Below we will go into the most common weld defects and how to detect them with NDT testing.
1. Porosity #
Gas porosity is visible as stretched or rounded insubstantial shady areas. They occur in bunches, separately or scattered throughout the casting. It is caused by gas being formed during the solidification process by unstable material on the mold surface or by moisture. It can also be caused by insufficient venting, core baking, or air getting trapped on the casting's surface before solidification is complete. Gas porosity is a term that is used to describe the shady dark spots that appear on the radiograph that have a 0-1 mm. diameter.
2. Slag lines and slag inclusion #
Slag lines and slag inclusion appear on the radiograph as uneven, dark shapes. They can be randomly distributed, clustered, or isolated. Slag lines appear as linear dark shades, intermittent or continuous along the weld's edge. Slag inclusions occur due to foreign materials becoming entrapped inside cavities during the welding process.
3. Incomplete penetration #
Incomplete penetration will appear on a radiograph as discontinuous or constant. They tend to be of uniform width and occur in the center of the weld. It is caused by the weld metal failing to fill in the root gap.
4. Fusion Defects #
A lack of fusion will appear on a radiograph in the form of a dark, thick line. It might also display as wavy and diffused, depending on how the defect is introduced in terms of the radiation beam. The flaw is caused by the weld metal failing to ruse with the previously deposited weld metal or the parent metal. When sidewall fusion is lacking, the radiographic image will display the appearance of a dark, narrow band running parallel with the weld bead.
5. Cracks #
Cracks will appear on a radiograph as jagged, straight, or sharp lines that have tapered ends. Cracks might appear in transverse or longitudinal directions. Cracks might occur in heat-affected zones and in the weld. This effect is caused by the weld metal rupturing during the solidification process due to fracture or shrinkage when cold, from poor handling, or uneven stresses.
6. Undercuts #
Undercuts will appear on a radiograph as dark lines with uneven width along the weld's edge. The defect is caused by a channel or groove being formed on the base metal's surface on the weld bead toe due to a high temperature.
7. Burn-through #
Burn-through will appears on a radiograph as an elongated, round, or dark area with a lighter ring surrounding it. It is caused by metal from the weld root melting or through a backing strip.
8. Icicles #
Icicles will appear on a radiograph as rounded white, secluded indications, irregularly and with a dark, small spot in the middle. Fused weld metal droplets that extend beyond the weld's roo cause this defect.
9. Tungsten inclusions #
Tungsten inclusions will appear on a radiograph in the form of white areas of uneven or round shape, either in a bunch or segregated. They are acquired by tungsten particles becoming trapped inside the weld metal. The particles are pieces that have broken off of the tungsten electrode.