| 摘要 |
PROBLEM TO BE SOLVED: To suppress increase in the weight and the production cost of a tank main body and prevent the generation of cracks at the base of a boss. SOLUTION: A reinforcing rib 122b extending from the base side of the boss 123 to a part near the top 122a of the tank main body 122 to partly increase the thickness in the base side of the tank main body 122 and the boss 123. Thus, since a mechanical strength in the base side of the boss 123 is improved, while the increase of the weight and the production cost of the tank main body (122) is suppressed, the generation of cracks in the base of the boss 123 can be prevented, even when the elastic limit (stretch limit) of the tank main body 122 is deteriorated by an aged chemical change such as a decomposition or a thermal stress (thermal distortion) due to hydrolysis or oxidation.
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