48 PRODUCTION/PROCESSING/HANDLING
used that showed excellent depth sizing performance even for pitting defects with unfavourable surface-to- depth ratios, ie even where the pit diameter is larger than the maximum depth only by a factor of two to three. Tight coil spacing in circumferential direction not only ensures high repeatability of spatial dimension measurements but also means that EC technology is very suitable for high-resolution mapping.
Conclusion
Fig. 3. Defect patterns (excerpts of C-scans) are shown twice, as EC (top) and MFL (bottom) data. The three vertical lanes differentiate between bore holes of different sizes and distances between them which were inspected in a 16-in joint with 12.6mm wall thickness. Whereas the high degree of overlap attests to the reliability of each one of the two methods, the subtle yet significant differences account for the highly beneficial synergetic effect of a combined use of the two technologies.
➠
The high lateral resolution of the EC technique leads to a more accurate distinction of individual pits in dense clusters: in contrast to MFL, the EC data furnished by the shallow internal corrosion tool clearly shows the separation between the two bore holes shown in Lane 2.
Bacterial corrosion
Fig. 4 shows a photograph (left) of a cluster of pitting in a steel plate with characteristics similar to top-of- line (TOL) and bacterial corrosion. The image (right) represents the same feature on the basis of EC sensor data.
A specific pseudo-lift-off conversion formula was
Rosen’s eddy current technology-based SIC tool is specifically designed to facilitate and optimise the process of monitoring shallow internal corrosion in pipelines. As there is virtually no restriction to the type of tools that can be fitted with eddy current technology, it can be used even under exceptionally challenging conditions which are prevalent in the oil and gas industries.
Due to its high lateral resolution of defect surface
measurements, EC technology not only accurately distinguishes individual pits in dense clusters but detects and sizes even marginal corrosion features with great accuracy, thereby providing invaluable information on asset degradation3. o
Enter 48 or ✔ at
www.engineerlive.com/iog
PhD Ralf Ahlbrink, physicist, and Thomas Beuker, product line manager inspection and testing, ROSEN Technology & Research Center, Lingen, Germany.
www.roseninspection.net
REFERENCES:
1. Argent, C, et al. Macaw’s Pipeline Defects. sl: Yellow Pencil Marketing, 2003. ISBN 0-9544295-0-8;
2. CO2 Top of the Line Corrosion in Presence of Acetic Acid: A
Parametric Study. Singer, M, et al. 2009. NACE CORROSION. Paper No. 09292;
3. DNV. Submarine Pipeline Systems. 2007. DNV-OS-F101;
4. In-Line Inspection of Dents and Corrosion Using ‘High Quality’ Multi- Purpose Smart-Pig Inspection Data. Beuker, T, Brown, B and Paeper, S, 2006. International Pipeline Conference.
Fig. 4. Pitting corrosion in a steel plate with a photograph of the feature on the left and the EC-based image of the same feature on the right (all values in mm).
www.engineerlive.com
5. Hagemaier, D J, Fundamentals of Eddy Current Testing. Columbus: American Society for NDT, 1990. ISBN 0-931403-90-1.
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