Titanium Pipe Welding Technology

The welding quality of titanium pipes has a direct influence on product performance stability and service life. Titanium readily reacts with oxygen, nitrogen, hydrogen and other gases at high temperatures.Thereby,during the welding of titanium pipes, it is necessary to control for the welding technologies to ensure the quality.

 

The seamless titanium pipes and welded titanium alloy pipes in Ruihang

 

 

 

(I) Selection of Welding Methods

• For thin-walled titanium pipes:

Tungsten Inert Gas Welding: Easy to operate, stable in quality, and strong in adaptability.

 

• For medium and thick-walled titanium pipes:

Plasma Arc Welding: High energy density, fast welding speed, and narrow weld seam.

 

• For high-end precision titanium pipes:

Electron Beam Welding, Laser Beam Welding: High-energy beam welding with small deformation and high weld quality. It can weld thick-walled materials, but the equipment cost is high.

 

All welding methods require inert gas protection for the welding area to avoid contact between high-temperature metal and air.

 

(II) Pre-Welding Preparation

• Cleaning for Welding Joints

Need to remove oxide scale, oil, moisture, and impurities from the joint surface.

20-30mm area on both sides of the joint.

Oxide Scale: Mechanical grinding with a stainless steel wire brush/grinding wheel or pickling. After pickling, rinse with clean water and dry thoroughly.

Oil and Moisture: Wipe and clean with organic solvents like alcohol and acetone.

 

• Assembly and Fixing

Too large gaps may lead to incomplete penetration and slag inclusion in the weld seam, while excessively small gaps will increase welding stress.

Fix thin-walled titanium pipes with special fixtures before welding.

 

(III) Control of Welding Process Parameters

• Current: A key parameter determining heat input. Too high current may cause weld overheating, coarse grains, and burn-through; too low current will result in incomplete penetration and poor forming.

 

• Speed: Need to match the current. Excessively fast speed leads to insufficient heat, easy incomplete penetration, and narrow and high weld seams; excessively slow speed causes excessive heat, weld overheating, coarse grains, and high oxidation risk.

 

• Argon Flow Rate: Insufficient flow rate cannot effectively protect the welding area, making the weld seam prone to oxidation; excessive flow rate wastes gas and generates turbulence to entrain air.

 

• Tungsten Electrode Diameter and Protrusion Length: The diameter is selected according to the current , and it needs to be ground into a sharp/conical shape to ensure stable arc; the protrusion length is controlled at 3-5mm. Excessively long length results in unstable arc and poor protection, while excessively short length causes overheating of the nozzle and affects operation.

 

(IV) Protection During Welding

• Triple Protection of the Welding Area

Molten Pool Protection: Keep the welding torch nozzle 5-10mm away from the workpiece, and use the argon gas from the nozzle to fully cover the molten pool.

Protection of High-Temperature Weld Seam Area: Before the weld seam cools below 400℃, use a trailing shield to move synchronously with the welding torch, and continue argon gas protection to prevent oxidation.

Backside Protection: For titanium pipe welding with requirements, install sealing devices at both ends, and pass argon gas into the pipe to expel air, avoiding oxidation of the inner wall.

 

• Welding Environment

Keep a clean and dry environment. Do not weld in windy, humid, or dusty environments.Need to prevent affecting the argon protection effect or contaminating the weld seam.

 

II. Key Points for Post-Welding Treatment

• Post-Welding Heat Treatment

Stress Relief Annealing: Temperature and holding time need to be controlled in a specific range, then air cooling or furnace cooling are required. It eliminates welding residual stress and prevents deformation and cracking during use.

Solution Aging Treatment: Suitable for titanium alloy titanium pipes that need to improve strength. The solution temperature is 800-950℃, followed by rapid cooling after holding; then aging treatment at 450-550℃ to precipitate strengthening phases and improve weld strength.

 

• Surface Cleaning and Trimming

Remove spatter, weld beads, and oxide scale on and around the weld seam by mechanical grinding or pickling; ensure a smooth transition between the weld seam and the base metal during grinding.

Perform pickling and passivation treatment to remove the oxide film and form a dense passivation film in order to improving corrosion resistance.

 

 

• Visual Inspection

The checking of the weld formation, width, and height. To ensure the flatness and smoothness on the surface , without defects like incomplete penetration, incomplete fusion, slag inclusion, porosity, or cracks.

 

• Non-Destructive Testing

Use Radiographic Testing and Ultrasonic Testing to detect problems for internal such as porosity, slag inclusion, and incomplete penetration.

Use Magnetic Particle Testing and Penetrant Testing to identify cracks, incomplete fusion, and other issues for Surface and Near-Surface.

 

• Special Performance Testing

Mechanical : For titanium pipes with special requirements, perform tensile, bending, and impact tests.

Corrosion Resistance: Verify corrosion resistance through salt spray tests and immersion tests.