Copyright Goodheart-Willcox Co., Inc. 280 Gas Tungsten Arc Welding Handbook This is caused by overheating of the crack edge. This is also a good situation for a dye penetrant test. 2. Perform a penetrant test on the grooved area. If no indication of a crack or defect is seen, remove the penetrant. 3. Grind .010″–.015″ (.25 mm–.38 mm) deeper. 4. Penetrant test the grooved area again. Continue penetrant testing, grinding, and retesting until the defect is found. 5. If the defect is still not found, X-ray to determine if the defect remains. If the crack is not found after removing metal halfway through the part, reweld the ground area. Then work from the opposite surface to remove the crack. Never grind a slot or a hole through the part. Repairing a slot causes excessive distortion in the adjacent areas or shrinkage and the possibility of more defects. The removal of defects in fi llet welds is diffi cult due to limited access of the grinder. If the penetrant is allowed to penetrate into the joint, it can cause many problems during weld repair. For a fi llet weld, it is easier to use visual inspection or radiographic tests to ensure that the defect has been removed. Preparing for Repair After the defect is removed, prepare the area for welding by removing all rough edges on the ground area. Any oil, grease, scale, or penetrant residue must be removed with alcohol or acetone. Do not use grit blasting in the grooved area. Grit material can become embedded in the ground area and become trapped in the weld repair. Welding for Repairs • If possible, use stringer beads with minimum amperage for minimum shrinkage of the joint. • Whenever possible, use a current-tapering (crater fi ll) control on amperage to prevent crater cracks. • Clean scale and oxides from each weld pass. • Visually inspect each weld pass after cleaning. • If the weld repair is deep, have an X-ray made after two or three completed passes to confi rm that new cracks have not formed. This should also be done if there is any doubt about removal of the original crack. • Always use a backing gas if the root of the weld may be exposed to air. • Where possible, use the original parameters for preheat, interpass temperature, and postheat. • Do not build the repair crown any higher than is required. Each pass that is made stresses the base of the weld due to shrinkage. • If the grain size must be controlled throughout the repair area, weld temper beads on top of the weld, as shown in Figure 18-33. Temper beads reduce the surface grain size and are removed after welding. Postweld Inspection All of the nondestructive testing (NDT) required for fi nal acceptance of the weld must be completed after the weld repair is done. This means that even if several inspections were satisfactory before the weld was rejected, all of the inspections must be redone. Repairs can cause new problems in a weld. After a repair is made, the entire weldment must be reinspected. Crack Oxide pocket Lack of fusion Porosity, wormhole Figure 18-32. The defects shown occur in the interior of a weld.