Quality level

A quality level is a graded tier of acceptable weld imperfections, published by a standard rather than invented per contract. ISO 5817 defines several such levels for steel, nickel and titanium joints, and ISO 10042 defines the equivalent levels for aluminium — two standards covering the same concept for different material families rather than one standard covering everything. Each level allows progressively less of a given imperfection type, such as porosity or lack of fusion, for a stricter level than for a more permissive one. The levels exist so a designer, a fabricator and an inspector can agree on one acceptance criterion by naming a level rather than by re-deriving it for every job.

Choosing a level is a design decision, not an inspection decision: it depends on the loading, the consequence of a defect going undetected, and often the governing product standard or client specification, and it is set before welding starts, not after a weld is made and then judged against whichever level it happens to pass. Once chosen, the level belongs in the WPS as one of the parameters the procedure has to satisfy, and the welder qualification test piece is judged against the same standard.

A quality level says nothing about a welder’s general skill or a procedure’s general soundness — it is scoped to specific imperfection types and specific inspection methods, and a weld can meet the required level for the imperfections that were actually inspected while carrying a different problem that inspection method does not detect. That scoping is why the level named in a specification always comes paired with the inspection methods required to verify it, rather than standing alone as a single pass/fail claim.