Causes and measures of cracks in titanium pipe and welding

Titanium welded pipe welding crack is a common quality defect in titanium alloy welding, because titanium alloy sulfur, phosphorus and carbon and other impurities are less, so in the grain boundary is generally not common low melting point eutectic, the effective crystallization temperature range is narrow, in the process of weld solidification shrinkage is small, so in the welding rarely appear hot cracks. If the quality of the base metal and the welding wire does not meet the standard requirements of the specification, there are quality defects in the case of itself, and there are harmful substances in the sandwich, there may be hot cracks, so in the welding should pay attention to the quality of the welding wire, and do a good job in the protection of harmful substances, strengthen the heat treatment after welding, you can effectively avoid the appearance of hot cracks.

Delayed cracks may occur in the heat affected zone during welding of titanium welded pipes, which generally appear within a period of time after welding. The occurrence of delayed cracks is basically related to hydrogen to a certain extent. Due to the diffusion of hydrogen in the molten pool and the low temperature zone to the heat affected zone in the welding process, the hydrogen content increases. Under the influence of stress, delayed cracks will occur. In order to prevent the occurrence of delayed cracks, the hydrogen content of the welded joint should be reduced as much as possible, the base material and welding wire with less hydrogen can be selected, and the cleaning work before welding is done, and the residual stress is eliminated after welding. Generally, titanium alloys with normal hydrogen content do not appear titanium hydride, so the probability of cracks in the weld is also very small. However, when the thick plate α+β titanium alloy is used for multi-layer welding, the use of industrial pure titanium as a filling material will cause the appearance of titanium hydride, which will cause hydrogen embrittleness.