Welding requirements and precautions for titanium alloy pipes
(1) Set up special welding workshops as far as possible. Smoking is strictly prohibited in the room. The environment is clean and dry and the convection of air is strictly controlled.
(2) Welders wear clean work clothes and degreasing gloves when welding. Bare-handed touching of parts is strictly prohibited.
(3) Degrease the welding area and wire surface with acetone.
(4) Protect argon with high purity, the purity is not less than 99.99%. The gas flow during welding shall protect the front and back of the bead according to the values specified in the process regulations.
(5) During the welding process, the argon flow rate of the argon gas and the welding tool nozzle in the titanium alloy pipes should be kept constant to prevent the convexity and concavity of the weld pool formation in the pipe.
(6) Short arc welding with small welding line energy should be used when welding.
(7) When spot welding the butt joint, the clearance is less than 30% wall thickness. Each weld should be welded as once as possible.
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(8) When welding, the welding tools should not swing from left to right and the melting end of the welding wire should not be moved out of the gas protection zone. Gas should be supplied 10-15s in advance when arc striking. The welding gun can not be lifted immediately when an arc is interrupted. The gas supply should be delayed for 15-30s until the temperature drops below 250 C.
Titanium alloy pipe welding process
1) Cleaning before welding
The generation of welding defects is closely related to the surface cleanliness of welding parts and wires. Oil, water, oxide film, and other dirt on the edge of the pipe joint within 15-20mm and the surface of welding wire should be cleaned before welding. Cleaning methods include chemical (pickling) or mechanical (stainless steel brushing) removal of surface scale. Acetone or alcohol should also be used to wipe the welds before welding. Cleaned welds must be welded within 24 hours, otherwise, they need to be cleaned again. It is best to dehydrogenate the welding wire after pickling and degrease it with acetone before welding.
2) Gas protection. In order to prevent the welded joint from being contaminated by harmful gases and elements at high temperatures during welding, the necessary argon protection must be carried out for the weld with a purity of 99.99%.
3) Selection of welding process parameters.
(1) Selection of welding wire. The brand of filler wire should be selected according to the base metal. Generally, the principle of homogeneity with the base metal is adopted. Sometimes, in order to improve the plasticity of the joint, the welding wire with a lower alloying degree than the base metal can be selected.
(2) Selection of power supply and polarity. The manual argon-tungsten arc power supply is usually used for titanium and titanium alloy welding, and a direct current is used for polarity connection.
(3) Selection of the tungsten electrode. The diameter of the tungsten electrode shall be selected according to the wall thickness of the titanium alloy pipe, generally between 1.0-3.0mm, and the tungsten electrode shall be ground into a cone of 25 ° ~ 45 °.
(4) Selection of welding current and other parameters.
