Evaluating maintenance strategies using a resilience index in a seawater desalination plant

This paper presents reliability, availability, and maintainability (RAM) analysis framework for evaluating the performance of a circulation system of water (WCS) used in a coal-fired power plant (CFPP). The performance of WCS is evaluated using a reliability block diagram (RBD), fault tree analysis (FTA), and Markov birth–death probabilistic approach. In this work, the system under study consists of five subsystems connected in series and parallel configuration namely condensate extraction pump (CEP), low-pressure feed water heater (LPH), deaerator (DR), boiler feed pump (BFP), high-pressure feed water heater (HPH). The reliability block diagram (RBD) and fault tree approach (FTA) have been employed for the performance evaluation of WCS. The Markov probabilistic approach based simulation model is developed. The transition diagram of the proposed model represented several states with full working capacity, reduced capacity, and failed state. The ranking of critical equipment is decided on the basis of criticality level of equipment. The study results revealed that the boiler feed pump affects the system availability at most, while the failure of deaerator affects it least. The availability of the system is optimized using the particle swarm optimization method. The optimized availability parameter (TBF, TTR) based modified maintenance strategy is recommended to enhance the availability of the plant system. The optimized failure rate and repair rate parameters of the subsystem are used to suggest a suitable maintenance strategy for the water circulation system of the thermal power plant. The proposed RAM framework helps the decision-makers to plan the maintenance activity as per the criticality level of subsystems and allocate the resources accordingly.

PurposeIn the present worldwide situation, the survival of a business is a major crucial aspect. The business cannot be succeeded unless it produces the anticipated production levels. Achievement of this can be possible only by maintaining the equipment into an adequate level. Load-Haul-Dumpers (LHDs), as the main workhorse and massive transporting machines, are highly utilized in underground mining operations. Despite the usage of LHDs, these are prone to the uneven and unexpected occurrence of potential failures. These are causes to minimize the production and productivity of capital intensive equipment. To get a good profitability index, it is very necessary to have the required levels of equipment reliability and availability. Estimation of reliabilities and availabilities play a critical role in the performance evaluation of equipment.Design/methodology/approachBy keeping the significance of the present research work in view in this research paper one of the well appropriate techniques such as fault tree analysis (FTA) was utilized to assess the reliability of the LHD system based on the function flow diagram. Best fit distribution of data sets were made by the utilization of Kolmogorov–Smirnov (K-S) test. Parametric estimation of theoretical probability distributions was done by utilizing the maximum likelihood estimation (MLE). Failure rate of each LHD system has computed based on the best fit results from “Isograph Reliability Workbench 13.0”. Reliability configuration of each LHD system has modeled using reliability block diagram (RBD), as well as the FTA.FindingsIndependent and identical distribution (IID) assumption of data sets was validated through statistic U-test (Chi Squared test). On the basis of test results, the data sets are in accordance with IID assumption. Therefore renewal process approach has been utilized for further investigation. Allocations of best fit distribution of data sets were made by the utilization ofK-S test. Parametric estimation of theoretical probability distributions was made by utilizing maximum likelihood estimation (MLE) method. Reliability of each individual subsystem has been computed according to the best fit distribution. The deductive method called RBD was utilized to investigate the given system reliability by analyzing with graphical representations of logic system and observed highest percentage of reliability as 69.44% (LH29). FTA has been utilized to investigate the availability percentage of a system and observed highest percentage value as 79.51% (LH29). This technique also helps to identify the most critical parts/cut sets by using Fussell-Vesely (F-V) importance measure.Research limitations/implicationsAs the reliability analysis is one of the complex techniques, it requires strategic decision-making knowledge for the selection of methodology to be used. As the present case study was from a public sector company, operating under financial constraints the conclusions/findings may not be universally applicable.Originality/valueThe present study throws light on this equipment that need a tailored maintenance schedules, partly due to the peculiar mining conditions, under which they operate. This analysis provides the information on several aspects such as present working condition of the machines, occurrence of various potential failure modes, influence of failure modes on its performance and reliable life aspects etc. Also, these investigations asses the forecasting of necessary managerial practices or control measures like possible design modifications and replacement actions of components to ensure the required levels of availability and utilization of the equipment. Both qualitative and quantitative analysis of FTA has been performed to determine the minimal/most influencing cut sets of the system and to estimate overall system availability within the work environment. Based on the computed results reasons for performance drop of each machine was identified and suitable recommendations were suggested to improve the performance of capital intensive systems.

