On the Design of Reinforcement for Openings and Nozzles in thin Spherical Pressure Vessels

Abstract

A simple plastic design approach is made to the problem of design of reinforcement for openings in thin spherical pressure vessels. The essence of the approach is to adjust the thickness and shape of the vessel in the vicinity of the opening so that the full limit pressure of the vessel may be carried with relatively little bending action. A novel constant-thickness shallow conical reinforcing pad emerges as a design which satisfies these requirements. The design, which is easily adapted to the reinforcement of nozzles, appears to have several important advantages over conventional designs not only in the plastic range but also in the elastic range, in which stress concentration factors are low.When the internal pressure is steadily increased, the resulting deformation does not effectively alter the ‘conical-spherical’ profile of the vessel, and the action is predominantly ‘membrane’ throughout the elastic, elastic-plastic and plastic ranges. It follows that simple plastic theory gives a good description of the plastic behaviour. This is in sharp contrast with the case of unreinforced nozzles, where plastic bending effects are superseded, as deflections become ‘large’ by membrane effects. Detail of welds, etc., must be designed by conventional procedures.