Titanium alloy pipes are widely used in chemical, aerospace, and marine engineering fields due to their excellent corrosion resistance and high strength. However, they are chemically active, difficult to weld, and require extremely high process control.
Titanium alloy pipe welding typically employs all-position welding in the field, which is significantly more challenging than stainless steel pipe welding. Titanium readily reacts with gases such as oxygen, nitrogen, and hydrogen above 400℃, leading to defects such as material embrittlement and cracking. Therefore, strict control of gas protection during the welding process is essential. This article systematically analyzes the key technological points of argon arc welding for titanium alloy pipes, covering aspects such as welding material selection, beveling, cleaning and drying, gas protection, operating techniques, and environmental control, providing technical reference for practical production.
I. Welding Consumables Selection and Argon Purity Requirements
1. Welding Consumables Selection Principles: Welding of titanium alloy pipes follows the principle of "equal strength matching," prioritizing welding consumables with compositions similar to the base metal. If suitable welding consumables are unavailable on the market, they can be cut from the base metal. For example, ERTi-2 welding wire can be used for Gr2 pure titanium pipes, and ERTi-5 welding wire can be used for Gr5 titanium alloy pipes.
2. Argon Purity Requirements: Argon purity directly affects the hardness and toughness of the weld, and has a significant impact on crack sensitivity. High-purity argon (≥99.99%) is required for pure titanium welding, and the argon purity for titanium alloy welding must also be ≥99.99%. The argon flow rate needs to be adjusted according to the pipe diameter; typically, the argon flow rate inside the pipe is 10-20 L/min, and the external shielding gas flow rate is 15-25 L/min.
II. Beveling and Cleaning Protection
1. Beveling Methods: Titanium tube cutting and beveling should be done using cold working methods (such as plasma cutting or abrasive wheel cutting). Flame cutting is strictly prohibited to avoid overheating and causing material oxidation and discoloration. The inner and outer surfaces of the bevel within a 20mm radius should be polished to a metallic luster with an abrasive wheel or stainless steel wire wheel, then deburred with a scraper and polished a second time to prevent wire snagging during cleaning.
2. Cleaning Process Key Points
Cleaning quality directly affects the formation of welding cracks and porosity.
The following steps must be followed:
1. Pickling: Use a mixed solution of 3% HF + 35% HNO₃ + H₂O. The soaking time should be adjusted according to the pipe diameter (usually 5-15 minutes);
2. Rinsing: Thoroughly rinse the pickling solution with clean water to avoid residue;
3. Drying: Dry with hot air or air dry naturally. Do not wipe with a cloth;
4. Pre-welding wiping: Before welding, wipe the bevel and a 50mm radius on both sides with acetone or alcohol to remove oil and impurities. Precautions:
• Welding must be completed within 4 hours after cleaning; otherwise, cleaning must be repeated;
• Rubber gloves are prohibited during cleaning; clean white cotton gloves should be worn;
• The pickling solution must be replaced regularly to prevent it from becoming ineffective.
III. Gas Protection and Temperature Control Argon Purging Inside the Pipe:
Argon purging inside the pipe must continue until welding is complete and the temperature of the welding area drops below 350℃.
Purging Method:
1. Sealing: Seal both ends of the pipe with rubber sealing plates (0.5-1mm gap from the inner diameter of the pipe);
2. Replacement: Purge with argon gas for 10-15 minutes before welding, and confirm the gas inside the pipe is pure argon using an open flame test;
3. Flow Control: Maintain positive pressure inside the pipe during welding to prevent air intrusion. External Front Protection: External front protection uses a large-diameter nozzle (diameter ≥20mm) and an extended shroud (length ≥150mm) to increase the protection range. Gas supply through the shroud must continue until the temperature of the welding area drops below 200℃ to prevent oxidation in the high-temperature zone.
By systematically controlling the above-mentioned key process points, defects such as cracks and porosity in the welding of titanium alloy pipes can be effectively avoided, ensuring that the quality of the welded joints meets the standard requirements.
Baoji Reliab Metal Materials Co.,Ltd
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