The study computes the availability of street lighting system in Warri. This system under study consists of subsystems that are known as workstations. A generator and sets of street light make up a workstation. The power source and the street lighting were modeled into series and parallel combinations. Reliability Block Diagrams and Path Tracing Method were employed assuming independent failure of the components. The availability of the set of street lightings, workstations and hence the availability of the system were determined. Results of the study show that users in Cemetery road had the least availability of 62.19% for the period. The implication is that users travelling along this road experienced wide variation of light that could lead to accidents.
 Keywords: Availability, Street Lighting and Reliability block diagram

Formalization of Reliability Block Diagrams in Higher-order Logic

Reliability Block Diagrams (RBDs) allow us to model the failure relationships of complex systems and their sub-components and are extensively used for system reliability, availability, dependability and maintainability analyses of many engineering systems. Traditionally, Reliability Block Diagrams (RBD) are analyzed using paper-and-pencil proofs or computer simulations. Recently, formal techniques, including Petri Nets and higher-order-logic theorem proving, have been used for their analysis as well. In this paper, we provide a concise survey of these available RBD analysis techniques and compare them based on their accuracy, user friendliness and computational requirements.

System level reliability and availability estimates are required to facilitate cost tradeoff studies associated with competing photovoltaic systems. Estimates of reliability are necessary in developing maintenance cost projections over the system lifetime. Availability estimates provide an input into annual energy generation projections. This paper describes a comprehensive approach to developing reliability and availability estimates for a large photovoltaic system. System reliability and availability were defined based on the operator's expectations and a Reliability Block Diagram (RBD) was developed to model system behavior. The RBD developed is a hierarchical reliability model. Larger functional elements are decomposed into smaller functional elements. The granularity of the model is determined by the level that failure data are collected. Field data, failure times and repair times, were collected and analyzed for a five year time period from a 4.6 MWdc photovoltaic system operated by Tucson Electric Power (TEP) at Springerville, Arizona. Failure and repair distributions were fitted to these field data. These results were then used to populate the RBD and produce system level estimates of reliability and availability. The results of these analyses are: 1. a summary of failures for each main component of the system, 2. a summary of failure distributions/rates and repair times for each main component, 3. system reliability and availability versus time projections, and 4. an estimate of the number of failures for each main component over the system's life.

A simulation program (SIMULAV) is presented that is capable of modeling large-scale reliability systems. The program can model the effect of such logistics characteristics as inventory, transportation, and facilities on the reliability and availability of the system. The program is written in Pascal and it consists of three main elements: a process-oriented simulation language, a minimal cut-sets algorithm, and a simulation model to estimate the availability of a complex system. The model is implemented using the process-oriented simulation language and its uses the minimal cut-sets to determine system failure. It assumes that the system can be represented by a reliability block diagram. Examples are modeled to show how SIMULAV can be used to assess the effect of some logistic parameters on the availability of the system. >

Agriculture is an important industry in the Province of British Columbia, especially in the Lower Mainland where fertile land in the Fraser River Delta combined with the enormous water resources of the Fraser River Estuary support extensive commercial agriculture, notably berry farming. However, where freshwater from inland meets saltwater from the Strait of Georgia, natural and man-made changes in conditions such as mean sea level, river discharge, and river geometry in the Fraser River Estuary could disrupt the existing balance and pose potential challenges to maintenance of the health of the farming industry. One of these challenges is the anticipated decrease in availability of sufficient freshwater from the river for irrigation purposes. The main driver for this challenge is climate change, which leads to sea level rise and to reductions in river flow at key times of the year. Dredging the navigational channel to allow bigger and deeper vessels in the river may also affect the availability of fresh water for irrigation. In this study, the salinity in the river was simulated using H3D, a proprietary three-dimensional hydrodynamic numerical model which computes the three components of velocity (u,v,w) in three dimensions (x,y,z) on a curvilinear grid developed specially for Fraser River, as well as scalar fields such as salinity and temperature. The results indicate various levels of impact to the salinity in the river and adaptive measures must be established to maintain the long-term viability of the industry. This study found that sea level rise and changes in river discharge would have a larger impact on the availability of fresh water than would channel deepening at the present sea water level. In a low river discharge regime, the impact from sea level change is more significant than in the high river discharge regime. On the other hand, the influence from changes in river discharge on withdrawal appears to increase when water level is lowered. Dredging the channel to accommodate larger vessels with deeper draft would further affect the salinity and shorten the withdrawal window; the effect of channel deepening becomes more pronounced in the lower flow period.

