Dynamic Plastic Deformation of Deepwater Steel Catenary Risers Under Extreme Cyclic Compressive Loading
Steel catenary risers (SCRs) on a large-heave-motion vessel are susceptible to compression in the riser touchdown zone (TDZ). Dynamic compression can lead to overstress under extreme or abnormal weather conditions. The response of an SCR under compression is highly nonlinear and sensitive to various factors. However, the current available industry design codes and practices do not provide a clear guidance to address the acceptability of compression, overstress, and the resulting plastic strains. In addition, the current analysis method used in industry common practice cannot capture accurately the nonlinear behavior of an SCR involving accumulated plastic deformation, hysteresis effects, and local buckling.
In this paper, a finite-element-analysis modeling method that uses combined beam and solid elements is presented. This method enables simulation of large plastic deformation, pipe ovality, and local pipe buckling in the TDZ of a deepwater SCR. The model is developed with Abaqus (Dassault Systèmes 2009). The SCR non- linear response is examined through dynamic analysis of a deep- water SCR that is hung from a semisubmersible. The key analysis results are compared with a nonlinear beam-element model. More- over, dynamic-ratcheting analysis under multiple plastic-strain cycles by use of the proposed solid-riser model is conducted to understand the plastic-strain accumulation and to check the acceptability of the survival response of a deepwater SCR under a series of severe hurricanes in its service life.
This paper presents the methodology for evaluating the compression and plastic deformation that could be experienced by deepwater SCRs, including the modeling approach, analysis results, possible failure modes, and conclusions. The impact of the study findings on the robustness and suitability of SCRs for deepwater application is discussed.
Executing Offshore Projects More Efficiently
Offshore project execution enhancement ideas are highlighted for debottlenecking, gas-hydrate-induced pipeline vibration, and the design of subsea systems for efficient startup.
Hydrate-Induced Vibration in an Offshore Pipeline
A computational fluid dynamics model is proposed to analyze the effect of hydrate flow in pipelines using multiphase-flow-modeling techniques. The results will identify the cause of pipeline failure, regions of maximum stress in the pipeline, and plastic deformation of the pipeline.
PHMSA Tags Construction Damage as Cause of Keystone Pipeline Spill
Weights used in the original construction of TransCanada’s Keystone Pipeline in South Dakota were identified as a preliminary cause of the failure that resulted in a 210,000-gal spill in November.
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