Cryogenic and LNG Applications for 9% Steel

Brittle-ductile transition is a natural process causing materials to shatter at low temperatures, instead of deforming. This usually affects steel, however, when alloyed with 9% Nickel, the brittle-ductile transition temperature of this metal is greatly reduced. This steel alloy can therefore remain ductile at low temperatures, whilst maintaining extreme toughness and tensile strength. These properties therefore make it ideal for applications within the manufacture of cryogenic substances, such as liquefied natural gas (LNG).

The Problem with the Brittle-Ductile Transition

The Methane Pioneer, a newly-rebuilt cargo ship, carried the initial shipment of liquefied natural gas on the 25^th of January 1959.

The process of liquifying natural gas (LNG) using the low temperature condensation technique leads to a drastically reduced volume. Comparatively, uncompressed gas has a volume up to 600 times larger and energy density which is 2.4 times smaller. This means that transporting LNG is far more economical.

Constructing pressure vessels utilizes steel. However, this metal becomes exceedingly brittle at lower temperatures. Reduction in ductility renders it hazardous for transporting LNG, as any collision could result in an explosion.

The phenomenon “brittle-ductile transition” leads to the reduction of ductility at low temperatures. Particularly, this transition occurs in crystal structures, such as carbon steel. This loss of ductility can be extremely dangerous. An example of this is the Titanic, which had a steel hull and therefore was affected by brittle-ductile transition in the cold waters of the North Atlantic sea. There were also numerous other low-profile failures which ultimately diminished the commercial interest around the use of steel cryogenic systems.

In the 1940s, a new material was developed which had a very low ductile-brittle transition temperature whilst maintaining the strength and ductility of carbon-steel. This new material was 9% nickel-steel.

9% Nickel Steel: A Tough and Ductile Low-Temperature Alloy

The uncommon properties of 9% Nickel-steel are derived from its crystal structure. Hypothetically, a material displays ductile properties when it’s crystal structure contains 5 separate “slip systems”, signifying that the individual atoms can be moved in 5 different ways with ease.

Typical steel has 2 or 3 slip systems at a low temperature, whereas nickel has an extensive number, which continue to function at low temperatures. Therefore, nickel never undergoes this phenomenon of ductile-brittle transformation. Furthermore, these numerous slip systems are preserved during the process of alloying nickel with other metals. At 9% steel to nickel proportions, the produced metal contains a minimal amount of “austenitic” steel molecules which contain intrinsically ductile properties. These molecules only make up approximately 4% of the steel’s volume, but their presence results in resistance to brittleness at low temperatures, while maintaining toughness.

Therefore, reduction of the carbon content within steel and expansion of the amount of Nickel results in an altered crystal structure which has ductile properties at excessively low temperatures. After additional heat treatment, this 9% Nickel-steel is also able to maintain ductile at temperatures down to -196 °C.¹ Coincidentally, LNG requires storage temperatures less than -162 °C.⁹

The Methane Pioneer utilized aluminum tanks, but the development of 9% Nickel (and other nickel steels) reformed the industry of LNG. It ensured that the manufacture, depository and transportation of LNG was exceedingly safe and cheap. Tanks composed of 9% Nickel steel guaranteed that LNG transportation grew into a very important factor of the international energy industry. This alloy has also become very useful within the application of LNG plants and immobile depositaries.

LNG tanks are frequently manufactured from high-Nickel steel tanks today, enclosed in an insulating coat and outer wall composed of concrete.¹²

Masteel (UK) supplies this alloy at two frequently used specifications. Firstly, ASTM A353 is available at plate thicknesses ≤ 100 mm. Secondly, ASTM 553 type 1 is available at plate thicknesses of ≤ 50 mm. Applications within manufacture and storage of cryogenic substances, such as LNG, oxygen and nitrogen, are ideal. This Nickel-steel is also useful within the application of manufacturing other pressure vessels, also attributed to its high resistance to fracture.

References

1. ArcelorMittal USA Plate 9% Nickel Steel: For use at cryogenic temperatures.
2. A Short History of LNG Shipping. Noble, P. G. (1959).
3. Growing Demand for Natural Gas. https://www.energy.gov/sites/prod/files/2013/04/f0/LNG_primerupd.pdf  
4. DoITPoMS - TLP Library The Ductile-Brittle Transition. (Accessed: 17^th March 2018)
5. Metallurgy of the RMS Titanic. Foecke, T. J. NIST Interagency/Internal Rep. - 6118 (1998).
6. JOM Article on The Titanic: Did a Metallurgical Failure Cause a Night to Remember? Available at: http://www.tms.org/pubs/journals/JOM/9801/Felkins-9801.html. (Accessed: 19^th March 2018)
7. History of Cryogenics: A Cryo Central resource from the CSA. Available at: https://cryogenicsociety-archive.org/category/cryo-central/. (Accessed: 17^th March 2018)
8. Properties of Metallic Materials for LNG Service. Craig, B. 
9. CH•IV | LNG Engineering & Consulting Services | A Clough Ltd. Member. 
10. Methane Pioneer: The First LNG Ship in the World. Available at: https://www.marineinsight.com/types-of-ships/methane-pioneer-the-first-lng-ship-in-the-world/ . (Accessed: 19^th March 2018)
11. Nickel steel plates. Grobblech.
12. Liquefied natural gas | Hamina LNG. 
13. Masteel Supply 9% Nickel Alloy Steel Plates. Available at: https://masteel.co.uk/news/9-nickel-alloy-steel-plates/. (Accessed: 19^th March 2018)

This information has been sourced, reviewed and adapted from materials provided by Masteel UK Ltd.

For more information on this source, please visit Masteel UK Ltd