International Journal of Reliability and Safety (10 papers in press)

Regular Issues

• A comparison study for bearing remaining useful life prediction by using standard stochastic approach and digital twin  
  by Jie Liu, Jørn Vatn, Viggo Gabriel Borg Pedersen, Shen Yin, Bahareh Tajiani 
  Abstract: Remaining useful life prediction is important for research of maintenance. It is common to use stochastic approaches to predict remaining useful life of components. On the other hand, there is a digital twin model developed by MATLAB for bearings real-time remaining useful life prediction. To have a better understanding of the advantages and disadvantages of these models, an experiment was designed and implemented to get real degradation data of bearings for model testing. Two stochastic approaches are selected which are Wiener process and geometric Brownian motion. The purpose of the paper is to compare the models for remaining useful life prediction with standard stochastic approaches and digital twin through real degradation data in order to find the comparison among them. Finally, the MATLAB digital twin model outperforms stochastic approaches in the early phases of prediction while remaining comparable in the latter stages. The paper could be used as a reference for further remaining useful life prediction research.
  Keywords: remaining useful life; digital twin; stochastic approach; bearing experiment.
  
  
• Post COVID-19 electrical load shedding on Cameroons northern interconnected grid: causes, safety impact and solution proposals  
  by Bouba Oumarou Aboubakar, HongXia Li, Ahmadou Bouba Oumarou 
  Abstract: This paper, after assessing and ranking power shortage causes in Cameroons northern interconnected grid, summarises the impact of power shortage on poor households and district hospitals. The results showed a drop of 40% of the supplied energy and the fluctuations of demand continued across the COVID-19 period till July 2021 after lockdown, thus a low influence of the pandemic. The results also revealed a low influence of temperature and precipitation on the energy crisis. Instead, it was found that the most important factor that led to power shortage was electricity production cost, which is higher than the market price. Out of seven hypotheses tested by the structural model developed, five were significantly supported and two were rejected. The hypothesis testing showed that electrical fire safety and patient care in hospitals are both positively significantly affected by load shedding, hospital management and users safety commitment and knowledge. Also, the results showed that neither safety knowledge nor safety impact is affected by demographic and socioeconomic variables. Using these results, a series of recommendations are given to energy practitioners and grid managers.
  Keywords: post COVID-19; load shedding; safety impact; structural equation modelling; Cameroon northern interconnected grid.
  
  
• Coordination reliability evaluation on raw material input and molten iron output for intelligent ironmaking system  
  by Jiahui Zhan, Yongjin Zhang, Yanjun Zhang, Tiejun Chun 
  Abstract: In intelligent ironmaking, the coordination reliability is of importance on the health condition of a blast furnace (BF) system. According to the basic principle of BF ironmaking, this paper proposes a method of measuring the coordination reliability using the input-output data of the BF system. The proposed method takes the difference between raw material input and molten iron output as an indicator to measure the coordination reliability. Real-time monitoring data and the functional relationship between raw material input and iron output are considered to formulate the coordination reliability model of a BF ironmaking system. By using the adjusted sampling technique, the batch sampling acceptance scheme is further developed on the coordination reliability of the BF ironmaking system. The data of one 1080 cubic-metre BF system is analysed to validate the proposed method.
  Keywords: coordination reliability; evaluation model; intelligent ironmaking system; batch sampling acceptance scheme.
  
  
• Performance of batch service queue model with second optional service, repairable breakdown and standby server  
  by Pikkala Vijaya Laxmi, Andwilile Abrahamu George, Hasan A.D.B. Qrewi 
  Abstract: In this paper, we investigate the performance of batch service queue with second optional service (SOS), repairable breakdown and warm standby server. Both primary operating and warm standby servers provide first essential service (FES) and SOS to customers. Switching warm standby server to replace failed primary operating server has a probability of failure for FES(SOS). We use Runge Kutta method to obtain the transient state probabilities and matrix-decomposition method to obtain the steady state probabilities of the model. Also, a cost model is presented to determine the optimal service rates so that the expected cost is minimized. Finally, the effect of the model parameters on the system behaviour is demonstrated through numerical results and discussions.
  Keywords: batch service queue model; first essential service; second optional service; repairable breakdown; standby server.
  
  
• Availability assessment of repairable Markov systems with an uncertain inspection period incorporating (M/M/s):(/FCFS) queue.  
  by Amisha Khati, Neelam Chantola, S.B. Singh 
  Abstract: In this research, a novel model for a Markov repairable system is proposed wherein there is an uncertainty in the inspection period, i.e., the inspection period is taken in such a way that whenever a fault is identified throughout the inspection, the inspection period is shortened for the next inspection. Further, if the time taken to repair the system failure is less than the pre-determined critical value, the failed elements of the system are repaired. And, if the system takes longer than the critical time to fully recover, it is considered completely failed, and then the failed system is replaced with a new one. The system is repaired under the (M/M/S):(?/FCFS) queue model, including working vacations. We have evaluated the proposed model's availability as a measure of reliability. For clarification, the results are supported by a numerical example.
  Keywords: availability assessment; Markov repairable system; uncertainty; critical repair time; (M/M/s):(∞/FCFS) queue.
  
