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# WHY DO LACK OF FUSION, LACK OF PENETRATION, AND SLAG INCLUSIONS OCCUR?
By definition, lack of fusion is described as the condition in which the deposited metal is not completely…
Tungsten inclusions are almost always associated with the GTAW process, which uses a tungsten electrode to establish the arc. If the electrode makes contact with the molten metal, the latter can solidify around the tip; when attempting to remove it, the tip can break off easily and become embedded within the weld metal if it is not removed by grinding.
Inclusions can also occur when the welding currents used are too high relative to those recommended for a particular electrode diameter. In such cases, the current density may exceed that necessary for the electrode to begin to break down, and its fragments are deposited in the weld metal. This can also occur if the welder incorrectly grinds or points the electrode tip.
If the grinding marks are oriented transversely to the electrode axis instead of being aligned longitudinally, they can become stress concentrators that could lead to electrode breakage, most likely at those points.
Other reasons why tungsten inclusions occur may include:
- Contact of the filler metal with the electrode tip while it is hot.
- Contamination of the electrode tip by spatter.
- Electrode extension greater than normal, resulting in overheating of the electrode.
- Inadequate shielding gas flow, resulting in oxidation of the electrode tip.
- Improper shielding gas.
- Defects in the electrode such as cracks.
- Excessive current for the electrode size.
- Incorrect grinding or pointing of the electrode.
- Electrode too small.
Tungsten inclusions are normally found on the surface of the weld metal unless there has been no opportunity to inspect between passes to detect the presence of such inclusions. If this has not been possible, the only way to detect them is by radiography. Because tungsten is denser than steel and aluminum, it will appear as a bright, well-defined area on the radiographic film. It is essential to detect and correct this defect as early as possible, since it can act as a stress concentrator, triggering an energy release or a future crack. If the project is large in scope, carefully review the radiographic inspections, as this defect can cause severe damage to the welded joint.