group replacement policies to the expected total cost rate.

The Operational Determinants of Utility Pole Decay and Optimal Replacement in the Pacific Northwest

Wood utility poles are central to many electrical distribution networks, yet there have been no published studies to determine what operational characteristics of utility poles are indicative of decay in the field. We apply survival analysis to a database of more than 17 $\thinspace$ 000 utility poles in the Pacific Northwest, and find that larger circumference poles decay sooner, that Douglas fir poles do not last as long as western red cedar poles, that a split top has a large negative impact, and that the presence of a transformer makes decay more likely. We use our estimates for the size of these effects to calculate a pole-specific optimal replacement time that minimizes the cost of the pole. Our results are regional, and may not apply generally, but we document how our approach can be adapted to any electrical distribution network.