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 there are less impurities in titanium alloy, such as sulfur, phosphorus and carbon, so low melting point eutectic is generally not common in grain boundaries, the effective crystallization temperature interval is narrow, in the process of weld solidification shrinkage is small, so there will be few hot cracks in welding. If the parent metal and the quality of welding wire are not up to the standard of the specification requirements, itself is the presence of defects, and exist in the interlayer of harmful substances, it may be hot crack, so when welding should pay attention to the quality of the welding wire, and to do a good job of protection of harmful substances, and strengthen the butt welding after heat treatment, can effectively avoid the occurrence of hot crack.

Delayed cracks may appear in the heat affected zone during welding of titanium welded pipes. Such cracks generally appear within a period of time after welding. The occurrence of delayed cracks is basically related to hydrogen to a certain extent. In the process of welding, hydrogen in the molten pool and base metal in the low temperature zone will diffuse to the heat affected zone, and thus the hydrogen content will increase, which will lead to the appearance of delayed cracks under the influence of stress. In order to prevent the appearance of delayed cracks, the hydrogen content of welded joints should be reduced as far as possible. Base metal and welding wire with less hydrogen content can be selected, and the cleaning work before welding and the elimination of residual stress after welding should be done well. In general, titanium alloy with normal hydrogen content will not appear titanium hydride, so the probability of cracks in the weld is very small. However, when the thick plate α+β titanium alloy is used for multi-layer welding, the industrial pure titanium is used as the filling material, which will lead to the appearance of titanium hydrid, resulting in hydrogen embrittering.