Many materials are embrittling at low temperatures, but two are rugged, even if they are usually used in hot environments like power plants.
Particularly low temperatures, sometimes well below -150°C, are required for superconducting materials in many areas of medicine, industry, research and science. Interesting examples are:
– Particle accelerators, nuclear fusion reactors and magnetic resonance imaging: Extremely low temperatures are required to operate superconducting magnets. Similarly:
– Quantum computers: The most well-known approach utilizes tiny circuits made of superconducting materials that can carry electrical current without resistance when cooled to extremely low temperatures.
– Storage of biological material: Cryotanks are used to store egg cells, sperm, tissue samples and even small organs or embryos. Cold environments are also essential for high resolution spectroscopy.
Furthermore, gases are liquefied at very low temperatures to cool machines and environments in scientific experiments. LNG and rocket fuels such as hydrogen and oxygen are also cooled. The applications are diverse, so it could be interesting to look into the materials used in such environments and applications. Many materials are embrittling in very low temperatures, but two seem to be robust enough, even if they are virtually used in the opposite direction: in very hot environments like thermal power plants (nuclear, coal or gas fired) and in rocket engines: Monel® and the stainless steel 316L.
Cryogenics demands materials that can withstand extremely deep temperatures without losing their structural integrity. Among the various materials used in cryogenics, Steel 316L and Monel® are prominent due to their exceptional properties. This article delves into the properties, advantages, and applications of Steel 316L and Monel® in cryogenics.
Stainless Steel 316L
316L is a low-carbon variant of the 316 stainless steel alloy, which primarily consists of iron, chromium, nickel, and molybdenum. The „L“ in 316L stands for „low carbon,“ which is enhancing its corrosion resistance and weldability.
– Corrosion Resistance: The addition of molybdenum increases resistance to pitting and crevice corrosion, making it highly suitable for environments exposed to chlorides and other corrosive substances.
– Cryogenic Toughness: The steel 316L maintains its toughness even at temperatures as low as -269°C (4K!), close to absolute zero. It does not become brittle, which is crucial for cryogenic applications.
– Mechanical Properties: It has good tensile strength, yield strength, and ductility, ensuring that it can withstand the physical stresses encountered in cryogenic applications.
The steel 316L is widely used in the construction of cryogenic vessels, pipelines, and storage tanks, especially where exposure to corrosive environments is anticipated. It is also used in forgings for cryogenic valves (hydrogen, helium), heat exchangers, and other components that must endure repeated thermal cycling. The material’s forgeability and weldability further enhance its suitability for complex shapes and structures in cryogenic systems.
Superalloy Monel®
This is a group of nickel-copper alloys, with Monel®400 and Monel®K-500 being the most used in cryogenic applications. It was named after Ambrose Monell, a former president of the nickel producer VALE. It is today a registered trademark of Special Metals Corporation, USA. These alloys contain around 63% nickel, 28-34% copper, and small amounts of iron, manganese, carbon, and silicon.
– Corrosion Resistance: Monel® is highly resistant to corrosion in a wide range of environments, including seawater, acids, and alkalis. This makes it particularly valuable in cryogenic applications involving corrosive substances.
– Cryogenic Toughness: Similar to Steel 316L, Monel® alloys retain their mechanical properties at cryogenic temperatures, including high strength and toughness. They are also resistant to stress-corrosion cracking.
– Mechanical Properties: Monel® has excellent mechanical properties, with high tensile strength and yield strength at virtually all temperatures.
The superior corrosion resistance makes it an excellent choice for applications involving not just low temperatures but also exposure to highly corrosive environments, such as those found in chemical processing plants and marine applications. Monel® is often used in the production of cryogenic pumps, forged valves and fittings, where both strength and corrosion resistance are paramount. The choice between the steel 316L and Monel® in cryogenics often comes down to specific application requirements, such as corrosion resistance, mechanical strength, and cost.
– Corrosion Resistance: While both materials offer excellent corrosion resistance, Monel has the upper hand in highly corrosive environments, particularly those involving harsh chemicals or seawater.
– Mechanical Properties: Both materials maintain their mechanical integrity at cryogenic temperatures, but Monel®K-500 provides higher tensile strength compared to 316L, making it preferable for applications demanding higher structural strength.
– Cost: Monel is generally more expensive than the steel 316L due to its higher nickel content and superior corrosion resistance. This cost factor often influences the choice of material, especially in large-scale applications where budget constraints are significant.
Conclusion
The steel 316L and the Monel® alloys are both critical materials in the field of cryogenics, each offering unique advantages. 316L is often chosen for its balance of corrosion resistance, toughness, and cost-effectiveness, making it suitable for a wide range of cryogenic applications. On the other hand, Monel® alloys are favored in environments where extreme corrosion resistance and higher strength are required, despite their higher cost.
The author, Thomas Henneke, is CEO of a small, but highly certified, drop forge in Western Germany and regularly writing popular scientific articles about steel and its varied applications.
KB Schmiedetechnik GmbH is a highly certified West German drop forge, located in Hagen (Westphalia) – between the historic „blade & metal“ region Solingen and the „soccer city“ Dortmund – specializing in small series production of safety-relevant closed die forgings from 200g to 130Kg unit weight of all forgeable steel grades including duplex stainless steels, nickel based, titanium and superalloys according to following standards and certifications:
– Pressure equipment: PED 2014/68/EU, AD 2000-W0, ASME
– Boiler construction/piping: Alstom, Babcock, CNIM, MHPS
– Nuclear technology: KTA (Germany), EDF/RCC-M (France)
– Shipbuilding/ Ocean engineering: ABS, BV, ClassNK, DNV, LR
Closed die drop forgings – Made in Germany of European Quality Steel!
Examples are pressurized parts for pressure equipment – forged valve parts like valve bodies and yokes/ bonnets, tube connections, boiler header caps, forged fittings, flanges, manifolds, L-pieces, Y-pieces, bifurcations, forged breeches/hoses and forged mechanical safety components like chain parts, rollers, bearings, connecting parts, fasteners, hooks, sockets, eyebolts, slings, hoists, special screw nuts, hydraulic components, pinion and gear blanks and more.
Contact
KB Schmiedetechnik GmbH – a German drop forge
Thomas Henneke
Buschmühlenstr. 62
58093 Hagen (NRW)
Phone: +492331350855
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Url: https://kb-schmiedetechnik.de/about-us.html
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