The research on the critical loading path of thick-walled pipes under external pressure and cyclic bending.

The effects of combined external pressure and cyclic bending on the pipe buckling mechanism are investigated by experiments and finite element analysis. Ten experiments are conducted and it is found that the loading paths of external pressure and cyclic bending have a great influence on the buckling pressure of thick-walled pipes. The loading path of pressure followed by cyclic bending (p → ck) is more dangerous than that of cyclic bending followed by pressure (ck → p). The material properties of kinematic hardening, loading application and mesh convergence are taken into consideration in rigorous FE models. The reason of the critical loading path is revealed from the aspects of section ovality and stress-strain accumulation. Sensitivity analysis is conducted on the loading patterns and axial tension. With the application of axial force, the pipe laying process is simulated more precisely which shows that pipe buckling capacity is more sensitive to the bending cycles in the presence of axial force. The comparison between numerical results and present specification shows that the API specification is conservative in predicting the collapse pressure of thick-walled pipes (D/t = 15–21) whose underestimation is about 11%~37% under the effect of cyclic bending. • Ten experiments and numerical models are conducted to investigate the different loading paths. • The critical loading path (p.→ ck) is determined which is analyzed from section ovality and hoop strain accumulation. • The effects of cyclic bending are reduced on the pipe collapse capacity with the presence of cyclic hardening behavior. • Quantification of the underestimation of the present API standard is compared with the numerical model. [ABSTRACT FROM AUTHOR]