Designing of stress relieve groove parameters for flat endplates of pressure boilers

The application of flat ends as closures in pressure boilers is a certain alternative for commonly used dished ends. However, it is inevitably joined with the stress concentration presence in the vicinity of the junction between the cylindrical pipe and the ending flat plate. The notch effect, which is observed in the connection area, is usually caused by the abrupt change of the inner wall shape and the lack of the curvature continuity in this region. The problem of the stress reduction in the transition zone between the cylindrical pipe and the endplate has been studied by researchers from many years and several proposals how to modify the shape of the respective elements have been established. On the base of these results, several designs for flat end closures are proposed in the codes applied in pressure boilers calculations. This paper shows the effectiveness of one of the design proposals, admitted by code EN 13445-3. In the proposed analysis the special attention are paid to flat ending plates with the circular stress relieve grooves. The parameters of the groove radii and location of its centre are set by a system of inequalities, which usually defines the region of admissible values for radii and position of the circular groove centre. The choice of these values strongly influences the stress concentration and in the considered code, no clear suggestions or justification is given how to choose the best groove parameters, providing the minimum stress concentration. In this report, the Authors show how to choose the best combination of the design parameters providing the minimum stress concentration.