Essential Variables and Qualification Ranges
The variables that define the envelope
A welder qualification is only valid within a range. The essential variables are:
- Process (and any combination).
- Base material group (e.g. carbon steel, stainless, aluminium - grouped by the standard's material grouping).
- Consumable (electrode/wire type and, in some cases, brand/classification).
- Position (PA, PB, PC, PD, PE, PF, PG per EN ISO 6947) and welding direction (uphill/downhill).
- Thickness of the test piece and the qualified thickness range.
- Joint type (butt, fillet, branch, etc.) and pipe vs plate.
- Welding current type/polarity where relevant.
How ranges work
Qualifying on a thicker test piece generally qualifies a range downward but not indefinitely upward; qualifying on a pipe may qualify plate and pipe within limits; qualifying in a higher position often covers lower positions but not vice versa. The exact numeric ranges are in the relevant part of EN ISO 9606 - learn the principle, then check the table.
Traps
- Assuming a thicker test piece qualifies unlimited thickness - it does not.
- Assuming a pipe test automatically qualifies plate - check the rule; usually pipe covers plate, not the reverse.
- Ignoring direction: a vertical-up qualification may not cover vertical-down.
- Confusing base-material group with exact grade - grouping allows some substitution but not all.
Rule of thumb
The harder the test (thicker, higher position, more difficult joint), the wider the range it grants. If a question asks "does qualification X cover job Y?", compare each essential variable systematically.
Worked example
A welder qualifies on 8 mm plate, butt joint, PF (vertical up), 111. A job requires 5 mm plate, butt, PA. Thickness 5 mm is within the downward range of 8 mm; PA is a lower position than PF; same process and joint. Likely covered - but verify against the table, not intuition.