Thinning of the castable refractory lining in a riser structure leads to refractory lining failures. Unscheduled and emergency shutdowns of a fluidized catalytic cracking unit at a petrochemical plant are not just costly to repair but result in significant loss of production. Material testing, thermo-mechanical structural analysis and the expertise of a refractory consultant were needed to work interactively to identify and define the conditions that cause refractory failures in the riser structure.
Excessive stresses perpendicular to observed cracks cause refractory failures. Finite element analysis methods were used to determine the levels of deformation and stress on a 100mm thick refractory lining in a 45m pipe structure with a 1,5m inner diameter. Various static and operational loading conditions that can lead to hoop stresses in the lining were investigated by using virtual twin models of real-world structures. Changes in material properties and lining thickness, static gravity load, constant force and variable springer supports, operational thermal loads and structural movement were all investigated in a series of Finite Element Analysis (FEA) simulations.
The engineering approach of combining Simera’s structural analysis expertise with material testing, refractory consultant expertise and the client’s knowledge of their operations and processes helped the team to develop an understanding of the cause of the riser refractory failures. More suitable materials were selected and anchor spacing was changed to reduce development of gaps and thinning of the lining. Operational work instructions were amended to prevent irreversible damage shutdowns. The petro-chemical Industry at present mostly use proven trial-and-error methods. Sophisticated analysis techniques as used here, taking into account the complexities of modelling refractories, are now maturing adequately to leverage the advantages of digital twin, thereby enabling better informed investment decisions.