Abstract
The use of Intelligent Pigs to survey pipelines as part of pipeline integrity management has become almost routine in the oil and gas industry. The now mature pipeline infrastructures of the world, together with more prescriptive regulatory regimes, is likely to lead to increasing needs of such inspections with the attendant increase in demand for methods of economical inspection to provide corrosion data for those lines that currently may not be accessible using conventional intelligent pigs.
A new industry sponsored study in the form of a Joint Industry Project has been undertaken aimed at demonstrating that the presence of internal corrosion in pipelines induces measurable and identifiable vibration in a carrier pig as it passes through the line. The study is based on the conjecture that it is possible to characterize pig vibrations in such a way as to differentiate between pipe that is, for example, corroded, un-corroded or may have wax present. The project saw the design and development of a new pig-mounted device for measuring and recording vibration. The theory developed into a series of trials in which the pig was passed through test loops and operational pipelines with known corrosion defects, thus allowing consideration to be given to the effects of line diameter, pig speed and pig design in interpreting the vibration measured. The results to date have demonstrated that it is indeed possible to differentiate reliably between line characteristics and conditions while pigging with water or liquid product.
In this paper the authors discuss the principles of the project, the design of the pigmounted vibration sensor and the constraints that the carrier pig design places on the capabilities of this new technology. Results to date and the ongoing field trials in operational pipelines in the North Sea are reviewed. Successful completion of these trials will offer operators an effective alternative to IP deployment for assessing the suitability of pipelines for continued service.
