Thermally Stressing Weld Zones
Cold shock testing is performed after welding and before Helium leak testing. Cold shocking is a way to thermally stress the welds and enlarge any potential voids or cracks in order to make them easier to detect during Helium leak testing. The basic process involves flooding the weld zone with liquid Nitrogen so that the part rapidly cools down then allowing it to warm back up to room temperature. In some cases a flame will be applied to rapidly warm up the weld and increase the amount of stress applied to the weld. Small parts can be totally submerged in LN2 while larger assemblies will have LN2 sprayed directly on the weld areas. When fabricating products for vacuum service even the tiniest leak can become a major problem. Aluminum welds are notorious for various weld defects like pitting and porosity so it becomes very important to stress the welds and increase the sensitivity of the leak test.