Essential Titanium Welding Practices For Heat Exchangers And Coil Fabrication

Titanium heat exchangers and titanium coils are applied in highly corrosive working conditions. The welding quality directly affects the sealing performance, anti-corrosion properties and service life of the equipment. Titanium materials  are prone to absorbing hydrogen, oxygen and nitrogen at high temperatures. It can easily cause weld embrittlement, pores and cracks. Welding must strictly follow three core principles: a clean working environment, inert gas protection and low heat input.

• · Use Gr1/Gr2/Gr5 titanium with grade verification; match same-spec fully cleaned titanium welding wires; adopt 99.99% high-purity argon as shielding gas.
• · Cut V-grooves mechanically or by plasma (gas cutting strictly prohibited). Thoroughly clean weld zone inside/outside, weld within 2 hours, and argon-purge the area pre-welding.
• · Implement wind, temperature and dust control; use dedicated anti-deformation tooling; equip complete double-sided argon protection facilities.

Adopt DCEN Gas Tungsten Arc Welding GTAW uniformly. Follow the low heat input principle with small current, fast welding speed, short arc and multi-layer multi-pass welding to reduce high-temperature dwell time, avoiding weld oxidation and grain coarsening.

1.Titanium Heat Exchangers

The tube end should protrude 1~2mm to ensure full penetration, and Z-shaped skip welding is adopted to prevent deformation.

Weld the inner side first and then the outer side, apply double-sided argon protection, and strictly control the size and process parameters of tack welding.

Weld the carbon steel base layer first, and weld the titanium layer with low heat input only after the base layer passes acceptance inspection.

2. Titanium Coils

Strictly control the misalignment during splicing and butt jointing, and rely on rollers to rotate at a constant speed for welding to ensure uniform weld formation.

Apply internal and external double argon protection for backing welding, and water cooling can be used for cover welding to strictly control the interpass temperature.

Unify the groove standard for elbow butt joints, and extend the argon protection time to avoid high-temperature oxidation on the inner side of the elbow.

• Arc ignition must be performed on a dedicated arc striking plate. Direct arc striking on the workpiece is prohibited. Standardize the welding direction for all-position welding.
• Enable current decay function during arc termination to completely fill the crater. Continue argon gas supply after arc extinction until the weld cools down to below 350℃.
• Tack welding shall follow the same process parameters as formal welding. Any defects in tack welds must be completely removed by grinding before formal welding.

1. Full-process Gas Protection Control

Adopt the bottom-in and top-out argon filling method inside the tube, and strictly control the internal oxygen content ≤50ppm. The welding trailing shield shall fit closely to the workpiece, and the argon flow rate shall be precisely controlled to avoid turbulent flow and oxygen leakage. Judge the welding quality by the weld surface color: silver white and light yellow are qualified, while blue purple and gray black indicate excessive oxidation, which requires grinding or cutting and re-welding.

2.Prevention and Control of Common Welding Defects

• Caused by impurities, water vapor, impure gas source and poor shielding effect. It can be effectively avoided by thorough pre-welding cleaning, using high-purity argon gas, standardizing shielding measures and adopting short arc welding.
• Caused by hydrogen intrusion, excessive heat input and high interpass temperature. Strictly control the moisture content of the shielding gas, adopt low heat input, cool down the interpass temperature to below 60℃, and perform post-weld annealing if necessary.
• Caused by improper groove size, insufficient welding current and excessively fast welding speed. Optimize the groove dimensions, match appropriate welding parameters, and swing the welding torch slightly and uniformly during welding.

3.On-site Cleanliness Management

Wear dust-free gloves during operation, and it is strictly prohibited to touch the welding area and welding wire with bare hands. Use special grinding tools for titanium materials, and it is strictly prohibited to mix tools used for dissimilar metals to prevent iron contamination. Clean up the defects of each weld pass completely before proceeding to subsequent welding.

• Visual Inspection: The weld shall be free of defects, with a reinforcement of 0~1.5mm, regular formation, silver white or light yellow surface color, and no oxidation traces.
• Non-destructive Testing: 100% penetrant testing for all welds; radiographic testing for critical welds; hydraulic pressure test for the complete equipment.
• Subsequent Treatment: Restore the anti-corrosion performance by pickling and passivation; repair unqualified welds according to the original process and conduct re-inspection; protect finished products from bumps and keep them away from carbon steel materials to prevent iron contamination.
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Ruihang Group mainly produces titanium products with the complete industry chain,including smelting,forging, straightening,rolling,surface treating,testing process. For any purchasing needs, feel free to contact us at email:Sam.Rui@bjrh-titanium.com