Welding 1G 2G 3G 4G: What the Position Codes Mean
The codes welding 1G 2G 3G 4G describe where a groove weld sits in space, not how strong it is. This page explains each position, the plate and pipe variants, and the shop conditions that decide which one a part falls into.
Welding 1G 2G 3G 4G: what the G and the number stand for
A position code has two parts. The letter tells you the joint type: G for a groove weld, F for a fillet weld. The number tells you where the weld axis sits relative to the welder and to gravity, from flat through overhead. When someone asks about welding 1G 2G 3G 4G 5G 6G, they almost always mean groove welds on a qualification test, not a production weld drawing.
The scale runs from easiest to hardest. 1G is flat, done on a bench with the metal lying down. 6G is a pipe fixed at 45° that the welder cannot rotate. Position is about access and gravity, not about the alloy or the process. A 6G coupon in carbon steel and a 6G coupon in stainless use the same geometry.
These codes come out of the ASME and AWS qualification systems. They exist so that a procedure qualified in one shop can be reviewed in another. If your drawing calls out a position, it is telling the welder how the part will be held, not how the joint is designed.
One caution. Position codes do not appear on most production drawings for machined parts. They show up on weld procedure specifications (WPS), procedure qualification records (PQR) and welder certificates. If you are reading a print and see 3G, look for the WPS number next to it.
The six positions and the conditions that define them
1G is a flat groove weld. The weld axis is horizontal or nearly so, and the welder works from above. Gravity pulls the molten pool into the joint, which is why this is the position every welder learns first. On plate, the coupon sits flat on a table. On pipe, the pipe is rotated so the weld stays at the top.
2G is horizontal. The plate stands vertical, the weld axis runs horizontal, and the welder works on the face of the joint from one side. The pool wants to sag downward, so travel speed and weave width matter more than in 1G. This is the position where most porosity and undercut problems first appear.
3G is vertical. The weld axis is vertical and the plate stands up. The welder travels either uphill or downhill. Uphill gives deeper penetration and is the default for structural work; downhill is faster but shallower. Both need tighter heat input control than 1G or 2G.
4G is overhead. The welder works from below with the pool hanging. Drop-through and burn-through are the main risks, so current is usually reduced and the arc kept short. Shops often run 4G only on thin sections or with a backing strip.
5G and 6G apply to pipe. In 5G the pipe axis is horizontal and the pipe is fixed; the welder walks around it, covering flat, vertical and overhead in one pass. In 6G the pipe sits at 45° and is also fixed, which combines all of the hard positions in a single coupon. Both require the welder to reposition their body, not the part.
A short note on fillets. The same logic exists as 1F through 4F, with no 5F or 6F. Fillet welds do not have the same pipe test structure as groove welds. Do not mix the two families when you read a certificate.
What a position code does and does not tell you
A position code on a certificate is a claim about the welder, not about the part. It says the welder passed a test in that orientation with a given process, thickness range and filler metal. It does not say the welder can run that position on every alloy or every joint design.
Thickness matters. A welder qualified on 10 mm plate is not automatically qualified on 25 mm plate, because heat sink and pass count change. Most codes set a qualified thickness range, often from the coupon thickness up to twice it. Check the range before you schedule the work.
Process matters too. GTAW, GMAW, FCAW and SMAW each carry their own qualification. A welder who holds 6G in GTAW is not qualified in FCAW until tested separately. Shops that run several processes keep a matrix, not a single certificate.
For a machined part that also gets welded, the position question usually arrives late. A fixture that holds the part for 3-axis milling may not hold it for a 3G weld. If the weld is in the same setup, expect the fixture to be redesigned or the weld moved to a second operation.
This is where an early review saves money. We look at the weld callout, the part geometry and the available access before quoting. If the position forces a second fixture, that cost shows up in the quote rather than on the shop floor.
