Welding of Titanium and Titanium Alloys

Titanium and titanium alloys are widely used in the chemical industry, shipbuilding industry, aerospace industry, and other specialized machinery manufacturing industries due to their excellent processing, mechanical, and corrosion resistance properties. However, the high-temperature chemical activity of titanium metal places special requirements on the welding process. Therefore, selecting a suitable and excellent welding process to avoid welding oxidation and defects is crucial for the welding of titanium and titanium alloys. Especially for the on-site welding of titanium pipes, special attention must be paid to process control to ensure that the product quality meets requirements.

Titanium Pipe Welding Operation Points
Welding Materials

(1) Argon Gas
Grade 1 argon gas should be used for welding titanium pipes. The argon purity should not be less than 99.99%, the dew point should be below -40℃, and the moisture content should be below 0.001 mg/L.

(2) Welding Wire
The composition of the welding wire used for welding titanium pipes should be the same as that of the base metal, and the surface should be free of defects such as burn marks, cracks, oxidation, or metallic and non-metallic inclusions. The welding wire should be dried before welding. Pipe Cutting and Beveling

① Pipe cutting and beveling should be performed mechanically in a specialized work area. Tools should be dedicated and kept clean to prevent iron contamination. Finished pipe ends should have a smooth surface, free from cracks, scale, and other defects. The maximum inclination deviation of the cut plane should not exceed 1% of the pipe diameter.

② Selection of Beveling Type: The selection of the beveling type and size should consider ease of ensuring weld joint quality, minimal filler metal to reduce cumulative gas absorption in the weld, prevention of decreased weld joint plasticity, ease of operation, and reduction of welding deformation.

Beveling Cleaning: After cleaning the bevel and the inner and outer surfaces within 25mm on both sides, use a fine file, austenitic stainless steel wire brush, milling cutter, or other mechanical methods to remove oxide film, burrs, and surface defects. Cleaning tools should be dedicated and kept clean to prevent iron contamination.

After mechanical cleaning, the bevel surface and welding wire should be degreased with sulfur-free acetone or ethanol before welding. The use of chlorinated solvents such as trichloroethylene and carbon tetrafluoride is strictly prohibited. Avoid attaching cotton fibers to the surface. If welding is not performed within 4 hours of cleaning, re-clean before welding.

The cleaning methods and requirements for titanium welding wire are consistent with those for bevel cleaning.

Weld Assembly and Tack Welding

(1) Weld Assembly: Tools used during titanium tube assembly must be made of austenitic stainless steel. Iron contamination should be avoided during assembly. The weld joints should be concentric, and the misalignment should not exceed the standard.

(2) Tack Welding: The tack welding distance for titanium tubes is generally 100–150 mm, and the tack welding length is 10–15 mm. The tack welding process is the same as the formal welding.

Welding Process

(1) Titanium tube welding uses tungsten inert gas (TIG) gas shielded welding with direct current positive polarity. Cerium tungsten electrodes are recommended, and the electrode tip should be ground into a conical shape.

(2) Due to the tendency for brittle fracture and coarse grains to occur during titanium tube welding, a low welding heat input should be selected when choosing the welding process. The welding process parameters are shown in the table below.

(3) Welding Technical Requirements

① Personnel participating in titanium tube welding should undergo specialized training before welding, master the welding techniques, and obtain the corresponding welding qualifications before participating in titanium tube welding operations.

② For titanium tube welding construction, a welding process card must be prepared and implemented. Welding heat input must be strictly controlled, and the dwell time in the high-temperature zone of the weld should be shortened to prevent the formation of brittle hard structures and coarse grains. The interpass temperature must not exceed 200℃.

③ During tungsten inert gas (TIG) welding, if the tungsten electrode touches the molten metal pool, welding should be stopped immediately, the contamination removed, and if necessary, the tungsten electrode tip ground down before welding resumes.

④ All welding operations should be carried out under argon protection. The welding torch nozzle should protect the molten pool, the welding torch drag shield should protect the hot weld, and the back side should be filled with argon to protect the weld and the inner surface of the near-weld zone. The protection measures should be sufficient and reliable and should meet the following requirements.

a. The nozzle diameter of the welding torch should preferably be ф12～20mm, and the emitted argon gas should maintain a stable laminar flow.

b. The type of welding torch shield should be determined according to the shape and size of the workpiece, requiring reliable protection and convenient operation.

c. The torch tube should be pre-filled with argon, air should be purged, and a slight positive pressure and flow should be maintained.

d. When igniting the arc, the welding torch must be supplied with gas in advance, and high-frequency arc ignition should be used; when extinguishing the arc, a current attenuation device and a gas delay protection device should be used, the arc crater must be filled, and atmospheric pollution should be avoided. During welding, the tape attached to the weld bevel should be removed as welding progresses.

e. During welding, the heated end of the filler wire should always be kept under argon protection. After the arc is extinguished, the filler wire should not be immediately exposed to the atmosphere; it should be removed when the weld is no longer protected. If the filler wire is contaminated and oxidized, the contaminated portion should be cut off.

f. When welding on-site, wind protection measures must be taken to prevent the influence of ambient wind on the welding shielding gas.

g. The welding area for titanium materials should be a separate area. If it is located in a workshop where steel is handled, a separate, enclosed titanium welding area should be designated. During welding, keep away from ventilation openings and open doors and windows. The area should be covered with insulating mats such as rubber.

h. During welding, the weld color should be closely observed to confirm the effectiveness and quality of gas protection. The weld color for titanium pipes is shown in the table below.

(4) Weld Repair

① Any weld defects discovered through non-destructive testing must be repaired. Before repairing, the causes of the defects should be analyzed, and a "Weld Repair Process Card" should be prepared based on the causes. Repair welding should be carried out according to the weld repair process specified in the "Weld Repair Process Card".

② The number of repairs for the same weld location should not exceed two. When a second repair is required, a quality analysis of the defective weld should be conducted, repair measures should be formulated, and the repair should be carried out after approval by the welding supervisor. This should be noted in the construction record.