REPAIRABLE SYSTEM AVAILABILITY MODEL WITH RESPECT TO LIFE DISTRIBUTION OF SPARE PARTS

The failed components of repairable systems are replaced with spare parts that may have different failure distributions from those of the components that have failed. The spare parts may be either the same as new, better than new, or worse than new. This is the reality in maintenance engineering. Repair with better spare parts is defined as ＂super repair＂. The failure distributions of the spare parts affect the availability of the components and their systems. A novel model is proposed to describe the availability of repairable systems across their operating time, at the level of their components, on the assumption that the failed components are immediately replaced. The model functions with arbitrary failure distributions of spare parts. It can be used to compute the availability of components and systems not only under perfect and imperfect repair but also under super repair.

Risk Assessment Based on Fault Tree Analysis for Damaged Pipe Repair During Operation in Petrochemical Plant

In petrochemical plant, the in-operation repairing is usually a repairing strategy with pressured inoperation repairing for avoiding huge economic losses caused by unplanned shutdown when some slight local leakage happens in pipes. This paper studies the effects of repairing strategies on the failure probability of the pipe systems in process industries based on the time-average fault tree approach, especially the in-operation repairing strategies including pressured in-operation repairing activities. The fault tree model can predict the effect of different repairing plans on the pipe failure probability, which is significant to the optimization of the repairing plans. At first pipes are distinguished into four states in this model, i.e., successive state, flaw state, leakage state and failure state. Then the fault tree approach, which is usually applied in the studies of dynamic equipment, is adopted to model the pipe failure. Moreover, the effect of pressured in-operation repairing is also considered in the model. In addition, this paper proposes a series of time-average parameters of the fault tree model, all of which are used to calculate node parameters of the fault tree model. At last, a practical case is calculated based on the fault tree model in a repairing activity of pipe thinning.

Meniscus repair with simultaneous anterior cruciate ligament reconstruction: Clinical outcomes, failure rates and subsequent processing

Purpose::To retrospectively analyze the clinical outcomes of meniscus repair with simultaneous anterior cruciate ligament(ACL)reconstruction and explore the causes of failure of meniscus repair.Methods::From May 2013 to July 2018,the clinical data of 165 patients who were treated with meniscus surgery and simultaneous ACL reconstruction,including 69 cases of meniscus repair(repair group)and 96 cases of partial meniscectomy(partial meniscectomy group)were retrospectively analyzed.The exclusion criteria were as follows:(1)ACL rupture associated with fracture,collateral ligament injury,or complex ligament injury;(2)a history of knee surgery;or(3)a significant degree of osteoarthritis.The 69 patients in the repair group were divided into the non-failure group(62 cases)and the failure group(7 cases)depending on the repair effect.Postoperative outcomes of the repair group and the partial meniscectomy group were compared.General conditions and postoperative outcomes of the failure group and the non-failure group were compared.During the median follow-up period of 28 months(range,4-65 months)after the second arthroscopy,postoperative outcomes of seven patients in the failure group were summarized.SPSS 25.0 statistical software was used for statistical analysis.A p value less than 0.05 was considered statistically significant.Results::Seven patients in the failure group who underwent the second arthroscopy were followed up for(30±17.4)months and their postoperative outcomes were summarized.Compared with the partial meniscectomy group,the International Knee Documentation Committee scores of patients in the repair group improved significantly(p=0.031).Compared with the non-failure group,more patients in the failure group were younger than 24 years(p=0.030).The median follow-up period was 39.5 months.All patients recovered well after subsequent partial meniscectomy and relieved clinical symptoms.Visual analog scale scores decreased significantly(p=0.026),and the International Knee Documentation Committee and Lysholm scores improved significantly(p=0.046 for both).Conclusion::The failure rate of meniscus repair in this study was 10.1%(7/69),all of which were medial meniscus tears.However,the surgical outcomes of ACL reconstruction were not affected,and there might be a role for graft protection.Therefore,meniscus retears can be successful treated by performing subsequent partial meniscectomy in patients with repair failure.