TIG Root Pass Techniques Explained

While welding thin and medium-thickness mild steel may be a breeze, even for beginners, the game changes when the thickness exceeds 1/2" or 1" inch.

Instead of using a high amp power source and thick electrodes that create intense heat and spatter, welders bevel the pieces to reduce the gap and use multiple passes to fill the joint.

The first pass in a multi-pass operation is known as the root pass. This is the foundation for future passes, and it can be carried out by any modern arc welding process.

In this article, we'll explain TIG root pass techniques and challenges and present tips for successful operation.

TIG Welding Root Pass on Stainless Steel
Source: https://www.youtube.com/shorts/_yOCYRqQ0PQ

What Is A Root Pass?

A root pass is the first pass in multi-pass welding, typically used when welding pieces that are thicker than 1/2 inches. Welders use multi-pass operation when dealing with thick metals to avoid excessive heat and large electrodes.

Root Pass, Hot Pass, Fill and Cover Passes in Welding
Source: https://www.youtube.com/watch?v=WzNRBSfVgi0

Instead of using a high amperage welder and large diameter electrodes, welders bevel the pieces at a specific angle and create a smaller diameter opening. This gap is known as the root opening, and filling this gap is known as welding a root pass.

You can weld the root pass with any arc welding method, but most welders prefer Stick welding. This is the preferred welding method for most multi-pass operations, such as pipeline welding, but you can also use TIG welding.

TIG Welding Root Pass

TIG welding root pass is typically used when welding aluminum or stainless steel pipes in buildings, heating, and power plants. GTAW is known for its high-quality results, so welders typically use it due to outstanding weld quality, cleanliness, and aesthetics.

TIG Welding Root Pass on Stainless Steel Pipe
Source: https://www.youtube.com/watch?v=k3nSYYgl54A&t=299s

Compared to Stick welding, the most popular root pass welding method, TIG is slower, requires higher skill to perform, and requires much more time spent in weld preparation. However, TIG welding is a preferred choice in critical applications and with delicate metals such as stainless steel or aluminum, where Stick doesn't shine.

Ultimately, welders can use TIG welding for the highest quality root pass and then fill the rest of the joint with Stick welding for quick and cheap operation. Of course, if the given application allows it or if there is a need for something like that.

TIG Welding Root Preparation

Before we talk about the techniques, we must mention the root preparation. Even though all procedures require well-aligned and clean pieces, TIG welding is known for its cleanliness, so everything must be well-prepared and squeaky clean.

The TIG welding root preparation requires the following:

• Proper bevel angle

• Moderate gap

• No land

• Little to no high/low (mismatch)

Source: https://www.researchgate.net/figure/Joint-edge-specifications-for-GMAW-of-plates-with-more-than-6-mm-thickness_fig2_303095768

The bevel angle is the angle of the beveled sides of the pipe or a plate. For TIG welding root pass, the typical bevel angle is between 30 and 40 degrees. ASME power piping specifications typically require a 37.5-degree bevel angle, while API codes might call for 30 degrees.

The root opening, or the gap in the TIG welding root pass, should be 1/16″ to 1/8". A typical gap for a tig root is 1/8", but the weld specification can call for a smaller or larger opening.

Gap in the TIG Welding Root Pass
Source: https://www.wje.com/knowledge/articles/detail/root-opening-considerations-for-fillet-welds

The root face, or land in root pass welding, is the flat spot on the sharp edge of the bevel. In TIG welding root pass, the land is typically 0 or no root face.

High/low in root pass preparation is typically known as a mismatch in the alignment. There is absolutely no need to have any mismatch or high/low in TIG root preparation, and to ensure so, you should measure the opening with a filler and evenly tackle the plates or pipes.

TIG Root Pass Techniques

Once you properly clean, prepare, and align the pieces, it is time to carry out the TIG welding root pass. The most common TIG root pass techniques are:

TIG Welding Root Pass
Source: https://www.youtube.com/shorts/VraM5gg1lNE

• Laywire TIG root pass%

• Keyhole TIG root pass

• Backfeed TIG root pass

• Walk-the-cup TIG

• Freehand TIG root pass

Keep in mind that there is no specific technique you must use to TIG weld root pass, but the specification can call for one way or another. Each has its ups and downs and particular applications, so let's discuss more.

Laywire TIG Root Pass

The Laywire TIG root pass technique is a pretty simple way to carry out a root pass, and the welders in the northern states often prefer it. This technique typically requires a 37.5 bevel angle, 0 land, and no mismatch.

What makes laywire TIG unique is the fact it uses stringer beads with no side-to-side movement. That is achieved by using the same diameter filler wire as the gap, typically 1/8" filler and gap.

Laywire TIG Root Pass Technique
Source: https://www.youtube.com/watch?v=e1RfmhkbWpM

As the name states, you lay the wire inside the root. Since the wire and gap are the same diameter, the TIG rod won't fall out. Using a tight arc and minimal torch angle, you move back and forth to push the molten metal across the joint.

