Rectangular tangential nozzles are often used as special process interfaces in petrochemical equipment（such as multiphase flow cyclone separators），but their structural strength design has not been clearly specified in design codes such as GB/T 150.The finite element limit load analysis method was used to calculate the pressure‑bearing capacity of cylindrical shells with rectangular tangential nozzles，and the weakening effects of rectangular tangential nozzles with different dimensionless structural parameters（width‑to‑diameter ratio W/D_i，diameter‑to‑thickness ratio D_i/T，and thickness ratio t/T） on the strength of the cylindrical shell were investigated.It was found that the cylindrical shell with a square tangential nozzle having a side length ratio of 1 has the maximum pressure‑bearing capacity.Therefore，a limit load reduction factor reflecting the strength reduction of the cylindrical shell due to the provision of a square tangential nozzle was defined.The influences of the three dimensionless structural parameters W/D_i，D_i/T，and t/T were studied，and regression analysis was performed on the limit load reduction factor based on a large number of numerical calculations.This is helpful for the strength design or safety assessment of cylindrical shells with square tangential nozzles.It was also found that for the same opening area，the pressure‑bearing capacity of the cylindrical shell structure with a square tangential nozzle is significantly lower than that with a circular tangential nozzle.In other words，the strength weakening effect of a square tangential nozzle on the cylindrical shell is significantly greater than that of a circular tangential nozzle.Therefore，from a strength perspective，using a circular tangential nozzle is more reasonable than using a square tangential nozzle.