Accurate corrosion depth mapping in inaccessible areas is a problem of major importance across a wide spectrum of industries. While several thickness gauging techniques are available, they are only applicable when the area to be inspected is directly accessible. In fact, standard gauging methods require a probing sensor to be scanned over the area where corrosion damage is expected. However, this is not always possible as access can be limited due to the presence of other structural members. As an example, determination of the depth of corrosion at supports of pipelines is a major issue in the petrochemical industry. At present the only reliable way to determine the corrosion depth accurately is to lift the pipe from the support and to use standard methods, thus resulting in a very costly and potentially hazardous inspection procedure. Here, we propose a tomographic approach similar to X-ray CT. However, instead of using ionizing radiation we employ guided ultrasonic waves that can be transmitted across the inspection area from a remote and accessible transducer location. While the interaction of photons with matter can be described by simple ray models in X-ray CT, scattering, diffraction and refraction phenomena characterise the encoding of mechanical property information in guided wave signals. These phenomena add much complexity to the problem of retrieving thickness maps in GWT and represent the main challenge of this proposal. Therefore, at a fundamental level this programme aims at developing a general approach to GWT that can address this complexity borrowing ideas developed in geophysical exploration and medical diagnostics. From a more applied perspective, we propose to develop a field deployable prototype for mapping corrosion at supports which will serve the twofold purpose of maintaining the research focussed on practical problems and of facilitating the translation of the proposed technology to industry. Moreover, the prototype will have a flexible design that will allow its application to corrosion mapping problems in inaccessible areas other than pipe supports to ensure that the proposed technology will have an impact across a wide spectrum of industries. This proposal is being submitted within the UK Research Centre in NDE to the targeted research programme, the funding for which is earmarked by EPSRC for industrially driven NDE research. It is supported by Shell and Petrobras who are contributing 90k cash as well as in-kind contributions to the project.