An LNG tank looks like an oil tank and is nothing like one. The differences all come from two facts: the contents are 160 degrees below ambient, and they are not under pressure.
Not a pressure vessel
Methane cannot be liquefied by pressure at ordinary temperatures — its critical temperature is about minus 82.6 degrees — so LNG is held cold rather than compressed. Tank pressure is only a few hundred millibar above atmospheric, enough to keep air out and manage boil-off.
That single fact makes tanks of a hundred thousand cubic metres and more affordable. A pressure vessel of that size would be impossible; an insulated one is merely difficult.
The metallurgy problem
At minus 162 degrees, ordinary carbon steel becomes brittle. It stops deforming before it breaks, which means a small defect propagates as a crack instead of being absorbed by local yielding.
The Cleveland disaster of 1944 is the reason everyone in the industry knows this. A tank built during wartime with a lower nickel content than specified failed, and a hundred and twenty-eight people died.
The answer since has been 9% nickel steel for the inner shell: nickel keeps the steel’s crystal structure tough at cryogenic temperature. It is expensive, produced by a small number of mills, and it works.
High-manganese steel is the newer alternative, using manganese to achieve the same low-temperature toughness at lower cost. It has moved from development into standards and commercial use for tanks and marine fuel systems, and it is one of the few places where the cryogenic materials list has grown in decades.
Full containment
Modern onshore tanks are built as full containment, which means two complete tanks, one inside the other.
The inner tank is the cryogenic alloy shell holding the liquid. The outer tank, usually prestressed concrete with a steel liner, is designed to hold the entire liquid contents and contain the vapour if the inner shell fails. Between them sits insulation — perlite, resilient blanket — and a suspended deck carries insulation above the liquid surface.
Older designs exist and explain some of what you see at long-established terminals. Single containment relies on a bund wall around the tank rather than an integral outer shell. Double containment has an outer wall that holds liquid but not vapour. Full containment is the standard for new build, and the difference matters enormously for exclusion zones, because the credible spill scenario is what sizes them.
Some terminals, particularly in Korea and Japan, use membrane tanks onshore — the same principle as a ship’s containment, with a thin barrier supported by a concrete structure.
Boil-off in storage
Tanks leak heat, just as ships do, and the contents evaporate — typically a very small fraction of a per cent a day, better than a ship because a tank is not moving and can be insulated without a volume penalty at sea.
The vapour is collected by boil-off compressors and either returned to the process, sent out to the grid, or reliquefied. It is never simply vented.
Rollover and stratification
The failure mode unique to large LNG storage is not structural.
Load a cargo of one composition on top of a heel of another, and the tank can settle into two stable layers of different density. Each layer warms and changes independently. Eventually the densities cross, the layers invert and mix suddenly, and the mixing releases a large volume of vapour in a short time — more than the relief system may be sized for.
This is rollover, and it is managed rather than engineered out: density and temperature are monitored at multiple depths, cargoes of differing composition are loaded through top or bottom fill to promote mixing, and tanks are recirculated when the readings suggest stratification is developing.
It is a good example of a hazard that is entirely about operating discipline rather than equipment.
What the tracker records
Global Energy Monitor’s terminal data covers capacity, status, ownership and location. Storage volume, tank count and containment type are not in the map export this site is built from, so they render as Not reported rather than being estimated.
For an import terminal, the figure that matters commercially is send-out rather than storage anyway — the rate gas can be pushed into the grid, not the size of the buffer behind it.