A fillet weld is a triangular weld used to join two surfaces that are at approximately right angles to each other. i.e., lap, tee and corner joints are normally welded with a fillet weld. A fillet weld should have a leg length equal to the plate thickness up to 3/8-inch plate. For plate thicknesses 3/8-inch and greater, a minimum of 3/8-inch leg length is required on all wet welds.
As with surface welding, the use of larger wet welding electrodes will result in greater weld metal deposition. However, the larger electrodes tend to produce more porosity (gas voids) in the deposited weld metal. Also, a larger single pass weld will have a lower toughness and an equivalent size multipass weld; this is the result of the tempering effect that each pass of the multipass weld has on the preceding passes.
For most positional work, a 1/8-inch electrode is recommended. Therefore, the welder will need to make a number of passes, usually 3 to 5, to achieve a 3/8-inch leg length. The number of runs will be determined by position and technique. The important point is not the number of runs, but obtaining the 3/8-inch leg length. In cases where the metal to be welded is thin and in all overhead work, a 1/8-inch electrode is required. Using the smaller electrode means more passes, but as previously stated, it allows succeeding passes to temper the preceding ones. Multipass welds using smaller diameter electrodes will actually result in higher quality wet welds with better metallurgical properties.