Today the most common method used for in-line pipeline inspection is Magnetic Flux Leakage (MFL) technology. The reliability and robustness of this technique continues to be the foundation for determining pipeline integrity. Nevertheless, there exists a certain limitation when using MFL techniques. Primarily, MFL is limited to detecting defects where material loss has occurred or a feature has an open discontinuous structure.
Given the structural nature of pipeline cracks, an ultrasonic based inspection technique is the best detection method to use. Traditional ultrasonic technologies (UT) based on piezoelectric transducers are only applicable when an adequate liquid couplant is available between the transducer itself and the pipe wall. Therefore, only liquid systems can be inspected.
Electro-Magnetic Acoustic Transducer (EMAT) technology is based on electro-mechanical conversion produced when an eddy current is applied within a static magnetic field. The resulting Lorentz forces and magnetostriction result in an interaction between the EMAT and the metal surface generating an acoustic wave within the material, eliminating the need for liquid couplant. The acoustic wave that propagates within the pipe wall is dependent on the dimensions and properties of the pipe material. Therefore, the presence of SCC and other crack features will disturb the guided-wave in such a way as to produce a reflection resulting in an echo. This echo can be detected and measured.
ROSEN’s new high-resolution RoCD2 tool provides such an approach. This tool service is based on a unique and highly effective implementation of an EMAT to induce guided acoustic waves within the pipe wall regardless of the pipeline contents. The result is a high quality and reliable signal precisely controlled in wave length and frequency limiting detection to cracks and crack colonies and minimizing detection of other intrinsic anomalies of the pipeline. In addition, the technique is used to collect coating disbondment information. Detecting these areas is important since SCC tends to occur in areas where the coating has disbonded. Together these results provide a proactive approach to help improve the overall integrity of a pipeline.
In 2006 ROSEN has released a new 16“ EMAT Crack Detection and Coating Dispondment tool (RoCD2) for oil and gas pipelines. The innovative technology has proven its performance during extensive in-house pull-tests on samples containing natural SCC colonies. The first surveys have been carried out in the 2nd quarter of 2006. ROSEN has developed correlation analysis software to accurately and reliably detect - and classify cracks, including SCC.
Field verification of the first inspection runs have verified the performance of ROSEN’s new EMAT technology and analysis methods in gas and liquid pipelines.