What is vacuum box testing of welds?

Vacuum box testing is a non-destructive method for leak testing welds and geomembranes. A bubble-forming solution is applied to the weld, a transparent vacuum box is placed over it and evacuated. Where the weld leaks, the solution reveals it by forming bubbles.

Which standard governs vacuum box testing?

Vacuum box testing is classified as method C3 in EN 1779, and the bubble principle is described in EN 1593. For particular applications, ASME BPVC Section V Article 10 Appendix II, ASTM E515, API 650 for tank bottoms, DVS 2225-2 for geomembranes and DVGW G 469 procedure E3 for district heating apply in addition.

What vacuum level does the test need?

The test vacuum depends on the standard: DVGW G 469 E3 requires 200 to 500 mbar, DVS 2225-2 about 300 mbar and ASME Section V at least around 150 mbar. The TP-series leak detectors reach an ultimate vacuum of −850 mbar and therefore cover every common requirement.

How sensitive is vacuum box testing?

In practice the detectable leak rate is around 10⁻⁴ to 10⁻³ mbar·l/s, equivalent to 10⁻⁵ to 10⁻⁴ Pa·m³/s. Under ideal conditions 10⁻⁵ mbar·l/s is achievable — the same order that ASTM E515 gives as the limit of sensitivity. That is far less sensitive than helium mass spectrometry, but sufficient for tank, vessel and membrane work.

Which defects does the test miss?

Vacuum box testing only finds defects that are open through to the surface. Embedded porosity, cavities and lack of fusion without an opening go undetected. On safety-related pressure components it therefore has to be combined with radiographic or ultrasonic testing.

Vacuum box, saddle, test frame — what is the difference?

Vacuum box, vacuum saddle, bubble test box and leak test frame all describe the same principle in different shapes, and manufacturers often use the terms interchangeably. Flat boxes and test frames cover long straight welds; saddles and shaped boxes sit on girth welds, corners and special geometries.

Which box suits which weld?

For girth welds on pipe there are circumferential boxes from DN 32 to over DN 1000; for straight welds, butt-weld boxes; and for shell-to-bottom welds or T-joints, fillet-weld boxes — both with a test length up to 700 mm per placement. Corner and cylindrical boxes cover internal and external corners as well as branches. All three standard types are normally 100 mm wide. For other geometries AB Industrie Service builds boxes to your drawing.

Which bubble solution is permitted?

The bubble-forming solution has to meet EN 14291, with defined surface tension, foam stability and corrosivity limits. ASME BPVC Section V expressly rules out household soap and washing-up liquid. For polymer geomembranes, DVS 2225-2 does permit soapy water.

Who may carry out a vacuum box test?

Normally a Level 2 leak testing (LT) operator to EN ISO 9712, often combined with visual testing (VT). What governs is the risk assessment and the requirements of whichever standard applies.

Do I need a vacuum gauge on the box?

For most users it is not necessary, because the test vacuum can already be read off the pump's gauge. A gauge on the box is a cost option and shows the vacuum right at the point of test. It is fitted at the works and cannot be retrofitted later.

Vacuum Box Testing of Welds | Equipment & Test Boxes

Vacuum box testing of welds · Method C3If it bubbles,
it leaks.
Full stop.

Vacuum box testing is a non-destructive method for leak testing welds and geomembranes — classified as method C3 in EN 1779. It is also known as vacuum testing or bubble leak testing. Apply the bubble-forming solution to the weld, place the transparent test box on top, evacuate. If a continuous leak path runs through the weld, air is drawn through it — and the solution reveals the leak as bubbles. You watch it through the Makrolon window. There is nothing to interpret: bubbles or no bubbles.

Six steps.
One clear result.How vacuum box testing of a weld actually works

The method is defined in the standards and mechanically simple: a pressure difference between the inside of the component and the evacuated box. A continuous leak path lets air through — and air in the solution is visible. The decisive advantage: the component only has to be accessible from one side. That is why vacuum box testing is the standard method for tank bottoms, bunds and open structures, where a pressure test is not possible at all.

SHEET 01LEAK DETECTORS · TP SERIESOIL-FREE · 230 V

TP 6 & TP 8 vacuum leak detectors

Dry-running rotary vane pump — no oil, no oil mist, little maintenance. NW 7,2 quick coupling for fast box changes on site. The two units differ only in pumping speed — more capacity means large boxes pull down faster.

Figure	TP 6	TP 8
Pumping speed	6 m³/h = 100 l/min	8 m³/h = 133 l/min
Ultimate vacuum	−850 mbar	−850 mbar
Coupling	NW 7,2	NW 7,2
Voltage	230 V	230 V
Weight	~11,6 kg	~11,6 kg
Sound pressure	62 dB(A)	62 dB(A)
Protection	IP 54	IP 54

Enquire about the TP 6 Enquire about the TP 8

TP 6 vacuum leak detector for vacuum box testing of welds, with vacuum gauge, on-off switch and NW 7,2 quick coupling — FIG. 1 · TP-SERIES LEAK DETECTOR WITH COUPLING AND CONTROL DETAILS

SHEET 02BOXES · CIRCUMFERENTIAL WELDS

Circumferential-weld boxes DN 32 – >1000

Fixed sizes DN 32–300 and adjustable boxes (DN 125–150 up to >1000) for girth and branch welds on pipe.

Circumferential-weld vacuum box for vacuum box testing of pipe welds, with Makrolon window, contact gasket and NW 7,2 quick coupling — FIG. 2 · CIRCUMFERENTIAL-WELD BOX WITH WINDOW, GASKET AND COUPLING

11 fixed · 5 adjustable sizes Enquire about circumferential boxes

SHEET 03BOXES · BUTT WELDS

Butt-weld boxes up to 700 mm

Elongated boxes for straight butt welds — tank floor plates, plate joints in vessel work. Test length up to 700 mm per placement; longer welds are covered by moving the box on with an overlap.