The increasing demand for water in arid regions has driven the adoption of seawater desalination plants as critical infrastructure for industrial and domestic applications. However, these plants face unique challenges, including high operational costs, environmental vulnerabilities, and system reliability concerns. The critical nature of these infrastructures demands maintaining elevated levels of availability and demonstrating robust resilience. Resilience is framed as the system’s capacity to recover from disruptions and maintain operational efficiency under varying conditions. Quantitative assessment of resilience is essential to facilitate the development and implementation of optimal strategies that ensure operational continuity. This paper puts into practice a novel approach to evaluate the resilience of a seawater intake and pumping system using permutation entropy computed using time series availability data derived from different maintenance strategies. The methodology integrates reliability block diagrams (RBD) and symbolic time series analysis to identify critical components and evaluate maintenance strategies. A case study of a seawater pumping station demonstrates the application of the proposed resilience index. The analysis explored four scenarios to evaluate how these changes improved the system’s resilience: the first three hypothetical scenarios involved testing improvements in the maintainability and reliability indexes of the critical pump. These improvements matched the values of these parameters to the benchmark of the pump, historically showing the best indicators, first one by one, separately, and then both changes simultaneously. The initial resilience index was 0.652 in the baseline scenario. Scenario 1 (reduction in MTTR) showed a negligible impact, while scenario 2 (reduction in downtime) increased the resilience index to 0.682. The combination of both (scenario 3) maintained the index at 0.682, emphasizing the importance of reducing downtimes. Scenario 4, which consisted of reducing and standardizing the frequency of planned maintenance to 100 h, significantly raised the resilience index to 0.778. The results highlight how adjustments in maintenance strategies, including the reduction in preventive interventions, impact the system’s resilience and availability. The study also underscores the importance of aligning maintenance strategies with resilience goals to enhance the operational reliability of marine infrastructure. By providing a quantitative tool for resilience assessment, this work contributes to the sustainable management of desalination plants and offers practical insights for engineers and decision-makers in the marine engineering and water management sectors.

The paper solves the problem of increasing the reliability of operation of the technological system of heavy machines by determining a rational strategy for its maintenance. The analysis of the literature showed that there are various indices of reliability, durability, maintainability, which partially characterize reliability, to assess the reliability of the technological system. To determine them, you must have a large number of statistical studies. But there is a need to develop universal mathematical dependencies to predict a specific maintenance strategy for the technical system of heavy machines. Research methods include static data collection of heavy machine tools, the reliability of which is determined mainly by machine downtime associated with the failure of cutting tools, which are the weakest element of the technological system. Mathematical processing of statistics results allows to determine the density distribution of system failures, as well as the intensity of failures and system recovery. A feature of the recovery of heavy machines is the location of their caliper on a high platform, which makes it difficult to replace the tool, whose weight reaches 25 kg. The paper presents a system of indicators of the reliability of the process of operation of the technological system of a heavy lathe, which consists of machine parts, tools and machine operator. Statistical analysis of the system allowed to identify the structure of the time of its technological work, the density of distribution of the system downtime associated with the maintenance of the tool. The maintenance of the technological system of a heavy machine is carried out by 2 machine operators (the main and the assistant). The paper considers two strategies of machine maintenance - independent and common. The criterion for choosing a rational strategy is the level of reliability of the system. A universal indicator of the reliability of the technological system is proposed to use the system availability ratio. It is assumed that the system can be in one of three possible states at a certain point in time: the system health state, the state when only one tool is operational, the state in which all tools are restored. The system availability function is the probability of being in a working system state. Using the Markov approach to assessing the reliability of the system, a matrix of transitions from one state of the system to another is written, which allows us to obtain algebraic equations, solving which we obtain mathematical models for determining the availability factor for various maintenance strategies of the technological system. Mathematical models of availability factor have been developed for two strategies for operating a heavy lathe technological system: independent maintenance of the system by machine operators and general maintenance by several machine operators. With the joint maintenance of a technological system by two machine operators, the level of reliability of the system is significantly increased compared with independent maintenance. For the general case with a certain number of cutting tools and a certain amount of machine operators, a mathematical expression was obtained for calculating the availability factor, which determines the probability of a healthy state of the system. The use of the developed mathematical models makes it possible to select the necessary system maintenance strategy to ensure a certain level of reliability of its operation. The developed mathematical models are used for statistical modeling of the maintenance of the technological system of a heavy lathe, whose downtime has a greater cost. Knowing the failure rate and system recovery, you can choose the necessary service strategy to obtain a desired level of reliability. Possible solution of the inverse problem for a given system availability in various combinations of λ and μ, which characterize the intensity of failures and recovery of the tool, which are implemented at the stage of tool selection. Since most often in production conditions heavy lathes are serviced by two machine operators, in this case the most effective from the point of view of reliability is the joint maintenance of the technical system.

