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Defects in the welds of titanium chemical processing equipment and their analysis: 1. Penetration failure – This occurs frequently during welding of thin sheets, for the following reasons: (1) Excessive assembly gaps make it difficult to support the molten metal; (2) An overly strong shielding gas flow on the back side pushes aside the molten metal; (3) Excessive current and too slow welding speed; (4) Dust or debris at the weld site can cause an explosion that displaces the molten metal in the weld pool. 2. Incomplete penetration – This happens when (1) the current is too low and the welding speed is too fast; (2) the arc is elongated, resulting in reduced heat input. 3. Undercutting – Undercutting refers to the formation of a recessed groove at the junction between the weld metal and the base material, which reduces the cross-sectional area of the weld and thus lowers its strength. There are two reasons: (1) The welding current is too high, resulting in undercut on the front side; (2) The force exerted by the shielding gas on the back side is too strong, causing the weld to bulge inward and leading to undercut on the back side. 4. Fracture: The factors that cause fractures in titanium welds are quite complex and involve many aspects, but the main ones are contamination by impurities such as hydrogen, oxygen, and nitrogen. Hydrogen embrittlement fracture occurs when the hydrogen absorption in the weld exceeds the solubility at room temperature, and the weld is also severely contaminated by elements such as oxygen and nitrogen. To prevent the cracking of titanium welds, in addition to adopting appropriate welding procedures and adding alloying elements to increase the solubility of hydrogen, it is crucial to avoid hydrogen absorption as well as contamination by oxygen and nitrogen; therefore, cleaning before welding and providing protection during the welding process are extremely important. 5. Stomata: There are two types of stomata, internal and external. External pores usually occur on the surface of the weld, while internal pores typically form near the fusion line. Generally speaking, hydrogen and oxygen, along with the adsorbed moisture and gases present on the surface, are some of the factors that contribute to the formation of pores. Its sources are mainly as follows: (1) Excess hydrogen and oxygen content in the base material and welding wire, along with a too-small groove that results in an excessive amount of molten material during welding; this leads to the formation of internal pores. (2) Inadequate shielding during welding, which causes absorption of large amounts of gas. (3) Improper surface cleaning, with contamination by oils and other organic substances. (4) Low purity of the shielding gas and high humidity. 6. Weld corrosion: When severely contaminated with iron, the weld will develop stable iron-rich regions, which form a corrosion cell together with the iron matrix, leading to electrochemical corrosion. Therefore, the machined groove must be pickled before welding can be carried out.