Plate Certification Does Not Cover a Fixed Pipe
A shop is awarded a contract for 6 in. NPS Schedule 40 carbon steel pipe spools. The joints are to be welded in the 5G position, with the pipe axis horizontal and the pipe fixed, using a GTAW root and SMAW fill and cap. The only available welder holds a current qualification: AWS D1.1, SMAW, 3G and 4G, 3/8 in. plate, E7018. He has 15 years of plate experience and has never welded pipe. Production starts in two days, and the customer will not accept a schedule delay. The pipe can be rotated on powered rolls if the procedure permits it.
1. Can the welder produce the 5G pipe joints under his current qualification? Explain what the qualification does and does not cover.
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No. His qualification covers SMAW on 3/8 in. plate in the 3G and 4G positions only.
Key points:
- Product form is an essential variable. A plate test does not qualify pipe. Pipe welding adds curvature, a closing root gap, and a fixed root that plate does not reproduce.
- Position is an essential variable. 3G plate is not equivalent to 5G pipe. In 5G the pipe axis is horizontal and the weld is made around a fixed circumference, including the overhead and vertical segments.
- Process is an essential variable. His SMAW qualification does not cover the GTAW root called for by the procedure.
Producing production pipe welds under this qualification would be a code violation regardless of his plate experience.
2. What practical options does the shop have to avoid a delay? Rank them and state the trade-offs.
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Options, roughly in order of practicality:
- Qualify the welder immediately on a pipe test. A 5G or 6G test on the production pipe size can be run and evaluated within two days. This is the cleanest route if a test coupon and inspector are available.
- Qualify him for GTAW root and SMAW fill on pipe simultaneously. If the production procedure uses both processes, the test must demonstrate both; a single SMAW pipe test does not cover the GTAW root.
- Rotate the pipe on rolls and weld in 1G, if the procedure and the customer's specification permit it. This changes the position and still requires a 1G pipe qualification, but the test and production are easier. Do not assume rotation is allowed without written acceptance.
- Subcontract to a welder already qualified for 5G pipe with GTAW root. Fast, but adds cost and may need customer approval.
Using him unqualified, or calling the plate test 'close enough,' is not an option.
3. If the shop decides to qualify him once on a 6G coupon, what does that buy compared with a 5G test, and what limits remain?
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- 6G is the broadest position test for pipe. It places the pipe at 45 degrees and fixed, so the welder must weld in all positions around the circumference. It typically qualifies him for 1G, 2G, 5G, and 6G within the code's rules.
- 5G is narrower. It covers fixed horizontal pipe but generally does not extend to 6G or to vertical pipe axes.
- Limits still apply: the test qualifies only the process(es), filler classification, and the thickness and diameter ranges permitted by the code. A test on 6 in. pipe may not qualify small-diameter pipe below the code's minimum, and a GTAW root must be included if production uses it.
- Continuity and records: the qualification must be documented and kept current.
The 6G test is the better investment if the shop expects varied pipe work.