The addition of an appropriate amount of nitrogen to F51 stainless steel not only improves the pitting and SCC resistance of the steel, but also does not significantly reduce the plastic toughness due to the severe coarsening of the grains in the heat affected zone of the weld, and is also insensitive to welding hot cracks. Therefore, the corrosion resistance and mechanical properties of the heat affected zone of the weld are improved. The SCC resistance, wear corrosion resistance and corrosion fatigue resistance in many media are better than those of austenitic stainless steel [1-5]. In particular, the SCC resistance in a Cl-containing environment is particularly excellent [6]. The H2S SCC resistance is better than that of S30403 and S31603. Stainless steel tee is the key pipe fitting used for the connection of pipeline branches, which is divided into two categories: equal diameter tee and different diameter tee according to the difference in the diameter of the pipe end. The product adopts hydraulic expansion, hot pressing forming or welding forming and other manufacturing processes, and the applicable materials cover stainless steel materials such as 304 and 316L, and conforms to more than ten international standards such as national standard (GB/T12459) and American standard (ASME B16.9). As the core component of the industrial pipeline system, the stainless steel tee undertakes the functions of diversion and confluence, pressure balance and direction conversion, and is widely used in petrochemical, natural gas transmission, power equipment, food and pharmaceutical industries, etc., and its corrosion resistance is enhanced by pickling and passivation processes