Bad Vibrations

Abstract

This article focuses on offshore drilling that is thought to be impossible. The depths are so great, and the pipes are so relatively insubstantial, that it seems a miracle anyone can get it to work. Strakes used in riser applications typically are made out of a high-strength plastic that is resistant, though not immune, to marine growth. Since such growth changes the hydrodynamic properties of the strakes, the devices are designed to ensure that they work even when encrusted with life. One company went so far as to test its wares with squares of shag carpet glued on. Fairings have the advantage of being cheaper than strakes. In addition, fairings have much lower drag than helical strakes and are much less sensitive to marine growth on their surface, which is a common problem. To accommodate shifting currents, fairings are only loosely attached to the risers; they swing around like weathervanes. Near the surface, where currents are most likely to change direction, strakes, which are onmidirectional, are often better bets. Hybrid systems—strakes on top, fairings below—are increasingly common.