In Dina gas field, piercing leakage occurred to ametallurgicalcomposite tee of main line. The cladding layer thickness, the position of corrosion, weld hardness, microstructure, and production process were analyzed. It concludes that the cause of the tee perforation is due to imperfect manufacturing process, which causes uneven cladding layer thickness of the tee girth weld and results in weld problem and perforation of cladding layer. The gas erosion of the base carbon steel causes pipe leakage through the dot or line perforation. According to this conclusion, it is believed that the same problem may exist in the same batch ofmetallurgicalcomposite tee produced by this process. It is found through detection that same issues exist at the same position in the same batch of tee in service. It is necessary to replace the tee with such issue and avoid the occurrence of the same perforated leakage, improve the essential safety of the device, and ensure the smooth operation of the gas field. This study provides reference for the analysis and treatment of themetallurgicalcomposite tee failure in gas-field main line.