Investigation and Validation of Finite Element Analysis Material Modeling for Integrity Assessment of Indented Pipe Under Static and Cyclic Loading

Mechanical damage in transportation pipelines is a threat to its structural integrity. There are many parameters that affect the severity of the mechanical damage which are related to the pipe geometry and material properties, the defect geometry and boundary conditions, the loading cycle, and the pipe state of stress. To understand those effects, the utilization of numerical finite element analysis (FEA) has been used extensively to supplement the expensive; and thus, limited full-scale tests. The actual pipe material exhibits a number of special features including nonlinear elasticity, anisotropy, and cyclic softening which need advanced material modeling techniques. However, the success of the numerical material model to actually simulate the pipe material behavior could not be studied in detail previously due to the insufficient experimental data especially in cyclic pressure loading. The objective of this paper is to investigate the effect of material modeling using FEA on the integrity assessment of dented pipe under static and cyclic loading by simulating pipe denting followed by subsequent pressure cycles. Several material models are tested and calibrated against the measurements of full-scale tests to find the effects of material modeling assumptions (e.g. isotropy, yield point, hardening rule). The results show that a combined material model simulating all special features of nonlinear elasticity, anisotropy, and cyclic softening gives a very close representation of experimental data in terms of strain values and fatigue cycles to failure. Therefore, detailed material properties are needed to conduct accurate integrity assessments of dented pipes especially under cyclic conditions.