Which aluminum alloy is used for LNG storage tanks?

You're involved in projects with Liquefied Natural Gas (LNG) and need to know about tank materials. Choosing the wrong alloy for LNG storage can lead to catastrophic failures due to extreme cold, posing immense safety and financial risks.

The primary aluminum alloy used for LNG storage tanks is 5083, due to its excellent strength, fracture toughness, and weldability at cryogenic temperatures as low as -162°C (-260°F).

At SWA Forging, we've specialized in manufacturing large-diameter aluminum alloy forged rings and discs since 2012. While our direct products might be components within larger systems, our deep understanding of aluminum alloy properties, especially under extreme conditions, is crucial for our clients, including traders and machining companies. Knowing which alloys perform best in demanding applications like LNG storage is part of this expertise.

What type of aluminum is used for gas tanks?

You're designing a gas tank and wondering if aluminum is suitable, and if so, which type. Using an inappropriate material for any gas containment can result in leaks, corrosion, or structural failure under pressure.

For general fuel tanks (gasoline, diesel), alloys like 5052¹ are used for good corrosion resistance. For cryogenic gas like LNG, specialized alloys such as 5083² are essential due to their excellent low-temperature toughness.

When discussing "gas tanks," it's important to specify the type of gas and operating conditions. For standard automotive gasoline or diesel fuel tanks, if aluminum is chosen (often for weight saving), an alloy like 5052 is common. It offers good formability and excellent corrosion resistance to fuels and atmospheric conditions. Steel and high-density plastics are also widely used for these applications.
However, when the "gas" is liquefied natural gas (LNG) or other cryogenic liquids like liquid nitrogen or oxygen, the material requirements change dramatically. The primary concern becomes performance at extremely low temperatures. Many common metals, including most carbon steels, become brittle and lose their toughness at cryogenic temperatures.
This is where specific aluminum alloys shine. The 5xxx series of aluminum alloys, which are alloyed primarily with magnesium, retain their ductility and toughness even at very low temperatures. Alloy 5083 is a standout in this category. It not only maintains its strength but also its ability to absorb energy before fracturing (toughness) at LNG temperatures of -162°C (-260°F). It also offers good weldability, which is vital for fabricating large and complex tank structures. I've often advised clients on the general principle: for extreme environments, whether high temperature or cryogenic, material selection is non-negotiable and must be based on proven performance.

What are LNG storage tanks made of?

You're looking into the construction of LNG storage tanks and need to know the primary materials used. The safety and integrity of these massive structures depend critically on choosing materials that can handle extreme cold and structural loads.

Large LNG storage tanks are primarily made from materials that retain excellent toughness at cryogenic temperatures (-162°C). The main choices are 9% nickel steel and specific aluminum alloys, most notably 5083.

LNG is stored at approximately -162°C (-260°F), a temperature at which many conventional structural materials become brittle and unsafe. Therefore, the selection of materials for LNG storage tanks is highly specialized.
The two dominant materials are:

1. 9% Nickel Steel (ASTM A553 Type I, A353): This steel alloy is specifically designed for cryogenic applications. It offers high strength and excellent fracture toughness at LNG temperatures. It's very common for large, land-based, full-containment LNG tanks. Its fabrication requires specialized welding procedures.
2. Aluminum Alloy 5083: This is the most widely used aluminum alloy for LNG applications.
   • Cryogenic Performance: 5083 (typically in the -O annealed temper or specific H-tempers for plates) exhibits excellent toughness, ductility, and good strength retention at LNG temperatures. Unlike ferritic steels, aluminum alloys do not have a ductile-to-brittle transition temperature and maintain their toughness.
   • Weldability: It has good weldability using processes like Gas Metal Arc Welding (GMAW) and Gas Tungsten Arc Welding (GTAW), often with 5183 filler wire. This is crucial for constructing the large, often spherical or cylindrical, tank shells.
   • Corrosion Resistance: Good resistance to atmospheric corrosion.
   • Weight: It's significantly lighter than steel, which can be an advantage in certain designs or for transportable LNG tanks.
     Other materials like austenitic stainless steels (e.g., 304L) also have excellent cryogenic properties and are used, particularly for smaller tanks, piping, or components, but for very large primary containment, 9% nickel steel and 5083 aluminum are the mainstays. At SWA Forging, while we don't forge the massive plates for tank shells, we deeply understand the critical material requirements. If we were asked to forge components like flanges or structural supports from aluminum for an LNG system, ensuring the correct alloy and temper for cryogenic service, like 5083-O, and providing full certification (ISO, SGS, BV, TUV as requested) would be paramount.

