Porosity in welding is caused by the presence of gases which get entrapped during the solidification process. The main gases that causes porosity are hydrogen, oxygen and nitrogen Porosity if present in large would reduce the strength of the joint.
- Slowing the welding speed to allow time for the gases to escape.
- Proper cleaning and preventing the contaminants from entering the weld.
- Proper selection of electrodes and filler materials.
Slag is formed by the reaction with the fluxes and is generally lighter, so it will float on top of the weld pool and would be chipped of after solidification. However the stirring action of the high intensity arc would force the slag to go into the weld pool and if there is not enough time for it to float, it may get solidified inside the fusion zone and end up as a slag inclusion. Also in multi pass welding, the slag solidified in the previous pass is not cleaned before depositing the next lead, which may cause slag inclusion.
- Cleaning the weld bead surface before the next layer is deposited by using a hand or power wire brush.
- Redesigning the joint to permit sufficient space for proper manipulation of the puddle of molten weld metal.
Incomplete fusion and penetration:
The main causes for this defect are improper penetration of the joint, wrong design of the joint or incorrect welding technique including the wrong choice of the welding parameters. The welding current if, is lower than required would not sufficiently. heat all the faces of the joint to promote proper fusion: Also, the improper cleaning of the joint hinders the fusion of the metal in the joint.
- Increasing the heat input.
- Changing the joint design.
- Ensuring that the surfaces to be joined fit properly.
- Proper cleaning of the joint.
This generally occurs at high temperature and the size can be very small to visible. The crack in most parts is intergranular and its magnitude depends upon the strains involved in solidification. They are more likely to form during the root pass when the mass of the base metal is very large compared to the weld deposited.
- Preheating the bare metal, increasing the cross sectional area of the root bead, or by changing the contour or composition of the weld bead.