Key Points Of TIG Welding For Titanium Alloy Pipes

Titanium reacts easily with oxygen, nitrogen and hydrogen at temperatures above 400℃, resulting in weld embrittlement, blowholes, cracks and other defects. For this reason, TIG welding must follow stringent processes featuring full-process inert gas protection, low heat input and clean construction.

 

 

Gas Tungsten Arc Welding (GTAW/TIG) with direct current electrode positive (DCEP) is the best method for titanium alloy pipes.

• Wall thickness ≤3mm: Full TIG welding
• Wall thickness ＞3mm: TIG backing welding + MIG filling and capping
• Strictly prohibited: Shielded metal arc welding (SMAW), CO₂ gas shielded welding, oxy-fuel welding

 

Equipment requirements:

• Equipped with high-frequency arc striking, current attenuation and delayed gas supply functions
• Delayed gas supply time ≥15s
• Cerium tungsten electrodes are selected, with the tip ground into a 30°–45° cone and a diameter of 1.0–3.0mm

 

 

1. Groove Preparation and Assembling

• V-groove is commonly used, with an angle of 60°–70° and a root face of 0.5–1.5mm
• Assembling gap of 1.0–2.0mm and misalignment ≤10% of the wall thickness
• Tack welding shall adopt the same process, with short weld spots and adequate protection; all defects must be ground off

 

2. Thorough Cleaning

• Mechanical cleaning: Remove oxide scale with stainless steel wire brushes or sandpaper
• Chemical cleaning: Acetone degreasing → Pickling with 5%HF + 35%HNO₃ solution → Rinsing with clean water → Drying
• Completed within 2 hours before welding; oil, water stains and dust are strictly prohibited
• Operators shall wear clean white gloves and are not allowed to touch the groove directly

 

3. Welding Environment

• Wind speed ≤1.5m/s; wind protection measures are a must
• Ambient temperature ≥5℃ and relative humidity ≤60%
• Local preheating to 50–100℃ in low-temperature environments; high-temperature preheating is forbidden

 

 

The success of titanium alloy welding depends on comprehensive argon gas protection without dead angles.

1. Requirements for Protective Gas

• Argon purity ≥99.99%, preferably 99.995%
• Dew point ≤-40℃ and water content ≤50mg/m³

 

2. Triple Protection Configuration

• Front nozzle protection: Flow rate of 8–15L/min with a large-diameter nozzle
• Backside argon filling protection: Flow rate of 5–10L/min; the two sides of the groove within 150–300mm shall be sealed with soluble paper
• Trailing shield protection: Length ≥100mm and flow rate of 5–8L/min to cover the high-temperature zone until cooling

 

3. Key Protection Operations

• Continue gas supply after arc extinction until the weld temperature drops to ≤350℃ before moving the welding torch
• The wire end shall remain in the protected area at all times and must not be moved out
• Interpass temperature for multi-layer welding ≤200℃; welding in a cold state is recommended

 

 

1. Principle of Low Heat Input

• Low current, short arc, fast welding speed and no torch oscillation
• Heat input control: 6–35kJ/cm
• Avoid coarse grain and plastic decline

 

2. Typical Parameters (for reference)

• Tungsten electrode diameter: 1.6–2.4mm
• Welding current: 50–90A for backing welding, 80–140A for filling welding
• Arc voltage: 10–15V
• Welding wire: Homogeneous with the base metal (ERTi-2/ERTi-4 for TA2/TC4 respectively)

 

3. Operational Specifications

• Welding torch inclination angle: 75°–85°; welding wire inclination angle: 10°–15°
• Minimize lateral oscillation of the welding torch to avoid damaging the gas curtain
• Random arc striking on the base metal surface is prohibited
• Fill the crater during arc extinction and adopt current attenuation to prevent shrinkage cavities

 

 

• Silvery white is the optimal weld color; the darker the color, the poorer the protection effect:
• Silvery white: Qualified
• Pale yellow: Qualified
• Dark blue: Slight oxidation, usable
• Gray/Off-white: Severe oxidation, must be chipped off and rewelded

 

 

Oxidation Embrittlement

• Causes: Protection failure, excessively high temperature
• Countermeasures: Strengthen triple protection, adopt delayed gas supply, strictly control interpass temperature

Blowholes

• Causes: Oil contamination, moisture, impure argon, improper flow rate
• Countermeasures: Thorough cleaning, use high-purity argon, maintain short arc, adopt appropriate flow rate

Cold Cracks/Plasticity Decline

• Causes: Hydrogen embrittlement, coarse grain
• Countermeasures: Strictly control hydrogen sources, apply low heat input, perform stress relief annealing if necessary

 

 

• Visual inspection: No cracks, blowholes, pits or oxidation on the weld surface
• Dye penetrant testing (PT) and radiographic testing (RT)
• Grind off severely oxidized areas and perform repair welding if necessary
• Vacuum annealing can be conducted on key components to improve plasticity and stability

 

 

Ruihang Elaborate Material Co., Ltd. provides high-quality titanium and titanium alloy products. Our stringent welding processes ensure that we fully meet our customers' requirements.For more details, please feel free to contact us by email: Sam.Rui@bjrh-titanium.com