First Deployment of Subsea Rotating Buoyancy to Mitigate Lateral Buckling of High Temperature Pipelines

Abstract

Abstract The paper seeks to address the challenges faced by High Pressure High Temperature (HPHT) subsea pipelines buckling mitigations and presents a new innovative solution that was evaluated from 2012 to 2016 and first deployed in 2017 then surveyed in 2018 after almost 6 months of operation. Laboratory tests, field tests, small scale tests, full scale tests, analytical derivations and finite element analyses were developed and used to mature the rotating buoyancy technology configuration as a new innovative solution. High pressure and/or high temperature subsea pipelines may experience lateral buckling which require special considerations to mitigate excessive plastic deformation and fatigue during start up and shut down cycle events. One of the widely used mitigation consists of attaching fixed buoyancy modules on engineered sections of the pipeline system. However, postproduction subsea surveys and engineering evaluations showed the currently used buoyancy mitigation methods create large soil berms that may significantly reduce pipeline fatigue life and the opportunity of life extension of the pipeline system. The rotating buoyancy system was developed to help solve this problem and increase the solution robustness to enable potential life extension and possibly reduce the stringent welding requirements at the buckled sections. It represents a step change in the way risks associated with buckling of high temperature and/or high pressure pipelines are managed and effectively mitigated. Between year 2015 and 2016, small scale and large-scale tests were performed using prototype fixed and rotating buoyancy modules to compare the current and new mitigation methods. This paper outlines the methods by which pipe-soil interaction can be simulated. It describes the validation and verification conducted, through experimental testing on both newly developed small-scale and large-scale testing rigs, coupled with computational modelling and analytical predictive calculations. The paper highlights the challenges faced when replicating seabed conditions and pipeline movements. It also highlights novel design aspects which offer improved traction in soft clay environment. The paper also presents the lessons learned during the 2017 offshore installation campaign and the 2018 results of the in-situ survey of the rotating buoyancy modules after the first 6 month of operations and future plans for next generation rotating buoyancy systems including digitalization. The subsea rotating buoyancy is a novel simple system deployed to provide a robust mitigation of subsea pipelines lateral buckling. It provides opportunity for potential increase of subsea pipeline life extension and potentially helps decrease the stringent welding requirement of the pipeline at the buckled sections.