Full-Scale Fairing Qualification Tests

Abstract

Production risers as well as drilling risers are often exposed to ocean currents. Vortex-induced vibrations (VIVs) have been observed in the field and can cause fatigue failure and excessive drag on the riser. In order to suppress VIV, fairings are often used. This paper presents qualification tests for two types of fairings: the short-crab claw (SCC) fairings and the AIMS dual flow splitter (ADFS) fairings. The short-crab claw fairing design is a novel design patented by the Norwegian deepwater project (NDP). As will be detailed in this paper, both the SCC and ADFS designs offer very low drag, completely suppress VIV, and are effective even when they are in tandem. A model test campaign was undertaken in the 200-m towing tank facility at the ocean, coastal, and river engineering in St. John's, NF, Canada. A rigid pipe with a diameter of 0.3556 m (14 in) was utilized for the experiments. This corresponds to prototype size for a production riser and a 1:3.8 scaled model for a 1.3716 m (54 in) drilling riser. Given that these tests were conducted at prototype scale, they were used to qualify the fairings for field deployment. Both fairings (SCC and ADFS) were very effective in suppressing VIV and reducing drag. The ADFS fairings are most effective for a span to diameter ratio of 1.75. For all fairing geometries, it was found that a small taper increases the fairing effectiveness considerably.