Vacuum Box Testing
is used to test the integrity of the seal between two plates, usually on a lap weld joint. A bubble solution is first applied to a clean, bare weld surface. The vacuum box is then placed over the joint and the compressor turned on until the gauge indicates a vacuum. Any tiny holes or cracks that penetrate through the joint will cause air to be drawn up from the opposite surface, through the solution, and will form bubbles.
Vacuum box testing is commonly used in tank inspections for roof and floor repairs. Special box shapes can be made to test corners and curved surfaces.