Once you reach the tack welds, you can spend some more time melting the tacks. That way, you even out the entire weld and get yourself a perfect root pass. Many welders prefer this method since it is fast and easy to master. Still, it requires proper preparation like any other root pass welding technique.

Pros and cons of Laywire TIG:

Pros:

• It is fast and easy to carry out.

• No side-to-side movement is required

• Yields pretty and strong welds

Laywire TIG Root Pass Welds
Source: https://www.youtube.com/watch?v=s7yoqpJbc7s

Cons:

• Requires a perfect fit-up

• It takes some time to get consistency and proper penetration

Keyhole Dip TIG Root Pass

Keyhole TIG root pass technique includes forming a keyhole in the root and then frequently dipping the filler rod. A keyhole is a literal hole in the material caused by its vaporization. This technique is used when deeper penetration and more material is needed on the outer side of the pipe or plate.

TIG Welding Keyhole Root Pass Technique
Source: https://www.youtube.com/shorts/exNFy4USzxE

Similar to lay wire, the keyhole dip technique requires a bevel angle of 37.5 degrees, clean pieces, a good fit-up with minimal or no highs/lows, and no land. However, this technique uses a one-diameter smaller TIG rod. For example, for a 1/8" gap, you'll use a 3/32" filler rod.

Using enough amperage and a tight arc with minimal side-to-side movement creates a keyhole. A keyhole requires frequent TIG rod dips, and it ensures that the root pass pokes through. You can also push a bit of extra rod into the puddle, and make sure you don't weave too much since you can spread the keyhole significantly. Once you catch the rhythm, you are set for success.

Keyhole TIG Root Pass Technique
Source: https://www.youtube.com/watch?v=4-KzWTthQuY

While many consider the keyhole dip TIG root technique challenging, it is pretty versatile. Although applications are not limited, this technique is preferred with tight gaps. However, if inexperienced, your keyhole can get out of hand in wider root openings, so it takes time and practice.

Pros and Cons Of Keyhole Dip TIG

Pros:

• You can easily see each bevel edge break down.

• Interactive and versatile

• Works well with tight gaps

Keyhole Dip TIG Welding Works with Tight Gaps
Source: https://www.youtube.com/watch?v=cc2mF8OOzzM

Cons:

• Keyhole can get out of hand

• It requires a lot of skill to master

• It is not the best choice for wide-root openings

Backfeed TIG Root Welding

Backfeed TIG root is another exciting and interactive technique for the root pass that is often favored by welders in the southern states. As the name states, this technique includes feeding the TIG rod from the back of the gap into the puddle. While this might sound complicated, this is a perfect technique for jobs where you can't get your head in to see, but you can get the torch in.

Backfeed TIG Root Technique
Source: https://www.youtube.com/watch?v=92081CwMP4o

The root preparation is similar to the other technique. A bevel angle of 30-40 degrees, based on specifications and requirements, will do just fine. Since you are feeding from the back side of the gap, you must provide an even fit-up with no highs/lows. You can achieve that by using the rod with the same diameter as the distance for the gap you want to get and tacking the points of the plate or pipe.

Since you are feeding from the back side of the gap, your TIG rod should be smaller than the root opening. A 1/8" gap with a 3/32" rod is a typical approach, but some welders also use a 5/32" gap with a 1/8" rod in specific applications.

The key to backfeeding is to find a comfortable way to hold the torch and feed the rod. Keep the electrode tip in the middle of the joint, but try not to touch and contaminate the tungsten with your rod. Quite opposite to the standard technique, you should keep the arc steady and in the center of the joint while weaving and feeding your rod into the joint.

Find a comfortable way to hold the torch and feed the rod during TIG backfeed root welding.
Source: https://www.youtube.com/watch?v=92081CwMP4o

Pros and Cons of Backfeeding TIG

Pros:

• Excellent for hard-to-reach places and out-of-position welding

• Yields sound reinforcement, weld strength, and aesthetics

• Great for broader root openings

• Can work with specific errors in alignment

Backfeeding TIG Root Technique on 6g Position
Photo by @texasarcwelding (TikTok)

Cons:

• Dislikes too many highs and lows

• It can be slow to perform

• It can require more skill than laywire TIG

Walk the Cup TIG For Root Pass

Walking the cup is the term you come across if you have ever explored pipeline welding, and this is one of the renowned and widely used TIG welding techniques in this industry. Many prefer this technique due to its ability to produce consistent quality welds while creating minimum operator fatigue.

Walk the Cup TIG For Root Pass
Photo by @saometalworks (TikTok)

Most welders turn to walk the cup TIG due to the unique challenges pipeline welding produces and the high skill requirements of the GTAW. In pipeline welding, maintaining the consistent arc length and consistently feeding the rod while changing the angles to accommodate the dynamics of welding can be challenging and tiring, even for the most experienced welders.

