Structural integrity assessments of high pressure pipelines with axial flaws using a micromechanics model

This study extends a micromechanics approach based upon the computational cell methodology to model ductile crack extension of longitudinal crack-like defects in a high strength pipeline steel. Laboratory testing of an API 5L X60 steel at room temperature using standard, deep crack C(T) specimens provides the data needed to measure the crack growth resistance curve for the material. A simple scheme to calibrate material-specific parameters for the cells employs this measured R-curve. A central focus of the paper is the application of the cell methodology to predict experimentally measured burst pressures for longitudinally pre-cracked pipe specimens. The experimental program includes large-diameter pipe specimens with different crack depth (a) and crack size (2c). Plane-strain computations are conducted on detailed finite element models for the pipe specimens to describe crack extension with increased pressure. The cell model predictions of crack growth response and burst pressure predictions are in good agreement with experimental measurements for the tested pipes. The present methodology holds significant promise as an engineering tool to simulate ductile crack growth and to predict the burst pressure of high pressure pipelines containing crack-like defects