Internal defect correction process of titanium pipe welds

The internal defect of the titanium alloy pipe weld is insufficient penetration, which refers to a defect in the workpiece, and the weld metal or the interlayer part of the weld is not fused. Inadequate penetration weakens the working cross-section of the weld, causing severe stress concentration and greatly reducing the strength of the joint. It often becomes the source of weld cracking. Slag inclusion: Non-metallic slag is caught in the weld, which is called slag inclusion. Slag inclusion reduces the working cross-section of the weld, causing stress concentration, which will reduce the strength and impact toughness of the weld. Gr9 Ti3Al2.5V Titanium Tube / Thin Wall Titanium Tube / titanium exhaust pipe

When the weld metal with pores is at high temperature, it absorbs too much gas (such as H2) or the gas (such as CO) produced by the metallurgical reaction inside the molten pool. It is too late to be discharged when the molten pool is cooled and condensed, and forms inside or on the surface of the weld. Holes are stomata. The existence of pores reduces the effective working cross-section of the weld and reduces the mechanical strength of the joint. If there are penetrating or continuous pores, it will seriously affect the sealing of the weldment. Cracks: During or after welding, the partial rupture of metal in the welded joint area is called a crack. Cracks can occur on the weld or in the heat-affected zones on both sides of the weld. Sometimes it happens on the outside of the metal, and sometimes it happens inside the metal.

Generally, according to the different mechanisms of crack occurrence, it can be divided into two categories: hot cracks and cold cracks. Hot cracks occur during the crystallization process from liquid to solid in the weld metal, mostly in the weld metal. The main reason for its occurrence is the presence of low-melting-point substances (such as FeS, melting point 1193°C) in the weld, which weakens the connection between grains. When subjected to large welding stress, it is easy to cause cracks between grains. . When welding parts and welding rods contain a lot of S, Cu, and other impurities, thermal cracks are prone to occur. Hot cracks have the characteristic of spreading along grain boundaries. When cracks penetrate the surface and communicate with the outside world, they have a significant tendency to hydrogenate. Cold cracks occur during the post-weld cooling process and mostly occur on the base metal or the fusion line where the base metal and the weld meet. The main reason for its occurrence is that the quenching mechanism is formed in the heat-affected zone or the weld, which causes cracks within the grains under the effect of high stress. When welding easy-to-quench titanium alloy materials with higher carbon content or more alloy elements, , most prone to cold cracking. Too much hydrogen melted into the weld can also cause cold cracks. Cracks are one of the most dangerous defects. In addition to reducing the load-bearing cross-section, they will also produce severe stress concentration. The cracks will gradually expand during use, which may eventually lead to damage to the component. Therefore, this kind of shortcoming is usually not allowed in the welding layout. Once found, it must be removed and re-welded.