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Braking Into Oil Production
Braking into oil production
Kopper Kooled brakes from Wichita Clutch, part of Altra Holdings, which have the ability to stay cool, are being used on semi-submersible oil platforms to ensure the rig remains in position during drilling
Semi-submersible drilling platforms are used for exploratory drilling of potential new sites. These self propelled platforms are capable of drilling in depths of up to 2400m and, once in position, they can use dynamic positioning to remain stationary. However, if the platform will remain in the same place for an extended amount of time, then a mooring pattern will be laid. Due to the size of the platforms and depths that they operate in it is essential that the mooring pattern is spread, often over an area of 6km, using a series of winches and brakes to control the cable payout.
In fact, a spread reaching 6km is necessary to ensure stability. To achieve this an anchor handling vessel is used which transport the anchors – ranging in number from eight to 16 - away from the platform and will then lay them. The payout tension has to be controlled as the anchor handling vessels move further from the semi-submersible rig and cable weight increases. Each corner of the platform is typically equipped with two mooring winches which, traditionally, need two secondary brakes: one for static holding once the anchors are laid; plus another, a slipping brake, to control the payout of the cable.
As an alternative to this method, Wichita Clutches Kopper Kooled dual acting water cooled dynamic brakes are capable of doing the job of both brakes, meaning that each winch needs only one secondary brake. The brake uses a piston assembly for positive brake tensioning and a fail safe spring set brake operation for emergency stopping and holding duties. It will control the payout of the cable at typical speeds of 40m/minute, generating typically 250 tonnes of tension on the cable. Once the anchors have been laid the multiple spring actuator will be applied for static holding. Disengagement of the static holding brake is achieved pneumatically and designed as a fail safe if there are any issues during mooring.
A cooling solution
In any braking application it is important to consider the heat dissipation capability of the brake. 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. During the payout of the mooring cables typical power levels of 1600kW of continuous heat energy can be produced due to the high torque slipping of the brake. A brake which is capable of high heat dissipation not only maintains reliability and extends operating life but it also allows the use of a smaller brake.
The Wichita brakes use copper cooling which is the most efficient method of heat dissipation in the range. Copper discs are used for high heat transfer from friction surface to the continuous flow of cooling water. The patented Jacket Design, coupled with the copper wear plates, provides precise stopping/ tensioning capabilities with very high heat dissipation characteristics.
Of additional benefit for such applications as this, the company can manufacture each brake to specific customer needs offering, for example, a saltwater corrosion protection package. Furthermore, while the brakes are displayed as providing up to 200,000Nm of torque, this can be increased by up to 50% if required. High end materials are used including a reinforced neoprene fast acting air tube, designed to assure quick and smooth stops, and a new friction material which lasts longer with less wear on the mating copper. The spring set air release brakes are suitable for fail safe protection, and high strength ductile iron construction is used throughout, with thick friction linings provided for a longer wear life.
The Kopper Kooled range is suitable for high intensity applications - ranging from use on semi-submersible platforms on the storage winches which hold the mooring cable and on winches utilised by the anchor handling vessels; as well as in oil/gas drilling, wind energy and tidal energy.
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