Weld Quality Levels: B, C and D Under DIN EN ISO 5817

An inspection certificate for a welded assembly lists porosity and a slight edge misalignment, but the drawing never states an acceptable limit for either. Without a quality level set under DIN EN ISO 5817, there's no objective way to decide whether that weld actually passes.

In brief: DIN EN ISO 5817 defines three quality levels for fusion-welded joints in steel, nickel, titanium, and their alloys: B (strict), C (moderate), and D (relaxed). Each level sets limits on imperfections such as porosity, lack of fusion, or edge misalignment. Without a level specified in the requirements document or drawing, there's no basis for objectively judging a weld at acceptance.

What does DIN EN ISO 5817 cover?

DIN EN ISO 5817 sets quality levels for imperfections in fusion-welded joints in steel, nickel, titanium, and their alloys, covering both fully penetrated butt welds and fillet welds. The standard applies to various welding processes, including manual and automated procedures, with beam welding excluded.

It covers imperfections such as porosity, lack of fusion, undercut, edge misalignment, and excessive weld reinforcement. For each imperfection type, the standard sets maximum permissible values per quality level, often scaled to material thickness. The current 2023 edition replaced an older 2014 edition without changing the fundamental three-level system itself.

What quality levels does DIN EN ISO 5817 define?

The standard distinguishes three quality levels: B, C, and D. Level B sets the strictest requirements, level D the most relaxed. Level C sits in between as the moderate level most commonly specified in practice. The DVS (German Welding Society) publishes its own guidance on which level suits which application.

In our quality inspections at Far East suppliers, we regularly see that without a quality level fixed in the requirements document, the manufacturer welds to whatever level suits them, usually the most convenient one. Only a contractually agreed level creates a basis that can actually be verified on the finished part.

What imperfections does the standard evaluate?

The most commonly checked imperfections include porosity, lack of fusion, undercut along the weld flank, edge misalignment between the joined plates, and excessive weld reinforcement. For each imperfection type, the standard sets concrete limits per quality level, often scaled to material thickness.

A single pore doesn't automatically make a weld defective. Only once the size, clustering, or location of an imperfection exceeds the limit permitted for that quality level does the weld count as non-conforming. Lack of fusion, where two weld passes fail to fully merge, is judged considerably more strictly than isolated small pores, since it directly weakens the load-bearing cross-section of the weld.

Which test method actually catches a given imperfection depends on the defect type:

How is the quality level set for a component?

The right quality level depends on load, safety relevance, and the regulatory context of the component, not a blanket default. Safety-relevant or fatigue-loaded structures generally require level B, general structural steel usually level C.

For steel components subject to CE marking under the EU Construction Products Regulation, the execution standard EN 1090 additionally specifies the minimum quality level required per execution class. That requirement then determines the quality level to fix in the requirements document, rather than leaving it to the buyer's free choice. Where a component is sourced without that link to an execution class, choosing the quality level is genuinely a matter for negotiation between buyer and manufacturer and should be decided deliberately rather than left open.

In practice, a fixed sequence works well:

• Clarify load, fatigue exposure, and safety relevance of the component

• Check whether CE marking under EN 1090 dictates a minimum quality level

• Fix quality level B, C, or D bindingly in the requirements document or drawing

• Agree on the test method and scope used to demonstrate compliance

• Require proof of the achieved level on the inspection certificate

How is compliance with the quality level checked?

Checking is usually done through visual inspection of the accessible weld surface, supplemented by non-destructive methods such as radiographic or ultrasonic testing for internal defects. Which test method is used, and to what extent, should also be fixed in the requirements document rather than decided after production. The German Welding Society's own guidance covers practical inspection routines in more depth. The standard itself is also distributed internationally through national standards bodies such as Austrian Standards, underlining how widely it's applied across German-speaking markets.

In one of our sourcing projects, a manufacturer had cleared components as "defect-free" by their own judgment, without any quality level contractually agreed. A subsequent visual inspection during incoming goods inspection uncovered edge misalignment clearly exceeding level C's limits. Without a quality level fixed beforehand, arguing the defect with the manufacturer proved difficult.

On a complete 3.1 inspection certificate, stating the achieved quality level is therefore part of the minimum scope you should check before releasing payment. If that information is missing from the certificate entirely, that absence itself is a sign that no binding quality level was ever agreed or checked, and it should be clarified before release.

What applies if the drawing doesn't state a quality level?

If the drawing carries no specification, there's no default quality level that automatically applies under DIN EN ISO 5817, unlike general tolerances per ISO 2768, which do apply by default without a special note. The quality level has to be actively agreed, otherwise there's no yardstick for judging a deviation in the first place. In practice, the manufacturer tends to pick whichever interpretation suits them best in that situation, which rarely works in the buyer's favor if a dispute comes up at acceptance. That's even more true in multi-tier supply chains, where an intermediary passes welding work on to a subcontractor: without a quality level fixed in writing, the requirement almost always gets lost along the way, and by the end it's hard to trace who applied which standard.

Frequently Asked Questions

What is DIN EN ISO 5817?

DIN EN ISO 5817 is the standard that sets quality levels for imperfections in fusion-welded joints in steel, nickel, titanium, and their alloys. It distinguishes levels B, C, and D, giving you the yardstick needed to objectively judge a weld at acceptance in the first place.

What quality level do I need for my component?

That depends on load and safety relevance: safety-relevant or fatigue-loaded components usually need level B, general structural steel usually level C, and lightly loaded structures often level D. If the component falls under CE marking per EN 1090, the execution class fixes the minimum level for you.

When does a weld need to be inspected?

Whenever a quality level has been contractually agreed and compliance needs to be demonstrated, typically at acceptance or during incoming goods inspection. For CE-marked components under EN 1090, inspection is mandatory regardless of any separate contractual agreement.

How large can a pore in a weld be?

That depends on the agreed quality level and the material thickness. DIN EN ISO 5817 sets tiered limits that are considerably tighter for level B than for level D. Without both figures, a pore diameter documented on an inspection certificate can't be judged at all.

Conclusion: the quality level decides whether a weld gets accepted

DIN EN ISO 5817 only becomes a reliable yardstick once the right quality level, B, C, or D, is fixed in the requirements document rather than debated at acceptance. Clarifying that upfront avoids disputes over rework or rejection once the finished component arrives. That applies to a single welding job just as much as to full assemblies where several weld types carry different loads and can genuinely justify different quality levels within the same component.

Line Up supports you in setting the right quality level in your requirements document and in quality-checking welded assemblies from Far East manufacturing, from the initial specification through evaluating the inspection certificate. 👉 Schedule a no-obligation consultation.