Heli Arc Welding: Process, Techniques and Key Uses

A fabricator switches a TIG machine from argon to helium to get deeper penetration on a thick aluminum bracket, then discovers the arc keeps wandering and the filler rod keeps floating off the puddle. Nothing about the machine changed — only the gas. That single swap is the whole story of heli arc welding: it is not a different process from TIG, but a different atmosphere inside the arc, and that difference rewards you with penetration and speed if you understand how to handle it.

What Heli Arc Welding Actually Is (And the Two Things the Name Means)

Heli arc welding is gas tungsten arc welding, usually called GTAW or TIG, performed with helium as the shielding gas. It may also mean a helium-argon blend, mixing helium into argon to dial in a balance of penetration, arc stability and cost. The arc, torch, power source and workpiece are all standard TIG. Only the gas between the tungsten tip and the pool changes, and with it the arc’s behaviour: how it strikes, how wide it spreads and how much heat it reaches the metal.

Everything else about TIG carries over untouched: filler rods, tungsten types, machine controls, fume extraction and inspection stay the same.

Where the Name Came From

The label “Heliarc” was coined by Northrop engineers in the early 1940s while they were developing the magnesium XP-56, an experimental aircraft for the United States Army Air Corps. Their process combined a tungsten electrode arc with helium shielding gas, and Heliarc was the natural shorthand: a helium-shielded arc.

The torch design that made it practical was patented by Russell Meredith in 1941. Helium had been available as a shielding gas long before, but it behaved poorly in a hand torch: lighter, different heat conduction, harder to ignite than argon. A stable, concentrated helium arc required a specific nozzle and gas path design, and only then did helium-shielded welding become practical.

• GTAW is the formal, standards-based AWS name. Use it when reading a spec or procedure.
• TIG is the trade name that became the everyday word, from “tungsten inert gas.”
• Heliarc is the historical trade name for the helium-shielded variant, still seen in 1940s aircraft work and old technical literature.

None of these are different processes, only labels for the same work. AWS has authored more than 350 welding standards, including specifications for tungsten electrodes and filler metals, all written around GTAW. Browse them in the AWS standards library.

The Second Meaning of “Heli Arc”

In pipe and tube work the phrase carries a second, completely different meaning. In piping and tube welding, “heli” often refers to helical or spiral torch travel. Instead of running the torch around the joint in a plain circle, the welder walks it in a spiral so the arc traces a helix around the circumference. On a large diameter round joint, a tight circular bead concentrates heat into one spot and can leave the middle poorly fused. A spiral averages heat around the whole circumference and works on fixed pipes that cannot be rotated under the torch.

That approach is a cousin of orbital welding, where the weld head rotates around a stationary tube under a pre-programmed power source.

1. Heli arc welding as a shielded gas process: TIG with helium or a helium blend, covered in full through aerospace TIG welding standards and training, gas selection, electrode choice and troubleshooting.
2. “Heli” as helical travel on tube: a torch movement technique for round joints, covered in its own chapter later on.

A Quick Glossary

Term	What it means
GTAW	Gas tungsten arc welding. The formal AWS process name.
TIG	Trade name for GTAW, from “tungsten inert gas.”
Heliarc	1940s trade name for helium-shielded tungsten arc welding.
Shielding gas	Inert gas blanketing the arc and pool, keeping air out.
DCEN	Electrode negative. Most arc heat lands in the work; deepest penetration.
DCEP	Electrode positive. Heat concentrates in the tungsten, which cleans oxides.
AC	Polarity reverses each cycle. Standard for aluminium and magnesium.
Autogenous weld	A weld with no filler metal added.
Filler rod	Consumable rod or wire fed into the pool.

How the Trade Bodies Describe It

TWI and AWS describe the process the same way. The TWI description of the TIG process is straightforward: the arc is struck between a pointed tungsten electrode and the workpiece, inside an inert atmosphere of argon or helium. The standard encyclopaedia description of GTAW frames argon and helium as the two common shielding gases used with a non-consumable tungsten electrode.

AWS publishes the tungsten electrode specification as A5.12, plus filler metal specifications including A5.18 for stainless steels and A5.14 for aluminium. Those are the documents you work to when you need a qualified procedure.

Heli arc welding is simply TIG with a different atmosphere inside the arc, and the rest of this guide covers what that atmosphere changes.

How the Helium-Shielded Arc Actually Works

Swapping argon for helium doesn’t change the torch, the electrode, or the fact that you’re striking an arc between a pointed tungsten and the workpiece in an inert atmosphere, as TWI describes TIG. What does change is the gas itself, and with it, the way heat moves through the weld.

The Arc Column in Action

A TIG torch holds a non-consumable tungsten electrode above the joint, leaving a gap of roughly 1.5 to 3 mm (0.06 to 0.12 in). As shielding gas flows from the cup into that space, a high-frequency spark ionizes it to start the arc. Once sustained, the high-frequency circuit drops out and a constant current power source takes over.

Rather than forcing a set voltage, a constant current machine forces a set amperage, letting voltage rise or fall with arc length. When the arc shortens, voltage drops. When it stretches, voltage climbs, raising the overall power of the arc. Inside that gap, the ionized gas forms a plasma column. Through joule heating, the current passing through both this column and the workpiece creates resistance, and that resistance is what turns electricity into the intense heat needed to form a puddle.

The Role of the Tungsten Electrode

The electrode never joins the weld. Its ability to do this comes down to one fact: tungsten has the highest melting point of any pure metal at 3,422 °C (6,192 °F). This allows it to withstand arc temperatures that would destroy nearly anything else.

