Numerical and experimental strength analysis of fire-tube boiler construction

Abstract

Norms, such as EN 12952-3 and EN 12953-3 handle the issues concerned with calculation of the pressurized boiler components, not however considering the influences of thermal strains that are often of vital importance for the integrity of boiler's construction. Application of FEM in boiler design in EN is suggested in calculating all components that are not covered by the norm. In this way, the calculation of thermal stress is left to the free will of designer and technical inspectorate which supervises and approves placement of a boiler into operation. This paper demonstrates that the influence of thermal stresses is great and that it must be taken into consideration when the boiler's construction is designed and its working life evaluated. It is shown that for every construction a numerical-experimental behaviour diagnostics should be conducted prior to putting it into operation. First, a numerical model must be experimentally verified and then it can be used in considering different parameters of strength diagnostics, such as distribution of membrane and bending stresses for substructures, and distribution of deformation energy. They indicate, in an optimal way, root causes of insufficiently good behaviour of the construction. Also, a dynamical calculation of natural oscillations should always be suggested.