LNG is methane held liquid at about −162 °C. Austenitic stainless is one of the few structural materials that is genuinely happy there — it gets tougher as it gets colder, where carbon steel gets brittle. The hose is not the difficult part of an LNG transfer. The difficult part is that everything it is bolted to changes length, and that the whole assembly has to be treated as a flammable-gas system the moment anything warms up.
What this service does to a hose
Contraction is the design case. Austenitic stainless contracts roughly 3 mm per metre going from ambient to −196 °C, and not far off that at LNG temperature. A ten metre transfer run gets about thirty millimetres shorter, and it does it every time the line is cooled down. If both ends are anchored, that movement has to be absorbed deliberately. The hose is usually the thing absorbing it, which means it must be sized on its flexing bend radius with the movement included, not cut to the length that reaches at ambient.
Cool-down is a thermal shock. The first flow into a warm line is a violent transient: liquid flashes to gas, the metal drops two hundred degrees in minutes, and everything tries to move at once. Slow, controlled cool-down is a procedure, not a nicety, and an assembly that survives steady-state running can still be destroyed by careless cool-downs.
External ice and the condensation cycle. An uninsulated cold line collects atmospheric moisture as frost, and each shutdown melts it. Repeated wet-dry cycling on the outside of a braid, in a coastal or humid location, is an external chloride pitting duty on a part everyone thinks of as internal.
It becomes flammable gas on warm-up. A trapped volume of LNG between two closed valves warms, boils and builds pressure very fast. That is a relief and procedure question rather than a hose one, but it belongs on the drawing before anyone specifies a hose.
What we would fit
| Element | What we would supply | Why |
|---|---|---|
| Hose | 304L or 316L annular corrugated. No liner | Austenitic grades keep their toughness at LNG temperature; a PTFE liner does not |
| Braid | Matching grade, sized conventionally | Pressure is rarely the constraint on a transfer line |
| Ends | Flanged or welded, with the flange material rated for the low temperature | The flange gets as cold as the hose and a carbon steel flange there is a hazard |
| Length | Sized on live length with the contraction of the whole run included | The hose absorbs movement the run generates, not just its own |
| Insulation | Specified by you; we will build to accept it | It changes the outside diameter and the support arrangement |
What we would not fit, and what happens
A PTFE-lined hose. The liner is not a cryogenic material and the differential contraction between liner and metal is a failure in itself.
Interlock hose. Not pressure-tight, on a flammable cryogen.
Carbon steel flanges or fittings at the cold end. They get as cold as the hose and they get brittle.
A hose cut to the ambient length. It will be in tension the first time the line is cooled down, every time, for its whole life.
What we need to size it
| We need | Because |
|---|---|
| Cryogen, temperature and working pressure | It sets the grade, the fittings and the relief case |
| Total run length and where the anchors are | The contraction of the run is what the hose has to absorb |
| How often the line is cooled down and warmed up | It is the fatigue duty and it is the one that is never sent |
| Whether insulation or vacuum jacketing is required | Vacuum jacketing is a different product; we will say if it is out of scope |
| Flange standard and material at both ends | Cold-end flange material is a safety item |
| The code the installation is built to | It decides what we can certify against |