Design and calculation of reactor D-481 fabricated in Carbon Steel, material SA516 Gr.70, design pressure 15.5 barg and design temperature 80ºC. The vessel operates in cyclic service, 72 cycles of 20min per day, 525600 cycles throughout the entire life. The equipment was designed and calculated under internal pressure in accordance with the ASME VIII Div.1 code. Fatigue verification in accordance with the ASME VIII Div.2 code was performed. Stress at critical points of the equipment were obtained through Finite Element Analysis.