These electrodes are covered by ISO 6848 and AWS A5.12, with standardized diameters, lengths, and doped grades such as lanthanated, ceriated, or zirconiated. Each grade is colour coded, and choosing the correct diameter for your amperage is crucial. Go too small for the current you’re running, and the tip will overheat and risk throwing tungsten into the puddle.

Why Helium Creates a Hotter Arc

Compared to argon, helium has two key traits. First, it has a higher ionization potential, meaning it takes more energy to create its conductive plasma. Second, it is several times more thermally conductive, so instead of confining heat to a narrow core, it spreads it outwards.

Together, these properties produce a wider, hotter arc column. The arc runs at a higher voltage for the same amperage, delivers more total heat into the joint, and can achieve deeper penetration. This is the driving force behind its use in many applications.

However, those same traits come with tradeoffs. The harder start, wider heat spread, and increased sensitivity to arc length mean less forgiveness. If a helium arc is stretched too far, voltage rises quickly, control becomes more difficult, and a stable root can be lost.

Polarity and Heat Distribution

Where the heat goes is determined by how you connect your torch and work clamp. For helium-shielded applications, this balance is especially noticeable.

Polarity	Where the heat goes	Typical use
DCEN (electrode negative)	About two-thirds of the heat into the workpiece, one-third into the electrode. Deep, narrow penetration.	Steel, stainless, nickel alloys, titanium, and automatic helium welding of aluminium.
DCEP (electrode positive)	More heat into the electrode. Provides oxide cleaning, but limits penetration.	Shallow joints under 1.6 mm (0.063 in) where cleaning is the priority.
AC	Alternates between cleaning (electrode positive) and penetration (electrode negative).	Aluminium and magnesium, where surface oxides must be removed as the puddle forms.

With modern square-wave AC machines, the electrode-positive half can be tailored to provide enough cleaning with less excess tungsten heating, making the puddle far easier to control than with older sine-wave transformers.

Finally, shielding has its own demands. Because helium is lighter than argon, it requires higher flow rates to achieve the same air exclusion. Following proper shielding gas flow practices is essential, and resources from Linde’s overview of tungsten inert gas welding paired with the GTAW process reference provide solid context for these gas-specific considerations.

Helium vs Argon: Choosing the Right Shielding Gas

Ask a shop to pick a shielding gas and most say argon without hesitating. That is the right default, but not the correct answer for every joint. The choice between argon, helium and the blends in between comes down to how much heat you want in the joint, and how much trouble you will manage to get it there.

100% argon remains the best all-round choice for TIG welding: affordable, widely available, excellent arc stability and starting characteristics. Helium is the specialist tool, producing a wider, hotter arc with higher heat input, so you can travel faster and push deeper into thick sections and high-conductivity metals such as copper and aluminium. The price is a less forgiving arc, especially at ignition.

Why Helium Changes the Heat

Argon and helium differ in two ways that matter at the torch: ionization potential and thermal conductivity. Helium needs more energy to ionize, so the arc column spreads wider and runs at a higher voltage. Its higher thermal conductivity then pushes more energy into the workpiece instead of letting it radiate away, giving a longer, wider, more energetic arc.

Gas suppliers describe helium as giving greater heat input, faster travel speeds and deeper penetration than argon at the same amperage, so you can cover a joint in fewer passes or reach a thickness argon will not penetrate in one go. The catch is ignition: helium resists ionization, so it is harder to strike. A solid high-frequency start handles it, while older units struggle to break the gap and the arc can wander at first. The ionizer is also less stable at low currents, which makes low-amp work the hardest territory.

Side-by-Side Comparison

Factor	100% Argon	Helium / He Blends
Arc stability	Excellent, forgiving	Good once running, weaker at low amps
Arc starting	Reliable, repeatable	Harder; needs HF start and pre-flow
Penetration	Moderate, thin to medium	Deep on thick or conductive metal
Heat input	Lower at a given current	Higher at a given current
Travel speed	Slower to match	Faster at same amperage
Weld appearance	Bright, domed bead	Wider, flatter, rougher
Current capacity	Higher at high amps	Lower practical maximum
Cost	Low, commodity price	Much higher per cubic foot

Weld appearance confuses newcomers: a helium bead is wider and flatter and shows more of the base metal colour than a bright argon bead. On stainless that can look duller than expected, but it is not contamination.

Gas Selection by Material

Material	Recommended Gas	Notes
Aluminium	Pure argon or 75% helium blend	Deeper penetration on thick sections; AC or DCEN
Stainless steel	Argon, or 2–5% hydrogen blend for mechanized work	Hot, narrow bead protects corrosion resistance
Carbon steel	Pure argon	Helium works but rarely worth the cost
Copper	Helium, or argon with small nitrogen addition	Conductivity eats heat; nitrogen carries the arc in
Titanium	Argon or argon/helium blend	Never hydrogen; purging mandatory
Magnesium	Argon or argon/helium blends	Hydrogen prohibited; control preheat

Argon-hydrogen blends of 2–5% hydrogen can raise heat input by roughly 10–20% on austenitic stainless and are common in mechanized stainless welding. Hydrogen is strictly prohibited for aluminium, titanium and carbon steel: it promotes porosity in aluminium and can cause cold cracking in steel.

Preheat matters most on aluminium and magnesium. Aluminium can be preheated to 175–200 °C (347–392 °F) to improve penetration and travel speed, while magnesium should stay at or below 150 °C (302 °F). Getting the base metal to temperature moves heat into the joint faster and keeps a hot, narrow helium arc fluid. See our guide to prepping aluminium for welding.

