Lessons Learned From Observing Walking of Pipelines with Lateral Buckles, Including New Driving Mechanisms and Updated Analysis Models

Abstract

Abstract Pipeline walking is a phenomenon that causes global axial movement of a whole pipeline. Pipeline walking has been observed on a number of pipelines to date and if left uncontrolled can lead to potential failures at connections or risers. Designing to control or mitigate pipeline walking can result in significant changes to field layouts and high installation costs associated with pipeline anchors, which have been installed on a number of recent developments. It is therefore essential to be able to assess whether walking is a potential issue early in the design process. Walking is a stepwise ratcheting mechanism that occurs during changes in operating conditions, particularly during shutdown and restart operations. A number of contributory mechanisms are known to cause pipeline walking:Sustained tension, applied to the end of a pipeline by a steel catenary riser (SCR);Seabed slopes, along the pipe length, defined by route bathymetry;Thermal transients, defined by changes in fluid temperature and thermal loading during shutdown and restart operations;Multiphase flow behavior during shutdown and restart operations. This last multiphase flow mechanism has only recently been identified from observation and measurement of operating systems and is not addressed by previously published analytic pipeline walking models developed by the SAFEBUCK JIP, published at OTC in 2006[1]. This fourth mechanism is described along with a discussion on the impact of multiphase flow on pipeline walking, axial friction response, anchor loading and route curve stability. A new analytic modeli is presented to assess pipeline-walking rates due to this behavior. This paper also illustrates pipeline-anchoring solutions that have been employed to control pipeline walking on a number of deepwater developments and discusses the issues with these control methods, including the increased potential for route-curve pullout. The paper also investigates the complex interaction between pipeline walking and lateral buckling. It is known that lateral buckles along a pipeline can significantly influence both pipeline walking and end expansion predictions. The complex cyclic interaction is explained and methods for predicting the cyclic response either analytically, or using FEA techniques, are described. i Errata - This revision includes updates to equation 11.