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Remove Moisture

Welding electrodes are vulnerable to atmospheric moisture. Bound moisture in electrodes yields porous welds.

If the electrodes used for welding contain traces of moisture, the water decomposes in the heat of the arc and the liberated hydrogen enters the lattice of the material, causing hydrogen embrittlement. The mechanism starts with lone hydrogen atoms diffusing through the metal. At high temperatures, the elevated solubility of hydrogen allows hydrogen to diffuse into the metal. When these hydrogen atoms re-combine in minuscule voids of the metal matrix to form hydrogen molecules, they create pressure from inside the cavity they are in. This pressure can increase to levels where the metal has reduced ductility and tensile strength up to the point where it cracks open (hydrogen induced cracking). High-strength and low-alloy steels, nickel and titanium alloys are most susceptible.

Stick electrodes for such materials, with special low-hydrogen coating, are delivered in sealed moisture-proof packaging. New electrodes can be used straight from the can, but when moisture absorption may be suspected, they have to be dried by baking (usually at 800 to 1,000 °F or 427 to 538°C) in a drying oven.

Preventing hydrogen embrittlement is critical. Detecting a defect is difficult and frequently found only after the weld is put into service.

Because the coating of the welding electrode is hygroscopic (readily absorbs moisture), it is a good idea to store welding electrodes at an elevated temperature in a holding oven at 120-150°C

If, due to improper handling or storage, the electrodes get exposed to atmosphere moisture for a long time, they may have to be rebaked at higher temperatures. Rebaking temperatures vary according to electrode type and manufacturers recommendation.

Dry Flux Too

Flux used for submerged arc welding is another source of hydrogen. Flux has to be dried prior to use especially on high strength steel. Always store flux in a controlled atmosphere with lowest possible relative humidity. Unused flux in opened bags should be stored in holding ovens. Flux used in critical applications may have to be dried as per manufacturer’s recommendation. If the flux has been exposed to moisture due to unfavourable handling or storage, redrying can help to return the flux to its original moisture-free state.

Click Here for a general guide on holding & baking temperatures for electrode & fluxes.

 
 
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