Thickness Range After a Single-Sided Butt Weld
A fabricator qualifies a welder under EN ISO 9606-1 using a mechanised 135 (MAG) test piece welded in a single pass from one side only, with a nominal plate thickness of 10 mm. The test piece passes visual, radiographic and bend testing. The production department now wants to use this welder on three jobs: (a) a 6 mm butt weld in the same material group, (b) a 16 mm butt weld in the same material group welded from both sides, and (c) a 4 mm fillet weld. The welder's qualification is being written up as a single entry on the certificate. The QA engineer asks you to state exactly what the qualification covers, and whether any of the three jobs requires a new test.
1. For the single-sided, single-pass 10 mm butt weld (process 135), what is the qualified thickness range for butt welds, and why?
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Under EN ISO 9606-1, a test piece welded from one side only in a single pass qualifies a thickness range of t to 2t (i.e. 10 mm to 20 mm) for butt welds. The lower limit is not reduced to 0.5t because that concession applies only where the test piece is welded from both sides (or with a backing that is subsequently removed). So the qualified range is 10–20 mm.
Consequence: job (a) at 6 mm falls below the qualified minimum and is not covered; job (b) at 16 mm falls inside 10–20 mm and is covered, even though the production weld is made from both sides - the qualification is more demanding (single side, no backing), so it extends to the easier case.
2. Is the 4 mm fillet weld covered by this butt-weld qualification?
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No. A butt-weld test does not automatically qualify fillet welds. Fillet welds require a separate fillet test piece (or a butt test piece that also includes a fillet, if the standard's test assembly permits it). The 4 mm fillet weld therefore requires a dedicated fillet qualification, with its own thickness/leg-length range.
Practical outcome: the certificate must show the butt range (10–20 mm) and a separate fillet entry, or the fillet job must be qualified before production.
3. Summarise the certificate entries and the action required for each of jobs (a), (b) and (c).
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| Job | Thickness / type | Covered? | Action |
|---|---|---|---|
| (a) | 6 mm butt, same group, single side | No - below 10 mm minimum | New butt test at a lower thickness, or a both-sides test to obtain the 0.5t lower limit |
| (b) | 16 mm butt, same group, both sides | Yes - within 10–20 mm | None; proceed |
| (c) | 4 mm fillet | No - butt test does not cover fillet | Dedicated fillet test piece |
Certificate entry: 135, butt, single side, t = 10 mm, qualified 10–20 mm; fillet: not qualified. The lesson is that the welding condition (one side, one pass) sets the lower limit, and butt and fillet qualifications are separate.