ISO 6520-1: Classification of Imperfections — Groups 1 to 6 with Examples
What is EN ISO 6520-1?
EN ISO 6520-1 (Welding and allied processes — Classification of geometric imperfections in metallic materials — Part 1: Fusion welding) is the reference standard for naming and coding imperfections detected in welding. It acts as the "dictionary" of welding imperfections.
For each imperfection it defines:
- Reference number (e.g., 100, 2011)
- Designation in English and French
- Technical description
- Illustrations (where applicable)
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The Six Groups of Imperfections
Group 1 — Cracks
Discontinuities produced by local rupture under the effect of stresses and/or temperature.
| Code | Designation | Typical location |
|---|---|---|
| 100 | Crack (general) | — |
| 101 | Longitudinal crack | In weld or HAZ |
| 102 | Transverse crack | In weld or HAZ |
| 103 | Radiating crack | Emanating from a point |
| 104 | Crater crack | At end of weld |
| 106 | Branching crack | In diverging branches |
Common causes: hydrogen in deposited metal, high residual stresses, fast cooling, high CE without preheat.
Group 2 — Cavities (Pores and Shrinkage)
Voids formed by trapped gases or shrinkage during solidification.
| Code | Designation | Form |
|---|---|---|
| 2011 | Isolated spherical pore | Spherical |
| 2012 | Uniformly distributed porosity | Multiple pores |
| 2013 | Localised (clustered) porosity | Grouped |
| 2015 | Surface pore | Open to surface |
| 2016 | Wormhole | Tubular, oriented |
| 202 | Shrinkage cavity | Contraction cavity |
Common causes: moisture in consumable or base material, insufficient shielding gas, excessive travel speed.
Group 3 — Solid Inclusions
Solid foreign matter trapped in the deposited metal.
| Code | Designation | Origin |
|---|---|---|
| 301 | Slag inclusion | Insufficient inter-pass cleaning |
| 302 | Flux inclusion | SAW/FCAW |
| 303 | Oxide inclusion | Contaminated surface |
| 304 | Metallic inclusion (W) | Tungsten electrode (TIG) |
Group 4 — Lack of Fusion and Penetration
Absence of metallurgical bonding between passes or between weld and base material.
| Code | Designation | Location |
|---|---|---|
| 401 | Lack of side-wall fusion | Groove face |
| 402 | Lack of inter-run fusion | Between overlapping beads |
| 403 | Lack of root fusion | Joint root |
| 4021 | Incomplete root penetration | Root |
Severity: Group 4 imperfections are generally unacceptable at any quality level of EN ISO 5817.
Group 5 — Incorrect Shape and Dimensions
Deviations from the prescribed geometry of the welded joint.
| Code | Designation |
|---|---|
| 501 | Undercut |
| 502 | Excess weld metal (butt) |
| 503 | Excess weld metal (fillet) |
| 504 | Excessive convexity |
| 506 | Root concavity |
| 507 | Linear misalignment |
| 508 | Angular misalignment |
| 515 | Incompletely filled groove |
Group 6 — Miscellaneous Imperfections
All imperfections not included in groups 1 to 5.
| Code | Designation |
|---|---|
| 601 | Arc strike |
| 602 | Spatter |
| 603 | Torn surface |
| 610 | Temper colour (oxidation) |
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Relationship with EN ISO 5817
EN ISO 6520-1 classifies imperfections. EN ISO 5817 evaluates their acceptability (dimensional limits by quality level B, C, D). Both standards are complementary and inseparable in inspection practice.
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How to Use in Inspection
- Detect the imperfection (VT, RT, UT, PT, MT)
- Identify the group and EN ISO 6520-1 code
- Measure relevant dimensions (length, width, depth)
- Compare with EN ISO 5817 limits for the specified quality level
- Accept or reject — record in report with standard code
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