There are three techniques to tig weld an open root. Here I lay out the pros and cons of each and talk about which one is my favorite and why.
What is Open Root Welding?
An open root is a gap between two pieces of metal, allowing them to be fused into one solid piece with welding. The gap lets the welder access the back of the pieces to achieve total fusion with no seam.
It's called an open root because a root is the first pass to be welded and the gap is welded first. The image below shows a 1/8 inch gap (the open root) between two sections of pipe.
When it comes to TIG welding, there are three ways to weld such an open root.
Laywire
A laywire open root is just like it sounds. You lay the wire...the filler rod...down against the gap and basically run it over with the puddle. The key here is prep. You want the root gap to be just a tiny bit smaller than the rod, so you can keep the filler rod pressed firmly against the gap as you weld.
Pros:
- Blazing fast
- Pretty
- Easy to be consistent
Cons:
- Best suited for good fit-ups
- Can close-up too much, causing lack of penetration
- Harder to see bevel edge, so it takes experience to know if it’s fusing right
Click HERE for a complete tutorial on the laywire open root method.
Backfeed
The backfeeding open root technique is also...just like it sounds. But unlike laywire, where the rod is on the top, here you feed the filler rod through the back side of the gap into the puddle. It's important to use a filler rod smaller than the gap, so it can fit through, and keep it attached to the puddle.
Pros:
- Easy to get good reinforcement, especially the bottom of pipe
- Works well with wide gaps and janky fitups
- It’s really fun and interactive
Cons:
- In my experience, it’s the slowest of the 3 methods
- More difficult to get perfectly consistent on the inside, can get too much reinforcement if not careful
- Harder to perfect than laywire
Keyhole Dip
You guessed it. The keyhole dip open root method is also just like it sounds. You let the puddle melt open a small hole into each side of the bevel edge, forming a sort of keyhole appearance, before dipping or feeding your filler rod into the puddle (which closes the keyhole), and you just repeat this process as you move along.
Pros:
- Unstoppable when mastered—you can easily see each bevel edge break down
- Works well on tight gaps
- Interactive and versatile
Cons:
- It’s the hardest to get down (in my experience) -- easy to have low spots on the inside or blow outs while welding, if not careful, while learning
- The worst method for wide gaps
- Can be tricky in certain spots in the field, to get both hands stable
Which Do I Prefer?
I like laywire the best. To me, it’s worth putting in the extra time on prep. It’s fast, clean, but mostly—it's just what I’m best at.
I use the keyhole dip on small diameter pipe (anything less than ¾") or when the gap is really closing in on me. And backfeeding, although really fun, I only use when I’m concerned about getting more reinforcement on the inside.
But everyone is different. A lot of the welders I know have their own unique styles or spin-offs of the core methods. You have to try them all to find out what you like best.