The Middle Ground: Argon/Helium Blends

Blends are where most practical compromise happens. Common mixes run 25% to 75% helium, and the trend is straightforward: more helium means more arc heat, better penetration and faster travel. The cost is degraded high-frequency start performance and a less stable arc at low current. A 25/75 blend is a common compromise for mixed-thickness work, letting one setup handle a 2 mm section and a 6 mm section without changing cylinders.

Flow Rates and the Helium Problem

Typical TIG gas flow falls between 10 and 35 cubic feet per hour, adjusted for nozzle size, torch design and ambient conditions. Shielding gas guidance notes that flow is one of the most commonly mis-set variables on the bench.

Because helium is lighter than argon, flow must run two to three times higher for equivalent shielding: a setup that ran beautifully at 15 cfh of argon will be under-shielded at the same flow with helium. Too much flow is not the answer, since excess flow creates turbulence at the nozzle, drags air into the arc and causes the porosity you were trying to avoid. Use the lowest flow that gives a laminar column, and fit a flow-meter regulator near the power source.

A Simple Decision Path

1. Thin material, general fabrication, stainless or carbon steel: pure argon, no debate.
2. Mixed thicknesses on one part: argon or a low-helium blend such as 25% helium.
3. Thick aluminium, copper, or any joint argon will not penetrate: helium or a 75% helium blend.
4. Reactive metals: argon or argon/helium, no hydrogen, full purging.
5. Unreliable arc starts: stay close to pure argon, and fix the high-frequency start and pre-flow first.

For the wider aerospace and tubing context behind these decisions, aerospace TIG welding standards and training covers the high-spec work where gas purity and control stop being negotiable.

Equipment, Tungsten Electrodes and Consumables for Heli Arc

Heli arc welding, better known as TIG or GTAW, relies on the same core setup as standard argon TIG. The difference comes down to a few parts that need to work harder to accommodate helium’s traits. Focus on the power source, torch, shielding path, and consumables to get clean results.

Power Source: Start Strength and Control

Any constant-current GTAW machine is suitable for heli arc, but not all start arcs equally. DC is used for steel, stainless, nickel, copper, and thin aluminium, while AC square wave is needed for aluminium and magnesium to break up its oxide layer. Pulsing can also be useful to balance penetration with heat input.

The most critical feature is high-frequency, non-contact arc start. Helium has a higher ionization potential than argon, so it takes more energy to strike an arc. As TWI describes TIG, the arc is struck between a pointed tungsten and the workpiece within an inert atmosphere of argon or helium. With that wider, less focused arc column, foot pedal control becomes even more important to keep heat precise.

Torch and Nozzles

For lower amperage jobs, an air-cooled torch will do the trick. Once you move past around 200 A, water-cooled torches are required, especially for heavy work on aluminium or copper that can push up to around 600 A. A slight torch tilt of 10 to 20 degrees will also help aim both the arc and shielding gas directly into the joint.

Nozzle choice can affect visibility as well. Alumina is the durable, cost effective option, while fused quartz lets far more light through for tight views of the puddle. Shape is just as important: a converging nozzle creates the most laminar flow for shielding. To maximize coverage, fit the largest nozzle diameter that your torch and joint access will allow.

Collet Body vs Gas Lens

For heli arc specifically, this is the upgrade that pays off most. A standard collet body relies on perforations that create a swirling gas flow, leading to more turbulence. A gas lens uses a stack of screens to straighten that flow into a uniform, laminar stream. This reduces the chance of air being pulled in and allows for more tungsten stick-out to reach corners or tight tube work.

Tungsten Electrodes

Tungsten selection is specified by AWS A5.12, with classes identified by their colour band. When working with helium, some types hold up far better than others:

Class	Colour	Typical use
WL15	Gold	Lanthanated, reliable all-round for AC and DC
WL20	Sky blue	Lanthanated, stable across a wide range of currents
WY20	Blue	Ceriated, great tip retention and arc start
WC20	Gray	Ceriated, common for AC aluminium
WZ8	White	Zirconiated, higher current capacity and electrode life

Lanthanated and ceriated electrodes are the most sensible for heli arc on either polarity. Zirconiated tungstens are also worth considering for heavier helium passes. Avoid thoriated (WT20, red band) types whenever possible due to their radioactive nature, as they can spit particles into the weld on AC and carry inhalation and disposal concerns.

Filler Metals and Gas Delivery

Always match your filler to your base metal. Use the correct AWS specification for the job, such as AWS A5.14 for aluminium, A5.9 for stainless, or A5.10 for copper-nickel alloys, and keep your rod diameter slightly under the puddle size.

For gas delivery, use a flow-meter regulator as close to the power source as possible for accurate readings. Most importantly, only use dedicated shielding gas hose. As Miller recommends, avoid green oxygen hose for shielding gas delivery, as it can increase the risk of contamination.

Step-by-Step Heli Arc Technique: From Prep to Crater

While the only difference between heli arc welding and standard TIG is the shielding atmosphere, that single change demands far more discipline. Helium produces a hotter, wider arc with less forgiveness on starts, meaning every step from prep to shut down must be deliberate. The following procedure focuses on the adjustments specifically required when running helium or helium blends.

Joint Preparation and Cleaning

With the lack of a strong cleaning action on DCEN, contamination is far more likely to cause porosity when using helium. Proper prep is not optional, it is your first line of defense.

