In this process, repairs can be made to a pipe containing a liquid, at a point a great distance from shut-off valves. By using liquid nitrogen a plug of liquid can be frozen on each side of the section of pipe to be opened.
This allows essential maintenance or upgrade work to be carried out on the frozen area without the need to empty the supply line or risk of leakage.
"Jackets" surrounding the pipe retain the liquid nitrogen. These jackets are made from aluminium tinfoil, wood or double skinned stainless steel.
Liquid nitrogen is used to fill the void between the jacket and the pipe's outer wall.
The double skinned stainless steel jacket is used to prevent the liquid nitrogen coming into direct contact with the pipe.
The very low temperature of the liquid nitrogen results in the freezing of the pipe contents or insulator. Time required and liquid used is largely dependent on:
Pipes from 15mm-1200mm can be frozen on pressures up to 4000psi (272 bar).
Care must be taken to prevent pipe fractures due to the combination of low temperature embrittlement and thermal contraction of the pipe.
The application is utilised in a diverse range of industries including:
The pipe contents being frozen are also wide and varied and include:
Since pipes repaired in this manner are often in excavated pits, great care must be taken to prevent nitrogen accumulation in the pit causing oxygen depletion and a resulting asphyxiation hazard.