As an alternative to radiography, a field-proven mechanised ultrasonic inspection system; is discussed. Called 'Rotoscan', this system has been developed for inspection of girth welds during construction of long-distance pipelines, both on- and offshore. The system is characterised by high inspection speed and instant recording of results. Unlike radiography, it provides immediate feedback to the welders. Recent technical improvements in flaw sizing and recording Have allowed the application of rejection/acceptance criteria of weld defects based on fracture mechanics. The development and actual use of such modern acceptance criteria support the introduction of mechanised UT. Worldwide applications proved that, contrary to expectations, ultrasonic inspection does not lead to higher weld repair rates than radiography. Between early 1989 and now, over 5000 km of pipeline (400,000 welds) were inspection by our organisation. Recent introduction of C-scan mapping enable the system to cope with most existing UT procedures and acceptance criteria, because of its capability to detect and quantify volumetric defects. Moreover, the integrated simultaneous TOFD function enables defect height estimation. The present system is capable of achieving a high Probability Of Detection (POD) together with a low False Call Rate (FCR). In the meantime, Rotoscan has been qualified in various countries, for different customers and for a variety of weld processes, pipe diameters and wall thicknesses. Because of its features, the now mature system has demonstrated its capabilities also for use on lay barges as an alternative to high-speed radiography.
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