Aker’s versatile modular top drive can be repaired quickly
Aker Solutions says its MH MDDM 1000™ top drive drilling system is the first true modular derrick drilling machine (MDDM) that meets 6th generation drilling requirements. The top drive was recognized this year by the Offshore Technology Conference’s Spotlight on New Technology award. The MDDM 1000 is the latest iteration of its original MDDM 1250 top drive that was developed several years ago with the support of Transocean. The aim then as now is to significantly reduce downtime and dramatically reduce the time to replace any parts that might wear out or fail. The top drive’s modular concept provides easy access to replace individual modules.
When parts or modules fail, the specific component can be replaced without interrupting other top drive systems. Also, the modular design and the number of quick connector devices reduces assembly time, resulting in faster delivery of a complete top drive.
In 2005, Transocean began investigating top drive drilling systems for its then newest drillships, the Enterprise class. Transocean came to Aker with a list of operating criteria that appears almost impossible to meet, including a 99.9% uptime on an annual basis, and reduced downtime for repairs and maintenance. A contract was agreed between Transocean and Aker Solutions to begin development on the design and field testing of a new top drive system.
The result was the MDDM 1250, with 1,250 tons lifting capacity, dual motors delivering 2,400 hp and more than 100,000 ft/lb of continuous drilling torque. Aker noted that with the redundant motor system, the top drive could deliver 80% of full drilling performance, even with only one motor operating. The first MDDM 1250 system was installed on Transocean’s Discoverer Clear Leader.
Transocean provided Aker with data based on the downtime history of 72 top drive drilling systems over a five year period. The data was used as a base for Aker to begin developing solutions to minimize top drive drilling system downtime. Analysis of the data determined the areas of the top drive system most susceptible to failure or repair that leads to downtime.
For example, Aker and Transocean found that the gearbox and the main swivel alloys were two of the worst areas for causing downtime of a top drive drilling system. As a result, Aker said it focused on deflection of the main shaft and the swivel housing/load frame while loaded. It is crucial that the main shaft and swivel housing/load frame have the same deflection in order to extend the life of the main bearing, Aker explained.
MDDM 1000 top drive
Once the MDDM 1250 was developed and commercialized, it was used as a platform to be able to quickly develop variations, such as the MDDM 1000, on a fast-track basis. It took 20 months from beginning the development of the MDDM 1000 until it was ready for installation and commissioning on Transocean’s Discoverer Luanda. The MDDM 1000 top drive underwent extensive testing prior to installation. For example, it was pull tested and run continuously for 96 hours. This test was conducted by connecting the main shaft to a dynamic braking table, including a torque measuring device, to study the full operational power and torque that it would experience in the field.
Repairing, replacing components
With the MDDM 1250 and 1000 top drive systems, one of Transocean’s primary concerns was the fast repair or replacement of the unit’s key components in order to reduce downtime. For example, Aker pointed out, a main shaft can take up to eight hours to change out. Transocean, however, wanted that reduced by half. Motors often take 10 or more hours to change. Transocean wanted that operation recued to less than four hours for the MDDM 1000. A team of engineers replaced the pipe handler in less than 90 minutes and changed the AC motor including the coupling and air flex brake in just over an hour.
Aker Solutions noted that these change outs occurred in a workshop environment where the engineers had access to cranes that may not be available offshore. They also were not affected by heaving of a vessel. However, according to Aker, repair times based on a list of 18 various repairs was cut by 41%.
Your results may vary, but the design of the MDDM 1250 and 1000 top drive drilling systems did result in a significant lowering of the time necessary to make repairs and change out parts, as noted in the table below.
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