Page 96: of Offshore Engineer Magazine (Aug/Sep 2014)

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the product is designed to be independent of direction, as the

Preventing fow can pass by the pipe on any route or path.

Traditionally manufactured

Flowlines using reaction injection molded damaging vibrations for polyurethane, each section of the

VIV suppression product would be molded and then allowed to long term pipeline protection cure for hours. However, more

Specifying the right vortex system will primarily restrain the damag- on the current and also the pipe’s posi- recent practices have seen the ing vibrations to an acceptable level, tion in the water; as currents are more product manufactured through induced vibration suppression while providing impact and abrasion prominent closer to the surface of the sea. thermoforming, using thermoplastic solution is vital to ensuring protection benefts. Specifcally, a solu- It is this reaction of vibration or, more materials. This process is much simpler tion which has been designed to stop specifcally, vortex induced vibration, than the traditional techniques and is six pipeline longevity. Jonathan Fox the formation of vortices will effciently which causes accelerated fatigue damage times faster, resulting in reduced lead explains. prevent the detrimental VIV behavior. to the structure and gives rise to prob- times, as well as project cost and time

The right VIV suppression solution lems such as pipe girth weld failure, savings. Thermoplastic materials also should incorporate overlapping and premature pipe failure or end connection he offshore oil and gas environ- exhibit the additional beneft of being interlining moldings which wrap around malfunction. By suppressing VIV, fatigue ment has experienced times of recyclable.

T the pipe and include three-start helical failure of the pipe’s structure can be change and development. About Similarly, with the ability to produce a strakes. This will provide the triangular reduced or even eliminated. 30% of the world’s oil production comes thinner product under the latest manufac- / trapezoidal strake profle required to from offshore areas* and with more turing practices, less material is required

VIV suppression prevent the formation of vortices and exploration and production activity taking to produce the same high performance thus eliminate VIV. It is important that A high-performance VIV suppression place in remote locations with deeper product. This not only makes the solution waters and harsher climates, subsea chal- more sustainable but also lightweight, lenges are increasing. Although produc- ensuring that it is easier to handle and tion platforms historically resided at dis- pre-install onshore, or install offshore. tances of 6mi from shore in 1970, projects The debilitating effect of drag on the struc- are now more often based a signifcant ture is also reduced due to the smaller 200mi from shore and in deeper waters. effective hydrodynamic diameter.

These developments mean deepwater fowlines are faced with greater pressures and temperatures, all while demands for longer lasting products continue to grow.

With this in mind, subsea solutions are required to perform more effciently and robustly to ensure that performance is guaranteed for the lifetime of the project.

A remaining challenge is the impact and severity of vortex induced vibration (VIV) on deepwater pipeline applica- tions. This includes steel catenary risers and rigid steel fowlines, which are unsupported over free spans.

The issues with VIV

In offshore conditions, VIV fatigue on a cylindrical structure is caused by the regular shedding of vortices from the pipe when subjected to a steady current.

As a fuid fows around a cylinder, separation of the wake cycles from one side to the other, coalescing along the length. This leads to an alternating trans- verse force whose frequency is depen- dent upon the fuid fow.

The J-Lay test rig

At certain water fow rates, the fre- applies a 20 te quency of the vortex shedding can match vertical load via the rollers whilst pulling the natural frequency of the pipe length, the product through causing it to vibrate. This reaction can

Image from Trelleborg Ofshore.

become more or less severe, depending

August 2014 | OE oedigital.com 98 098_OE0814Flowlines2_Trelleborg.indd 98 7/22/14 11:19 PM