Shielding Gas Basics: Argon Flow, Coverage, and Oxidation Prevention

What Shielding Gas Does in TIG

In TIG welding, shielding gas forms a protective envelope around two critical areas: the molten weld puddle and the hot tungsten electrode. At welding temperatures, oxygen and nitrogen from air react aggressively with the puddle and the tungsten. The results show up as oxidation, porosity, brittle weld metal, unstable arc, and tungsten contamination. Argon (and argon-based mixes) displaces air at the arc so the puddle solidifies without absorbing oxygen/nitrogen, and the tungsten stays clean and stable.

Think of shielding as “coverage.” You are not just setting a number on the regulator—you are managing a stable, laminar gas blanket that stays intact from arc start through cooling.

Choosing Gas for Beginner Materials

Step-by-step: pick the right gas

• Mild steel: Use 100% argon for standard TIG practice. It provides stable arc starts and adequate shielding for clean steel work.
• Stainless steel: Use 100% argon for most beginner joints. Stainless is sensitive to oxidation; good coverage and post-flow matter as much as the gas choice.
• Aluminum: Use 100% argon for typical AC TIG on common thicknesses. It supports stable cleaning action and puddle control for learning.

Mixed gases (advanced contexts, kept practical)

You may encounter argon mixes later for specific goals (more heat, faster travel, deeper penetration), especially on thicker sections or production work. Common examples include argon/helium blends (often for aluminum or copper alloys) and small additions of hydrogen in specialized stainless applications. Treat these as “process tuning” tools: they can change arc characteristics and heat input, but they do not replace correct coverage, cup choice, and torch distance.

Coverage Is a System: Flow Rate, Cup Size, and Torch Distance

Shielding quality is the combined result of (1) flow rate, (2) cup size and gas delivery, and (3) how you hold the torch. Changing one often requires adjusting the others.

1) Setting argon flow rate (and why too much can be worse)

Argon flow is commonly set using a flowmeter. Your goal is enough flow to maintain coverage without creating turbulence. Excessive flow can create a venturi effect and turbulence at the cup edge, which can pull surrounding air into the shielding stream. That can cause oxidation even though the flow number is high.

Continue in our app.

• Listen to the audio with the screen off.
• Earn a certificate upon completion.
• Over 5000 courses for you to explore!

Or continue reading below...

Download the app

Step-by-step: establish a baseline flow

1. Start with a moderate baseline appropriate for your cup size and indoor conditions. If you need a simple starting point, begin around 15–20 CFH (approximately 7–10 L/min) for many common setups.
2. Run a short bead on scrap with consistent torch angle and distance.
3. Inspect for oxidation/porosity cues (see the “Reading oxidation and heat tint” section). If oxidation appears despite clean technique, adjust coverage variables in this order: draft control → torch distance → cup size → flow rate.
4. Increase flow in small steps if coverage is weak (for example, +2–3 CFH at a time). Stop increasing once oxidation improves; if oxidation gets worse at higher flow, you’ve likely crossed into turbulence.

Quick symptoms: low flow vs excessive flow

2) Cup size: how it affects coverage

The cup shapes and directs the gas. A larger cup generally provides a wider, more forgiving shielding envelope, especially helpful for stainless and for joints where the puddle is exposed longer. A smaller cup can work well in tight access but is less tolerant of drafts and torch movement.

Step-by-step: match cup size to the job

1. General practice: Use a medium cup for most flat practice beads and fillets.
2. Stainless or wider puddles: If you see heat tint spreading or oxidation at the toes, try a larger cup before cranking up flow.
3. Tight corners: If you must use a smaller cup, compensate with tighter torch distance and better draft control rather than excessive flow.

3) Torch distance and angle: keep the gas blanket intact

Shielding gas coverage is strongest close to the cup. As you lift the torch, the gas stream spreads and mixes with air. Long arc length and excessive torch-to-work distance are common causes of oxidation for beginners even when the flow setting seems “right.”

Step-by-step: set torch distance for reliable shielding

1. Keep the cup close to the work while maintaining control and visibility. Avoid “floating” high above the puddle.
2. Maintain a consistent angle so the gas stream stays centered over the puddle. Sudden angle changes can expose the puddle edge to air.
3. Watch the puddle edges: if the edges look dull/dirty or the puddle seems to “skin over,” treat it as a shielding warning and correct distance/angle first.

