Although traditional methods based on ultrasonic waves have been proven to be adequate for the detection of potential cracks in pipelines, accurate characterization and sizing may be limited. With traditional methods, the assessment of the suspicious area must be conservative to justify remaining fitness for service. Due to such conservatism, a costly repair or replacement maybe required.
In this paper, we will present and discuss potential improvements for detection and sizing of complex cracking such as fatigue cracks or stress corrosion cracks using the latest advances in ultrasonic technology and software processing with the Applus IWEX system. This system can acquire full matrix capture (FMC) data and process this data in real time into representative images from the FMC data. The system has been qualified and validated already for applications such as the inspection of new construction girth welds, and in this paper, we will demonstrate the performance of the technology with a use case which is representative for an in-service pipeline application, such as the detection and assessment of complex cracking. This will be demonstrated with an imaging strategy like the Total Focusing Method (TFM) and with the latest implemented imaging strategy based on Phase Coherent Imaging (PCI).
First, we will introduce and compare the principles of ultrasonic imaging based on TFM and PCI. The benefits and limitations for the inspection of pipelines will be contrasted and discussed. Then, a representative use case with actual cracks will be presented, whereby images are constructed with both TFM and PCI. From the images, the benefits and limitation can be illustrated.
Furthermore, we will evaluate and discuss conditions for adequate and optimal performance of the technology, and we will discuss practical considerations.