Tuesday, June 9, 2015

Oil Rig to Freight Laden Container Ship - Large Speciality Motors are an Expensive Essential Item

But What Happens When They Go Wrong?
Shipping News Feature

MEXICO – WORLDWIDE – When large speciality motors catastrophically fail at sea, finding a suitable replacement within days, not months, is critical to bring production back online and minimize loss of revenue. Whether for sophisticated thrusters or naval weaponry, or more mundane equipment such as compressors, winches or pumps, large speciality motors are used throughout the marine industry. Therefore, when one of these motors catastrophically fails at sea, the ramifications can range from minor annoyance to the cessation of work for anything from an oil rig to a containership laden with freight, with the resultant downtime costing hundreds of thousands of dollars in lost revenue.

This was the scenario that Sealion Shipping Ltd faced when its aft starboard azimuth thruster failed in the waters off Mexico, rendering the vessel’s dynamic positioning (DP) system inoperable. As a provider of onshore, offshore and sub-sea support internationally to the oil and gas industry, each support vessel in the Sealion fleet utilises DP as a standard feature to carry a diverse range of equipment, cargoes, and personnel to offshore drilling rigs and platforms.

Dynamic positioning requires the use of the azimuth thrusters working in tandem with sophisticated GPS reference and other sensors in order to work properly. Dynamic positioning is vital to vessels working in the energy recovery sector, so, when the aft starboard motor failed, the support vessel could no longer utilise the system. This threatened to take the vessel offline, potentially with a significant loss of revenue, requiring an expensive and extremely lengthy repair before the ship was fully operational again.

For Sealion Shipping, the first priority was to keep the ship in operation, and earning revenue, until the motor was repaired. As an interim measure, a tug was employed at some cost to help maintain the vessel’s position, hardly a satisfactory solution and an extra cost to the operators. Sealion Shipping meanwhile contacted the motor manufacturer, Swiss headquartered ABB, and was told it would have to be removed and sent to a central repair facility in France. Sealion Shipping estimates that to ship the motor from Mexico to France and back, along with time for repair, would have taken 4-5 months, a situation which the offshore industry group simply couldn’t live with and it concentrated on finding a company that could supply an alternative motor as quickly as possible.

While simply purchasing a new motor and installing it quickly would appear to be the obvious solution, it is not, as replacement motors from just about any manufacturer can take 20 - 26 weeks to arrive and furthermore, simply jotting down the nameplate specifications and ordering an off-the-shelf replacement is not sufficient.

Speciality motors like those used in the marine industry are highly engineered for demanding applications where accelerated loads, high torque and other high stress conditions exist. A standard motor, on the other hand, even if rated at the same horsepower, speed and voltage may not stand up to the task over time resulting in more misery. Another issue is that today’s motors tend to be quite a bit smaller dimensionally. New motors, therefore, often do not fit the existing footprint, or base, of the original model and, although the base can be modified, this is another step that takes time and money.

With limited time to identify, purchase and install a replacement motor, Sealion Shipping looked to source a used, shore-side industrial motor. A new marine-duty motor would take several months to build and surplus units were scarce. The search was limited to North America due to the ship’s location but, during an intensive search, Sealion Shipping contacted the Louis Allis Company in Warrior, Alabama, and a company which for more than 110 years has been manufacturing and repairing this type of motor.

Originally founded in 1901 as a DC motor manufacturing firm by Milwaukee businessman Louis Allis, the company soon shifted to AC motors. Facing stiff competition from early motor giants such as GE and Westinghouse, the company decided to focus on speciality motors instead of mass-produced offerings. Today, Louis Allis is still manufacturing speciality motors up to 20,000 Horsepower, along with standard NEMA motors, in-stock recertified units, and motor repair services.

Fortunately, Louis Allis had a 3,500 HP motor in its inventory that could be delivered within the 10 days it would take the vessel to return to port. Although the main propulsion motors were 2-speed, the replacement was only single-speed but fortunately, it was adequate for the DP and the ship’s manoeuvring requirements.

To facilitate speed of delivery, Louis Allis stocks used and surplus speciality motors it has purchased and refurbished. This includes taking the motor completely apart, cleaning it, replacing the bearings, varnish coating the windings, rebalancing, reassembling and conducting sophisticated testing. These units are ready for delivery at a moment’s notice, as opposed to the 2-3 months for a new motor.

The problems in this case however didn’t stop there, before it could be shipped and put into use the motor required a number of modifications. The replacement motor was air-cooled, an issue that would inevitably increase the temperature within the engine room. Sealion Shipping preferred a water-cooled unit, like the ABB motor it was replacing, but that was not possible within the time requirement. The temperature problem was manageable, however, and plans were made to convert to water cooling at a future date (work that Louis Allis completed several months later).

Perhaps the most difficult modifications involved converting the standard NEMA (American) motor to fit the metric specifications and footprint of the French ABB motor. Sealion Shipping did not have construction drawings of the motor on hand, so instead videotaped a series of measurements of various aspects of the motor, as well as the mounting details, and, with this limited information, Louis Allis had to custom remanufacture the motor so it could be a drop-in replacement. This even included ensuring that it would physically fit through a hole cut into the deck of the ship.

The replacement motor was shipped by Louis Allis and arrived within the 10 days and, due to its responsiveness, Louis Allis was also asked to repair the failed ABB motor. Once the repairs were complete, the installation could occur during future scheduled maintenance or dry dock.

Photo: The motors coming out of Louis Allis premises range up to 20,000 HP.