5. Thermal compensation

As the internal piping is cooled by the cryogenic fluid, it contracts in length. The usual value used for thermal contraction is 3 mm/m for a temperature difference of around 220°C between ambient temperature + 20°C and liquid nitrogen temperature – 196°C. The shrinkage of stainless steels is negligible between – 196 and – 273 °C.

As the outer shell remains at room temperature, this contraction must be compensated for.

The various compensation solutions, in order of preference and simplicity, are :

• use of the natural flexibility of the internal piping; the minimum length L to compensate for contraction without exceeding the permissible stress is obtained using the simplified formula in the standard NF EN 13480 (metallic...