consistent and not sag. The weld bead should be convex. Figure 12-23 parts E and F show two defects in bead shape. Complete (100%) penetration is generally required only on a weld with a groove-type joint. A weld bead with 100% penetration will show a small, uniform bead-like bump on the root side of the weld. Fillet welds seldom require 100% penetration. They do, however, require enough to penetrate past the intersection of the two pieces being welded. The welding symbol often specifi es a leg size and weld size large enough to ensure adequate penetration. Poor penetration on a fi llet weld cannot be inspected visually. diameter and pausing very briefl y. Moving the electrode forward causes the keyhole to open slightly. As soon as you see both pieces of base metal melt and the keyhole open, move the electrode backward one-half of the electrode’s diameter. This backward motion adds weld metal to the weld pool and fi lls in the weld pool. This process of moving forward one electrode diameter, pausing, and then moving back one-half electrode diameter is repeated as the weld progresses along the joint. See Figure 12-22. Proper application of this technique results in consistent penetration and a uniform ripple in the weld bead. This same technique is used making a fi llet weld. The major difference is there is no keyhole to observe. Move the electrode forward the diameter of the electrode. Pause briefl y and watch the arc melt into the root of the weld. Then move the electrode backward one-half of its diameter. This will add weld metal to the weld pool and create a uniform ripple. If properly applied, this technique produces consistent penetration and a uniform ripple, just like it does on a butt weld. Weld Defects Defects that may occur include overlap, undercut, voids in the weld face, incorrect weld size and shape, and lack of penetration on a groove-joint weld. Overlap occurs when the weld toe is not fused into the base metal. Figure 12-23 parts A and B show examples of overlap. Undercut occurs when the base metal at the weld toe area is melted but is not fi lled with fi ller metal. This causes a weak area in the weldment. See Figure 12-23 parts C and D for two examples of undercut. Slag inclusions are caused when slag is trapped during a multiple-pass weld. Slag must be completely removed after each weld pass to prevent slag inclusions. Porosity can be seen on the surface of some welds. Some porosity can be beneath the surface and not visible on a completed weld. Welding with a long arc or improper electrode motion can cause porosity. Welds that are too wide, too narrow, have too much buildup, are underfi lled, or butt joints that do not have complete penetration can be found by visual inspection. The weld face should be Overlap Undercut Lack of penetration Narrow bead B D F E Excessively convex C Undercut A Overlap Goodheart-Willcox Publisher Figure 12-23. Study these cross sections and diagrams of weld defects. A—Overlap on a fillet weld. B—Overlap on a groove weld on a butt joint. C—Undercut on a fillet weld. D—Undercut on a groove weld on a butt joint. E—A poorly contoured fillet weld. F—A narrow weld bead without complete penetration on a square groove butt joint. Chapter 12 SMAW: Flat Welding Position 181 Copyright Goodheart-Willcox Co., Inc.