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The in-line inspection of pipelines via the use of intelligent PIGs (pipeline inspection gages) that concerns the detection and sizing of metal loss (e.g., caused by corrosion) is a well-established technology for liquid pipelines as well as gas pipelines. Magnetic flux leakage and ultrasonic techniques are used for inspection. The application of conventional ultrasonic techniques is normally restricted to liquid lines because a liquid coupling medium is required. For reliable crack detection, only the ultrasonic technique has proven suitable. The cracking in pipelines is induced by fatigue crack growth and stress corrosion cracking in addition to manufacturing-related phenomena. The state of the art of in-line crack inspection is discussed, especially as regards typical examples of weld inspection. Special emphasis is placed on data evaluation and interpretation

Pipetronix has developed a new generation of internal inspection device for the detection of cracks in pipelines. Since its commercial introduction in October 1994 the tool, UltraScan CD (Crack Detection), has successfully inspected nearly 1,000 km of operating oil and gas pipelines. The runs were followed by verification excavations at specific locations selected from the collected data. Comparison of the findings with corresponding verifications from excavations illustrate the sensitivity and reliability of the inspection method and the ability of the tool to accurately discriminate between different types of defects. The performance has proved the UltraScan CD to be a reliable internal inspection device for the detection of cracks (SCC, fatigue and other crack like defects) on pipelines. As a result, the German TÜV (authorized by the German Government to verify the compliance with Regulations covering the operation and inspection of pipelines) has approved the use of UltraScan CD as a substitute for hydrostatic pressure testing of pipelines.

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