Metal tanks, usually made of steel, have been used to store various fluids, gases and liquids, such as for example, but not limited to, gases, water, chemicals and petroleum products, such as crude oil, fuel oil, diesel fuel and gasoline. The tank has a sidewall, usually but not necessarily circular, a top usually attached to the sidewall at the top, and a bottom wall connected to or near the bottom of the sidewall. Some of the tanks are placed on foundations, while others are built on the ground. Corrosion has been a problem with the tanks, and corrosion can result in leakage. Generally, leakage must be contained or better yet prevented. Various techniques have been used to prevent corrosion. One of the more popular ones is to provide anode-cathode protection to the tanks, and particularly, the tank bottoms. Even with such protection a tank bottom can corrode, and with the passage of years, say 10 to 20, in order to extend the tank's life, a new or second bottom is provided for the tank. Previously the usual approach was to reconstruct the existing tank to provide a second or new bottom a foot or less above the corroded, original tank bottom. The new bottom was secured or welded to the existing sidewall. The old, corroded bottom in effect was still electrically in contact or connected to the sidewall, and the sidewall was connected to the new bottom wall. Thus, the old bottom tended to prevent the cathodic protective current from protecting the new bottom, as the old bottom shielded the new bottom from such protective current flow.
USPTO Backgrounds
USPTO Backgrounds