Vortex-induced vibration (VIV) suppression devices minimize pipeline excitation during offshore current events, thereby reducing accelerated fatigue failure of pipeline components and minimizing current-related disruption on producing operations. Ideally VIV suppression devices are installed as the pipeline is being built onshore or as the riser is being assembled offshore onboard a pipe-lay vessel.
Retrofitting VIV suppression devices is often a necessary pipeline/riser intervention. New methods and tooling are bringing down the price of VIV suppression hardware and associated installation times. This paper follows Shell Global Solutions (US) Inc. VIV suppression hardware retrofit tooling and method evolution from first requirement through theircurrent tooling configurations and installation methods.
A case study was conducted, and our customer elected to install additional suppression fairings for vortex-induced vibration on two export pipeline steel catenary risers (SCRs). The VIV suppression hardware installed on the risers was designed and fabricated by Shell Global Solutions (US) Inc. (Shell GSUS) and was in the form of six-foot long fairing sections separated by load bearing collars. For hardwareinstallation, our customer teamed with Shell GSUS to develop a method and associated tooling to allow the fairing assemblies to be installed. The method of installation included a TLP-based work-class ROV and VIV suppression device installation tooling developed by Shell GSUS. The method and equipment was utilized without affecting flow line operations and with minimal impact on TLP resources. This case study reviews the planning, procedures and results of a deepwater, vertical SCR VIV suppression retrofit project.
Vortex-induced vibration (VIV) can best be described as follows: As fluid passes a tubular under tension, vortices are shed on the down-current side. These vortices create fluctuating lift and drag forces causing the tubular to move perpendicular to the current. This perpendicular movement is the phenomenon known as vortex-induced vibration. VIV has become a significant challenge to structure and pipeline designers as offshore energy development moves into ever deeper water.
VIV can be limited by using several methods. One method shortens the vortices correlation length by installing helical fins known as strakes. The helical fin arrangement shortens the correlation length of the vortex, reducing the lift and drag forces on the tubular. The strake has been used successfully in deep water and is a simple, robust method of suppressing VIV.
There are disadvantages to using strakes, though. Strakes increase the diameter of the tubular by the combined height of the vortex interrupting fins. Additional strength must be factored into a riser system design to account for the additional drag force caused by the greater diameter of the tubular as a result of adding strakes. Strakes require periodic cleaning as marine growth creates drag that shortens or bridges the fins.
