FEATURE SPONSOR BOLTING, TORqUING & TENSIONING
ENCE IN WIND FARM LOCATIONS TORQUE
Torque, in this context, is essentially the measurement of rotational force applied to a threaded fastener. Where the torque is either under or over the manufacturer’s specification, it can cause considerable damage to the turbine structure. Mitigating against this risk must therefore be a priority in order to safeguard the health and safety of operatives and also the life expectancy of the turbine.
It is true to say that over the last few decades, knowledge and understanding of torque in a variety of applications has increased significantly. Needless to say, monitoring and maintenance tools and solutions have also changed to take this into account. Thirty to forty years ago, the success of bolting was sometimes judged by the number of broken bolts found on the ground, around the turbine base. The overarching effects of these failures was not fully realised at the time.
In fact, during many preventative maintenance activities, across a variety of sectors, bolts are rarely undone; simply re-done through a process of tightening to ensure that relaxation of the connection is corrected. Most electric tools are unfortunately unable to complete this task due to the potential for over-torquing in the region of 100 per cent plus – yet despite this fact, many operations and maintenance teams are unaware of the limitations of electric tools in this respect.
UNDERLYING COSTS AND FAILURES While the cost of replacing bolts as a result of over torquing could be considerable, there is also the potential for a high rise in warranty costs. On foundation flanges for example, over torqued bolts may lead to cracks in the concrete foundations. Further costs would equally be involved if faults occur in the tower for example. The extent of the damage however, has the potential to vary considerably. One of the key technical implications of over or under torque however, is the potential for vibrations in the turbine - which presents a real risk of catastrophic failure. The relaxation of joints as a result of bolts becoming loose, premature wear on a number of components, damage to the steel or concrete structure or even fire are all possible consequences.
TOOLS REQUIREMENT – A PROBLEM To put this into context, in many wind farm locations maintenance operatives are required to use a variety of tools to get the job done. For example, in the turbine tower; an operative would require one tool to run down the bolts and then a hydraulic wrench to achieve final torque. The reality of using these two tools could present a number of complications, particularly with regard to ease of operation and manoeuvrability. Health and safety is therefore a key concern.
Furthermore, when triggering electric multipliers on bolts that have already been tightened, a dangerous over-torque can be achieved due to the slow response time of controllers, high motor start currents and high motor inertias. In some cases, this over-torque can be in the region of 100 per cent. When triggered multiple times in this type of condition, there is an extreme danger that the application may fail due to the overstress of the joint.
CONTINUED...
www.windenergynetwork.co.uk
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