Lateral Buckling and Walking of Pipelines

14 April 2011 London Evening Meeting

Chairman Emil Maschner, J P Kenny

Report

Flyer

Presentations

Lateral Buckling Analysis of Deepwater Pipe-in-Pipe Flowlines

Sherif El-Gebaly, INTECSEA

Highly insulated pipe-in-pipe (PIP) systems are often required for deepwater developments to meet stringent thermal requirements. The high operating temperatures encountered generally lead to buckling on the seabed, involving complex interaction between inner pipe, outer pipe and seabed. Accordingly, the flowline must be engineered to buckle laterally in a controlled manner such that the strains arising remain within fatigue and ultimate limit states. Advanced finite element analysis (FEA) is required to model the actual seabed profile and complex cyclic non-linear soil resistance in the axial and lateral directions, which strongly influence both buckle initiation and post-buckle response. Treatment of forged pipeline components such as J-lay collars and bulkheads, and mechanical interaction of inner and outer pipe also present significant analysis and design challenges. This presentation described some of the specific modelling and design challenges recently encountered in INTECSEA.

Post-Operational Feedback on the Design of a Deep Water HP/HT Flowline Subjected to Lateral Buckling

Arek Bedrossian and Graeme Roberts, Subsea 7

In 2010 Subsea 7 carried out a post-operational analysis of a reel-laid pipeline which had been designed and installed by Subsea 7 based on the controlled lateral buckling principle. The objective was to develop an FE model based on its operating status and to confirm its present and future integrity. Different types of man-made buckling triggers were incorporated along the flowline and these were all modelled. The presentation briefly described the modelling approach adopted and there will be some discussion about the difficulties overcome during the analysis. The importance of keeping records, during the fabrication, installation and operation, was highlighted. A demonstration was given of the impact of retrospective increase in conservatism in guidelines for some aspects of pipeline design, in particular ECA according to DNV guidelines.

Overview of the SAFEBUCK Joint Industry Project

David Bruton, Atkins

The SAFEBUCK JIP addresses the key design challenges of lateral buckling due to the compressive forces created by internal pressure and temperature, which has led to a number of failures, including three full-bore ruptures and one abandonment. A related challenge is pipeline walking, due to non-uniform expansion and contraction of the pipeline, which has led to one failure and a number subsea interventions to prevent failure. The aim is to safely design and control the initiation of lateral buckles at regular intervals along a pipeline, and to control pipeline walking by anchoring or other means. This presentation summarised key areas of research and development undertaken by the JIP, captured in the SAFEBUCK Design Guideline, including the development of engineering models and the testing of pipe-soil interaction, fatigue and local buckling, as well as outlined work underway now, in the final phase of the JIP.