Leak Testing — Bubble Test in Belgium
Bubble leak testing reveals through-wall leaks in a welded assembly or an enclosure. LCNDTEST performs it with compressed air or a vacuum box, never with helium: a direct, immediate method well suited to tanks, piping and tank floors.
What is bubble leak testing?
Bubble leak testing is a non-destructive method that reveals through-wall defects in a wall or a welded assembly. The principle is direct: a pressure difference is established across the wall under test and a foaming agent is applied to the accessible face. Wherever a path crosses the wall, gas escapes and forms bubbles visible to the naked eye.\n\nLCNDTEST uses two techniques, both with air: internal pressurisation, where the enclosure can be pressurised, and the vacuum box, where only one face is reachable. In the latter case a transparent box fitted with a seal is pressed against the area under test and evacuated; ambient air then crosses the defect from outside to inside and foams the applied agent.\n\nWe do not perform helium testing. Air bubble testing is not aimed at laboratory-grade micro-leaks: it detects through-wall defects in industrial enclosures and welds, with an immediate result, readable on site and without heavy instrumentation.
Inspection methodology
The area under test is first cleaned and degreased: an oil film or scale can temporarily plug a defect and mask a leak. Test parameters are then agreed with the client: test pressure or vacuum level, hold time, choice of foaming agent and the applicable acceptance criterion.\n\nFor internal pressurisation, the enclosure is brought progressively to the agreed pressure and held long enough to stabilise. The foaming agent is brushed or sprayed over all welds and connections to be examined. The inspector watches the surface for the full prescribed period: a leak shows as a single growing bubble, or as a stream of fine bubbles.\n\nWith the vacuum box, the box is moved in successive overlapping sections so that the entire weld is covered. Each position is observed for the required time before moving on. Every indication is marked, photographed and recorded. The report states the technique used, the pressure or vacuum applied, the agent used, the coverage achieved and the precise location of each leak found.
Industrial applications
- Vacuum-box testing of floor and shell welds on atmospheric storage tanks
- Leak testing of piping and headers after erection or repair
- Verification of shell, course and nozzle welds on fabricated pressure equipment
- Testing of containers, caissons and welded enclosures before commissioning
- Leak location on in-service installations, alongside a pressure test
Advantages of bubble testing
- Immediate visual result: the leak is located precisely, with no deferred interpretation
- Works where only one face is accessible, thanks to the vacuum-box technique
- No ionising radiation, therefore no exclusion zone and no radiation protection constraints
- Light, fast set-up, including on site and at height
- Controlled cost compared with instrumented leak-detection methods
Reference standards
EN 1593 • EN ISO 20485 • ASME Section V Article 10 • API 650 annex for tank floors
Frequently asked questions
Air bubble testing answers the ordinary industrial need: detecting through-wall defects in a weld or an enclosure, with an immediate result that can be verified on the spot. Helium detection targets far lower leak rates and belongs to a different kind of installation. We therefore test with compressed air or a vacuum box, and we state this explicitly in every report.
A pressure test verifies the mechanical strength of the equipment at a pressure above its service pressure. A leak test verifies the absence of leakage, generally at a much lower pressure. The two are complementary and are often carried out one after the other.
It needs a surface flat and clean enough for the box seal to hold. On complex geometries or very irregular surfaces, internal pressurisation or another method is preferable. We assess this when preparing the intervention.