In welding circles, porosity refers to the occurrence of cavities in a weld bead. A porous weld is considered to have been contaminated and is associated with a number of problems.

It is therefore important for a manufacturing engineer to understand the various causes of weld metal porosity and the possible strategies that one can adopt to reduce the likelihood of weld contamination. A few of these causes and their solutions are discussed below for trainee welding specialists.

Moisture on the Electrodes

Moisture contamination is among the most common causes of weld metal porosity. For this reason, baked electrodes are recommended for use in the welding process so as to prevent the introduction of moisture into the weld metal.

Electrodes often become wet due to improper storage and handling prior to and during the welding process. They may also get damp through the condensation of steam emanating from welding activities on lap joints and/or heavy plates.

Proper storage of electrodes in a dry area is key to preventing weld metal porosity. Electrodes should also not be left exposed to the air.

However, it is important to point out that electrodes should have a minimal amount of moisture for increased weld-ability. As such, they should not be overbaked prior to the welding process.

Contamination of the Metal Surface

Metal surface contamination is another common cause of weld metal porosity. Contamination in this context refers to the presence of impurities on the surface of the metal to be welded. Common impurities that may cause weld metal porosity include grease, oil and flux.

Metal surface contamination is especially common with aluminium metal, and it occurs in the form of an oxide layer on the outer surface of the metal.

Preventing weld metal porosity as a result of metal surface contamination requires the welder to thoroughly clean the metal prior to the welding process.

Excessive Use of Shielding Gas

Last but not least, weld metal porosity may occur when an excessive amount of shielding gas is used in the welding process. This is because the excess gas can easily be entrapped into the weld metal.

In order to prevent corrosion as a result of excess shielding gas, welders need to ensure that they use the right amount of shielding gas as recommended by the instruction manual for the machine being used. This information can also be found in the instruction guides that accompany electrodes and electrode wires.