1. Cracks in Welding Seams of Titanium Alloy Seamless Pipes

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

When welding titanium and titanium alloy seamless pipes, when the weld seam contains high oxygen and nitrogen content, the performance of the weld seam or heat affected zone becomes brittle, and under the action of large welding stress, cold cracks may appear. 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, coupled with the diffusion and aggregation of hydrogen atoms towards the high stress areas of this zone, resulting in the formation of cracks. The main way to prevent the occurrence of delayed cracks is to reduce the source of hydrogen in welded joints.

2. Blowhole Problems in Welding Seams of Titanium Alloy Seamless Pipes

When welding titanium alloy seamless pipes, porosity is a major problem that is often encountered. 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 the protection of high-purity argon gas, and the purity of argon gas should not be less 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 tube holes. 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 the occurrence of turbulence, which affects the protection effect.

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