Drafts, Fans, and Shop Air: The Hidden Shielding Killer

Even a correct flow rate can fail if air movement disrupts the gas envelope. Drafts from open doors, fans, HVAC vents, or compressed-air tools can push shielding away from the puddle and tungsten.

Step-by-step: draft control checklist

• Pause fans aimed at the work area during welding.
• Shield the weld zone from cross-breezes (simple barriers or repositioning the work can help).
• Listen and observe: if shielding problems appear only at certain bench positions or times, suspect airflow before changing gas settings.

Pre-flow and Post-flow: Protecting Starts, Stops, and the Tungsten

Shielding is needed before the arc starts and after it stops. Pre-flow purges air from the cup area so the arc starts under argon. Post-flow protects the cooling puddle and, importantly, the tungsten while it is still hot and reactive.

Step-by-step: practical pre-flow use

1. Set a short pre-flow so argon is present at arc start (often around 0.2–0.5 seconds on many machines).
2. If you’re welding in a drafty area or using a larger cup, you may benefit from slightly longer pre-flow to ensure the cup is fully purged.

Step-by-step: practical post-flow use

1. Start with a few seconds of post-flow and adjust based on amperage and how hot the tungsten gets. Higher amperage generally needs longer post-flow.
2. Keep the torch in place over the end of the bead until post-flow finishes. Moving away early exposes the cooling crater and hot tungsten to air.
3. Use tungsten appearance as feedback: if the tungsten turns dull, oxidized, or crusty after stopping, increase post-flow and/or hold position longer.

Gas Delivery Problems: Leak Checks and Simple Diagnostics

Shielding issues are not always “settings.” Small leaks, loose fittings, damaged hoses, or a mis-seated torch back cap can reduce effective shielding at the cup even when the flowmeter reads correctly.

Step-by-step: quick leak and delivery check

1. Confirm cylinder valve and regulator connections are snug and correctly seated.
2. Pressurize the system and listen for hissing along the regulator, hose, and torch connections.
3. Use a leak-detection solution (soapy water works) on suspect joints; bubbles indicate a leak.
4. Check torch consumable seating: a misaligned cup or loose parts can disrupt gas flow patterns and create turbulence.
5. Verify actual flow: if your setup allows, briefly flow gas and feel for consistent output at the cup (without contaminating the cup or tungsten). Inconsistent flow can indicate restrictions or leaks.

Reading Oxidation and Heat Tint as Shielding Feedback

Your weld surface is a real-time indicator of shielding quality. Learn to treat color and surface texture as a diagnostic tool rather than guessing at settings.

Stainless steel: heat tint tells you about oxygen exposure

On stainless, heat tint (straw, bronze, blue, purple, gray) forms when the surface oxidizes while hot. Some tint is common, but heavier/darker tint generally indicates more oxygen exposure or prolonged high heat. If you see heavy blue/gray tint close to the bead, suspect inadequate coverage, too much torch distance, drafts, or insufficient post-flow.

Mild steel: surface soot and porosity cues

Mild steel may show a dull, dirty-looking bead, soot at the toes, or pinholes/porosity when shielding is compromised. If the bead suddenly becomes rough or peppered with tiny holes, check for drafts, then verify flow and leaks.

Aluminum: black soot and “sugary” contamination signs

Aluminum is very sensitive to shielding disruption. Black soot, a dirty-looking puddle, or a grainy/contaminated bead surface can indicate poor shielding coverage (often from drafts, excessive torch distance, or turbulent flow). If the arc becomes erratic and the tungsten shows contamination quickly, treat it as a shielding and technique alarm.

Step-by-step: use appearance to tune shielding

1. Make a short test bead with steady torch distance and travel.
2. Inspect the bead and the stop crater (the crater is often where shielding fails first).
3. If oxidation is localized at the end, increase post-flow and hold the torch over the crater until gas stops.
4. If oxidation is along the whole bead, address drafts and torch distance first, then adjust cup size/flow.
5. If oxidation worsens as you increase flow, reduce flow and focus on stabilizing torch position and blocking drafts.