| AN 01-25CN-2 | PARAGRAPH 6 |
(4) TO REPAIR THE OIL TANKS. (a) CLEANING PROCEDURE-To eliminate the danger from possible ignition of explosive gases when repairing aircraft oil tanks, the following precautions should be taken: 1. No repairs requiring the application of heat will be accomplished on oil tanks installed in an air. plane. 2. The oil tank will be flushed for 15 minutes with hot water entering at the bottom of the tank and overflowing at the top. This procedure should remove all deposits of oil adhering to the sides of the tank. 3. After flushing with hot water, clean the tank with live steam, passing the steam through the tank for a minimum period of one hour. The oil tank will be mounted so that there is an opening at the top and one at the bottom, or the lowest point of the tank. The live steam will be fed in at the top opening and allowed to escape through the bottom opening. All other openings will be closed. 4. If facilities for steam-cleaning are not available, the flushing with hot water, as specified in 2. will be continued for a minimum period of one hour, following which the interior of the tank will be thoroughly dried with compressed air. This is not as positive , a method of removing combustible material and fumes as the steam-cleaning. Therefore, it should not be used unless absolutely necessary. 5. When the exterior of the oil tank or fuel shell is to be cleaned with paint remover or any combustible solvents, this cleaning will be done prior to flushing or steaming of the interior of the tank. 6. The repair work should be done as soon as possible after the tank has been cleaned and dried. Under no circumstances will a tank that has been flushed or steam-cleaned and dried be allowed to stand more than 30 minutes before being |
repaired. Tanks that are allowed to stand in excess of this period will be re-cleaned before applying any heat. 7. When oil tank repairs can be accomplished by soldering, it will not be necessary to steam-clean the tank, provided all oil has been completely drained from the tank and caution is used in heating the soldering irons so that they will not be heated to the point at which they will cause particles of dust to become incandescent, as this condition is sufficient to ignite an explosive mixture in the tank.
(b) Failures in oil tanks can usually be repaired by simply welding the crack. The paint coatings should first be removed for a distance of at least 3 inches all around the crack. This can be done by the application of paint remover, -which should then be thoroughly removed as outlined above. (c) A small hole (3/64 inch to 1/16 inch in diameter) should then be drilled at each end of the crack to prevent its progression under the welding beat or after the tank is again in service. The welding can then be accomplished, using an oxy-hydrogen flame. The flame should be adjusted to a neutral condition with the hydrogen gage set about-5 pounds above the oxygen gage. A filler rod of the same material as the tank shell can be used, although 5% silicon rod, if available, is generally easier to handle and gives better results in complicated welds. United States Aluminum Company Flux 22, or equivalent, should be used. It is mixed to a paste condition with water, the part to be welded is coated with it, and the rod dipped in it. Enough heat should be applied to form a bead on the inside of the joint being welded, but care should be exercised to prevent melting holes in the material. A good practice to follow is to weld from each end of a crack toward the center to prevent the crack's progressing ahead of the flame. (d) TESTING TANKS AFTER REPAIRS.Before installing the oil tank in the airplane, it must be tested under water to 5 psi. |
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