Two-ply 16GS+08X13 steel column stress-strain state analysis with metal delamination taken into account

Abstract

Columns are the main mass transfer equipment used in oil refining processes. In this regard, in order to save expensive materials, two-ply steel columns became widely used. Currently, the determination of residual life of such columns is based on standard methods of strength calculations for vessels and apparatuses. However, the existing methods of strength calculations are based on a simplified representation of the column apparatus at various stages of calculation and do not provide a comprehensive picture of its stress-strain state (SSS) taking into account geometrical features and the fact that the shell is double-layer. It is known that SSS of equipment produces considerable influence on the processes of damage accumulation during operation. One of the most prevalent defects in the shell of two-ply steel columns is delamination between the main layer and cladding layers due to the formation of a decarburized layer in the process of continuous operation. The column stress-strain state was analyzed in this paper with the use of ANSYS software implementing the finite element method, considering as follows: the size and location of manholes and nozzles; dead load and operating parameters; the results of investigations of two-ply 16GS+08X13 steel column mechanical properties in the as delivered condition and after continuous operation at a thermal cracking unit; double-layer shell. It is established that the maximum stresses in the most loaded bottom of the column with a nominal wall thickness in a double-layer model reach 228 MPa, which is almost 80 MPa higher than the stress values obtained for a single-layer model. The dependence of maximum stress values on the size of delamination defect is determined with the defect being located in the most loaded and the least loaded zones of the column bottom for the metal being in the as delivered condition and after continuous operation.