A procedure followed during the installation of an underground tank and pipe system to confirm the integrity of the system before the excavation is backfilled. Immediately prior to installation, while a new tank is still resting on the surface alongside the excavation, all openings in the tank, except one, are sealed. Through this remaining opening, compressed air with a pressure no greater than 5 psig is introduced into the tank.
While the tank remains under pressure, workers using mops, sponges, or garden sprayers, coat the exterior surface of the tank with a soapy water solution. They then inspect the tank surface for the presence of bubbles. If none appear, the soundness of the tank is proven. The presence of bubbles, however, indicates a leak, a pinhole size leak, perhaps, but still a leak. If a leak is revealed, corrective action must be taken before the tank can be placed in the ground.
Piping systems can also be subjected to an air/soap test, prior to introduction of backfill into the excavation. When piping systems are tested, all fittings, joints, and piping surfaces are soaped. Normally, the air pressure used for primary piping tests is about 50 psig. Less pressure is used for testing secondary piping interstices. This pressure/soap testing is similarly conducted on other DoubleWall containment vessels such as Tank/Turbine sumps, transition sumps and under dispenser sumps.
Sometimes new tanks are subjected to an air/soap test after they have been placed in the excavation, and after all piping has been connected. This allows for the testing of risers and tank connections, as well as the tank and piping.