Stop the flow. Keep the work focused.

External cooling can form a temporary ice plug in a suitable water-filled pipe, isolating one section for selected work. It may be considered for local valve replacement, pipe modifications or maintenance where conventional isolation is difficult.

Suitability depends on pipe material, diameter, pressure, fluid, temperature, flow and working conditions. Safety controls and system operation must be assessed; the method is not universal and does not remove every isolation hazard.