Strakes

The Allbrown Universal Strake System for VIV Suppression.

The system was first used in 1979 for British Hydrocarbons in the English Channel , it has since evolved into what it is today. Over the 36 years it has undergone constant improvement in terms of materials and attachment methodology.

The strake system comprises discrete lengths of a specially designed extrusion with a Stainless Steel (316) core. The configuration is a 3 start helix with a pitch of between 10 and 15 diameters per revolution. The stand up height is a nominal 10% for the standard system. Typical ASRs (amplitude suppression ratios ) are 79/80% for this configuration.

Higher stand up height can give a higher suppression ratio but always has a drag penalty which is proportional to the frontal area presented to the current. It is a balance between the two and analysis will determine the requirements that are more important in each case. Pitch can also effect the drag and suppression performance.

The current method of attachment is by banding, this can be either a 316 stainless band or for more permanent installations a hybrid glass reinforced band is available (HCL Fasteners) which some customers have specified.

The Allbrown strake system has a long track record when applied to the offshore drilling industry – as you can see from our Client List

One of the features of the latest system is that it does not slip as the cirumferential pressures applied by the banding are only applied at the strake stand up point and not spread over the whole diameter. The track record speaks for itself from large diameters on buoyant drilling risers to small diameter completion risers.

TRACK RECORD FOR STRAKES

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