Accu-Freeze Pipe Freezing Systems are available from the Pipestoppers Division of Huntingdon Fusion Techniques HFT. Accu-Freeze works by reducing the pipe fluid to a temperature below its freezing point and developing a freeze plug. This controlled method of pipe freezing uses liquid nitrogen (LN₂) to freeze stationary liquids in a section of pipe or tubing. The nitrogen is passed through a coil surrounding the pipe, producing a frozen plug inside and hence preventing flow through the part to be removed.