2000-Deepwater-Pipeline-and-Riser-Technology-Conference-Deepwater-Riser-VIV-Fatigue-and-Monitoring.pdf

DEEPWATER RISER VIV, FATIGUE AND MONITORING Dr Frank Lim and Dr Hugh Howells 2H Offshore Engineering Limited Woking, Surrey, UK Presented at Deepwater Pipeline Riser Technology Conference, Houston, March 6-9 2000 ABSTRACT Vortex induced vibration is (VIV) is a major design issue for all deepwater riser systems operating in regions where severe current can be expected, such as the Gulf of Mexico and offshore Brazil. Cross-flow vibrations of a riser in severe currents can diminish the riser fatigue life, dictate the riser arrangement, fabrication details, vessel layout, installation method, and thus have significant cost impacts at all stages of the field development. The limitations of existing analytical methods and test data for predicting deepwater riser VIV response are discussed. This shows that in-service monitoring or full scale testing is essential to improve our understanding of VIV response and confidence in its predictions. A number of monitoring and test programmes are described and some of the key findings reported. Based on the experience, instrumentation requirements for monitoring VIV response are described and a design approach to deal with VIV is proposed. INTRODUCTION Oil and gas production in deep and ultra-deep water depths presents many challenges, one of them being the design of technical and cost effective riser systems. In almost all deepwater areas where hydrocarbons are found, severe current loading is invariably expected. High current can generate vortex-induced vibrations that give rise to high rates of riser fatigue damage accumulation. As water depth increases, riser designs become more varied and VIV behaviour presents one of the biggest uncertainties facing the riser engineers. A great deal of experimental work, mostly on a reduced scale, has been conducted from which analytical tools to predict riser VIV response have been developed. However, as new riser configurations are developed to cope with the increasing water depths and res