Defects in Welding
1. Porosity: Gas porosity get to be visible as round or stretched insubstantial shady spots, occurring separately or in bunches or scattered all through the casting. This is caused by gas formation during solidification by evaporation of moisture or unstable material from the mold surface. Insufficient core baking, venting or capture of air in the cope surface of the casting before complete solidification could also be the reason. The term ‘gas porosity’ is used to refer to shady dark spots on the radiograph, whose diameters are normally inside 0 to 1 mm.
2. Slag inclusion and slag lines show up on the radiograph as dark, uneven shapes. These may be isolated, clustered or randomly distributed. A slag line appears as a linear dark shade, continuous or intermittent along the edge of the weld. Slag inclusions happen because of entrapment of foreign materials in the cavities during welding.
3. Incomplete penetration appears on the radiograph as constant or discontinuous dark lines, typically of uniform width, happening in the middle of the weld. This is caused by the failure of the weld metal to fill the root gap.
4. Lack of fusion appears on the radiograph as a thick, dark line. It may also show as diffused and wavy, depending upon the defect introduction with respect to the radiation beam. This flaw is caused by the failure of the weld metal to ruse with the parent metal or previously deposited weld metal. In case of lack of sidewall fusion, the radiographic image illustrates the appearance of a narrow, dark band parallel to the weld bead.
5. Cracks appear on the radiograph as sharp, straight or jagged dark lines with tapered ends. Cracks may appear in longitudinal or transverse directions. Cracks may occur in the weld and heat affected zones. The effect is caused by the rupture of the weld metal during solidification due to shrinkage or by fracture when cold, because of uneven stresses and poor handling.
6. Undercuts appear on the radiograph as dark lines of uneven width along the edge of the weld. This defect is caused by the formation of a groove or a channel on the surface of the base metal at the toe of the weld bead due to high temperature.
7. Burn through appears on the radiograph as a dark, round or elongated area surrounded by a lighter ring. This is caused by the melting of metal from the root of the weld or through the backing strip.
8. Icicles appear on the radiograph as secluded, white, rounded indications, irregularly with a small, dark spot in the center. This is caused by fused droplets of weld metal extending beyond the root of the weld.
9. Tungsten inclusions appear on the radiograph as white areas of round or uneven shape, either segregated or in bunch. This is acquired by the entrapment of tungsten particles in the weld metal. These particles are broken pieces from the tungsten electrode.