ISO 6520-1 group 3 · Solid inclusions
ISO 6520-1 reference 3041 is a fragment of electrode shed into the pool during GTAW. Cause matrix, why radiography reads it with unusual clarity, and the standards that govern acceptance.
Tungsten inclusion is specific to a single process family: it only occurs where a non-consumable tungsten electrode is in use, almost always GTAW, including the GTAW-based deposition processes used in wire-arc additive manufacturing. Reference 3041 sits under 304, metallic inclusion, alongside copper (3042) and other metals (3043).
Every cause traces back to the electrode tip failing mechanically or thermally: dipped into the pool, overloaded for its diameter, ground wrong, started by contact instead of high frequency, or left contaminated after a previous event. None are pool-chemistry causes the way porosity or slag inclusion are, so the prevention list reads as an equipment and technique checklist rather than a process-window one.
It is also the one solid inclusion radiography reads with unusual clarity: tungsten’s density against the surrounding weld metal produces a sharp, well-defined indication, unlike the softer signature typical of slag or a gas pore.
See reference 301, slag inclusion, the process-window relative, and reference 401, lack of fusion, the other buried planar imperfection GTAW root passes are prone to.
| Cause | Mechanism | Control |
|---|---|---|
| Electrode dipped into the pool or filler rod | Momentary contact between the tungsten tip and molten metal transfers a fragment of electrode directly into the weld. | Set and hold arc length from a measured value rather than by eye, and qualify a torch height that keeps clearance from the pool and the rod. |
| Current too high for the electrode diameter | An overloaded tip overheats, balls, and can shed particles into the arc column before it visibly fails. | Match electrode diameter and type to the qualified current range instead of pushing one electrode across a wider window. |
| Electrode ground on the wrong wheel or to the wrong geometry | A wheel shared with other materials, or a grind angle that leaves a ragged tip, both increase the chance of a fragment breaking free in service. | Dedicate a grinding wheel to tungsten and qualify a taper angle, then check it against the qualified geometry, not by eye. |
| Contact starting instead of high-frequency or lift-arc starting | Scratch-starting the electrode against the workpiece stresses and can fracture the tip at the exact moment the arc initiates. | Use the starting method the equipment and procedure specify; treat a change of starting method as a procedure change, not a convenience. |
| Contaminated or oxidised electrode tip | A tip that has already picked up base metal or has oxidised in air becomes brittle and sheds more readily under thermal cycling. | Re-grind or replace a discoloured or contaminated tip before the next run rather than continuing on it. |
The column that matters most is the last one. An inspection family marked as not finding this imperfection will not find it however carefully it is applied, and planning around that is cheaper than discovering it during a final examination.
| Family | Method | Capability | What it sees |
|---|---|---|---|
| Visual | Visual testing to ISO 17637 | Limited | A surface fragment can sometimes be seen as a bright, hard spot. A fragment carried under the bead is not visible at all. |
| Thermal | In-process infrared thermography | Limited | Tungsten does not melt into the pool, so it leaves a weaker thermal signature than a gas or slag defect. Treat a thermal anomaly here as a prompt to review the pool footage, not as confirmation. |
| Camera | High-speed weld pool imaging | Supporting signal | Can capture the actual dip or contact event, and an operator reviewing footage after a reported inclusion can often find the moment it happened. |
| NDT | Radiographic testing to ISO 17636 | Primary route | Tungsten's high density gives it strong, unambiguous radiographic contrast against the surrounding weld metal, which is why radiography is the standard route for this specific inclusion. |
Therness pages never reproduce a standard's acceptance values: those tables are copyrighted and belong in the copy you hold. What follows is the pointer — which document governs, and which part of it to open.
| Standard | Clause topic | Note |
|---|---|---|
| ISO 5817 | Quality levels for inclusions, indexed by ISO 6520-1 reference number | Tungsten is a metallic inclusion under 304; check which inclusion row the quality level applies to it before grading. |
| API 1104 | Acceptance for pipeline girth welds, assessed by radiographic interpretation | Pipeline acceptance is its own regime; do not carry a structural criterion into it. |
Most weld imperfections are produced by conditions that exist while the arc is running. Therness records those conditions on every weld, so a suspect run is known on the shift that made it rather than in a batch report.
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