• General cleaning: Cleaning with alcohol or acetone immediately before welding is essential, as oxides on both the filler metal and workpiece will create porosity.
• Aluminium and magnesium: These metals form a refractory oxide layer within minutes of exposure to air. This oxide must be removed with a dedicated stainless steel wire brush. AC is the normal choice for these materials, as alternating current removes this layer throughout the weld.
• Carbon and alloy steels: For rusted or scaled steel, grit blasting plus brushing is heavily recommended. This is especially important for DCEN, as there is no cathodic cleaning action to break it down.

From here, focus on accurate fit-up. For dissimilar metals, a proper gap and bevel are crucial. Utilize a solid fixture or clamp strategy to prevent any movement, as the higher heat input from helium will exaggerate warping on poorly secured joints. For those looking to perfect their prep work, resources such as Aluminum Cleaner for Welding: How to Prep Aluminum Right go into greater detail on reactive metals.

Pre-Flow, Arc Start, and Establishing the Puddle

Due to helium’s higher ionization potential, ignition is less consistent than pure argon. To combat this, a minimum pre-flow of 0.2 seconds is recommended to purge the torch and shielding gas line before striking the arc. On machines with adjustable pre-flow, it is often worth adding a little extra time when running 100% helium.

Once the arc is struck, establish your puddle with the torch tilted back about 10–15 degrees from vertical. Keep your arc length short and steady, as helium is far more arc-length sensitive than argon. A longer arc will cause the heat to spread out rapidly, instantly increasing distortion and risking a loss of shielding.

Filler Feeding, Rhythm, and Crater Fill

Now that your puddle is established, feed your filler rod from the leading edge of the pool and keep it inside the gas shield at all times. Fall into an alternating rhythm of advancing the torch and adding filler. For aluminium GTAW, filler rods such as 4043 and 5356 are commonly used, whilst 308/309 stainless fillers are often chosen for 4130 chromoly steel, as they are less prone to cracking.

As you approach the end of your weld, discipline is vital. Welding current is normally reduced at the end of a weld so the crater can solidify without crater cracking. Gradually taper your amperage down with the foot pedal whilst feeding a small amount of filler to tie off the pool. Following this, utilize your post-flow to protect the hot tungsten and solidifying pool. As a reliable guideline, post-flow time in seconds can be calculated by dividing welding amperage by 10, with a minimum of eight seconds recommended.

Worked Examples

• Example 1: 1.6 mm Aluminium Bracket (AC) – For this thin, conductive part, use AC with a 75% helium blend for added travel speed. If the bracket was much thicker, pure helium with DCEN may be considered. Regardless of blend, immaculate oxide removal and a tight fit-up are mandatory to avoid worm tracking and porosity.
• Example 2: 3 mm 304 Stainless Tube Butt Joint (Autogenous) – For this joint, run autogenous helium with strict back purging of the bore. Any oxygen reaching the underside will ruin corrosion resistance. This level of purge discipline is a staple within Aerospace TIG Welding: Standards, Techniques, and Training, where joint integrity is paramount.

Helium will never forgive rushed prep, a wandering arc length, or a neglected crater. Treat gas choice, flow control, and heat discipline as part of your procedure, and run every new joint on a scrap coupon first. That small investment of time is the difference between a wandering, contaminated weld, and the deep, clean penetration that heli arc welding is known for.

Where Heli Arc Welding Shines: Aerospace, Tube, and Thin-Wall Work

Ask any shop welding for aircraft or missile programs what their drawings specify on thin-wall tube, and the answer is almost always gas tungsten arc welding, often with helium or a helium blend. No other arc process delivers the same combination of properties.

Why aerospace built the process

The Heliarc trade name was born in an aircraft context, and aerospace is still where helium-shielded GTAW does its most demanding work. Airframe structures, hydraulic and fuel lines, rocket motor cases and missile bodies need welds that are chemically clean and mechanically predictable at thicknesses barely more than paper.

Three properties make GTAW the natural fit. Our aerospace TIG welding standards and training overview covers the qualification side:

• Chemical integrity. The puddle sits inside an inert shield, so it is not contaminated by atmospheric oxygen, hydrogen or nitrogen the way flux-shielded and many gas-shielded processes allow. Gas tungsten arc welding can deposit metal matching the base material chemistry, and TWI describes the process as an arc struck between a pointed tungsten electrode and the workpiece in an inert atmosphere.
• Precise heat control on thin sections. A narrow, concentrated arc lets the welder melt a thin wall without burn-through, warping or grain distortion.
• Filler discipline. The electrode is non-consumable, so filler goes in only where the specification calls for it. Many aerospace joints run autogenous, with no filler at all.

Helium adds one more lever. Its higher thermal conductivity pushes more heat into the workpiece than argon does, so a welder moving to helium shortens the arc length and trims amperage to keep heat where the drawing wants it. Used well, that separates a spec-compliant joint from one that is not.

Orbital welding: from X-planes to process plants

Orbital welding was first implemented in the 1960s to mitigate fluid leaks in the X-planes series of experimental aircraft. Aerospace adopted it first, for hydraulic and fuel lines, and it spread into rocket and missile production, commercial aircraft, petrochemical, semiconductor and biopharmaceutical work. The ESAB guide to orbital welding traces that progression.

The torch travels around a stationary tube on a pre-programmed power source, so current, travel speed, pulse timing and gas flow repeat identically on every joint in the batch, exactly what a customer qualification or a code requires. Head design follows the work: closed heads suit smaller to medium diameter tube and autogenous welding, open heads take larger diameters with filler wire added.

