Parameters Affecting the Local Buckling Response of High Strength Linepipe

Abstract

The local buckling response and post-buckling mechanical performance of high strength linepipe subject to combined loading state was evaluated using the finite element (FE) simulator abaqus/standard v6.12. The constitutive model parameters were established through laboratory tests and the numerical modeling procedures were verified with large-scale experiments investigating the local buckling response of high strength linepipe. The numerical predictions demonstrated a high level of consistency and correspondence with the measured experimental behavior with respect to the peak moment, strain capacity, deformation mechanism, and local buckling response well into the postyield range. A parametric study on the local buckling response of high strength plain and girth weld pipelines was conducted. The loading conditions included internal pressure and end rotation. The pipe mechanical response parameters examined included moment–curvature, ovalization, local strain, and modal response. The magnitude and distribution of the characteristic geometric imperfections and the end constraint, associated with the boundary conditions and pipe length, had a significant influence on the predicted local buckling response. The importance of material parameters on the local buckling response, including the yield strength (YS), yield strength to tensile strength ratio (Y/T), and anisotropy, was also established through the numerical parameter study. For girth weld linepipe, the study demonstrated the importance of the local high/low misalignment, associated with the circumferential girth weld, on the local buckling response.

Numerical Assessment on the Mechanical Performance of Pressure Pipe CIPP Liner with Local Defects in the Outer Host Pipe

“…local buckle waveform), which is consistent with recent studies on the local buckling response of energy pipelines (e.g. Fatemi and Kenny, 2017;Kenny et al, 2016). The ovalization data also indicates the buckling mechanism remains localized at the pipe mid-length section (i.e.…”

“…In reference to recent studies on the local buckling of energy pipelines, the near zero pipe ovality at the 1.0D section suggest the mechanical response is over-constrained by the pipe length and end boundary conditions (e.g. Fatemi and Kenny, 2017;Kenny et al, 2016), which has a significant moderating effect on the local buckling response. The influence of pipe length on the liner mechanical response is addressed later in this thesis study.…”

“…As shown in Figure 2.4, this approximation is reasonably accurate for true strain magnitudes less than 0.01, which is greater than the predicted liner strain for this study. As discussed by Fatemi and Kenny (2017), depending on the nature of the anisotropic behaviour then the Hill potential function could be utilized for larger strain magnitudes associate with local buckling of high strength steel pipelines subject to internal pressure and bending loads. The CIPP liner/host pipe interface contact pressure, shear stress and slip potential introduces nonlinear behaviour, even for elastic material response, that was defined through surface contact pairs.…”

“…The DR ratio is a key non-dimensional geometric parameter influencing the pipe mechanical performance when subject to internal pressure and external loads (e.g. Fatemi and Kenny, 2017;Kyriakides et al, 2007;Timoshenko and Gere, 1961). The CIPP liner yield strength of 20 MPa was based on the study by Brown et al, (2008) For the D/t ratio investigated in this study, of 40, 60 and 80 as summarized in Table 2 In this study, the normalized hoop stress was observed to be a local maximum, across the range of liner dimension (D/t) and hoop stress to yield (σh/σy) ratios examined, at a void ratio (d/D) of 0.4, which is consistent with the findings by Allouche et al, (2005).…”

“…Physical modelling and numerical simulation studies on the local buckling response of high strength steel pipe suggest the anisotropic behaviour of the CIPP liner may trigger bifurcation mechanisms in the longitudinal direction through interaction between the axial and circumferential mode response when subject to combined loads of internal pressure and bending (e.g. Fatemi and Kenny, 2017;Kenny et al, 2016). Brown et al, (2014) used continuum FEA to examine the performance of the CIPP liner for LS3, as defined by Allouche et al, (2005).…”