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EN ISO 5817, acceptance criteria and test methods
No weld is perfect – there will always be small irregularities. The question is not whether there's anything, but whether what there is falls within what the requirements allow. For that purpose there are standardized quality levels and control methods that make 'good enough' measurable.
The standard EN ISO 5817 defines quality levels for irregularities in fusion-welded joints in, among other things, steel. It defines three levels – designated B, C, and D – where B is the strictest and D the mildest. For each type of irregularity, the standard specifies how much may be accepted at each level.
The current edition is ISO 5817:2023 (4th edition). It applies to fusion-welded joints in steel, nickel and titanium. Aluminium has its own standard, ISO 10042.
| Level | Meaning |
|---|---|
| B | Strictest requirements — minimum allowed irregularity |
| C | Mid-level |
| D | Mildest of the three — largest allowed irregularity |
The first and most widespread inspection is the visual (VT): you look at the seam with your eye, possibly with a magnifier and measuring tool. Many errors — surface porosity, burn-through, poor seam shape, lack of root penetration on accessible sides — can be caught visually if you know what to look for.
When the requirements are higher, or errors can lie hidden inside the seam, non-destructive testing is used, where the part is examined without being destroyed. The methods supplement each other: some find surface defects, others find defects inside the material.
With destructive testing, the workpiece is destroyed to examine the weld's properties — for example by bending, pulling or cutting it open and looking at the cross-section. It is used among other things for qualifying procedures and welders, where you want to prove the strength and quality of a representative sample.
It is not always best to choose the strictest level. A higher requirement costs more in time, preparation and control, and if it is not necessary for the structure's safety, it is waste. The designer chooses the level based on load and consequence, and the welder performs it — neither more nor less.
For the welder control is not just a judgment but a source to become better. Each identified irregularity points back to a cause in preparation setting or technique. The one who uses the control results to adjust their work quickly raises their own quality level.