Why GTAW beats the alternatives in high-spec work

GTAW is preferred over GMAW, FCAW, PAW, SAW and laser welding in critical applications for three reinforcing reasons: superior strength and mechanical properties, purer welds free of atmospheric oxygen, hydrogen and nitrogen, and automation that removes the human variability that would surface in a leak test or fatigue report. Laser welding competes on thin material, but it is capital-intensive with narrower joint geometry options, while GTAW handles complex prep, filler addition and repair in one setup.

Where the process dominates

Sector	Typical work	Why GTAW wins
Pharmaceutical & biotech	Stainless process tubing and vessel seams	Hygienic, contamination-free joints
Semiconductor	Ultra-high-purity gas and chemical delivery lines	No flux residue or filler contamination
Food & dairy	Stainless product-contact pipe	Cleanable, corrosion-resistant, no slag
Oil & gas	High-pressure pipe and instrument tubing	High integrity under pressure
Power generation	Boiler tube, headers, nuclear components	Corrosion and cracking resistance
Shipbuilding	Stainless pipe and hydraulic systems	Traceability and mechanical integrity
Aerospace	Hydraulic lines, fuel lines, airframe	Heat control on thin sections, chemical fidelity

The stainless steel corrosion advantage

One benefit is missed on job sites: overheating stainless steel during welding causes carbon precipitation at grain boundaries and a loss of corrosion resistance. The narrow, controlled heat input of orbital GTAW prevents that, which is why stainless process piping is welded this way. The same logic applies to exotic alloys, as our guide to Alloy 20 welding procedures shows.

There is also a quieter niche with national consequences. GTAW welds resist corrosion and cracking over long time periods, making the process the choice for sealing spent nuclear fuel canisters, where decades of service life matter.

NASA publishes a process specification for automatic and machine orbital tube GTAW of steel and nickel alloys, the NASA specification for orbital tube welding spelling out everything from joint preparation to parameter control. For comparison, the AWS standards catalogue runs to more than 350 documents covering process specifications, filler metals and qualification. Once a weld is written into a spec like that, it is no longer a technique question but a documentation question, and that is why helium-shielded GTAW holds its place in aerospace, tube and thin-wall work.

Helical Arc Welding: The Other “Heli Arc” on Tube and Pipe

If you searched “heli arc” expecting helium, pause. In tube work, “heli” almost always means helical: the torch travels in a spiral around a round joint, not a straight circle across it. That is a different idea from helium-shielded TIG, and the two are easy to mix up.

Why a Weld Wraps Around the Joint

Picture a stainless steel pipe header, 100 mm in diameter, plumbed into a skid and unable to rotate. Clamp a TIG torch to one side and walk it around by hand, or travel the torch in a helix: a slow spiral climbing the pipe, gaining a little lift each pass.

A circumferential weld concentrates its heat in one band, so a large-diameter joint gets a wide heat-affected zone, more distortion, and a bead whose properties vary from top to bottom as the arc angle changes. A helical path averages heat input around the circumference, keeping the weld uniform and the distortion symmetric.

It helps when the workpiece cannot be rotated and when a spiral weave blends heat around a joint thicker in one place than another. It is also popular on bicycle frames, exhaust headers and handrails, where the bead’s appearance matters.

How Orbital Welding Differs

Orbital welding is the automated version of the same idea. In an orbital system, the torch rotates 360° around a stationary pipe or tube joint while a computer-controlled power source holds current, travel speed, pulse timing and gas switching constant. The head clamps around the tube, and the result repeats every time.

According to ESAB’s orbital welding guide, the process covers a wide range of tube diameters and materials. The NASA process specification for automatic and machine orbital tube GTAW of steel and nickel alloys shows how specified this becomes at high stakes: shielding gas, purge requirements and arc length control are verified.

One common orbital configuration is autogenous welding, with no filler metal at all. Westermans notes that autogenous orbital TIG is common on tubes under roughly 38 mm outside diameter, where thin-wall tube joins with a clean, full-penetration weld and no filler.

Joint Preparation Does the Heavy Lifting

There is no filler rod to fill a gap, so every millimetre of fit-up comes from the preparation itself. Tube ends must be square-cut, burr-free and matched to within a fraction of a millimetre. A gap, a burr or cutting oil produces a defect that no parameter adjustment can fix.

That is why orbital tube work runs on dedicated tooling: orbital pipe saws and facing machines cut the tube and machine the end face to the specified angle and finish, and tube-to-tube laser alignment systems hold joint geometry. On your own bench, a decent aluminum cleaner and proper joint prep routine applies the same discipline.

Purging Is Not Optional

Purging with an inert gas is essential for most orbital TIG applications. Flood the bore with argon so the root never sees atmospheric oxygen. Without purge you get internal oxidation, porosity and lost corrosion resistance in stainless. The tell-tale sign is a grey or brown tint on the root, and on code-critical work that is an automatic reject.

Inflatable purge plugs are the professional answer: they seal the bore on both sides of the joint, hold a low, stable flow and give you a window to watch the root bead form. Cardboard discs and stuffed rags are not a substitute: they leak, they shift, and the root oxidises anyway.

Choosing the Gas for Tube Work

• Grade 4.5 argon (99.995%) is the standard shielding gas for most orbital TIG work, including stainless and carbon steel tube.
• Grade 4.8 argon (99.998%) is required for reactive metals such as titanium, tantalum and zirconium, where trace oxygen or water vapour matters.
• Argon-helium blends appear where more energy input is needed without hydrogen: heavier stainless, nickel, copper or aluminium tube.
• Argon-helium-nitrogen mixtures are specified for duplex and super duplex stainless steels, where argon and nitrogen maintain corrosion resistance.

