Aerials set up faster than cranes and let workers safely reach more areas on the turbine.
Working 60 to 90m off the ground is not for the faint of heart. Yet wind-farm techs do it all the time. On occasion, to inspect blades and towers, they rappel out of a nacelles or get a lift in a basket carried up by a crane.
More recently, aerial work platforms with long reaches have been making an appearance on U.S. wind farms to relieve the technician’s tension. The platforms are used to assess weld integrity on tower sections, clean the blades, locate bonding or lamination defects within the blade, and provide reports on possible manufacturer defects or structural damage that might have occurred during transport or erection.
Problems with cranes
Until aerial platforms made their appearance, maintenance and inspection work may have been done by lifting a worker in a sling, or letting him rappel from the nacelle. However, the U.S. Department of Labor, Occupational Safety & Health Administration (OSHA) regulation 1926.550 (g)(2) says, “The use of a crane or derrick to hoist employees on a personnel platform is prohibited, except when the erection, use, and dismantling of conventional means of reaching the worksite, such as a personnel hoist, ladder, stairway, aerial lift, elevating work platform or scaffold, would be more hazardous or is not possible because of structural design or worksite conditions.” A basket suspended from a crane is among the least preferred methods for accessing overhead areas on a turbine.
Other methods of overhead access use a hoist mounted to the tower. The service technician, however, does not have the same amount of positioning control provided by an aerial, nor can the tech reach areas such as the nacelle’s underside.
Aerial work platforms solve the problems of other methods by being easier and faster to set up, and they eliminate having the service technician make the tiresome climb inside the tower to reach the nacelle prior to operation.
Aerial work platforms may look like cranes from a distance because the most visible feature of both devices is the boom
structure reaching into the air. The platforms serve an entirely different purpose than cranes, which are actually material handlers that lift tremendous loads. Aerial work platforms, on the other hand, are intended to lift techs and tools to overhead areas for inspection and maintenance work.
The wide use of aerial work platforms on turbines is rapidly increasing for reasons that include better operator safety
and higher productivity. The aerial devices feature a rigid platform permanently attached to a telescopic boom. Most feature hydraulic, electrical, and pneumatic outlets in the platform that let service technicians and operators use a variety of tools when elevated. The platforms can also be equipped with waterways that allow high-pressure washing from the platform while built-in cameras let ground personnel view real time images of what is happening overhead.
An aerial device also lets service technicians and operators in the platform control its movement and position from a control station on the platform. Technicians suspended from the tip of a crane boom for maintenance tasks rely on the crane operator hundreds of feet away to position the basket.
Furthermore, the turntable deck on the aerial includes a duplicate control station and intercom that connects platform and ground personnel. The controls include platform load sensors, overload alarms, wind-speed indicators, and emergency descent systems. Most aerials also feature interlocks that prevent lifting the booms until the outriggers have sufficient ground pressure and the unit is correctly leveled. With these systems in place, aerials are far safer for operators and technicians than using a basket suspended from a crane.
Until recently, the use of aerial work platforms on North American wind farms was limited because the tallest machines could only reach up to a maximum of 72m. Recently however, taller aerials with working heights of 90m and 100m, and platform capacities of 1,000 lb or more, have been delivered to companies in North America for lease or rental.
As erectors place turbines on taller towers, aerial devices will continue to offer higher working heights. In fact, machines in Europe are available with working heights of up to 112m. There, aerial work platforms have been used for many years to service turbines, and are the preferred method of inspecting and maintaining blades and tower exteriors.
Ready in 20 min
From the time an aerial is driven onto the site it can be positioned, set-up and elevated to an overhead area in 15 to 20 minutes or less. Credit for the short set up goes to advanced controls and one-button automatic leveling of the outriggers on some machines. On a multi-tower site, this alone can save considerable time and money in transportation and set-up costs.
In a recent conversation regarding repairs to a turbine in which a crane was used to access the blades, it was mentioned that the type of crane brought to the site required 12 flatbed trucks for its many sections and counterweights, plus cribbing needed to stabilize the ground where the crane was to operate. Reportedly, it took over one full day to assemble the crane and a similar period to disassemble and reload it when the work completed. Transport costs alone approached $50,000. This was for repairs to one tower. The fully assembled crane and counterweights were too heavy to be driven to other towers that needed repair on the same wind farm. Other types of cranes may cost less to transport, but they still require more time to erect than aerial work platforms or other methods of performing inspection and maintenance on turbines and blades.
While aerial work platforms are somewhat new to the wind industry in North America, they have been used successfully for many years in construction and maintenance operations in a wide variety of petrochemical, government, commercial, and industrial jobs. They provide access to overhead areas and have been proven to be among the safest and most reliable equipment for increasing productivity. WPE
-William Hindman President Industrial Marketing Systems Des Planes, Ill imscomm.com
Filed Under: Safety