TIG Welding Titanium: Purge Chambers, Trailing Shields & Color Guide

TIG welding titanium demands complete inert gas shielding on the weld face, the heat-affected zone (HAZ), and the back side of the joint until the metal cools below 500°F. Any exposure to air above this temperature causes oxygen and nitrogen absorption that embrittles the weld and creates visible discoloration. Use 100% argon at 99.995% purity minimum, DCEN polarity, and ERTi-2 filler for commercially pure (CP) titanium or ERTi-5 for Ti-6Al-4V alloy.

Titanium itself is straightforward to weld. It flows nicely, has good puddle control, and produces clean beads. The difficulty is entirely in gas shielding. If you can keep air away from hot titanium, you can weld it.

Why Titanium Needs Complete Shielding

Titanium absorbs oxygen and nitrogen above about 500°F. Unlike steel, which forms a surface oxide that protects the underlying metal, titanium absorbs these elements into its crystal structure. This absorption is permanent and cannot be reversed by grinding or cleaning. It makes the metal hard, brittle, and crack-prone.

At welding temperatures (3,000°F+), the absorption rate is extreme. Even brief exposure to air creates an alpha case layer that’s harder than the base metal and cracks under stress. This means you need gas shielding that covers:

1. The weld pool (standard torch cup/gas lens handles this)
2. The trailing HAZ (needs a trailing shield or chamber)
3. The back side (needs back purging or a sealed chamber)
4. The hot filler rod tip (keep it in the gas envelope)

Shielding Options

Full Purge Chamber (Glove Box)

A sealed, argon-filled enclosure where all welding takes place. The chamber is purged of air before welding begins, and oxygen content is monitored throughout. This is the most reliable method and the only one acceptable for aerospace and medical titanium.

Setup requirements:

• Sealed chamber with welding glove ports
• Argon inlet and outlet with flow control
• Oxygen analyzer reading below 20 ppm before welding
• Clear viewing window (polycarbonate or tempered glass with shade lens)
• Adequate volume for the part and torch movement

Purge chambers range from small acrylic boxes for bracket work to full walk-in rooms for large fabrications. For small shop work, a clear plastic storage bin with holes cut for the glove ports and torch cable works. Seal every joint with silicone or aluminum tape.

Trailing Shield

A trailing shield is an attachment that bolts to the TIG torch and extends the argon coverage behind the arc. As the torch moves forward, the trailing shield keeps shielding gas flowing over the cooling weld and HAZ.

Trailing shields work for open-air welding when a chamber isn’t practical. They require higher gas flow (30-50 CFH total between the torch and the trailing shield) and careful torch movement. Any sudden direction change or speed variation can leave the HAZ unprotected.

Trailing shield requirements:

• Must extend 4-6 inches behind the arc
• Fine mesh diffusers (stainless screen or sintered bronze) distribute gas evenly
• Flow rate: 15-25 CFH through the trailing shield, plus normal torch flow
• The shield must cover the full width of the HAZ, not just the weld bead

Back Purge

The root side of any full-penetration joint must be shielded with argon. Use purge dams in pipe or sealed backing fixtures on plate. Back purge flow should be 5-15 CFH, and oxygen content below 100 ppm for critical work, below 500 ppm for non-critical applications.

For detailed back purge setup instructions, see back purging stainless TIG welds. The techniques are identical for titanium, but the oxygen thresholds are stricter.

Weld Color Quality Chart

The color of a cooled titanium weld tells you exactly how much oxygen and nitrogen contamination occurred. This color chart is the primary quality inspection tool for titanium welds.

The color appears on both the weld face and the back side. Both surfaces must meet the acceptance criteria. A silver weld face with a blue back side means the back purge failed, and the root is compromised even though the face looks perfect.

CP Titanium vs. Alloy Titanium

Commercially Pure (CP) Titanium

CP grades (Grade 1, 2, 3, 4) contain no significant alloying elements. They range from Grade 1 (softest, most ductile, 35 ksi yield) to Grade 4 (strongest CP grade, 70 ksi yield). Grade 2 is the most common for general fabrication.

CP titanium is the easiest titanium to weld. It’s forgiving on heat input, doesn’t crack, and doesn’t need post-weld heat treatment. Use ERTi-2 filler for all CP grades.

Ti-6Al-4V (Grade 5)

The workhorse alloy, containing 6% aluminum and 4% vanadium. It’s twice as strong as CP Grade 2 (120+ ksi yield) and used in aerospace, motorsport, and high-performance applications.

Ti-6Al-4V is more sensitive to contamination and heat input than CP grades. The aluminum content makes it more reactive with oxygen. It’s also prone to hydrogen embrittlement if exposed to moisture. Use ERTi-5 filler (matching composition) and keep shielding even tighter than for CP titanium.

Other alloys (Ti-3Al-2.5V, Ti-6Al-2Sn-4Zr-2Mo) each have specific filler requirements. Consult the material spec sheet for filler and procedure recommendations.

