Standard: AA CRYO
ALUMINUM ALLOYS FOR CRYOGENIC APPLICATIONS
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Cryogenics is the science of cold. Its name, appropriately, is derived from the Greek word kryos, which means "icy cold." A cryogenic process, therefore, utilizes low temperatures to produce a physical change in a liquid, gas or solid.
Except in research laboratories, cryogenics was a little used science until about 35 years ago. Processes utilizing extremely low temperatures, however, date back to 1908 when attempts to liquefy helium gas first proved successful (1). Since then cryogenic processes have been used to liquefy other gases, notably nitrogen and oxygen, and to make certain materials superconductive (2). Cryogenic temperatures are also used to achieve super-conducting capabilities and to achieve specialized surgical techniques.
The means of achieving cryogenic conditions have been adequately described in various technical references (1,3) and lie beyond the scope of this work. This publication deals principally with the advantages of utilizing aluminum and aluminum alloys for cryogenic equipment for the process industries. Its purpose is to convey useful ideas to the designer and user of cryogenic equipment in this field, through illustration of typical successful equipment, and to share the technical data compiled from tests conducted by the aluminum industry to help further the state of the art.
The field of cryogenics may be assumed to deal with temperatures below about −100°C (− 190°F). At these temperatures, many materials undergo changes in their physical structure which severely limit their usefulness in cryogenic applications. Some metals, like many steels for example, become extremely brittle.
Aluminum alloys, however, have been demonstrated (4) to have an unusual ability to maintain their ductility and resistance to shock loading at extremely low temperatures down nearly to absolute zero (−273°C, −459°F). As temperature decreases below room temperature, their tensile and yield strengths actually improve as the temperature decreases, and ductility as toughness of most alloys increase as well, as we will demonstrate in this publication. Even at the lowest test temperatures available, in liquid helium at −273°C (−452°F), strengths remain high and ductility and toughness remain well above room temperature for most classes of alloys. Consequently aluminum alloys offer distinct advantages when used as materials of construction for cryogenic equipment or for structures that will experience cryogenic cold.
While the focus of this publication is on these relatively low temperatures (−100°C to −273°C), the data herein also serve to illustrate well why aluminum and its alloys are ideal candidates for structural applications in arctic environments, and other situations where temperatures ranging from below room temperature to −100°C govern design conditions(5).
|Organization:||The Aluminum Association Inc.|
|Document Number:||aa cryo|
|Most Recent Revision:||YES|