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.The Olet is a reinforced pipe fitting used for branch pipe connection, which has been widely used abroad in recent years. It replaces the traditional branch pipe connection types such as reducing tees, reinforcement plates, and reinforced pipe sections. It has outstanding advantages such as safety and reliability, reduced cost, simple construction, improved medium flow channel, series standardization, and convenient design and selection. It is increasingly widely used in high-pressure, high-temperature, large-diameter, and thick-walled pipelines, replacing the traditional branch pipe connection method.