Amperage Settings

Titanium settings are similar to stainless steel. The “1 amp per thou” rule applies, with adjustments for joint type.

Tungsten Selection

Use 2% ceriated (gray band) or 2% lanthanated (blue band) tungsten for titanium. Grind to a sharp point with a 20-25 degree included angle. A sharp point gives precise arc control, which matters when you’re welding inside a chamber with limited dexterity.

Never use thoriated tungsten for titanium. Thoriated tungsten can shed small particles that contaminate the weld. The radioactive concern is secondary to the contamination risk in this case.

Tungsten diameter follows the same sizing as steel. See the tungsten electrode guide for complete diameter-to-amperage charts.

Material Preparation

Titanium preparation is more demanding than any other common metal:

1. Degrease with acetone or isopropyl alcohol. Use lint-free wipes only. Shop rags leave fibers.
2. Mechanically clean the joint with a new stainless steel wire brush or carbide burr. Never use a brush that has touched other metals. The slightest iron contamination creates hard spots.
3. Handle with nitrile gloves. Fingerprint oils create porosity and discoloration. Once cleaned, don’t touch the joint area with bare hands.
4. Clean filler rod with acetone and a lint-free wipe. Store clean rod in a sealed tube.
5. Clean the tungsten by wiping with acetone before inserting into the collet.
6. Weld within 1 hour of cleaning. Titanium’s surface doesn’t reoxidize as fast as aluminum, but oils from handling and airborne contaminants accumulate.

Technique Notes

Travel Speed

Move at a moderate, consistent speed. Titanium has good puddle control and doesn’t require the frantic pace of copper or the slow precision of aluminum. The puddle is well-behaved and easy to read once you’ve worked with it.

Filler Addition

Dip filler into the leading edge of the puddle, same as any other TIG metal. Keep the hot filler rod tip inside the gas shield between dips. If you pull the rod out of the argon envelope, the tip oxidizes and deposits contamination into the next dip. Many welders keep the rod almost touching the puddle and rotate it rather than pulling it back.

Post-Flow

Set post-flow to 1 second per 10 amps of final welding current, minimum 15 seconds. The trailing shield or chamber must maintain coverage until the weld and HAZ cool below 500°F. On thin titanium, this takes 15-30 seconds. On thick sections, it can take over a minute.

Tack Welding

Every tack weld on titanium must be made under the same shielding conditions as the final weld. Tacks made in open air will be contaminated and must be ground out before final welding. If using a trailing shield, make sure the tack area receives full trailing gas coverage.

Common Problems and Fixes

Blue or Purple Welds

Insufficient gas shielding. Check in this order:

1. Verify oxygen level in chamber (must be below 50 ppm for silver welds)
2. Check trailing shield flow and coverage area
3. Look for air leaks in chamber, hose fittings, or torch connections
4. Increase post-flow time
5. Slow travel speed so the trailing shield covers the HAZ longer

Porosity

Usually caused by moisture or hydrocarbon contamination. Clean everything more aggressively. Check that gas hoses are dry and that the argon cylinder hasn’t been stored outside in wet weather. Purge gas lines for 30+ seconds before striking the arc.

Cracking

Uncommon in CP titanium. In Ti-6Al-4V, cracking usually indicates excessive oxygen contamination or hydrogen embrittlement. Verify gas purity, check for moisture sources, and ensure proper cleaning procedures. If cracking persists, the base metal may have been contaminated before you received it (check the material certification).

Tungsten Contamination

If the tungsten touches the titanium puddle, the tungsten alloys into the weld and creates a hard inclusion. Stop immediately. Grind out the contaminated area, regrind the tungsten, and restart. Titanium picks up tungsten inclusions more readily than steel because the molten titanium aggressively wets tungsten.

Gas Purity Requirements

Standard welding-grade argon (99.996%, Grade 4.6) is adequate for most titanium work. For aerospace and medical applications, use ultra-high purity argon (99.999%, Grade 5.0).

Never use argon with any reactive gas mixed in. Argon/CO2 and argon/O2 mixes used for MIG welding will instantly ruin a titanium weld. Verify the cylinder label before connecting. Color-code your regulators so a MIG argon mix can’t accidentally get connected to a TIG torch.

Gas line cleanliness matters. Rubber hoses absorb moisture and outgas at low levels. For critical titanium work, use stainless steel braided PTFE hoses. At a minimum, purge any rubber hose for 60 seconds before welding to flush moisture.

Safety Considerations

Titanium itself is non-toxic, but titanium dust and fine chips are flammable. Titanium fires burn extremely hot (3,000°F+) and cannot be extinguished with water (water decomposes into hydrogen and oxygen, making it worse). Use Class D fire extinguishers or dry sand to smother titanium fires.

Grinding titanium creates sparks that can ignite nearby combustibles. Keep the grinding area clean and away from solvents. A titanium chip fire in a shop vac is a serious hazard.

Welding fumes from titanium are relatively low toxicity compared to stainless or copper alloys, but standard welding ventilation practices still apply.