Reliable terminal headers are needed to safely transmit electrical power and signals for the LNG pumps, compressors and turbine expanders, which operate in the cryogenic pressure vessel. The headers have to be resilient enough to withstand extreme temperature shifts while remaining reliably gas- and pressure-tight.
Because terminal headers are so critical to safety, most cryo-applications – especially those that operate under high pressure – require a redundant electrical and mechanical sealing to maintain the pressure integrity even if one of the seals would fail. This means that the two pressure barriers need to be hermetically and electrically connected, yet mechanically decoupled from the other.
In other set-ups, two single barrier feedthroughs that are integrated into a pipe are internally connected to achieve a so-called double seal. However, this is a rather space-consuming solution. In contrast, SCHOTT has developed far more compact designs that are equipped with two hermetically connected, but completely separate glass-to-metal sealed pressure barriers.
A more compact double seal design
“Our double-sealed Eternaloc® terminal headers are designed to combine superior safety with compactness”, says Thomas Goettlinger, Sales Director LNG at SCHOTT Electronic Packaging. The glass is melted to the conductor and the flange over the entire length of the pressure-proof seal. Yet, the glass does not protrude the flange, which enables such a compact design. Eternaloc® feedthroughs have fewer parts, less joints to be sealed and a dramatically reduced weight and size. This is an especially relevant aspect once space and weight are restricted, for example in off-shore applications.
Besides being a great dielectric isolator, glass is a very reliable sealing material. In contrast to ceramics, glass melts directly to metal. No brazing or welding is required that often tends to corrode in harsh environments and may show fissures over time. As opposed to epoxy, glass is inorganic and therefore non-aging, which means maintenance-free performance over a virtually unlimited service-time.
In double-sealed Eternaloc® feedthroughs, the hermetic space in between the two seals furthermore offers the possibility of nitrogen purging for periodic or permanent leakage monitoring as well as inertisation of both pressure barriers. If not required, the inner chamber can also be closed and certified as a flameproof enclosure.
More information can be found here: www.schott.com/lng
Eternaloc® is a registered trademark of SCHOTT AG.