Welding vertical down: when it is allowed and how to run it
A vertical-down weld runs fast and looks tidy, but it forgives far less than welding uphill. Below: when the technique is allowed, when it is not, and what settings to use.
When you weld downhill
Downhill is for thin plate up to roughly 4 mm, where welding uphill would burn through. The second case is the root run on transmission pipelines with cellulosic electrodes, where the downward direction is written into the procedure. The third is galvanised sheet and car body work, where speed and low heat input matter.
When you must not
Not on thick material and not on load-bearing structures. The pool runs ahead of the arc, penetration stays shallow, and under a good-looking bead sits lack of fusion that no eye will catch. Basic electrodes are not made for downhill: the slag overtakes the pool. If the WPS does not allow the downward direction, the WPS decides.
How to run it
Keep the arc short and aim it into the pool, never ahead of it. Hold the electrode at 70–80° to the plate with the tip pointing up, so the arc pushes the molten metal backwards. Travel fast and without weaving: every pause becomes an overlap. Take the current 10–15 % higher than for uphill on the same thickness.
Guide settings for a cellulosic electrode
| Thickness, mm | Electrode diameter, mm | Current, A |
|---|---|---|
| 1,5 | 2,0 | 55–75 |
| 2,0 | 2,5 | 70–95 |
| 3,0 | 2,5–3,2 | 90–120 |
| 4,0 | 3,2 | 110–150 |
| 5,0 | 3,2–4,0 | 130–170 |
Electrodes and wire
For downhill stick welding use cellulosic E6010 and E6011 or thin rutile electrodes. Basic ones are out. In MIG/MAG downhill is run in short arc on thin sheet; a flux-cored wire must carry the downhill position in its designation, otherwise the slag cannot keep up.
Common mistakes
Travelling too slowly — the pool overtakes the arc and leaves an overlap with lack of fusion under it. Too long an arc — slag runs into the bead. Weaving as if welding uphill: on a downhill run it makes no sense and only chills the edge.
What the standard says
The vertical-down position is PG to EN ISO 6947; the American equivalent is 3G downhill. A qualification passed in PG does not cover PF: they are two different positions and two different test pieces.
Frequently asked questions
Is a downhill weld weaker?
Not in itself, but it gives less penetration. On thin sheet that is a benefit; on thick plate it is a drawback, because the same number of runs carries less load. That is why load-bearing structures are welded uphill.
Which electrodes are used downhill?
Cellulosic E6010 and E6011, and thin rutile electrodes. Basic electrodes are unsuitable for downhill: the slag overtakes the pool and ends up in the weld.
Does a PF qualification cover downhill welding?
No. PF is vertical up, PG is vertical down; under EN ISO 9606-1 they are separate positions with separate test pieces. Neither replaces the other.
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