Creep rupture assessment of cyclically heated 3D pressure pipelines with volumetric defects using a direct numerical approach

Creep rupture assessment is a significant issue in the field of high-temperature structural integrity. In this paper, the creep rupture assessment of 3D pressure pipelines with volumetric defects subjected to cyclic thermo- mechanical loadings is done using a direct numerical approach within the framework of stress compensation method (SCM). For calculation of creep rupture limit, an extended shakedown analysis scheme with yield strength correction is essentially performed, where the revised yield strength is determined as the minimum of the plastic yield strength and the creep rupture strength of material corresponding to a specified elevated temperature and rupture time. This direct numerical approach performs the creep rupture assessment by using the given creep rupture data of material rather than simulating the degenerative process of material based on creep damage constitutive equations under a specified loading history. The numerical approach is incorporated into commercial finite element software of Abaqus. Parametric studies on geometric dimensions of part-through slot affecting the creep rupture limit of 3D pressure pipelines with volumetric defects are conducted. Numerical results shown in this study indicate that the direct numerical approach accurately identifies the creep rupture limit boundary of the pressure pipeline, verified by the elastic-plastic cycle-by-cycle analysis. Failure mecha- nisms, such as local creep rupture, global creep rupture and global plastic rupture are detected under different loading combinations. These results give the helpful information for in-service integrity assessment of defective pressure pipelines at elevated temperature, and demonstrate the applicability and application prospect of the direct numerical approach in solving questions relevant to design or life assessment of other engineering structures.