Shipbuilding and marine fabrication
Weld monitoring for shipbuilding
High-volume welding under classification-society rules. The codes that apply, the four monitoring pain points that cost yards most, and which Therness signal addresses each.
ISO 6520-1 group 5 · Imperfect shape and dimension
Excess weld metal (ISO 6520-1 ref. 502): causes and detection
ISO 6520-1 reference 502 covers excess weld metal, reinforcement piled above the joint face. Cause matrix, why visual inspection leads, and the standards that set the acceptance limit for your material and code.
- ISO 6520-1 reference
- 502
- Group
- 5 — Imperfect shape and dimension
- Also called
- Excess reinforcement, Overfill
Excess weld metal is ISO 6520-1 group 5’s most forgiving-looking imperfection and also its easiest to over-correct. The reinforcement sits above the joint face rather than inside a discontinuity, so on a static structure it often reads as harmless: more metal, more strength. The danger is usually in the correction rather than the excess itself — an aggressive grind or a gouging pass to bring a proud cap flush can gouge into sound parent material, and the re-weld needed to fix that gouge adds a heat cycle the original joint never needed.
On cyclically loaded work the calculus changes. A steep transition from the reinforcement down to the parent surface is a stress concentration in its own right, closer in effect to a shallow notch than to extra load-bearing metal, which is why fatigue-governed codes profile the cap rather than only measuring its height above the plate.
The cause matrix is almost entirely a parameter story: travel speed, current and wire feed speed relative to each other. Watching those values per pass, rather than judging the bead by eye once the run is finished, catches a drifting procedure before a full pass has to be ground back and re-qualified.
Typical causes
| Cause | Mechanism | Control |
|---|---|---|
| Travel speed too slow for the current or wire feed speed set | More filler is deposited per unit length than the joint needs, and the excess sits on top of the joint rather than tying into the sidewalls. | Measure travel speed against the qualified procedure; on manual work it is the parameter most likely to drift as a welder chases a full-looking bead. |
| Wire feed speed or current above the qualified range | More filler arrives per unit time than the arc can spread into a flat profile, and it builds up as reinforcement instead. | Log wire feed speed and current per pass against the qualified window rather than the panel dial setting. |
| Multiple passes with no dressing between them | Each additional pass adds height without removing the crown left by the one before it, especially on a wide multi-pass groove. | Grind or dress cap passes to a consistent profile and treat the pass sequence as part of the procedure, not an operator preference. |
| Joint gap or bevel angle wider than designed | A wider groove needs more filler to fill flush, and filling it flush leaves more metal above the surface than a narrower joint would. | Control fit-up to the qualified tolerance; a widening trend across a batch is a fixturing problem, not a series of unrelated welds. |
Detection: which route finds 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, with weld profile gauges | Primary route | The imperfection sits on the surface and is directly measurable, which is why every code treats visual inspection as the intended route here. |
| Thermal | In-process infrared thermography | Supporting signal | A growing bead width and height changes the cooling footprint pass to pass, which flags a drifting parameter before the cap is finished. |
| Camera | High-speed weld pool imaging | Supporting signal | Shows the pool building up faster than the arc advances, which is the moment travel speed can still be corrected. |
| NDT | Radiographic and ultrasonic testing to ISO 17636 and ISO 17640 | Limited | Neither method targets a shape imperfection with no volumetric or planar discontinuity; extra weld metal, if anything, complicates reading whatever lies beneath it. |
Where acceptance is defined
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 excess weld metal, indexed by ISO 6520-1 reference number | The permitted profile depends on the selected quality level and on weld width. Read it in the standard. |
| AWS D1.1 | Visual acceptance for weld reinforcement profile on structural steel | The structural code profiles the cap independently of ISO 5817's own criterion. |
| API 1104 | Reinforcement height acceptance for pipeline girth welds | Pipeline acceptance is assessed on its own terms, separate from structural criteria. |
| ISO 10042 | The equivalent quality levels for aluminium and its alloys | Use this instead of ISO 5817 whenever the parent material is aluminium. |
See the condition, not the consequence
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.
