FABRICATION AND ASSEMBLING ERRORS INFLUENCE ON THE FATIGUE STRENGTH OF THE SPHERICAL TANKS SHELL-CALCULUS SIMULATIONS

One analyses, for a 1000 mc spherical tank, equatorial supported by 10 cylindrical pillars (which stores propylene at 2.1 MPa), the influence of the different type fabrication and assembling errors on the spherical shell stress concentration factors. First there are presented the calculus results for the welds flaws influences on the stress concentration factor. Afterwards, with the aid of an original MathCAD program, there are calculated the influence of the fabrication errors (local losses of wall thickness, flattening, assembling eccentricities of the supporting system) on the spherical shell state of stress, taking into account a complex loading (working/storage pressure/hydraulic test pressure, wind, hydrostatic pressure, own weight, deformation restraint (due to horizontal forces determined by the temperature difference between working conditions and assembling conditions and also by the seismic loadings) exerted by the supporting system on the spherical shell and loadings due to the supporting system discontinuities). The influences of the two types of errors are then superposed. Finally is calculated the fatigue number of cycles in the presence of all types of errors.