1, the first method: ordinary automotive sheet metal method. This method is aimed at places with relatively flat depressions. Through careful observation, we can know that when welding the stretching point with electric welding machine, we should start from the periphery of the depression first, not from the center, and it is best to use slow force instead of the impact of the sheet metal hammer.

2. The second method: cutting and welding. This method is aimed at large depressions, and it is difficult to correct them with the above method. First, cut the concave part (pay attention to fire prevention before operation, because there is mixed gas of oil and gas in the oil tank, which is very easy to cause explosion and dangerous situation), then reshape the cut part of sheet metal, finally weld the corrected workpiece back to its original position, and finally polish and spray paint.

3. The third method: frost heaving can be used to repair. This method is aimed at the large sag, that is, first drain the oil in the tank, unload the tank from the frame, flush the inside and outside of the tank with water, then turn off the switch of the tank and fill it with clear water. Tighten the box cover, and then put the oil tank filled with clean water into the freezing pool (there are such pools in cold storage, cold storage factories and places where popsicles and sorbets are made) for freezing, and pay attention to slightly exposing the depression to the freezing liquid level.

4. The fourth method: the subtle operation of crowbar. This method is used when the concave area of the fuel tank is small. This method tests patience and eyesight, and is suitable for oil tanks with undamaged paint, especially painted oil tanks. First of all, we should prepare crowbars with various bending angles and small hammers with rubber heads, and rubber heads should also be installed on crowbars. Secondly, lamps with strip lights should be equipped. Finally, enough patience and time are needed.