Joshua Crayton, blade services manager at Rope Partner, a US-based rope access provider for wind turbine inspection and repair, suggests a cradle-to-grave mentality is the route to long-term reliability.
"It starts at the point of purchase," Crayton says.
"Buyers must ask what specific challenges the proposed wind farm site presents and then look at the details."
At this point the buyer and future operator of the turbines must set clear quality control demands.
Crayton says the ability to maintain oversight of manufacturing quality control throughout the process depends on the relationship with the manufacturer.
"There is an opportunity when producing multi-million dollar turbine orders to sow in certain expectations of manufacturers," says Crayton.
"It depends on how willing the manufacturer is to agree to requests from developers or allow engineers to look at the manufacturers’ processes."
Damage in transit
Even if blades pass the quality control test at the manufacturer, many sustain damage in transit to site.
Crayton advises that blades should be inspected immediately on delivery so that damage incurred between the factory gate and the project site can be repaired before installation.
"Most damage in transit is relatively minor but the challenge transportation companies face is increasingly difficult as blades are getting bigger and heavier," says Crayton.
"Even with a straight road you have to accept that blades are designed to hang from towers, not to be bounced along in a cradle on a truck.
Transit can cause leading-edge composite damage and often damage is under the surface of the blade and difficult to spot."
In the operational life of a blade, the first two years give a crucial baseline of wear and tear, says Crayton.
"It is important to inspect up-close and document the findings, using a knowledgeable servicing company."
Real long-term planning starts towards the end of the blade’s warranty period. "A pre-warranty inspection is very important," says Crayton.
"Inspect internally and externally in advance so that warranty claims can be made on time."
After that, post-warranty inspections need to be made at regular intervals, such as two years.
Crayton says methodical examination is important. A key external inspection technique is non-destructive testing (NDT).
"That means tap-testing the blades. Advanced NDT is proven to detect known issues." It can flag up voids in the bonded zone of the blades or if they have been compromised in any way, he says.
Internal examination is also required, affected by issues of confined space and air quality, with permits sometimes needed.
"Costs are exacerbated due to the additional manpower and equipment which are necessary," Crayton says. Nonetheless, lack of maintenance will definitely affect the lifespan of a blade.
"Composites have a longer life than metal, but the increase in scale when it comes to turbine size, and particularly weight, is also an unknown factor over a 20-year period," he adds.
Owners must know their asset. "Take into account site-specific considerations such as rain, ice, dust and lightning," he says.
"Look at blade protection options — leading edge tape or coating, for example. There is no route map for the end of a blade’s life, but one definite measure is care of the leading edge.
There is no reason to let blades operate without leading-edge protection."
A cradle-to-grave inspection regime throughout a turbine’s life is a must. "Ignorance is bliss" says Crayton, "until reality bites."