Quality Level
The quality level is a standardized classification according to ISO 5817. It defines how large weld imperfections may be without the weld failing. The higher the loading of the component, the stricter the quality level.
Physicochemical Mechanism of Action
The quality level does not change any material. It is a set of rules. It assigns to each weld an allowable imperfection size. These imperfections act like notches. Large notches concentrate stress and reduce load-bearing capacity.
Metallurgical Relevance & Risks in Welding
If the welder chooses too lenient a quality level, the weld may have oversized pores, lack of fusion, or undercut. These imperfections reduce the load-bearing cross-section. Under dynamic loading, cracks start at these notches. Under static loading, the weld may fracture brittlely. The quality level does not specify hardness or strength. Hardness is determined by cooling rate and alloy.
Workshop Practice & Instructions
ISO 5817 defines three quality levels: B (highest requirement), C, D (lowest requirement). For dynamically loaded components or pressure vessels, the standard requires B or C. For statically loaded components, D is often sufficient. The required quality level is specified on the drawing or welding procedure specification. Example pore limit: In level B, a single pore may be at most 0.1 × plate thickness, maximum 3 mm. In level D, it is 0.3 × plate thickness, maximum 5 mm. Imperfections exceeding the limit must be ground out and re-welded.