International Journal of Reliability and Safety (6 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.
  
  
• 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.
  
  
• 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.
  
  
• Multi-failure mode correlation and dynamic reliability evaluation of helical gears of ring die pellet mill  
  by Risu Na, Kaifa Jia, Haitang Cen, Weiguo Zhang, Quan Zhang 
  Abstract: Aiming at the low reliability of the gear transmission system of SZLH420 ring die granulator and the unsatisfactory evaluation results at the present stage, the multi-failure mode correlation calculation and dynamic reliability evaluation of helical gear were carried out. Traditional gear reliability evaluation is limited to a single failure mode, but in actual operation, multiple failure modes affect each other, resulting in poor reliability evaluation results. In this paper, the functional functions of each failure mode were constructed based on the stress-strength interference model, then the Monte Carlo method was used to simulate the static reliability of helical gear with multiple failure modes, and the dynamic reliability was calculated based on the Gamma strength degradation theory. Finally, the correlation of multiple failure modes was calculated using the Copula function. Then the reliability of the most accurate system is obtained. The results show that this method can effectively solve the problem of poor reliability evaluation quality and provide a theoretical basis for the subsequent optimization of gear.
  Keywords: helical gear; reliability; correlation; strength degradation; dynamic evaluation.
  DOI: 10.1504/IJRS.2023.10054210
   
  
• A study on step stress partially accelerated life test under adaptive type-II progressive hybrid censoring for inverse Lomax distribution  
  by Intekhab Alam, Mustafa Kamal, Ahmadur Rahman, Nayabuddin  
  Abstract: Using traditional life tests in testing and reliability theory may result in extremely few failures by the completion of the experiment, leading to poorer estimations. To get the required failure as rapidly as possible for better estimation, products are exposed to higher stress levels, and this process is known as accelerated life testing. This paper develops a step stress partially accelerated life test that employs adaptive type-II progressive hybrid censoring scheme and assumes that the lifespan of test items follows a two-parameter inverted Lomax distribution. The likelihood and log-likelihood functions are created for adaptive type-II progressive hybrid censoring scheme data in order to get the point and interval of the model parameters using the maximum-likelihood estimation approach. Furthermore, using a Monte Carlo simulation analysis, the biases and mean square errors of the maximum-likelihood estimators are estimated to examine their performances in the presence of censoring introduced in this work.
  Keywords: partially accelerated life test; inverse Lomax distribution; Newton Raphson; adaptive Type-II progressive hybrid censoring; simulation study.