Argon-hydrogen is used in mechanised stainless welding for speed, but hydrogen is strictly off the table for aluminium, titanium and carbon steel because of porosity and cold cracking.

When Manual Helical Work Still Wins

Orbital equipment is not automatically right. It demands capital, maintenance (tungsten condition, cooling unit cleanliness, cable checks, annual power source calibration) and skilled operators who can qualify procedures. A shop without that commitment gets worse results from an orbital head than a good manual welder with a ground machine.

Manual TIG still fits low volumes, irregular or non-circular joints, one-off repairs where a rotating head cannot be applied, and tube too small to clamp a head around. Those are the scenarios the manual helical technique was built for.

Before you order helium, confirm which “heli” you need. “Helium-shielded” changes the atmosphere inside the arc; “helical” or “spiral travel” changes the torch path, and your gas is likely standard grade 4.5 argon with a proper purge plug.

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Common Heli Arc Mistakes and How to Fix Them

A heli arc procedure can drift out of spec without anybody touching the machine. A cylinder runs low, a nozzle gets swapped, a hose gets pinched under a bench, a bay door opens down the hall. Here is a symptom-first troubleshooting list, weighted toward the faults that show up most often once helium replaces argon.

Porosity in All Its Forms

Porosity is the number one heli arc defect, and the cause is nearly always the shielding gas rather than the metal. Helium is lighter than argon, so it needs more flow to protect the pool, but pushing that flow further is exactly what creates the turbulence that drags air into the arc. Miller’s guide to shielding gas in TIG spells out the balance: at low flow the gas streams smoothly off the nozzle, while at high flow it eddies and can oxidise the puddle mid-pass.

• Flow too high. The classic cause. Drop to the lowest rate that still shields the pool.
• Nozzle too small. Use the largest practical converging nozzle for the longest laminar flow column.
• Drafts. An open bay door or extraction fan strips protection from the pool. Screen the area.
• Long gas lines surging. A surge at arc start sucks air in. Fit the flowmeter regulator at the power source, not the cylinder end.
• Contaminated torch. Inspect the insulators, cup and torch body, and run a dedicated hose rather than shared or improvised line.

One assembly habit prevents a whole family of defects: tighten the collet body or gas lens before the back cap. Fit the back cap first and atmospheric gas leaks into the torch, spoiling the electrode, the nozzle and the weld in one stroke.

The Wandering Arc

Helium’s higher ionization potential makes ignition harder and the arc less stable, so a helium arc that will not sit still is not automatically a machine fault. Extend the pre-flow slightly, confirm the machine has a high-frequency start, and check that the electrode material suits the polarity. If the trouble is arc starts rather than mid-weld wander, back the helium off and run an argon/helium blend. The TWI overview of TIG practice is a useful reference for electrode selection and gas setups.

Tungsten Contamination and Spitting

Tungsten inclusions in the deposit are radiographically detectable, which in aerospace or pressure work means a rejected part. Prevent them rather than chase them: change to a different electrode type or a larger diameter for your amperage, grind the tip to an angle that matches how you hold the torch, and keep the tungsten fully inside the gas shield so it cannot touch the filler or the puddle. A lightly contaminated tip can often be saved with a diamond abrasive wheel; once it has melted back into a ball, change it. The overview of gas tungsten arc welding is a solid reference for electrode types and their behaviour.

Oxide, Discolouration and a Dirty Work Surface

Rainbow discolouration on stainless and a dull grey film on aluminium both point to failed shielding or a surface that was never clean. Before blaming the gas, fix the joint. Mechanical preparation is what removes aluminium’s oxide layer, and no amount of shielding rescues a dirty plate. Check the gas supply too: a shielding gas containing an oxygen compound such as carbon dioxide will contaminate the tungsten electrode quickly and make it unusable for TIG, so CO2 is never acceptable here. Linde’s process guide sets out the purity requirements in detail.

Crater Cracks, Undercut and Excessive Penetration

• Crater cracks. Fill the crater with filler before you stop, then taper the current down slowly so the pool closes gently instead of freezing with a hole in it.
• Undercut. Too much heat for the joint, too little filler, or travelling too fast so the arc drags the pool edge. Add filler earlier and slow down slightly.
• Excessive penetration or burn-through. Over-amperage or an arc held too long. Reduce current, shorten the arc, or fit a backing bar.
• Dilution on dissimilar metals. Fit-up must be accurate, with the right gap and bevel angle, filler added quickly, and a small pool kept so base metal does not wash into the deposit.

Distortion and Heat-Affected-Zone Problems

Preheating is generally unnecessary for mild steel under about an inch thick, but low-alloy steels often need it. Preheat slows the cooling rate and reduces the risk of hard, brittle martensite forming in the heat-affected zone. Our guide to alloy steel welding electrodes covers the wider picture on those grades.

TIG concentrates heat into a small pool, and that tightness is what makes heat-treated aircraft steel awkward to weld. A TIG weld in 4130 chromoly can crack almost as soon as it is finished, which is why many are reheated to red heat and cooled slowly to relieve locked-in stress. The EAA’s notes on aircraft welding and steel tube fabrication are worth reading before you start.

Most heli arc faults trace back to a short list: flow too high, a nozzle too small, a draft, an arc held too long, or a dirty joint. Check those five before you reach for the machine controls.

Safety, Cost and the Skill Curve of Heli Arc Welding

Three questions decide whether a shop adopts heli arc welding: is it safe for the people doing it, does the gas bill make sense, and can the welders get good at it? Heli arc is the same arc as TIG, so most of what you already know applies. But the atmosphere inside the arc changes the hazards, running costs and learning curve in ways worth planning for before you buy the first cylinder of helium.

