GEAR-PLANETARY 3074163 - Caterpillar

Applying heat to a tank which has held flammable liquids, even when "empty," can result in the residual flammable liquid or vapor igniting with explosive force. This can result in injury or death. DO NOT weld or flame cut on any tank that has held flammable liquid without taking the proper precautions.
DO NOT WELD AN EMPTY FUEL TANK.
An empty fuel tank can not be cleaned sufficiently to ensure that all the flammable vapors have been removed. Vapors remain even after cleaning with steam or washing with a caustic solution. Besides, caustic solutions can also be explosive when heated, adding to the danger of welding on the tank. To prepare a fuel tank for welding:
1. Fill the tank with carbon dioxide, or2. Fill the tank with water.Fill the Fuel Tank with Carbon Dioxide
This is done by covering (plugging) all openings, except the filler hole, and filling the tank with carbon dioxide from a CO2 fire extinguisher. Then, put a board, or some other object with a flat surface, over the filler hole to keep the carbon dioxide in the tank. After this is done, the welding, alteration, or repairs can be made using proper welding practices.
Fill the Fuel Tank with Water
When filling the tank with water, all openings, except the filler hole, must be covered. The water must be kept at the very top of the filler hole at all times to be sure there is no cavity or space where vapors can collect. Again, after this has been done, the welding, alteration, or repairs can be made using proper welding practices.
After welding, fuel tanks must be drained and filled with fuel and methanol (methyl alcohol) mixture. A ratio of 0.5 L (1 pt) methanol to 38 L (10 gal) of fuel is satisfactory. The methanol will mix with the water and burn with the fuel.
DO NOT WELD A CLOSED HYDRAULIC TANK.
To prepare a hydraulic tank for welding:
1. Remove the cover.2. Position the tank so that the surface being welded is on top. This position makes sure that any oil left in the tank flows away from the welding area.With no cover on the hydraulic tank, there is little danger of a build-up of explosive vapors.
Do not put water in a hydraulic tank. Water can damage the valves. If necessary, carbon dioxide can be harmlessly used when welding hydraulic tanks. See "Fill the Fuel Tank with Carbon Dioxide," for the correct procedure.