On development of test equipment for strengh and leak tests of submersibles designed to probe extreme depths of World Ocean

Object and purpose of research. The object of study is an upgradation of the unique land-based pressure tank DK-600 of Krylov State Research Centre designed to test underwater technologies for strength and leak under external pressures from 90 to 100 MPа. The purpose is to support acceptance tests of pressure hulls and equipment for advanced manned autonomous submersibles of extreme diving depths to 11 500 m. In accordance with the world practices in development of deepwater submersibles it is required to achieve pressures of about 135–140 МPа. Materials and methods. С использованием современных численных методов Preliminary calculations of strength are performed using up-to-date numerical methods (FE analysis), the choice of structural material is validated as weldable steel forgings, strength category 750–800 МPа. Main results. The procedure and setup are suggested (Capsule DК-600) to provide the said tests by placing a special splittype intermediate Capsule capable to generate 135–140 МPа on the test object inside the pressure tank DК-600 with pressures of 85–90 МPа. The Capsule can accommodate a test object of up to 2400 mm (transverse dimension). Conclusion. Results of an exploratory design study are presented to upgrade the unique land-based pressure tank, which would put the KSRC hydrobaric tank at the world forefront in terms of proof pressures for testing the strength and reliability of extremely deep diving submersibles measuring within 2400 mm (transverse dimension).

Numerical modelling of hydrogen release and dispersion

Hydrogen is the most abundant element on earth, being a low polluting and high efficiency fuel that can be used for various applications, such as power generation, heating or transportation. As a reaction to climate change, authorities are working for determining the most promising applications for hydrogen, one of the best examples of crossborder initiative being the IPCEI (Important Project of Common European Interest) on Hydrogen, under development at EU level. Given the large interest for future uses of hydrogen, special safety measures have to be implemented for avoiding potential accidents. If hydrogen is stored and used under pressure, accidental leaks from pressure vessels may result in fires or explosions. Worldwide, researchers are investigating possible accidents generated by hydrogen leaks. Special attention is granted to the atmospheric dispersion after the release, so that to avoid fires or explosions. The use of consequence modelling software within safety and risk studies has shown its’ utility worldwide. In this paper, there are modelled the consequences of the accidental release and atmospheric dispersion of hydrogen from a pressure tank, using state-of-the-art QRA software. The simulation methodology used in this paper uses the “leak” model for carrying out discharge calculations. This model calculates the release rate and state of the gas after its expansion to atmospheric pressure. Accidental release of hydrogen is modelled by taking into account the process and meteorological conditions and the properties of the release point. Simulation results can be used further for land use planning, or may be used for establishing proper protection measures for surrounding facilities. In this work, we analysed two possible accident scenarios which may occur at an imaginary hydrogen refuelling station, accidents caused by the leaks of the pressure vessel, with diameters of 10 and 20 mm, for a pressure tank filled with hydrogen at 35 MPa / 70 MPa. Process Hazard Analysis Software Tool 8.4 has been used for assessing the effects of the scenarios and for evaluating the hazardous extent around the analysed installation. Accident simulation results have shown that the leak size has an important effect on the flammable/explosive ranges. Also, the jet fire’s influence distance is strongly influenced by the pressure and actual size of the accidental release.

A theoretical analysis of temperature rise of hydrogen in high-pressure storage cylinder during fast filling process

During the fast filing process, thermal stress is generated due to the increase in the pressure and temperature of hydrogen in the hydrogen storage tank. For its safety purpose, it is necessary to predict and control the temperature change in the tank. The aim of this study is quantitative analysis of the final temperature and the mass of the hydrogen in the tank through experimental and theoretical methods. In this paper; Theoretical model for adiabatic and non-adiabatic real filling processes of high pressure hydrogen cylinder has been proposed. The cycle of filling process from the initial vacuum state is called the “First cycle.” After the first cycle is completed, there is a certain residual pressure in the tank. Then the second filling process called “Second cycle” begins. The final temperature in fast filling of hydrogen storage cylinders depends on targeted pressure, initial pressure and temperature, and mass filling rate. The final temperature of hydrogen in the tank was calculated from the real gas equation of state, mass and energy conservation equations. As a result of the analysis, based on the first cycle analysis of high pressure tank, the final temperatures were calculated to be 442.11 K for the adiabatic filling process, and 422.37 K for the non-adiabatic process. Based on the second cycle analysis of high pressure tank, the final temperature were obtained as 397.12 K and 380.8 K for the adiabatic and non-adiabatic processes, respectively. The temperatures calculated from the theoretical non-adiabatic condition were lower than those from the adiabatic condition by 5%. The results of this study can provide a reference basis in terms of how to control the temperature in the actual hydrogen storage tank during the fast filling process and how to improve safety.