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Exploration • Drilling • Field Services


Marine clutches and brakes – keeping their cool


Neil Wright assesses the requirements of modern marine clutches and brakes, which play such a crucial role in a variety of applications.


A


s marine exploration for oil and gas continues to greater depths, so the equipment used to exploit the new reserves needs to perform on a whole new level. However, it is not sufficient


to just increase the size of new products as space on vessels remains limited. Tis requires designers to be innovative and develop new materials, especially when heat dissipation forms such a crucial performance aspect. Tere is a wide range of marine applications


that employ clutches and brakes for the safe control of various processes. One of the more arduous examples is the control of mooring cables on semisubmersible drilling platforms. When these vessels are to remain on station for an extended period, a mooring pattern – often over an area of 6km – is spread using a series of winches and brakes to control the cable pay-out. Anchor handling vessels are used to transport and lay up to 16 anchors. Tis requires the pay- out tension to be controlled as the vessels move further away from the platform and the cable weight increases. Typically each corner of the platform is equipped with two mooring winches. Tese traditionally required two secondary brakes; one for static holding once the anchors are laid and a second slipping brake to control cable pay-out. By using the latest design techniques Wichita Clutch has developed a dual acting, water-cooled dynamic braking system, capable of doing both jobs. Te brake will control the pay-out of the cable at typical speeds of 40m/minute, generating around 250 tonnes of tension on the cable. In any braking application it is important to consider the brakes heat dissipation capability. If the heat generated by the friction of the cable tensioning duty exceeds the convection capacity of the unit to dissipate it, the brakes operation may become compromised. Providing a brake which is capable of high heat dissipation not only maintains reliability and extends operating life, it also allows the use of a smaller brake which provides cost savings. Copper discs are used for high heat transfer from


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friction surface to the continuous flow of cooling water. Te use of an advanced water jacket design, coupled with the copper wear plates, provides precise stopping/tensioning capabilities with very high heat dissipation characteristics. Te industry standard has been to use cast iron


water jackets, alternating with copper wear plates, to dissipate the high heat generated in heavy-duty tensioning applications. In marine environments however, salt corrosion


creates maintenance issues that necessitates too- frequent repair or replacement of the cast iron water jackets. To address this issue, Wichita engineers have


developed a composite material for use in the new water jackets which has undergone extensive stress testing and extended durability testing to assess the corrosion resistance for offshore applications. Te new composite material provided greatly


improved corrosion resistance but also reduced the overall weight of the water jacket, in some units by more than 50%. Te overall results of these design changes have delivered a 35% increase in heat absorption compared to previous heavy duty designs. l


Neil Wright is Managing Director of Wichita Clutch, Bedford. UK. www.wichita.co.uk


Fig. 1. The marine environment is extremely harsh and delivering equipment capable of performing reliably and efficiently requires expert design engineers combined with advanced materials technology.


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