In order to check the installation quality, deformation under low temperature and smooth condition of pipelines, valves and field installed air separation plant in air separation column, needs to be further tighten the flange bolts at low temperature. It is necessary to start freezing before filling the cold insulation box with cold insulation material, which is called naked cooling. During naked cooling, the rectification column, main condensing evaporator and other main equipment shall be cooled to the minimum temperature for 2 hours respectively, and then the whole air separation unit shall be cooled for 3 to 4 hours. The deformation and leakage of each part shall be checked in detail, and the flange bolts shall be tightened again. After defrosting, the flange shall be heated to normal temperature before gas seal test can be conducted.