Why position drives fixture design on welded assemblies
Access decides position more than the drawing does. A joint that is 1G on the bench becomes 3G the moment it is welded into a frame that cannot be flipped. The geometry did not change; the handling did. Engineers who design for welding keep the joint reachable in at least one easy position.
Heat is the second constraint. In 3G and 4G, the pool is fighting gravity, so current is reduced and travel speed is raised. That lowers heat input and can lower penetration. On thick sections, a backing strip, a larger root gap or a different process may be needed to hold penetration without sagging.
Distortion is the third. Flat and horizontal welds cool more evenly than vertical and overhead welds, so they distort less. On a long frame, a 1G weld sequence with balanced passes usually holds flatness better than the same joint welded in 3G.
For machined-then-welded parts, plan the sequence. Weld first, then machine the critical faces, so the heat does not move a finished datum. If the weld must come after machining, leave stock and take a light finish pass after cooling.
We machine a lot of weld-ready components in 6061, 304 stainless and 4130 steel. The weld prep, the fit-up gap and the position all get reviewed before the first cut.
Position, orientation and what makes it hard
Groove welds, plate and pipe
| Code | Orientation | Main difficulty | Typical use |
|---|---|---|---|
| 1G | Flat, axis horizontal | Almost none; pool self-supports | Bench work, small frames |
| 2G | Plate vertical, axis horizontal | Sagging pool, undercut on the upper toe | Tanks, structural webs |
| 3G | Axis vertical, plate upright | Heat input control, uphill vs downhill | Column splices, pipe racks |
| 4G | Overhead, welder below | Drop-through, burn-through | Repair welds, thin plate |
| 5G | Pipe horizontal, fixed | Welder moves around part | Piping spools, qualification |
| 6G | Pipe at 45°, fixed | All hard positions in one pass | Pipe welder certification |
Pick the position before the process
If the joint can be rotated, design for 1G and 2G and take the lower cost and lower distortion. If it cannot be moved, accept 3G, 4G or 6G and budget for slower travel, tighter heat control and a fixture that holds the part fixed.
Common questions
Do 1G, 2G, 3G and 4G apply to fillet welds?
No. Fillet welds use the F series: 1F, 2F, 3F and 4F. The G series covers groove welds. The two families are tested and certified separately, so a certificate that lists 3G does not cover 3F work.
Some older documents mix the two by mistake. Check the joint type on the drawing before you match it to a welder certificate.
Is 6G harder than 5G?
Yes, in practice. In 5G the pipe axis is horizontal, so the welder can rotate around the pipe and keep a steady stance. In 6G the pipe is fixed at 45°, which forces the welder to change body position across the whole pass.
Both are fixed-pipe tests, but 6G combines flat, vertical and overhead in one coupon, so most codes treat it as the broader qualification.
Can a welder qualified in 3G weld a 4G joint?
Usually not. Position qualifications are specific to the orientation tested. A 3G certificate covers vertical groove welding, not overhead. Overhead needs its own test because the failure modes are different.
If a job mixes positions, list each one and check the certificate against the list. Shops often hold several positions on one welder.
Does the position code tell me the weld strength?
No. Position code and strength are separate. Strength comes from the joint design, the filler metal, the procedure and the penetration achieved. A 1G weld and a 6G weld with the same WPS can meet the same strength requirement.
Position affects how hard the weld is to make and how much defect risk it carries, not the design strength written on the drawing.
What thickness range comes with a position qualification?
It depends on the code and the coupon thickness. Most systems qualify from the coupon thickness up to about twice that thickness, with limits on the minimum as well.
Check the qualified range on the procedure qualification record before you assign the work. A welder qualified on thin plate may not be qualified on a heavy section.
Can you machine a part that will be welded in 6G?
Yes. We machine weld-ready parts in aluminium, stainless and steel, and we review the weld prep, root gap and fixture access during quoting. The position is part of that review.
If a fixed position forces a second fixture, we flag it before cutting so the cost is visible up front.
Send us the weld callout with the drawing
We review position, fixture access and weld prep before quoting, so the price you get matches the work on the floor.
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