A storage tank for an easily polymerizable compound has acceptance piping and delivery piping with a circulation line directly connecting the acceptance piping to the delivery piping or with circulation lines respectively connecting the acceptance piping to the storage tank and the storage tank to the delivery piping. A method of storing an easily polymerizable compound in the storage tank includes circulating the compound in the storage tank through the circulation line(s), where the compound can be (meth)acrylic acid being produced and/or purified with the temperature of purified (meth)acrylic acid being supplied to or removed from the storage tank being regulated to not be higher than the temperature thereof in the tank. A method of joining pipes for-transporting a corrosive liquid using flanges, bolts, and nuts made of a material having resistance to corrosion by the corrosive liquid.