This term is used to describe the oxides and other nonmetallic solid materials that are entrapped in weld metal or between weld metal and base metal. Slag inclusion may be caused by contamination of the weld metal by the atmosphere, however, they are generally derived from electrode-covering materials or fluxes employed in arc welding operations; or in multilayer welding operations, if there is failure to remove the slag between passes. It can be prevented by proper groove preparation before each bead is deposited and correcting the contours that will be difficult to penetrate fully with successive passes.

9.4 LACK OF FUSION

It occurs due to the failure of the adjacent bead to bead and weld metal and base metal fusing together. This may happen due to the failure to raise the temperature of the base metal or failure to clean the surfaces before welding.

9.6. LACK OF PENETRATION

This defect, occurs when the weld metal fails to reach the root of the joint and fuse the root faces completely. It is caused by using incorrect electrode size with respect to the form of the joint, low welding current, inadequate joint design and fit-up. It occurs more often in vertical and overhead welding positions.

9.7 FAULTY WELD SIZE AND PROFILE

A weld, otherwise deposited correctly without a defect may not be acceptable due to the shape of its profile. Excessive or lack of reinforcement are both defective. Defective profiles on butt welds are shown in Fig. 9.4 while Fig. 9.5 describes desirable, acceptable and defective profiles on fillet welds. These faults arise from the use of an incorrect welding procedure and could be eliminated if the following factors are considered:

(a) correct joint preparation and fit-up

(b) proper electrode size and welding current