Overview
ABSTRACT
This article deals with safety in any cryogenic system, both during operation and in the event of accidental overpressure leading to the opening of the safety device. The overpressure can be the consequence of very large heat loads in a tank or circuit of cryogenic fluid owing to a loss of vacuum or a cryogenic fluid leakage into the vacuum chamber. A method to size the safety device (bursting disk, safety valve) is presented. Recommendations are also given.
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Read the articleAUTHORS
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Éric ERCOLANI: Engineer, Head of the Laboratoire Calculs et Conception Cryogéniques, Service des Basses Températures, Institut Nanosciences et Cryogénie, CEA Grenoble
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Philippe GULLY: Researcher in the Service des Basses Températures, Institut Nanosciences et Cryogénie, CEA Grenoble
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Jean-Marc PONCET: Engineer, Deputy head of the Service des Basses Températures, Institut Nanosciences et Cryogénie, CEA Grenoble
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Chantal MEURIS: Researcher in the Service des Accélérateurs, de Cryogénie et de Magnétisme, Institut de Recherche sur les lois Fondamentales de l’Univers, CEA Saclay
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Laurent MIQUET: Safety engineer, Institut Nanosciences et Cryogénie, CEA Grenoble
INTRODUCTION
Risks in cryogenics arise mainly from the presence of fluids in a liquid state at low temperature in tanks or piping. These systems contain quantities of fluid that, when heated to ambient temperature, will occupy much greater volumes. For example, a single litre of liquid helium will occupy about 780 L at 300 K at atmospheric pressure.
These risks, which include anoxia, explosion and burns, occur during normal operation in various situations (storage and handling of cryogenic fluids). Accident situations leading to accidental heat inputs can cause pressure rises, often very rapid, in parts of the system. These systems must therefore be fitted with safety devices (pressure relief or check valves, or rupture disks) in order to forestall excess pressure. Without such a safety device, a system can be subjected to considerable pressures that may reach hundreds of bars (for example 480 bar for a tank of helium or nitrogen half-filled with liquid), with a readily imagined risk of explosion.
It is therefore absolutely vital to take safety into account when any cryogenic system is being designed. This article presents safety considerations not only in normal operating conditions, but also in accident situations for all cryogenic systems in which a fluid at low temperature is used.
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KEYWORDS
burst disk | safety valve | safety | |
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Safety in cryogenics
Conventional safety in cryogenics and operation
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