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EN ISO 5817 quality level C, and what it means for your seams
Level C is what EXC2 asks for. It is not a grade of steel, not a coating class, and not an instruction to make the weld look nice. It is a table of limits.
EN ISO 5817 is the standard that says how much imperfection a fusion-welded joint in steel is allowed to carry. It sets three quality levels: B, the most stringent, C in the middle, and D the most permissive. Nothing else about the weld is in it. It does not tell you the process, the consumable, the sequence or the preheat; it tells you what the finished seam is allowed to look like.
EN 1090-2 connects the two standards. Execution class EXC2 is assigned quality level C, EXC3 and EXC4 get level B, and EXC1 gets level D. So when a fabricator says "EXC2, level C", the second half is not an extra claim: it is what the first half already implies.
What the level actually controls
The standard works through the imperfections that occur in real welding and puts a limit on each: undercut, excess weld metal, excess penetration, incompletely filled groove, root concavity, porosity, inclusions, lack of fusion, cracks. Most of the limits are expressed relative to the material thickness rather than as one absolute number, which is why a limit that is generous on 20 mm plate is tight on 4 mm.
Two things stay the same at every level. Cracks are not permitted at any level, in any of the three. And a weld that is inside the table is acceptable whether or not it is handsome. The standard is about function, not about appearance, and a supplier who grinds every seam smooth is spending your money on something the standard never asked for.
What it is not
- Not a steel grade. Level C has nothing to do with S235 or S355, or with any material property.
- Not a coating or surface class. That is EN ISO 8501 for preparation and the paint specification for the system.
- Not a tolerance class. Straightness, flatness and dimensional deviation are EN ISO 13920 and the geometric tolerances of EN 1090-2, a different subject entirely.
- Not a testing method. How the weld is examined is EN ISO 17637 for visual testing and the relevant standard for each non-destructive method.
What to put on your drawing
If level C is right for the part, you do not have to write anything: it follows from EXC2. The case worth thinking about is the seam that needs more. A fatigue-loaded weld, a joint that a crack would propagate from, a seam that will be machined afterwards and must be sound to the root: these can justify level B, and the right way to ask is to mark the specific seams on the drawing rather than raising the whole part.
Blanket level B on a complete frame is one of the more expensive lines a drawing can carry. It raises the inspection extent, it raises the rework rate, and on most of the seams it buys nothing, because most of the seams were never the ones carrying the load that mattered. Marking four welds costs a fraction of marking forty.
How it is checked here
Every weld is inspected visually, and what was inspected and what was found is recorded. Non-destructive testing beyond that is done on request or where the drawing calls for it. Our welding quality system is certified to EN ISO 3834-2, and EN ISO 5817 is one of the documents named in that certificate scope alongside EN ISO 15609-1, EN ISO 15614-1, EN ISO 17662 and EN ISO 13920.
If your drawing calls for a level, a testing extent or an acceptance criterion that is not the standard one, put it on the drawing rather than in the email. The drawing is what reaches the welding coordinator; the email is not.