Vacuum Box Leakage Testing Service

Vacuum Box Testing of butt, fillet and lap weld

Vacuum box testing is a non-destructive examination (NDE/NDT) used for locating welding leaks. A vacuum box and a compressor create a high or low-pressure vacuum and a detergent solution is applied to the test area. The detergent bubbles help to identify the leaks within the created pressure envelope. The main objective of the Vacuum box testing technique is to locate leaks in welds due to through-thickness discontinuities. This is accomplished by applying a solution to a weld and creating a differential pressure across the weld causing the formation of bubbles as leakage gas passes through the solution. This testing is to be performed prior to any main vessel or tank testing following the completion of all welding. This article will briefly explain the leak testing procedure using the vacuum box method that can be used for all metals.

Required Equipment for Vacuum Box Testing

Vacuum box test method employs the following equipment for welding checks

• a compressor: approximate flow 6 m^3 per minute under 7 bar
• An air pipe between the compressor and vacuum box.
• A vacuum box, which enables to obtain a depression of 500 m-bar, which can be controlled by means of a vacuum manometer located on the box. The manometer shall have a range of 0 psi (0 m-bar) to 15 psi (1020 m-bar).
• A liquid detergent mixed with water makes soapy water.
• Bubble solution which produces a film. That does not break away from the area to be tested and the bubbles formed shall not break rapidly due to air drying or low face tension.
• Soups or detergents for cleaning shall not be used.
• If the ambient temperature is below freezing, add ethylene glycol to the solution (antifreeze).
• General lighting or individual lighting if necessary. The minimum light level shall be 100 foot-candles (1000 lux)
• A brush (diameter not less than 50 mm)
• A metallic brush and/or a grinding machine.