Effectiveness of Polyethylene Helical Strakes in Suppressing VIV Responses After Sustaining High Roller-Load Damage During S-Lay Installation

ABSTRACT

Helical strakes are an important Vortex Induced Vibration (VIV) suppression device for Steel Catenary Risers (SCR’s).   This paper presents the results of two sets of hydrodynamic tests performed at MARIN, on a 12” pipe fitted with 16D Helical Polyethylene strakes.   The first set of tests established the suppression efficiency of the strakes for the Intact Configuration (no deformation).  The second set of tests established the performance of the same strakes after undergoing a roller test in which the fins and the body of the strakes have sustained permanent deformations due to a simulated high contact load on the roller of a stinger during an S-lay installation.  The type of permanent deformations sustained by the strakes can be described as bulging of the strake body, and permanent folding of the fins.   Both configurations of the strakes (Intact and Deformed) were tested at high and low Reynolds numbers (velocities of 2.5 m/s and 0.5 m/s) and at different reduced velocities Vr.   The results show that for the Deformed strakes configuration, there was no appreciable decrease in the VIV suppression efficiency of the strakes from a design consideration.  The test results indicated that both Intact and Deformed strakes were at least 90% efficient in suppressing VIV.   Therefore, based on the tests reported in this paper, the Polyethylene strakes were deemed acceptable to use on the SCR’s even when using the S-Lay installation method.

Boubenider, R., Alptunaer K., Fourchy, P.J., De Wilde J., “Effectiveness of Polyethylene Helical Strakes in Suppressing VIV Responses After Sustaining High Roller-Load Damage During S-Lay Installation,” OTC 19289, Presented at the 2008 Offshore Technology Conference, May 8, 2008, Houston, Texas.