TABLE OF CONTENTS Offshore as well as onshore pipelines in operation are under internal pressure. The scenarios for developing axial compression outlined in Chapter 11 also apply to a pressurized pipeline. The general features of plastic buckling under axial compression and internal pressure are similar to those of pure axial loading, presented in Figure 11.2. The cylinder first wrinkles at an increasing load. The wrinkle amplitude grows, leading eventually to a limit load instability. A pipeline will fail by localized collapse at this strain, and as a result this constitutes a limit state. The biaxial state of stress lowers the axial stress levels of the various critical events described in Figure 11.2 but, as will be demonstrated, has a smaller effect on the corresponding strains. In addition, the pressure has a stabilizing effect on the axisymmetric mode, making a switch to non-axisymmetric modes more difficult. These features of the problem are first illustrated experimentally. The formulation for predicting the onset of plastic wrinkling is then developed, followed by a study of how wrinkles grow, localize and lead to collapse.
Lee [12.1] reported results from buckling experiments on cylindrical shells under combined internal pressure and axial compression. The experiments were conducted on tubes made of a soft aluminum alloy (Al-3003-0). The ends of the tubes were clamped, and consequently the onset of wrinkling was masked and was not reported. The axial stress at the onset of collapse was measured for different loading paths.
Combined loading experiments on line...
