Tungsten inclusion: what it is and how to spot it

Use this diagram

Copy this HTML to show the diagram with a credit link<img src="https://filletgauge.com/charts/weld-discontinuities/tungsten-inclusion.svg" alt="Two views of a tungsten inclusion. A: a groove weld cross-section with a small angular black chip in the GTAW root pass. B: a radiograph strip where two small spots are brighter than the weld band and one round spot is darker" width="100%"><p><a href="https://filletgauge.com/guides/tungsten-inclusion?utm_source=embed&amp;utm_medium=referral&amp;utm_campaign=figure_embed&amp;utm_content=tungsten-inclusion.svg">Tungsten reads light on film; a gas pore reads dark. Original drawing, not to scale. by Fillet Gauge</a></p>

How to recognize a tungsten inclusion

1. Start with the process. Only GTAW and plasma arc use a tungsten electrode. A tungsten inclusion in an SMAW cap pass would be a puzzle; in a GTAW root it is a known risk.
2. Look at the radiograph. Tungsten is much denser than steel, so it blocks more radiation and shows as a bright, sharp white spot on the film. Almost every other buried discontinuity, porosity and slag included, shows darker than the weld. That contrast is the tell.
3. Expect it to be small. Inclusions are usually tiny fragments, single or in a small group, often near where the arc was started or where the welder dipped the electrode.
4. On a cut section, it is a small, hard, metallic particle that doesn't etch like the weld around it.

How it is found

You won't usually see tungsten on the surface, because the particle sinks into the pool. Radiography is the method that finds it reliably. On a finished weld, a visual inspector's clue is indirect: a contaminated, discolored spot where the welder touched down, or a weld that was stopped and restarted after a dip. When a governing document addresses inclusions, it usually treats tungsten with the other inclusion types, so read your document rather than guessing.

Common mix-ups

• Tungsten or porosity on film. Bright is tungsten, dark is gas. Getting the brightness backwards is the classic slip.
• Tungsten or slag. Slag needs flux, which GTAW doesn't use, and shows dark on film. Tungsten is bright and comes from the electrode.
• Tungsten or spatter. Spatter sits on the plate surface. Tungsten is inside the weld.

Why it forms

The electrode dips into the pool or touches the filler wire. The welder uses a scratch start instead of a high-frequency or lift-arc start. The current is too high for the electrode size, so the tip melts and drops. The tip was ground poorly and splits. Each cause points to its fix: keep a steady arc length, start the arc without contact, and match the electrode to the current.

Tungsten inclusions on the CWI exam

On Part A, tungsten inclusions tie together two areas: Joining and Cutting Processes, at least 14%, where GTAW is covered, and NDE Fundamentals, at least 8%, where you read what radiography shows. On Part B they fit Welding Inspection and Discontinuities and NDE Application whenever a radiograph or report is in front of you. On Part C, look up how your code's radiographic criteria handle inclusions.

Practice it

Drill bright-versus-dark film reads in the NDE methods quiz. Then compare tungsten with the other trapped materials: slag inclusions and gas in weld porosity. Every type is listed in the weld discontinuities guide.

Check the rest of Part B

Take the free 10-question check. It's weighted to the Part B outline, scored by domain and needs no signup, so you see whether NDE reads or another domain costs you the most points.

Sources

Show the list

• What is Tungsten Inert Gas (TIG or GTA) Welding? (Job Knowledge 6), TWI. Retrieved 25 Oct 2026.
• CWI Part A Fundamentals Examination Information, American Welding Society, Rev. 03.01.2024. Retrieved 20 Oct 2026.
• Discontinuity names follow AWS A3.0, Standard Welding Terms and Definitions. Every description here is our own wording.