Type II storage vessel, which consists of a metallic liner hoop wrapped with a carbon fiber-resin composite to work at high pressure, has been widely adopted as the fuel container for compressed natural gas (CNG) vehicles. The general vessel, manufactured by welding enclosures to an open-end cylinder, shows uniform thickness throughout the whole liner, while the high pressure vessel, fabricated by the deep drawing and ironing (D.D.I) and spinning processes, has the integral junction part of cylinder with increased end thickness along the meridian direction. This study established a design method for improvement of failure resistance and inner capacity of the seamless CNG pressure vessel (Type II) through finite element analysis with consideration of thickness variation. Autofrettage pressure is used to enhance fracture performance and fatigue life of the vessel, and variations of stress behaviors in the liner and composite were analyzed during the autofrettage process. The influence of the composite on generation of compressive residual stress was investigated. In order to verify advantages of the D. D. I. and the spinning processes for structural safety at the end closure, the stress distribution considering thickness variation was compared with that with uniform thickness, and the maximum inner capacity objective satisfying structural reliability was obtained. The inner capacity of the proposed model with the ratio of major axis to minor axis, 2.2, was expanded by 4.5. Theoretical equivalent stresses were compared with those from the simulations, and the technique of FEM was verified.

Background: Close surveillance of Legionella in the plumbing systems of medical institutions is required because of the higher morbidity and mortality of nosocomial legionellosis. We experienced an outbreak of legionellosis in a university hospital, managed with a chlorine dioxide infusion system. Methods: Multiple contaminations with Legionella were reported in the annual water surveillance in June 2019. A task force was established to prevent the outbreak of legionellosis, and the entire plumbing system of the hospital was investigated. Initial measurement was done according to the action manual of the Korean Disease Control and Prevention Agency, including cleaning of hot water tanks, superheating and flushing, point-of-use management (change of showerheads and taps on washstands), and application of filters in higher-risk areas. Further shock hyperchlorination for the cooling tower and cleaning of the water tank were performed since persistent contamination was reported in these areas. Nevertheless, there was an outbreak of three presumable cases of in-hospital legionellosis. A continuous infusion of chlorine dioxide (ClO 2 ) was planned to decontaminate the hospital's plumbing. Equipment for ClO 2 infusion was installed by May 2020, with terminal monitors of residual chlorine and a feedback system. A repeated environmental culture study was also planned. Furthermore, a preemptive surveillance system including active monitoring for patients tested with Legionella urinary antigen was developed, and a newer response manual for legionellosis was distributed. Results: Isolation of Legionella in hospital water was first noted in June 2019. Since then, Legionella has been identified in 6 out of 47 samples in five surveillances by the public health center. Furthermore, 6 out of 85 samples were reported to be positive for Legionella by inhospital water cultures. Two patients were diagnosed with nosocomial legionellosis within 3 months of the initial response. After the installation of the ClO 2 continuous infusion system in May 2020, no isolation of Legionella was reported in the next two whole environmental surveillance. No further cases of bacterial inoculation or Legionella infections have been reported so far. Conclusion:The outbreak of nosocomial legionellosis was successfully terminated with the continuous infusion of ClO 2 into the premise plumbing system of the hospital. Sporadic outbreaks

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The liner of type 3 high-pressure vessel is manufactured by a D.D.I.(Deep drawing and ironing) process for the cylinder part, which is a continuous process that includes a drawing process to reduce the diameter of the billet and a subsequent ironing process to reduce the thickness of the billet. But the wall thickness of type 3 pressure vessel liners used in vehicles and ships is required to be 5mm. Excessive wall thickness not only increases the weight of hydrogen vehicles and ships equipped with type 3 high-pressure vessels but also deteriorates their transportation efficiency. But the forming process of the cylinder part of the high-pressure vessel liner(Al6061) has a total of 3 stages (1st deep drawing with blank holder, 2nd redrawing, 3rd redrawing + ironing) through which the wall thickness is manufactured up to 6.8mm in the actual field. In this study, the maximum drawing ratio and die inflow angle in the first-stage deep drawing process by using the shape factor formula of the tractrix die and combined process (redrawing + ironing) in the third stage were determined in order to manufacture a liner with a wall thickness of 5 mm within the existing 3 stages, including saving of die costs. Using damage value verified through FEA and experiment and based on the above results, design of the D.D.I. process (3 stages) was performed, and its results were verified.

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