Low temperature liquid tank

1. A low temperature liquid tank comprising:

a storage tank having a bottom portion obtained by joining a plurality of bottom plates; and

a support portion supporting the bottom portion,

wherein the support portion includes:

an outer support portion supporting a margin of the storage tank including a sidewall of the storage tank; and

an inner support portion disposed inside the outer support portion and having a heat insulation in which creep occurs when a load is applied to the heat insulation,

an initial height of an upper surface of the inner support portion is set so that, during a service life of the low temperature liquid tank, maximum bending stress applied to the bottom plates due to a difference between a height of the upper surface of the inner support portion and a height of an upper surface of the outer support portion remains equal to or smaller than an allowable bending stress of the bottom plates,

wherein the initial height of the upper surface of the inner support portion is set to be higher than that of the upper surface of the outer support portion, and

wherein due to the creep when a load is applied, the upper surface of the inner support portion is lowered during the service life of the low temperature liquid tank, and wherein the initial height of the upper surface of the inner support portion is set so that the maximum bending stress applied to the bottom plates remains equal to or smaller than the allowable bending stress over the service life as the upper surface of the inner support portion is lowered.

2. The low temperature liquid tank according to claim 1 , wherein the inner support portion has a height setting plate that prescribes the initial height of the upper surface of the inner support portion.

3. The low temperature liquid tank according to claim 2 , wherein the height setting plate is a heat-resistant board disposed on the heat insulation.

4. The low temperature liquid tank according to claim 1 , wherein an edge of the outer support portion which is adjacent to the inner support portion is chamfered.

5. The low temperature liquid tank according to claim 1 , wherein the heat insulation is a rigid plastic foam.

6. The low temperature liquid tank according to claim 4 , wherein the heat insulation is a rigid plastic foam.

7. The low temperature liquid tank according to claim 1 ,

wherein the outer support portion is a peripheral section of the support portion, and the inner support portion is a midsection of the support portion; and

the outer support portion and the inner support portion are provided on a base plate.

8. The low temperature liquid tank according to claim 1 , wherein the bottom plates include at least one plate extending between the inner support portion and the outer support portion, and wherein the initial height is set so that the bending stress applied to the at least one plate remains equal to or smaller than the maximum allowable bending stress over the service life as the upper surface of the inner portion is lowered.

9. The low temperature liquid tank of claim 8 , wherein during the service life, the height of the upper surface of the inner support portion becomes lower than that of the upper surface of the outer support portion.

10. The low temperature liquid tank of claim 1 , wherein during the service life, the height of the upper surface of the inner support portion becomes lower than that of the upper surface of the outer support portion.