EN 1090-2 Weld Inspection — Visual, UT, MPI Methods for European Fabrication
Complete guide to weld inspection and non-destructive testing (NDT) per EN 1090-2:2018. Execution classes EXC1 through EXC4, acceptance levels B, C, D for weld imperfections, visual inspection, ultrasonic testing, magnetic particle inspection, and practical European fabrication quality requirements.
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Execution Classes — EN 1090-2 Table 1
| Class | Description | Typical Structures | NDT Requirements |
|---|---|---|---|
| EXC1 | Basic — non-structural | Agricultural buildings, light poles | None |
| EXC2 | Standard — most buildings | Office buildings, industrial halls | Visual only |
| EXC3 | Higher — critical structures | Bridges, high-rise, stadiums | Visual + UT/MPI |
| EXC4 | Special — extreme structures | Nuclear, offshore, seismic-critical | Full NDT |
Most building structures in Europe are EXC2 or EXC3. EXC4 is rare and typically specified only for special structures.
Weld Quality Levels — EN ISO 5817
EN ISO 5817 defines three quality levels for weld imperfections:
| Level | Description | Typical Application |
|---|---|---|
| B | Stringent | Fatigue-loaded, EXC4 structures |
| C | Intermediate | Standard buildings, EXC2/EXC3 structures |
| D | Moderate | Non-structural, EXC1 |
For EXC2 buildings, quality level C is typical. For EXC3 bridges, quality level B may be required.
Visual Inspection (VT) — EN 17637
Visual inspection is the primary NDT method and is required for all execution classes.
Visual Inspection Checklist
| Aspect | Acceptance Criterion (Level C) |
|---|---|
| Weld dimensions | Within ±10% of specified throat/size |
| Undercut (shallow) | ≤ 0.5 mm for t ≤ 10 mm, ≤ 1.0 mm for t > 10 mm |
| Undercut (deep) | Not permitted |
| Cracks (any type) | Not permitted |
| Surface porosity | ≤ 2% of surface area in any 100 mm² |
| Overlap | Not permitted |
| Excess weld metal (butt) | ≤ 1.0 mm + 0.1 × weld width |
| Excess weld metal (fillet) | ≤ 1.0 mm + 0.1 × a |
| Root concavity | ≤ 1.0 mm (butt welds) |
| Stray arc strikes | Not permitted on parent metal |
Ultrasonic Testing (UT) — EN ISO 17640
Ultrasonic testing is required for full-penetration butt welds in EXC3 and EXC4 structures.
UT Acceptance Criteria per EN ISO 11666 (Level C)
| Weld Thickness (mm) | Max Indication Length | Max Amplitude (compared to reference) |
|---|---|---|
| 8-15 | 5 mm | Reference level -4 dB |
| 15-30 | 8 mm | Reference level -4 dB |
| 30-60 | 12 mm | Reference level -6 dB |
| 60-100 | 18 mm | Reference level -6 dB |
UT is typically calibrated using a reference block with 3 mm side-drilled hole (SDH) per EN ISO 17640.
UT Coverage Requirements
| Execution Class | Butt Welds | T-joints (full pen) | Fillet Welds |
|---|---|---|---|
| EXC1 | None | None | None |
| EXC2 | 10% | None | None |
| EXC3 | 100% | 25% | 10% |
| EXC4 | 100% | 100% | 50% |
Magnetic Particle Inspection (MPI) — EN ISO 17638
MPI is used for detecting surface and near-surface cracks in ferromagnetic steel.
MPI Acceptance Criteria — EN ISO 23278 (Level C)
- Linear indications > 3 mm for t < 10 mm — not permitted
- Linear indications > 0.3 × t for t ≥ 10 mm — not permitted
- Rounded indications > 4 mm — not permitted
- Any crack indication — not permitted
MPI is particularly important for:
- Weld toes of cruciform joints
- Tack welds incorporated into final welds
- Root passes of butt welds (with MPI access)
- Flame-cut edges in tension zones
Radiographic Testing (RT) — EN ISO 17636
RT is an alternative to UT for butt welds, typically used where UT geometry is difficult.
| Method | Standard | Typical Application |
|---|---|---|
| X-ray (film) | EN ISO 17636-1 | Shop fabrication |
| X-ray (digital) | EN ISO 17636-2 | Shop and field |
| Gamma ray | EN ISO 17636-1 | Site, confined spaces |
RT is slower and more expensive than UT but gives a permanent record (radiograph). UT is preferred for shop fabrication in European practice.
Inspection Personnel Certification
All NDT personnel must be certified per EN ISO 9712:
| Level | Capability | Supervised By |
|---|---|---|
| 1 | Perform specific NDT under supervision | Level 2/3 |
| 2 | Perform and interpret NDT, report results | Level 3 (admin) |
| 3 | Develop procedures, train, approve Level 1/2 | — |
For EXC3 structures, UT must be performed and interpreted by Level 2 personnel. For EXC4, Level 2 with specific product endorsement is required.
Frequently Asked Questions
What NDT is required for a standard steel building frame per EN 1090-2?
For a standard EXC2 steel building frame, EN 1090-2 requires visual inspection (VT) of all welds — no ultrasonic or MPI is required for routine connections. For EXC3 buildings (e.g., high-rise > 50 m, theatres, stadiums), full UT coverage of butt welds and partial MPI of T-joints is required per Table 26.
What is the acceptance level for weld imperfections in building structures?
For EXC2 building structures, use EN ISO 5817 quality level C as the acceptance criterion. Level C allows minor imperfections (undercut ≤ 0.5 mm, limited porosity) but prohibits cracks, incomplete fusion, and lack of penetration. For EXC3 and EXC4, level B (stringent) applies.
Related Pages
- Welding Procedure — EN 1090-2 WPS requirements
- Weld Capacity — Fillet weld per EN 1993-1-8
- Weld Symbols — EN 22553 weld symbols
- All European References
Educational reference only. NDT requirements per EN 1090-2:2018. Acceptance criteria per EN ISO 5817. Verify execution class and NDT scope per project specification. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent verification.
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