Stress intensity factor for a circumferential crack in a coke drum under two-dimensional transient temperature distribution

Abstract

Coke drums are subjected to extreme temperature cycling in service, leading to circumferential cracking in the drum wall. For a deeper understanding in the cracking mechanism, stress intensity factor (SIF) for a circumferential crack in a coke drum was investigated in this paper. Based on two-dimensional heat conduction theory and classical thin shell theory, analytical solutions for the transient temperature distribution, displacement, and thermal stress in the drum wall during hot feed filling and water quench steps were determined. The weight function method (WFM) was applied to investigate the mode I SIFs based on the analytical thermal stress solutions. Numerical simulations using finite element method (FEM) were also performed to validate the analytical solutions for both the thermos-elastic field and the SIFs. The effects of shell geometry, operating parameters and material properties on the SIF during the water quench step were discussed. It is shown that the SIF increases significantly as crack depth increases. A greater shell thickness or lower diameter to thickness ratio results in lower SIFs. Lower rising rate and higher temperature of quench water can reduce the SIF. The SIF increases as the thermal conductivity and thermal expansion coefficient of the drum wall materials increase. Finally, the SIFs for Cr–Mo steel and carbon steel coke drums are also discussed.