Butt-weld vacuum box up to 700 mm for vacuum box testing of straight welds, with long window, contact gasket and shut-off valve; vacuum gauge optional — FIG. 3 · BUTT-WELD BOX WITH WINDOW AND SHUT-OFF VALVE — GAUGE OPTIONAL

for straight welds Enquire about butt-weld boxes

SHEET 04FILLET WELDS

Fillet-weld boxes up to 700 mm

For shell-to-bottom welds and T-joints — wherever two plates meet at an angle. Test length up to 700 mm per placement.

Fillet-weld vacuum box up to 700 mm for vacuum box testing of shell-to-bottom welds and T-joints, with angled contact gasket and shut-off valve; vacuum gauge optional — FIG. 4 · FILLET-WELD BOX WITH ANGLED CONTACT GASKET

for angled joints Enquire about fillet-weld boxes

SHEET 05SPECIAL SHAPES

Corners, cylinders & custom builds

External and internal corners, cylindrical boxes for branches and pontoon covers. Beyond that we build boxes to your geometry — any fillet-weld angle, welded-in branch penetrations, tight internal corners.

Special vacuum box shapes for vacuum box testing: cylindrical box for branches and pontoon covers, rectangular box and corner box, each with shut-off valve and optional vacuum gauge — FIG. 5 · SPECIAL SHAPES — CYLINDRICAL, RECTANGULAR AND CORNER BOX

built to your geometry Enquire about a custom box

SHEET 06SOLUTION & ACCESSORIES

Bubble solution and connections

The leak detection spray has to meet EN 14291: defined surface tension, foam stability, corrosivity limits. Spray 400 ml (stable down to −15 °C) or concentrate 5 L / 25 L. Plain washing-up liquid does not meet the ASME requirement.

Applying: Pump spray bottle for the concentrate.
Connecting: Vacuum hoses and NW 7,2 couplings.
Measuring: Vacuum gauge 0 to −1 bar — optional, reads the vacuum directly at the box. No gauge can read beyond about −1 bar: that would be absolute vacuum.
Setting: Vacuum regulating valve for the level the standard requires.

Spray, drums & accessories Enquire about the solution

SHEET 07MAINTENANCEWEAR PARTS

Carbon vanes and filters

The dry-running pump needs no oil changes, but it does need cleaning inside from time to time: the carbon vanes shed fine dust. Together with moisture from the solution, that can cause sticking and corrosion.

After every test: Let the pump run on for at least 30 minutes so the moisture is driven out of the pumping chamber. Switching off too early leaves residual moisture inside — it binds the carbon dust and leads to corrosion.
1–2× a year: Open the pump and clean the pumping chamber.
Spare parts: Carbon vanes and filters can be reordered individually — on request.

on request Enquire about vanes and filters

Box, saddle,
frame, hood.Vacuum box types by weld configuration

Vacuum box, vacuum saddle, test frame and test hood all work on the same principle and differ only in shape. Depending on the maker, the same tool is called a vacuum test box, bubble test box, leak test frame or simply a vacuum hood. The name matters less than what the contact gasket has to seal around.

Box type	Application	Typical sizes
Circumferential box	pipe girth welds, branches, repair areas	DN 32–300 fixed · DN 125 – >1000 adjustable
Butt-weld box	long straight welds, floor plates	up to 700 mm long
Fillet-weld box	shell-to-bottom welds, T-joints	up to 700 mm long
External-corner box	outer corners on vessels and bunds	to geometry
Internal-corner box	inner corners, confined areas	to geometry
Cylindrical box	branches, pontoon covers	to geometry
Custom build	any fillet angle, branch penetrations, inner corners	to your drawing

Box type

Application

Typical sizes

Circumferential box

pipe girth welds, branches, repair areas

DN 32–300 fixed · DN 125 – >1000 adjustable

Butt-weld box

long straight welds, floor plates

up to 700 mm long

Fillet-weld box

shell-to-bottom welds, T-joints

up to 700 mm long

External-corner box

outer corners on vessels and bunds

to geometry

Internal-corner box

inner corners, confined areas

to geometry

Cylindrical box

branches, pontoon covers

to geometry

Custom build

any fillet angle, branch penetrations, inner corners

to your drawing

Standard	Vacuum	Hold time	Note
DVGW G 469 E3	200–500 mbar	≥ 30 s	district heating
DVS 2225-2	~300 mbar	≥ 10 s	~100 mm overlap
ASME Sec. V, Art. 10	≥ ~150 mbar	5–10 s	≥ 50 mm overlap
API 650	~200 mbar	–	tank bottoms

Standard

Vacuum

Hold time

Note

DVGW G 469 E3

200–500 mbar

≥ 30 s

district heating

DVS 2225-2

~300 mbar

≥ 10 s

~100 mm overlap

ASME Sec. V, Art. 10

≥ ~150 mbar

5–10 s

≥ 50 mm overlap

API 650

~200 mbar

–

tank bottoms

Which box suits your weld?

Weld type, diameter, standard — tell us what you need to test. We will put together the right set of pump, box and solution. Straight answers, no detours.

Vacuum box testing of welds · Method C3If it bubbles,
it leaks.
Full stop.

Six steps.
One clear result.How vacuum box testing of a weld actually works

Visual check & cleaning

Check against a reference leak

Apply the bubble solution

Place the box, evacuate

Watch

Mark, retest