Judgment method of leakage in cold box

In order to achieve the function of cold insulation, the cold box of air separation is strictly sealed, so how to judge if there is internal leakage? If there is leakage in the cold box, the normal cold production will be insufficient, and the main cold liquid level will continue to drop; In addition, when the gas pipeline in the cold box leaks, the composition of the gas escaping from the cold box will change, which can also be judged from the analysis of the composition of the gas escaping from the cold box; Furthermore, the position of the leakage can be roughly determined by directly observing the frosting position outside the cold box.