Refineries, the chemical industry, airports etc. have an existing stock of thousands of storage tanks, the majority of which were manufactured in the sixties. Depending on the field of industry they are used in, these tanks contain environmentally harmful fluids such as gasoline or petroleum oil in the petrochemical industry or acids in the chemical industry. Other than in newly constructed tanks, there are few possibilities in preventive leak detection in older tank constructions, as the bottom plate is in direct contact to the ground. Hidden corrosion in this structural element has caused a series of catastrophic petroleum spills in the past. In response to these spills, guidelines which specify how and when to inspect tanks have been established globally to guarantee their structural integrity. To allow the inspection of the tank's bottom plate in particular, using state of the art techniques and equipment, the tanks are taken out of service and prepared for the inspection. This preparation process requires draining, washing, degassing and ventilating the tank which is a very polluting, time consuming and expensive process. A review of existing approaches has shown that automated inspection systems where a crawler carries the inspection probes, while the tank remains filled, can circumvent the need for the preparation process. However, there are some serious limitations to such systems as the crawlers used are in direct contact with the tank's structure, where obstacles inside the tanks present a problem. To make such remotely operated vehicular systems more flexible and reliable, this study investigates the fundamental requirements and replaces the crawler with a remotely operated submersible. The critical review of currently available ROVs showed that it would be difficult to procure such a vehicle and so it was decided to develop a new ROV, where aspects of operational environment (use in different petrochemical fluids), high lateral stability as well as advantageous design with respect to the subsequent controller design have been taken into account. It has been shown that this design strategy led to a vehicle where linear controller design strategies could be applied. An analysis of its suitability for use in different petrochemical fluids is provided by a detailed study of the materials that have been used and the flexibility to adjust its buoyancy which has been built in. The lateral stability of the vehicle which is a prerequisite to performing the desired plate thickness measurement is demonstrated and the reliability and robustness of the control system that was employed is also considered. A final field experiment has shown the reliable interaction of the system components and that the inspection system provides a useful and desirable capability for use under field conditions. Finally, an analysis of the system's performance has also shown its economic viability.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:416565 |
| Date | January 2005 |
| Creators | Krejtschi, Jürgen Klaus |
| Publisher | University of South Wales |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://pure.southwales.ac.uk/en/studentthesis/in-service-above-ground-storage-tank-inspection-with-a-remotely-operated-vehicle-rov(bfb370ee-4306-49be-bc1b-16e841c8f76c).html |
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