A new connection structure between hydrogen nozzle and sphere head in a hydrofining reactor

This paper presents a study of the residual stress in the welding connection between hydrogen nozzle and spherical head in a hydrofining reactor. A sequential coupling finite element program is developed to analyze the residual stress in nozzle-to-sphere connection. The results show that large residual stresses are generated in the weld and weld/parent interface during the welding of hydrogen nozzle. Large axial stress is generated on the internal surface of hydrogen nozzle due to the angular deformation, which has a great effect on hydrogen induced cracking (HIC) and stress corrosion cracking (SCC). Based on the residual stress distribution character, a new connection structure between hydrogen nozzle and head is developed. A stressless flanging is proposed to insert into the nozzle to isolate the residual stresses, which can be useful to prevent HIC and SCC. To cover all the residual stresses effectively, the arc length of flanging should be not less than 80 mm.