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Cracks and porosity in the weld of titanium pipe and titanium alloy pipe

1. Weld crack of titanium pipe and titanium alloy pipe

Titanium alloy welding, the welding joint of hot cracking formation of possibility is very small, it is because the titanium and titanium alloy in the impurities such as S, P, C, and so formed by S, P, rarely generate low melting eutectic in grain boundary, combined with effective crystallization temperature range is narrow small, titanium and titanium alloy solidification shrinkage small, weld metal does not produce hot crack.

During the welding of titanium and titanium alloy, when the content of oxygen and nitrogen in the weld is high, the properties of the weld or the heat-affected zone become brittle, and cold cracks will appear under the action of larger welding stress.It is characterized by a crack that occurs several hours or longer after welding as a delayed crack.It is shown that hydrogen diffusion during welding is the main cause of this kind of crack.In the welding process, hydrogen diffused from the high temperature deep pool to the lower temperature heat affected area. The increase of hydrogen content increased the amount of TiH2 precipitated in this area, and increased the brittleness of the heat affected area.The main way to prevent this delayed crack is to reduce the source of hydrogen in the welded joint.

2. Porosity in the weld of titanium pipe and titanium alloy pipe

When titanium tube is welded, stoma is a main problem that often encounters.The root cause of stomatal formation is the result of hydrogen influence.The main technological measures to prevent the generation of air holes include:

  1. 1) welding shall be carried out under the protection of high purity argon, and the purity of argon shall not be lower than 99.99%

  2. 2) thoroughly remove the organic matter such as scale grease on titanium tube, titanium plate and the eye surface of titanium plate tube.It can be cleaned chemically or mechanically.

  3. 3) apply good gas protection to the molten pool, control the flow and velocity of argon gas, prevent turbulence and affect the protection effect.

  4. 4) select appropriate welding process parameters and welding specifications, increase the retention time of deep pool, facilitate bubble escape, and effectively reduce porosity.



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