1. Cracks in Welding Seams of Titanium Alloy Seamless Pipes

When welding seamless titanium alloy pipes, the possibility of thermal cracks occurring in the welded joints is very low. This is because the impurities such as S, P, and C in titanium and titanium alloys are very low, and the low melting point eutectic formed by S and P is rarely generated at grain boundaries. In addition, the effective crystallization temperature range is narrow, and the shrinkage during solidification of seamless titanium and titanium alloy pipes is small, so the weld metal will not produce thermal cracks.

When welding titanium and titanium alloy seamless pipes, when the oxygen and nitrogen content of the weld is high, the performance of the weld or heat affected zone becomes brittle, and cold cracks will appear under the action of larger welding stress. Its characteristic is that cracks occur several hours or longer after welding, which is called delayed cracks. Research has shown that the diffusion of hydrogen during the welding process is the main cause of this type of crack.

During the welding process, hydrogen diffuses from the high-temperature deep pool to the lower temperature heat affected zone. The increase in hydrogen content increases the amount of TiH2 precipitated in this zone, increasing the brittleness of the heat affected zone. In addition, due to the volume expansion of hydrogen compounds during precipitation, significant structural stress is caused, and hydrogen atoms diffuse and aggregate towards the high stress areas of this zone, resulting in the formation of cracks. The main way to prevent the occurrence of such delayed cracks is to reduce the source of hydrogen in welded joints.

2. Pore issues in seamless titanium alloy pipe welds

Pore is a common problem encountered during the welding of titanium alloy seamless pipes. The fundamental reason for the formation of pores is due to the influence of hydrogen. The main process measures to prevent the formation of pores are:

1) Welding should be carried out under high-purity argon protection, and the argon purity should not be lower than 99.99%.

2) Remove organic matter such as oxide skin and oil stains from the surface of titanium tubes, titanium plates, and titanium plate tubes. Chemical and mechanical methods can be used for cleaning.

3) Apply good gas protection to the molten pool, control the flow rate and flow rate of argon, and prevent turbulence, which may affect the protection effect.

4) Choosing appropriate welding process parameters and specifications, increasing the deep pool residence time to facilitate the escape of bubbles, can effectively reduce porosity.