Figure 10. Effective axial force profiles in the flowline during various load steps in the simulation. A buoyancy module at position 1500 triggers a lateral buckle.


fatigue loads (i.e. stress ranges) to a level where the accumulated fatigue damage is within the tolerances for the flowline's girth welds.


Over the past year,Technip has begun creating scripting tools to mine the vast amount of simulation results created during a global lateral buckling simulation. The current tools search every section point in every flowline (PIPE31H) element to locate the largest stress range during each loading cycle. A loading cycle includes the heating and pressurization of the flowline, simulating “normal” operation, and the depressurization and cooling down seen when the pipeline system is shut down. The magnitude and location of the maximum stress range is noted and used in the fatigue calculations. Figure 11 shows the history of stress at two locations along the pipeline. These are locations with the largest predicted stress range in the flowline at different loading cycles. In the early loading cycles, the lateral deflections of the flowline were minimal and the largest stress range was predicted to be at the flowline-PLET connection. With each loading cycle lateral displacements were accumulating at a critical location along the flowline. Eventually, at about the 25th loading cycle, the perturbation of the flowline’s geometry became large enough that a large buckle formed and the magnitude of stress range (and fatigue damage) increased greatly. Results like those in Figure 11 have caused a reassessment of how many loading cycles must be included in lateral buckling/fatigue design simulations.


2009 SIMULIA Customer Conference 11


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