Most procedures involve running the steam, water, or gas  through the tank for a stated period of time. Adapters may  need to be fashioned or purchased for the fill port to enable  proper cleaning. Follow the manufacturer’s procedure for  the proper time to keep the cleaning medium in the tank and  for prepping the tank for welding in general. purging. Again, follow all manufacturer guidance to insure  a safe airworthy repair.  After a seam or a damaged area is welded, you must clean  the tank of any flux or debris that may have fallen into the  tank. Water rinsing and acid solutions are commonly used.  A leak check to ensure the repair is sound follows a welded  repair. This can be done by pressurizing the tank with a  specified amount of air pressure and using a soapy solution  on all seams and the repaired area. Bubbles form should air  escape. The amount of air pressure used for a leak check is  very low. One half to 3.5 psi is common. Use an accurate  regulator and pressure gauge to prevent overpressurization  that could deform or otherwise damage the tank. Tanks  ordinarily supported by aircraft structure when installed  should be similarly supported or reinstalled in the airframe  before pressurization.  Figure 14-90  shows an aircraft fuel  tank being welded and the repaired tank installed in the frame  of an antique aircraft. Riveted tanks are often repaired by riveting. The seams  and rivets are coated with a fuel resistant compound when  assembled to create a leak-free container. This practice is  followed during a patch repair, or when repairing a seam,  which may require replacing the rivets in the seam. Some  minor leak repairs may only require the application of  addition compound. Follow manufacturer’s instructions.  The compound used may be heat sensitive and require inert  gas purging to prevent degradation from hot water or steam  Synthetic bladder tanks have a limited service life. At some  point, they seep fuel beyond acceptable limits and need to be  replaced. Bladder tanks are usually required to remain wetted  with fuel at all times to prevent drying and cracking of the  bladder material. Storage of bladder tanks without fuel can  be accomplished by coating the tanks with a substance to  prevent drying, such as clean engine oil that can be flushed  from the tank when ready to return to service. Follow all  manufacturer’s instructions for the care and repair of these  common tanks. It is important to ensure that bladder tanks  are correctly secured in place with the proper fasteners when  reinstalling them in the aircraft after a repair.  Terneplate aircraft fuel tanks that are assembled by soldering  are also repaired by soldering. All patches have a minimum  amount that must overlap the damaged area. Flux used in  soldering must be removed from the tank after the repair  with techniques similar to that used on a welded tank. Follow  manufacturer’s instructions. Bladder fuel tanks that develop leaks can also be repaired.  Most commonly, they are patched using patch material,  adhesive, and methods approved by the manufacturer. As  with soldered tanks, the patch has a required overlap of the  damaged area. Damage that penetrates completely through the  bladder is repaired with an external, as well as internal, patch.  Soldered Tanks Bladder Tanks Riveted Tanks Figure 14-90.  A rigid removable fuel tank with welded seams is repaired by welding. 14-48