Discontinuity
Tungsten inclusion
A fragment of tungsten electrode broken off into the weld pool during gas tungsten arc welding, leaving a hard, brittle, very dense particle embedded in the deposit.
TitleTungsten inclusion
ClassInclusion
ViewIndicative
What it looks like
- Small, irregular, angular particles rather than the smooth outlines of gas or slag
- On film, distinctly bright white spots because tungsten is far denser than steel and blocks radiation
- May be visible on the weld surface as a hard grey speck that resists filing
- Frequently found near an arc start where the electrode touched down
Why it happens, and how it is stopped
Causes
- Touching the tungsten electrode into the weld pool or the filler rod while welding
- Excessive current for the electrode diameter, melting and spitting the tip into the puddle
- Scratch starting instead of using a high-frequency or lift start, breaking the tip on contact
- A split, contaminated, or improperly ground electrode tip shedding fragments in the arc
- Loss of shielding gas allowing the hot electrode to oxidise and crumble
Prevention
- Maintain arc length so the electrode never contacts the pool or the filler wire
- Match electrode diameter and type to the current being used, and grind the tip properly
- Use high-frequency or lift arc starting rather than scratching the electrode on the work
- Grind away any contaminated tip completely before restarting after a dip
How it is found
Which examination methods can see it, and what it is about the discontinuity that makes them able to.
- RTTungsten's high density makes it one of the few discontinuities that appears lighter than the surrounding weld on film, so it is unmistakable.
- VTA tungsten particle sitting at or near the surface can be seen and felt during in-process inspection of the root or fill passes.
- UTThe particle is a small, hard reflector with a sharp acoustic mismatch, giving a compact echo distinct from the softer response of slag.
How inspectors think about it
- Tungsten particles are rounded rather than planar, so they are generally weighed on size and quantity like other volumetric inclusions.
- The hardness and brittleness of the particle matter more than its bulk, because it can act as an initiation point in a deposit that is otherwise ductile.
- Its unmistakable bright appearance on film means the discussion is almost never about identification, only about size, count, and location within the weld.
General reasoning only. The accept/reject limits for your work come from the code or specification governing the job, which this site does not reproduce.
Related discontinuities
Slag inclusionNon-metallic slag trapped inside the weld instead of floating to the surface, most often left in a corner or undercut of a previous pass and then buried by the next one.Oxide inclusionSurface oxide folded into the weld pool rather than broken up by the arc, most troublesome on aluminium where the oxide skin melts far above the metal it covers.Uniformly scattered porosityRounded gas pockets frozen into the weld metal and spread fairly evenly through the deposit, rather than bunched together or lined up, showing that shielding or cleanliness was marginal for the whole pass.Arc strikeA small localised melted spot where the arc touched the base metal outside the joint, quenched instantly by the surrounding cold plate into a hard, brittle, crack-prone patch.