According to the ITER requirement, the availability of the poloidal field (PF) coil power supply system must be 98.3% during the life cycle of ITER. In order to meet this requirement, Reliability, Availability, Maintainability, and Inspectability (RAMI) analysis has been applied for analyzing the availability and reliability of the PF power supply system. First, the function analyses, which are described using the Integration Definition Function–language Ø or IDEFØ model are performed. Second, the failure mode effect and criticality analyses are used to calculate the risk level, present the potential causes and effects, and provide the risk mitigation actions to reduce the risk level for each failure. Third, the reliability block diagram is built to simulate the availability and reliability of the system. RAMI analysis provides a method that can be followed to improve the availability and reliability of the system, and from the results, the design requirement can be satisfied.

Industrial steam boilers are prone to occurrences such as equipment failures, human errors, and common-cause failures in a context of sophisticated maintenance, inspection, and testing management. These events will have an impact on reliability of safety-related systems as well as the overall risk level. To analyze the impact of item failures on system availability, reliability block diagrams (RBD) are commonly used, taking into account their physical arrangement in the system. In this research, the RBD technique is utilised to estimate the reliability of boiler systems used in Indian textile industries. Furthermore, the boiler system reliability before and after the preventative maintenance PM task is compared.KeywordsSteam boilerRBD modelPreventive maintenance intervalReliability

Availability and reliability evaluation of chilled water and electricity generation of a cogeneration plant depend on individual components availability and reliability in particular the electricity and chilled water generation system. This paper deals with modeling of chilled water availability and reliability of a cogeneration power plant using probabilistic and reliability block diagram approach. The under study cogeneration plant consists of four main components namely; gas turbines (GT), electric chillers (EC), thermal energy storage tank (TES) and steam absorption chillers (SAC). These components exist with three possible states: full working, reduced capacity working and failed. To incorporate all three states, multi-state theory is adopted. A transition and reliability block diagram represent the operational behavior and logical order of the system. Availability and reliability of chilled water system are compared with actual and traditional availability and reliability using statistical evaluation. Results of the study could be useful to develop a proper and effective maintenance strategy for a system.

Boolean algebra method to calculate network system reliability indices in terms of a proposed FMEA

Nuclear power plants (NPPs) are subjected to events such as equipment failures, human errors and common-cause failures, in an environment of complex maintenance, inspection and testing managements. These events will affect the reliability of safety-related systems, as well as the risk level of the plant. Reliability block diagram (RBD) is often used to analyze the effect of item failures on system availability, taking into account their physical arrangement in the system. Fault tree (FT) is a commonly used technique for analyzing risk and reliability in nuclear, aeronautical and chemical industries. It represents graphically the basic events that will cause an undesired top event. Loss of electrical power is one of the main events that influences safe operation of NPPs, as well as accident prevention and mitigation. In case of unavailability of offsite power, emergency diesel generators (EDGs) supply onsite electrical power. This paper carries out reliability analyses of EDGs of NPPs using both RBD and FT techniques. Each technique has its own advantages and disadvantages, allowing a variety of qualitative and quantitative analyses. Outcomes using these two techniques are compared for a typical NPP EDG system.