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728 M A T E R I A L S E V A L U A T I O N • J U L Y 2 0 2 1 ME TECHNICAL PAPER w A B S T R A C T Fossil fuel power plants are complex systems containing multiple components that require periodic health monitoring. Failures in these systems can lead to increased downtime for the plant, reduction of power, and significant cost for repairs. Inspections of the plant’s superheater tubes are typically manual, laborious, and extremely time- consuming. This is due to their small diameter size (between 1.3 and 7.6 cm) and the coiled structure of the tubing. In addition, the tubes are often stacked close to each other, limiting access for external inspection. This paper presents the development and testing of an electrically powered pipe crawler that can navigate inside 5 cm diameter tubes and provide an assessment of their health. The crawler utilizes peristaltic motion within the tubes via inter- connected modules for gripping and extending. The modular nature of the system allows it to traverse through straight sections and multiple 90° and 180° bends. Additional modules in the system include an ultrasonic sensor for tube thickness measurements, as well as environmental sensors, a light detecting and ranging (LiDAR) sensor, and camera. These modules utilize a gear system that allows for 360° rotation and provides a means to inspect the entire internal circumference of the tubes. KEYWORDS: internal pipe crawler, robotics, inspection, superheater tubes Introduction The power generation of a superheater power plant relies on burning coal to boil water and convert it to steam. The super- heated steam, produced in the combustion chamber, is directed to the turbines of the plant to generate electricity by converting the kinetic energy of the fluid into electrical energy. The combustion chamber contains numerous pipes, typically found in a coiled structure, that operate at tempera- tures up to 540 °C and pressures between 10 to 1000 bar. In addition, the tubes range from 1.3 to 7.6 cm in diameter (Dehnavi et al. 2017). These tubes are located in the hottest region of the steam generator and can fail if maintenance and inspections are conducted infrequently. Prolonged operation can result in the rupture of critical components, stemming from plastic deformation and surface oxidation (Abraham et al. 2018). To avoid failure, an inspection of the superheater tubes should be done periodically. Typically, these inspections are conducted externally, and are often manual and time- consuming. They are also challenging, as some areas are diffi- cult to reach and the environment can be dangerous for humans. Recently, robotic inspections have seen an increase in utilization as an alternative to human-based examinations (Nayak and Pradhan 2014). One approach using robotic inspections is to conduct the evaluation on the external surface of the pipes or tubes (Kapayeva et al. 2017). These devices (Shang et al. 2008 Balaguer et al. 2000 La Rosa et al. 2002 Longo and Muscato 2004 Tavakoli et al. 2013 Park et al. 2002) crawl on the external surface of the tubes using different adhesion mechanisms including suction (Longo and Muscato 2004), thrust propellers, and magnets (Tavakoli et al. 2013). These systems can detect pinholes, cracks, and thick- ness reduction due to erosion and corrosion using sensors such as electromagnetic acoustic transducers (Park et al. 2002) and other nondestructive tools. Although some of the technical issues with external systems have been addressed, there are still some challenges that need to be investigated. This includes the potential diffi- culty of navigating on pipes with limited external access. An example includes boiler superheater tubes, which are often stacked and do not allow for the external inspection of the tubes inside the combustion chamber. Internal inspection systems offer an alternative to the more conventional external approach. These systems do not have issues with the external constraints but have their own challenges due to the reduced Development of an Innovative Inspection Tool for Superheater Tubes in Fossil Fuel Power Plants by Caique Lara†, Julie Villamil†, Anthony Abrahao†, Aparna Aravelli†, Guilherme Daldegan†, Sharif Sarker†, Daniel Martinez‡, and Dwayne McDaniel* Materials Evaluation 79 (7): 728–738 https://doi.org/10.32548/2021.me-04212 ©2021 American Society for Nondestructive Testing † Mechanical and Materials Engineering Applied Research Center, Florida International University ‡ George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology * Mechanical and Materials Engineering Applied Research Center, Florida International University mcdaniel@fiu.edu