The harsh environment of a boiler in a coal-fired powerplant stresses and wears out the constituent water walls which then must be repaired. It is a continual struggle between a large fire ball, cinder stalactites, and steam or water cannons to break down the build-up. When an actual hole develops in the water wall, there is severe inefficiencies which tend to cause the plant to be shut down for repair. Since every hour of shutdown represents large potential losses in the vicinity of $20,000 to $100,000 per hour, minimizing downtime is imperative.
TTU researchers have been developing inspection robots which can crawl vertically up the water pipes in boiler carrying inspection sensors to measure tube wall thickness. These robots can work on walls too hot for human workers, and can begin long before scaffolding to hold human workers can be built. The quicker the "bad" sections can be identified for replacement, the better.
Several different prototypes have been build over the course of the research program, but a common design characteristic is a dual tank track design with "magnetic feet".
A dedicated robotics labratory with its own lathe and mill, combined with off-the-shelf parts and talented researchers, makes robot fabrication at TTU a reality.
Designs have varied from a large 50 pound version which can easily lift a graduate student off the ground, to a compact 20 pound version which can be lifted onto a water-wall via small access panels.
Typically power for the robot is via a power "tether" which is dragged behind the robot. A telerobotic operator is currently required, but more and more autonomy is being added. Video and sensor feedback is via wireless communication and the robot can be "driven" via the video information sent to an operator monitor.
Any commercial sensor can be outfitted for use with the inspection robot. At this time, TTU researchers are not designing their own sensors, but instead are utilizing 3rd party transducers. Various mechanisms for following the irregular surface of the water-wall have been developed as well as tube-to-tube positioning mechanisms, and tube following mechanisms.
Further advancements in spatial indexing for thickness measurements, and autonomy of inspections are being developed in this ongoing research effort.
The same basic concept employed in the water-wall robot has been extended to any steel tank inspection. This simpler task does not require the robot to navigate over layers of built up fly-ash, old welds, and rust accumulation as typical tanks are kept in better condition than the inside of a boiler. Tank owners did request at least one modification to the design, and that was a "shoe" to protect the paint on the tank. A thin layer of plastic was added to the design of each "boot" to prevent scuffing of paint.
A sample output screen of a wall thickness transducer is shown in Figure 6. Reitterating any instrument could be used, and a custom interface could be designed to meet a companies data requirements.
This is an ongoing research program which has lots of potential to help the Electric Power Industry. Other inspection mechanisms are also being planned an may get reported here in the future.