5083 Aluminum for LNG Storage Tanks: Data, Build Practice, and What to Specify
LNG tanks hold gas at -162 °C. The shell metal must stay ductile at that temperature, weld cleanly into a pressure boundary, and resist marine corrosion. That is why 5083 aluminum alloy has been the standard choice for spherical LNG tanks since the first LNG carriers were built. Below is the material data, the manufacturing practice that produces sound tanks, and the specification points you need when buying plate.
5083 Material Data (What You Are Actually Buying)
5083 is an Al-Mg alloy. For marine and cryogenic service, the relevant tempers are H116 and H321 (strain-hardened, stabilized). Typical guaranteed values per ASTM B928 / EN 485:
| Property | 5083-H116 / H321 |
|---|---|
| Tensile strength | 290–365 MPa (42–53 ksi) |
| Yield strength (0.2%) | ≥ 215 MPa (31 ksi) |
| Elongation (2 in.) | ≥ 12% |
| Density | 2.66 g/cm³ |
| Melting range | 570–640 °C |
Nominal composition (wt %): Mg 4.0–4.9, Mn 0.40–1.0, Cr 0.05–0.25, Si ≤ 0.40, Fe ≤ 0.40, Cu ≤ 0.10, Zn ≤ 0.25, Ti ≤ 0.15.
Why these numbers matter: the H temper + stabilization is what prevents sensitization and intergranular corrosion after welding. A 5083 plate in O or H1xx temper is not automatically fit for a welded seawater or cryogenic structure. If a quote does not state the temper and the governing standard (ASTM B928, EN 485, or a class-rule supplement), ask.
How Spherical LNG Tanks Are Built
Moss-type LNG carriers carry several independent spherical tanks. Each sphere is assembled from cold-formed 5083 shell plates. The proven sequence has three stages:
- Small assembly – individual plates are formed to curvature, edges machined to bevel, and joined into panels.
- Ring assembly – panels are built into complete ring sections on jigs.
- Final assembly – rings are stacked and welded into the full sphere.
The sphere rests on a cylindrical slide seat at the equator, welded to a steel base in the double bottom. Aluminum and steel cannot be welded directly, so the joint uses transition pieces (explosion-bonded or friction-stir) between the aluminum shell and the steel seat.
The Three Controls That Decide Shell Quality
- Circumference accuracy. Every ring must match its neighbour. Yards pre-calculate weld shrinkage and adjust assembly dimensions so the closed circumference lands inside the tolerance. Ring circumference is normally controlled to roughly ±1 mm per metre of perimeter.
- Angular distortion. Weld shrinkage pulls the shell out of round. Control comes from bevel design and welding sequence management, not from post-weld correction.
- Roundness. Measured by triangulation and computed against the ideal sphere. Out-of-round shells concentrate stress under thermal cycling at -162 °C.
Welding: Methods and Why They Were Developed
LNG tank fabrication drove most of today’s thick-plate aluminum welding practice. Three methods matter:
Thick-wire, high-current MIG (flat position). Used for the long panel seams. The assembly is rotated on a jig so every weld is run flat — highest deposition rate, cleanest bead, fewest passes. One pass per side is achievable on moderate thicknesses.
All-position MIG. Used for vertical and circumferential seams. The head oscillates and current is modulated to hold penetration as the weld position changes from near-flat to overhead.
Narrow-gap MIG. Uses a smaller groove angle than conventional V-grooves. It cuts weld metal volume, shortens welding time, and sharply reduces distortion — the three cost drivers in thick aluminum fabrication. It also simplifies automation because each layer takes fewer passes.
Shielding gas is an argon-helium mix; helium raises heat input to stabilize penetration in thick sections. Gas purity is the hidden quality lever. Moisture in the gas causes porosity, so tank yards control dew point well below ordinary shop standards and weld in air-conditioned halls. If your fabricator cannot state their shielding-gas dew point, treat it as a red flag.
Inspection That Keeps Tanks Leak-Tight
A cryogenic tank is a pressure vessel; leaks are not repairable in service. Standard practice:
- Incoming material: mill test certificates (composition + mechanical), dimensional and visual checks.
- Welds: radiographic testing (RT) on longitudinal and circumferential seams, ultrasonic testing (UT) for internal defects, dye-penetrant (PT) on surfaces — typically 100% RT on tank shell seams, with PT on all weld surfaces.
- Geometry: curvature, angular distortion, and roundness checks after each assembly stage.
- Leak testing: pneumatic and vacuum-box tests in the workshop; hydrostatic test after installation on the ship.
- Procedure qualification: tensile and bend tests on procedure coupons before production; test coupons cut from actual seams during production.
Specifying 5083 Plate: What to Ask the Supplier
These points separate a tank-grade supplier from a commodity seller:
- Class approval. Plate for classed LNG or pressure vessels must come from a mill with the required approvals — commonly DNV, ABS, BV, NK, CCS. The certificate is held by the producing mill; your supplier must be able to pass it through with the material. Ask for the certificate scope (alloy, temper, thickness range) before quoting.
- Temper and standard, in writing. State “5083-H116 per ASTM B928” or the equivalent EN/class rule in the order. Do not accept a generic “5083 marine grade.”
- Traceability. Every plate carries a heat number tied to its MTC. For a pressure boundary this is mandatory, not optional.
- Thickness tolerance and flatness. Weld fit-up depends on edges being square and plate being flat. Ask for the supplier’s thickness tolerance and flatness limits — poor edge quality shows up as fit-up rework in your shop.
- Surface and packing. Marine plate should ship with protective film or paper interleaving. Salt-laden humidity stains plate before it reaches the welder; ask how plate is packed for sea freight.
- Inventory and lead time. Standard marine thicknesses (6–50 mm is the common tank-building range) held in stock cut lead time sharply. If the supplier carries 5083-H116/H321 inventory, ask which sizes are in stock now.
FAQ
Q: Is 5083 the only alloy used for LNG tanks?
A: It is the dominant choice for spherical LNG tank shells. 5086, 5052, and 5059 appear in some designs and components. Steel options (9% Ni, austenitic stainless) are used for other LNG containment systems; aluminum’s advantage is low density, excellent low-temperature toughness, and no post-weld heat treatment.
Q: H116 or H321 — which should I order?
A: Both are stabilized, strain-hardened tempers for welded marine service. H321 is processed with controlled grain structure and is commonly preferred where the design code or class society specifies it. Order the temper your class rule or design code names; if neither does, H116 is the safer default for general marine use and H321 for applications requiring the controlled-grain variant.
Q: What documents must come with the plate?
A: Mill test certificate (chemical composition, tensile/yield/elongation per heat), certificate of conformity to the ordered standard and temper, class certificate copy if class-approved, and heat-number traceability per plate. For tank or pressure-vessel work, all four are expected.
About Delin Aluminum
Delin Aluminum has supplied 5083, 5086, and 5754 plate and sheet in H116/H321 tempers for over 10 years. Our partner mills hold DNV certification — the approval most marine buyers require — with other major classification societies available on request.
Related Reading
- Marine Grade Aluminum Plate
- 5083 vs 5059 Aluminum Plate: Which Resists Corrosion Better?
- Marine Aluminum Welding & Hull Construction Guide
- marine aluminum grades and tempers
- 5083 vs 5059 for long-life service
- 5083 plate for tank shells
Sources: 5083 data per ASTM B928 / EN 485; tank fabrication practice per the translated Kawasaki Heavy Industries LNG spherical tank construction report.
