Patent ID: 7314058

Claim:
A reservoir tank comprising: a tank body for storing a liquid, wherein said tank body comprises a roof, a tank bottom plate and a tank wall, said tank wall being constituted of plural wall members, and wherein said plural wall members are welded to each other, and welding lines of said plural wall members are alternately arranged in a vertical direction; and a double bottom disposed at the bottom of said tank body; wherein (1) said double bottom comprises: (a) a detection port for detecting gas concentration, (b) a double bottom plate disposed so as to keep a gap relative to a tank bottom plate of said tank body, (c) a side wall cylindrically protruding upward from a periphery of said double bottom plate, said side wall surrounding said tank bottom plate and being fixed to said tank body, and a sealed space being formed by said tank bottom plate, said double bottom plate and said side wall; and (2) said detection port is formed in said side wall of said double bottom plate.