Using a robot, a special “cool” laser and a “gun” that fires a surfacing compound, a team from the Cooperative Research Centre for Welded Structures (CRC-WS) has demonstrated that damaged steam turbine blades can be totally renovated without removing them from their mounting.
The trial was conducted at TXU Australia's Torrens Island Power station, near Port Adelaide in South Australia. A collaborative partner with the CRC-WS since 2003, TXU Australia provided financial and specialist expertise to the project.
The treatment involves re-surfacing the blades - each worth $20-25,000 - with a secret metallic formulation that extends their working life almost indefinitely, says CRC-WS chief executive officer Dr Colin Chipperfield.
By repairing the blades in situ the CRC-TXU team had also slashed the costly downtime required to dismantle, repair and rebuild power station turbine blading, he said.
TXU Asset Manager Ralph Villarosa said it was highly successful. With some further fine tuning of the cladding process the technology offered huge potential for the power industry.
“De-blading a turbine rotor for repairs is a major exercise both in downtime and cost, and we have found that conventional welding repairs have not met our stringent safety requirements,” he said. “We are very hopeful that this technology offers a cost effective solution to refurbishing turbine blades.”
Dr Chipperfield said low pressure turbine blades were susceptible to pitting and erosion from wet steam, requiring replacement at 10-15 years depending on operating conditions.
“Our technology makes it possible for them to last the life of the power station.
“This could mean a saving of up to $10 million over the life of the average power station. For Australia, that might well save $200 million or more - and for the world, well, the sky's the limit.”
Dr Chipperfield said the repair philosophy combined three separate technologies - a programmable robot, a direct diode laser and a “gun” that fed the metallic compound into the eye of the laser, which deposited it along the edge of the turbine blade.
The laser was mounted on a coaxial head that enabled it to reach into otherwise inaccessible places due to blade configurations.
The direct diode laser - the only one of its kind in Australia – focuses very intense light on a very small spot on the blade surface. This small spot transmits little heat and so avoids causing distortion or heat-stress to the precision-shaped blades. The laser is also transportable, permitting repairs to be conducted in-situ at the power station.
The laser-cladding process deposits a wear-resistant coating with superior bonding and performance over conventional brazed erosion shields. The CRC believes it lasts 10 times longer than the original metal of the blade itself.
Dr Chipperfield said the successful trial had triggered intense interest in the technology, both among local power generators and big international firms which made turbines and blades.
“The current challenge is to turn this into a full-blown product and take it to the world," he said, indicating talks were already underway with a potential commercial partner.
Despite consisting of state-of-the-art robotics and laser technology, he estimated the price-tag of a robot repair rig was not high - a maximum of perhaps $400,000 - and would pay for itself quickly.
The CRC is already working to establish the size of the potential Australian market for steam turbine repair. It is possible more than half of our 39 power stations could use the technology.
“We're very excited at the potential of this Australian-designed technology, not only for steam turbines, but also for use in gas turbines, boilers, impellers, hydroelectric turbines and other applications.”
Dr Chipperfield saids the research addressed National Research Priority Three - frontier technologies for transforming industry.