The Arc Is Bright, and Brightness Is a Hazard

Because GTAW produces no smoke to obscure the arc, the arc light is considerably brighter than in stick or MIG welding. That visibility helps the welder and hurts everyone nearby. Ultraviolet radiation from the arc causes photokeratitis, better known as arc eye, along with skin burns that often show up hours later rather than right away. TWI’s TIG job knowledge makes the same point: no fume means a very bright arc, so eye and skin protection have to be taken seriously.

• An auto-darkening helmet with a shade lens matched to the amperage you are running
• Flame-resistant clothing with full head and neck coverage
• Leather gloves and sleeves that close over the forearms
• Welding curtains around nearby workers who are not welding, since they block UV from reaching eyes and skin

OSHA’s welding, cutting and brazing resources spell out the core requirements, and they are worth reading before a new welder starts rather than after the first complaint.

What the Arc Does to the Air Around It

The GTAW arc can break down surrounding air to form ozone and nitrogen oxides. These gases react with lung tissue and moisture to create nitric acid and ozone burn, which is why ventilation quality matters more than many shops assume. Watch exposure duration, room air movement and fume extraction performance. And remember that a helium atmosphere displaces air, so a poorly ventilated space behaves very differently than the same space running on argon.

Manganese is the fume that deserves the most attention. Welding steel and stainless releases manganese-containing fume, and confined space welding can significantly increase exposure to it.

Exposure limit	Value	Source
Recommended exposure limit, 8-hour TWA	1 mg/m³	NIOSH
Short-term exposure limit	3 mg/m³	NIOSH
Permissible exposure limit, ceiling	5 mg/m³	OSHA

Prolonged exposure to manganese concentrations above 1 mg/m³ may lead to manganism, a Parkinsonian syndrome with tremors, slowness of movement, muscle rigidity and poor balance. Some of that damage is irreversible, which is exactly why the ceiling limit and the confined space rules exist. More on fume exposure and control is available through NIOSH’s welding health and safety resources.

Material-Specific Hazards

Titanium welds at high temperature and reacts readily with air, so titanium work has to be purged and protected from air at every stage, cooling included. Aluminium and magnesium are highly flammable, which changes the fire plan rather than just the PPE. Where these materials are involved, this guide to aerospace TIG welding standards, techniques and training shows the level of control and documentation typically expected.

The Cost Question

Helium and high-helium mixes cost materially more per cubic foot than argon. That is the trade: you pay more to buy the heat and penetration helium delivers. Spend it where it earns its keep, on thick aluminium, copper and stainless joints that need deeper penetration, and work where faster travel speed offsets the gas price. Everywhere else, a blend in the 25 to 75 percent helium range gives most of the benefit for a fraction of the cost. When comparing suppliers, look past per-cubic-foot pricing to delivery, cylinder and equipment costs, as this overview of welding gas supply, cylinders and safety explains.

The Skill Curve

GTAW is harder to master than MIG or stick. It is significantly slower, and it asks you to coordinate torch angle, filler feeding and heat control at the same time. Heli arc adds two more demands: disciplined gas flow and a more temperamental arc start, because helium’s higher ionization potential makes ignition less forgiving. Expect to burn through coupons before you touch production parts.

Formal qualification is where most serious work lands. AWS offers welder performance and welding procedure qualification programs, and codes such as AWS D1.2 for structural aluminium and D17.1 for aerospace define what the testing has to prove. This overview of what an aluminium welding course covers, its costs and career outcomes is a useful place to start, while the AWS standards library holds the actual acceptance criteria.

The practical takeaway is simple: adopt heli arc where the physics earns the spend, not everywhere. Qualify it properly, write down the gas mix and flow rates, and the process will reward you with deeper, faster, cleaner welds than the same torch running on pure argon.

A Practical Heli Arc Checklist and Final Thoughts

Understanding why a helium-shielded arc behaves the way it does only gets you so far. The shops that run heli arc welding cleanly work from a short, repeatable checklist instead of memory. Two minutes of checks before, during and after a job catches the small faults that quietly ruin welds: a nozzle fitted backwards, a flow rate set twice as high as it needs to be, a crater filled too late.

Before the Arc Strikes

• Confirm material and thickness. Trust the cut piece, not the drawing. Check for mill scale, anodising, galvanising and old heat tint. On aluminium, cleanliness right up to the joint decides the weld: our guide to prepping aluminium for welding explains why oxide is the difference between a sound weld and a porous one.
• Pick the gas deliberately. Pure argon for thin sections and general work. An argon/helium blend for mixed thicknesses where you want more heat without losing arc starting. High helium for copper, thick aluminium and joints where penetration matters more than cosmetics.
• Verify polarity before striking. DCEN for steel, stainless, nickel and most tube work. AC or square-wave AC for aluminium and magnesium.
• Match tungsten class and diameter to the amperage and grind a tip angle for the job. A 2.4 mm electrode carrying 120 A will contaminate the work long before the machine complains.
• Set the flow rate, then verify laminar flow before committing to a joint.
• Fit the nozzle and gas lens correctly. Gas lens behind the collet body, collet body screwed down properly, back cap tight. Check the torch cup for cracks and confirm the lens is not scored.
• Confirm high-frequency start and adequate post-flow. Helium’s higher ionization potential makes starts less forgiving, so the starter and the timed gas delay do more for you than on pure argon.
• Check fit-up: even gap, clean land, and a tack sequence that will not lock in stress.