So, instead of positioning and holding the torch on top of the weld, welders decided to use the larger cup, which can sit on the edges of the root. Similar to laywire, the TIG rod is placed inside the joint. To produce the welds, you start moving the cup in a zig-zag motion, ergo the name walking the cup.

Walking the cup, TIG requires clean and well-prepared pieces. The bevel angle will once again depend on the specifications, but you don't want to go too wide. The much more critical factor is the size of the cup, which is determined based on the size of the root. However, most typical applications require a size 6 cup (3/8 inch). The key is to let your cup rest well inside the opening. The tungsten stickout, in this case, is also 3/8 inch, and it shouldn't touch the base metal or the wire, or it will get contaminated.

The Tungsten Stickout of TIG Walk the Cup For Root Pass
Photo by @welddotcom (TikTok)

Unlike other TIG root techniques, walking the cup uses a slightly larger rod than the root opening. For example, a 3/32-inch groove needs a 1/8-inch filler metal diameter. The reason is you should press the rod against the joint so a smaller diameter could easily fall through the root.

As you walk the cup, you should work with your hand rather than your wrist, which feels much less tiring. The size of the cup should allow you to zig-zag to both sides of the root, providing the proper penetration and good tie-in of the root pass. Keep the filler metal at the leading edge of the weld puddle and walk the cup all around the pipe.

According to most welders, this could be one of the most challenging root pass techniques. However, walking the cup is almost the standard for anyone using TIG welding in the pipeline industry, so mastering it can open many doors.

Walking the Cup on TIG Root Pass
Source: https://www.youtube.com/watch?v=ipJuNYcdRDo&t=94s

Pros And Cons On Walking The Cup TIG

Pros:

• One of the widely used techniques in pipeline welding

• Reduces the operator fatigue and provides consistency

• It can be used on most materials

• Produces highly aesthetic and high-quality welds

TIG Walking the Cup Welds
Source: https://www.youtube.com/watch?v=ipJuNYcdRDo&t=94s

Cons:

• High skill requirements

• It is not suitable for aluminum as the hot cup can leave a trailed impression along the groove.

• It is slower than Stick welding and requires frequent cup changing.

Freehand TIG Root Pass

The freehand TIG root pass technique is a versatile choice that many welders turn to when other methods are impossible to use. Quite the opposite of walking the cup, your torch is not seated onto the joint. It is like regular TIG welding, where you move your torch with your fingers resting on the piece and feed the filler as you move.

Freehand TIG Root Pass Technique
Source: https://www.youtube.com/watch?v=f5MIZaDpNbg

The main issue with this technique is that you don't have the proper support like walking the cup. Instead, you will manually have to control the arc length and torch movement, which makes it highly challenging and can cause fatigue in the larger runs.

Meanwhile, the TIG root preparation is similar to that of other techniques. Bevel angles and the opening size will depend on the thickness of the pipe of the plates and weld specifications. Like with other techniques, cleanliness, good alignment, and a 0 landing are recommended.

Regarding the wire feeding, you can adjust it to your preferences. Typically, freehand requires a slight weaving motion, so you can use a slightly smaller diameter rod or the same size rod as your root opening. You can lay the wire inside the joint like with laywire or walk the cup, or you can dub it in like with the regular TIG technique.

Freehand TIG Root Pass Welding Process
Photo by @artofthearc (TikTok)

Generally, a freehand TIG root pass is used when you cannot use other techniques or weld specifications, which strictly calls for freehand TIG. However, freehand is not recommended for beginners or inexperienced welders, as it requires a lot of practice to keep the hand and, therefore, the arc length, feeding, and weaving consistent and steady.

Pros and Cons of Freehand TIG Root Technique

Pros:

• Doesn't have strict rules or technique requirements

• Looks a lot like a regular TIG welding

• It can be used to produce sound and aesthetic welds

Freehand TIG Root Pass Welds
Source: https://www.youtube.com/watch?app=desktop&v=FcjLTmSfQMo

Cons:

• It requires a lot of skill and practice

• With little support, it can be hard to maintain a steady and consistent arc.

• Welders typically use it when other methods are impossible to carry out.

Conclusion

TIG welding root pass is often preferred due to the cleanliness, high-quality results, and aesthetics of Gas Tungsten Arc Welding (GTAW). However, this is a challenging method, and the same rules apply when welding a root pass.

The good thing is that you can use one of a few methods when TIG welding a root pass, which can make the entire process faster or easier. For example, laywire TIG root is fast and easy to carry out, keyhole dip TIG produces good reinforcement, and walking the cup is standard for the root pass in the pipeline industry.

In the end, you can always use the freehand TIG to do things your way, but be ready for lots of practice and time spent perfecting the root pass welding. Creativity is always important in welding, and you can use it to get the best results.

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