New DOT pipeline integrity regulations require operators to assess pipeline sections that previously could not be inspected by conventional in-line-inspection processes, i.e., smart pigs. The new rules for gas pipelines allow the use of Direct Assessment to evaluate the integrity of these lines. Over the last four years Guided Wave UT has been used to inspect interstate pipelines regulated by DOT/OPS. The method is recognized as one of the key technologies in the Direct Assessment process. Long-range ultrasonic inspection or guided wave ultrasonic testing was commercially introduced in early 1998 for in-service monitoring of pipes and pipelines. The oil, gas and chemical process industries now use it for detection of corrosion and other metal loss defects and it has gained acceptance as a valid means of assessing the condition of pipes and pipelines where inspection preparation or access is difficult or expensive. The use of the technology is especially significant in view of the high percentage of unpiggable gas pipelines in the United States and government emphasis on pipeline integrity assessment. The technique has been extensively used in the field for evaluating the condition of pipes in the range of 2 to 48 inches in diameter and has performed well in identifying corrosion in pipes in a variety of situations. As with any new technology, a crucial stage in gaining acceptance by industry as a proven inspection and monitoring tool is the performance achieved in real field situations. Over the last two years, several validation exercises have been partially funded by The Research and Special Programs Administration (RSPA) and The Office of Pipeline Safety (OPS) in conjunction with research in this methodology. These validation exercises are serving to establish confidence in guided wave UT for regulators and pipeline operators alike. This paper briefly reviews the guided wave process and compares some of the field data obtained with the actual as-found pipe conditions. The paper generally looks at the research underway in field applications of long-range ultrasonic technology that is contributing to the development of new and better equipment. Next generation equipment sets are already being developed and the capabilities of these units will permit more flexibility in data acquisition, improved sensitivity and extension of the inspection range.
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