Triple-shell tank

A triple shell tank comprising:

• an inner tank;
• an intermediate tank covering the inner tank;
• and an outer tank covering the intermediate tank,
• wherein the inner tank includes an inner tank side plate, an inner tank roof, and an inner tank bottom plate, the inner tank side plate being assembled by stacking a plurality of circular steps formed by arranging a plurality of inner tank side plate pieces in a circular ring shape,
• the intermediate tank includes an intermediate tank side plate, an intermediate tank roof, and an intermediate tank bottom plate, the intermediate tank side plate being assembled by stacking a plurality of circular steps formed by arranging a plurality of intermediate tank side plate pieces in a circular ring shape, and
• the circular steps of the intermediate tank side plate include
• a lowermost step formed of an intermediate tank side plate piece for height adjustment having a height corresponding to a height difference between the inner tank bottom plate and the intermediate tank bottom plate, and
• a second step on the lowermost step formed of an intermediate tank side plate piece arranged at a same height position as an inner tank side plate piece of a lowermost step in the circular steps of the inner tank side plate.