Vacuum Box Leak Testing (VBLT)
Effective leak detection method for welded joints, tank floors, and pressure boundaries using vacuum differential to identify through-wall defects.
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What is Vacuum Box Leak Testing?
Vacuum Box Leak Testing (VBLT) is a non-destructive testing method used to locate leaks in welded joints, particularly in tank floors, roofs, and shell-to-bottom welds. A transparent box is placed over the test area after applying a soap solution, and vacuum is applied inside the box.
If there is a through-wall defect, the pressure differential forces air through the leak, creating bubbles in the soap solution that are visible through the transparent viewing window. This method is simple, reliable, and widely accepted for leak detection.
- Detects through-wall leaks
- Visual confirmation of defects
- Suitable for tank inspection
- Cost-effective leak detection
Where VBLT is Applied
Common applications for vacuum box leak testing in industrial facilities
Storage Tank Floors
Testing bottom plate welds and annular ring welds in above-ground storage tanks for product containment assurance.
Tank Roof Welds
Inspection of floating roof and fixed roof weld seams to prevent vapor emissions and water ingress.
Ship Hull Welds
Testing hull plate welds and compartment boundaries for watertight integrity in marine applications.
Membrane Liners
Leak testing of welded membrane liners in containment areas and environmental protection systems.
How Vacuum Box Testing Works
Surface Preparation
The weld area is cleaned to remove dirt, scale, and debris. The surface must be reasonably smooth for proper seal.
Solution Application
A soap or bubble solution is applied generously over the weld area to be tested.
Vacuum Application
The vacuum box is placed over the test area and sealed. Vacuum is applied to create pressure differential.
Leak Detection
Through-wall defects are identified by continuous bubble streams visible through the viewing window.
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