Nonlinear Analysis of Flexibility and Local Stress Distribution at Nozzle-Shell Intersection Considering Refractory Lining Rigidity

The reactors and re-generators in RFCC and FCC units in refineries are provided with concrete refractory linings. The influence of these linings on the flexibility of the nozzle-shell intersections and the local stress distributions around those intersections is not considered in present designs. In this paper, three-dimensional, nonlinear finite element analyses were performed to evaluate the influence of refractory lining rigidity on the flexibility of nozzle-head intersections. The results of these analyses can be applied to the thermal stress analysis of piping to obtain reaction forces and moments on nozzles. The application of flexibility factors results in a reduction of the reaction forces and moments. The influence of refractory lining rigidity on the local stress distributions around the intersections was also studied. To perform this investigation, three types of finite element models were adopted: • Nozzle-head intersections without refractory lining; • Nozzle-head intersections with refractory lining (adhesive boundary between steel and lining); • Nozzle-head intersections with refractory lining (contact boundary between steel and lining). Shell elements were applied to the nozzle, head and cylindrical shell, and solid elements were applied to the refractory lining. A boundary element was applied to express the contact boundary, which transfers only a compressive force. As a conclusion, a new design procedure for nozzle-head intersections with refractory linings is proposed.