During the Weld

• Keep the filler rod inside the gas shield at all times. If you can see the rod tip clearly, it is likely in atmosphere rather than in the shield. Break the rod only inside the cup.
• Keep the arc short and steady, with the electrode and workpiece separated by roughly 1.5 to 3 mm. Helium spreads heat and rewards a tight arc, but a long arc raises voltage and widens the pool.
• Watch the first few seconds. With helium, an unstable start is the earliest warning you will get. If the arc wanders off the work, check electrode condition and consider a blend with more argon.
• Fill the crater. Taper the current down and add a little filler at the end of the bead to avoid a crater crack.
• Listen to the work. A steady, quiet crackle is normal. A spitting, popping arc means the tungsten or the joint is dirty.

After the Weld

• Clean the tungsten and inspect it. A blackened or lumpy tip tells you the amperage is too high for the electrode diameter, or the rod touched the pool.
• Write down what you ran. Gas mix, amperage, volts, travel speed, electrode, nozzle and flow rate. This is the most useful habit in the whole process, because it is what makes the next weld repeatable.
• Inspect the joint for porosity, undercut and oxidation colour. On stainless, a straw or blue tint on the bead means heat input or shielding was off and corrosion resistance is compromised.

Prove It on Scrap First

Trial welds on scrap coupons of the same material and thickness are the standard way to confirm a parameter set before production work. Cut a few offcuts, weld them, section them, and look at the penetration profile, the bead shape and the oxide colour. Adjust and repeat until the coupon looks like the one you want on the job, then transfer those numbers to the real part. If your work is regulated or aerospace-adjacent, expectations are higher again, and our overview of aerospace TIG welding standards and training shows how tightly these procedures are written and verified.

Final Thoughts

Strip away the name and heli arc welding is simply TIG running in a different atmosphere. The arc, the tungsten, the machine and the technique are the same ones you already know. What changes is how the gas behaves under heat, and that single change decides whether you get deeper penetration, faster travel and a cleaner bead on thick or high-conductivity metal, or a wandering arc that fights you from the first second.

The best results come from treating gas choice, flow control and heat discipline as part of the procedure rather than a consumable detail. Run the checklist, prove the parameters on coupons, write the procedure down, and heli arc welding stops being a process you have heard about and becomes one you can actually weld with.

Frequently Asked Questions

Is heli arc welding the same as TIG welding?

Yes. Heli arc welding is gas tungsten arc welding performed with helium (or a helium–argon blend) as the shielding gas. The electrode, power source and mechanics are identical to TIG; only the atmosphere around the arc changes, which alters heat input, penetration and arc-start behaviour.

Is helium better than argon for TIG welding?

Not in general. Helium produces a hotter, wider arc with higher heat input and deeper penetration, which is a genuine advantage on thicker sections, copper and aluminium. Argon remains the better all-round choice because it is cheaper and gives more consistent arc starts, so use helium where penetration or conductivity actually demands it.

Why does my arc wander and wander when I weld with helium?

Helium has a higher ionization potential than argon, so it is harder to ionize and the arc is less stable to start and maintain. Extend the pre-flow, confirm a high-frequency start is active, check the tungsten is the right type and diameter for the current, and consider an argon/helium blend if starts are the persistent problem.

Can you weld aluminium with a heli arc machine?

Yes, and helium is often the better choice on thicker aluminium because of the extra penetration and heat input. Aluminium normally needs alternating current so the electrode-positive half-cycle breaks down the oxide layer, and joints under about 1.6 mm may be welded with DCEP. Filler such as 4043 or 5356 is typically used, and the work must be clean, dry and oxide-free.

What gas flow rate should I use for helium TIG?

Typical TIG flow runs between 10 and 35 cfh, but helium is lighter than argon, so you generally need two to three times the flow of argon to get equivalent shielding coverage. Use the lowest rate that keeps the gas column laminar, and fit a flow-meter regulator close to the power source so you can measure and adjust it.

Can you weld steel with heli arc?

Yes. Steels are most often welded with DCEN, using pure argon for thin work and introducing helium as thickness increases. Preheating is generally unnecessary for mild steel under an inch thick, but low-alloy and tool steels may need it to slow cooling and prevent martensite or cracking in the heat-affected zone.

Does ‘heli arc’ also mean helical welding of pipe and tube?

In tube and pipe work the word is sometimes used for helical or spiral torch travel that spreads heat around a round joint, which is a different concept from helium-shielded GTAW. It is worth clarifying which one you mean, because the tooling, fixturing and quality-control requirements are completely different.

Which tungsten electrode should I use for heli arc welding?

Lanthanated or ceriated electrodes such as WL15 or WL20 give good arc starting and stability for most DC work, while zirconiated WZ8 handles higher current capacity and electrode life. For AC welding of aluminium and magnesium, prefer pure or zirconiated tungsten, since thoriated types are more likely to spit particles into the weld.

What safety gear do I need for heli arc welding?

You need an auto-darkening helmet with an appropriate shade lens, flame-resistant clothing, leather gloves and full head and neck coverage, because the GTAW arc is exceptionally bright and rich in UV light. You also need good fume extraction and ventilation: the arc breaks down air into ozone and nitrogen oxides, and OSHA and NIOSH both publish specific controls for welding fume and gas exposure.

Is heli arc welding harder to learn than MIG?

Considerably. It requires coordinating torch angle, filler feeding and heat control with two hands, and the result depends on constant-current behaviour and a clean, well-prepared joint. It is also slower than MIG. That said, it produces the highest-quality, most corrosion-resistant welds, and for thin-wall and non-ferrous work the extra control is usually worth the effort.