• For more than 12 years, Linde has been specialising in UN portable tanks for helium (known as HELICS™).
• HELICS™-tanks optimize the transportation of liquid helium and ensure smooth delivery anywhere in the world.

The ability to remain liquid at extremely low temperatures is one of helium’s invaluable properties. That is what makes this rare gas indispensable in so many clinical settings. It is used to cool the magnetic coils of MRI machines. Research institutes like CERN also rely on liquid helium to operate their particle accelerators. Only the liquid form of the gas is capable of bringing the temperature of the magnetic coils down to 2 Kelvin, or minus 271 degrees Celsius, making them superconductive. Thanks to these extremely strong magnetic fields, accelerated atomic nuclei remain on a circular orbit and can be used for physics experiments. In hospital MRI scanners, the magnetic moments of the protons are used to visualize human tissue. In 2018, one quarter of all helium used worldwide was required in liquid form. MRI scanning is the main application. Looking beyond healthcare, the semiconductor industry harnesses other useful properties of helium, namely its inert nature and high thermal conductivity. Since helium forms no chemical compounds, it classifies as an inert gas. This makes it popular for other industrial applications such as welding.

In order to transport this valuable raw material from its sourcing locations to customers all over the world, Linde has developed special cryogenic transportation tanks marketed under the name HELICS™ (formerly Helicon). Around 250 of these tanks are currently in use around the globe. Richter and his team are able to pinpoint the exact location of each HELICS tank, coordinate the retanking process, and arrange global transport routes. The 12-meter-long containers can be filled with approximately 40,000 liters of liquid helium, which corresponds to around 28,000 cubic meters of helium in gaseous form. At the core of every HELICS tank is a stainless steel vessel filled with liquid helium. This is suspended in a vacuum-insulated space by means of a sophisticated fixture. This helps to protect against vibration and shock, while also keeping ambient heat transfer to a minimum. The tanks feature an extremely effective vacuum, which is virtually free of molecules which would otherwise conduct heat,” says Richter. In addition, the vessels are surrounded by a super-insulation layer and an “icy shield” composed of over one metric ton of liquid nitrogen. This liquid nitrogen slowly evaporates and has to be topped up periodically. By refilling the liquid nitrogen, the Linde experts ensure that very little heat reaches the cryogenic helium. Richter explains the structure as follows: “The insulation layer combines materials that reflect the thermal influx with materials of low conductivity. This keeps the interior temperature as low as possible.”

With their user-friendly design, the HELICS tanks double up as transport and storage vessels. “The helium tanks go to our regional subsidiaries – in Germany, for instance, this would be Lohhof near Munich,” says Richter, “where our colleagues either withdraw the inert gas in liquid form to fill dewars, which have a capacity of between 30 and 450 liters, or otherwise transfer the gaseous helium from the tanks into gas cylinders.” For this, the liquid has to be vaporized first or – in the case of cryogenic gas – preheated in a heat exchanger and then compressed. “If liquid helium is to be withdrawn, the pressure in the container must be as low as possible – 0.5 bar is ideal. If a HELICS tank has a pressure of 5.5 bar, for example, gaseous helium has to be withdrawn first in order to reduce the pressure. Only then can liquid helium be transferred.” These physical properties mean that liquid helium customers cannot use the full tank load of product as liquid. The actual amount available to them ultimately also depends on the route and duration of the transport. Linde guarantees a holding time of up to 40 days in HELICS tanks.