Miniature Mobile Systems for Inspection of Ferromagnetic Structures

Power plants require periodical inspections to control their state. To ensure a safe operation, parts that could fail before the next inspection are repaired or replaced, since a forced outage due to a failure can cost up to millions of dollars per day. Non-Destructive Testing (NDT) methods are used to detect different defects that could occur, such as cracks, thinning, corrosion or pitting. Some parts are inspected directly in situ, but may be difficult to access; these can require opening access holes or building scaffoldings. Other parts are disassembled and inspected in workshops, when the required inspection tools cannot be moved. In this thesis, we developed innovative miniature mobile systems able to move within these small and complex installations and inspect them. Bringing sensors to difficult-to-access places using climbing robots can reduce the inspection time and costs, because some dismantling or scaffolding can be eliminated. New miniature sensors can help to inspect complex parts without disassembling them, and reduce the inspection costs, as well. To perform such inspections, miniature mobile systems require a high mobility and keen sensing capabilities. The following approach was used to develop these systems. First, different innovative climbing robots are developed. They use magnetic adhesion, as most structures are made of ferromagnetic steel. Then, vision is embedded in some of the robots. Performing visual inspections becomes thus possible, as well as controlling the robots remotely, without viewing them. Finally, non-visual NDT sensors are developed and embedded in some of the robots, allowing them to detect defects that simple vision cannot detect. Achieving the miniaturization of the developed systems requires strong system integration during these three steps. A set of examples for the different steps has been designed, implemented and tested to illustrate this approach. The Tripillars robots, for instance, use caterpillars, and are able to climb on surfaces of any inclination and to pass inner angles. The Cy-mag3Ds robots use an innovative magnetic wheel concept, and are able to climb on surfaces of any inclination and to pass inner angles, outer angles and surface flips. The Tubulos robots move in tubes of 25 mm diameter at any inclination. All robots embed the required electronics, actuators, sensors and energy to be controlled remotely by the user. Wireless transmission of the commands signals allows the systems to maintain their full mobility without disturbing cables. Integrating Hall sensors near the magnetic systems allows them to measure the adhesion force. This information improves the security of the robots, since when the adhesion force becomes low, the robots can be stopped before they fall. The Tubulo II uses Magnetic Switchable Devices (MSDs) for adhesion. An MSD is composed of a ferromagnetic stator and one or more moving magnets; it has the advantage of requiring only a low force to switch on or off a high adhesion force. MSDs have the advantage of being easy to clean of the magnetic dust that is present in most real environments and that sticks strongly to magnetic systems. As an additional step toward inspection, a camera is embedded on the Cy-mag3D II and the Tubulos. It allows these robots to inspect visually the structures the robots move in, and to control them remotely. The perspective of a climbing robot in an unknown environment is often not enough to give the user a sense of its scale, and to move efficiently in it. A distance sensor is designed and embedded on the Cy-mag3D II, which increases the user's perception of the environment substantially; Finally, an innovative miniature Magnetic Particle Inspection (MPI) system was developed to inspect turbine blades without disassembling them. An MSD is used to perform the required magnetization. The system can automatically inspect a flat surface, performing all the required steps of MPI: magnetize, spray magnetic particles, record images under UV light and demagnetize. Thanks to the strong integration and miniaturization, the system can potentially inspect complex parts such as steam turbines

Catalytic steam reformer tubes non-destructive inspection technology investigation and advancement : a dissertation presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Engineering at Massey University, Manawatu Campus, New Zealand

Catalytic Steam reforming is a chemical synthesis process used in the production of hydrogen by mixing hydrocarbon with steam in the presence of a metal-based catalyst. This is achieved in a steam reformer plant where the mixture of gases is elevated to high pressure and temperature through a continuous process for efficient mass production of syngas to meet the global hydrogen demand. One of the challenges in operating a steam reformer plant is monitoring and maintaining the tubular reactors (Reformer tube). Under the severe service conditions the tubes a subjected to various degradation mechanism which ultimately determine the service life. With the tubes accounting to over 20% of the capital cost of a reformer plant, it is of great significance to maximise the service life of each tubes, which has been the motivation to the advancement in metallurgy and NDT technology around reformer tubes from the introduction of Catalytic Steam reforming in the early 20th century. Under the influence of long-term exposure of mechanical stressing and elevated temperature, reformer tube is subjected to a material degrading phenomenon call creep deformation. In 1952, F.R. Larson and J. Miller devised the Larson-Miller Parameter which predicts the lifetime of a material based on service temperature and stress-rupture time and for decades this method was used design and managed reformer tubes on a time-based strategy of 10,000 service hour. However, case studies have time and time shown premature rupture of reformer tube causing unexpected downtime resulting in significant loss in production and asset. Hence engineers and researchers have worked on a more direct method of assessing the remaining service life of reformer tubes. Inline pipe inspection is a hot area of research in robotics and automation. Eddy current, laser profilometry, ultrasonic and infrared thermography is the four technology that is currently dominating the Reformer industry, of which laser profilometry assessment being the only method capable of early stage creep detection. While other fields of pipe inspection have advanced and industrially applied over past decades, it is the author's opinion that NDT technology for reformer tube is outdated with areas of innovation. The aim of this research is to investigate an alternative solution to overcome the challenges and limited faced in modern systems and contribute to the advancement of NDT of Catalytic Steam reformer tubes. Presented in this dissertation is a new framework for an autonomous Reformer Tube inspection system, which incorporates a number of innovative elements for improved creep damage assessment. The program for this work is comprised of three studies. In the first study, the challenges around process profilometry dataset is demonstrated, the limitation in the available methods is discussed, and the impacts in regards to detection creep deformation is identified. Based on the finding, a three-stage creep detection algorithm (CDA) is derived, offering a dynamic solution to distinguish two modes of isotropic and anisotropic creep deformation. The system is experimentally assessed using a set of profilometry measurements collected from retire reformer tube. In the second study, a novel method for tracking a motion of an object moving inside a reformer tube is devised. Literature study showed that conventional profilometry system suffers from measurement uncertainty cause from an uncontrolled rotation of measurement instruction during an inspection. Because location information gives valuable insight as to the performance of the plant, the long-range optic solution is conceptualised, based on polarising filters and Malus Law, to overcome these limitations. In this research, a proof of concept experiment is conducted to evaluate and justify the conceptual method through the development of a working prototype. This novel technique is named Optical Position Tracking (OPT) system. Presented in the final study is an autonomous reformer tube inspection system developed on the basis of the results and finding in the first portion of the research. The contribution of this research is demonstrated with a working prototype justifying the practicality of CDA and the OPT system. The design incorporates wireless communication, modular design, and modern semiconductor sensing technology. In conclusion, this research met the first milestone for an ongoing research to progress the NTD industry