  
• Reliability assignment of a heavy-duty CNC machine tool spindle system based on fault tree analysis  
  by Hongxia Chen, Junfeng Zhang, Chenguang Li, Jihua Wang, Chuncheng Guo 
  Abstract: In order to improve the reliability of heavy-duty CNC machine tools, it is of great significance to study the distribution of machine tool reliability indicators and improve its reliability in the design and manufacturing stages of machine tools. Owing to the complex structure of heavy-duty CNC, less fault data, and multi-source heterogeneity of fault causes, the traditional single reliability assignment method cannot be well handled. Machine Tool In this paper, the spindle system of a certain type of heavy CNC machine tool is studied, and the reliability of the spindle system of the machine tool is allocated based on FTA. Firstly, a fault tree model is established according to the fault data of the machine tool spindle system. The model is divided into three layers: top events, middle events, and bottom events. Then, for each layer of events, the distribution of reliability indicators is carried out based on probability importance analysis, reliability redistribution method, and analytic hierarchy process. Finally, the top-down reliability distribution results are obtained after analysis. By synthesising multiple distribution methods, the reliability distribution index is more in line with the actual situation. After comparing the differences before and after the reliability index distribution, the design and improvement are aimed at the weak parts of reliability, thereby improving the reliability of the machine tool.
  Keywords: heavy-duty CNC machine tool spindle system; FTA; reliability assignment; reliability index.
  
  
• Reliability analysis by Markov model and stochastic estimator of stochastic Petri nets  
  by Hamid El-Moumen, Nabil El Akchioui, Mohammed Hassani Zerrouk 
  Abstract: In our study, we were interested in the reliability of large discrete systems. These studies can be based on Markov models or on Stochastic Petri Nets (SPNs) that are generally used for the analysis and synthesis of the models used in the different phases of a systems life. Markov models or SPNs are perfect for many cases, still, they suffer from the combinatorial explosion when analytically their states numbers increase as the complexity of the dynamic systems grows accordingly with their components. This issue is reflected in the slowness of these models to accomplish convergence. These different modelling tools make it possible to deduce the average behaviour and to obtain the performance indicators of the system studied, either by calculation or by estimation. We will present the Markov analysis of a system whose state space is finite as well as its estimator obtained using SPNs.
  Keywords: Petri net; stochastic Petri net; stochastic estimator; Markov model; reliability analysis.
  
  
• Blast resistance prediction of clay brick masonry wall strengthened with steel wire mesh, and C-FRP laminate under explosion loading: a finite element analysis  
  by Mohd Shariq, S.M. Anas, Mehtab Alam 
  Abstract: A detailed finite element micro-model of an unreinforced masonry (URM) wall of clay bricks, 1600 mm x 2100 mm x 240 mm, is made in ABAQUS/Explicit-v.6.15 code and analysed considering strain rate effects under the 5 kg-TNT explosion load at 0.58 m/kg1/3 scaled distance in free air. Results are validated with the available blast test results. Strengthening of the wall is considered by providing (1) steel wire mesh of diameter 2.50, 3.50, and 4.50 mm on the (a) rear face only and (b) on both the faces; (2) C-FRP wrapping of a thickness (a) 0.50 mm and (b) 0.60 mm on the rear face only, and (c) 0.30 mm on both the faces of the wall. Response of wall with each strengthening technique applied in this study is discussed. Application of 4.50 mm wire mesh on both the faces and 0.50 mm C-FRP sheet on the rear face makes the wall respond with comparable performance under the considered blast loading.
  Keywords: explosion loading; masonry walls; building safety; clay bricks; steel mesh; C-FRP wrapping; blast resistance; damage.
  DOI: 10.1504/IJRS.2022.10051370
   
  
• Pre-chamber spark ignition: a reliability analysis of pre-chamber valve functions  
  by Faraz Akbar, Sarah Zaki 
  Abstract: A pre-chamber ignition allows spark-ignition engines to operate in lean air-fuel settings. It improves fuel efficiency and reduces emissions. In this study, a reliability analysis of a single GE Jenbacher J620 natural gas engine was done. It was operational on continuous load in the power generation sector in Karachi, Pakistan. A bathtub curve of the GE J620 pre-chamber gas valve (PCV) was generated. The three-year industrial data comprised PCV failures that occurred between two overhauls. During infant mortality, the curve revealed 7 failures during 1000 hours. This decreased to a failure for the next two cycles of thousand hours each. There was a 40% decrease in reliability after 1500 hours. Exponential distribution revealed that the mean time-to-failure (MTTF) was 545.5 hours. This study was the first of its kind in the facility. Previously, much time was lost in breakdown maintenance. Thus, it helped to increase the systems reliability.
  Keywords: bathtub curve; exponential distribution; failure rate; fuel injection; gas engine; pre-chamber combustion; pre-chamber spark ignition; pre-chamber valve; probability density function; reliability.
  
  
• Prognostic model for reliability assessment of emergency shutdown valves used in oil and gas facilities  
  by Ewa Laskowska, Jørn Vatn, Shen Yin 
  Abstract: The surveillance of Emergency Shutdown Valves (ESVs) used in oil and gas facilities is of paramount importance for both process safety and production assurance. ESVs are vulnerable to degradation and their testing often requires production shutdown, impeding production availability. Currently used reliability quantification methods are oversimplified and unable to capture the degradation of ESVs. In this work, the Markov framework is used to derive the degradation model for ESVs based on the empirical condition monitoring data. The approach shows how to make degradation data the input of the degradation model yet provide the output in the form of the standard reliability measure, Probability to Fail on Demand (PFD). In addition, the proposed phase-type extension of the model improves the predictive capacity of the model compared with common approaches. It has been demonstrated on real condition monitoring data that the proposed approach is competitive with existing methods for the reliable quantification of ESVs.
  Keywords: prognostic model; reliability assessment; emergency shutdown valves; probability of failure on demand; multiphase Markov; phase-type; degradation modelling; condition-based maintenance.