Welding is used for structural joining in many industries, and a watertight seal of the welded joint is not always required. A complete seal of a weld is critical in other industries, such as fire protection, to ensure a leak-free sprinkler system. This article is how you can and should seal aluminum joint welds.
Weld porosity leaks can be very small and difficult to detect unless a system is pressurized. These micro porosities can go undetected for a long time. Pin-prick leaks can be so small that they look like condensation on the pipes. These types of leaks can cause ceiling damage and provide a breeding ground for mildew and mould. Others can only drip once the system is pressurized, causing damage to ceilings, floors, furniture, and personal property.
“Does it always make sense to drill a hole for gas expansion when sealing or capping an aluminium weld, as we do with steel?”
The simple answer is no. But, and there is always a but, knowing what is going on with your weld will help you make good project decisions.
It is critical to remember that cosmetic aluminium welds must be visually appealing and structurally sound, but they are not coded as structural or high-pressure vessels. Structural, high-pressure, and nuclear welds must adhere to strict weld procedure specifications; you must be qualified on those welds by a CWI; and the welds must undergo nondestructive testing to ensure their structural integrity.
What to avoid when you seal aluminum?
Avoid the following when sealing your aluminium weld:
Welds that are defective or incomplete. Either of these could allow a liquid to enter or a gas to escape from your weldment.
Contamination. Contamination weakens the fusion zone and reduces corrosion resistance while also changing mechanical properties.
Gas was trapped. This can result in a gummy part of the weld that is difficult or impossible to close.
Gas expansion while still inside your weldment causes the gummy weld at the end of a bead. If you need to get the gas out quickly, drill a small hole in the weldment. Once everything has cooled down and the gas has dissipated, you can return and seal it up. You should be able to seal without issue as long as you don’t significantly raise the temperature of your weld.
Another method to prevent gas expansion is to intentionally stop your weld 12 in. short on the closing weld. Allow the weldment to cool and the gas to escape before proceeding. Step away and begin your next project, or perhaps have lunch. After everything has cooled down, clean the welding area to reduce or eliminate the oxide layer that has most likely formed during the cooling process. Finally, finish your weld bead.