What are ISO 5817 quality levels?

ISO 5817 defines three quality levels for fusion-welded joints: Level D (lowest/moderate), Level C (intermediate/standard), and Level B (highest/stringent). Each level specifies maximum permissible dimensions for various weld imperfections.

When should I specify quality level B?

Level B is required for highly stressed welds, fatigue-loaded structures, pressure vessels, and safety-critical components. It demands the smallest imperfections and highest quality. Level C is the default for general structural work.

What imperfections does ISO 5817 cover?

ISO 5817 covers: undercut, excess weld metal (reinforcement), linear misalignment, angular misalignment, incomplete penetration, porosity, slag inclusions, cracks (not permitted at any level), lack of fusion, and various surface imperfections.

How is undercut limit determined?

Undercut limits depend on the quality level: Level B allows ≤0.5mm (max), Level C allows ≤0.5mm (short) or ≤1mm, Level D allows ≤1.0mm. The actual limit also depends on plate thickness.

Are cracks ever acceptable per ISO 5817?

No. Cracks are not permitted at any quality level (B, C, or D) per ISO 5817. Any crack detected in the weld, HAZ, or base metal requires repair regardless of size.

Free Engineering Tool

Weld Quality Levels — ISO 5817

Check if a measured weld imperfection meets ISO 5817 quality level B, C, or D. Select imperfection type and enter the measured value.

ISO 5817Levels B / C / DFusion Welding

Acceptance Check

Level D (Moderate)

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Level C (Standard)

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Level B (Stringent)

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ISO 5817 Acceptance Limits (Simplified)

Imperfection	Level D	Level C	Level B
Undercut	≤1.0 mm	≤0.5 mm	≤0.5 mm
Excess reinforcement (butt)	≤2.0 mm	≤1.5 mm	≤1.0 mm
Linear misalignment	≤1.5 mm	≤1.0 mm	≤0.5 mm
Single pore	≤4.0 mm	≤2.5 mm	≤1.5 mm
Incomplete penetration	≤1.0 mm	Not permitted	Not permitted
Cracks	Not permitted at any level

These are simplified values for plate thickness 3–30 mm. Actual limits per ISO 5817 depend on plate thickness and may include percentage-based criteria.

Weld Quality Levels ISO 5817 Checker | Free Online Tool

Published by Nikolai Shelkovenko on February 15, 2026 February 15, 2026

Acceptance Check

ISO 5817 Acceptance Limits (Simplified)