Which aluminum alloy is known as aircraft aluminum?

You often hear the term "aircraft aluminum" and want to know which specific alloys it refers to. Understanding this helps appreciate the high-performance end of the aluminum alloy spectrum.

"Aircraft aluminum" most commonly refers to high-strength alloys like 2024 (copper-alloyed) and 7075 (zinc-alloyed), selected for their exceptional strength-to-weight ratios, fatigue resistance, and overall performance in aerospace applications.

The designation "aircraft aluminum" isn't for a single alloy but rather a group of high-performance aluminum alloys specifically developed and stringently qualified for aerospace applications. The two most prominent members of this group are:

• 2024 Aluminum Alloy:
  • Composition: Primarily alloyed with copper (around 4.4%), plus magnesium and manganese.
  • Key Properties: Known for its excellent fatigue resistance, good strength (especially in T3, T351 tempers), and relatively good fracture toughness.
  • Applications: Widely used for fuselage structures, wing tension members, and other components subjected to cyclic stress. Its damage tolerance is a key feature.
  • Considerations: It has relatively poor corrosion resistance compared to other aluminum alloys and is often used in a clad form (Alclad 2024) or requires protective coatings. It's also not readily weldable by fusion methods.
• 7075 Aluminum Alloy:
  • Composition: Primarily alloyed with zinc (around 5.6%), plus magnesium and copper.
  • Key Properties: One of the highest strength aluminum alloys available (especially in the T6 temper). It offers a very high strength-to-weight ratio.
  • Applications: Used for highly stressed structural parts like wing spars, landing gear components, and fuselage frames.
  • Considerations: Can be susceptible to stress corrosion cracking (SCC) in certain tempers (T73 and T76 tempers offer improved SCC resistance but with some strength reduction).
    While other alloys like 6061 are used in general aviation or for secondary structures, 2024 and 7075 are the workhorses when people speak of "aircraft grade" for critical applications. The knowledge of how these alloys achieve their properties through composition and heat treatment is something we leverage at SWA Forging when discussing high-strength solutions with our clients, even if their application isn't aerospace.

What are LNG fuel tanks made of?

You are looking into LNG as a fuel for vehicles or ships, and need to understand what their fuel tanks are made from. Material choice is vital for safety, efficiency, and compliance with strict regulations for cryogenic fuel containment.

LNG fuel tanks for vehicles and ships are typically made from materials that maintain toughness at -162°C, primarily 5083 aluminum alloy or austenitic stainless steels (like 304L), due to their excellent cryogenic performance, weldability, and for aluminum, its light weight.

LNG fuel tanks, whether for marine vessels, trucks, or buses, must safely contain fuel at -162°C (-260°F) under various operating conditions, including vibrations and potential impacts. The material selection criteria are similar to large storage tanks but with added emphasis on weight for mobile applications.

1. Aluminum Alloy 5083 (and similar 5xxx series):
   • This is a very common choice, especially for marine LNG fuel tanks and many road transport applications.
   • Light Weight: Aluminum's lower density compared to steel helps improve the vehicle's fuel efficiency or cargo capacity.
   • Cryogenic Toughness: Excellent retention of strength and ductility at LNG temperatures.
   • Weldability: Good weldability allows for the fabrication of complex tank shapes designed to fit specific vehicle chassis or ship hulls.
   • Corrosion Resistance: The 5xxx series alloys have good corrosion resistance, particularly important in marine environments (e.g., 5083-H116 or H321).
2. Austenitic Stainless Steels (e.g., 304L, 316L):
   • These also offer excellent toughness and strength at cryogenic temperatures.
   • They are highly corrosion-resistant.
   • Often used for smaller tanks, piping, valves, and fittings within the LNG fuel system. While heavier than aluminum, their robustness and ease of fabrication for smaller, intricate parts can be advantageous. 304L (low carbon) is preferred for welded structures to minimize sensitization and maintain corrosion resistance.
3. 9% Nickel Steel: While excellent for large static storage, it's less common for smaller, mobile LNG fuel tanks due to its higher weight and typically more complex fabrication requirements for smaller scales compared to aluminum or stainless steel.
   The tanks also incorporate sophisticated insulation systems (e.g., vacuum insulation with perlite or multi-layer superinsulation) to minimize heat leak and LNG boil-off. Our focus at SWA Forging on high-quality, certified materials means we appreciate the critical nature of these choices.

Conclusion

For LNG storage, 5083 aluminum is key due to its cryogenic toughness. This differs from "aircraft aluminum" like 2024 or 7075, which are chosen for strength-to-weight in aerospace.