In the last decade and a half, the pipeline industry has gained significant experience in both the design and operation of pipeline systems exposed to lateral buckling. JIPs, design guidelines and recommended practices such as SAFEBUCK (Reference ), HOTPIPE (Reference ) and DNV RP-F110 (Reference ), together with operational feedback have significantly contributed to the development of comprehensive methods to determine robust lateral buckling design solutions. Most of this knowledge has been gained from understanding the behaviour of HP/HT (high pressure/ high temperature) small, light diameter systems, which buckle more predictably at operating conditions well below design conditions. Medium to large diameter, concrete coated pipelines are generally considered to be less prone to lateral buckling by comparison (due to expected milder design conditions), however the consequence of their buckling is far more severe and can prove extremely difficult to control.
Fundamentally, the knowledge acquired and general lateral buckling design methodologies developed for HP/HT systems can be applied for the design of larger, heavier pipelines, however there are a number of key differences in the behaviour of both systems which warrant special considerations.
Key considerations include (a), effective axial force and critical buckling force development (impacting susceptibility and initiation considerations), (b) severe post-buckle response on-seabed (impacting the acceptance of uncontrolled buckling for definition of buckle trigger spacing and extents), and (c), the consequence of introducing buckle triggers. Additional design complexity is introduced for systems installed in shallow water, which are exposed to more severe metocean conditions than deepwater HP/ HT systems. This requires heavy concrete weight coating (CWC) for stabilisation, resulting in strain localisation at field joints, concrete stiffening effects and complex interaction with hydrodynamic loading, typically ‘competing against’ intuitive global buckling design.
All of the above factors result in lateral buckling design solutions for medium to large diameter, concrete coated pipelines becoming rather challenging.