Internal defect correction process of titanium alloy tube and titanium tube weld

Internal defects of Grade 2 Pure Titanium Pipe welds Incomplete penetration refers to a defect that the workpiece is not fused with the weld metal or the weld layer. Incomplete penetration weakens the working section of the weld, resulting in severe stress concentration, which greatly reduces the strength of the joint, which often becomes the source of weld cracking. The slag inclusion weld contains non-metallic slag, which is called slag inclusion. Slag inclusion reduces the working section of the weld, resulting in stress concentration, which will reduce the strength and impact toughness of the weld.

When the stomatal weld metal is at high temperature, it absorbs too much gas (such as H2) or gas (such as CO) due to metallurgical reactions inside the molten pool, which cannot be discharged in time when the molten pool cools and condenses, and forms inside or outside the weld. Holes are stomata. The existence of pores reduces the useful working 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 the metal in the area of ​​the welded joint is called a crack. Cracks can occur in the weld as well as in the heat-affected zone on both sides of the weld. Sometimes it happens on the outside of the metal, sometimes it happens inside the metal.

Usually, according to the different mechanisms of cracks, they 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, and most of them occur in the weld metal. The main reason for this is the presence of low melting point substances (such as FeS, melting point 1193 ° C) in the weld, which weakens the connection between the grains. . When the welding parts and electrodes contain a lot of impurities such as S and Cu, thermal cracks will easily occur. Hot cracks are characterized by spreading along grain boundaries. When the crack penetrates the surface and communicates with the outside world, it has a significant tendency to hydrogenate. Cold cracks occur during the post-weld cooling process, mostly on the base metal or the fusion line between the base metal and the weld. The main reason for its occurrence is that the heat-affected zone or the weld constitutes a quenching structure. Under the effect of high stress, the internal fracture of the grain is caused. When welding easily quenched titanium alloys with higher carbon content or more alloying elements. , most prone to cold cracks. Too much hydrogen melted into the weld can also cause cold cracks. Crack is one of the most dangerous defects. In addition to reducing the load-bearing section, severe stress concentration will occur. During use, the crack will gradually expand and eventually cause damage to the component. Therefore, this disadvantage is usually not allowed in the welding layout, and once found, it must be removed and re-welded.