While most of the defects discussed thus far are appearance defects, incomplete penetration may result in structural failure from one of two causes. First of all, with incomplete penetration there may not be sufficient weld metal to withstand the stresses developed in the joint. Secondly, incomplete penetration may result in a cracking of the weld.

1. The welding speed is too fast.
   
2. Welding speed is too slow.
   
3. Improper joint preparation.



4. Insufficient welding current.
.


5. The electrode used is too large.

1. Do not weld too rapidly or too slowly. If the speed of travel is too fast, insufficient weld metal is deposited. If the weld is too slow, you will achieve a large weld, however the large liquid weld puddle becomes a barrier to the arc's ability to penetrate the base metal, leaving a large weld, with little penetration.



2. Be sure to allow sufficient gap at the bottom of the weld. Use a back-up bar if possible. Chip or cut out the back of the joint, then deposit a back-up bead. Never expect excessive penetration from an electrode. If the plates are over 3/16 inches thick, bevel them.



3. Be sure to use sufficient welding current to attain proper penetration.



4. When welding in narrow grooves, use small diameter electrodes.