Offshore: Collapse Limit and Propagation Buckling checks

• For complete details search AutoPIPE help for "Collapse Limit" and Supplemental documents - DNV OS F101 2012 Tutorial
• "Buckling Due to External Pressure" from ground water, earth loads, and surcharge loads on a buried PE pipe shall not cause the pipe to buckle (HDPE -2011 - Section 3221.1).
• Model's Piping code must be set to DNV - 2012 editions and later (DNV, DNVGL-F101, DNV-ST-F101).
  • The collapse limit (external overpressure) at any point along the pipeline must meet the following criteria (equation 5.10) (system collapse check):
  • Propagation Buckling - The propagation buckling criteria is given as below. Propagation buckling cannot be initiated unless local buckling has occurred.

Buried Piping Upheaval Buckling 

AutoPIPE supports evaluation of buried pipes for upheaval buckling. When buried pipelines are initially deformed due to manufactured overbends, they are subject to upheaval buckling when axial compressive forces are applied. Upheaval buckling can be significant enough to expose previously buried pipes, exposing them to damage from external elements.

AutoPIPE will perform upheaval buckling analysis on all physical nodes (i.e. non-soil nodes) using the associated soil identifier for that node point (node points without soil properties are ignored).

K. Peters theory on upheaval buckling contains a definition for F_restr that is available as an alternative for compressive axial forces due to loading calculated by the AutoPIPE static analysis engine. 

• For complete details search AutoPIPE help for "Upheaval Buckling" and Supplemental documents - Upheaval Buckling Tutorial.
• When modeling soil properties open the soil calculator and enter values as needed. Also, press the "Upheaval Buckling" dialog, and make selections as needed. 
• AutoPIPE's upheaval buckling analysis 
  • Only applies buckling calculations
    • Due to vertical loading. Lateral loads are not considered for buckling prevention.
    • Occurs only at bend / kinked (imperfection) node points that are modeled as a coordinate defect lateral to the general pipe axis. Straight run points are not considered because AutoPIPE assumes isotropic properties in the pipe and would only have pure compression / tension loads that would not develop lateral loads.
  • Vertices where at least one leg is vertical shall not be considered for upheaval buckling due to a singularity in the determination of buckling angle.
  • Choose Thermal and pressure axial force values from AutoPIPE's iterative analysis forces and moments calculations or calculated based on K. Peters Compression Force Calculations. All other upheaval calculations will use the decided force values.  
• When calculating actual slope deflection, AutoPIPE calculates the slopes based on the nodes preceding and following the node of interest. These nodes may not necessarily be x±λ/2.